Osteology of Eoraptor lunensis (Dinosauria, Sauropodomorpha)

Abstract

We describe the basal sauropodomorph Eoraptor lunensis, based on the nearly complete holotypic skeleton and referred specimens, all of which were discovered in the Cancha de Bochas Member of the Ischigualasto Formation in northwestern Argentina. The lightly built skull has a slightly enlarged external naris and a spacious antorbital fossa with a prominent, everted dorsal margin and internal wall lacking any pneumatic extensions into surrounding bones. The tall quadrate is lapped along its anterior margin by the long, slender ventral process of the squamosal, and the lower jaw has a mid-mandibular joint between a tongue-shaped splenial process and a trough in the angular. All but the posterior-most maxillary and dentary crowns have a basal constriction, and the marginal denticles are larger and oriented more vertically than in typical theropod serrations. Rows of rudimentary palatal teeth are present on the pterygoid. Vertebral centra are hollow, although not demonstrably pneumatized, and all long bones have hollow shafts. The radius and ulna are more robust, the manus proportionately shorter, and the manual unguals less recurved than in the contemporaneous basal theropod Eodromaeus murphi. An outstanding feature of the manus of Eoraptor is the twisted shaft of the first phalanx of the pollex, which deflects medially the tip of the ungual as in basal sauropodomorphs. The long bones of the hind limb have more robust shafts than those of Eodromaeus, although in both genera the tibia remains slightly longer than the femur.

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Braincase of shape Panphagia protos (Dinosauria,
Sauropodomorpha)
Paul C. Sereno a , Ricardo N. Martínez b & Oscar A. Alcober b
a Department of Organismal Biology and Anatomy, and Committee on Evolutionary Biology ,
University of Chicago , 1027 East 57th Street, Chicago , Illinois , 60637 , U.S.A.
b Instituto y Museo de Ciencias Naturales , Universidad Nacional de San Juan , San Juan ,
Argentina , CP5400
To cite this article: Paul C. Sereno , Ricardo N. Martínez & Oscar A. Alcober (2012) Braincase of shape Panphagia protos
(Dinosauria, Sauropodomorpha), Journal of Vertebrate Paleontology, 32:sup1, 83-179, DOI: 10.1080/02724634.2013.820113
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Society of Vertebrate Paleontology Memoir 12
Journal of Vertebrate Paleontology
Volume 32, Supplement to Number 6: 83–179
©2013 by the Society of Vertebrate Paleontology
OSTEOLOGY OF EORAPTOR LUNENSIS (DINOSAURIA, SAUROPODOMORPHA)
PAUL C. SERENO,*,1 RICARDO N. MART´
INEZ,2and OSCAR A. ALCOBER2
1Department of Organismal Biology and Anatomy, and Committee on Evolutionary Biology, University of Chicago,
1027 East 57th Street, Chicago, Illinois, 60637, U.S.A., dinosaur@uchicago.edu;
2Instituto y Museo de Ciencias Naturales, Universidad Nacional de San Juan, San Juan, Argentina CP5400, martinez@unsj.edu.ar;
oalcober@unsj.edu.ar
ABSTRACT—We describe the basal sauropodomorph Eoraptor lunensis, based on the nearly complete holotypic skeleton and
referred specimens, all of which were discovered in the Cancha de Bochas Member of the Ischigualasto Formation in north-
western Argentina. The lightly built skull has a slightly enlarged external naris and a spacious antorbital fossa with a prominent,
everted dorsal margin and internal wall lacking any pneumatic extensions into surrounding bones. The tall quadrate is lapped
along its anterior margin by the long, slender ventral process of the squamosal, and the lower jaw has a mid-mandibular joint
between a tongue-shaped splenial process and a trough in the angular. All but the posterior-most maxillary and dentary crowns
have a basal constriction, and the marginal denticles are larger and oriented more vertically than in typical theropod serrations.
Rows of rudimentary palatal teeth are present on the pterygoid. Vertebral centra are hollow, although not demonstrably pneu-
matized, and all long bones have hollow shafts. The radius and ulna are more robust, the manus proportionately shorter, and
the manual unguals less recurved than in the contemporaneous basal theropod Eodromaeus murphi. An outstanding feature of
the manus of Eoraptor is the twisted shaft of the first phalanx of the pollex, which deflects medially the tip of the ungual as in
basal sauropodomorphs. The long bones of the hind limb have more robust shafts than those of Eodromaeus, although in both
genera the tibia remains slightly longer than the femur.
RESUMEN—Describimos el sauropodomorfo basal Eoraptor lunensis basados en el esqueleto pr´
acticamente completo del
holotipo y espec´
ımenes referidos, todos ellos descubiertos en el Miembro Cancha de Bochas de la Formaci ´
on Ischigualasto, en
el noroeste de Argentina. El gr´
acil cr´
aneo tiene las narinas externas ligeramente agrandadas, una amplia fosa antorbital con
un margen dorsal prominente y evertido, y ausencia de extensiones neum´
aticas en los huesos circundantes. El alto cuadrado
presenta todo su margen anterior solapado por el delgado proceso ventral del escamoso y la mand´
ıbula tiene una junta medial
entre un proceso linguoide del esplenial y un canal en el angular. Todas las coronas dentarias y maxilares, menos las m´
as
posteriores, tienen una constricci ´
on basal y los dent´
ıculos marginales son largos y orientados m´
as verticalmente que en el
aserrado t´
ıpico de los ter ´
opodos. El pterigoideo tiene filas de dientes palatales rudimentarios. Los centros de las v´
ertebras
son huecos, aunque no demostrablemente neumatizados, y todos los huesos largos tienen las di´
afisis huecas. El radio y la ulna
son m´
as robustos, la mano proporcionalmente corta y los ungueales manuales menos recurvados que en el contempor´
aneo
ter ´
opodo basal Eodromaeus murphi. Una caracter´
ıstica sobresaliente de la mano de Eoraptor es la rotaci ´
on de la primera
falange del pulgar, que desv´
ıa medialmente la punta del ungueal como en los sauropodomorfos basales. Los huesos largos de
las piernas tienen di´
afisis m´
as robustas que aquellas de Eodromaeus, aunque en ambos g´
eneros la tibia es ligeramente m´
as larga
que el f´
emur.
INTRODUCTION
Much of the current knowledge about the earliest dinosaurs
comes from Late Triassic–aged (Carnian–early Norian) strata of
the Ischigualasto Formation in northwestern Argentina (Currie
et al., 2009) and the Santa Maria Formation in southeastern
Brazil (Langer, 2005). Herrerasaurid theropods, measuring 3–4 m
in length, were among the first to be discovered, namely, Her-
rerasaurus ischigualastensis from Argentina (Reig, 1963; Sereno
and Novas, 1992, 1994; Sereno, 1994) and Staurikosaurus pricei
from Brazil (Colbert, 1970; Bittencourt and Kellner, 2009). Re-
cent work in the Ischigualasto Formation of Argentina has added
another herrerasaurid, Sanjuansaurus gordilloi, to this group (Al-
cober and Mart´
ınez, 2010).
Basal dinosaurs of short body length, 2 m or less, were
discovered along with the first herrerasaurids (Pisanosaurus;
Casamiquela, 1967; Bonaparte, 1976), although more complete
remains would not come to light in either Argentina or Brazil
until the 1990s. In Argentina, one basal theropod, Eodromaeus
(Mart´
ınez et al., 2011), and three basal sauropodomorphs, Eo-
raptor (Sereno et al., 1993), Panphagia (Mart´
ınez and Alcober,
2009), and Chromogisaurus (Ezcurra, 2010), have been described.
Two additional basal sauropodomorphs have been described from
*Corresponding author.
Brazil, Saturnalia (Langer et al., 1999, 2007; Langer, 2003) and
Pampadromaeus (Cabreira et al., 2011).
The holotypic specimen of Eoraptor lunensis comprises the sin-
gle most complete skull and postcranial skeleton of a Carnian-
aged dinosaur. During the 1991 Argentine-American Expedition,
one of the authors (R.N.M.) lifted its skull from a reddish-gray
siltstone outcrop in the lower portion of the Ischigualasto For-
mation in the Valle de la Luna (‘Valley of the Moon’) of Is-
chigualasto Provincial Park (Gore, 1993) (Figs. 1, 2A). The re-
gion local to the find is known as Cancha de Bochas (‘Field of
Balls’), named after the abundant sandstone concretions in the
area that weather free as spheroids (Fig. 2D). The skull was com-
pletely covered by a layer of gray hematitic cement, except for
the labial surface of two maxillary crowns (Fig. 2C). The remain-
der of the skeleton lay underneath a thin layer of matrix ex-
cept for the distal one-half of the tail, which had eroded away
(Fig. 2B). The following description is based primarily on the holo-
typic skeleton.
Other, less complete material referred to Eoraptor lunensis
came to light before and after discovery of the holotypic spec-
imen (Table 1). Some of these specimens provide important in-
formation unavailable or poorly exposed in the holotype, such as
vertebral morphology obscured by articulation and the complete
morphology and articular relations of the distal crus and proximal
tarsals. The most important of these was discovered in the wall of
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84 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 1. Type locality of Eoraptor lunensis in the Ischigualasto For-
mation at the southern end of the Valle de Luna in a fossiliferous area
known as Cancha de Bochas. Photograph taken in 1991 looking south with
lava-capped Cerro Morado in the background (photograph by P.C.S.).
the trench during excavation of the holotype and preserves two an-
terior dorsal vertebrae and most of an articulated right hind limb,
none of which was encrusted with the hematitic cement present
on the adjacent holotypic skeleton. We discuss several aspects of
TABLE 2. Blocks composing the holotypic skeleton of Eoraptor lunen-
sis (PVSJ 512) after mechanical preparation (see Fig. 4).
Block Description
1 Skull, proatlas, atlas, and anterior portion of the axis
2 Axis (posterior portion) and cervical vertebrae 3–8 and
associated ribs
3 Cervical vertebra 9, dorsal vertebrae 1 and 2 and associated ribs
4 Right manus
5 Dorsal vertebrae 3–5 and associated ribs, right scapulocoracoid,
right forelimb except the manus, and distal left scapular blade
6 Left forelimb
7 Dorsal vertebrae 6–12 and associated ribs, both pubic blades,
most of the left hind limb, and some gastralia
8 Articulated series of partial gastralia
9 Dorsal vertebrae 13 and 14 and associated ribs
10 Dorsal vertebra 15, sacrum, caudal vertebrae 1–3 and associated
chevrons, associated ribs, both ilia, proximal pubes and ischia,
and most of the right hind limb
11 Distal portion of the right pes
12 Distal ischia, distal right femur, and proximal right tibia and
fibula
13 Caudal vertebrae 4 and 5 and associated chevrons
14 Caudal vertebrae 6–9 and associated chevrons
15 Caudal vertebrae 10–12 and associated chevrons
16 Caudal vertebrae 13–17 and associated chevrons
cranial and postcranial function in light of the new descriptive and
comparative information.
Institutional Abbreviations—AMNH, American Museum of
Natural History, New York, New York, U.S.A.; MACN, Museo
Argentino de Ciencias Naturales, Buenos Aires, Argentina;
MCZ, Museum of Comparative Zoology, Harvard University,
Cambridge, Massachusetts, U.S.A.; MOR, Museum of the Rock-
ies, Bozeman, Montana, U.S.A.; MWC, Museum of Western
Colorado, Grand Junction, Colorado, U.S.A.; NHMUK, The
Natural History Museum, London, U.K.; PVSJ, Museo de Cien-
cias Naturales, Universidad Nacional de San Juan, San Juan,
Argentina; UCMP, University of California, Museum of Paleon-
tology, Berkeley, California, U.S.A.; USNM, National Museum of
Natural History, Washington, D.C., U.S.A.; UUVP, University of
Utah, Vertebrate Paleontology Collections, Salt Lake City, Utah,
U.S.A.; YPM, Yale University, Peabody Museum, New Haven,
Connecticut, U.S.A.
MATERIALS AND METHODS
Fossil Preparation
The holotypic skeleton of Eoraptor lunensis (PVSJ 512) was
contained within a single irregular concretion that formed a
TABLE 1. Holotypic and referred material of Eoraptor lunensis.
Specimen Maturity Description
PVSJ 512
(holotype)
Adult Skull and articulated skeleton lacking most of left scapulocoracoid, most of left manual phalanges, and
caudal vertebrae posterior to caudal vertebra 17
PVSJ 559 Adult Two anterior dorsal vertebrae, rib shafts, partial right hind limb including a femur lacking the head, tibia,
distal one-half of the fibula, astragalus, calcaneum, and metatarsal fragments
PVSJ 745 Subadult Lower portion of the braincase including the basioccipital and basisphenoid, several partial cervical and
dorsal vertebrae, portions of right and left ilia, section of ischial shaft, proximal and distal ends of both
femora, proximal end of both tibiae, proximal end of right fibula, and proximal ends of two metatarsals
PVSJ 852 Subadult Right femur
PVSJ 855 Adult Right femur
PVSJ 860 Adult Proximal and distal ends of left femur, distal end of right femur, proximal and distal ends of right tibia,
proximal end of left tibia, and proximal end of right fibula
PVSJ 862 Subadult Proximal end of right humerus, distal ends of both femora, distal end of right tibia, proximal end of right
fibula, and right astragalus
PVSJ 876 Adult Right femur lacking midsection
All specimens come from the Cancha de Bochas Member of the Ischigualasto Formation in the local region known as Cancha de Bochas. PVSJ 559 was
found in the wall of the trench around the holotypic skeleton (PVSJ 512) during excavation.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 85
FIGURE 2. Type locality of Eoraptor lunensis in the Ischigualasto Formation. A, view to the south of the excavation site showing a shallow drainage
(by the left hand of P.C.S.) that truncated the tail at midlength. B, holotypic skeleton (PVSJ 512) as exposed prior to jacketing. C, the skull and neck of
the holotypic skeleton (PVSJ 512) encrusted in a hematitic matrix. D, spheroidal, hematitic, sandstone concretions weathering out near the type locality
in Cancha de Bochas (‘field of balls’), Valle de Luna, Ischigualasto.
thin layer over most of the external bone surfaces (Fig. 2B, C).
The concretion and surrounding matrix blend together; both are
composed of a red-brown, hematitic, muddy siltstone, which
was tightly adhered to the beige-colored bone. Although the
matrix is calcareous, it was not detectably weakened by topi-
cal treatment with strong hydrochloric acid. Preparation, there-
fore, was accomplished entirely by hand with carbide-tipped
dental picks and pneumatic scribes with final cleaning by air
abrasives (Fig. 3). The skull and anterior-most end of the
cervical column was separated from the remainder of the
postcranial skeleton, which was divided into 15 blocks (Fig. 4;
Table 2).
Anatomical Orientation and Terms
We employ traditional, or ‘Romerian,’ directional terms over
veterinarian alternatives (Wilson, 2006). ‘Anterior’ and ‘poste-
rior,’ for example, are used as directional terms rather than the
veterinarian alternatives ‘rostral’ or ‘cranial’ and ‘caudal.’ We fol-
low Wilson (1999) and Wilson et al. (2011) regarding terminology
for vertebral laminae and fossae, respectively.
Computed Tomography
Computed tomographic (CT) scans were taken of the holotypic
skull of Eoraptor lunensis (PVSJ 512) at the High-Resolution X-
ray Computed Tomography Facility at The University of Texas
at Austin. Three orthogonal rotations (roll, pitch, yaw) and three
orthogonal slice movies (coronal, horizontal, sagittal) are avail-
able online (http://digimorph.org/specimens/Eoraptor lunensis).
Although the CT imaging provides valuable information on cross-
sectional shape and on some internal morphology, discerning the
boundaries between bone, tooth, and matrix in many regions of
the skull is difficult or impossible.
More useful cross-sectional information was gleaned from
breakage surfaces between skeletal blocks (Fig. 4), which provided
information on the internal structure of the axial column and many
long bones.
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86 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 3. Photograph of the skull of Eorap-
tor lunensis (PVSJ 512) after preparation. A,
lateral view of the right (down) side of skull. B,
enlarged right lateral view of the snout. Scale
bar equals 5 cm in Aand2cminB.
GEOLOGIC SETTING
Stratigraphic Position
The Ischigualasto-Villa Uni´
on Basin of northwestern Argentina
is part of an extensional rift system that developed within the
southern end of South America and southern Africa during an
early stage in the breakup of southern Pangaea (Currie et al.,
2009). The basin fill comprises a thick nonmarine sequence of
Triassic rocks, the Agua de le Pe ˜
na Group, which includes the
mid-Carnian to early Norian Ischigualasto Formation (Fig. 1; see
Mart´
ınez et al., 2011; Mart´
ınez et al., 2013).
The most abundant vertebrate fossils come from the lower two
members (La Pe ˜
na and Cancha de Bochas members), which are
well exposed along the southern edge of the basin in a region
called the Valle de la Luna. All of the remains of Eoraptor lunen-
sis come from the Cancha de Bochas Member in the Valle de
la Luna (Fig. 1), which has been radioisotopically dated to the
mid-Carnian (ca. 231.4 Ma; Rogers et al., 1993; Mart´
ınez et al.,
2011). The holotypic specimen of Eoraptor lunensis (PVSJ 512)
was found approximately 93 m above the unconformity between
the Los Rastros and Ischigualasto formations in an overbank de-
posit composed of reddish-gray, calcareous and hematitic, muddy
siltstone. Referred specimens come from near the same level and
area (Table 1; Mart´
ınez et al., 2013).
Associated Fauna
Fossil vertebrates found near Eoraptor lunensis within the
local area of the Cancha de Bochas include the basal thero-
pod Herrerasaurus ischigualastensis (Novas, 1994; Sereno, 1994,
2007a; Sereno and Novas, 1994), the traversodontid cynodont
Exaeretodon argentinus (Bonaparte, 1966), the carnivorous
cynodonts Ecteninion lunensis (Mart´
ınez et al., 1996), Probele-
sodon sanjuanensis (Mart´
ınez and Forster, 1996) and Probain-
ognathus sp. (Bonaparte and Crompton, 1994), the dicynodont
Ischigualastia jenseni (Cox, 1965), the crurotarsan archosaur
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FIGURE 4. Drawing of the skeleton of Eoraptor lunensis (PVSJ 512) in left lateral view showing by colored areas the division of the specimen into 16 blocks after mechanical preparation
(see Table 2). Dashed line indicates a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bar equals 10 cm.
87
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FIGURE 5. Photograph of the skeleton of Eoraptor lunensis (PVSJ 512) in left lateral view. A small ventral block with several partial gastralia is not included. Scale bar equals 10 cm.
88
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FIGURE 6. Drawing of the skeleton of Eoraptor lunensis (PVSJ 512) in left lateral view. Abbreviations:I–V, manual and pedal digits I–V; C1,4,5, cervical vertebra 1, 4, 5; CA1,4,6,11,
14,17, caudal vertebra 1, 4, 6, 11, 14, 17; ch4,6,11,14,16, chevron 4, 6, 11, 14, 16; co, coracoid; D1,5,10,15, dorsal vertebra 1, 5, 10, 15; dt4, distal tarsal 4; fe, femur; fi, fibula; ga, gastralia; h,
humerus; il, ilium; is, ischium; l, left; pu, pubis; r, right; S1, sacral vertebra 1; sc, scapula; ti, tibia. Dashed line indicates a missing margin; hatching indicates a broken surface; shading indicates
matrix. Scale bar equals 10 cm.
89
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FIGURE 7. Photograph of the skeleton of Eoraptor lunensis (PVSJ 512) in right lateral view. Small ventral block with several partial gastralia is not included. Scale bar equals 10 cm.
90
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FIGURE 8. Drawing of the skeleton of Eoraptor lunensis (PVSJ 512) in right lateral view. Small ventral block with several partial gastralia is not included. Abbreviations:I–V, manual and
pedal digits I–V; C3,5,7,9, cervical vertebra 3, 5, 7, 9; CA4,12, caudal vertebra 4, 12; ch7, chevron 7; co, coracoid; D10,15, dorsal vertebra 10, 15; dt4, distal tarsal 4; fe, femur; fi, fibula; ga,
gastralia; h, humerus; il, ilium; is, ischium; l, left; pu, pubis; r, right; ra, radius; sc, scapula; ti, tibia; ul, ulna. Dashed line indicates a missing margin; hatching indicates a broken surface; shading
indicates matrix. Scale bar equals 10 cm.
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FIGURE 9. Composite drawing of the skeleton of Eoraptor lunensis (PVSJ 512) in left lateral view, with information added from the opposite side when bones are obscured by matrix. Small
ventral block with several partial gastralia is included. Abbreviations:I–V, manual and pedal digits I–V; C1,3,5, cervical vertebra 1, 3, 5; CA1,4,6,11,14,17, caudal vertebra 1, 4, 6, 11, 14,
17; ch4,6,11,14,16, chevron 4, 6, 11, 14, 16; co, coracoid; D1,5,10,15, dorsal vertebra 1, 5, 10, 15; dt4, distal tarsal 4; fe, femur; fi, fibula; ga, gastralia; h, humerus; il, ilium; is, ischium; l, left;
pu, pubis; r, right; ra, radius; S1, sacral vertebra; sc, scapula; ti, tibia; ul, ulna. Dashed line indicates a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bar
equals 10 cm.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 93
Saurosuchus galilei (Sill, 1974), and abundant remains of the rhyn-
chosaur Scaphonyx sanjuanensis (Huene, 1926a). For a complete
faunal list, see Mart´
ınez et al. (2013).
Taphonomy
The holotypic skeleton of Eoraptor lunensis was buried on
its right side (Figs. 2A–C, 4–9). The jaws are tightly opposed,
and the skull and neck are flexed dorsally. Both hind limbs are
folded close to the body. This configuration suggests that the in-
terspinous ligaments on the dorsal aspect of the cervical column
and flexor tendons on the ventral aspect of the hind limbs short-
ened before burial, as a result of subaerial desiccation, tetanus,
or both (Marshall Faux and Padian, 2007). These ligaments
and tendons are larger and/or more numerous that those that
effect the opposing action on the axial column or hind limb,
and so perhaps it is not surprising that they control postmortem
movement.
Subaerial exposure prior to burial is also suggested by the
poorer preservation of bone surfaces on the left (upper) side of
the skeleton. This is particularly apparent in the pelvic girdle and
hind limb, which were covered in concretion and could not have
been altered by recent erosion. The skull shows similar differen-
tial preservation (left/upper side weathered; right/lower side well
preserved), but some loss on the upper side is probably the result
to surface erosion (Figs. 10–13).
All skeletal elements are preserved in articulation except the
right scapula, which was dislocated and rotated from the underside
of the carcass to the opposite side of the rib cage (Fig. 9). It is not
clear how this dislocation took place, because the associated right
forelimb remains close to its anatomical location on the underside
of the carcass (Figs. 7, 8). Postmortem scavenging is a weak ex-
planation for this displacement, because no tooth marks nor other
signs of selective postmortem movement are discernable. The gas-
tral cuirass, for the most part, is in a position anterior to the distal
end of the pubes, and so the trunk cavity appears to have been
intact at final interment (Fig. 9).
Although the carcass may have been dehydrated before burial,
there are no skin impressions. The carpals, tarsals, and cartilage-
covered ends of the long bones are sometimes difficult to distin-
guish from the matrix. The external surface of the left astragalus,
for example, blends into the surrounding matrix. In some cases,
the boundaries between bones have been nearly obliterated by
postmortem mineralization and recrystallization. The articulated
proximal ends of the right tibia and fibula, for example, blend to-
gether where they are in contact.
All vertebral centra and long bones are hollow, with extensive
internal cavities bounded by thin walls. As a result, some bones
have been crushed and flattened after burial. The medullary cavity
in the left ulna, for example, has collapsed so that the medial side
of the bone is concave rather than convex. Postmortem crushing
is strongest in the left forelimb, although many bones have local
areas of collapse or brittle fracture.
A very small (3 mm long), subconical, recurved crown is pre-
served lying against the posterior side of the right posterolateral
wing of the parietal at the back end of the skull. The crown
does not belong to Eoraptor but pertains to an unknown small
carnivore. Because the crown does not appear to be transversely
compressed or striated, it is unlikely to be from a carnivorous
archosaur. Other disarticulated bones from animals larger than
Eoraptor, such as the crurotarsan archosaur Saurosuchus, were
also found near the skeleton. Because articulated and disarticu-
lated vertebrate fossils were fairly common in the general area
(Cancha de Bochas) where the skeleton of Eoraptor was discov-
ered, there is probably no special significance to the proximity of
the small tooth and occiput of Eoraptor.
A second partially articulated specimen of Eoraptor (PVSJ
559) was discovered in the outer wall of the excavation trench
around the holotypic skeleton (Fig. 2A). It consists of two ante-
rior dorsal vertebrae, rib shafts, a partial articulated right hind
limb including a femur (lacking the head), tibia, distal one-half
of the fibula, astragalus, calcaneum, and metatarsal fragments
(Table 1).
Skeletal Maturity
At the time of death, the holotypic skeleton appears nearly ma-
ture and may have been approaching maximum adult body size.
Most of the bones of the skull are tightly articulated, and the neu-
ral arches and centra are fully coossified along the vertebral col-
umn. The apparent separation of some neural arches from their
respective centra (e.g., anterior cervical vertebrae, mid-caudal ver-
tebrae) is due to postmortem fracturing of the thin lateral wall of
the neural canal. The best-preserved and exposed vertebrae in-
clude cervical vertebrae 5–7 and 9, dorsal vertebrae 7 and 9, and
caudal vertebrae 8 and 11 (Fig. 9). In these vertebrae, the neural
arch and centrum are intimately articulated with partial or com-
plete obliteration of the neurocentral suture.
A few sutures, nevertheless, remain open and unfused in the
holotypic specimen. These include the neurocentral sutures in the
sacral vertebrae, the contact between the sacral ribs and iliac blade
(‘iliocostal junction’; Wilson, 2011), and the scapulocoracoid su-
ture. The holotypic skeleton (PVSJ 512), thus, may have been a
young adult approaching skeletal maturity.
Adult Body Length
Nearly all of the referred material is very comparable in size;
some specimens are slightly larger and others slightly smaller
than the holotype (Table 1). The long bones of the partial hind
limb found in the trench wall (PVSJ 559) near the holotype are
approximately 9% longer (tibial length =170 vs. 156 mm). The
preserved portion of the holotypic skeleton (skull to mid-tail)
measures 90 cm in length. Caudal vertebrae 1–17 constitute ap-
proximately one-half of tail length, judging from other dinosaurs
that do not show caudal elongation or other caudal specializations
(e.g., Plateosaurus; Huene, 1926b). The anterior one-half of the
tail measures 30 cm, suggesting an overall body length of 120 cm
for the holotypic skeleton. PVSJ 559, in turn, would measure
approximately 130 cm in length.
Although a larger sample size is needed to increase confidence,
it may well be that Eoraptor lunensis, like the closely related
basal sauropodomorphs Panphagia protos (Mart´
ınez and Alcober,
2009), Chromogisaurus novasi (Ezcurra, 2010), and Pampadro-
maeus barberenei (Cabreira et al., 2011), reached maximum body
length at just under 150 cm in length.
SYSTEMATIC PALEONTOLOGY
DINOSAURIA Owen, 1842
SAURISCHIA Seeley, 1887
SAUROPODOMORPHA Huene, 1932
EORAPTOR Sereno, Forster, Rogers, and Monetta, 1993
EORAPTOR LUNENSIS Sereno, Forster, Rogers,
and Monetta, 1993
(Figs. 3–93)
Holotype—PVSJ 512, articulated skeleton lacking portions of
the left side of the skull, caudal vertebrae distal to caudal vertebra
17, most of the left scapula, left coracoid, left manual unguals, and
the distal two phalanges of right pedal digit III (Figs. 5–9).
Type Locality and Horizon—S31◦064, W68◦5418, along the
northeastern edge of Cancha de Bochas, Valle de la Luna, Is-
chigualasto Provincial Park, San Juan, Argentina. The skeleton
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94 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 10. Stereopair of the skull of Eoraptor lunensis (PVSJ 512) in right lateral view. Scale bar equals 5 cm.
was located approximately 93 m above the base of the Is-
chigualasto Formation (Rogers et al., 1993).
Age—Mid-Carnian on the basis of a radioisotopic date
(Ar40/Ar39) not far in section below the type locality (Rogers et al.,
1993) and recently recalibrated to 231.4 Ma (Gradstein and Ogg,
2009; Mart´
ınez et al., 2011).
Revised Diagnosis—Small basal sauropodomorph with the fol-
lowing autapomorphies: premaxilla posterolateral process slen-
der with tongue-shaped distal expansion; nasal with transversely
broad, horizontal shelf with a convex lateral margin that over-
hangs the antorbital fossa; pterygoid process on posterior palate
margin that articulates laterally in a synovial socket in the ec-
topterygoid; narrow premaxilla-maxilla diastema approximately
one crown in width; maxillary crowns with a prominent lateral em-
inence; accessory articular process on the medial aspect of mid-
cervical prezygapophyses; extreme hollowing of dorsal centra and
neural arches.
Eoraptor lunensis can be differentiated from Panphagia protos
by its shallow neurovascular groove on the lateral aspect of the
dentary, less pronounced ridge on the lateral aspect of the suran-
gular, less expanded distal scapular blade (approximately twice
neck width), more perpendicular distal border on scapular bade,
longer pubic blades (more than four times distal blade width), tib-
ial cnemial crest and opposing proximal condyles more anteropos-
teriorly expanded, tibial distal end more transversely expanded,
and the ascending process and posterior fossa on the astragalus
much broader transversely (approximately one-third the width of
the astragalus).
Eoraptor lunensis can be differentiated from Chromogisaurus
novasi by the more strongly inturned femoral head, the markedly
asymmetrical shape of the fourth trochanter, the tibial cne-
mial crest and opposing proximal condyles more anteroposte-
riorly expanded, and the tibial distal end more transversely
expanded. Several of these points of distinction may have been
influenced by weathering or crushing in Chromogisaurus novasi,
which is not as well preserved as material pertaining to Eoraptor
lunensis.
Referred Specimens—One referred specimen (PVSJ 559) was
found in the wall of the excavation trench approximately 25 cm
from the holotypic skeleton. Other specimens (PVSJ 745, 852, 855,
860, 862, 876) were found in the same region (Cancha de Bochas)
and include a few braincase elements, some cervical and dorsal
vertebrae, two partial hind limbs, and three femora (Table 1). Two
specimens, PVSJ 559 and 862, are well preserved and provide the
best view of the morphology of the anterior dorsal vertebrae, fe-
mur, tibia, fibula, and proximal tarsals.
PVSJ 559 is the most complete referred specimen and thus
has the most overlap with other sauropodomorphs from the Is-
chigualasto Formation. The tibia and astragalus have the broad
proportions characteristic of Eoraptor lunensis compared with
Panphagia protos, as differentiated above. The ascending pro-
cess of the astragalus in PVSJ 559 and 862, for example, con-
stitutes approximately one-third of the width of the bone, un-
like the much narrower condition in Panphagia protos (Mart´
ınez
and Alcober, 2009:fig. 9D). The prominent anteromedial cor-
ner of the astragalus in both specimens (PVSJ 559, 862) is a
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 95
FIGURE 11. Drawing of the skull of Eoraptor lunensis (PVSJ 512) in
right lateral view. Abbreviations:a, angular; apmf, anterior premaxillary
foramen; asaf, anterior surangular foramen; d, dentary; ec, ectopterygoid;
emf, external mandibular fenestra; f, frontal; j, jugal; m, maxilla; m2,8,
14, maxillary tooth 2, 8, 14; n, nasal; p, parietal; pl, palatine; pm, premax-
illa; pm1,2,4, premaxillary tooth 1, 2, 4; po, postorbital; pra, prearticular;
prf, prefrontal; psaf, posterior surangular foramen; q, quadrate; qj, quadra-
tojugal; sa, surangular; sf, subnarial foramen; sq, squamosal. Dashed line
indicates a missing margin; hatching indicates a broken surface; shading
indicates matrix. Scale bar equals 5 cm.
sauropodomorph synapomorphy, but that feature cannot differ-
entiate among sauropodomorph genera within the Ischigualasto
Formation.
Referral of the more fragmentary specimens is more tentative
(PVSJ 852, 855, 860, 876). The bone most commonly preserved
among these specimens is the femur, which in its entirety or as bro-
ken ends does resemble the femur in the holotype. Among other
Ischigualasto sauropodomorphs, however, the femur is known
only in Chromogisaurus novasi and is crushed. So referral of these
specimens to Eoraptor lunensis on the basis of the femur is not
strongly supported and must remain tentative.
DESCRIPTION
Skull Overview
The skull of Eoraptor is subtriangular in lateral and dorsal views
and deeper than wide in posterior view (Figs. 10–19; Table 3). The
external naris is slightly enlarged as in other sauropodomorphs,
such that its maximum diameter is at least 50% that of the orbit
(Fig. 20). The orbit in Eoraptor is large relative to skull length.
This is viewed here as an allometric consequence of small body
size, because it is the usual condition in dinosaurs of comparable
size (e.g., Lesothosaurus; Sereno, 1991). The sidewalls of the or-
bit are concave dorsally and posteriorly. In anterior of the skull
(Fig. 18), the orbital flange on the postorbital projects laterally.
The sidewall of the skull is occupied by a large antorbital
fossa, which does not extend as diverticulae into bordering cra-
nial bones, as commonly occurs in neotheropods (Figs. 21, 22).
The ventral margin of the antorbital fossa and anterior end of
the snout have neurovascular openings similar to that in basal
sauropodomorphs, which include anterior dentary and premax-
illary foramina, a subnarial foramen, and a row of foramina on
the maxilla that ends in one large foramen that opens posteriorly
(Figs. 21–23). The row of foramina ventral to the antorbital region
with the posterior-most foramen opening posteriorly characterizes
basal sauropodomorphs (e.g., Plateosaurus, Galton, 1984; Mas-
sospondylus, Sues et al., 2004; Adeopapposaurus, Mart´
ınez, 2009).
The lacrimal has only a shallow antorbital invagination and shares
the anterodorsal margin of the orbit margin with a relatively large
prefrontal, as is common among basal sauropodomorphs (Figs. 24,
25; Sereno, 2007b). The laterotemporal fenestra has a broad, hour-
glass shape in lateral view and is bordered posteriorly by slender
opposing processes of the squamosal and quadratojugal, as is also
TABLE 3. Measurements (in mm) of the skull of Eoraptor lunensis
(PVSJ 512).
Dimension Measurement
Skull length 123
Preorbital skull length 54
Posterior skull height 43
Width of quadrate condyles 10
Transverse width of occiput (36)
Quadrate height 34
Maximum diameter of external naris 15
Minimum interorbital orbital width 17
Maximum snout width 32
Maximum temporal width (42)
Vertical diameter of orbit 34
Anteroposterior diameter of orbit 33
Maximum length of antorbital fossa 36
Maximum length of antorbital fenestra 20
Length of upper tooth row 68
Drop in jaw articulation (from maxillary alveolar margin) 7
Maximum height of lower jaw 18
Length of lower jaw 110
Paired structures are measured from the right side. Skull length and pos-
terior skull height were reduced to account for minor displacement of the
upper temporal bar and dislocation of the head of the quadrate from the
squamosal, respectively. Maximum snout width was increased slightly to
account for imbrication of the nasals near the midline. Parentheses indi-
cate estimated measurement.
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96 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 12. Stereopair of the skull of Eoraptor lunensis (PVSJ 512) in left lateral view. Scale bar equals 5 cm.
typical of basal sauropodomorphs (Fig. 26; Sereno, 2007b). On the
better-preserved right side of the skull, the quadrate is disarticu-
lated from the squamosal. The quadrate cotylus of the squamosal
surrounds the quadrate head, unlike the more exposed articulation
seen in many theropods (e.g., Herrerasaurus; Sereno and Novas,
1994) (Figs. 26, 27).
