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PaleoBios 23(2):1–30, July 15, 2003
© 2003 University of California Museum of Paleontology
The pelvic and hind limb anatomy of the stem-sauropodomorph
Saturnalia tupiniquim (Late Triassic, Brazil)
MAX CARDOSO LANGER
Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, BS8 1RJ Bristol, UK.
Current address: Departamento de Biologia, Universidade de São Paulo (USP), Av. Bandeirantes, 3900 14040-901
Ribeirão Preto, SP, Brazil; mclanger@ffclrp.usp.br
Three partial skeletons allow a nearly complete description of the sacrum, pelvic girdle, and hind limb of the stem-
sauropodomorph Saturnalia tupiniquim, from the Late Triassic Santa Maria Formation, South Brazil. The new
morphological data gathered from these specimens considerably improves our knowledge of the anatomy of basal
dinosaurs, providing the basis for a reassessment of various morphological transformations that occurred in the
early evolution of these reptiles. These include an increase in the number of sacral vertebrae, the development of a
brevis fossa, the perforation of the acetabulum, the inturning of the femoral head, as well as various modifications
in the insertion of the iliofemoral musculature and the tibio-tarsal articulation. In addition, the reconstruction of
the pelvic musculature of Saturnalia, along with a study of its locomotion pattern, indicates that the hind limb of
early dinosaurs did not perform only a fore-and-aft stiff rotation in the parasagittal plane, but that lateral and medial
movements of the leg were also present and important.
INTRODUCTION
Saturnalia tupiniquim was described in a preliminary
fashion by Langer et al. (1999) as the basal-most
sauropodomorph dinosaur, an assignment generally accepted
(Galton 2000a, Kellner and Campos 2000). Further work
by the author (Langer 2001a, b, 2002) has confirmed the
position of this dinosaur as the most basal member of the
sauropodomorph lineage. Yet, Sauropodomorpha Huene,
1932 is currently defined as a node-based taxon including
Prosauropoda Huene, 1920 and Sauropoda Marsh, 1878
(Salgado et al. 1997, Sereno 1998, Yates 2003a, Langer
2002), and Saturnalia does not belong to either of these
groups. Instead, it is clearly more basal in the dinosaur phy-
logenetic tree than any sauropod or “prosauropod.” Ac-
cordingly, Saturnalia cannot be regarded as a
sauropodomorph sensu stricto, and is better considered a
taxon in the stem-lineage (Jefferies 1979) to that group.
The three known skeletons of Saturnalia come from the
same locality (Langer et al. 1999) in the Upper Santa Maria
Formation, Rio Grande do Sul state, south Brazil (Barberena
et al. 1985, Langer 2001a). These beds encompass, together
with the Ischigualasto Formation of North-western Argen-
tina, the Ischigualastian “reptile-age” of Bonaparte (1982),
which is usually dated as Carnian (Rogers et al. 1993, Lucas
1998). Accordingly, Saturnalia is equivalent in age to the
more famous Argentinean “oldest-known dinosaurs,”
Herrerasaurus ischigualastensis Reig, 1963 and Eoraptor
lunensis Sereno et al., 1993.
MATERIALS AND METHODS
Saturnalia tupiniquim is based on its syntypical series
(Langer et al. 1999) housed at the Museu de Ciências e
Tecnologia PUCS, Porto Alegre (MCP). This includes the
holotype (MCP 3844-PV), a well preserved skeleton con-
sisting of most of the presacral vertebral series, both sides
of the pectoral girdle, right humerus, partial right ulna, right
radius, both sides of the pelvic girdle with the sacral series,
left femur and most of the right limb; and two paratypes:
MCP 3845-PV, a partial skeleton including the caudal part
of the skull with braincase, the natural cast of a mandibular
ramus bearing teeth, presacral series including caudal cervi-
cal and cranial trunk vertebrae, both sides of the pectoral
girdle, right humerus, right side of the pelvic girdle and
most of the right hind limb; and MCP 3846-PV, an incom-
pletely prepared skeleton, from which a partial tibia and foot,
as well as some trunk vertebrae, are visible. All these speci-
mens are semi-articulated (taphonomic class I of Holz and
Barberena 1994), and show good to excellent preservation
(taphonomic class I of Holz and Schultz 1998).
The distinctive preservation of the skeletal remains of
Saturnalia tupiniquim allows the recognition of various
osteological traces (trochanters, scars, etc.) left by the at-
tachments of major groups of muscles. Accordingly, some
insights on its pelvic limb myology are presented here. The
tentative identifications of the musculature corresponding
to each of these traces are inferences based on a “phyloge-
netic bracket” approach (Witmer 1995, Hutchinson 2001a).