The dorsal skull roof is more fractured than is either side
of the skull (Figs. 14, 15). The fracturing is most pronounced
posterior to the orbits, where the roof over the braincase is
offset several millimeters to the right. Postmortem transverse com-
pression of the skull is most apparent on the roof of the snout,
where the right nasal overlaps the left. The oval supratemporal
fossa has a rounded anterior rim, unlike the sharply defined edge
and depression in Herrerasaurus (Sereno and Novas, 1994).
The palate is transversely compressed and slightly dislodged
from its natural articulation with the skull roof and braincase
(Fig. 16). Anteriorly, the palatines have been displaced dor-
sally toward the skull roof, as seen through the left antorbital
fenestra (Fig. 21). The dorsal displacement of the palate is
greatest at its anterior end, where the footplate of the vomer is
lodged against the roof of the nasals within the external naris
(Fig. 28). The posterior palate has been transversely compressed,
the pterygoids overlapping unnaturally in the midline (Fig. 29).
Judging from the gap between the pterygoid and basipterygoid
processes, the palate has slid anteriorly and slightly dorsally away
from its natural articulation with the basisphenoid (Figs. 29, 30),
with a small amount of displacement in this direction preserved
where the right ectopterygoid arches to contact the jugal (Fig. 31).
The occiput and most proximate axial elements are fractured
and partially disarticulated, which occurred before or during final
burial of the skeleton (Fig. 19). Most of the basioccipital appears
to have broken away, leaving a gap along the ventral margin of the
foramen magnum.
The lower jaws are preserved in natural articulation against the
quadrate condyles on both sides, and the tooth rows are engaged
within the snout (Figs. 17, 32). The relationship between the ante-
rior ends of the lower jaws and snout, therefore, is well preserved
and quite significant; the lower jaws are noticeably shorter than the
upper jaws (Fig. 17), which is not the case in theropod dinosaurs
found in the same horizons (e.g., Herrerasaurus; Sereno and No-
vas, 1994:figs. 1F, 5). The midsection and posterior-most tip of the
left lower jaw broke away during surface weathering, because the
fracture surfaces appear fresh (Figs. 12, 13). That breakage opened
the medial aspect of the opposing lower jaw to preparation, where
all but the anterior end is exposed (Figs. 33, 34).
No sclerotic ossicles nor any part of the hyoid apparatus is pre-
served. Although it is possible that the hyoid apparatus was lost
during surface erosion, the same cannot be said for the sclerotic os-
sicles, because the orbits were full of matrix when discovered. Os-
sified sclerotic rings, which surely were present in life, most likely
were lost prior to or during final burial.
The premaxillary and maxillary teeth are preserved on both
sides of the skull (Figs. 35–37). Only the base of the prominent
third dentary tooth is exposed (Fig. 35B). Recent preparation be-
tween the premaxillary teeth has exposed the anterior end of the
dentary alveolar margin, showing that the smaller first dentary
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 97
FIGURE 13. Drawing of the skull of Eoraptor lunensis (PVSJ 512) in
left lateral view. Abbreviations:a, angular; apmf, anterior premaxillary
foramen; ar, articular; d, dentary; ec, ectopterygoid; f, frontal; j, jugal; l,
lacrimal; lc, lacrimal canal; m, maxilla; m4,11, maxillary tooth 4, 11; n,
nasal; p, parietal; pl, palatine; pm, premaxilla; pm1,4, premaxillary tooth
1, 4; po, postorbital; pra, prearticular; prf, prefrontal; psaf, posterior suran-
gular foramen; pt, pterygoid; q, quadrate; qj, quadratojugal; sa, surangular;
sp, splenial; sq, squamosal; stf, supratemporal fossa. Dashed line indicates
a missing margin; hatching indicates a broken surface; shading indicates
matrix. Scale bar equals 5 cm.
tooth is inset about the space of one alveolus from the anterior end
of the dentary, as in Panphagia (Mart´
ınez and Alcober, 2009) and
many basal sauropodomorphs (Sereno, 2007b; Mart´
ınez, 2009).
Tiny palatal teeth are preserved on both pterygoids along
prominent medial and diagonal ridges (Figs. 38, 39). Palatal teeth
of similar size and distribution were reported in the contempora-
neous basal theropod Eodromaeus (Mart´
ınez et al., 2011). Palatal
teeth are not present on the ventrally projecting mandibular flange
and would not be visible in lateral view of the cranium (Fig. 40).
Dorsal Skull Roof
Premaxilla—The premaxilla has a subtriangular body that
contacts the maxilla medially and ventrally and the nasal dor-
sally (Figs. 10–15, 18, 23). The body is divided equally into a
posterior concave portion that forms the narial fossa and an ante-
rior convex portion that is pierced by neurovascular foramina. The
largest foramen, the anterior premaxillary foramen (sensu Sereno,
1991), is located on both sides above the second premaxillary tooth
near the ventral margin of the narial fossa (Fig. 23). It opens an-
teroventrally into the anterior end of the premaxillary body.
Ornithischians such as Lesothosaurus (Sereno, 1991) usually
have an anterior premaxillary foramen near the anteroven-
tral margin of the narial fossa as in Eoraptor. In basal
sauropodomorphs such as Plateosaurus (Sereno, 2007b) and
Adeopapposaurus (Mart´
ınez, 2009), two or three foramina open
into the premaxilla along the posterior side of a bill attachment
surface, but these are located outside the narial fossa. In theropods
such as Allosaurus (Madsen, 1976), a foramen is usually present
but located farther dorsally on the floor of the external naris and
often on the internal aspect of the premaxilla. There is no fora-
men in this position in Eoraptor. The condition in Eoraptor most
closely resembles that in many ornithischians.
A second external premaxillary foramen is present only on the
left side (Figs. 12, 13). Like the anterior premaxillary foramen, it
is located within the narial fossa near its ventral margin. No other
openings are visible in lateral view of the premaxilla.
The dorsal (internarial) and posterolateral processes of the pre-
maxilla are very slender in Eoraptor (Figs. 12–15, 20). The ta-
pering dorsal process extends distally just beyond the midpoint
of the internarial bar, which arches slightly above the adjacent
nasal roof of the snout. Eoraptor appears to have a simple ‘V’-
shaped premaxilla-nasal suture, as opposed to the more complex
‘W’-shaped suture present in most theropods (Figs. 14, 15; Mad-
sen, 1976). Unfortunately, the premaxilla-nasal suture beyond this
point cannot be followed with certainty.
The right posterolateral process is completely preserved and
articulates against the anterior margins of the right maxilla and
nasal, excluding the former from the margin of the external naris
(Figs. 20, 22). On the left side of the skull, the distal portion of
the left posterolateral process has broken away, exposing a shal-
low trough for its reception on the nasal. The shape of the distal
half of the posterolateral process of the premaxilla is unique. It ex-
pands slightly from the narrow midshaft to form a crescent-shaped
process.
Maxilla—The maxilla articulates with the premaxilla anteriorly,
the nasal anteriorly and dorsally, the lacrimal and jugal poste-
riorly, and the palatine medially (Figs. 10–13, 20–23). Several
neurovascular foramina open laterally on the maxilla. Most
conspicuous is a series of foramina on the narrow ramus below the
antorbital fossa. Most of these are directed anteroventrally, pre-
sumably to supply the marginal tissues of the lips. The posterior-
most foramen, however, is larger than the others and opens
into a groove that passes posteriorly toward the jugal (Fig. 21).
The anterior-most foramen is also slightly larger than the others
(Fig. 22). The size, location, and direction in which these foramina
open is most similar to the condition in basal sauropodomorphs
(e.g., Plateosaurus, Sereno, 2007b; Massospondylus, Sues et al.,
2004; Adeopapposaurus, Mart´
ınez, 2009). The alignment of these
foramina strongly suggest that they are interconnected by a canal
within the maxilla, although no such passage can be discerned in
computed tomographic cross-sections of the skull of Eoraptor.
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98 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 14. Stereopair of the skull of Eoraptor lunensis (PVSJ 512) in dorsal view. Scale bar equals 5 cm.
The subnarial foramen is located between the premaxilla and
maxilla near the alveolar margin and is best preserved on the right
side (Figs. 10–13, 20, 23). Most of the margin of the foramen is
formed by a notch in the maxilla (Fig. 23). The foramen passes
medially between the maxilla and premaxilla to open ventral to
the premaxillary palate, as in basal sauropodomorphs (Sereno,
2007b; Mart´
ınez, 2009), Herrerasaurus (Sereno and Novas, 1994),
and other saurischians that retain this foramen. Another fora-
men, present only on the left side, is situated near the anterior
margin of the maxilla just above the subnarial foramen (Fig. 13).
No other openings are present on the maxilla. The anterior ex-
tremity of the antorbital fossa, which is well preserved on both
sides, does not have a promaxillary fossa or fenestra as occurs
in the basal sauropodomorph Pampadromaeus (Cabreira et al.,
2011), the basal theropods Herrerasaurus (Sereno, 2007a) and Eo-
dromaeus Mart´
ınez et al., 2011), and the basal ornithischian Het-
erodontosaurus (Sereno, 2012).
Eoraptor does not have a ‘subnarial gap,’ or arched diastema,
akin to that in coelophysoids (contra Nesbitt et al., 2009). The
subnarial foramen, best preserved on the right side (Fig. 23),
is bordered by the premaxilla and maxilla and is situated dor-
sal to a short premaxillary-maxillary diastema. The alveolar mar-
gin above the first maxillary tooth curves dorsally, which is
matched by a corresponding prominence on the alveolar mar-
gin of the articulated dentary (Fig. 23). The axis of the short
first maxillary tooth, in addition, is not vertical but rather is
canted slightly anteroventrally toward the diastema, as best pre-
served on the right side (Figs. 20, 35C, D). Thus, the diastema
very likely has functional significance during the procurement
or processing of foodstuffs. In computed tomographic coronal
cross-section, the slightly enlarged third dentary tooth is posi-
tioned near the dorsal expansion in the alveolar margin of the
dentary (Fig. 35A, B). We removed matrix from the base of
the crown of this tooth, which projects dorsally into the palatal
area medial to the maxillary tooth row. In sum, there is a short
premaxilla-maxilla diastema with particular relations with adja-
cent teeth, namely, the first maxillary tooth and the third dentary
tooth.
This condition, however, is very different than that in coelo-
physoid theropods. In coelophysoids, there is no subnarial fora-
men, and the premaxilla articulates loosely with the maxilla
(Tykoski, 2005). The premaxilla lacks the dorsolateral process that
articulates on the lateral aspect of the snout present in Eoraptor.
The better-developed, arched diastema in ceolophysoids is open
laterally to receive the tip of the dentary tooth, and the posterior
premaxillary and anterior maxillary teeth are directed toward one
another (Tykoski, 2005; Sereno, 2012:fig. 91). Some confusion may
have arisen regarding the condition in Eoraptor due to preserva-
tional factors on the left side of the skull, where the first maxillary
tooth is partially dislodged and points much more strongly ante-
riorly (Figs. 12, 13). Also, the edges of the premaxilla and max-
illa are slightly ajar, which has obscured the ventral rim of the
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 99
FIGURE 15. Drawing of the skull of Eoraptor lunensis (PVSJ 512) in dor-
sal view. Abbreviations:aprf, articular surface for prefrontal; ec, ectoptery-
goid; f, frontal; j, jugal; l, lacrimal; m, maxilla; n, nasal; p, parietal; pm, pre-
maxilla; po, postorbital; prf, prefrontal; so, supraoccipital; sq, squamosal;
stf, supratemporal fossa. Dashed line indicates a missing margin; hatching
indicates a broken surface; shading indicates matrix. Scale bar equals 5 cm.
subnarial foramen. The presence of a subnarial foramen and aki-
netic premaxilla-maxilla suture in Eoraptor has been interpreted
correctly in several places (Sereno et al., 1993; Langer and Benton,
2006; Mart´
ınez et al., 2011).
The antorbital fossa (Figs. 20–22) is well developed on the max-
illa and is much broader anteriorly than in the basal theropod Her-
rerasaurus, which has an unusually narrow fossa. This width of the
fossa is considerably narrower dorsal and ventral to the antorbital
fenestra. The anterior rim of the fossa, which forms the anterior
portion of the external antorbital fenestra (sensu Witmer, 1997),
is slightly everted (Figs. 21, 22, 40A). There is no development
of deep pneumatic invaginations or accessory fenestrae or foram-
ina in the antorbital fossa, in contrast to the closely related Pam-
padromaeus (Cabreira et al., 2011) and most tetanuran theropods
(e.g., Allosaurus; Madsen, 1976). The antorbital fossa, however, is
slightly invaginated under the anterior and ventral margins, except
above the fourth through sixth maxillary teeth, where the ventral
floor of the fossa is visible in lateral view (Fig. 21). The rim of the
external antorbital fenestra in this region is lower and sharper than
the more everted, rounded form of the remainder of the opening.
Only the posterior portion of the rim, thus, resembles the raised
relief and rounded cross-sectional profile of the antorbital rim in
coelophysoids (e.g., Coelophysis).
The surface of the fossa is gently concave anterior to the antor-
bital fenestra and dorsal to the fourth to seventh maxillary teeth
(Figs. 21, 22). Dorsal to this region, the fossa becomes distinctly
dorsoventrally convex, as preserved on both sides. The fossa ven-
tral to the antorbital fenestra is narrow and trough-shaped, fac-
ing dorsally as much as laterally. In places on both sides of the
skull, the surface of the fossa has collapsed into underlying tooth
crypts. The ‘D’-shaped inner opening, the internal antorbital fen-
estra (sensu Witmer, 1997), is some 30% longer than dorsoven-
trally deep (Fig. 40A).
An articular trough on the posterior ramus of the maxilla ac-
commodates the lacrimal, jugal, and palatine. Of these, the flaring
ventral ramus of the lacrimal establishes the broadest contact with
the maxilla (Figs. 20, 21, 24). The maxilla-lacrimal suture is over-
lapped anteriorly by a short prong-shaped process of the palatine,
which extends from the posteroventral corner of the antorbital
fenestra (Fig. 24). Posteriorly, the maxilla-lacrimal suture is over-
lapped by the flat, triangular anterior ramus of the jugal.
The posterior ramus of the maxilla tapers to a very slender pro-
cess that extends posteriorly as far as the posterior border of the
orbit (Figs. 10, 11). The process articulates in a slot on the ventral
margin of the anterior ramus of the jugal (Fig. 31). The slender
maxillary process is completely preserved on the right side, where
it lies adjacent to the articular slot on the jugal.
Only a portion of the posterior ramus of the maxilla is visible
in medial view. The maxillae articulated with each other proxi-
mally by way of anteromedial (=palatal) processes. These pro-
cesses are exposed in dorsal view, forming the floor beneath the
external nares. Judging from the tight articulation of these pro-
cesses in the midline, the vomer footplate (Fig. 28) may have been
located above the position of the second maxillary tooth, as in Her-
rerasaurus (Sereno and Novas, 1994).
Nasal—The nasal spans approximately one-half of the length
of the skull (Figs. 10–15, 41). It is proportionately shorter than in
long-snouted theropods such as Herrerasaurus and Coelophysis,in
which it forms more than one-half of skull length. Sutural contacts
of the nasal include the premaxilla, maxilla, lacrimal, prefrontal,
and frontal. In lateral view, the internarial bar arches slightly
above the sloping margin of the skull roof; crushing has slightly ex-
aggerated the change in angle as the internarial bar joins the roof
of the snout on the right side (Fig. 20). This condition is highly
reminiscent of that in many basal sauropodomorphs, such as Pla-
teosaurus, when this fragile region of the snout has been carefully
reconstructed (Sereno, 2007b:fig. 4). The postnarial portion of the
nasal is arched gently anteroposteriorly and transversely, with the
prominent, overhanging lateral margin of the bone slightly up-
turned (Figs. 14, 15, 20, 21). The region immediately adjacent to
the internasal suture is not as depressed as in Herrerasaurus.
The posterodorsal (internarial) process is the most slender pro-
cess of the nasal (Fig. 23). It tapers in width from a horizontal
sheet of bone above the posterior corner of the external naris to
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100 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 16. Stereopair of the skull of Eoraptor lunensis (PVSJ 512) in ventral view. Scale bar equals 5 cm.
a narrow, transversely compressed process at its tip. Near its ex-
tremity, the suture with the premaxilla is either fused or obliter-
ated during fossilization. It appears to have a simple ‘V’-shaped
termination between the premaxillary processes (Figs. 14, 15).
The subtriangular anteroventral process of the nasal forms the
posterior margin of the external naris and is overlapped laterally
by the posterolateral process of the premaxilla and the maxilla
(Fig. 22). The ventral tip of this process rests on the anterior
margin of the maxilla just medial to the posterolateral process of
the premaxilla. The broad posterior process of the nasal overlaps
the frontal but is weathered along its distal margin on both
sides (Figs. 14, 15). A portion of the posterior margin of the left
nasal appears to be preserved in articulation with the frontal. As
best as can be discerned from this specimen, the nasal-frontal
suture seems to be similar to that of Herrerasaurus and many
other theropods (Allosaurus; Madsen, 1976), with an anteriorly
projecting ‘V’-shaped embayment between the posterior ends of
the nasals (Fig. 15).
The nasal forms a thin, laterally projecting shelf over the antor-
bital fossa (Fig. 40A). In dorsal view, the thin shelf flares laterally
posterior to the narial region (Fig. 41). A portion of the shelf on
the left side was damaged after molding the skull and was replaced
with a cast piece.
The lateral margin of the nasal turns medially where it meets
the lacrimal, as seen in dorsal view (Figs. 14, 15). Close examina-
tion of this margin suggests that the inset suture actually hooks
slightly anteriorly. The nasal, therefore, appears to have a rudi-
mentary posterolateral prong, with the lacrimal inserting between
this prong and the rest of the nasal (Langer and Benton, 2006).
This is best preserved on the right side, where only the distal tip
of the nasal process is broken away. A similar process (postero-
lateral process of the nasal) is present, but better developed, in
many theropods, such as Ceratosaurus (MWC 1.1) and Allosaurus
(Madsen, 1976:pl. 5B). In these theropods, the notch is deeper
than in Eoraptor, and the nasal process overlaps the lateral side
of the lacrimal. The development of at least a rudimentary nasal
posterolateral prong also occurs in some basal sauropodomorphs,
such as Plateosaurus (Sereno, 2007b:fig. 5B), although others show
no such development (Adeopapposaurus; Mart´
ınez, 2009).
Lacrimal—The anterior ramus of the ‘L’-shaped lacrimal is ap-
proximately half as long as the ventral ramus (Figs. 10–13, 20, 21,
24, 25, 40A). The lacrimal is overlapped dorsally by the nasal, me-
dially by the prefrontal, and laterally by the jugal and a hook-
shaped process of the palatine. It rests in a trough on the maxilla
ventrally and has a ‘W’-shaped suture with the maxilla on the wall
of the antorbital fossa.
There is no development of pneumatic spaces within the body
of the lacrimal as occurs in many large theropods (e.g., Allosaurus;
Madsen, 1976). The posterodorsal corner of the fossa, however, is
slightly invaginated as in Herrerasaurus (Sereno and Novas, 1994).
That invagination is best developed on the anterior ramus of the
lacrimal (Figs. 24, 25).
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 101
FIGURE 17. Drawing of the skull of Eoraptor lunensis (PVSJ 512) in
ventral view. Abbreviations:a, angular; d, dentary; ec, ectopterygoid; j, ju-
gal; l, lacrimal; lfo, lacrimal fossa; m, maxilla; m2,11,14, maxillary tooth
2, 11, 14; n, nasal; p, parietal; pl, palatine; pm1,4, premaxillary tooth 1,
4; pra, prearticular; prf, prefrontal; psaf, posterior surangular foramen; pt,
pterygoid; q, quadrate; qj, quadratojugal; sa, surangular; sp, splenial; sq,
squamosal; sym, symphysis. Dashed line indicates a missing margin; hatch-
ing indicates a broken surface; shading indicates matrix. Scale bar equals
5cm.
The orbital surface of the lacrimal, also best preserved on the
right side, is narrow ventrally where it forms a rounded orbital
rim (Fig. 24). A broad groove midway along the ventral ramus
passes dorsally into a large lacrimal foramen, located at approxi-
mately one-third of the way along the ventral ramus. Medial to the
lacrimal foramen and groove, a narrower groove accommodates
the slender tip of the ventral process of the prefrontal.
Prefrontal—The ‘L’-shaped prefrontal contacts the nasal anteri-
orly, the lacrimal laterally, and the frontal posteriorly (Figs. 10–13,
20, 24, 41). The dorsal surface of the prefrontal is gently convex,
whereas the orbital surface is concave. Most of the posterior pro-
cess rests in a deep slot on the lateral side of the frontal. This slot-
ted prefrontal-frontal articulation can be seen in cross-sections of
the orbital rim on both sides. The posterior end of the slot in the
frontal is well exposed on the right side, where the posterior pro-
cess of the prefrontal has broken away.
The ventral process narrows dramatically in width as it passes
along the medial side of the lacrimal foramen (Fig. 24). The tip of
the ventral process appears to be broken away on the right side,
where it is exposed. An articular groove on the lacrimal for this
process extends along at least two-thirds of the length of the ven-
tral ramus of the lacrimal. The presence of a very slender, elon-
gate ventral process equal to the posterior process in length char-
acterizes many saurischians (Plateosaurus, Galton, 1984:fig. 3; Al-
losaurus, UUVP 5519, contra Madsen, 1976:pl. 4A, B).
Frontal—Sutural contacts of the frontal include the nasal and
prefrontal anteriorly and the postorbital and parietal posteriorly,
although the exact course of some of these sutures is difficult
to discern because of surface weathering and marked fracturing
(Figs. 14, 15, 41). Contact between the frontal and the braincase
is not exposed. The frontal has a broad articular surface for the
nasal anteriorly, partially exposed on the left side and fully ex-
posed on the right. Only the lateral portion of the left nasal-
frontal suture is preserved, which is ‘V’-shaped and pointed pos-
teriorly. The prefrontal-frontal suture is exposed on both sides of
the skull and has been described in detail above (Fig. 24). The
frontal-frontal suture is straight, rather than interdigitating, and
forms a butt joint in the midline. The frontal-postorbital suture is
most complete on the right side, where the narrow medial process
of the postorbital rests in an articular depression on the frontal
behind the orbital rim. Posterior to this contact, the surface of
the frontal curves ventrally to form most of the anterior wall of
the supratemporal fossa. The frontal and parietal have been dis-
articulated by right lateral movement of the parietals and brain-
case relative to the rest of the skull. The frontal-parietal suture
zigzags from one supratemporal fossa to the other (Figs. 14, 15,
41). A median notch is formed by the paired frontals, into which
inserts a median triangular process of the parietals. The form
of the suture, such as whether it was interdigitating, cannot be
determined.
Parietal—The parietal contacts the frontal anteriorly and the
squamosal, supraoccipital, and exoccipital-opisthotic posteriorly
(Figs. 14, 15, 19, 41). Contact with other portions of the brain-
case is not exposed. Due to the degree of fracturing, it cannot
be determined whether the parietals were fused. On the better-
preserved left parietal, a raised sinuous edge seems to mark the
medial border of the supratemporal fossa, as is the case in Her-
rerasaurus (Sereno and Novas, 1994). The thin posterolateral wing
of the parietal extends from near the midline toward the head of
the quadrate. The posterior process of the squamosal, however,
separates the parietal and head of the quadrate (Figs. 27, 40A).
Postorbital—The triradiate postorbital contacts the frontal me-
dially, the squamosal posteriorly, and the jugal ventrally (Figs. 10,
11, 14, 15, 26, 27). The postorbital probably contacted the pari-
etal and laterosphenoid on the wall of the supratemporal fossa,
but this region is too fractured to interpret with confidence. All
but the tip of the medial process of the left postorbital has broken
away. The right postorbital, on the other hand, is complete but has
broken into four pieces, which have drifted apart. By reassembling
the pieces, the right postorbital has medial and posterior processes
that are subequal in length and a ventral process that is longer
(Figs. 10, 11). A crescentic orbital flange extends anteriorly from
the central part of the postorbital. The orbital surface of this flange
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102 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 18. Stereopair (A) and drawing (B) of the skull of Eoraptor lunensis (PVSJ 512) in anterior view. Abbreviations:a, angular; apmf, anterior
premaxillary foramen; asaf, anterior surangular foramen; d, dentary; ec, ectopterygoid; emf, external mandibular fenestra; f, frontal; j, jugal; l, lacrimal;
m, maxilla; m1,4,9, maxillary tooth 1, 4, 9; n, nasal; p, parietal; pl, palatine; pm, premaxilla; pm1–4, premaxillary teeth 1–4; po, postorbital; pra,
prearticular; prf, prefrontal; psaf, posterior surangular foramen; q, quadrate; qj, quadratojugal; sq, squamosal. Dashed line indicates a missing margin;
hatching indicates a broken surface; shading indicates matrix. Scale bars equal 3 cm in Aand2cminB.
and of the medial and ventral processes are concave and partially
enclose the orbital cavity, as is well seen in anterior view of the
skull (Fig. 18).
The ventral process has a gently concave lateral surface and is
subtriangular in cross-section (Fig. 26). At midlength the process
is slightly broader anteroposteriorly than transversely. Its rela-
tively robust distal tip curves onto the medial aspect of the jugal.
The transversely flattened posterior process inserts into a slot on
the anterior process of the squamosal (Figs. 26, 27). The medial
process, which projects anteromedially into a slot on the dorsal
surface of the frontal, is particularly slender compared with that
in Herrerasaurus (PVSJ 407) and does not participate significantly
in the wall of the supratemporal fossa (Figs. 10, 11, 14, 15, 41).
Squamosal—The squamosal has four processes, anterior,
ventral, posterior, and medial, which collectively contact the
postorbital anteriorly, the parietal and exoccipital-opisthotic
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 103
FIGURE 19. Stereopair (A) and drawing (B) of the skull of Eoraptor lunensis (PVSJ 512) in posterior view. Abbreviations:ana, atlantal neural
arch; ar, articular; ax, axis; p, parietal; popr, paroccipital process; pro, proatlas; q, quadrate; so, supraoccipital. Dashed line indicates a missing margin;
hatching indicates a broken surface; shading indicates matrix. Scale bars equal 2 cm.
(paroccipital process) posteriorly, and the quadrate and quadrato-
jugal ventrally (Figs. 26, 27). The anterior process is broadest and
is missing portions of its thin ventral edge. As in Herrerasaurus,it
does not appear to expand anteriorly. The medial process, which is
only partially exposed, articulates against the posterolateral wing
of the parietal. The small posterior process is broken just behind
the socket for the quadrate, where it is compressed anteroposteri-
orly and has a subrectangular cross-section. The posterior surface
of the posterior process is flat and articulated against the paroc-
cipital process (Fig. 27). The complete posterior process probably
extended distally no more than 2 mm, as suggested by the length
of the adjacent posterolateral wing of the parietal.
The ventral process of the squamosal is preserved proximally
and distally on the right side (Fig. 26). The base of the process is
anteroposteriorly compressed and articulates against the anterior
side of the everted lateral process of the quadrate. The slender
distal portion of the process is preserved along the anterior
margin of the quadrate. Its tip contacts the quadratojugal, passing
onto its medial side. The squamosal and quadratojugal, therefore,
exclude the quadrate from the border of the laterotemporal fen-
estra. The slender proportions and length of the ventral process
of the squamosal differ markedly from the short, transversely
compressed process in many theropods, such as Herrerasaurus
(Sereno and Novas, 1994). On first inspection, some basal or-
nithischians, such as Lesothosaurus, appear to have a similar
slender ventral process. A considerable portion of the process,
however, wraps around the quadrate shaft; the ventral process,
when fully exposed in Lesothosaurus, is transversely compressed
and tongue-shaped (Sereno, 1991). Pampadromaeus (Cabreira
et al., 2011) and other basal sauropodomorphs, in contrast, have a
slender ventral process identical to that in Eoraptor (Galton,
1984; Sereno, 2007b; Mart´
ınez, 2009; Mart´
ınez et al., 2011).
The body of the squamosal has a shallow, arcuate laterotem-
poral fossa on its lateral surface, positioned between the anterior
and ventral processes (Fig. 26). The articular cup for the head of
the quadrate is unusually deep, as compared with Herrerasaurus or
most other saurischians; it is fully exposed on the right side where
it has a depth in excess of 2 mm (Fig. 27). The upper portion of
the quadrate head would not have been exposed in lateral view
(Fig. 40A). In ventral view, the quadrate cotylus is subtriangular,
the lateral wall of which has a sagittal orientation (Fig. 27). The
long axis of the articular cup has an anteromedial-posterolateral
orientation.
Jugal—The jugal, best preserved on the right side, has ante-
rior, dorsal, and posterior processes that collectively contact the
maxilla, lacrimal, postorbital, quadratojugal, and ectopterygoid
(Figs. 10–13, 20, 24, 26, 31, 40A). The forked posterior process of
the jugal is the most slender. Unlike Herrerasaurus (PVSJ 407) and
many other theropods, however, the anterior process that forms
the ventral margin of the orbit is narrower than the dorsal pro-
cess, as in the closely related sauropodomorph Pampadromaeus
(Cabreira et al., 2011).
The anterior process of the jugal expands at its anterior end,
where it overlaps the lacrimal and approaches the tip of the pala-
tine in the posteroventral corner of the antorbital fossa (Fig. 20).
There is a low, flat surface on the lacrimal immediately above the
anterior end of the jugal, which appears to be an articular sur-
face. If so, it suggests that the dorsal margin of the thin anterior
end of the jugal is missing. With its dorsal margin restored accord-
ingly, the anterior process of the jugal would have expanded in
dorsoventral height anterior to the orbit, a common and primitive
condition among theropods (e.g., Herrerasaurus; Sereno and No-
vas, 1994) and also present in Pampadromaeus (Cabreira et al.,
2011). A deep slot along the ventral margin of the jugal accom-
modates the slender posterior process of the maxilla (Figs. 10, 11,
31). The external edge of the slot is swollen and, anteriorly, this
rounded edge joins the ventral rim of the antorbital fossa, which
has a similar rounded cross-section (Fig. 31). This is the only or-
namentation of the jugal in Eoraptor, and it closely resembles
the condition in Pampadromaeus (Cabreira et al., 2011). In Her-
rerasaurus, in contrast, the external surface of the jugal is rugose
with a low crest.
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104 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 20. Stereopair (A) and drawing (B)
of the snout in the skull of Eoraptor lunensis
(PVSJ 512) in right lateral view. Abbreviations:
antfe, antorbital fenestra; antfo, antorbital fossa;
apmf, anterior premaxillary foramen; d, dentary;
f, frontal; j, jugal; l, lacrimal; lf, lacrimal fora-
men; m, maxilla; m2,15, maxillary tooth 2, 15;
n, nasal; nf, narial fossa; pm, premaxilla; pm1,4,
premaxillary tooth 1, 4; pl, palatine; pomf, poste-
rior maxillary foramen; prf, prefrontal; sf, subnar-
ial foramen. Dashed line indicates a missing mar-
gin; hatching indicates a broken surface; shading
indicates matrix. Scale bars equal 2 cm.
The exposed portion of the dorsal process is short and subtrian-
gular. Its dorsal tip is obscured by overlap of the postorbital. The
posterior process is ‘V’-shaped and slotted for articulation with the
quadratojugal (Fig. 26). The slotted jugal-quadratojugal articula-
tion is constructed, as in Pampadromaeus and in other saurischi-
ans; the deeper dorsal prong of the jugal overlaps the quadratoju-
gal laterally, whereas the ventral prong of the jugal wraps around
its ventral margin to overlap the quadratojugal medially (right
side, PVSJ 512). These posterior processes are subequal in length
and terminate midway along the lower temporal bar.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 105
FIGURE 21. Stereopair (A) and drawing (B)
of the left antorbital region in the skull of
Eoraptor lunensis (PVSJ 512) in lateral view.
Abbreviations:antfe, antorbital fenestra; antfo,
antorbital fossa; l, lacrimal; lc, lacrimal canal; m,
maxilla; m4,11, maxillary tooth 4, 11; n, nasal; pl,
palatine; pomf, posterior maxillary foramen; prf,
prefrontal; pt, pterygoid. Dashed line indicates a
missing margin; hatching indicates a broken sur-
face; shading indicates matrix. Scale bars equal
2cm.
Quadratojugal—The ‘L’-shaped quadratojugal is best pre-
served on the right side (Figs. 10, 11, 26, 32, 40A). The quadra-
tojugal and quadrate appear to be coossified between the jaw
articulation and quadrate foramen on the right side, where the
former overlaps the latter (Fig. 32). On the left side, in contrast,
they are disarticulated and do not appear to have been coossified
(Figs. 12, 13). Quadratojugal-quadrate fusion, which is present
in Herrerasaurus (PVSJ 407), is more commonly reported among
theropods than sauropodomorphs (Gilmore, 1920). The dorsal
process of the quadratojugal curves onto the anteromedial surface
of the lateral flange of the quadrate, where these bones are sepa-
rate and partially disarticulated. The strap-shaped dorsal process
has a relatively uniform width (3 mm) (Fig. 26). Above midheight
on the quadrate shaft, the distal end of the dorsal process inserts
between the tip of the ventral process of the squamosal and the
lateral flange of the quadrate.
The anterior process of the quadratojugal is much shorter than
the dorsal process, but has an equivalent maximum width at its
proximal end as seen in lateral view. Throughout its length, it is
transversely compressed but twists from a vertical orientation near
its base to angle dorsomedially-ventrolaterally, where it inserts be-
tween the posterior articular processes of the jugal (Fig. 26).
The quadratojugal contributes to the lateral-most edge of the
jaw articulation (Figs. 26, 32). A notch on the ventral margin
of the quadratojugal separates a tab-shaped posteroventrally di-
rected process that reaches the jaw articulation. The distal extrem-
ity of this process and a portion of the quadrate condyle are bro-
ken away on the right side (Figs. 26, 32). On the left side, this
process appears to oppose the surangular in natural articulation
(Figs. 12, 13). The quadratojugal and surangular make only a nar-
row, restricted contribution to the jaw joint.
Palate
The exposed bones of the palate include the quadrate, ptery-
goid, palatine, ectopterygoid, and vomer (Figs. 16, 17, 28–32, 40A).
The epipterygoid, if ossified, is not exposed and is not discernable
in computed tomographic cross-sections.
Quadrate—The quadrate contacts the squamosal dorsally and
anteriorly, the pterygoid medially, the quadratojugal laterally, and
the articular and surangular ventrally (Figs. 10–13, 16, 17, 26, 32).
The deep articular cotylus in the squamosal for the head of the
quadrate (Fig. 27) separates the quadrate from the paroccipital
process. The quadrate is taller relative to skull length, and the
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106 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 22. Stereopair (A) and drawing (B) of the anterior portion of the right antorbital region of the skull of Eoraptor lunensis (PVSJ 512) in right
posterolateral view. Abbreviations:antfe, antorbital fenestra; antfo, antorbital fossa; en, external nares; m, maxilla; m1,6, maxillary tooth 1, 6; n, nasal;
pm, premaxilla; sf, subnarial foramen. Dashed line indicates a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bars
equal 1 cm.
condyles are narrower than in Herrerasaurus. The quadrate shaft
is bowed rather than straight in lateral view. With the maxillary
tooth row aligned horizontally, the quadrate head is located pos-
terior, rather than anterior, to the jaw articulation (Figs. 10–13).
The quadrate head is subrectangular in lateral view and trans-
versely compressed (Fig. 26). The crescentic lateral flange of
the quadrate arches laterally from the shaft, diverging from the
quadrate just below the head. In posterior view, a deep notch
FIGURE 23. Stereopair (A) and drawing (B) of the anterior end of the skull of Eoraptor lunensis (PVSJ 512) in right anteroventrolateral view.
Abbreviations:adf, anterior dentary foramen; apmf, anterior premaxillary foramen; d, dentary; en, external nares; l, left; m, maxilla; m3, maxillary
tooth 3; n, nasal; nf, narial fossa; pm, premaxilla; pm1,2,4, premaxillary tooth 1, 2, 4; r, right; sf, subnarial foramen; sym, symphysis. Dashed line
indicates a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bars equal 1 cm.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 107
FIGURE 24. Stereopair (A) and drawing (B) of the anterior portion of the right orbit in the skull of Eoraptor lunensis (PVSJ 512) in posterolateral
view. Abbreviations:antfe, antorbital fenestra; antfo, antorbital fossa; aprf, articular surface for the prefrontal; f, frontal; j, jugal; l, lacrimal; lf, lacrimal
foramen; m, maxilla; n, nasal; pl, palatine; prf, prefrontal. Dashed line indicates a missing margin; hatching indicates a broken surface; shading indicates
matrix. Scale bars equal 1 cm.
ventral to the lateral flange forms most of the margin of the
quadrate foramen (Fig. 32). The lateral flange supports both
the dorsal process of the quadratojugal and the ventral process
of the squamosal along its anterior margin (Fig. 26).
The quadrate condyles are poorly exposed. On the right side,
lateral and medial edges of the condyles can be seen on each side
of the jaw articulation (Fig. 32). Although small portions of the
condyles are missing laterally and medially, their maximum width
FIGURE 25. Stereopair (A) and drawing (B) of the posterodorsal corner of the right antorbital fossa in the skull of Eoraptor lunensis (PVSJ 512)
in anterolateral view. Abbreviations:antfe, antorbital fenestra; antfo, antorbital fossa; f, frontal; l, lacrimal; lfo, lacrimal fossa; n, nasal; prf, prefrontal.
Hatching indicates a broken surface; shading indicates matrix. Scale bars equal 1 cm.
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108 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 26. Stereopair (A) and drawing (B)of
the right laterotemporal region in the skull of Eo-
raptor lunensis (PVSJ 512) in lateral view. Abbre-
viations:aj, articular surface for the jugal; asaf,
anterior surangular foramen; j, jugal; p, parietal;
po, postorbital; psaf, posterior surangular foramen;
q, quadrate; qf, quadrate foramen; qh, quadrate
head; qj, quadratojugal; sq, squamosal. Dashed
line indicates a missing margin; hatching indicates
a broken surface; shading indicates matrix. Scale
bars equal 2 cm.
FIGURE 27. Stereopair (A) and drawing (B) of the right squamosal in the skull of Eoraptor lunensis (PVSJ 512) in ventral view. Abbreviations:ap,
anterior process; po, postorbital; pp, posterior process; qc, quadrate cotylus; vp, ventral process. Hatching indicates a broken surface; shading indicates
matrix. Scale bars equal 1 cm in Aand5mminB.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 109
FIGURE 28. Drawing of the anterior end of the vomera in the skull of
Eoraptor lunensis (PVSJ 512) in ventral view. Abbreviations:en, external
nares; fp, footplate; l, left; n, nasal; pm, premaxilla; pm3,4, premaxillary
tooth 3, 4; r, right; sh, shaft. Double hatch marks indicate matrix. Scale bar
equals 5 mm.
can be measured accurately and only slightly exceeds shaft width.
The medial condyle is positioned slightly ventral and anterior to
the lateral condyle. Unlike some dinosaurs, including some basal
sauropodomorphs (Plateosaurus; Sereno, 2007b:fig. 6A), the ven-
tral margin across the condyles is nearly horizontal.
The pterygoid ramus of the quadrate extends from the medial
edge of the shaft, as partially exposed on the right side. The ven-
tral edge of the pterygoid ramus curls posteromedially to form a
horizontal shelf as in Herrerasaurus.
Pterygoid—The central portion of the pterygoid is well ex-
posed in ventral view, and a small portion of the anterior ra-
mus is visible through the left antorbital fenestra above the pala-
tine (Figs. 16, 17, 29, 30, 38). Of the three principal rami of the
pterygoid (anterior, mandibular, quadrate), only the quadrate ra-
mus is hidden by matrix. The palate has been compressed trans-
versely, which has closed the interpterygoid vacuity, displaced
the right pterygoid over the left as were the nasals on the skull
roof, and separated the palate and braincase at the basiptery-
goid articulation (Fig. 29). In palatal view, the pterygoid overlaps
the ventral surface of the palatine, butts against the ectoptery-
goid laterally, and wraps around the basipterygoid processes
posteriorly.
The anterior ramus of the pterygoid is long, projecting an-
terodorsally at an angle of about 45◦from the basipterygoid articu-
lation, which is located medial to the posterior border of the orbit.
As in other archosaurs, the posterior one-third of the anterior ra-
mus flares to form a ventrally facing subtriangular flange (Fig. 29).
The medial margin, exposed on the left pterygoid, is raised in ven-
tral view. More anteriorly, as seen through the antorbital fenestra,
this ridge has expanded into a vertical plate, which probably in-
serts between the posterior ends of the vomera. The lateral edge
of the anterior ramus just reaches the border of the postpalatine
fenestra, separating the palatine and ectopterygoid (Figs. 29, 30).
The pterygoid-ectopterygoid suture courses posteromedially from
the margin of the postpalatine fenestra and, after a short distance,
turns posteriorly passing just lateral to a ridge with rudimentary
palatal teeth (Fig. 29).
Near the basipterygoid articulation, the pterygoid-
ectopterygoid suture courses across the mandibular ramus of
the palate, which projects ventrolaterally into the adductor fossa
of the lower jaw (Fig. 30). The pterygoid contribution to this
ramus is a distinctive subrectangular strut, which forms the medial
one-half of its posterior margin. Proximally, this pterygoid strut
is narrow and overhangs the adjacent concave surface of the ec-
topterygoid (Figs. 29, 30). Distally, the process becomes broader
with a concave ventral surface. Its rounded, subrectangular distal
end articulates in a deep socket in the ectopterygoid. The end
of the strut on the left pterygoid is disarticulated and exposed
(Fig. 29). Its rounded, polished appearance and disposition within
a deep socket in the ectopterygoid has the appearance of a syn-
ovial joint. The basal sauropodomorph Pampadromaeus appears
to have a similar strut at the posterior end of the pterygoid
(Cabreira et al., 2011:fig. 2g). Although more detail is needed for
Pampadromaeus, this unusual structure of the posterior palate
may characterize a subset of basal sauropodomorphs. A very
different condition occurs in later-appearing genera, such as
Plateosaurus (Sereno, 2007b) and Adeopapposaurus (Mart´
ınez,
2009). In these genera, the pterygoid extends farther laterally to
form the posterolateral corner of the mandibular ramus, where
it is overlapped either dorsally or ventrally, respectively, by the
ectopterygoid. In basal theropods such as Herrerasaurus and
Allosaurus, the pterygoid similarly extends farther laterally and is
overlapped dorsally by a thickened, hook-shaped process of the
ectopterygoid.
A short pterygoid process is present in Eoraptor, which is de-
veloped as a subtriangular, wedge-shaped process projects posteri-
orly near the midline (Figs. 29, 38). It partially encloses the medial
aspect of the basipterygoid articulation.
Palatine—The palatine, which is exposed in ventral view on the
palate and in dorsal view through the left antorbital fenestra, con-
tacts the pterygoid medially and the maxilla and lacrimal laterally
(Figs. 16, 17, 21, 24, 29, 30, 40A). The broad anterior portion of
the bone, which has been displaced dorsally on the left side, forms
a trapezoidal sheet that angles ventrolaterally away from the mid-
line. Its dorsolateral surface is relatively flat except near its junc-
tion with the maxilla, where there is a raised, angular lip along its
lateral margin (Figs. 21, 24). This raised lip extends posteriorly as
a short, hook-shaped process that overlaps the ventral end of the
lacrimal.
In ventral view, the palatine is overlapped along a long, medial
contact by the pterygoid (Fig. 29). Laterally, the palatine is sutured
to the maxilla along its medial edge in the antorbital fossa, a lateral
contact that is lengthened by a slender anterior process (Fig. 21).
The palatine forms most of the margin of the postpalatine fenestra
but does not reach the ectopterygoid. Unlike many coelurosaurian
theropods (e.g., Tyrannosaurus; Brochu, 2002), there are no acces-
sory foramina between the palatine and pterygoid.
Ectopterygoid—The ectopterygoid is best preserved on the
right side, where it contacts the pterygoid and jugal (Figs. 29–31,
33A, B). The lateral process is a dorsoventrally compressed strut
that arches from the jugal along the orbital margin to the mandibu-
lar flange (Fig. 31). The distal end expands into a flat process, par-
tially exposed under the orbital bar, for articulation with the jugal.
The slender posterior process of the maxilla is held within a groove
in the jugal and as a result does not contact the ectopterygoid.
In palatal view, the ectopterygoid articulates medially against the
pterygoid. The anterior portion of the ectopterygoid-pterygoid su-
ture, which is partially disarticulated on the left side, is straight.
More posteriorly, the suture diverges slightly laterally away from
the diagonal palatal tooth row on the pterygoid.
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110 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 29. Stereopair (A) and drawing (B) of the posterior palate in the skull of Eoraptor lunensis (PVSJ 512) in ventral view. Abbrevia-
tions:aec, articular surface for the ectopterygoid; as, articular surface; bpt, basipterygoid process; bs, basisphenoid; bt, basal tubera; dp, depression;
ec, ectopterygoid; fo, foramen; mf, mandibular flange; mr, mandibular ramus; pi, pit; pl, palatine; ppf, postpalatine fenestra; ppr, posterior pro-
cess; pt, pterygoid; t, tooth. Hatching indicates a broken surface; double hatch marks indicate matrix. Scale bar in Aequals 2 cm and in Bequals
1cm.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 111
FIGURE 30. Stereopair (A) and drawing (B) of the posterior palate in the skull of Eoraptor lunensis (PVSJ 512) in ventromedial view. Abbreviations:
af, adductor fossa; bpt, basipterygoid process; c, coronoid; ec, ectopterygoid; lp, lateral process; m, maxilla; mf, mandibular flange; mr, mandibular
ramus; palt, palatal teeth; pl, palatine; ppf, postpalatine fenestra; pra, prearticular; pt, pterygoid. Dashed line indicates a missing margin; hatching
indicates a broken surface; shading indicates matrix. Scale bars equal 1 cm.
The mandibular flange is a broad, subtriangular sheet of bone
more than one-half of which is formed by the ectopterygoid (Fig.
33A, B). It extends ventrolaterally into the adductor fossa of the
lower jaw. The palatal surface of the mandibular flange is gen-
tly concave. The shallow concavity, which is not invaginated, is
deepest near the anterior and posterior rims formed, respectively,
by the ectopterygoid and pterygoid. There is no evidence that
this shallow depression housed a pneumatic sac, as is the case in
the invaginated depression present on the ventral aspect of the
ectopterygoid in most theropods (e.g., Tyrannosaurus; Brochu,
2002).
Vomer—The diamond-shaped footplate of the vomer is dis-
placed dorsally and lies on the ventral aspect of the nasals within
the narial passage (Fig. 28). The dorsoventrally flattened footplate
and the exposed anterior portion of the shaft are coossified as a
single element. More posteriorly on the palate, the vomer may
FIGURE 31. Stereopair (A) and drawing (B) of the ventral portion of the right orbit in the skull of Eoraptor lunensis (PVSJ 512) in ventromedial
view. Abbreviations:ec, ectopterygoid; j, jugal; l, lacrimal; m, maxilla; po, postorbital; ppf, postpalatine fenestra. Dashed line indicates a missing margin;
hatching indicates a broken surface; shading indicates matrix. Scale bars equal 1 cm.
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112 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 32. Stereopair (A) and drawing (B) of the right jaw articulation in the skull of Eoraptor lunensis (PVSJ 512) in posterodorsolateral view.
Abbreviations:a, angular; ar, articular; ltf, laterotemporal fenestra; q, quadrate; qf, quadrate foramen; qj, quadratojugal; sa, surangular. Dashed line
indicates a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bars equal 1 cm.
have diverged as a paired bone, although no further evidence of
the form of the vomera can be discerned from computed tomo-
graphic cross-sections.
Braincase
The occiput is fractured into many pieces, which have shifted
from their original positions (Fig. 19). The basisphenoid, the only
complete exposed bone in the braincase, lies near its natural po-
sition posterior to the palate (Fig. 29). Computed tomographic
cross-sections unfortunately do not clarify the morphology of the
braincase.
Supraoccipital—The central portion of the supraoccipital is pre-
served a few millimeters from its natural articulation with the pari-
etals. Little can be said about its morphology beyond the fact that
there is a prominent nuchal eminence or crest for attachment of
nuchal ligaments that would have been visible in dorsal view of the
skull (Figs. 14, 15), as in Herrerasaurus (Sereno and Novas, 1994).
There may have been a foramen between the parietal and supraoc-
cipital (Fig. 41). A portion of the lateral margin of the foramen
magnum may pertain to the exoccipital-opisthotic, but its identity
remains speculative, as do many occipital fragments.
Basisphenoid—In ventral view, the basisphenoid has a sub-
quadrate shape (Fig. 29). The central portion of the ba-
sisphenoid is concave in ventral view, bounded anteriorly and
posteriorly by crests, the former a web of bone between the
basipterygoid processes and the latter the basal tubera. The lat-
eral margins are broadly open rather than enclosed by a bony
walls. We identify this shallow structure as a basisphenoid depres-
sion (Fig. 29) rather than a ‘basisphenoid fossa,’ the term used to
describe the deeper, invaginated structure present in Eodromaeus
(Mart´
ınez et al., 2011) and neotheropods such as Ceratosaurus and
Allosaurus.
The basipterygoid processes are very robust, pyramidal pro-
cesses (Fig. 29). These do not resemble the transversely com-
pressed, plate-like processes in Eodromaeus (Mart´
ınez et al.,
2011) or other basal theropods. Rather, they are closer in form
to the condition in basal sauropodomorphs such as Plateosaurus
(Galton, 1984; Sereno, 2007b) and Adeopapposaurus (Mart´
ınez,
2009). In lateral view, they project below the basal tubera. In
posterior view, they project ventrolaterally at approximately 45◦
from the horizontal. In ventral or lateral view, the processes
project much more strongly ventrally than anteriorly. Each pro-
cess has a distinct shaft proximal to an expanded oval articu-
lar end. The broad, wedge-shaped articular surface is fitted to a
notch at the posterior end of the pterygoid; a flat surface, con-
stituting one-half of the wedge-shaped articular end, is exposed
in ventral view. A small foramen opens on the anterior side
of the lamina joining the bases of the basipterygoid processes
(Fig. 29).
The basal tubera are separated in the midline by a very shallow
notch and project ventrally as a fan-shaped plate of bone. In the
midline dorsal to the notch, a cylindrical pit passes into the body
of the basisphenoid (Fig. 29).
Lower Jaw
The following description is based almost entirely on the well-
preserved holotypic right lower jaw (Figs. 10–13, 16, 17, 20, 23,
30, 32, 33A, B, 34, 40B, C). The jaws are preserved in natural
articulation. The quadrate condyles on both sides are seated
within the respective articular cotyli, and the tooth rows are fully
engaged. Given the articulation at the jaw joints, it can be seen
that the dentaries do not extend as far anteriorly relative to the
premaxillary arcade in Eoraptor as is typical in theropods. The tip
of the dentary lies adjacent to the third premaxillary tooth on each
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 113
FIGURE 33. Drawings of the lower jaw in the skull of Eoraptor lunensis (PVSJ 512). A, Posterior two-thirds of the right lower jaw in ventromedial
view. B, midsection of the right lower jaw in medial view. C, midsection of the right lower jaw in ventral view. Abbreviations:a, angular; af, adductor
fossa; ar, articular; atr, articular trough; c, coronoid; d, dentary; ec, ectopterygoid; emf, external mandibular fenestra; imf, internal mandibular fenestra;
fo, foramen; m, maxilla; mf, mandibular flange; pl, palatine; ppf, postpalatine fenestra; pra, prearticular; pt, pterygoid; q, quadrate; sa, surangular; sp,
splenial. Dashed line indicates a missing margin; hatching indicates a broken surface; double hatch marks indicate matrix. Scale bars equal 1 cm.
side (Figs. 16, 17, 20). In Herrerasaurus (PVSJ 407), in contrast,
the dentary tips lie adjacent to the second premaxillary tooth and
immediately posterior to the first premaxillary tooth (Sereno and
Novas, 1994:fig. 1F). The gap anterior to the dentary ends, we sug-
gest below, may be indicative of the presence in life of a small
keratinous lower beak in Eoraptor, a condition well described in
larger-bodied basal sauropodomorphs (Sereno, 2007b; Mart´
ınez,
2009).
Dentary—The dentary is the longest and most robust element
of the lower jaw (Figs. 10–13, 16, 17, 20, 23, 33A, B, 34, 40B, C). It
is proportionately longer than in Herrerasaurus (PVSJ 407), con-
stituting more than half of the length of the lower jaw, as measured
from the tip to the anterior margin of the mandibular fenestra.
Its sutural contacts include the splenial medially and the surangu-
lar and angular laterally. The dentary also may contact the coro-
noid and intercoronoid medially, but this region is obscured by
the maxilla. Several neurovascular foramina open along a ven-
trally curved groove located on the anterior one-half of the den-
tary near the tips of the anterior maxillary crowns (Figs. 10–13, 20,
40B). This groove is best preserved on the left side, which has an
unusually large foramen near its anterior end (Figs. 12, 13). The
groove dissipates under the second maxillary tooth. A neurovas-
cular groove of similar form and position is present in Panphagia
and Pampadromaeus (Mart´
ınez and Alcober, 2009; Cabreira et al.,
2011).
The anterior one-half of the dentary resembles in some fea-
tures that of Herrerasaurus. In ventral view of the anterior end,
the flat facet of the dentary symphysis is exposed on the left
side, showing that the symphysis was restricted to a 4-mm sec-
tion at the anterior end of the dentary ramus (Figs. 23, 40C).
The facet is oblique to the sagittal plane, indicating that the den-
taries have suffered some transverse compression after burial, as
is also the case with the dorsal skull roof and palate. Several
additional foramina exit the anterior end of the dentary below
the tips of the premaxillary crowns, most notably two large an-
terior dentary foramina near the alveolar margin (Fig. 23, 40B).
This condition closely resembles that in basal sauropodomorphs
(Plateosaurus,Adeopapposaurus), in which the foramina appear
to have supported a keratinous bill (Sereno, 2007b; Mart´
ınez,
2009).
The posterior one-half of the dentary is plate-like, with a sharp
ventral edge that is narrower than the adjacent splenial. The pos-
terior end of the dentary is forked, as preserved on the right side
(Figs. 10, 11, 40B). The arched margin between the dorsal and ven-
tral processes of the posterior end is somewhat fragmented but
clearly would have formed the anterior margin of the mandibular
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114 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 34. Stereopairs of the lower jaw of Eoraptor
lunensis (PVSJ 512). A, posterior two-thirds of the right
lower jaw in ventromedial view. B, midsection of the right
lower jaw in medial view. Scale bars equal 2 cm.
fenestra. The dorsal process may be slightly shorter than the ven-
tral process but is not completely exposed. The ventral portion of
the dorsal process is overlapped by the surangular, but whether
it fits into a slot in the surangular cannot be determined. Its
form, however, differs from the specialized dentary process in Her-
rerasaurus (PVSJ 407), which is very slender, ‘T’-shaped in cross-
section, and fitted into a narrow slot in the surangular (Sereno and
Novas, 1994). The ventral process in Eoraptor overlaps the ante-
rior end of the angular (Figs. 10, 11, 40B). The dorsal margin of
this process may have broken away, judging from the broad sur-
face on the angular with which it may have articulated.
Surangular—The surangular forms the most lateral portion of
the jaw articulation, where it contacts the ventral edge of the
quadratojugal and the lateral condyle of the quadrate (Figs. 10, 11,
32, 40B, C). Other contacts include the dentary, splenial, and prob-
ably the coronoid anteriorly, the angular and prearticular ven-
trally, and the articular posteriorly. The surangular forms the pos-
terior margin of the external mandibular fenestra. Unlike many
derived theropods, such as Ceratosaurus and Allosaurus (Gilmore,
1920), the coronoid margin of the surangular ventral to the ju-
gal is anteroposteriorly convex in lateral view (Fig. 40B, C), as in
Panphagia (Mart´
ınez and Alcober, 2009). It is also transversely
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 115
FIGURE 35. Premaxillary and anterior maxillary teeth of Eoraptor lunensis (PVSJ 512). Stereopair (A) and drawing (B) of left premaxillary and ante-
rior maxillary teeth in lateral view. Stereopair (C) and drawing (D) of the right premaxillary and anterior maxillary teeth in lateral view. Abbreviations:
adf, anterior dentary foramen; apmf, anterior premaxillary foramen; d, dentary; d3, dentary tooth 3; m, maxilla; m1,2,3, maxillary tooth 1, 2, 3; nf,
narial fossa; pm, premaxilla; pm1,4, premaxillary tooth 1, 4; sf, subnarial foramen. Dashed line indicates a missing margin; hatching indicates a broken
surface; shading indicates matrix. Scale bar equals 1 cm.
broad and rounded in dorsal view. The surangular ridge anterior
to the jaw articulation is very poorly developed in Eoraptor, and
the small posterior surangular foramen is positioned not far from
the jaw articulation (Figs. 10, 11, 40B). In Herrerasaurus (PVSJ
407), in contrast, the surangular ridge is developed as a promi-
nent ridge, and the posterior surangular foramen is positioned far-
ther from the jaw articulation. In Eoraptor, an additional foramen,
the anterior surangular foramen, exits the external surface of the
surangular above the external mandibular fenestra. The retroartic-
ular process projects posteriorly, as in the basal sauropodomorphs
FIGURE 36. Stereopairs of the maxillary teeth of Eoraptor lunensis (PVSJ 512). A, right middle maxillary teeth 4–11 in lateral view. B, left middle
maxillary teeth 4–10 in lateral view. Scale bar equals 1 cm.
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116 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 37. Drawings of premaxillary and maxillary teeth of Eoraptor lunensis (PVSJ 512) and Eodromaeus murphi (PVSJ 561). A, posterior max-
illary tooth 10 of Eoraptor lunensis in right lateral view. B, middle maxillary tooth 4 of Eoraptor lunensis in right lateral view. C, anterior maxillary
tooth 2 of Eoraptor lunensis in right lateral view. D, premaxillary tooth 3 of Eoraptor lunensis in right lateral view. E, maxillary tooth 3 of Eodromaeus
murphi in medial view. Dashed line indicates a missing margin; hatching indicates a broken surface. Scale bar equals 3 mm.
Panphagia and Pampadromaeus (Mart´
ınez and Alcober, 2009;
Cabreira et al., 2011). It is not upturned as in the basal thero-
pod Herrerasaurus (PVSJ 407). An inturned, plate-shaped process
of the surangular anterior to the quadrate condyle is partially ex-
posed in medial view (Figs. 33A, 34).
Angular—The angular extends from its articulation with the
dentary and splenial to a point very near the posterior end of the
retroarticular process, where its slender distal tip has broken away
(Figs. 10, 11, 32, 33). As in the basal sauropodomorphs Panpha-
gia (Mart´
ınez and Alcober, 2009) and Pampadromaeus (Cabreira
et al., 2011), the angular and surangular constitute a smaller pro-
portion of the length of the lower jaw than in Herrerasaurus.
The angular overlaps the surangular dorsally and articulates in a
groove between the surangular and prearticular posteriorly. An-
teriorly, the angular is overlapped laterally by the dentary. Its
ventral margin curls medially, where there is a shallow, smooth,
lanceolate-shaped depression for the posterior tip of the splenial,
which has broken away (Fig. 33). The depression for the splenial
tip is located on the ventromedial aspect of the angular and forms
the concave portion of the concavo-convex splenial-angular articu-
lation characteristic of most theropods. Given the smooth articular
surface, it is quite possible that some movement at this articulation
was possible. In Herrerasaurus (Sereno and Novas, 1994) and Stau-
rikosaurus (pers. observ.), in contrast, the splenial-angular joint
has the opposite concavo-convex configuration, with an articular
fossa on the splenial posterior process.
Splenial—The splenial contacts the dentary laterally and the
coronoid, prearticular, and angular posteriorly (Figs. 33, 34). In
medial view of the lower jaw, the splenial overlaps the preartic-
ular along a long contact. A shallow notch in this border and
an adjacent groove along the anterior margin of the preartic-
ular constitute the margins of the small internal mandibular
fenestra (Figs. 33A, B, 34), as in Panphagia (Mart´
ınez and Al-
cober, 2009). A slightly larger opening is present in larger-bodied
basal sauropodomorphs such as Plateosaurus (Galton, 1984). In
theropods, in contrast, the internal mandibular fenestra is often
proportionately larger, with a deeper notch on the posterior mar-
gin of the splenial (e.g., Tyrannosaurus; Brochu, 2002). Dorsal to
the small internal mandibular fenestra in Eoraptor, the thickened
dorsal margin of the splenial meets the anterior end of the coro-
noid. Just below this contact, the splenial margin has a notch; the
notch may have an articular function or it may constitute the mar-
gin of a small foramen (Figs. 33A, B, 34, 40C). No other foramina
are present on the splenial, in contrast to many theropods, which
have a splenial notch or foramen or notch near the ventral margin
of the bone (‘mylohyal foramen’ in Tyrannosaurus; Brochu, 2002).
The posterior end of the splenial overlaps the angular
(Fig. 40C). Although its distal end is broken away on the right
side, an articular depression on the ventromedial aspect of the an-
gular shows where the tip would have articulated (Figs. 33C, 34).
In Herrerasaurus (PVSJ 407) and Staurikosaurus (pers. observ.),
in contrast, the distal end of the splenial twists onto the ventral
aspect of the angular and has a transversely concave, rather than
transversely convex, articular surface (Sereno and Novas, 1994).
Coronoid—The triradiate coronoid has a short, slender pos-
teroventral process, a longer posterodorsal process, and a much
longer anterior process (Figs. 33A, B, 34, 40C). The prearticular
provides the main sutural contact, although the coronoid reaches
the splenial anteriorly and probably the dentary posterodorsally.
The posteroventral process is anteroposteriorly compressed and
has a slot along its ventral margin, into which articulates the
thin dorsal edge of the prearticular (Fig. 33B). As preserved
on the right side, this articulation is slightly ajar, exposing the
opposing articular surfaces. The posterodorsal process is trans-
versely flattened. Its distal tip and contacts are not exposed. The
anterior process is also transversely flattened and extends to a
common junction with the prearticular and splenial (Fig. 33A, B,
34). This junction of bones on the medial side of the lower jaw is
positioned considerably anterior to the contact between the den-
tary and surangular on the lateral side (Fig. 40C). In neotheropods,
in contrast, these medial and lateral articulations are positioned
adjacent to one another, functionally dividing the lower jaw into
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 117
FIGURE 38. Palatal teeth of Eoraptor lunensis (PVSJ 512) in ventral
view. Abbreviations:dp, depression; fo, foramen; pl, palatine; ppr, pos-
terior process; pt, pterygoid; t, tooth. Hatching indicates a broken surface;
shading indicates matrix. Scale bar equals 5 mm.
anterior and posterior units, as is well described in Tyrannosaurus
(Brochu, 2002).
Intercoronoid—The presence of an intercoronoid bone anterior
to the coronoid cannot be determined in Eoraptor, because of the
presence of matrix between the anterior ends of the lower jaws.
A separate, strap-shaped intercoronoid bone is present just ven-
tral to the alveolar border of the dentary in Panphagia (Mart´
ınez
and Alcober, 2009), similar to the condition in larger-bodied basal
sauropodomorphs such as Plateosaurus (Brown and Schlaikjer,
1940) and Adeopapposaurus (Mart´
ınez, 2009). No intercoronoid,
however, was reported in the many available skulls of the basal
sauropodomorph Massospondylus (Sues et al., 2004). Given the
phylogenetic proximity of Panphagia to Eoraptor, it is likely that a
slender intercoronoid will eventually be shown to be present (Fig.
40C).
Prearticular—The prearticular is an elongate, plate-like bone
that extends from the middle of the lower jaw, anteriorly, to the
distal end of the retroarticular process, posteriorly (Figs. 33, 34,
40C). It contacts the coronoid dorsally, the splenial and angular
ventrally, and the articular posteriorly. The anterior end of the
prearticular is tongue-shaped. Its anterior margin has a groove for
the internal mandibular opening. A raised lip is developed along a
FIGURE 39. Diagonal palatal tooth rows on the right pterygoid of Eo-
raptor lunensis (PVSJ 512) in ventral view. A, drawing of pterygoid tooth
rows. B, photograph of pterygoid tooth rows. Abbreviations:pc, pulp
cavity; t, tooth. Hatching indicates a broken or abraded surface; shad-
ing and double hatch marks indicate matrix. Scale bars equal 5 mm in A
and B.
portion of its border of the adductor fossa, posterior to which it be-
comes a narrow shaft 3 mm in height. More posteriorly, it expands
as a thin sheet under the articular. As the suture passes near the
jaw articulation, the prearticular and articular are coossified. The
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118 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 40. Reconstruction of the skull of Eoraptor lunensis (PVSJ 512). A, cranium in left lateral view. B, lower jaw in left lateral view. C, lower jaw
in medial view. Intercoronoid and most dentary teeth based on Panphagia protos (Mart´
ınez and Alcober, 2009). Abbreviations:a, angular; adf, anterior
dentary foramen; af, adductor fossa; antfo, antorbital fossa; apmf, anterior premaxillary foramen; ar, articular; asaf, anterior surangular foramen; bo,
basioccipital; c, coronoid; d, dentary; d1,20, dentary tooth 1, 20; eantfe, external antorbital fenestra; ec, ectopterygoid; emf, external mandibular
fenestra; en, external naris; eo, exoccipital; f, frontal; fo, foramen; gl, glenoid; gr, groove; iantfe, internal antorbital fenestra; ic, intercoronoid; imf,
internal mandibular fenestra; j, jugal; l, lacrimal; m, maxilla; m1,17, maxillary tooth 1, 17; Mfo, foramen of Meckel’s canal; n, nasal; nf, narial fossa;
orfl, orbital flange; p, parietal; pl, palatine; pm, premaxilla; pm1,4, premaxillary tooth 1, 4; po, postorbital; pomf, posterior maxillary foramen; popr,
paroccipital process; ppf, postpalatine fenestra; pra, prearticular; prf, prefrontal; psaf, posterior surangular foramen; pt, pterygoid; q, quadrate; qj,
quadratojugal; sa, surangular; sf, subnarial foramen; sp, splenial; sq, squamosal; stf, supratemporal fossa; sym, symphysis. Dashed line indicates bone
edge obscured by matrix.
suture is visible again more posteriorly on the retroarticular pro-
cess (Figs. 33A, 40C).
Articular—Non-articular surfaces of the articular are exposed
dorsally and medially on the right retroarticular process (Figs.
33A, 34A, 40C). Other surfaces are obscured by the quadrate
condyles, surangular, and prearticular. The articular and quadrate
form the majority of the jaw joint, which is partially exposed poste-
rior to the right quadrate. Although its exact shape in dorsal view
cannot be seen, it can be determined that the long axis of the coty-
lus is oriented at a right angle to the long axis of the skull, dip-
ping only slightly ventromedially. Posterior to the jaw articulation,
the dorsal surface of the articular is deeply concave. The articu-
lar, which appears to be only loosely attached to the enveloping
surangular and prearticular, forms the bulk of the retroarticular
process. With a subtriangular shape in dorsal, medial, and lateral
views, the retroarticular process projects posteriorly and closely
resembles that in Pampadromaeus,Panphagia, and other basal
sauropodomorphs (Galton, 1984; Sues et al., 2004; Sereno, 2007b;
Mart´
ınez, 2009; Mart´
ınez and Alcober, 2009; Cabreira et al., 2011).
The basal theropod Eodromaeus (Mart´
ınez et al., 2011) has a sim-
ilar retroarticular process, although the process is more upturned
and complex in Herrerasaurus (Sereno and Novas, 1994). There
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 119
FIGURE 41. Reconstruction of the cranium of Eoraptor lunensis (PVSJ
512) in dorsal view. Abbreviations:antfo, antorbital fossa; apmf, anterior
premaxillary foramen; en, external naris; f, frontal; j, jugal; l, lacrimal;
m, maxilla; n, nasal; p, parietal; pm, premaxilla; po, postorbital; popr,
paroccipital process; prf, prefrontal; so, supraoccipital; sq, squamosal; stf,
supratemporal fossa. Dashed line indicates estimated position of suture or
bone edge.
is no development of a pendant medial process on the articu-
lar, which characterizes allosauroid theropods (e.g., Allosaurus;
Gilmore, 1920:fig. 15B).
A foramen that is slightly larger than the posterior surangular
foramen opens posteroventral to the jaw articulation on the me-
dial side of the articular (Figs. 33A, 34A, 40C). A groove passes
posteroventrally into the foramen, which probably provided pas-
sage for a branch of cranial nerve VII.
Teeth
General Features—The tooth rows are most complete on the
right side of the skull, which was buried in the sediment when
originally discovered (Figs. 10, 11, 35–37). The tooth rows con-
tain four premaxillary and 17 maxillary teeth. The number of den-
tary teeth can be estimated from the computed tomography (CT)
data of the partial left dentary and from comparison to the closely
related genus Panphagia. The anterior 14 dentary teeth are pre-
served in the left dentary. Panphagia has 22 or 23 dentary teeth,
and the holotypic skull of Eoraptor probably had at least 20 den-
tary teeth. Palatal teeth are also present and restricted to the ptery-
goid (Figs. 38, 39).
The first tooth in the upper tooth row is situated at the an-
terior extremity of the premaxilla near the midline; there is no
gap between the anterior-most teeth in each premaxilla. The last
tooth in the upper tooth row, the 17th maxillary tooth, is situ-
ated under the orbit (Figs. 10, 11, 40A). Extension of the tooth
row under the orbit is the primitive condition for saurischians, re-
tained in basal sauropodomorphs such as Plateosaurus and in basal
theropods such as Herrerasaurus and ceratosaurians (Tykoski and
Rowe, 2004). The last tooth in tetanurans, in contrast, is located at
the anterior margin of the orbit (Gauthier, 1986).
The upper tooth row in Eoraptor is interrupted by the presence
of a short diastema between the premaxilla and maxilla that is
roughly equivalent to the width of a single tooth (Figs. 35, 40A).
Tooth size decreases adjacent to the diastema; the last premaxil-
lary crown and first maxillary crown are distinctly smaller than ad-
jacent crowns. Computed tomographic cross-sections suggest that
the third dentary tooth, the base of which has been exposed on the
left side (Fig. 35A, B), is slightly enlarged and positioned opposite
the diastema.
Preparation between the premaxillary teeth reveals that the
small first dentary tooth is inset about the length of one alveolus
from the anterior end of the ramus. Retraction of the first den-
tary tooth to accommodate a lower keratinous bill is a feature
present in Panphagia and other basal sauropodomorphs (Sereno,
2007b; Mart´
ınez, 2009). At first, it appears that Pampadromaeus
does not exhibit similar retraction of the first dentary tooth, given
the position of the first tooth in the preserved dentary and skull re-
construction (Cabreira et al., 2011:fig. 2). A close-up photograph,
however, shows that the first tooth is dislodged anteriorly from its
alveolus (Cabreira et al., 2011:fig. S4). That first alveolus, seen in
lateral view as a concave dip in the alveolar margin, is clearly inset
from the end of the dentary, which is marked by several neurovas-
cular foramina.
Fully exposed premaxillary and anterior maxillary crowns
(Figs. 35–37) have a similar crown profile to that in basal
sauropodomorphs, such as Panphagia (Mart´
ınez and Alcober,
2009), Pampadromaeus (Cabreira et al., 2011), Adeopapposaurus
(Mart´
ınez, 2009), and Plateosaurus (Galton, 1984). All teeth in the
upper tooth rows appear to have a basal constriction and all but
the posterior-most crowns are gently recurved. In erupting teeth,
the basal constriction and eminence may be obscured by the alve-
olar margin, because the upper part of the crown appears more
similar in profile to that common among theropods. The constric-
tion is weakest just posterior to the center of the maxillary tooth
row around maxillary tooth 10 (Fig. 37A). The small, subtrian-
gular posterior maxillary crowns have lost any recurvature and
have a shape in lateral view resembling primitive ornithischian
cheek teeth (Figs. 10, 11, 20). Whether the basal constriction is
present in dentary crowns cannot be determined, although such is
likely given the matching form of the dentary teeth in Panphagia
(Mart´
ınez and Alcober, 2009), Pampadromaeus (Cabreira et al.,
2011), and Saturnalia (Langer et al., 1999).
Another feature of the dentition of Eoraptor is the presence
of a rounded eminence on the lateral side of the upper crowns
(Figs. 35–37). This rounded eminence is well preserved along the
entire upper tooth row on the left side of the skull (Figs. 35A,
B, 36B). Some of the crowns in the right maxillary tooth row
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120 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
have been crushed flat. All crowns appear to exhibit this emi-
nence, which is also present in Panphagia (Mart´
ınez and Alcober,
2009) and Pampadromaeus (Cabreira et al., 2011). Even the short
posterior-most maxillary teeth have a bulbous lateral crown sur-
face. In premaxillary and anterior maxillary teeth, the eminence
is offset toward the anterior crown margin, which is offset medial
to the posterior margin. A similar eminence could not have been
present on the medial crown surfaces because many of the maxil-
lary crowns lie flat against the dentary.
The crowns have marginal denticles at a density of about six per
millimeter on both anterior and posterior margins (Fig. 37). The
denticles along the mesial margin are present only on the distal
two-thirds of the crown margin and extend farther toward the base
of the crown on the distal margin. This asymmetry in marginal
ornamentation is also the case in Panphagia (Mart´
ınez and Al-
cober, 2009:fig. 5) as well as in the crowns of many theropods
(Norell and Makovicky, 1999). Our use of the term ‘denticle,’
rather than ‘serration,’ for the marginal crown structures in Eorap-
tor is somewhat arbitrary, because they appear to be intermediate
in size and orientation between the larger, subconical, obliquely
inclined denticles in basal sauropodomorphs such as Plateosaurus
and the smaller, wedge-shaped, perpendicular serrations in many
theropods and in the caniniform crowns of heterodontosaurid or-
nithischians (Sereno, 2012). The denticles in Panphagia,Pam-
padromaeus, and Saturnalia appear similar but are in need of fur-
ther detailed comparison.
A general replacement pattern is apparent in the maxillary
tooth rows in Eoraptor, judging from the erupted crowns; inter-
nal details are not visible in the available computed tomographic
scan. Every third position in the maxillary tooth rows is either va-
cant or has a tooth undergoing eruption. In the left maxillary tooth
row, these include the third, fifth, eighth, and 11th tooth positions
(Figs. 12, 13). In the right maxillary tooth row, these include the
third, sixth, ninth, and 12th tooth positions (Figs. 10, 11). This pat-
tern is not as clear in the premaxillary teeth or in the most poste-
rior maxillary teeth, and the eruption pattern in the dentary tooth
rows is not exposed or visible in computed tomographic images.
Premaxillary Teeth—Of the four premaxillary teeth, the first
has the straightest crown and the second and third are the largest
(Figs. 35, 40A). All have denticulate crown margins. The alveolar
margin on the premaxilla slopes slightly anteroventrally, increas-
ing the effective length of the premaxillary crowns relative to those
in the maxilla as in Pampadromaeus (Cabreira et al., 2011). The
eight crowns in the premaxillary dental arcade project ventrally
around the more rounded, bulbous ends of the dentaries. In an-
terior view of the skull, the maxillary teeth are tucked just out of
sight behind the premaxillary arcade (Fig. 18).
Maxillary Teeth—Maximum tooth size occurs in the fourth or
fifth position in each maxillary tooth row, posterior to which tooth
size decreases (Figs. 10, 11, 36, 40A). The maxillary tooth row ex-
tends farther posteriorly than the opposing dentary tooth row, as
is common among herbivorous and carnivorous basal saurischians.
The posterior end of the maxillary tooth row diverges laterally,
following the curve of the jugal. The tooth crypts for the maxillary
teeth fill the body and posterior ramus of the maxilla, which as a
consequence has collapsed in places from postmortem transverse
compression.
Palatal Teeth—Rudimentary palatal teeth are present on two
prominent ridges on the pterygoid. The parasagittal tooth row,
which is exposed only on the left pterygoid, has approximately 30
teeth. The diagonal row has approximately 20 teeth. The number
of palatal teeth is approximately 100 teeth. (Figs. 38, 39).
Palatal teeth of similar size and location have been described
in the basal theropod Eodromaeus (Mart´
ınez et al., 2011). In the
basal sauropodomorph Pampadromaeus (Cabreira et al., 2011),
only the medial row was described, although it is very easy to
lose either of these rudimentary tooth rows during preserva-
tion or preparation. It now appears likely that both branches
of Saurischia (Theropoda, Sauropodomorpha) originally retained
rudimentary palatal teeth on the pterygoid. There are no teeth
on the palatine or on the footplate of the vomer. Whether
there were any teeth more posteriorly on the vomer cannot be
determined.
The palatal teeth in Eoraptor are similar in form. They are sub-
cylindrical without apparent recurvature and have a subcircular or
oval cross-section, the smaller crowns often the more subcircular.
They vary in diameter from just under 1.0 mm to approximately
0.5 mm and have a maximum height of approximately 2 mm. Thus,
compared with a maxillary tooth from the middle of the tooth row,
the palatal teeth are one-third to one-sixth the mesiodistal diame-
ter and about one-third or less the height of the crown.
None of the crowns have complete apices, and so the form of the
crown tip remains unknown. It is unlikely that all of the tips of the
palatal teeth could have been lost during preparation of the holo-
typic cranium, which was accomplished under high-power magni-
fication. More likely, some or all of the tips of the palatal teeth,
which surmount prominent palatal ridges, were lost from abrasion
during feeding. At ×50 magnification, the palatal teeth do not ap-
pear to have an external enamel layer. They appear to be made
solely of dentine with a central pulp cavity (Fig. 39).
On the ridge near the medial margin of the pterygoid, the
palatal teeth appear to be distributed in a single row (Fig. 38).
Tooth size is smallest anteriorly and gradually increases in size
posteriorly. The most anterior teeth exposed near the midline are
positioned under the anterior margin of the orbit.
The teeth on the diagonal ridge on the pterygoid do not appear
to be distributed randomly (Figs. 38, 39). Multiple rows appear to
be present, with longitudinal alignment of teeth best preserved on
the right side and side-by-side alignment best preserved on the left
side. Thus, it appears there may be as many as 10 teeth in a single
row based on the left side and as many as three subparallel rows
based on the right side. Matrix was left between the teeth in each
diagonal tooth area for support.
Postcranial Skeleton Overview
The postcranial description of Eoraptor is based largely on the
holotypic postcranial skeleton (PVSJ 512), which was divided into
15 blocks that were left in articulation (Fig. 4; Table 2). Only crit-
ical portions of the right manus have been disarticulated to better
understand the morphology and function of digit I (Figs. 75, 76).
No specimen preserves caudal vertebrae or even centra distal to
caudal vertebra 17 (Fig. 9). There are no clavicles, sternal plates,
or sternal ribs. Ossified sternal plates and sternal ribs are unlikely
to have been present in Eoraptor, given the high level of articu-
lation of the skeleton and the completeness of the pectoral gir-
dles, forelimbs, and gastral cuirass. Although the same is true for
the absence of ossified clavicles, it is possible these elements may
have been lost, given some postmortem movement of the pectoral
girdles. Ossified clavicles have been recorded in members of all
three major clades of dinosaurs (Ornithischia, Saurpodomorpha,
Theropoda) (Bryant and Russell, 1993).
The most important referred specimen for this description is
PVSJ 559, which includes two largely disarticulated and uncrushed
anterior dorsal vertebrae and a partially articulated right hind
limb (Table 1). These elements provide important information on
the axial column and the anatomy and articulation between the
bones of the hind limb. The skeletal silhouette of Eoraptor lunen-
sis, nonetheless, is based on the holotypic skeleton, as the bones it
lacks have yet to be recovered in referred material (Fig. 93). Mea-
surements of the postcranial skeleton are in Tables 4–11; compar-
ative measurements and ratios can be found in Tables 12 and 13.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 121
FIGURE 42. Stereopair (A) and drawing (B) of the proatlas, atlas, and fragments of the axis of Eoraptor lunensis (PVSJ 512) in dorsolateral view.
Abbreviations:aepi, atlantal epipophysis; ana, atlantal neural arch; apoz, atlantal postzygapophysis; ar, articular; ax, axis; l, left; od, odontoid; p, parietal;
popr, paroccipital process; pro, proatlas; q, quadrate; r, right; so, supraoccipital; t, tooth. Dashed line indicates a missing margin; hatching indicates a
broken surface; shading indicates matrix. Scale bars equal 2 cm.
Axial Skeleton
The axial column is complete from the proatlas to mid-caudal
vertebra 17 (Fig. 9; Tables 4–6). The remainder of the tail had
eroded away by the time the skeleton was discovered (Fig. 2A,
B). Eoraptor has nine cervical, 15 dorsal, three sacral, and an un-
known number of caudal vertebrae (Figs. 9, 93; Table 5). The cer-
vical vertebrae are broken and eroded anteriorly (Fig. 42). Postax-
ial cervical vertebrae are well exposed on their right (down) side
(Figs. 43–48). Dorsal vertebrae are best exposed on their left (up)
side (Figs. 5, 6, 51, 52A). A disarticulated pair of anterior dorsal
vertebrae (first and second dorsal vertebrae) in a referred spec-
imen (PVSJ 559) provides useful information unavailable in the
articulated column of the holotype (Fig. 50). The three sacral ver-
tebrae have been prepared and exposed largely in dorsal view.
Particular attention was paid to the form and articular relations
of the first sacral rib (Fig. 53). Caudal vertebrae are best exposed
on their left (up) side (Figs. 5, 6, 55–59).
Proatlas—The proatlas consists of a pair of plate-shaped ossifi-
cations of the neural arch that articulate between the occiput and
the atlas. They are preserved near their natural positions, the left
side more completely exposed (Fig. 42; Table 4). The broad dorsal
surface of the element has a gentle sigmoid shape, and in lateral
view it appears subtriangular. The prezygapophysis is longer, thin-
ner, and more pointed than the postzygapophysis and is preserved
TABLE 4. Measurements (in mm) of the left proatlantal and atlantal
neural arches of Eoraptor lunensis (PVSJ 512).
Dimension Measurement
Proatlas, maximum length 12
Proatlas, maximum width 4
Atlas, maximum length of neural arch 13
in articulation with the rim of the foramen magnum. The postzy-
gapophysis overlaps the atlantal prezygapophysis. The short lat-
eral process curves ventrally, partially enclosing the neural canal.
Eoraptor is the only early basal sauropodomorph in which
the proatlas is known. The proatlas is also preserved in the
contemporaneous theropods from Ischigualasto, Herrerasaurus
(Sereno and Novas, 1994) and Eodromaeus (Mart´
ınez et al.,
2011). In Herrerasaurus (PVSJ 407), the proatlas is flatter, with
little development of a lateral process (Sereno and Novas,
1994). The proatlas is also preserved in Allosaurus (MOR 660),
Deinonychus (MOR 747), and an increasing number of non-avian
theropods.
Atlas—The left atlantal neural arch is preserved in lateral view
near its natural position (Fig. 42; Table 4). The triradiate neural
arch has a short prezygapophysis that contacts the proatlas, and
a longer, broader postzygapophysis that articulates with the axis.
The postzygapophysis and a long, posteriorly projecting epipoph-
ysis have separated from the anterior portion of the neural arch,
exposing a cylindrical cross-section (Fig. 42). In Herrerasaurus
(Sereno and Novas, 1994:fig. 11), the neural arch has a more slen-
der form and the posterior extension that contains the postzy-
gapophysis is plate-shaped rather than cylindrical. The location of
the atlantal intercentrum and rib is uncertain.
Axis—The best-preserved portions of the axis are the pre- and
postzygapophyses and the ventral margin of the centrum (Fig. 42).
An odontoid process may be preserved, fused to a portion of the
axial centrum. An adjacent concave articular surface may repre-
sent a portion of a fused axial intercentrum. A ventral keel is
present on the axial centrum.
The subtriangular prezygapophysis faces dorsolaterally and is
similar to that in Herrerasaurus (Sereno and Novas, 1994:fig. 11),
except that it is flat rather than slightly convex. The postzy-
gapophyses and base of the neural spine are also very simi-
lar. The postzygapophyses flare laterally from the neural arch in
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122 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 43. Stereopair (A) and drawing (B) of cervical vertebrae 2–8 of Eoraptor lunensis (PVSJ 512) in right lateral view. Abbreviations:acdl,
anterior centrodiapophyseal lamina; C2–8, cervical vertebrae 2–8; ca, capitulum; di, diapophysis; epi, epipophysis; lr, lateral ridge; ns, neural spine;
pcdl, posterior centrodiapophyseal lamina; podl, postzygodiapophyseal lamina; poz, postzygapophysis; prdl, prezygodiapophyseal lamina; prz, prezy-
gapophysis; r, rib; sp, spine. Dashed line indicates a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bars equal
2cm.
dorsal view and extend posteriorly as epipophyses, the tips of
which have been broken off. The postzygapophyseal facet is sub-
triangular, as in Herrerasaurus (PVSJ 407). Although there is a
small, subtriangular fossa between the postzygapophyses, a hor-
izontal interpostzygapophyseal lamina is not present as in Her-
rerasaurus (Sereno and Novas, 1994), which floors the fossa bridg-
ing between the medial edges of the postzygapophyses.
Postaxial Cervical Vertebrae—The entire postaxial series is
preserved in articulation (Figs. 43–49; Table 5). The first nine pre-
sacral vertebrae are regarded as cervical vertebrae, based on the
form and position of their rib articulations and the form of their
associated ribs (see below). The centra of cervical vertebrae 3 and
4 are flattened and fragmented (Fig. 43). Their neural arches, how-
ever, are more intact and can be used to assess the relative lengths
of their centra.
As in Herrerasaurus (PVSJ 407), centrum length increases grad-
ually from the axis to the fourth and fifth cervical vertebrae, af-
ter which it decreases dramatically (Table 5). There is approxi-
mately a 30% reduction in the length of the middle to posterior
cervical centra and an even greater reduction in the distance be-
tween pre- and postzygapophyses of the neural arch. In lateral
view, middle cervical centra (C5, C6) are parallelogram-shaped;
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 123
FIGURE 44. Stereopair (A) and drawing (B) of cervical vertebra 5 of Eoraptor lunensis (PVSJ 512) in right lateral view. Abbreviations:aprz, accessory
prezygapophyseal process; C5, cervical vertebra 5; di, diapophysis; epi, epipophysis; k, keel; lr, lateral ridge; ns, neural spine; pa, parapophysis; prz,
prezygapophysis; sh, shaft; sp, spine; tu, tuberculum. Dashed line indicates a missing margin; hatching indicates a broken surface; shading indicates
matrix. Scale bars equal 1 cm.
the anterior face is elevated when the posterior face is oriented
vertically (Figs. 43, 44). This shape is also present in the sev-
enth and eighth cervical centra. The ninth cervical centrum shows
no elevation of the anterior face, but rather it is weakly trape-
zoidal (Fig. 47). The shapes and lengths of the cervical centra
indicate that the ninth cervical vertebra functioned as a transi-
tional link between the dorsal series and the rising cervical series
(Fig. 49).
In cross-section, the presacral vertebrae are extremely hollow
(Fig. 52). The neural canal is enlarged and extends dorsally into
the neural arch. A thin horizontal septum divides the neural canal
from the internal cavity of the centrum. The lateral walls of the
FIGURE 45. Stereopair (A) and drawing (B) of cervical vertebrae 5 and 6 of Eoraptor lunensis (PVSJ 512) in dorsal view. Abbreviations:C4–7,
cervical vertebrae 4–7; epi, epipophysis; ns, neural spine; poz, postzygapophysis; prz, prezygapophysis; r, rib; sp, spine, tp, transverse process. Dashed
line indicates a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bar equals 2 cm.
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124 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 46. Stereopair (A) and drawing (B) of cervical vertebrae 5 and 6 of Eoraptor lunensis (PVSJ 512) in ventral view. Abbreviations:C5,6,
cervical vertebra 5, 6; di, diapophysis; k, keel; pa, parapophysis; r, rib. Dashed line indicates a missing margin; shading indicates matrix. Scale bar equals
2cm.
centrum are very thin; the anterior and posterior articular faces
are relatively thicker. Although the cervical vertebrae are hollow,
there are no invaginated pneumatic openings in any part of the
axial column in Eoraptor, in contrast to Eodromaeus (Mart´
ınez
et al., 2011).
The sides of the centra posterior to the parapophyses are con-
cave. On the fifth and sixth cervical vertebrae, a crest is present
on the ventrolateral margin of the centrum opposite the rib shaft
(Fig. 43, lr). It is strongest in the sixth cervical vertebra, where it
extends the length of the centrum from the parapophysis to the
posterior rim. A similar crest may have been present in anterior
cervical vertebrae, as occurs in Herrerasaurus (Sereno and Novas,
1994:fig. 11), but the sidewalls of the centra are not preserved. The
crest is absent in the seventh through the ninth cervical vertebra. A
low ventral keel is present on the axis and on all other cervical ver-
tebrae preserving this region (C5–C9). It is lost abruptly in the first
dorsal vertebra (Fig. 48). In a referred specimen (PVSJ 559), the
first two dorsal vertebrae maintain a ventral keel (Fig. 50). Ante-
rior and posterior faces of the cervical centra are moderately con-
cave throughout the series.
In the fifth and sixth cervical vertebrae, the parapophysis is de-
veloped as a dorsoventrally compressed strut projecting ventro-
laterally from just behind the rim of the centrum (Figs. 43, 44).
In more posterior cervical vertebrae, the parapophysis shortens in
length, broadens in area of attachment, and moves dorsally onto
the side of the centrum just below the neurocentral junction. In
the ninth cervical vertebra, the parapophysis is represented by a
raised welt of considerable size on the anterior rim of the centrum.
The most anterior diapophyses that are preserved are also on the
fifth and sixth cervical vertebrae, where they are developed as ven-
trolaterally projecting processes. In the fifth cervical vertebra, the
process is slender and subcylindrical (Fig. 44). In the sixth cervi-
cal vertebra, the base of the process is considerably broader and
dorsoventrally compressed. This trend continues in the seventh
cervical vertebra, in which the entire process is flattened (Fig. 43).
In the posterior-most cervical vertebra (C9), the end of the di-
apophysis is more robust, with an oval articular surface (Figs. 47,
48).
A cross-pattern involving four laminae around the diapoph-
ysis first appears in rudimentary form in the seventh cer-
vical vertebra, in which the transverse process is stronger
and dorsoventrally flattened (Fig. 43). These include the pre-
and postzygodiapophyseal laminae above, which connect the
diapophysis to the zygapophyses, and the anterior and posterior
centrodiapophyseal laminae below, which connect the diapophysis
to the dorsal corners of the centrum (Wilson, 1999). In the pre-
ceding vertebra, laminae extend anteriorly and posteriorly from
the base of the diapophysis but dissipate before reaching another
vertebral structure. In the ninth cervical, the laminae are well de-
veloped and fully exposed (Figs. 47, 48). The anterior centrodi-
apophyseal lamina is lower in relief than the others. It eventually
disappears in the dorsal column, as the parapophysis approaches
the diapophysis (Fig. 47).
Except for a single prezygapophysis on the third cervical ver-
tebra, which is disarticulated from the axial postzygapophysis, the
articular facets between the cervical neural arches are visible only
in articulation (Fig. 43). In the third cervical vertebra, the oval
prezygapophyseal facet is relatively flat. The axial postzygapoph-
ysis suggests that the articulation angled ventromedially at about
20◦from the horizontal. More posteriorly in the cervical series,
the inclination of the zygapophyseal articulation increases, and
the articular surface becomes transversely arched (Fig. 43). The
zygapophyseal articulation between the eighth and ninth cervical
vertebrae, which is visible in cross-section, is inclined at more than
50◦from the horizontal and has a gentle transverse flexure of the
articular surface.
An unusual accessory articular process arises from the me-
dial side of the base of the prezygapophysis in the middle cer-
vical vertebrae, and it is present in at least the fifth and sixth
cervical vertebrae (Fig. 44). It is flattened transversely, and its
articular surface is inclined anteroventrally, with a similar, al-
though not identical, orientation as the principal prezygapophy-
seal articular facet. It articulates near the posteromedial margin
of the postzygapophysis. This accessory prezygapophyseal pro-
cess in middle cervical vertebrae has not been described before.
It may be unique to Eoraptor, although there is little comparative
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 125
FIGURE 47. Stereopair (A) and drawing (B) of cervical vertebra 9 and dorsal vertebrae 1 and 2 of Eoraptor lunensis (PVSJ 512) in right lateral view.
Abbreviations:C8,9, cervical vertebra 8, 9; ca, capitulum; D1–3, dorsal vertebrae 1–3; di, diapophysis; h, humerus; k, keel; pa, parapophysis; podl,
postzygodiapophyseal lamina; poz, postzygapophysis; prdl, prezygodiapophyseal lamina; prz, prezygapophysis; r, rib; sp, spine; tu, tuberculum. Dashed
line indicates a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bars equal 2 cm.
information in other basal sauropodomorphs such as Panphagia,
Pampadromaeus, and Saturnalia.InPanphagia, a cervical ver-
tebra originally described as the eighth (Mart´
ınez and Alcober,
2009:fig. 6B) corresponds better with the fourth or fifth cervi-
cal vertebra in Eoraptor, given the elongate proportions of the
centrum, the low, elongate profile of the neural spine, the nar-
row proportions of the transverse process, and the anteroventral
position of the diapophysis. It does not have the accessory prezy-
gapophyseal process.
The postzygapophyses have larger articular surfaces than corre-
sponding prezygapophyses and extend slightly beyond the edges
of the latter in articulation (Fig. 45). Prominent prong-shaped
epipophyses are present on the atlantal neural arch, the axis, and
the third through the fifth cervical vertebrae. Weak epipophyses
are present on the sixth cervical vertebra, and they are absent in
more posterior cervical vertebrae (Figs. 43, 49).
The neural spines are lower throughout the cervical series in Eo-
raptor than in Herrerasaurus (Sereno and Novas, 1994:fig. 12). On
the third and probably also the fourth cervical vertebra, the spine
is developed as a low crest (Fig. 43). In the fifth cervical vertebra,
the spine is subtriangular and very thin (Fig. 44). In the sixth verte-
bra, the spine is broken but was probably developed much as in the
preceding vertebra. The neural spine has a more restricted base in
the seventh and eighth vertebrae, but not until the ninth vertebra
does the spine take the form of a thickened, subrectangular strut
(Figs. 43, 44, 47, 49). All spines are erect rather than angled pos-
terodorsally. Unlike Herrerasaurus (Sereno and Novas, 1994:fig.
11B), none of the cervical vertebrae have a deep fossa between the
postzygapophyses and the base of the spine. Unlike Eodromaeus,
there is no development of cervical pleurocoels or their posterior
extension as an external groove or trough (Mart´
ınez et al., 2011:fig.
2B).
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126 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 48. Stereopair (A) and drawing (B)
of cervical vertebra 9 and dorsal vertebrae 1
and2ofEoraptor lunensis (PVSJ 512) in ven-
tral view. Abbreviations:C8,9, cervical vertebra
8, 9; ca, capitulum; D1,2, dorsal vertebra 1, 2;
h, humerus; hy, hypapophysis; k, keel; pa, para-
pophysis; prz, prezygapophysis; r, rib; sp, spine;
tp, transverse process. Dashed line indicates a
missing margin; hatching indicates a broken sur-
face; shading indicates matrix. Scale bars equal
2cm.
Dorsal Vertebrae—There are 15 dorsal vertebrae (Figs. 47, 48,
50–52; Table 5). The form of the centrum, transverse process, neu-
ral spine, and corresponding rib change dramatically between the
last cervical (C9) and first dorsal vertebrae (Figs. 47, 48, 50A). The
shorter centrum of the first dorsal vertebra has a prominent hypa-
pophysis (Fig. 48); the parapophysis has shifted dorsally to strad-
dle the neurocentral suture (Fig. 50A); the transverse process is
very robust and elevated (Figs. 47, 48, 50A); the neural spine is
deeper than broad (Figs. 47, 50A); and the rib is approximately
twice the size of that associated with the ninth cervical vertebra
(Fig. 48).
The length of the centra in the dorsal series gradually becomes
longer in the first six dorsal vertebrae, after which length stabilizes
at around 20 mm. The centra are spool-shaped with gently concave
anterior and posterior faces. The first dorsal has a well-developed,
wedge-shaped hypapophysis extending below the anterior artic-
ular face (Figs. 48, 50). The second dorsal may also have a very
rudimentary hypapophysis, but the centrum is not completely
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 127
TABLE 5. Measurements (in mm) of postatlantal vertebrae of Eoraptor lunensis (PVSJ 512).
Vertebra Centrum length
Centrum height
(posterior)
Interzygapophyseal
length†Neural spine height
(maximum)
Neural spine length
(maximum)
C2 — — 24 — —
C3 — — 27 — —
C4 24 10 30 — —
C5 24 10 32 6 12
C6 23 11 28 — —
C7 20 (11) 27 7 8
C8 18 — 21 7 7
C9 17 12 20 4 6
D1 17 12 20 8 5
D2 16 (12) — — —
D3 16 — — — —
D4 17 — — 10 11
D5 (19) — — 11 11
D6 20 — — 10 13
D7 20 14 — 10 15
D8 21 15 — 10 17
D9 20 14 — 11 (17)
D10 21 14 — 14 17
D11 22 15 — 13 17
D12 23 15 — 13 17
D13 21 15 — 14 17
D14 20 15 — 16 18
D15 18 15 — 16 17
S1 (19) — — 16 17
S2 (19) — — 16 17
S3 20 (15) — 17 17
CA1 17 — — 16 16
CA2 20 — — 20 13
CA3 22 15 — 22 13
CA4 20 (15) — 22 12
CA5 20 (14) — 21 11
CA6 21 14 — 21 12
CA7 20 14 — — —
CA8 19 13 — — —
CA9 19 13 — 15 9
CA10 18 13 — 15 9
CA11 18 13 — 14 9
CA12 17 12 — 11 7
CA13 17 12 — 11 7
CA14 17 12 — 9 7
CA15 17 12 — 9 9
CA16 17 11 — 6 7
CA17 20 10 — — —
Interzygapophyseal length given only for the axis to the first dorsal vertebra. Neural spine length was measured from the neural arch just above the
zygapophyses to the distal end of the spine. Parentheses indicate estimated measurement; dash indicates unknown measurement. Abbreviations:C,
cervical; CA, caudal; D, dorsal; S, sacral.
†Excluding epipophysis.
exposed (Fig. 48). Both have a low ventral keel in PVSJ 559 (Fig.
50A, D).
As in the cervical vertebrae, invaginated pneumatic openings
are not present anywhere on the centrum, despite the fact that
the vertebrae are extremely hollow. In cross-sections of the sixth
and 13th dorsal vertebrae, for example, the neural canal expands
ventrally into the upper one-half of the centrum (Fig. 52C). The
lower one-half of the centrum is separated from the neural canal
by a thin septum. The external walls of the centrum do not exceed
1 mm in thickness. Small internal pockets in the neural arch are
also visible in a cross-section through the zygapophyseal region of
the 14th dorsal vertebra (Fig. 52B).
The parapophysis is located on the anterodorsal corner of the
centrum in the first and second dorsal vertebrae but shifts onto
the neural arch posteroventral to the prezygapophysis by the fifth
or sixth dorsal vertebra (Figs. 50, 51). In the eighth dorsal verte-
bra, the parapophysis is developed as a stout cylindrical process
4 mm long. It is positioned on the anterior side of the diapoph-
ysis, which is longer (1 cm). The diapophysis is robust, cylindrical,
and upwardly directed in the anterior dorsal vertebrae. Starting
with a length of 5 mm in the first dorsal, the diapophysis achieves
a length of more than 10 mm in the third and fourth dorsal ver-
tebrae, where it is dorsoventrally compressed. The diapophyses
decrease in length to about 4 mm posterior to the ninth dorsal ver-
tebra (Fig. 51). As far posteriorly as the 12th dorsal vertebra, the
diapophysis is positioned posterodorsal to the parapophysis and is
substantially longer than the former; the articulating two-headed
ribs confirm this observation. The processes of the 13th dorsal ver-
tebrae are not well exposed. In the 14th and 15th dorsal vertebrae
(Fig. 52A), the parapophysis is located on the anteroventral aspect
of the diapophysis, which has increased in length to approximately
10 mm.
The angle of the zygapophyseal articulation decreases across
the dorsal series from more than 50◦above the horizontal in the
first dorsal vertebra to less than 20◦in the 14th dorsal vertebra
(Fig. 52). A hyposphene-hypantrum articulation appears abruptly
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128 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 49. Reconstruction of cervical vertebrae 2–9 and cervical ribs 3–8 of Eoraptor lunensis (PVSJ 512). Abbreviations:C2,5,9, cervical vertebra
2, 5, 9; di, diapophysis; epi, epipophysis; pa, parapophysis; r, rib; tp, transverse process. Dashed line indicates a missing margin.
in the second dorsal vertebra, where a descending medial lip on
the postzygapophysis is present (Fig. 50B). A cross-section of the
postzygapophyses of the 14th dorsal vertebra shows a strongly
flexed articular surface and presence of a hyposphene (Fig. 52A,
B). Hyposphene-hypantrum articulations in the dorsal series in
Eoraptor, thus, were likely present posterior to the first dorsal
vertebra.
The cross-pattern of laminae around the diapophysis that char-
acterizes the posterior cervical vertebrae (pre-, postzygodiapophy-
seal laminae; anterior and posterior centrodiapophyseal laminae)
are present in the anterior dorsal vertebrae (Fig. 50A, B). The ele-
vated parapophysis engages the anterior centrodiapophyseal lam-
TABLE 6. Measurements (in mm) of the chevrons of Eoraptor lunensis
(PVSJ 512).
Chevron number Proximodistal length
2 (20)
3—
4 (30)
5 (33)
6 (34)
7 (35)
8 (32)
9 (29)
10 (28)
11 (27)
12 (26)
13 (25)
14 (24)
15 (23)
16 (22)
17 —
Chevron number corresponds with the number of the anterior of the two
caudal vertebrae with which it articulates (i.e., chevron 2 articulates be-
tween caudal vertebrae 2 and 3). Parentheses indicate estimated measure-
ment; dash indicates unknown measurement.
ina in the first dorsal, which becomes the paradiapophyseal lam-
ina (Fig. 50A). There is no centroparapophyseal lamina extend-
ing from the parapophysis anteroventrally to the centrum. The
four aforementioned laminae separate three fossae, which are best
developed in the anterior dorsal vertebrae (Fig. 50A, B). From
anterior to posterior, these are the prezygapophyseal centrodi-
apophyseal, centrodiapophyseal, and postzygapophyseal centro-
diapophyseal fossae (Wilson et al., 2011:fig. 5). The neural arch
laminae decrease in strength posteriorly along the dorsal series.
Pre- and postzygodiapophyseal laminae are absent in the 13th and
14th dorsal vertebrae (Fig. 52), in contrast to the condition in Her-
rerasaurus, in which the cross-pattern is maintained throughout
the dorsal series (Novas, 1994:fig. 1).
The neural spines are plate-like throughout the dorsal series,
never exceeding 2 mm in width (Fig. 51). There is no develop-
ment of spine tables or distal thickenings of any sort. The first
dorsal vertebra has a subrectangular neural spine that is taller
than wide (7 mm by 5 mm, respectively) (Fig. 47, 50A). This is
actually the narrowest neural spine in the entire vertebral col-
umn; the posterior-most cervical spine is second narrowest, with
a width of 6 mm (Table 5). Anteroposterior spine width increases
in more posterior dorsal vertebrae, measuring 8 mm in the second
dorsal vertebra and 11 mm in the fourth dorsal vertebra. Spine
width increases more rapidly than spine height, so that all dor-
sal spines except the first are broader than tall. A typical mid-
dle dorsal spine measures 17 mm in width and 15 mm in height.
A small triangular spinoprezygapophyseal fossa is present at the
base of the spine facing anteriorly and a deeper spinopostzy-
gapophyseal fossa is present between the postzygapophyses facing
posteriorly.
Sacral Vertebrae—There are three vertebrae that attach to
the ilium and, by this criterion, are regarded as sacral vertebrae
(Figs. 53, 54; Table 5). Their configuration is very similar to that
in Eodromaeus and Herrerasaurus. The posterior two have very
broad attachments to the iliac blade and clearly represent the pri-
mordial tetrapod pair (Romer, 1956). These two vertebrae are not
coossified, as is clear from exposure of the ventral aspect of the
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 129
FIGURE 50. Dorsal vertebrae 1 and 2 of Eoraptor lunensis (PVSJ 559). A, dorsal vertebra 1 in right lateral view. B, dorsal vertebra 2 in left lateral
view. C, dorsal vertebra 1 in dorsal view. D, dorsal vertebra 1 in ventral view. Abbreviations:D1,2, dorsal vertebra 1, 2; fos, fossa; hpo, hyposphene; hy,
hypapophysis; k, keel; ns, neural spine; pa, parapohpysis; pcdl, posterior centrodiapophyseal lamina; podl, postzygodiapophyseal lamina; poz, postzy-
gapophysis; ppdl, paradiapophyseal lamina; prdl, prezygodiapophyseal lamina; prz, prezygapophysis; tp, transverse process. Dashed line indicates a
missing margin. Scale bar equals 2 cm.
third sacral centrum, although individually the neural arches and
ribs of all sacral vertebrae are fused.
In the holotype (PVSJ 512), the sacrum has been sheared an-
teroposteriorly; the left pelvic girdle is positioned posterior to the
right, and the attachment of the right sacral transverse processes
are slightly ajar. Despite this distortion, the position of the sacral
transverse processes relative to the ilium on each side appears to
have been maintained. On both sides, for example, the third sacral
vertebra has a broad attachment to the brevis shelf, and this is the
expected location of this attachment judging from other basal ar-
chosaurs with two or three sacral vertebrae. It is likely, therefore,
that the first sacral vertebra attached to the preacetabular process
of the ilium, as preserved on the right side of the sacrum (Fig. 53C).
The third sacral vertebra has a strongly parallelogram-shaped
centrum with ventral offset of the posterior face. The neural spine
of the third sacral vertebra is subquadrate. The strap-shaped trans-
verse process of the first sacral vertebra is truncated along a
straight edge distally, which is located adjacent to the distal end
of the preacetabular process of the ilium. The truncated form of
the end of the rib strongly suggests that it attached the ilium at
an angle similar to that preserved on the right side (Fig. 54). The
transverse processes of the second and third sacral vertebrae are
much broader and attach to the iliac blade above the acetabulum
and along the brevis shelf, respectively.
The length of the sacral centra, the low-angle articulation of
the sacral zygapophyses (as seen between the first and second
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130 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 51. Stereopair (A) and drawing (B) of dorsal vertebra 10 of Eoraptor lunensis (PVSJ 512) in left lateral view. Abbreviations:ca, capitulum;
D9, dorsal vertebra 9; ns, neural spine; pa, parapophysis; poz, postzygapophysis; prz, prezygapophysis; r, rib; tp, transverse process. Dashed line indicates
a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bars equal 1 cm.
sacral vertebrae), and the plate-shaped, subquadrate neural
spines are similar to the condition in the posterior dorsal
vertebrae.
The sacral ribs are completely coossified with the sacral trans-
verse processes (Figs. 53, 54). The first sacral transverse process
and rib form a slender, dorsoventrally flattened strut that is pre-
served in place, projecting from high on the neural arch toward
the anterior end of the preacetabular process (Fig. 53C). The trun-
cated end is shaped to articulate the preacetabular process of the
ilium. The narrow form and elevated position on the neural arch of
FIGURE 52. Reconstruction of dorsal vertebra 14 and cross-sections (observed on breakage planes) through several vertebrae and a chevron in
Eoraptor lunensis (PVSJ 512). A, reconstruction of dorsal vertebrae 14 in left lateral view (dashed line indicates cross-section in B). B, cross-section of
dorsal vertebra 14 through the posterior aspect of the neural spine and zygapophyses as seen in posterior view. C, cross-section through dorsal vertebra
13 anterior to the neural spine as seen in anterior view. D, cross-section through caudal vertebra 9 anterior to the neural spine as seen in posterior
view. E, cross-section through the shaft of chevron 12 (anterior toward top of page) as seen in distal view. Abbreviations:ce, centrum; di, diapophysis;
fos, fossa; gr, groove; hpo, hyposphene; nc, neural canal; ns, neural spine; pa, parapophysis; poz, postzygapophysis; prz, prezygapophysis; tp, transverse
process. Dashed line in Aindicates cross-section shown in B; hatching in B–Eindicates a broken surface. Scale bar equals 1 cm in B–Dand 5 mm in E.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 131
FIGURE 53. Stereopair (A) and drawing (B) of sacral vertebrae and ribs and magnified drawing of the first sacral vertebra and rib (C)ofEoraptor
lunensis (PVSJ 512) in dorsal view. Abbreviations:ail, articular surface for the ilium; aprap, articular surface for the preacetabular process; as, astragalus;
ca, calcaneum; CA1,2, caudal vertebra 1, 2; D15, dorsal vertebra 15; di, diapophysis; dt3,4, distal tarsals 3, 4; mt1–5, metatarsals 1–5; ns, neural
spine; poap, postacetabular process; pped, pubic peduncle; prap, preacetabular process; prz, prezygapophysis; pu, pubis; r, rib; ru, rugosity; S1–3, sacral
vertebrae 1–3; tp, transverse process. Dashed line indicates a missing margin; hatching indicates a broken surface; double hatch marks and shading
indicate matrix. Scale bars equal 3 cm in Aand Band1cminC.
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132 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 54. Reconstruction of the sacrum and right and left ilia
of Eoraptor lunensis (PVSJ 512) in dorsal view. Abbreviations:il,
ilium; poap, postacetabular process; pped, pubic peduncle; prap,
preacetabular process; ru, rugosity; S1–3, sacral vertebrae 1–3; sas,
supraacetabular crest.
the first sacral transverse process and rib suggest that the rib was
previously free as the most distal of dorsal ribs and subsequently
was incorporated into the sacrum.
The transverse processes and ribs of the second and third sacral
vertebrae are fan-shaped in dorsal view, with more robust distal
attachment surfaces than the first. The transverse process and rib
of the second sacral vertebra contacts the ilium above the acetab-
ulum; and those of the third sacral vertebra contact the ventrome-
dial margin of the postacetabular process.
Caudal Vertebrae—The first 17 caudal vertebrae and the
prezygapophyses of the 18th caudal vertebrae are preserved in
articulation (Figs. 9, 55–59; Table 5). The last preserved caudal
vertebra in Eoraptor (CA17) is unmodified, with a strong neural
spine, small zygapophyses that angle at about 50◦, strut-shaped
transverse processes, and a long chevron (Fig. 58). Because more
distal caudal vertebrae are not known in the holotypic or referred
material (Table 1), the form of the distal half of the tail cannot
be determined by direct observation in Eoraptor at this time.
Some distal caudal vertebrae are known for the closely related
genera Panphagia (Mart´
ınez and Alcober, 2009:fig. 6H) and
Pampadromaeus (Cabreira et al., 2011:fig. 1). In neither case are
the centra or prezygapophyses lengthened, so it is probable that
the distal tail was similar in Eoraptor. A stiffened distal tail with
elongate centra and lengthened prezygapophyses characterizes
Herrerasaurus (Novas, 1994), Eodromaeus (Mart´
ınez et al., 2011),
and nearly all neotheropods. In basal theropods, such as Her-
rerasaurus and Eodromaeus, the elongate prezygapophyses that
stiffen the tail first appear in the caudal series between caudal ver-
tebrae 20–25, posterior to the last preserved vertebra in Eoraptor
(CA17).
The spool-shaped caudal centra become more transversely
pinched than the dorsal centra, starting with the second caudal ver-
tebrae. The centra of sacral vertebra 3 and anterior caudal verte-
brae 1 and 2 are parallelogram-shaped, such that the posterior face
is lowered, which lowers the axis of the tail (Fig. 9). In anterior or
posterior view, the gently concave faces of the caudal centra have
a subtriangular shape due to the narrowness of the ventral half
of the centrum and the transverse breadth of the spacious neural
canal. In cross-section, the caudal centra show the same hollowed
condition that is present in presacral cross-sections (Fig. 52). As
seen in the ninth caudal vertebra, the neural canal fills the neu-
ral arch from the top of the centrum to the base of the neural
spine (Fig. 52D). A thin septum may have been present flooring
the canal, as in the dorsal vertebrae. The centrum is solid near the
articular ends but is extremely hollow in between. The sidewalls of
the ninth caudal vertebra, for example, are less than 1 mm thick. It
is not surprising, therefore, that local areas of the caudal column
have collapsed.
The first caudal centrum is shorter than the adjacent third sacral
and second caudal vertebrae (Fig. 9; Table 5), its parallelogram-
shaped centrum offsetting slightly ventrally the remainder of the
tail. In the second caudal vertebra, centrum length returns to
that typical of the dorsal and sacral vertebrae (20 mm), and this
length is maintained through the seventh caudal vertebra. Cen-
trum length decreases gradually in the eighth through the 17th
caudal vertebra. Because centrum height decreases somewhat
faster than centrum length in the caudal series, the middle caudal
centra have progressively longer proportions (Fig. 59).
The transverse processes are very well developed throughout
the anterior and middle caudal vertebrae and are always about
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 133
FIGURE 55. Stereopair (A) and drawing (B) of caudal vertebrae 3–5 of Eoraptor lunensis (PVSJ 512) in left lateral view. Abbreviations:CA3,5,
caudal vertebra 3, 5; ch4, chevron 4; di, diapophysis; ns, neural spine; poz, postzygapophysis; tp, transverse process. Dashed line indicates a missing
margin; hatching indicates a broken surface; shading indicates matrix. Scale bars equal 2 cm.
20% longer than the neural spines (Figs. 9, 59). In the first and
second caudal vertebrae, the transverse processes appear to an-
gle posterolaterally, which avoids contact with the postacetabular
process of the ilium. In the fifth caudal vertebra, the transverse
process is blade-shaped and expands from a narrow proximal end
(6 mm) to a broad distal end (12 mm) (Fig. 55). Transverse pro-
cesses of this general shape are present until the 14th or 15th cau-
dal vertebra, in which they are subrectangular (Figs. 57, 58). The
transverse processes in the succeeding two vertebrae are notice-
ably narrower.
In the fifth caudal vertebra, the zygapophyses articulate at
an angle of 50–60◦, and this orientation is maintained through-
out the middle caudal vertebrae (Figs. 55–58). The neural spines
are proportionately much taller in the anterior caudal vertebrae
than in the dorsal and sacral vertebrae. In the fifth caudal ver-
tebra, for example, the neural spine is 9 mm wide at its narrow-
est point above the base and 21 mm tall (Fig. 55). Because neu-
ral spine height decreases more rapidly than spine width, spine
proportions become progressively broader in the mid-caudal ver-
tebrae. The spine of the 13th caudal vertebra is 10 mm tall
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134 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 56. Stereopair (A) and drawing (B) of caudal vertebrae 6–9 of Eoraptor lunensis (PVSJ 512) in left lateral view. Abbreviations:CA6–9,
caudal vertebrae 6–9; ch5–8, chevrons 5–8; ns, neural spine; tp, transverse process. Dashed line indicates a missing margin; hatching indicates a broken
surface; shading indicates matrix. Scale bars equal 2 cm.
and 7 mm wide, and by the 17th caudal vertebra, spine height
and width appear to be subequal (Fig. 58). The best-preserved
neural spines (CA4, 5, 10, 13) show that the increase in distal width
of the spine is due to a tab-shaped expansion along the posterior
margin. The anterior margin of the caudal neural spines, in con-
trast, is straight. The axis of the spine in lateral view is inclined
posterodorsally at approximately 20◦from the vertical in all pre-
served caudal vertebrae.
Presacral Ribs—With the exception of the atlantal rib, the pre-
sacral ribs are preserved near their natural articulation with the
vertebral column (Fig. 9). Most of the ribs, however, remain in the
matrix, and none is completely exposed. Some of the cervical ribs
appear to be fused to the vertebrae, whereas others are clearly dis-
articulated (Fig. 43).
Portions of the ribs of the second through the fourth cervi-
cal vertebrae are exposed on the left side of the cervical series
(Figs. 43, 44). As in more posterior cervical ribs, the rod-shaped
shafts of the anterior cervical ribs are directed posteriorly and
overlap the ventral aspect of the succeeding rib. This overlap is en-
hanced by a long, anteriorly projecting spine (Fig. 60A) that is first
preserved in the fourth cervical rib. The cervical rib shafts, thus,
form a structurally continuous rod aligned parallel to the cervical
centra.
The fifth and seventh cervical ribs are nearly completely ex-
posed and provide more complete information on the form of
middle cervical ribs (Figs. 44, 60A). Anteriorly, there are three
prominent processes set at nearly right angles to one another.
A long, pointed spinous process projects anteriorly beyond the
anterior end of its respective centrum. It has sharp dorsal and
ventral margins, a crescentic cross-section, and articulates ven-
trolaterally with the shaft of the next anterior rib. The tubercu-
lum and capitulum of the seventh cervical rib are well exposed
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 135
FIGURE 57. Stereopair (A) and drawing (B) of caudal vertebrae 9–12 of Eoraptor lunensis (PVSJ 512) in left lateral view. Abbreviations:CA9–12,
caudal vertebrae 9–12; ch9–11, chevrons 9–11; tp, transverse process. Dashed line indicates a missing margin; hatching indicates a broken surface;
shading indicates matrix. Scale bars equal 2 cm.
(Fig. 60A). The capitulum is broader than the tuberculum and
projects medially and somewhat anterodorsally. The tuberculum
is narrower and is directed dorsomedially toward the diapoph-
ysis. The rib spine and shaft are offset ventrolateral to the ven-
tral margin of the cervical centra. The distal portion of the rib
shaft is flattened and has a subrectangular cross-section. The broad
articular surface of the shaft faces dorsomedially, and the shaft ex-
tends posteriorly to the end of the next vertebra, as shown by an
articular scar on the shaft of the sixth cervical rib for the shaft of
the fifth cervical rib. Thus, the tip of the fifth cervical rib overlaps
the midshaft of the sixth cervical rib, which overlaps the spinous
process of the seventh cervical rib (Fig. 49).
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136 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 58. Stereopair (A) and drawing (B) of caudal vertebrae 13–17 of Eoraptor lunensis (PVSJ 512) in left lateral view. Abbreviations:ach,
articular surface for chevron; CA12–18, caudal vertebrae 12–18; ch12–16, chevrons 12–16; prz, prezygapophysis; tp, transverse process. Dashed line
indicates a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bars equal 2 cm.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 137
FIGURE 59. Reconstruction of caudal vertebrae 1–17 and chevrons 2–16 of Eoraptor lunensis (PVSJ 512) in left lateral view. Abbreviations:CA1,5,
10,15, caudal vertebra 1, 5, 10, 15; ch2,5,10,16, chevron 2, 5, 10, 16; tp, transverse process. Dashed line indicates a missing margin.
The spinous process of the eighth cervical rib is narrower and
flatter and only about one-half of the length of that of the sev-
enth cervical rib (Fig. 43). The capitulum is longer and points more
strongly anteriorly than medially. The ninth cervical rib, which is
dislocated ventrally, has a low, short spine as in the preceding rib,
and its shaft has a triangular, rather than a quadrangular, cross-
section (Fig. 60B).
The first dorsal rib is approximately twice the diameter and
length of the last cervical rib, which may indicate that it was the
first rib that attached to a cartilaginous sternum (Fig. 60B). The
form of the rib also differs. The spine, for example, is reduced to a
low ridge. The capitulum is much longer than the tuberculum, and
both lie in nearly the same plane as the proximal shaft of the rib
(Fig. 60B).
The fourth dorsal rib measures approximately 95 mm (tubercu-
lum to shaft end) and may be the longest in the rib cage. The fifth
dorsal rib is shorter (approximately 90 mm), as are more posterior
ribs such as the seventh (approximately 70 mm) and 14th (less than
30 mm). The capitulum remains long in the first five dorsal ribs be-
cause the distance between the diapophysis and parapophysis re-
mains the same. Although the parapophysis moves dorsally from
the centrum onto the neural arch in the anterior dorsal vertebrae,
FIGURE 60. Posterior cervical and anterior dorsal ribs of Eoraptor lunensis (PVSJ 512). A, seventh cervical rib in right lateral view. B, proximal ends
of ninth cervical and first dorsal ribs in right lateral view. C, reconstruction of seventh cervical rib in left lateral view. Abbreviations:as, articular surface;
C9, cervical vertebra 9; ca, capitulum; D1, dorsal vertebra 1; r, rib; sh, shaft; sp, spine; tu, tuberculum. Dashed line indicates a missing margin; hatching
indicates a broken surface. Scale bar equals 1 cm in Aand B.
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138 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
the transverse process increases in length. In the mid-dorsal ver-
tebrae (D8–12), however, the transverse process becomes shorter
and, as a result, the capitulum is reduced to the length of the tu-
berculum (Fig. 51).
Chevrons—In the following description, chevrons are identified
according to the vertebra with which they share their primary (an-
terior) articulation (Figs. 55–59; Table 6). There are no chevron
facets between caudal vertebrae 1 and 2; the first chevron base is
preserved in place articulating with well-developed facets between
caudal vertebrae 2 and 3. Thus, the most anterior chevron is iden-
tified as the chevron 2, because it articulates between the second
and third caudal vertebrae (Fig. 59).
The chevron of the second caudal vertebra is incomplete dis-
tally but appears to be only about two-thirds the length of
succeeding chevrons (Figs. 9, 59). All succeeding chevrons are
longer than the neural spines of their associated caudal verte-
brae. Furthermore, because the height of the caudal neural spines
decreases along the caudal column more rapidly than the length
of the chevrons, the more posterior chevrons are longer relative
to their associated caudal neural spines. Thus, anterior chevrons
are approximately 40% longer than their associated neural spines,
whereas posterior chevrons are more than twice as long. The
chevrons increase in length distally along the proximal column,
reaching a maximum in the chevron of the seventh caudal verte-
bra (Table 6). Distal to this chevron, length decreases gradually.
Several of the tips of the chevrons projected beyond the concre-
tion that encased the skeleton and were eroded away.
The proximal ends of the chevrons are strongly concave in ante-
rior or posterior view, which corresponds with the narrow propor-
tions of the ventral margin of the caudal centra. The major articu-
lar facet occurs on the anterior side of the base and is oriented at a
high angle to the axis of the proximal end of the chevron (Fig. 56).
The smaller posterior facet, in contrast, is located at a very low
angle to the axis of the shaft. At least in the middle caudal verte-
brae, the asymmetry of the proximal facets reflects the posterior
inclination of the chevron. The principal chevron facet on the pos-
terior margin of the 14th and 15th caudal centra has nearly verti-
cal orientation and projects below the opposing facet on the 15th
and 16th caudal centra, respectively (Fig. 58). This arrangement of
facets accommodates a posteroventrally inclined approach by the
chevron.
The saddle-shaped proximal articular end encloses the hemal
canal in all anterior and middle caudal chevrons. A trough passes
distally from the oval opening of the hemal canal along the an-
terior and posterior margins of the base of the chevron. Incipient
anterior processes are developed to each side of the hemal canal in
anterior caudal chevrons and appear in lateral view as little more
than a bend in the anterior margin of the chevron.
The shafts of the chevrons are transversely compressed through-
out their lengths. In lateral view, the shafts narrow in width before
slowly expanding toward the distal blade. At its narrowest width
in lateral view, the shaft bends distinctly posteriorly, so that the
blade of the chevron is oriented at an angle approximately 30◦
from the axis of the caudal column. All of the chevron shafts nar-
row in width before expanding toward the blade, and there is no
discernible trend along the caudal series in the angle of the bend
in the shaft. Surprisingly, the shaft and blade of each chevron are
hollowed; a transversely compressed cavity, sometimes with some
spongy bone infilling, extends down the shaft and into the lobe-
shaped end of each chevron, as seen in many cross-sections (Fig.
52E).
Gastralia—Rows of gastralia are preserved on both sides of
the skeleton near the distal end of the pubes (Fig. 9). The best-
preserved section includes five elements that arch over the distal
ends of the pubic blades, as seen in right lateral view of the skele-
ton. In left lateral view, more gastralia are visible in the same re-
gion anterior to the left pes (Figs. 7, 8). Nothing can be said about
their number or arrangement as an articulated cuirass. Prepara-
tion of these slender rods was very difficult, because the boundary
to surrounding matrix was not always distinct. They measure ap-
proximately 1–2 mm in diameter. Circular and oval cross-sections
are visible. It is entirely possible that two elements are present
to each side of the midline, although no such articulation can be
distinguished.
Pectoral Girdle
The scapula and coracoid are best preserved on the right side
(Figs. 9, 61–64; Table 7). On the left side, only the distal end of
the scapular blade is preserved. Clavicles were not found in the
holotypic skeleton and may not have been ossified in Eoraptor,as
discussed above. Alternatively, they may have been lost, because
the right scapulocoracoid has moved from its original position to
the opposite side of the specimen and because most of the left
scapulocoracoid is not preserved.
Scapula—The form of the scapula in Eoraptor more closely re-
sembles the condition in basal sauropodomorphs such as Saturna-
lia (Langer et al., 2007) than that in basal theropods or ornithis-
chians (Figs. 61–63, 64A, B). With the long axis of the scapular
blade held vertically, the scapular glenoid is shallow and faces pos-
teroventrally and slightly laterally. The margin between the rim of
the glenoid and the blade is concave in lateral view, which differs
from the convex margin in Herrerasaurus.
The neck of the scapular blade is proportionately broader than
in the strap-shaped blade in Herrerasaurus (Sereno, 1994) or the
narrow-necked but more expanded distal blades in Eodromaeus
(Mart´
ınez et al., 2011), Tawa (Nesbitt et al., 2009), and heterodon-
tosaurids (Sereno, 2012). The blade, nonetheless, is proportion-
ately more elongate compared with neck width than in Panphagia
TABLE 7. Measurements (in mm) of the pectoral girdle, humerus, ulna,
and radius of Eoraptor lunensis (PVSJ 512).
Dimension Measurement
Scapula
Maximum length 81
Maximum proximal width (lip of glenoid to
acromion)
40
Depth of glenoid 7
Blade length 61
Blade proximal end (neck), minimum width 13
Blade distal end, width 27L
Coracoid
Maximum length 22
Maximum width (posterior process to acromion) 37
Humerus
Maximum length 85
Maximum proximal width 28
Maximum distal width 23
Deltopectoral crest length 37
Transverse shaft diameter 11
Minimum shaft diameter 6
Ulna
Maximum length 64
Maximum proximal width 14
Maximum distal width 9
Minimum shaft diameter 6
Radius
Maximum length 63
Maximum proximal width (10)
Maximum distal width 8
Minimum shaft diameter 6
Paired structures are measured from the right side except as indicated (L,
left). Parentheses indicate estimated measurement.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 139
FIGURE 61. Stereopair (A) and drawing (B) of the right scapulocoracoid of Eoraptor lunensis (PVSJ 512) in lateral view. Abbreviations:ac, acromion;
cof, coracoid foramen; gl, glenoid; h, humerus; l, left; lp, lateral process; ocb, origin of m. coracobrachialis; otri, origin of m. triceps longus; pi, pit; r, rib;
scb, scapular blade; scf, scapulocoracoid fossa. Dashed line indicates a missing margin; hatching indicates a broken surface; shading indicates matrix.
Scale bars equal 2 cm.
(Mart´
ınez and Alcober, 2009) and Saturnalia (Langer et al., 2007),
in which blade length is less than 2.5 times neck width. The pos-
terior margin of the scapular blade is more rounded than the an-
terior margin, and as in Herrerasaurus (Sereno, 1994), the blade
follows a gentle sigmoid curve in posterior view. At the distal end
of the blade, the posterior corner has a tab-shaped extension (Fig.
64B). The distal end of the blade has an approximately symmetri-
cal profile, whereas in Panphagia (Mart´
ınez and Alcober, 2009)
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140 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 62. Stereopair (A) and drawing (B) of the right scapulocoracoid of Eoraptor lunensis (PVSJ 512) in posterolateral view. Abbreviations:ac,
acromion; cof, coracoid foramen; gl, glenoid; l, left; lp, lateral process; ocb, origin of m. coracobrachialis; otri, origin of m. triceps longus; pi, pit; r,rib;
scb, scapular blade; scf, scapulocoracoid fossa. Dashed line indicates a missing margin; hatching indicates a broken surface; shading indicates matrix.
Scale bars equal 2 cm.
FIGURE 63. Stereopair (A) and drawing (B) of the right coracoid of Eoraptor lunensis (PVSJ 512) in ventral view. Abbreviations:ac, acromion; cof,
coracoid foramen; gl, glenoid; l, left; lp, lateral process; obic, origin of m. biceps; ocb, origin of m. coracobrachialis; pi, pit; r, right or rib; scb, scapular
blade; scf, scapulocoracoid fossa. Dashed line indicates a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bar equals
2cm.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 141
FIGURE 64. Reconstruction of the left scapulocoracoid of Eoraptor lunensis (PVSJ 512) in posterior (A), lateral (B), and ventral (C) views. Abbre-
viations:ac, acromion; cof, coracoid foramen; gl, glenoid; lp, lateral process; obic, origin of m. biceps; ocb, origin of m. coracobrachialis; otri, origin of
m. triceps longus; pi, pit; scb, scapular blade; scf, scapulocoracoid fossa. Dashed line indicates a missing margin.
and Saturnalia (Langer et al., 2007) the anterior corner of the
blade is considerably shorter than the posterior corner. Eoraptor
has an oval depression on the lateral aspect of the acromion, which
may have served as an attachment area for supracoracoideus
musculature.
Coracoid—Relative to the scapula, the coracoid in Eorap-
tor (Figs. 61–63, 64C) is smaller than in Herrerasaurus and Eo-
dromaeus (Mart´
ınez et al., 2011) and slightly smaller than in
Saturnalia (Langer et al., 2007). In ventral view, the coracoid
is oval, with a height about twice its breadth (Fig. 64C). The
strongly arched external surface can be divided into three dis-
crete areas—dorsal, ventral, and anterior. These surfaces meet at
a sharp corner, here termed the lateral process. The dorsal surface
comprises the upper one-half of the coracoid. It is gently concave
anteroposteriorly and has been regarded in theropods as the area
of insertion of the supracoracoideus muscle (Raath, 1977; Langer
et al., 2007). A deep notch along the border nearest the scapula
forms most of the margin of the coracoid foramen.
The ventral surface comprises most of the ventral one-half of
the coracoid and is deflected medially along a well-marked angle
that joins the lateral process (Fig. 64C). This surface, in turn, is
divided by a subtle bend into two gently concave surfaces, anterior
and posterior, which have been regarded in theropods as the areas
of insertion of the deltoideus and coracobrachialis longus muscles,
respectively (Raath, 1977).
The posterior surface of the coracoid is subquadrate and deeply
concave. It is commonly regarded as the area of insertion for the
coracobrachialis brevis muscle (Raath, 1977; Langer et al., 2007).
A marked pit is present near its medial margin, and the most pos-
terior corner of this surface, the posterior process, is blunt and
rounded (Fig. 64C), as in Saturnalia (Langer et al., 2007) and other
basal sauropodomorphs. In most theropods, in contrast, the pos-
terior corner is developed as a prominent hook-shaped process
(e.g., Herrerasaurus; Sereno, 1994). The partially exposed medial
surface of the coracoid is dorsoventrally concave. The coracoid
glenoid equals the scapular glenoid in size but faces somewhat
more laterally.
Forelimb
Humerus—The proximal end of the humerus is most com-
plete on the right side, although the articular end is weathered
(Figs. 65, 66, 67A–C; Table 7). The broad, plate-shaped proxi-
mal end closely resembles that in Herrerasaurus (Sereno, 1994).
The head is developed as a modestly rounded expansion situ-
ated in the middle of the proximal end on its posterior aspect
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142 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 65. Stereopair (A) and drawing (B) of right humerus, radius, and ulna of Eoraptor lunensis (PVSJ 512) in anteromedial view. Abbreviations:
btu, biceps tubercle; D1–4, dorsal vertebra 1–4; dpc, deltopectoral crest; mtu, medial tuberosity; ol, olecranon; r, rib; ra, radius; rac, radial condyle; raf,
radial fossa; ul, ulna; ulc, ulnar condyle. Hatching indicates a broken surface; shading indicates matrix. Scale bars equal 2 cm.
(Fig. 61). A medial tuberosity is present but is less prominently de-
veloped and lower in position than that in Herrerasaurus (Sereno,
1994). It is unlikely that the more subtle expression of these fea-
tures in Eoraptor is simply a correlate of small body size or im-
maturity, because these features are prominently expressed in
subadult specimens of Herrerasaurus (MACN 18.060; Reig, 1963)
that are closer in size to the largest specimens of Eoraptor. The
deltopectoral crest is developed as a curved flange that extends
along the proximal 45% of the humerus. Its external margin is di-
rected about 75◦away from a transverse axis through the distal
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 143
FIGURE 66. Stereopair (A) and drawing (B)
of right humerus, radius, and ulna of Eoraptor
lunensis (PVSJ 512) in medial view. Abbrevi-
ations:btu, biceps tubercle; dpc, deltopectoral
crest; hd, head; mtu, medial tuberosity; ol, ole-
cranon; r, rib; ra, radius; raf, radial fossa; ul,
ulna; ulc, ulnar condyle. Dashed line indicates a
missing margin; hatching indicates a broken sur-
face; shading indicates matrix. Scale bars equal
2cm.
condyles. The external margin of the crest is thickest in its middle
third, tapering to a thin edge before joining the shaft.
The shafts of both humeri have been flattened postmortem.
Neither seems to have been strongly bowed, as occurs in some
theropods (e.g., Tawa, Nesbitt et al., 2009; Dilophosaurus, Welles,
1984). Rather, the shaft seems to follow a gentle sinuous curve in
lateral view and is straight in anterior view as in Saturnalia (Langer
et al., 2007).
The distal end of the humerus is divided into a transversely
convex radial and ulnar condyles. In anterior view, the radial
condyle does not round as far proximally onto the shaft as
in Herrerasaurus (Sereno, 1994:fig. 4A), but it is situated dis-
tal to a radial fossa as in the latter species. The distal end is
more generalized than that in Herrerasaurus because it lacks
the well-developed entepicondyle, ectepicondyle, and associated
pits that characterize the latter species. It most closely resembles
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144 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 67. Reconstruction of the left humerus, ulna and radius of Eoraptor lunensis (PVSJ 512). Humerus in anterior (A), proximal (B), and distal
(C) views (anterior toward bottom of page). Ulna in medial (D) and proximal (E) views. Radius in medial (F) and distal (G) views (anterior toward
bottom of page). Abbreviations:btu, biceps tubercle; dpc, deltopectoral crest; hd, head; mtu, medial tuberosity; ol, olecranon; ra, radius; rac, radial
condyle; raf, radial fossa; ul, ulna; ulc, ulnar condyle.
Saturnalia in these regards (Langer et al., 2007), although the del-
topectoral crest and distal condyles do not expand as far from the
shaft. In general, the humerus and other long bones of the fore-
limb are more robust in Saturnalia, which is probably not due to
its somewhat larger (ca. 30%) maximum body size.
Ulna—The three-dimensional shape of the proximal articular
surface of the ulna cannot be reconstructed with confidence due
to severe flattening of both ulnae (Figs. 65, 66, 67D, E). In lateral
view, the olecranon process is very low and rounded, unlike the
proximally prominent process in Saturnalia (Langer et al., 2007)
and in the theropods Herrerasaurus (Sereno, 1994) and Eodro-
maeus (Mart´
ınez et al., 2011). In either lateral or medial view, the
proximal articular surface is oriented almost at a right angle to the
shaft axis (Figs. 65, 67D).
Relative to the length of the ulna, the shaft appears to be pro-
portionately more robust than that in Saturnalia or Herrerasaurus,
although some of the apparent width is due to flattening of the
shaft, which has an elliptical cross-section. Flattening of the ulnar
shafts has removed most of their natural twist, such that the trans-
verse axes of both proximal and distal ends lie in nearly the same
plane. The shaft of the ulna was not in contact with that of the ra-
dius, as is clear from the positions of these bones in both forelimbs
(Figs. 8, 65, 66). A substantial interosseous space is present. In
theropods such as Herrerasaurus (Sereno, 1994) and Eodromaeus
(Mart´
ınez et al., 2011), in contrast, the shafts of the ulna and radius
are in contact for much of their length.
The distal end of the ulna is slightly expanded transversely and
appears to a have a simple transversely convex surface for articu-
lation with the carpus, as in Saturnalia and Eodromaeus.InHer-
rerasaurus, in contrast, the distinctive distal articular surface of the
ulna rounds onto the anterior side of the distal end (Sereno, 1994).
Radius—The better-preserved right radius is best exposed in
medial view (Figs. 65, 66, 67F, G). Its proximal end appears
to be flattened transversely, with an anteroposteriorly convex
articular surface. The cylindrical shaft is smooth and lacks the
prominent biceps tubercle present in Herrerasaurus (Sereno,
1994:figs. 6–8). The slightly smaller, subcylindrical distal end is
transversely convex and similar to that in Saturnalia (Langer et al.,
2007). In Herrerasaurus, in contrast, the distal end is squared, with
a gently concave distal articular surface.
Carpus—The carpus is poorly preserved (Fig. 68). Through-
out the skeleton, postmortem weathering and diagenesis more
strongly affected cartilage-covered articular surfaces than perios-
teum on bone shafts, and the carpus is no exception. Although it
is clear that several elements are present, their margins are often
indistinct. Drawings were made under magnification, using water
or acetone to enhance color differences. The left carpus is the bet-
ter preserved of the two (Fig. 68B). On the right side, only the
lateral carpals are preserved and are difficult to distinguish from
fragments of the distal end of the right ulna (Fig. 68A).
The left carpus may preserve the radiale and ulnare, two large
ossifications distal to the radius and ulna, respectively (Fig. 68B).
Both appear to have a tabular shape. The bone tentatively iden-
tified as the radiale appears to be tipped, its broader surface fac-
ing ventrally. Its ventral margin may be fused via diagenesis to a
smaller distal element, which could represent an enlarged distal
carpal 1, as occurs in many basal sauropodomorphs, such as Pla-
teosaurus (Sereno, 2007b). In the right carpus, there are several
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 145
FIGURE 68. Drawings of right and left carpi of Eoraptor lunensis (PVSJ
512). A, right carpus in dorsal view. B, left carpus in ventral view. Abbre-
viations:dc, distal carpal; mc1–5, metacarpals 1–5; ra, radius; rae, radiale;
ul, ulna; ule, ulnare. Dashed line indicates a missing margin; hatching in-
dicates a broken surface; light shading indicates matrix. Scale bars equal
1cm.
TABLE 8. Measurements (in mm) of the right manus of Eoraptor
lunensis (PVSJ 512).
Bone Maximum length
Digit I
Metacarpal 1 14
Phalanx 1 14
Ungual 14
Digit II
Metacarpal 2 20
Phalanx 1 12
Phalanx 2 12
Ungual 14
Digit III
Metacarpal 3 21
Phalanx 1 10
Phalanx 2 9
Phalanx 3 8
Ungual (12)
Digit IV
Metacarpal 4 16
Digit V
Metacarpal 5 10
Ungual length is measured perpendicular to a chord across the proximal
articular end. Parentheses indicate estimated measurement.
tabular ossifications proximal to metacarpals 4 and 5 (Fig. 68A).
The proximal ossification is largest and probably represents the
ulnare, whereas the more distal ossifications probably represent
distal carpals.
From the available information in the holotype, the carpus in
Eoraptor is composed of at least six ossifications and possibly more
(Fig. 73D). There is some suggestion that distal carpal 1, the most
medial distal carpal, is larger than the others. In larger-bodied
basal sauropodomorphs such as Massospondylus, distal carpal 1
overlaps distal carpal 2 (Sereno, 2007b). The carpus in Eoraptor
appears to have been well ossified and is composed of more than
three elements. Beyond these two observations, there is no spe-
cial similarity to the well-ossified carpus in Herrerasaurus (Sereno,
1994) or Eodromaeus (Mart´
ınez et al., 2011). Nor is there any
similarity to the carpus in the more derived tetanuran theropods,
which is characterized by an enlarged semilunate carpal proximal
to metacarpals 1 and 2 (Ostrom, 1969; Sullivan et al., 2010).
Metacarpus—Because the left metacarpals have been crushed
dorsoventrally (Fig. 68B), the following description is based
mainly on the right metacarpals, which are completely expos-
ed in dorsal and proximal views and partially exposed in ventral
and distal views (Figs. 69–74). Although crushed and less com-
plete, the left metacarpals retain important information on carpal-
metacarpal and intermetacarpal articular relations.
Eoraptor retains all five manual digits, as in several other basal
saurischians and ornithischians (e.g., Sereno, 2007b; Mart´
ınez,
2009; Sereno, 2012). In all dinosaurs except sauropods and
hadrosauroids (Sereno, 1997), the lateral digits of the manus (dig-
its IV, V) and their respective metacarpals are reduced relative
to the three inner digits (digits I–III; Table 8). In Eoraptor and
Eodromaeus, metacarpals 4 and 5 are more strongly developed
relative to metacarpals 1–3 than they are in the theropods Her-
rerasaurus (Sereno, 1994:fig. 15) or Tawa (Nesbitt et al., 2009).
In the first two genera, for example, metacarpal 4 is longer than
metacarpal 1, whereas the reverse is true in Herrerasaurus and
other theropods that retain metacarpal 4. All five metacarpals, as
well as the bones of the forearm and the phalanges, have some-
what stouter proportions in Eoraptor than in Eodromaeus or Her-
rerasaurus (Figs. 9, 67, 73).
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146 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 69. Stereopair of right manus of Eoraptor lunensis (PVSJ 512) in dorsolateral view. Scale bar equals 2 cm.
The proximal ends of the metacarpals have flat intermetacarpal
articular surfaces, which indicate that the metacarpal bases
were bound together by ligaments that limited their movement
(Figs. 69–73). In proximal view, the bases of the metacarpals ar-
ticulate to form an arch (Fig. 73B), which can be restored to
its probable natural curve (Fig. 73C). Overlap of the bases of
the metacarpals in an arched configuration in proximal view may
be plesiomorphic for Dinosauria. The manus of the basal or-
nithischian Lesothosaurus diagnosticus, for example, also shows
an overlapping, arched condition comparable to that in Eo-
raptor. A new reconstruction of the Lesothosaurus metacarpus
is given here, based on the single known, partially articulated
manus for this early ornithischian (Fig. 77; Table 14). Com-
plete preparation and more detailed study of this manus are
warranted.
The articulation of the bases of the metacarpals in Eodro-
maeus (Mart´
ınez et al., 2011), Herrerasaurus (Sereno, 1994:fig.
15), and most neotheropods is distinctive; the bases of the ma-
jor metacarpals (1–4) are dorsoventrally deep and wedge-shaped
in proximal view, with flat intermetacarpal surfaces. A similar
condition has arisen in heterodontosaurid ornithischians, which
have block-shaped metacarpal bases (Sereno, 2012). The condi-
tion in Eoraptor is more generalized, showing some overlap of
metacarpals along an arch but not the more compact configura-
tion seen in neotheropods and heterodontosaurids.
Metacarpal 1 is particularly stout (Fig. 76). It is shorter and
slightly broader than metacarpals 2 and 3, as in Herrerasaurus
(Sereno, 1994:fig. 11) and Eodromaeus (Mart´
ınez et al., 2011).
In proximal view, the triangular articular surface is broader than
deep and is transversely convex (Fig. 73B, C). The base of
metacarpal 1, as preserved in the left manus (Fig. 68B), is clearly
inset proximally into the carpus relative to the base of metacarpal
2, as characterizes many larger-bodied basal sauropodomorphs
(Sereno, 2007b). The proximal one-third of the shaft articulates
against metacarpal 2, as preserved in the left metacarpus. The re-
mainder of the shaft is dorsoventrally flattened. In dorsal view, a
shallow dorsal extensor depression that is present to accommo-
date the intercondylar process of the proximal phalanx is present
proximal to the lateral distal condyle (Figs. 70, 71, 73A, D, 74,
76). The distal condyles are strongly asymmetrical; the deeper and
broader lateral distal condyle extends farther distally. In dorsal
view, a transverse axis through the distal condyles is offset approx-
imately 20–25◦from the perpendicular to the long axis of the bone
(Figs. 70, 73A, D, 76). The offset of 30◦in Herrerasaurus is sim-
ilar (Sereno, 1994:fig. 14A). The distal condyles are also rotated
approximately 20◦relative to the base, such that the lateral collat-
eral ligament pit is more broadly exposed in dorsal view (Figs. 70,
73A, D, 74). In Herrerasaurus, this rotation is somewhat greater
(approximately 30◦).
The proximal articular surface of metacarpal 2 is deeper than
broad, the opposite of the proportions of metacarpal 1 (Figs. 69,
71, 73B, 74). Much of the proximal articular surface of the right
metacarpal 2 is broken away. The remainder of metacarpal 2
is very similar to that in Herrerasaurus, except that the shaft is
straight rather than bowed ventrally. Medial and lateral sides of
the proximal end of the shaft are flattened for articulation against
metacarpals 1 and 3, respectively, the former contact occurring in
a vertical plane and the latter contact with metacarpal 2 overlap-
ping metacarpal 3 (Figs. 72, 73) as in Herrerasaurus (Sereno, 1994).
At midlength the shaft is dorsoventrally compressed before it ex-
pands toward the distal condyles. Dorsally, there is a shallow dor-
sal extensor depression for the dorsal intercondylar process of the
proximal phalanx (Figs. 70, 71, 73A, D, 74). This articular depres-
sion is shifted slightly toward the lateral side of the distal end of
the metacarpal as in Herrerasaurus (Sereno, 1994), suggesting that
hyperextension of the phalanges would have deflected digit II to-
ward digit III. The partially exposed distal condyles of metacarpal
2 are deeper than in Herrerasaurus. In dorsal view, the lateral
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 147
FIGURE 70. Stereopair (A) and drawing (B) of right manus of Eoraptor lunensis (PVSJ 512) in dorsal view. Abbreviations:I–V, manual digits I–V; ag,
attachment groove for ungual sheath; clp, collateral ligament pit; ded, dorsal extensor depression; dip, dorsal intercondylar process; mc1,5, metacarpal
1, 5; ph, phalanx; un, ungual; vip, ventral intercondylar process. Dashed line indicates a missing margin; hatching indicates a broken surface; shading
indicates matrix. Scale bar equals 2 cm in Aand1cminB.
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148 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 71. Stereopair (A) and drawing (B) of the right metacarpals of Eoraptor lunensis (PVSJ 512) in dorsal view. Abbreviations:I,III, manual
digit I, III; amc2, articular surface for metacarpal 2; clp, collateral ligament pit; ded, dorsal extensor depression; dip, dorsal intercondylar process; mc1–5,
metacarpals 1–5; ph, phalanx; vip, ventral intercondylar process. Dashed line indicates a missing margin; hatching indicates a broken surface; shading
indicates matrix. Scale bars equal 1 cm.
distal condyle was probably larger than the medial, judging from
the shape of the opposing articular surface on the proximal pha-
lanx. In ventral view, only the medial distal condyle projects from
the matrix, which suggests that the distal condyles are rotated
about the long axis of the metacarpal as in metacarpal 1 (Figs. 72,
74). A similar size differential and rotation is present at the distal
end of metacarpal 2 in Herrerasaurus (Sereno, 1994:fig. 14B).
Metacarpal 3 is slightly longer than metacarpal 2. Its proxi-
mal end is gently convex rather than concave as in Herrerasaurus
(PVSJ 373; Sereno, 1994). The shape of the proximal articular sur-
face also appears to be opposite that of Herrerasaurus—broader
than deep (Fig. 73B, C). The proximal end, however, has been
affected by crushing on the ventral side of the metacarpal base.
After restoration, the subquadrate shape of the articular surface
remains transversely broader than deep, the opposite of the con-
dition in Herrerasaurus (Sereno, 1994). In Eoraptor, metacarpal 3
has a more slender midshaft than metacarpal 2, whereas in Her-
rerasaurus they are subequal. In dorsal view of the distal end,
the surface is damaged (Fig. 71). A dorsal extensor depression,
if present, would have been small and shallow (Fig. 73A, D). In
ventral view, the distal condyles are not fully exposed (Fig. 72).
The ventral margin of the medial condyle, however, projects from
the matrix, with no exposure of the lateral condyle. This suggests
that the distal condyles are rotated in the same direction as in
metacarpals 1 and 2, as in Herrerasaurus.
Metacarpal 4 is shorter than metacarpals 2 and 3 but longer than
metacarpal 1 (Figs. 69–73). In proximal view, the subtriangular ar-
ticular surface is broader than deep (Fig. 73B, C). Even with some
depth added as a correction for crushing, the proximal articular
end is not quite as deep as that in Herrerasaurus. A single, un-
divided distal articular condyle is present as in Herrerasaurus.In
Eodromaeus, in contrast, metacarpal 4 has divided distal condyles
(Mart´
ınez et al., 2011).
In dorsal view of the proximal end, a large triangular facet
on the medial side articulates against the posterior aspect of
metacarpal 3 (Figs. 71, 72). The shaft has a subtriangular cross-
section, with a flattened medial surface facing metacarpal 3 and
a rounded lateral edge. There is some torsion in the shaft oppo-
site to that in metacarpals 1–3 and opposite to that in metacarpals
1–4 in Herrerasaurus. The distal end, which is broader dorsoven-
trally than wide transversely, is rotated both by torsion in the shaft
of the bone and by its position on the metacarpal arch, such that
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 149
FIGURE 72. Stereopair (A) and drawing (B) of the right metacarpals of Eoraptor lunensis (PVSJ 512) in ventral view. Abbreviations:I,III, manual
digit I, III; amc2,4, articular surface for metacarpal 2, 4; mc1–5, metacarpals 1–5; ph, phalanx. Dashed line indicates a missing margin; hatching indicates
a broken surface; shading indicates matrix. Scale bars equal 1 cm.
the large medial collateral ligament pit is visible in dorsal view
of the manus (Fig. 73D). There is no development of an opposing
lateral collateral ligament pit. The distal articular surface is subtri-
angular and has divided distal condyles. A small proximal phalanx
may have been present as in Herrerasaurus (Sereno, 1994) and Eo-
dromaeus (Mart´
ınez et al., 2011), although none is preserved (Fig.
73A).
Metacarpal 5 is the shortest metacarpal, with a length ap-
proximately two-thirds that of metacarpals 1 and 4 (Table 8).
Metacarpal 5 is longer and broader than in Herrerasaurus
(Figs. 69–74). The proximal articular surface is missing its lateral
edge but appears to be deeper than it is broad (Fig. 73B, C). The
rod-shaped shaft has a concave medial edge and tapers toward a
rounded distal end, which lacks collateral ligament pits. The rudi-
mentary form of the distal end could indicate the absence of pha-
langes in manual digit V (Fig. 73A, D, 74).
Manual Phalanges—The phalangeal formula, based on the
well-preserved right manus of the holotype, is 2∗-3∗-4∗-(1)-
0, in which parentheses indicate estimation; a zero indicates
that the respective metacarpal is present but lacks phalanges;
and an asterisk indicates that the digit has a terminal un-
gual (Figs. 73A, D, 74; Table 8). Although no phalanges are
present in manual digit IV, the well-formed medial collateral
ligament pit and distal articular surface on metacarpal 4 sug-
gest that at least a single rudimentary phalanx was probably
present.
Except for the unguals, phalangeal length decreases distally
within manual digits I–III (Figs. 73A, D, 74; Table 8). This is the
primitive dinosaurian condition common in larger-bodied basal
sauropodomorphs such as Plateosaurus. In theropods, in contrast,
the penultimate phalanges are longer than the preceding pha-
lanx, as seen in Herrerasaurus (Sereno, 1994) and Eodromaeus
(Mart´
ınez et al., 2011). The manual unguals are also less trenchant
than those in the basal theropods Herrerasaurus (Sereno, 1994)
and Eodromaeus (Mart´
ınez et al., 2011), or those in heterodon-
tosaurid ornithischians (Sereno, 2012).
The proximal manual phalanges of manual digits I–III have
shorter, more robust proportions than in Herrerasaurus and Eo-
dromaeus and, in general, are shorter relative to the metacarpus
(Figs. 73D, 74). The relative length of phalanx 1 within digit I,
however, is more variable in basal saurischians from Ischigualasto.
In Eoraptor, phalanx 1 of digit I is equal to that of metacarpal 1;
in Eodromaeus it is shorter (Mart´
ınez et al., 2011), and in Her-
rerasaurus it is longer than metacarpal 1 (Sereno, 1994).
The proximal articular surface of phalanx 1 of digit I is subtrian-
gular, with prominent dorsal and ventral intercondylar processes
and an expanded socket laterally to accommodate the large lat-
eral distal condyle of metacarpal 1 (Fig. 75C). The shape of the
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150 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 73. Left manus of Eoraptor lunensis (PVSJ 512). A, left manus (reversed from right) in exploded dorsal view with phalanges of digit I
rotated so their sagittal plane is vertical. B, left metacarpus (reversed from right) in proximal view (dorsal toward bottom of page). C, reconstruction
of articulated left metacarpus in proximal view showing metacarpal arch. D, reconstruction of articulated left carpus and manus in dorsal view showing
articulated orientation of digit I. Abbreviations:I–V, manual digits I–V; ag, attachment groove for ungual sheath; clp, collateral ligament pit; dc1,5,
distal carpal 1, 5; ded, dorsal extensor depression; dip, dorsal intercondylar process; mc1–5, metacarpal 1–5; ph, phalanx; rae, radiale; ule, ulnare; un,
ungual. Dashed line indicates a missing margin; hatching indicates a broken surface. Scale bar equals 1 cm in Aand B.
proximal end is similar to that in Herrerasaurus, but the inter-
condylar processes are more prominent and pointed. With the in-
tercondylar processes held along a vertical axis, the distal condyles
are rotated approximately 35◦(Fig. 75B), such that the lateral
distal condyle is positioned dorsal to the medial condyle in neu-
tral pose. In Eodromaeus, in contrast, there is negligible rota-
tion of the distal condyles (Mart´
ınez et al., 2011:fig. 1G). In Her-
rerasaurus, there is approximately 15◦of rotation in the same di-
rection as in Eoraptor (Sereno, 1994:fig. 14A). In larger-bodied
basal sauropodomorphs such as Massospondylus, 45–60◦of ro-
tation are present within phalanx 1 of digit I (Sereno, 2007b:fig.
9D–F). The condition in Eoraptor bears a striking resemblance
to that in basal sauropodomorphs. Maximum extension of manual
digit I in Eoraptor positions the ungual vertically (Fig. 76C, top),
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 151
FIGURE 74. Right manus of Eoraptor lunensis (PVSJ 512) in exploded lateral view. Abbreviations:I–V, manual digits I–V; ag, attachment groove for
ungual sheath; amc2–4, articular surface for metacarpals 2–4; clp, lateral collateral ligament pit; ded, dorsal extensor depression; dip, dorsal intercondylar
process; ftu, flexor tubercle; vip, ventral intercondylar process. Dashed line indicates a missing margin. Scale bar equals 1 cm.
with the plane through the ungual canted at approximately 45◦,as
seen in dorsal view (Fig. 76B). Maximum flexion of manual digit I
in Eoraptor positions the ungual past the vertical and at an angle
of 90◦to the axis of the penultimate phalanx (Fig. 76C, bottom).
Throughout this rotary arc, the ungual of manual digit I in Eo-
raptor is canted so that its medial side is exposed in dorsal view
(Fig. 76).
The direction of rotation of the distal condyles relative to
the phalangeal base is opposite to the direction of rotation in
metacarpal 1, as is also the case in Herrerasaurus (Sereno, 1994:fig.
14A). The greater degree of rotation in Eoraptor, however, di-
rects the ungual medially, exposing the medial aspect of the un-
gual in dorsal view (Figs. 73A, D, 76A), which is not the case in
Herrerasaurus (Sereno, 1994:fig. 15, left), Eodromaeus (Mart´
ınez
et al., 2011:fig. 1G), or Lesothosaurus (Fig. 77C). The distal gingly-
mus in Eoraptor is transversely narrow, deeply cleft, and rounded
dorsally (Figs. 75B, 76A). The medial collateral ligament pit is
shallower than the lateral pit, and the dorsal extensor depression is
well developed. In dorsal view, the lateral distal condyle extends
farther distally than the medial distal condyle, deflecting the un-
gual medially (Fig. 76A).
Phalanx 1 of digit II (Figs. 69, 70, 73A, 74) is shorter than
the proximal phalanx of digit I but longer than that of digit III,
as in Herrerasaurus (Sereno, 1994:table 4). In Eodromaeus,in
contrast, phalanx 1 of digit II is slightly longer than the proxi-
mal phalanx of digit I (Mart´
ınez et al., 2011). The subtriangu-
lar proximal articular surface is asymmetrical; the medial edge
is nearly vertical, whereas the lateral edge has an expanded
socket laterally for the lateral distal condyle of metacarpal 2,
as in Herrerasaurus and Eodromaeus. A prominent dorsal inter-
condylar process is present and associated with a dorsal exten-
sor depression; the ventral intercondylar process is not exposed.
The medial collateral ligament pit is shallower than the lateral,
and the distal ginglymus is deeply cleft, as in Herrerasaurus and
Eodromaeus.
Phalanx 1 of digit III is the shortest of the proximal phalanges
(Figs. 69, 70, 73A, 74). The proximal articular surface, which is par-
tially exposed, appears to be the most symmetrical and has a trans-
versely broad ventral intercondylar process, as in Herrerasaurus
and Eodromaeus. Distally, the lateral collateral ligament pit is
deeper than the medial pit, and the lateral distal condyle extends
farther distally than the medial distal condyle, as in Herrerasaurus
and Eodromaeus.
The intermediate manual phalanges include phalanx 2 of digit
II and phalanges 2 and 3 of digit III (Figs. 69, 70, 73A, 74). The
proximal end of phalanx 2 of digit II is proportionately deep, with
pointed dorsal and ventral intercondylar processes and an asym-
metrical subtriangular articular surface that accommodates the
larger lateral distal condyle of the proximal phalanx. There is little
torsion in the shaft, and thus the phalanx is very similar to inter-
mediate phalanges in Herrerasaurus and Eodromaeus. The distal
condyles are prominent dorsally, but their dorsal edges and the
dorsal extensor depression are damaged. The intermediate pha-
langes in digit III are badly crushed and preserve few details. Each
has a dorsal intercondylar process, collateral ligament pits, and a
distal ginglymus (Fig. 70).
The manual unguals are relatively broader transversely and less
recurved than in the theropods Herrerasaurus (Sereno, 1994) and
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152 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 75. Drawings of phalanges of manual digit I in Eoraptor lunen-
sis (PVSJ 512). A, proximal phalanx and ungual of right manual digit I in
medial view. B, proximal phalanx of right manual digit I in distal view. C,
proximal phalanx of right manual digit I in proximal view. Abbreviations:
ag, attachment groove for ungual sheath; clp, collateral ligament pit; dip,
dorsal intercondylar process; ftu, flexor tubercle; ldc, lateral distal condyle;
mcot, medial cotylus; mdc, medial distal condyle; vip, ventral intercondylar
process. Dashed line indicates a missing margin; hatching indicates a bro-
ken surface; dotted line indicates location in A of other views. Scale bar
equals 5 mm.
Eodromaeus (Mart´
ınez et al., 2011). In Eoraptor, the distal tip of
the ungual does not extend far below the base, when the base is
held vertically (Fig. 74). In nearly all theropods including Her-
rerasaurus (Sereno, 1994) and Eodromaeus (Mart´
ınez et al., 2011),
the distal tip of the ungual is located considerably ventral to the
proximal articular surface, when that surface is oriented vertically.
For each of the best-preserved unguals (digits I and II), maximum
depth is only 150% of maximum width. In Herrerasaurus (Sereno,
1994:figs. 14, 15), Allosaurus (Madsen, 1976:pl. 44), and nearly all
theropods, the manual unguals have a maximum depth ranging
from 200–300% of maximum width.
The unguals of digits I and II are subequal in length and nearly
identical in form (Figs. 69, 70, 73A, D, 74). The main difference
between these two unguals lies in the depth of the proximal end,
that of digit I being slightly greater than that of digit II (Fig. 74).
The ungual of digit III resembles the other unguals but is smaller
in all dimensions, measuring about 75–85% of their length. The
tips of all three unguals are broken away.
Pelvic Girdle
The pelvic girdle is partially obscured in right and left lateral
views by the articulated hind limbs (Figs. 78, 79, 83; Table 9). The
only missing portions include the distal end of the left ilium, which
was eroded at the surface, and the distal end of the right pubis,
which was fractured and abraded prior to final burial of the skele-
ton. The pelvic girdle has been transversely compressed, such that
the pubic blades overlap one another in the midline, and sheared
anteroposteriorly, such that the left side is shifted about 1 cm an-
terior to the right side (Fig. 78).
The sutures are not closed between the sacral ribs and ilia or be-
tween the three bones on each side of the pelvic girdle. The distal
ends of the ischia, however, appear to be coossified, although this
TABLE 9. Measurements (in mm) of the pelvic girdle of Eoraptor
lunensis (PVSJ 512).
Dimension Measurement
Ilium
Blade length (pre- to postacetabular process) 82
Blade maximum depth (from supraacetabular lip) 34
Pubic peduncle length 24
Pubic peduncle, maximum transverse width, distal
end
12
Pubic peduncle, maximum dorsoventral depth, distal
end
16
Acetabulum, anteroposterior diameter 30L
Brevis shelf, transverse width of distal end, outside 12
Brevis shelf, transverse width of distal end, inside 9
Ischium
Length (pubic peduncle to foot) 114
Midshaft, dorsoventral shaft diameter 7
Midshaft, transverse shaft diameter 5
Distal end, maximum anteroposterior width 16
Distal end, maximum transverse width 6
Pubis
Maximum length (from iliac peduncle) 121
Iliac peduncle, transverse width of distal end 8
Blade length 95
Blade, proximal transverse width 27
Blade, midlength transverse width 21
Blade, distal transverse width 17
Maximum diameter of pubic fenestra 10
Measurements are from the right side except as indicated otherwise
(L, left).
also may be the result of plastic deformation or diagenesis during
fossilization (Fig. 81).
Ilium—Relative to the vertebral column, the ilium is as long as
in Herrerasaurus (Novas, 1994:fig. 3A), spanning approximately
four and one-half centra from anterior to posterior extremi-
ties (Fig. 79). The iliac blade is more than twice the maximum
depth above the acetabulum (Fig. 82A) and closely resembles
the proportions in Panphagia (Mart´
ınez and Alcober, 2009) and
Saturnalia (Langer, 2003). Among herrerasaurids, the ilium is
closer in form to Chindesaurus (Long and Murry, 1995:fig. 181)
than Herrerasaurus (Novas, 1994:fig. 5) or Staurikosaurus (Col-
bert, 1970:fig. 8A), given the planar form and subtriangular shape
of the preacetabular process. The low profile and short preac-
etabular process differ from the deeper preacetabular process in
the theropod Eodromaeus (Mart´
ınez et al., 2011). The thin blade,
which is only 1 mm thick, is concave laterally as seen in dorsal
view (Fig. 54). In lateral view, its dorsal margin is also arched (Fig.
82A).
A raised attachment scar is present on the lateral aspect of the
preacetabular process opposite the attachment of the first sacral
rib (Figs. 78, 79, 82A), which is similar to that in Plateosaurus
(Huene, 1926b), Staurikosaurus,andChindesaurus. The ventral
margin of the preacetabular process is not continuous with the
anterior margin of the pubic peduncle of the ilium. As in Pan-
phagia,Saturnalia, and Herrerasaurus, rather, it joins the pedun-
cle on its lateral side, creating a narrow medial fossa (Fig. 82A). A
similar configuration is present in Staurikosaurus,Chindesaurus,
and in tetanuran theropods such as Allosaurus,Tyrannosaurus,
and Deinonychus.
The postacetabular process is longer than the preacetabular
process in lateral view of the ilium (Fig. 82A). It tapers distally
to a squared end, the posterodorsal corner of which is rounded.
As in the sauropodomorphs Panphagia and Saturnalia, an arched
brevis fossa is present in Eoraptor, unlike the herrerasaurids Her-
rerasaurus,Staurikosaurus,andChindesaurus. Partially exposed
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 153
FIGURE 76. Drawings of right manual digit I of Eoraptor lunensis (PVSJ 512) in various poses based on manipulations of cast bones. A, neutral pose
in dorsal view. B, fully extended pose in dorsal view. C, fully extended (above) and fully flexed (below) poses in medial view. Abbreviations: I, manual
digit I; clp, collateral ligament pit; ded, dorsal extensor depression; dip, dorsal intercondylar process; ftu, flexor tubercle; mc1, metacarpal 1; ph, phalanx;
un, ungual; vip, ventral intercondylar process. Ungual tip reconstructed. Scale bar equals 5 mm.
on the right side, the arched brevis fossa has lateral and medial
walls of equal depth (Fig. 82D). In ventral view, the width of
the fossa is constant, and the third sacral rib attaches along the
ventral margin of the medial wall. In coelophysoids, in contrast,
the width of the fossa expands distally, and the sacral rib attach-
ments rise across the postacetabular process to its posterodorsal
corner.
The supraacetabular crest is strongly developed but does not
overhang most of the acetabular space as in Panphagia (Mart´
ınez
and Alcober, 2009:fig. 8A). It has a sigmoidal external margin that
is continuous anteroventrally with the posterior margin of the pu-
bic peduncle (Fig. 82A).
The stout pubic peduncle angles about 20◦below the hori-
zontal (Figs. 78, 79, 82A). It has a subquadrate shape in lateral
view and a subtriangular cross-section and distal articular surface
(Fig. 82B). The medial side of the peduncle is slightly convex
dorsoventrally, whereas the lateral, acetabular, and distal surfaces
are gently concave. In distal view of the peduncle, the dorsoven-
tral height (16 mm) is greater than the width of the acetabular
surface (12 mm). The ischial peduncle is exposed only on the left
side, where it has slid anteriorly on its contact with the ischium
(Fig. 79). In lateral view, the posterior margin of the ischial pe-
duncle is concave, which separates the peduncle more distinctly
from the postacetabular process than in herrerasaurids (Fig. 82A).
The ventral-most portion of the posterior margin is not exposed.
A broad antitrochanteric surface is exposed within the acetabulum
(Fig. 82A).
Ischium—Nearly all of the ischium is exposed in either right
or left lateral view, from which a composite reconstruction was
made (Figs. 78–82). In lateral view, the broad, plate-shaped prox-
imal end has a shallow acetabular embayment closer to that in
Panphagia (Mart´
ınez and Alcober, 2009) than the deeper em-
bayment partially preserved in Saturnalia (Langer, 2003). The
posterior margin of the iliac peduncle is convex, and a lateral crest
passes from the peduncle down the shaft. The acetabular margin
of the ischium is best exposed on the right side; only the posterior
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154 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 77. Right manus of Lesothosaurus di-
agnosticus (NHMUK RU B17). A, stereopair of
right manus as preserved in partial articulation,
showing metacarpal 2 (above) and the proximal
portion of digit III (below). B, reconstruction
of the articulated right metacarpus in proximal
view. C, reconstruction of the preserved bones
of the right manus in dorsal view. Abbrevia-
tions:I–V, manual digits I–V; clp, collateral lig-
ament pit; ded, dorsal extensor depression; mc1,
5, metacarpal 1, 5; un, ungual. Scale bar equals
1cminA.
portion is covered by the femur (Figs. 78, 83). The raised anterior
corner of the ischial antitrochanter is exposed, anterior to which is
a non-articular margin at least 7 mm long. The posterior portion of
the ischial antitrochanter is exposed on the left side (Fig. 79). The
short pubic peduncle (9 mm) has a subtriangular cross-section that
is dorsoventrally deeper (12 mm) than transversely broad (8 mm).
Proximally, the shaft is plate-shaped, with a sinuous ventral
margin along which there is no development of an obturator pro-
cess. The ischial symphysis extends along most of the length of
the bone, beginning proximally at the base of the pubic pedun-
cle and continuing to the distal end of the shaft (Fig. 82E, G,
I). At midlength the shafts are hollow and have a subtriangu-
lar cross-section that is dorsoventrally deeper (7 mm) than trans-
versely broad (5 mm) (Figs. 81, 82G). Distally, the ischium ex-
pands gradually in depth and, to a lesser extent, in width (Figs. 81,
82A).
The distal end of the ischium has a depth of 17 mm and a
width of 7 mm and is truncated at a high angle (ca. 60◦)tothe
horizontal in lateral view (Figs. 80, 81, 82A). A subtriangular
distal end (Fig. 82I) is typical of basal sauropodomorphs, such
as Saturnalia (Langer, 2003), Plateosaurus (Huene, 1926b), and
Adeopapposaurus (Mart´
ınez, 2009). In Panphagia, the distal end
has a more crescentic shape, although the shaft does have a lat-
eral ridge offset to its dorsal margin (Mart´
ınez and Alcober, 2009).
In both Panphagia and Saturnalia, the distal end of the ischium
is expanded to a greater degree than in Eoraptor. In theropods,
in contrast, the distal end of the ischium is rounded or trun-
cated roughly horizontally, as in Herrerasaurus (Novas, 1994) and
various basal neotheropods (e.g., Carnotaurus, Bonaparte et al.,
1990; Dilophosaurus, Welles, 1984; Coelophysis, Colbert, 1989; Al-
losaurus, Gilmore, 1920; Madsen, 1976).
Pubis—The pubis, the longest element in the pelvic girdle,
projects anteroventrally from the acetabulum and is best exposed
in right lateral view (Figs. 78, 79, 82A, C, F, H). The proximal
end is divided between the articular surfaces for the ilium and is-
chium and an intervening acetabular margin (Fig. 82A). Of the
three, the iliac articular surface is the longest and thickest portion
of the proximal end. The acetabular margin and iliac peduncle are
plate-shaped, and both angle medially toward the median symph-
ysis, which seems to run the entire length of the bone. A shallow
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 155
FIGURE 78. Stereopair (A) and drawing (B) of the pelvic girdle and right hind limb of Eoraptor lunensis (PVSJ 512) in lateral view. Abbreviations:
I–III, pedal digits I–III; ap, ambiens process; as, astragalus; at, anterior trochanter; ca, calcaneum; CA1–3, caudal vertebrae 1–3; D15, dorsal vertebra 15;
dt4, distal tarsal 4; fe, femur; fi, fibula; ft, fourth trochanter; ga, gastralia; is, ischium; l, left; mt2–5, metatarsals 2–5; of, obturator foramen; ph, phalanx;
poap, postacetabular process; prap, preacetabular process; pu, pubis; r, right; S1, sacral vertebra 1; ti, tibia; tp, transverse process; un, ungual. Dashed
line indicates a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bars equal 5 cm.
groove passes out of the acetabulum. A large oval obturator fora-
men, with an anteroposterior diameter of approximately 10 mm,
is located in the thin medial portion of the proximal end of the pu-
bis and would have had only a narrow medial margin separating it
from its opposite (Figs. 78, 82A). There are no additional openings
in the proximal end of the pubis.
The plate-shaped blade faces anteriorly (Figs. 78, 82A). Along
with its opposite, it is gently arched transversely. The thickened
lateral edge of the proximal blade curls posteriorly (Fig. 82C),
whereas the majority of the blade is composed of a nearly planar
sheet of bone only 2 mm thick (Fig. 82H). Proximally, a prominent,
dorsoventrally compressed ambiens process is present along the
lateral margin (Fig. 82A). In anterior view, the width of the blade
decreases gradually such that the distal end is 60% the width of
the proximal end (Fig. 82C, H). The distal end, which is well pre-
served on the left side, is slightly swollen along its ventral margin
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156 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 79. Stereopair (A) and drawing (B) of the pelvic girdle and left hind limb of Eoraptor lunensis (PVSJ 512) in lateral view. Abbreviations:ant,
antitrochanter; as, astragalus; CA1, caudal vertebra 1; D14,15, dorsal vertebra 14, 15; dt3,4, distal tarsal 3, 4; fe, femur; is, ischium; l, left; mt4, metatarsal
4; pa, parapophysis; plf, posterolateral flange; pped, pubic peduncle; prap, preacetabular process; pu, pubis; r, rib or right; S1–3, sacral vertebra 1–3; sac,
supraacetabular crest; ti, tibia. Dashed line indicates a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bars equal
3cm.
(Fig. 82A). There is no development of a pubic foot as occurs in
Herrerasaurus,Eodromaeus, and other theropods.
Hind Limb
The elongate long bones in the distal segments of the hind
limb in Eoraptor are consistent with the proportions of a cur-
sorial biped (Carrano, 1999). The tibia exceeds the femur in
length, and metatarsal 3 is greater than one-half the length of
the tibia (Table 10). All of the long bones, including all non-
ungual phalanges, and at least the proximal tarsals are hollow.
Although the following description of the hind limb is based pri-
marily on the holotypic skeleton (Figs. 83, 87, 89, 90), many as-
pects of the femur and tibia are better preserved in referred
material (Table 1). A partial, articulated right hind limb (PVSJ
559) was found in the wall of the excavation trench around the
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 157
FIGURE 80. Stereopair (A) and drawing (B) of the distal right ischium, distal right femur, and proximal right tibia of Eoraptor lunensis (PVSJ 512) in
lateral view. Abbreviations:fe, femur; fi, fibula; is, ischium; ti, tibia. Dashed line indicates a missing margin; hatching indicates a broken surface; shading
indicates matrix. Scale bars equal 3 cm.
holotypic skeleton and provides the most complete information
for the femur, tibia, distal fibula, and proximal tarsals (Figs. 84–86,
88).
Femur—The maximum length of the proximal end of the femur
is approximately twice its minimum width. With the axis through
the distal condyles oriented transversely, the long axis of the prox-
imal end projects anteromedially toward the acetabulum at about
50◦from a transverse axis. In this regard, Eoraptor resembles Sat-
urnalia (Langer, 2003:fig. 4), Herrerasaurus (Novas, 1994:fig. 7E),
Staurikosaurus (Colbert, 1970:fig. 11A), and basal neotheropods
(e.g., Coelophysis; Padian, 1986:fig. 5.4C). The head, which is par-
tially exposed, forms the hemispherical medial extremity of the
proximal end (Fig. 83). The lateral rim of the head is very promi-
nent as in Saturnalia (Fig. 83). On the medial side of the proximal
end, the head is delimited posteriorly by a sulcus for the ligament
of the head, posterior to which is a rounded medial tuberosity and
trough.
The anterior trochanter is developed as a vertical process, most
of which is attached to the anterolateral margin of the proximal
shaft (Figs. 83, 86). The anterior surface of the femoral shaft adja-
cent to the anterior trochanter is flattened as in Saturnalia and less
than the extent that occurs in herrerasaurids (Novas, 1994). An
additional vertical rugosity seems to be present on the posterior
margin of the shaft, opposite and slightly proximal to the anterior
trochanter (Fig. 83).
The trochanteric shelf (Fig. 84E, F) and its associated sig-
moidal rugosity are similar in general form and position to that
in the basal dinosauriforms Marasuchus (Sereno and Arcucci,
1994a) and Silesaurus (Dzik, 2003) and in other basal dinosaurs
such as Saturnalia (Langer, 2003), Herrerasaurus (Novas, 1994),
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158 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 81. Stereopair (A) and drawing (B) of the distal ischia, distal right femur and proximal right tibia and fibula of Eoraptor lunensis (PVSJ 512)
in medial view. Abbreviations:fe, femur; is, ischium; l, left; r, right; ti, tibia. Hatching indicates a broken surface; shading indicates matrix. Scale bars
equal 3 cm.
and coelophysoids (Rowe, 1989; Tykoski and Rowe, 2004). The
crest descends and then traverses the proximal femoral shaft as a
trough with a raised rugose external ridge, attenuating as a low ru-
gose scar on the posterolateral aspect of the shaft (Figs. 84D, F,
86A), presumably for attachment of the ischiotrochantericus mus-
cle (Carrano and Hutchinson, 2002). At that point, the rugosity
diverges, with one branch continuing posteroventrally to join the
proximal end of the fourth trochanter and the other joining a ridge
passing down the lateral aspect of the femoral shaft as an intermus-
cular line (Figs. 84F, 86A).
The fourth trochanter, located on the posteromedial side of the
shaft one-third of the distance from the head along the femur, is
developed as a prominent subrectangular flange, measuring about
22 mm along its external margin and 7 mm wide (Fig. 84F). As the
flange expands from the shaft, a subtle proximal corner is present
that is more prominent than in Saturnalia (Langer, 2003:fig.4B,
E). The distal corner of the flange, likewise, is more prominent
than in Saturnalia, such that it is slightly pendant at its apex.
In general, however, the fourth trochanter in Eoraptor resem-
bles the subquadrate, hatchet-shaped fourth trochanter in basal
sauropodomorphs (e.g., Massospondylus, Cooper, 1981; Adeopap-
posaurus, Mart´
ınez, 2009) and Herrerasaurus (Novas, 1994) than
the more symmetrical, crescentic flange typical of theropods,
such as Eodromaeus (Mart´
ınez et al., 2011) and Tawa (Nesbitt
et al., 2009). Scars indicate the likely attachment areas for caud-
ofemoralis brevis and longus muscles (Fig. 84C, F).
The anterior aspect of the distal end of the femur is marked by a
large, subtriangular rugose area for attachment of the femorotib-
ialis musculature (Figs. 84H, 86A). In Herrerasaurus (Novas,
1994), Eodromaeus (Mart´
ınez et al., 2011), and other theropods
(e.g., Allosaurus; Gilmore, 1920), this attachment area is often de-
pressed to form a shallow fossa. The distal articular surface of the
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 159
FIGURE 82. Reconstruction of the pelvic girdle of Eoraptor lunensis (PVSJ 512) in left lateral view with cross-sections. A, pelvic girdle. B, distal
articular end of pubic peduncle. C, cross-section of the proximal end of the pubic blades. D, distal end of the iliac postacetabular process. E, cross-
section of the proximal end of the ischiae. F, distal articular end of pubic peduncle of ischium. G, cross-section of ischial shafts at midlength. H, distal
ends of pubes. I, distal ends of the ischia. Abbreviations:acet, acetabulum; ant, antitrochanter; ap, ambiens process; bfo, brevis fossa; of, obturator
foramen; ofl, obturator flange; pi, pit; pub, pubic blade; ru, rugosity; sas, supraacetabular shelf. Dashed line in Aindicates position of cross-sections and
in C,E,andC,G–Iindicates the midline; hatching indicates a cross-sectional view; shading indicates view of distal end.
femur has subequal anteroposterior and transverse maximum di-
mensions (Fig. 84G). There is no anterior intercondylar groove,
but the posterior intercondylar groove is well developed and sep-
arates the medial condyle from the smaller lateral condyle. The
fibular condyle is located anterior to the lateral condyle, separated
distally and laterally by shallow troughs (Fig. 84D, G). There is
no development of a sharp tibiofibular crest on the rounded lat-
eral condyle, which is well developed in ceratosaurian theropods
and birds (Rowe, 1989:fig. 4F). A broad area in the center of
the distal articular surface is concave (Fig. 84G), as in Saturnalia
(Langer, 2003) and herrerasaurids (Herrerasaurus, Novas, 1994;
Staurikosaurus, Bittencourt and Kellner, 2009). The distal end of
the femur is nearly indistinguishable from that in Saturnalia.
Tibia—The proximal articular end of the tibia is subtriangular,
about one-third longer than wide (Fig. 85F). The cnemial crest
forms the rounded anterior apex of the articular surface and in
lateral view projects a short distance above the remainder of the
proximal end (Fig. 85E), as in Panphagia (Mart´
ınez and Alcober,
2009:fig. 9A) and Herrerasaurus (Novas, 1994:fig. 8B). In Saturna-
lia, the central portion of the proximal end is more prominent than
that over the cnemial crest (Langer, 2003:fig. 5A).
Two condyles are developed on the remainder of the proxi-
mal articular surface. The medial condyle is the largest (12 mm
width) and is separated from the lateral condyle (7 mm width) by
a shallow notch (Fig. 85B, F). The lateral condyle is set anterior to
the medial condyle and has a distinct beveled posterolateral edge
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160 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
TABLE 10. Measurements (in mm) of the femur, tibia, fibula, and prox-
imal tarsals of Eoraptor lunensis (PVSJ 512).
Dimension Measurement
Femur
Length 152L
Head, maximum anteroposterior width 27
Head, maximum transverse width 14
Head to apex of fourth trochanter (distal notch) 55
Midshaft, anteroposterior diameter 21
Midshaft, transverse diameter 21
Distal end, maximum transverse width 25
Distal end, maximum anteroposterior depth 25
Tibia
Length 156
Proximal end, maximum anteroposterior width 30
Proximal end, maximum transverse width 21L
Midshaft, anteroposterior diameter 13
Midshaft, transverse diameter 12
Distal end, maximum distal width 19
Distal end, posterolateral flange thickness 6
Fibula
Length 154
Proximal end, maximum anteroposterior width 21L
Proximal end, maximum transverse width 7L
Midshaft, anteroposterior diameter 10
Midshaft, transverse diameter 8
Distal end, maximum with (oblique axis) 15
Astragalus
Maximum transverse width 27
Tibial depression, minimum thickness 9
Ascending process, height to apex 6
Calcaneum
Maximum transverse width 11
Maximum dorsoventral depth (posterior portion) 8
Distal tarsal 3
Maximum transverse width (12)
Maximum dorsoventral depth 6
Distal tarsal 4
Maximum transverse width 13
Body, maximum dorsoventral depth (medial edge) 6
Heel, maximum dorsoventral depth 7
Measurements are from the right side except as indicated otherwise (L,
left). Parentheses indicate estimated measurement.
(Fig. 85E, F). In lateral view of the proximal end, the shaft bears
a strong fibular crest (Fig. 85E). At midlength the shaft is sub-
cylindrical. The transversely expanded distal end curves slightly
anteriorly and medially, as seen in medial and posterior views, re-
spectively (Fig. 85B, C).
The subquadrate distal end of the tibia is approximately 20%
broader transversely than deep anteroposteriorly (Fig. 85H). In
distal view, a curving articular surface accommodates the wedge-
shaped ascending process of the astragalus (Fig. 85H), which is
very similar to that in Saturnalia (Langer, 2003). A relatively thin
posterolateral flange (6 mm) projects laterally, backing the ascend-
ing process of the astragalus and approaching, but not contacting,
the fibula (Figs. 85G, H, 87, 88B, F). A groove that separates the
posterolateral flange from the remainder of the tibia curves from
the distal end onto the lateral aspect of the shaft (Figs. 86B, 87A,
C). The form of the distal end of the tibia is nearly identical in
Eoraptor,Panphagia, and Saturnalia (Langer, 2003).
Fibula—The fibula is exposed in lateral view in the holotypic
skeleton (PVSJ 512), the left side preserving the proximal end,
and the right side preserving the central shaft and distal end. A
disarticulated distal end of the fibula is also available (PVSJ 559).
The proximal articular surface of the fibula is crescentic, with an
anteroposterior length that is three times its maximum width. The
external margin is slightly convex and the internal concave. The
anterior trochanter, if present at all, is a low rugosity on the ante-
rior margin of the proximal shaft. The cross-section of the shaft is
cylindrical at midlength.
The distal end has an elliptical articular surface, the long axis
of which angles posterolaterally (Figs. 85K, 88C). In lateral view,
the distal end of the fibula angles posteroventrally at approxi-
mately 25◦(Fig. 85I, J). The posterolateral margin of the distal
end projects as a prominent posterior tuberosity, which overhangs
the calcaneum posteriorly (Figs. 85I–K, 88B, C). The distal end
of the fibula extends ventral to the tibia in articulation, where
it contacts the calcaneum and astragalus (Fig. 88A, B). Fibular
contact with the astragalus occurs on the lateral aspect of the as-
cending process, a configuration that closely matches that in basal
sauropodomorphs (Cooper, 1981).
Astragalus—The astragalus is partially exposed in the holo-
typic skeleton (Fig. 87) and fully exposed in two referred speci-
mens (PVSJ 534, 862). In the holotype, the posterior one-half of
the bone has sheared off, exposing hollow pockets in the body
of the astragalus (Fig. 87). That cross-section also shows that
the astragalus is nearly three times as wide transversely as it is
thick dorsoventrally. In dorsal view (Fig. 88G), the astragalus is
transversely broad, its maximum anteroposterior depth measuring
only 65% of its transverse width, compared with 75% in Panpha-
gia (Mart´
ınez and Alcober, 2009:fig. 9D) and Saturnalia (Langer,
2003:fig. 6A).
The anterolateral corner of the astragalus is very prominent in
dorsal or ventral view in Eoraptor,asinPanphagia,Saturnalia,
FIGURE 83. Stereopair of right ilium, proximal femur, distal tibia and fibula, and ankle of Eoraptor lunensis (PVSJ 512) in lateral view. Scale bar
equals 5 cm.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 161
FIGURE 84. Partial right femur of Eoraptor lunensis (cast of PVSJ 559). A, anterior view. B, posterior view. C, medial view. D, lateral view. E, lateral
view (close-up) of trochanteric shelf and fourth trochanter. F, posterolateral view (close-up) of fourth trochanter. G, distal view. H, anterior view (close-
up) of distal end. Abbreviations:cfb, m. caudofemoralis brevis scar; cfl, m. caudofemoralis longus scar; fco, fibular condyle; ft, fourth trochanter; gr,
groove; lco, lateral condyle; mco, medial condyle; ri, ridge; ru, rugosity; ts, trochanteric shelf. Dashed line indicates a missing margin. Scale bar equals
5cminA–Dand2cminE–H.
and other basal sauropodomorphs (Fig. 88G, H). The dorsal sur-
face of the astragalus is predominated by the tibial articular sur-
face, which articulates against all but the anteromedial corner
and posterior fossa. The posterior fossa provides vascular sup-
ply to the astragalus via a large foramen (Fig, 88E). The postero-
lateral flange of the tibia extends across this region (Fig. 88B),
but a gap separates the flange from the surface of the fossa (Fig.
88C). In dorsal view, the anteromedial corner of the astragalus
can be seen extending beyond the tibia (Fig. 88C). In medial
view (Fig. 88F), the ventral articular surface of the astragalus is
beveled parallel to the surface of the ascending process, which
reduces the thickness of the posterior portion of the astragalus.
In ventral view, the articular surface is saddle-shaped, with a dis-
tinct bulge ventral to the anterolateral corner. That bulge is sepa-
rated form the distal articular surface by a low, rounded diagonal
crest.
A small anterior fossa is present, within which are situated a
few small foramina (Fig. 88A, D). The ascending process is wedge-
shaped, and has a concave articular facet laterally for contact with
the fibula. Laterally, the astragalus meets the calcaneum along a
complex suture. As seen in dorsal view (Fig. 88G), the astragalus
projects laterally over the calcaneum along its anterior and poste-
rior margins and receives in return a short, subtriangular process
of the calcaneum (Fig. 88D, E, H). The concave articular socket
for the distal end of the fibula faces laterally and undercuts the
upper portion of the ascending process.
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162 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 85. Right tibia and distal fibula of Eoraptor lunensis (cast of PVSJ 559). Right tibia in anterior (A), posterior (B), medial (C), and lateral
(D) views. Proximal end of the right tibia in lateral (E) and proximal (F) views. Distal end of the right tibia in posterior (G) and distal (H) views. Distal
end of the right fibula in lateral (I), medial (J), and distal (K) views. Abbreviations:aas, articular surface for the astragalus; aasc, articular surface for
the astragalar ascending process; aca, articular surface for the calcaneum; cc, cnemial crest; fcr, fibular crest; gr, goove; lco, lateral condyle; mco, medial
condyle; no, notch; plf, posterolateral flange; ptu, posterior tuberosity. Scale bar equals 5 cm in A–D, 2 cm in E–H,and2cminI–K.
A wedge-shaped ascending process projects dorsally from the
lateral portion of the astragalus (Fig. 88D–I). Its anterodorsal face
is flat; its posterior face is gently concave and bordered dorsally
by a rounded posteriorly protruding edge of the process; its lateral
face is deeply concave to receive the medial edge of the distal end
of the fibula (Fig. 88A, I). The ascending process, which is identical
in form to that in Panphagia and Saturnalia, inserts into the distal
end of the tibia.
Calcaneum—The subtriangular calcaneum is nearly identical to
that in Saturnalia (Langer, 2003:fig. 6G, H). It is partially pre-
served in articulation in the holotypic skeleton, with the posterior
portion of the bone sheared off (Fig. 87). As with the astragalus,
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 163
FIGURE 86. Drawing of the left femur, tibia,
and fibula of Eoraptor lunensis in left lateral
view based on PVSJ 512 and 559. A, femur.
B, tibia. C, fibula. Abbreviations:aasc, articu-
lar surface for the astragalar ascending process;
aca, articular surface for the calcaneum; at,an-
terior trochanter; cc, cnemial crest; fco, fibular
condyle; fcr, fibular crest; fmt, m. femorotibialis
attachment; ft, fourth trochanter; gr, groove;
iml, intermuscular line; istr, m. ischiotrochanter-
icus scar; lco, lateral condyle; mco, medial
condyle; plf, posterolateral flange; ptu, posterior
tuberosity; ts, trochanteric shelf. Dashed line in-
dicates bone margins based on PVSJ 512. Scale
bar equals 5 cm.
there is a hollow space within the body of the calcaneum exposed
on the breakage surface.
The subtriangular articular surface for the fibula is slightly con-
cave anteroposteriorly and transversely and elevated above the
smaller, subtriangular, rugose surface of the posterior tuberosity
(Fig. 88G). The articulation with the astragalus is complex but
precisely similar to that in Saturnalia (Langer, 2003). There is
a pair of short, subtriangular medial articular processes for the
astragalus, one above and one below a wedge-shaped lateral pro-
cess on the astragalus (Fig. 88G, H). As seen in dorsal view, the
smaller dorsomedial calcaneal process is positioned just posterior
to the middle of the astragalus, where it overlaps the astragalus
as part of the articular surface for the fibula (Fig. 88G). As seen
in ventral view, the larger ventromedial process is situated more
posteriorly, extending under the astragalus to articulate within a
well-defined notch (Fig. 88H). Together these processes appear to
lock the calcaneum to the astragalus, eliminating the possibility of
rotary movement of one against the other.
The distal articular surface is moderately convex. In ventral
view, however, a substantial portion of the calcaneum is devoted
to a concave, irregular non-articular surface between the posterior
tuberosity and the medial process (Fig. 88H). In dorsal view, the
posterior margin of the calcaneum also forms an irregular, non-
articular surface between the contact with the astragalus and the
posterior tuberosity (Fig. 88G). The fibula clearly articulates over
this entire area (Fig. 88C). In lateral view, there are two depres-
sions, the larger of the two here termed a fossa and the smaller a
pit (Fig. 88I).
Distal Tarsals—Distal tarsal 3, best exposed in the right ankle of
the holotype (Fig. 89C, D), is a lozenge-shaped bone that articu-
lates proximally with the astragalus and distally with metatarsals 2
and 3. It becomes thicker dorsoventrally toward its posterior edge.
Distal tarsal 4 articulates with the astragalus and calcaneum
proximally and metatarsals 4 and 5 distally (Figs. 87, 89). As
preserved in the hyperextended right ankle, it is dislodged from
its natural articulation over the lateral side of the metatarsus and
partially overlaps distal tarsal 3. As in basal dinosauromorphs
(e.g., Lagerpeton,Marasuchus; Sereno and Arcucci, 1994a, 1994b),
Herrerasaurus (Novas, 1994), and Saturnalia (Langer, 2003), the
dorsal (anterior) portion of distal tarsal 4 is proximodistally
compressed. The concave proximal surface of this portion of the
bone articulates with the convex distal surface of the astragalus
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164 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 87. Stereopairs (A,B) and drawings (C,D) of the right ankle of Eoraptor lunensis (PVSJ 512) in anterolateral (A,C) and posterior (B,
D) views. Abbreviations:as, astragalus; asp, ascending process; ca, calcaneum; dt3,4, distal tarsal 3, 4; fi, fibula; he, heel; hs, hollow space; mt1–5,
metatarsals 1–5; pi, pit; plf, posterolateral flange; ti, tibia. Dashed line indicates a missing margin; hatching indicates a broken surface; double hatch
marks indicate matrix. Scale bars equal 3 cm in Aand Band1cminCand D.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 165
FIGURE 88. Right distal tibia, distal fibula, astragalus, and calcaneum of Eoraptor lunensis (cast of PVSJ 559). Right tibia, fibula, astragalus, and
calcaneum in articulation in anterior (A), posterior (B), and dorsal (C) views. Astragalus and calcaneum in articulation in anterior (D), posterior (E),
medial (F), dorsal (G), ventral (H), and lateral (I) views. Abbreviations:afi, articular surface for the fibula; as, astragalus; asp, ascending process; ati,
articular surface for the tibia; ca, calcaneum; dmpr, dorsomedial process; fi, fibula; fo, foramen; fos, fossa; no, notch; pi, pit; plf, posterolateral flange;
plpr, posterolateral process; ptu, posterior tuberosity; ti, tibia; vmpr, ventromedial process. Dark shading in Cindicates the cross-section of the tibial
and fibular shafts. Scale bar equals 2 cm.
and calcaneum; the convex distal surface articulates with the
concave proximal end of metatarsal 4. The ventral (posterior)
portion comprises a transversely compressed, non-articular heel,
which projects ventrally (posteriorly). There is a rounded trough
laterally at the proximal end of the heel. This trough, which faces
laterally and distally, constitutes the articular surface for the
medial portion of the proximal end of metatarsal 5 (Fig. 89D).
Metatarsus—Although not fully visible on either side, the
metatarsus is complete and articulated on both sides (Figs. 87, 89,
90; Table 11). The proximal one-half of the more fully exposed
right metatarsus has undergone some dorsoventral compression.
Here the proximal articular ends of metatarsals 4 and 5 are ex-
posed (Fig. 89). The proximal articular ends of metatarsals 1–3
are covered on both sides, so the shape and articulation of these
metatarsals was estimated from dorsal and ventral views of the
right metatarsus (Fig. 91A). At midshaft, metatarsals 1–4 are cylin-
drical and hollow (Figs. 87A, C, 89A, B).
Although metatarsal 1 is preserved on both sides, it is partially
obscured by matrix and other bones (Fig. 89). It is the shortest
and most slender of the four fully formed metatarsals, with a rel-
ative length (56% that of metatarsal 3) identical to that in Satur-
nalia (Langer, 2003). Relative to metatarsals 2 and 3, metatarsal
1inEoraptor is proportionately shorter than in Herrerasaurus
(63% and 54%, respectively, in Eoraptor; 70% and 61%, respec-
tively, in Herrerasaurus). The proximal one-half of the shaft is
transversely compressed and fitted against the shaft of metatarsal
2. It extends proximally as far as the other metatarsals and
covers most of the medial aspect of metatarsal 2. As in Saturna-
lia (Langer, 2003) and Herrerasaurus (Novas, 1994), metatarsal 1
would have contributed to the proximal articular surface of the
metatarsus (Fig. 91).
The distal one-half of the shaft of metatarsal 1 becomes rounded
and then dorsoventrally compressed. The distal end is asymmet-
rical, the medial condyle shorter and narrower than the lateral
condyle. It is also rotated such that the medial condyle is shifted
posteriorly relative to the lateral condyle. The functional signifi-
cance of this asymmetry is that the phalanges in pedal digit I are
directed posteromedially during flexion. As in metatarsals 2–4, the
division of the distal articular surface into discrete condyles occurs
only on the ventral aspect of the distal end. The dorsal aspect of
the distal end is marked by a shallow dorsal extensor depression,
as in metatarsals 2–4. A collateral ligament pit is present medially.
The presence of a lateral ligament pit cannot be determined, be-
cause that surface is not exposed.
Metatarsal 2 is 89% of the length of metatarsal 3 and slightly
shorter than metatarsal 4, the reverse of the condition in
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166 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 89. Stereopairs (A,C) and drawings (B,D) of right pes of Eoraptor lunensis (PVSJ 512) in dorsal (A,B) and ventral (C,D) views. Midshaft
cross-sections are shown (in B) for metatarsals 2–5. Abbreviations:I–IV, pedal digits I–IV; amt4,5, articular surface for metatarsal 4, 5; bfo, brevis
fossa; ca, calcaneum; CA, caudal vertebra; clp, collateral ligament pit; ded, dorsal extensor depression; dt3,4, distal tarsal 3, 4; fi, fibula; he, heel; mt1–5,
metatarsals 1–5; ns, neural spine; ph, phalanx; poap, postacetabular process; ti, tibia; un, ungual; vip, ventral intercondylar process. Dashed line indicates
a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bar equals 3 cm.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 167
FIGURE 90. Stereopairs (A,C) and drawings (B,D) of right pedal phalanges of Eoraptor lunensis (PVSJ 512) in lateral (A,B) and medial (C,D)
views. Abbreviations:I–IV, pedal digits I–IV; clp, collateral ligament pit; ded, dorsal extensor depression; mt2–4, metatarsals 2–4; ph, phalanx; un,
ungual. Dashed line indicates a missing margin; hatching indicates a broken surface; shading indicates matrix. Scale bar equals 3 cm.
Saturnalia (Langer, 2003). Much of the proximal one-half of the
bone (Fig. 89) is transversely compressed and articulates against
the shafts of adjacent metatarsals. The base of the bone, however,
appears to be quite deep, slightly deeper than broad (Fig. 91). The
distal one-half becomes dorsoventrally compressed (Figs. 89, 90).
Subtle curvature in the shaft and the precise orientation of the dis-
tal condyles cannot be determined because of postmortem crush-
ing. The distal ginglymus is asymmetrical as in metatarsal 1, with a
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168 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
TABLE 11. Measurements (in mm) of the pes of Eoraptor lunensis
(PVSJ 512).
Bone Maximum length
Digit I
Metatarsal 1 45
Phalanx 1 21
Ungual 15
Digit II
Metatarsal 2 72
Phalanx 1 25
Phalanx 2 19
Ungual 17
Digit III
Metatarsal 3 81
Phalanx 1 27
Phalanx 2 22
Phalanx 3 18
Ungual (18)
Digit IV
Metatarsal 4 74
Phalanx 1 18
Phalanx 2 14
Phalanx 3 12
Phalanx 4 11
Ungual 16L
Digit V
Metatarsal 5 35L
Measurements are from the right side except as indicated otherwise (L,
left). Ungual length is measured perpendicular to a chord across the prox-
imal articular end. Parentheses indicate estimated measurement.
larger lateral condyle that extends farther distally. The lateral col-
lateral ligament pit is considerably more deeply incised than the
medial pit. The dorsal extensor depression is shallow as in Satur-
nalia, rather than the incised arcuate trough that occurs in Her-
rerasaurus.
Metatarsal 3, the longest metatarsal (Figs. 89, 91), measures
53% of the length of the tibia, which is indistinguishable from
the proportions in Saturnalia (54%; Langer, 2003) and slightly
greater than that in Herrerasaurus (48%) (Table 13). The trans-
versely compressed proximal half of the bone is deeper dorsoven-
trally than the other metatarsals with subequal dorsal and ventral
widths, as in Herrerasaurus (PVSJ 373). It has a flat articular sur-
face for metatarsal 4. In the right metatarsus, the long axis of the
shaft of metatarsal 3 appears to curve slightly laterally, as in Her-
rerasaurus (PVSJ 373). The distal end shows the same asymmetry
as in metacarpals 1 and 2, namely that the lateral condyle extends
farther distally than the medial condyle and is slightly broader, as
in Saturnalia (Langer, 2003) and Herrerasaurus (PVSJ 373). Un-
like metatarsals 1 and 2, however, the condyles and collateral lig-
ament pits are subequal in size.
Metatarsal 4 is slightly longer than metatarsal 2 (measuring 91%
of the length of metatarsal 3) (Figs. 89, 91). The subtriangular
proximal end has medial, dorsal, and ventral surfaces. The proxi-
mal third of the shaft is flattened for contact with metatarsal 3. The
dorsal surface of the proximal end is broader transversely than in
other metatarsals. The ventral surface lies adjacent to the shaft of
metatarsal 5 but does not form an articulation with it. The shaft
is bowed slightly laterally, remaining dorsoventrally compressed
throughout its length. The distal condyles are also broader than
deep, a primitive proportion also present in Herrerasaurus (No-
vas, 1994). The asymmetry of the distal end is opposite that in
metatarsals 1–3; the medial condyle is larger and extends farther
distally than the lateral condyle. The ventral edge of the lateral
condyle projects laterally, broadly exposing the lateral collateral
ligament pit in dorsal view. Medial and lateral collateral ligament
FIGURE 91. Reconstruction of the left pes of Eoraptor lunensis (PVSJ
512). A, metatarsals 1–5 in proximal view. B, pes in dorsal view. Abbrevi-
ations:I–V, pedal digits I–V; ag, attachment groove for ungual sheath; clp,
collateral ligament pit; ded, dorsal extensor depression; mt1–5, metatarsals
1–5; ph, phalanx; un, ungual. Dashed lines indicate bones not preserved in
either right or left pes.
pits are developed equally, and no dorsal extensor depression is
visible.
Metatarsal 5 is the shortest metatarsal (43% of the length of
metatarsal 3), with a relative length similar to that in Saturnalia
(45%; Langer, 2003) (Figs. 89, 91). Its full length is preserved on
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 169
TABLE 12. Maximum length (in mm), comparative ratios of metacarpals 3–5, and manual phalangeal formula in Eoraptor lunensis (PVSJ 512),
Eodromaeus murphi (PVSJ 562), Herrerasaurus ischigualastensis (Sereno, 1994), Coelophysis bauri (MCZ 4329), Massospondylus carinatus (Cooper,
1981), Adeopapposaurus (Mart´
ınez, 2009), Lesothosaurus diagnosticus (Sereno, 1991), Heterodontosaurus tucki (Santa Luca, 1980), and Camptosaurus
dispar (Gilmore, 1909).
Taxon mc3 mc4 mc5 mc4/3 mc5/3 Phalangeal formula
Eoraptor lunensis 21 16 10 0.76 0.48 2∗-3∗-4∗-(1)-0
Eodromaeus murphi 28 21 10 0.75 0.36 2∗-3∗-4∗-1-1
Herrerasaurus ischigualastensis 62 33 15 0.53 0.24 2∗-3∗-4∗-1-0
Coelophysis bauri 105 68 — 0.65 — 2∗-3∗-4∗-1-X
Massospondylus carinatus (49) (44) (27) 0.90 0.55 2∗-3∗-4∗-3-2
Lesothosaurus diagnosticus 13 9 5 0.69 0.39 2∗-?-?-?-1
Heterodontosaurus tucki 21 15 8 0.75 0.38 2∗-3∗-4∗-2-1
Camptosaurus dispar 76 60 40 0.79 0.53 2∗-3∗-4∗-2-1
Metacarpal measurements for Massospondylus are estimated from Cooper (1981:fig. 35). Parentheses indicate estimated measurement; dash indicates
unknown measurement. Abbreviations:∗, terminal phalanx is an ungual; mc3–5, metacarpals 3–5; X, digit absent (i.e., metacarpal and phalanges
absent).
the left side, although the form of the proximal end is better shown
on the right side. The proximal end is ‘L’-shaped, composed of a
broad, dorsoventrally compressed main shaft and a narrow lateral
flange that tapers distally and disappears at midshaft. The proxi-
mal articular surface is confined to the main shaft, which is beveled
medioventrally and articulates against a trough on the lateral side
of the distal tarsal 4. The shaft narrows in width from midshaft,
which is dorsoventrally compressed, to the distal end, which is
cylindrical.
Pedal Phalanges—The phalangeal formula of the pes is 2∗-3∗-
4∗-5∗-0 (Fig. 91). The ungual of pedal digit III is the only pha-
lanx missing on both sides. The absence of phalanges in pedal
digit V is based on the left side, where metatarsal 5 is complete
and articulated; the distal end of the right metatarsal 5 is broken
away (Fig. 89). A single rudimentary phalanx is present in pedal
digit V in Herrerasaurus and in some other saurischians (e.g., Pla-
teosaurus; Huene, 1926b), and it is possible that a similar small
phalanx was originally present in Eoraptor.
Except for the ungual in pedal digit IV and probably the un-
gual in digit III, phalangeal length decreases distally within pedal
digits I–IV (Fig. 92; Table 11). The non-ungual pedal phalanges
have slightly deeper proportions and narrower midshafts than in
Herrerasaurus (PVSJ 373), which appears to be an allometric con-
sequence of larger body size in Herrerasaurus and more so in Al-
losaurus (Madsen, 1976:pl. 54). The transverse width of the proxi-
mal and distal ends are subequal, except for the proximal phalanx
of pedal digit I, which is narrower distally.
The proximal phalanges in pedal digits II–IV are noticeably
more robust than succeeding non-ungual phalanges (Figs. 89–92).
Their proximal articular ends are deeper dorsoventrally than
broad transversely. In pedal digit I, the subtriangular base of pha-
lanx 1 is deeper than broad in Eoraptor, whereas the opposite is
TABLE 13. Skull and long bone lengths (in mm, upper part of table) and limb proportions (in%, lower part of table) of Eoraptor lunensis (PVSJ 512),
Saturnalia tupiniquim (MCP 3844-PV; Langer, 2003; Langer et al., 2007), Adeopapposaurus mognai (Mart´
ınez, 2009), Eodromaeus murphi (Mart´
ınez
et al., 2011), Herrerasaurus ischigualastensis (Sereno, 1994), and Heterodontosaurus tucki (Sereno, 2012).
Measure or ratio Eoraptor Saturnalia Adeopapposaurus Herrerasaurus Eodromaeus Heterodontosaurus
Skulla114 — 165 282e(120) 115
Humerus 85 98d167 (175) 85 83
Radius 63 61 106 153 64 58
Metacarpal 3 21 — 44 62 28 22
Femur 152 155 227 345 160 112
Tibia 156 158 210 315 165 145
Metatarsal 3 81 84 153 165 (100) 68
Humerus/forelimbb50% — 53% 45% 48% 51%
Radius/forelimb 37% — 33% 39% 36% 36%
Metacarpal 3/forelimb 12% — 14% 16% 16% 14%
Tibia/femur 103% 102% 93% 91% 106%f130%
Metatarsal 3/femur 53% 54% 67% 49% (63%) 61%
Femur/hind limbc39% 39% 39% 42% 38% 35%
Tibia/hind limb 40% 40% 36% 38% 39% 45%
Metatarsal 3/hind limb 21% 21% 26% 20% 24% 21%
Humerus/femur 56% 63% 74% 51% 53% 74%
Forelimb/hind limb 43% — 54% 47% 42% 50%
Parentheses indicate estimate. Measurements represent the average of right and left long bone lengths when both are available.
aSkull length is measured between the anterior tip of the premaxilla and posterior extremity of the occipital condyle.
bForelimb length equals sum of humerus, radius, and metacarpal 3.
cHind limb length equals sum of femur, tibia, and metatarsal 3.
dHumerus length is from the similar-sized paratypic specimen (MCP 3845-PV).
eSkull length is based on the comparably sized specimen PVSJ 407, because the skull is not preserved in the specimen with the most complete long
bones (PVSJ 373).
fAverage of 103% and 109%, based on PVSJ 560 and 562, respectively.
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170 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
FIGURE 92. Right pedal phalanges of Eoraptor lunensis (PVSJ 512) in exploded lateral view. Abbreviations:I–IV, pedal digits I–IV; ag, attachment
groove for ungual sheath; clp, collateral ligament pit; ded, dorsal extensor depression; dip, dorsal intercondylar process; vip, ventral intercondylar
process. Dashed line indicates a missing margin. Scale bar equals 1 cm.
true in Herrerasaurus (PVSJ 373). This proportional difference is
not simply an allometric consequence of larger body size in Her-
rerasaurus, because Allosaurus has intermediate (subequal) pro-
portions (Madsen, 1976) at a considerably larger body size. The
distal condyles of this phalanx are rotated such that the medial
collateral ligament pit is broadly exposed in dorsal view when the
major axis of the proximal end is held vertically. This rotation,
which directs the ungual more posteriorly than laterally, is oppo-
site that in metatarsal 1, in which the medial collateral ligament pit
faces ventrally. The same torsion is present in phalanx 1 of pedal
digit I in Herrerasaurus (Novas, 1994:410). The distal ginglymus is
unequally divided; the lateral distal condyle is broader and more
rounded than the medial as in Herrerasaurus (PVSJ 373; contra
Novas, 1994:410).
The length of phalanx 1 of pedal digit I is proportionately
the same in Eoraptor and Herrerasaurus (29% and 30%, respec-
tively, of the length of metatarsal 2) (Fig. 89). However, because
metatarsal 1 is more than 5% shorter in Eoraptor as described
above, the joint between the proximal phalanx and ungual is more
proximally located. In Eoraptor, this joint is positioned proximal
to the end of metatarsal 2, whereas in Herrerasaurus it is coin-
cident with the distal end and would place the ungual closer to,
and perhaps lightly in contact with, the substrate. In Eoraptor, the
ungual of pedal digit I could not have effectively engaged the sub-
strate during locomotion. In both cases, nonetheless, pedal digit I
is located too far proximally to have borne significant weight.
Except in phalanx 1 of pedal digit I, there is no development
of ventral intercondylar processes among the proximal phalanges.
Dorsal intercondylar processes are rudimentary as well, although
distal extensor depressions are marked particularly in the prox-
imal phalanges. The proximal articular surfaces of the proximal
phalanges in pedal digits II–IV are broader than deep, especially
so in pedal digits III and IV (Figs. 89, 90). Although in theropods
phalanx 1 of pedal digit III always has a subrectangular prox-
imal articular surface (modified in deinonychosaurids by strong
intercondylar processes; Ostrom, 1969:fig. 75), the same surface
in pedal digit IV in ceratosaurians and tetanurans is deeper than
broad to accommodate the narrowed, subtriangular distal articu-
lar surface of metatarsal 4 (e.g., Liliensternus, Huene, 1932; Al-
losaurus, Madsen, 1976). In Eoraptor and Herrerasaurus, in con-
trast, the proportions of the distal end of metatarsal 4 and proxi-
mal end of phalanx 1 remain broader than deep.
Except in phalanx 1 of pedal digit I, deep dorsal extensor de-
pressions are present dorsal to the distal condyles (Figs. 89–91).
The distal ginglymi are slightly asymmetrical, following closely
similar asymmetries in Herrerasaurus (PVSJ 373). In phalanx 1 of
pedal digits II and III, the lateral distal condyle is broader and
extends farther distally than the medial condyle. In phalanx 1 of
pedal digit III, the lateral condyle is canted away from the verti-
cal, exposing the lateral collateral ligament pit in dorsal view (also
present in Allosaurus; Madsen, 1976:pl. 53). In phalanx 1 of pedal
digit IV, a reverse asymmetry is present in which the medial dis-
tal condyle is broader and extends slightly farther distally. These
asymmetries have the effect of spreading the toes from the cen-
ter of the metatarsus and positioning a greater area of condylar
surface perpendicular to the axis of the distal phalanges.
The intermediate phalanges in pedal digits II–IV are more sym-
metrical than the proximal phalanges (Figs. 89–92). The dorsal in-
tercondylar process is better formed than the ventral process. The
ginglymi are well developed and appear to be symmetrical. All
have dorsal extensor depressions and medial and lateral collateral
ligament pits of approximately equal depth.
The pedal unguals (Figs. 91, 92), like the manual unguals, are
noticeably less recurved than common among theropods such
as Herrerasaurus (PVSJ 373), Eodromaeus (PVSJ 560), and Al-
losaurus (Madsen, 1976). When the proximal articular surface is
oriented along a vertical axis, the distal tip of the ungual is not
positioned very far ventrally. In Herrerasaurus (PVSJ 373) or Al-
losaurus (Madsen, 1976), in contrast, the tip of the ungual is dis-
placed ventrally beneath the base by a distance greater than the
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 171
TABLE 14. Measurements (in mm) of the right manus of
Lesothosaurus diagnosticus (NHMUK RU B17).
Bone Maximum length
Digit I
Metacarpal 1 8.9∗
Phalanx 1 6.0∗
Ungual 5.0
Digit II
Metacarpal 2 12.2∗
Phalanx 1 5.4
Digit III
Metacarpal 3 12.1
Phalanx 1 6.3
Phalanx 2 5.3
Digit IV
Metacarpal 4 9.6∗
Phalanx 1 3.9
Phalanx 2 2.2∗
Digit V
Metacarpal 5 4.8
Phalanx 1 1.8
Measurements marked with an asterisk differ from, and supersede, those
in Sereno (1991:table 1). Metacarpals 2 and 3 were identified in Sereno
(1991) as metacarpals 3 and 2, respectively.
vertical depth of the base. All of the unguals, including the un-
gual of pedal digit I, lack flexor tubercles ventral to the proximal
articular surface. The ventral surface is flat, and the cross-section
at midlength is subtriangular. The ungual of pedal digit III is not
preserved; it was probably slightly longer than the unguals of pedal
digits II and IV, or about 18 mm in length.
DISCUSSION
Autapomorphies of Eoraptor lunensis
Below we list seven features that we regard as diagnostic (au-
tapomorphic) for Eoraptor, because they are generally absent in
other basal dinosaurs. All of these features are treated in the de-
scription above.
(1) Premaxilla with slender posterolateral process with distal ex-
pansion. In Eoraptor, the posterolateral process of the pre-
maxilla is a ribbon-shaped bone that terminates in a pointed
tongue-shaped lobe (Figs. 22, 40). The form of this process is
unique among dinosaurs.
(2) Deep lateral nasal shelf overhanging antorbital fossa. Al-
though the nasal usually forms a prominent edge along the
dorsal margin of the antorbital fossa in saurischians, in Eo-
raptor the nasal is further developed as a thin horizon-
tal shelf that overhangs the antorbital fossa (Fig. 20). This
was originally preserved on both sides in the holotypic skull
(PVSJ 512), but some damage has occurred to one of the
edges after it was molded. In dorsal view, the lateral mar-
gin of the nasal is convex (Figs. 14, 15, 41). Such a strongly
projecting nasal margin is exceptional among saurischians,
although data are currently lacking from closely related
basal sauropodomorphs (e.g., Panphagia,Pampadromaeus,
Saturnalia).
(3) Pterygoid-ectopterygoid synovial joint on posterior margin of
palate. In Eoraptor, the pterygoid has a robust lateral process
that extends along the posterior margin of the palate, termi-
nating in an articular head that fits into a socket on the ec-
topterygoid (Figs. 29, 30). Such an articulation has not been
reported in other dinosaurs, in which the pterygoid and ec-
topterygoid contact one another along butt or scarf joints. Re-
cently, the pterygoid of the closely related sauropodomorph
Pampadromaeus has been figured and may have a similar
pterygoid process (Cabreira et al., 2011:fig. 2g). If that proves
to be the case, this feature may unite these genera or a subset
of basal sauropodomorphs.
(4) Narrow premaxilla-maxilla diastema (rounded posterior mar-
gin on premaxilla, small first maxillary tooth). In Eoraptor,a
short diastema is present between premaxillary and maxillary
tooth rows due to a short edentulous margin at the anterior
end of the maxilla under the subnarial foramen (Figs. 20, 35).
The first tooth in the maxilla is shorter than adjacent teeth in
the premaxilla and maxilla. The third dentary tooth that op-
poses the diastema is slightly enlarged. Some functional differ-
entiation is strongly suggested by the diastema and the change
in crown size between premaxillary and maxillary tooth rows
(see below, Form and Function, Dental Specialization).
(5) Maxillary crowns with a prominent lateral eminence or crest.
All maxillary crowns in Eoraptor have a prominent linear
eminence, or rounded crest, on the labial side of the crown
(Figs. 20, 36). A discrete linear crest of this prominence
is not present in other basal sauropodomorphs (Panpha-
gia,Saturnalia,Pampadromaeus) or basal theropods (Her-
rerasaurus,Eodromaeus,Tawa). A linear crest of this sort
is not known in sauropodomorphs and basal ornithischians
(Pisanosaurus, Bonaparte, 1969; Lesothosaurus, Sereno, 1991;
Huayangosaurus, Sereno and Dong, 1992).
(6) Extreme hollowing of the axial column. In Eoraptor, all of
the long bones of the skeleton, as well as the shafts of the is-
chium, ribs, and chevrons, are hollow. Although marked hol-
lowing of at least the long bones is common to all theropods,
hollowing of the axial column is carried to an extreme in
Eoraptor. The walls of the centra and neural arches are very
thin, in some places as thin as 0.5 mm. The hollow space in the
neural arch and centrum is not partitioned or filled with can-
cellous bone, has no external communicating diverticuli, and
therefore was not pneumatic.
(7) Accessory prezygapophyseal process in middle cervical verte-
brae. At least some of the middle cervical vertebrae in Eo-
raptor have a small accessory process on the medial side of
the prezygapophysis (Fig. 44). It articulates with the medial
portion of the postzygapophysis of the next anterior verte-
bra. This accessory articular process, the function of which
remains obscure, has not been reported elsewhere among
dinosaurs.
Phylogenetic Relationships
Eoraptor lunensis was placed by Sereno et al. (1993) and Sereno
(1999) as the basal member of Theropoda on the basis of phy-
logenetic analyses that identified synapomorphies uniting Eorap-
tor with Herrerasaurus and other theropods. In the years fol-
lowing the debut of Eoraptor, opinion varied regarding the phy-
logenetic interpretation of Eoraptor. In a short note, Padian
and May (1993) suggested that neither Eoraptor nor Her-
rerasaurus are theropods (or possibly even dinosaurs), although
there was no analysis or supporting character evidence. Other au-
thors examined the fossil material and drew conclusions similar to
those we suggested in 1993—that Eoraptor was a basal theropod
(Novas, 1994; Tykoski, 2005; Nesbitt et al., 2009; Ezcurra, 2010;
Nesbitt, 2011). An opposing camp emerged with the view that Eo-
raptor was a more basal saurischian, outside both Theropoda and
Sauropodomorpha (Langer, 2004; Mart´
ınez and Alcober, 2009;
Brusatte et al., 2010; Langer et al., 2010). We now regard Eoraptor
as a basal sauropodomorph (Mart´
ınez et al., 2011), and there are
important events that led us to this new understanding.
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FIGURE 93. Skeletal silhouette of Eoraptor lunensis based principally on the holotypic skeleton (PVSJ 512). Estimated tail length distal to caudal vertebra 17 is based on the proportions
of three mid-caudal vertebrae in the closely related basal sauropodomorph Panphagia protos (Mart´
ınez and Alcober, 2009:fig. 6H). Abbreviations:C2,9, cervical vertebra 2, 9; D1,15, dorsal
vertebra 1, 15; S1,3, sacral vertebra 1, 3; CA1,17, caudal vertebra 1, 17.
172
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 173
Firstly, the material basis for phylogenetic assessment has
changed markedly (Sereno and Mart´
ınez, in review). When orig-
inally described in 1993, the holotypic specimen of Eoraptor
(PVSJ 512) was only partially exposed. Important referred spec-
imens that include well-preserved proximal tarsals had yet to
be prepared and identified (PVSJ 559, 862; Table 1). Isolated
bones thought to pertain to Eoraptor are now known to belong
to a similar-sized contemporary—a basal theropod later named
Eodromaeus murphi. It was not until excellent remains of this
dinosaur were discovered in 1996 and prepared several years
later that its distinction from Eoraptor was revealed (Mart´
ınez
et al., 2011). In the 20 years since the discovery of Eoraptor,
the dinosaurian fauna in the Cancha de Bochas Member of the
Ischigualasto Formation is now understood to include several
small-bodied basal saurischians (Eoraptor,Panphagia, Mart´
ınez
and Alcober, 2009; Chromogisaurus, Ezcurra, 2010; Eodromaeus,
Mart´
ınez et al., 2011).
Secondly, two key discoveries came to light while working on
the holotypic skeleton of Eoraptor for this monograph. We dis-
covered that, prior to its final fossilization, slight disarticulation of
digit I in the well-preserved right manus of Eoraptor (Fig. 69) had
obscured a remarkable derived feature known only among large-
bodied basal sauropodomorph dinosaurs (Sereno, 2007b)—the
medial rotation in the shaft of proximal phalanx of manual digit
I that directs the tip of the ungual inward (Fig. 73D). The rota-
tion of this digit in natural articulation was removed incidentally
during burial (Fig. 69). We reassembled manual digit I in natural
articulation using bone casts as part of our reinterpretation of the
relationships of Eoraptor (Mart´
ınez et al., 2011).
We also realized that the lower jaws of Eoraptor seemed slightly
short relative to the upper jaws (Figs. 16, 17) and that the anterior
end of the dentaries also had vascular openings (Fig. 23) similar
to those of many larger-bodied basal sauropodomorphs thought
to have a small keratinous lower bill (Sereno, 2007b; Mart´
ınez,
2009). By preparing between the premaxillary teeth, we were able
to verify evidence from the computed tomography (CT) data that
the first dentary tooth in Eoraptor,asinPanphagia (Mart´
ınez and
Alcober, 2009), is inset a short distance from the anterior end of
the dentary.
Thirdly, the discovery of Panphagia in Ischigualasto (Mart´
ınez
and Alcober, 2009) and Saturnalia in southeastern Brazil (Langer
et al., 1999, 2007; Langer, 2003) highlighted postcranial features
in the girdles and hind limb shared with later sauropodomorphs.
The new material also documented the relatively short length of
the centra in the distal half of the tail, in contrast to the condition
in the contemporaneous theropods Herrerasaurus (Novas, 1994)
and Eodromaeus (Mart´
ınez et al., 2011). The striking similarities
between Eoraptor and Panphagia and Saturnalia became appar-
ent. More recently, the discovery in southeastern Brazil of well-
preserved cranial remains of Pampadromaeus (Cabreira et al.,
2011) has extended the striking similarities between Eoraptor and
Brazilian genera to include the skull.
We reconsider the relationships of Eoraptor and other basal
dinosaurs elsewhere (Sereno and Mart´
ınez, in review). Evidence
is mounting that Eoraptor and several other taxa from the Is-
chigualasto and Santa Maria formations (Panphagia,Saturnalia,
Pampadromaeus) are basal sauropodomorphs.
Form and Function
Cranial Pneumaticity—The antorbital fossa in Eoraptor ap-
pears to have been occupied by one large air sac emanating from
the nasal cavity, as in living birds (Witmer, 1990). The maxilla and
lacrimal form most of the osseous medial wall of the fossa, which
is smooth and bounded by a prominent external rim (Figs. 20, 40).
The dorsal portion of this rim is particularly pronounced, with the
nasals extending laterally as a sharp-edged, horizontal shelf that
overhangs the antorbital fossa. In dorsal view, the convex contour
of the nasal shelf (Figs. 14, 15, 41) resembles the comparable mar-
gin in the snout of Plateosaurus (Sereno, 2007b). The posterodor-
sal corner of the antorbital fossa, which is slightly invaginated, is
formed by the lacrimal, with a small contribution from the ante-
rior ramus of the jugal (Figs. 24, 40). A much broader portion of
the osseous medial wall of the fossa is formed by the anterior ra-
mus of the palatine, the everted ventral rim of which appears to
have cupped the edge of the pneumatic sac (Fig. 21).
Unlike most theropods, there is no evidence in Eoraptor of
any accessory diverticuli into the maxilla anteriorly (Fig. 22),
the lacrimal dorsally (Fig. 25), the jugal posteriorly (Fig. 24),
or the palatine medially (Fig. 21). Recently, a fossa of some
depth was described in the maxilla at the anterior end of the
antorbital fossa in the closely related Brazilian sauropodomorph
Pampadromaeus (Cabreira et al., 2011:fig. 2). In a similar posi-
tion in the maxilla, a small fenestra was described recently in
the basal theropods Herrerasaurus (Sereno, 2007a) and Eodro-
maeus (Mart´
ınez et al., 2011), although another basal theropod
shows no discrete fossa or fenestra in this location (Tawa; Nes-
bitt et al., 2009). Similarly, a small blind depression was recently
described in the maxilla of the early ornithischian Heterodon-
tosaurus (Sereno, 2012), although other basal ornithischians show
no evidence of a depression in this region (Lesothosaurus; Sereno,
1991). These openings or fossae correspond in location with
the promaxillary diverticulum common among neotheropods.
Whether they are homologous or not is an open question,
given their variable expression and distribution at the base of
Dinosauria.
In theropods, additional pneumatic spaces are present in the
quadrate and articular (diverticulae of the middle ear sac in living
birds), the basisphenoid, and the ectopterygoid (diverticulae of the
nasopharynx). Because the quadrate and articular are in contact
and the distal end of the quadrate is not exposed in anterior view,
the pneumaticity of these bones cannot be evaluated. In ventral
view, the basisphenoid is gently concave, with a small pit near its
junction with the basioccipital. There is no development of a deep
median fossa, as characterizes Eodromaeus (Mart´
ınez et al., 2011)
and most neotheropods. Other portions of the braincase, such as
the parasphenoid, are hidden by matrix or broken. There is no de-
velopment of an invaginated fossa on the ectopterygoid, as is well
developed in many tetanuran theropods.
In summary, cranial pneumaticity in Eoraptor appears to be lim-
ited to a simple, single antorbital diverticulum of the nasal cavity,
as is typical of most basal sauropodomorphs and ornithischians.
None of the accessory diverticuli of the antorbital sinus that char-
acterize theropods is present in Eoraptor.
Cranial Kinesis—Distortions of the cranial skeleton during
feeding in living vertebrates are reflected in the form and
position of osseous joints within the skull (Versluys, 1910,
1912). Despite a literature rich in descriptive models, accurate
measurement of cranial distortion in living animals has been
achieved only recently (Smith and Hylander, 1985; Condon, 1987;
Iordansky, 2011). In the Nile monitor (Varanus), it now is clear
that cranial kinesis does occur during feeding, with several de-
grees of angular rotation about several joints in the skull (Con-
don, 1987). The timing of these movements suggests that they play
a role in seizing, subduing, and swallowing prey (Frazzetta, 1962,
1986; Boltt and Ewer, 1964; Rieppel, 1979), rather than serving
only as a shock absorbing mechanism during the strike.
Proposed models for cranial kinesis in dinosaurs have recently
come under criticism for lack of sufficient lines of evidence, includ-
ing integrated kinematic linkages within the cranium and evidence
of musculature that could have driven or controlled intracra-
nial movement (Holliday and Witmer, 2008). This long-overdue
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174 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
critique has yet to address kinesis within the lower jaws, where
the most interesting joint morphology is located in Eoraptor
(Fig. 33).
In the cranium of Eoraptor, most of the synovial joints are fairly
typical and plesiomorphic for dinosaurs (Holliday and Witmer,
2008). The quadrate head inserts into a deep cup on the ventral
aspect of the squamosal (Fig. 27), forming a joint that is disar-
ticulated on the right side of the cranium (Fig. 26). In Eoraptor,
the cotylus would have covered the entire head of the quadrate,
which has the usual smooth and bounded articular surface of a
synovial joint. In other basal dinosaurs, the squamosal cotylus is
not as deep as in Eoraptor.InHerrerasaurus, for example, a por-
tion of the quadrate head is exposed in lateral view (Sereno and
Novas, 1994). There is no evidence, therefore, to suggest signifi-
cant movement at the squamosal-quadrate joint (‘dorsal quadrate
joint’ in lepidosaur models).
The basipterygoid processes are unusually robust in Eoraptor.
They project as stout columns that are expand slightly toward
their articular ends (Figs. 29, 30). These processes are approxi-
mately twice the diameter and length of those of in Herrerasaurus
and Lesothosaurus, relative to the length of the braincase or skull
(Sereno, 1991; Sereno and Novas, 1994) and may have provided
extra support to the posterior palate, which has broad mandibu-
lar flanges for the attachment of pterygoideus musculature (Fig.
33A, B). They most closely resemble the stout basipterygoid pro-
cesses in larger-bodied basal sauropodomorphs, such as Adeopap-
posaurus (Mart´
ınez, 2009:fig. 10). By contrast, the basipterygoid
processes in the similar-sized contemporaneous theropod Eodro-
maeus terminate as expanded, but thin, plates (Mart´
ınez et al.,
2011).
The posterior margin of the broad, triangular mandibular flange
in Eoraptor has an unusual pterygoid-ectopterygoid joint (Figs. 29,
30). The pterygoid forms as a robust ventrolaterally projecting
strut that expands distally to an articular head lodged in an ar-
ticular socket in the ectopterygoid. The pterygoid head is smooth
and appears to have been enclosed in a synovial capsule, judging
from the disarticulated view of the process on the left side of the
palate (Fig. 29). Pampadromaeus may have had a similar joint in
the posterior palate (Cabreira et al., 2011:fig. 2g). The function of
this apparently synovial joint on the posterior palate is unknown.
Other articulations within the cranium in Eoraptor include
tongue-and-groove joints (maxilla-jugal, jugal-quadratojugal,
prefrontal-frontal, postorbital-frontal, squamosal-postorbital),
scarf joints (lacrimal-prefrontal, jugal-postorbital), squamous
joints (nasal-frontal, lacrimal-jugal, quadrate-quadratojugal,
pterygoid-quadrate, pterygoid-palatine) (Figs. 10–17), and butt
joints (jugal-ectopterygoid, maxilla-palatine). The frontal-parietal
suture, which is the ‘mesokinetic’ hinge in lepidosaur models, is
not well preserved (Figs. 14, 15).
The form of most of these sutures is common among theropods
across a wide range of body size. Along the ventral mar-
gin of the cranium, tongue-and-groove articulations predomi-
nate (quadratojugal-jugal-maxilla), suggesting that very minor
telescoping may have occurred in the posterior one-half of
the skull as described in Syntarsus (Raath, 1977:160). Along
the dorsal orbital margin, the frontal is notched for the pos-
torbital and slotted for the prefrontal, the functional signifi-
cance of which remains obscure. A large prefrontal is much
more common in basal sauropodomorphs and ornithischians
than in theropods, which eventually eliminate the prefrontal as
a separate bone (lost or fused to the posterior aspect of the
lacrimal).
The potential for kinetic premaxillae in Eoraptor (Tykoski,
2005) was an important line of evidence supporting the position
of Eoraptor within Theropoda (Nesbitt et al., 2009). In the coelo-
physoids Dilophosaurus,Coelophysis, and Syntarsus, the unusual
overhanging premaxillary dental arcade may not have been an-
chored immovably to the maxilla (Tykoski, 2005; Sereno, 2012:fig.
91). In those forms, the premaxilla-maxilla articular contact is very
reduced laterally, which is indicated by extreme reduction of the
premaxillary posterolateral process and an arched diastema that
has eliminated the subnarial foramen, whereas interpremaxillary
contact is broadened (external nares and narial fossa retracted).
In Eoraptor, in contrast, the premaxillary posterolateral process
is long and slender, the diastema is short and shallow, a subnarial
foramen is present between the premaxilla and maxilla for pas-
sage of neurovascular structures, and interpremaxillary contact is
not expanded (Figs. 23, 35, 40). There is no evidence to suggest
kinesis at the anterior end of the snout in Eoraptor.
Intramandibular Kinesis—An intramandibular joint with dorsal
and ventral articulations is present in Eoraptor (Sereno, 2007a);
the ventral articulation is better exposed (Fig. 33). Although the
tapering, tongue-shaped posterior end of the splenial is broken
away, its form is shown by the articular trough on the ventrome-
dial edge of the angular. In Herrerasaurus, this ventral joint is bet-
ter developed than in Eoraptor, with the tongue-shaped end of the
splenial fitted ventrally to the polished hook-shaped anterior end
of the angular. Also in Herrerasaurus, the dorsal joint between the
toothed anterior moiety (dentary, splenial) and bones that com-
pose the remainder of the lower jaw is fully exposed (Sereno and
Novas, 1994). This two-part construction of the lower jaw is well
known among small- and large-bodied theropods (Brochu, 2002)
and may have been managed by spring ligaments rather than mus-
cles (Sampson and Witmer, 2007).
Except for Eoraptor, an intramandibular joint has not been
described outside Theropoda, if one accepts herrerasaurids as
basal theropods. Interestingly, the concavoconvex polarity of
the joint differs in the earliest saurischians to exhibit this
morphology—Herrerasaurus and Eoraptor.In the former and its
close relative Staurikosaurus (P.C.S., pers. observ.), the splenial
has a concave surface fitted to a convex surface on the angular.
The conformation of these surfaces is reversed in Eoraptor and
neotheropods.
In Eoraptor, the ventral joint is not as well developed as in
herrerasaurids or neotheropods (Fig. 33). Nonetheless, the sple-
nial does not contact the angular medially along a broad scarf
joint, but rather tapers in width and twists under the angular,
its tip residing in a smooth trough on the angular. That trough
is slightly dorsoventrally convex, suggesting that whatever intra-
mandibular flexure the ventral joint allowed would have occurred
in a vertical plane. It would not have facilitated transverse bend-
ing of the mandible to widen the gape as occurs in some snakes
(Sereno and Novas, 1994). In Eoraptor, the dorsal intramandibu-
lar joint between the anterior (dentary, splenial) and posterior
(surangular, coronoid, prearticular, angular) moieties is not well
exposed laterally. In medial view, its anterior location relative to
the ventral joint suggests limited intramandibular flexion (Fig. 33).
In theropods with enhanced intramandibular flexion, such as the
abelisaurid Majungasaurus, dorsal and ventral joints are posi-
tioned over one another (Sampson and Witmer, 2007). In addi-
tion, the dentary is shortened, the external mandibular fenestra is
enlarged, the dorsal joint is reduced to peg-in-socket articulations,
and the ventral sliding joint is expanded (Sampson and Witmer,
2007). None of these features is present in Eoraptor.
Yet, the form of the ventral joint and the portion of the dor-
sal joint exposed in medial view suggest limited intramandibu-
lar flexion was possible. There is no additional information on
the intramandibular joint in available specimens pertaining to
Panphagia,Pampadromaeus,orSaturnalia. This condition may be
plesiomorphic for Saurischia and subsequently reduced and lost
among herbivorous sauropodomorphs and enhanced among car-
nivorous theropods.
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 175
Dental Specialization—The dentition in Eoraptor has recently
been compared with teeth of a similar-sized contemporaneous
basal theropod Eodromaeus, the carnivorous diet of which is not in
dispute (Mart´
ınez et al., 2011:fig. 1D, E). The comparison is partic-
ularly revealing in terms of crown shape and size and orientation
of the marginal ornamentation. In Eoraptor, the distal margin of
the crown is straight or only slightly concave in labial view, rather
than consistently concave and contributing to the recurvature of
the crown (Fig. 37). In Eoraptor, the marginal ornamentation, par-
ticularly that on the mesial margin, resembles ornithischian denti-
cles that project toward the crown apex rather than strictly perpen-
dicular to the crown edge (Fig. 37C). Such ornamentation on the
maxillary crowns in Eoraptor, which is similar to that of the den-
tary crowns of Panphagia and Pampadroameus, suggests a pulping
function suitable for plant matter, rather than a meat-cutting func-
tion suitable for slicing. Theropod crowns suitable for the latter
function tend to be more finely serrate, transversely compressed,
and recurved (Mart´
ınez et al., 2011:fig. 1D, E). In Eoraptor, there
are approximately six denticles per millimeter, whereas there are
nine serrations per millimeter in Eodromaeus (Mart´
ınez et al.,
2011). The comparison of ornamentation size we regard here as
particularly suitable, given the similar body size in Eoraptor and
Eodromaeus.
The first dentary tooth in Eoraptor, in addition, is retracted
from the anterior end of the dentary, which is marked by a pair
of conspicuous neurovascular foramina—features that character-
ize plant-eating basal sauropodomorphs (Sereno, 2007b; Mart´
ınez,
2009). These features and the short length of the lower jaws sug-
gest that there may have been a small keratinous beak at the an-
terior end of the lower jaws in Eoraptor and Panphagia. Recently,
the closely related basal sauropodomorph Pampadromaeus was
described as lacking the inset at the anterior end of the tooth row
(Cabreira et al., 2011). Close-up images of the anterior end of the
dentary, however, suggest that the first alveolus is inset in Pam-
padromaeus as in Eoraptor.InPampadromaeus, the first dentary
tooth is partially dislodged from its alveolus and shifted mesially,
giving the impression that the tooth row extended to the anterior
end of the dentary (Cabreira et al., 2011:Suppl. Info.).
Crown recurvature, particularly when weakly expressed as
in Eoraptor, cannot stand alone as an arbiter of diet.
Sauropodomorph and ornithischian herbivores often retain some
recurvature in their crowns, especially in the premaxillary series.
Likewise, a short upper diastema that opposes a dentary crown
does not necessarily indicate carnivorous habits.
Heterodontosaurid ornithischians present some similarities to
Eoraptor in that both upper and lower teeth are inset from the
ends of the jaws and replaced by keratinous beaks. In the case of
the lower jaw, a specialized bone (the predentary) supports the
beak. Although there is no such specialized bone among basal
sauropodomorphs, there is increasing evidence that many have
small lower (and upper) beaks to support a cropping or pluck-
ing function (Sereno, 2007b; Mart´
ınez, 2009). We have yet to dis-
cover a carnivorous dinosaur—or for that matter a carnivorous
extant lizard—that has retained teeth for predation and that has
inset these teeth from the anterior end of the lower or upper jaws
(Sereno, 2012). This favors Eoraptor as a herbivore.
Crown morphology by itself is not decisive in this case, nor is
the presence or absence of palatal teeth, which are now known in
both Eoraptor and Eodromaeus. Claiming that Eoraptor might be
an omnivore or insectivore at a subadult or adult body length of
ca. 1–1.5 m are hypotheses in need of supporting evidence. Dietary
inferences, including the proposition of omnivory (Barrett et al.,
2011), must be based on a broader array of information tied to
extant analogs (Zanno and Makovicky, 2011).
Hollowing of the Axial Column—A striking feature of the axial
column is the extreme hollowing of the centra and neural arches
that has reduced the external walls of the vertebrae to a thick-
ness of less than 1 mm. The hollowing is accomplished by internal
cavities apparently without any pneumatic communication to the
exterior of the bone. Non-vertebral elements of the axial skele-
ton, such as rib and chevron shafts, are solid in many theropods
but have central cavities in Eoraptor. The function of this ex-
treme skeletal hollowing, comparable to that in any theropod, is
unknown. Because Eoraptor is among the smallest of dinosaurs, it
is difficult to suppose that reduction of skeletal weight as a primary
driving factor.
The observed hollowing is very difficult to explain away as an
artifact of diagenesis. The spaces and sometimes-uniform wall
thicknesses do not appear to be a random artifact or some bone-
destroying process, which would likely have created openings to
the exterior.
Axial Column Function—The cervical centra in basal di-
nosaurs, such as Eoraptor and Herrerasaurus, do not have
the tightly fitted, concavoconvex articular surfaces present in
neotheropods. Judging from the shape of the centra and their
preserved articulation, nevertheless, the cervical column in Eo-
raptor followed a sigmoid curve in neutral articulation that
elevates the skull significantly above the level of the dorsal col-
umn (Figs. 43, 93). Several aspects of the cervical vertebrae suggest
that the cervical column was capable of significant dorsoventral
and lateral flexion. The low, plate-shaped neural spines in the mid-
cervical vertebrae would allow significant dorsoventral flexion by
muscles attaching between the neural spines and well-developed
epipophyses, as occurs in living birds (principally the longus colli
dorsalis muscle: Harvey et al., 1968; Raath, 1977). The zygapophy-
seal facets in anterior and middle cervical vertebrae are broad,
with a shallow inclination (20–30◦from the horizontal) that would
have permitted extensive lateral flexion (Fig. 43). In this regard,
the function of the unique accessory prezygapophyseal process in
the middle cervical vertebrae of Eoraptor remains unknown. All
of the cervical ribs are joined by overlapping spines and rib shafts
to form a slender, flexible rod, positioned ventrolateral and paral-
lel to the cervical series. The slender form of the cervical column
and its associated ribs (Figs. 49, 60) would have permitted signifi-
cant dorsoventral and lateral flexion.
Anterior and middle caudal vertebrae have prominent blade-
shaped neural spines, substantial transverse processes, and long
chevrons, which increase in length in that order in each vertebra
(Fig. 59; Tables 5, 6). These processes indicate that the dorsal, lat-
eral, and ventral musculature of the tail was well developed and
that significant dorsoventral and lateral excursion of the tail was
possible. Because the caudal series is not preserved posterior to
the 17th caudal vertebra, it cannot be determined in Eoraptor if
the distal caudal vertebrae had elongate centra stiffened in artic-
ulation by elongate prezygapophyses, as occurs in Herrerasaurus,
Eodromaeus, and nearly all neotheropods. The absence of such
distal caudal vertebrae in close relatives (Panphagia, Mart´
ınez and
Alcober, 2009; Pampadromaeus, Cabreira et al., 2011) suggests
that the tail of Eoraptor was similar to that in large-bodied basal
sauropodomorphs (Fig. 93)—long and muscular but not stiffened
as a narrow beam.
Forelimb Function—In general form and proportions, the fore-
limb of Eoraptor closely resembles that in Saturnalia (Langer
et al., 2007) and large-bodied basal sauropodomorphs, such as Pla-
teosaurus (Huene, 1926b). In Eoraptor, the forearm was composed
of stout long bones with a substantial interosseous gap (Fig. 93), as
preserved in articulation in the holotypic skeleton (Fig. 9) and in
the basal sauropodomorph Adeopapposaurus (Mart´
ınez, 2009:fig.
18K, L). In Herrerasaurus (Sereno, 1994), Eodromaeus (Mart´
ınez
et al., 2011), and other theropods, in contrast, the forearm bones
are appressed along their shafts, ostensibly as an enhancement of
raptorial function.
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176 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 12
Although the carpals are not well preserved, there is evi-
dence of a radiale, ulnare, and possibly a large distal carpal 1
(Figs. 68, 73D). The base of metacarpal 1 may be inset into the
carpus. Both of these features are consistent with the carpus
in basal sauropodomorphs (Sereno, 2007b). The well-preserved
carpi in the theropods Herrerasaurus and Eodromaeus also have
a substantial radiale and ulnare, but distal carpal 1 is small and
metacarpal 1 is not inset into the carpus (Sereno, 1994; Mart´
ınez
et al., 2011).
The twisted form of phalanx 1 of manual digit I in Eorap-
tor directs the tip of the ungual medially (Figs. 73D, 76A), a
unique adaptation of the manus previously known only in large-
bodied basal sauropodomorphs (Sereno, 2007b; Mart´
ınez, 2009).
The function of the unusual basal sauropodomorph pollex is un-
known. The relatively short length of the forelimb compared with
the hind limb in Eoraptor (43%, see below) and metacarpal 3 com-
pared with the forelimb (12%, see below) suggests that the manus
and its modified pollex probably were not specialized for a loco-
motor function.
Digital proportions within the manus and the manual pha-
langeal formula, in general, resemble those in other basal di-
nosaurs in the retention of five manual digits and the reduc-
tion or elimination of the phalanges in manual digits IV and V
(Table 12). In Eoraptor, metacarpals 4 and 5 are longer relative
to metacarpal 3 than in Herrerasaurus, a theropod with a well-
developed raptorial manus (Sereno, 1994). In later larger-bodied
basal sauropodomorphs such as Massospondylus that were proba-
bly using the manus periodically in locomotion, metacarpals 4 and
5 become relatively even stronger than in Eoraptor, the former
attaining a length 90% that of metacarpal 3 (Table 12).
Limb Proportions—In Eoraptor, forelimb length is 43% that
of the hind limb (Fig. 93; Table 13). In this proportion, Eorap-
tor most closely resembles the basal theropod Eodromaeus (42%)
among the genera tabulated for comparison. The large-bodied
sauropodomorph Adeopapposaurus (54%), the basal theropod
Herrerasaurus (47%), and the long-armed ornithischian Het-
erodontosaurus (50%) have forelimbs that are longer relative to
their hind limbs (Table 13). Within the forelimb, the manus is par-
ticularly short in Eoraptor relative to forelimb length (12%; using
metacarpal 3 as a proxy for manual length). In other taxa sampled,
manual length is at least 14% or more of forelimb length.
The hind limb in Eoraptor has exactly the same proportions as
Saturnalia (Table 13). In both genera, the tibia is slightly longer
than the femur, and metatarsal 3 is slightly more than one-half
femoral length. The larger-bodied Adeopapposaurus is typical for
more derived basal sauropodomorphs, with a tibia slightly shorter
than the femur (93%), as is also the case in Herrerasaurus (91%).
Eodromaeus (106%) and particularly Heterodontosaurus (130%)
have more cursorial proportions in the hind limb.
The picture that emerges from the limb proportions of Eoraptor
is that it has a somewhat shorter forelimb and manus and less cur-
sorial hind limb proportions than the contemporaneous, similar-
sized theropod Eodromaeus. Individual long bones of adult spec-
imens of these dinosaurs are distinguishable on the basis of their
relative robustness; for long bones of equal length, Eoraptor has
more robust long bones than Eodromaeus. The larger predator
Herrerasaurus has a longer forearm and manus (as a proportion
of forelimb length) than in Eoraptor, which along with trenchant
claws is clearly an adaptation for grasping prey. In the hind limb,
Eoraptor has exactly the same proportions as in Saturnalia, both
of which would have been less fleet of foot than Eodromaeus.
CONCLUSIONS
Eoraptor lunensis provides the most complete view so far of the
skeletal anatomy of a dinosaur from the dawn of the dinosaur
era in mid-Carnian time (ca. 230 Ma). Although its skull and
postcranial skeleton are remarkably similar to the contempora-
neous theropod Eodromaeus, telltale signs of an entirely differ-
ent way of life are preserved in its dentition, skull, and postcranial
anatomy.
In the dentition, a suite of characters is related to the acqui-
sition of a predominantly or wholly herbivorous diet. These in-
clude a gentle swelling of the crown base and rise of a rounded
eminence leading to the crown apex in maxillary teeth, the sup-
pression of crown recurvature, the greater inclination of denticles
on the anterior crown margin, and the retraction of the first den-
tary tooth from the anterior end of the lower jaw. The lower jaws,
which have closed in natural articulation in the holotypic skull, end
short of the premaxillary arcade, suggesting that there may have
been a small keratinous lower beak as in many large-bodied basal
sauropodomorphs.
Elsewhere in the skull, there are features supportive of a re-
lationship at the base of Sauropodomorpha, most notably the
enlarged external naris, a distinctive linear pattern of vascular
openings on the maxilla below the antorbital fossa, and the slen-
der ventral process on the squamosal. The lower jaw has an in-
tramandibular joint with limited mobility between the splenial
and angular; the polarity of the sliding joint is similar to that
seen in neotheropods (angular concave, splenial process con-
vex). Other cranial sutures and joints do not support a partic-
ularly kinetic skull, which otherwise is notable for the reten-
tion of approximately 100 rudimentary palatal teeth and the
presence of an unusual pterygoid-ectopterygoid joint along the
posterior margin of the palate. Pampadromaeus, a similar-sized
basal sauropodomorph from southeastern Brazil, preserves cranial
bones that are strikingly similar to Eoraptor.
In the postcranium, the axial column and hind limbs remain
remarkably primitive and have identical proportions to another
similar-sized basal sauropodomorph from southeastern Brazil,
Saturnalia. Differences between Eoraptor and the contemporane-
ous basal theropod Eodromaeus are most apparent in the skull,
forelimb, and pelvis. Unlike Eoraptor,Eodromaeus has a promax-
illary fenestra and laterally compressed, recurved, and serrated
teeth. In the forelimb, Eodromaeus (and Herrerasaurus) have ap-
pressed the shafts of the radius and ulna and specialized the in-
ner three manual digits for grasping. In contrast to Eoraptor, the
manus in these forms is longer relative to other forelimb segments
and is tipped with elongate penultimate phalanges and trenchant
unguals. In the pelvic girdle, Eoraptor shows the classic broad
pubic apron common to large-bodied basal sauropodomorphs,
whereas Eodromaeus (and Herrerasaurus) have narrowed distal
pubes, turning them posteriorly to form a pubic foot common to
later theropods.
An outstanding adaptation in the manus of Eoraptor is the spe-
cialized ‘twisted’ pollex that characterizes all larger-bodied basal
sauropodomorphs (‘prosauropods’). The distal condyles of the
first phalanx of the pollex are rotated approximately 35◦, direct-
ing the ungual medially. The modified pollex is unlikely to have
appeared as a locomotor adaptation, given that Eoraptor has a rel-
atively short forelimb and has hind limb proportions (tibia slightly
longer than the femur) that are consistent with bipedal posture at
speed.
ACKNOWLEDGMENTS
We are deeply indebted to C. Abraczinskas for her skillful
renderings from bones, and for the arrangement and labeling
of all figures and final drafts of reconstructions. We thank S.
Nesbitt and M. Carrano for their detailed reviews of the
manuscript, which resulted in many improvements, and C.
Abraczinskas, J. Fronimos and E. Moacdieh for proofing portions
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SERENO ET AL.—BASAL SAUROPODOMORPH EORAPTOR 177
of the text and figures. We also thank R. Masek, I. Morrison, and
W. Simpson for their skill in preparation and molding of the holo-
typic skeleton of Eoraptor lunensis, the Field Museum of Natural
History and the Royal Ontario Museum for providing laboratory
facilities, and the High-Resolution X-ray Computed Tomography
Facility at The University of Texas at Austin for CT imaging. This
research was supported by the National Science Foundation re-
search grant BSR 8722586 (to P.C.S.), Petroleum Research Fund
of the American Chemical Society (grant ACS-PRF 22637-G8) (to
P.C.S.), the David and Lucile Packard Foundation (to P.C.S.), Na-
tional Geographic Society (to P.C.S.), Whitten-Newman Founda-
tion, and the Island Fund of the New York Community Trust (to
P.C.S.), and Universidad National de San Juan (to R.N.M. and
O.A.A.).
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