Obviously, birds and crocodiles are used as the main ele-
ments of comparison, because they are the only extant
archosaur groups, and the closest living “relatives” of
Saturnalia.
The following anatomical account is based mainly on MCP
3844PV, except where explicitly stated otherwise. Relevant
information was also obtained from the paratypes, especially
MCP 3845PV. Measurements of all available pelvic skeletal
elements of the three specimens of Saturnalia are presented
in Tables 1–5 (see Appendix). Anatomical nomenclature fol-
lows the conventions of the compendium “The Dinosauria”
2PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
(Weishampel et al. 1990, p. 6–7) and the “Nomina
Anatomica Avium” (Baumel 1993).
Unless noted to the contrary, the term “basal dinosaurs”
is used herein to broadly include basal saurischians such as
Herrerasaurus, Staurikosaurus, Guaibasaurus, and Eoraptor
(Langer 2003), as well as basal theropods such as
Liliensternus, Megapnosaurus, and Dilophosaurus (Carrano
et al. 2002); basal “prosauropods” as Thecodontosaurus,
Efraasia, and Plateosaurus (Yates 2003a); and basal orni-
thischians such as Lesothosaurus, Scelidosaurus, and
Heterodontosaurus. Additionally, the sauropodomorph di-
nosaurs from the Stubensandstein of Germany are treated
according to the alpha-taxonomy proposed by Yates (2003b).
Additional institutional abbreviations: BMNH, Natural
History Museum, London; BRSUG, Department of Earth
Sciences, University of Bristol; GPIT, Instutut für Geologie
und Paläontologie, Tübingen; MB, Museum für
Naturkunde, Berlin; MCZ, Museum of Comparative Zool-
ogy, Cambridge; MCN, Fundação Zoobotânica do Rio
Grande do Sul, Porto Alegre; PVL, Fundacíon Miguel Lillo,
Tucumán; PVSJ, Museo de Ciencias Naturales, San Juan;
QVM, Queen Victoria Museum, Harare; SMNS, Staatlisches
Museum für Naturkunde, Stuttgart.
COMPARATIVE DESCRIPTION
Sacral Vertebrae and Ribs
The sacrum of Saturnalia (Figs. 1A–B) includes two main
vertebrae, which represent the plesiomorphic archosaur ele-
ments (Romer 1956, Ewer 1965, Cruickshank 1972, Sereno
and Arcucci 1994). Their platycoelic centra are not fused to
one another, or to any other centrum, and lack ventral keels.
Both vertebrae are firmly attached, but not fused, to the ilia
by means of massive ribs and transverse processes. The last
trunk vertebra is placed cranial to the iliac preacetabular
alae, and differs from that of Herrerasaurus (Novas 1994)
because its transverse processes do not touch either the ilia
or the ribs of the first sacral. Accordingly, as also seen in
Staurikosaurus (Galton 1977), and some basal
“prosauropods” (Galton 1976, 1999, 2000b), Saturnalia
does not present trunk vertebrae added to the sacrum. In
this respect it differs from Eoraptor (Sereno et al. 1993),
theropods (Welles 1984, Cuny and Galton 1993), ornithis-
chians (Janensch 1955, Galton 1974, Scelidosaurus—BMNH
6704) and most sauropodomorphs (Young 1941a, 1942,
Cooper 1981, Galton 1999, Riojasaurus—PVL 3808), all
of which bear at least one dorsosacral vertebra.
The two vertebrae caudal to the two main sacrals of
Saturnalia are placed within the boundaries of the iliac
postacetabular alae. The transverse processes of the
caudalmost of these do not reach either the ilia or the trans-
verse processes of the second sacral, while the cranial ele-
ment has uncertain relations to the sacrum (see discussion
below). Accordingly, in contrast to most other archosaurs,
dinosaurs always have more than two vertebrae placed within
the limits of the iliac alae (Novas 1994). This condition
seems to have been achieved in two ways: the craniocaudal
compression of the vertebrae, as seen in Herrerasaurus
(Novas 1994), and to a lesser degree also Staurikosaurus
(Galton 1977), or the elongation of the preacetabular and/
or postacetabular iliac alae. Saturnalia does not have con-
stricted vertebrae in the sacral area, and is similar to most
dinosaurs in this respect. Accordingly, the presence of four
vertebrae within the limits of its ilia is due to the elongation
of the postacetabular alae.
The centra of the two main sacral vertebrae of Saturnalia
are more slender towards the central part of the sacrum.
The cranial articulation of the first of these, as well as the
caudal articulation of the second, is broader and more ro-
bust. This is distinct from the general morphology of the
sacral vertebrae of dinosaurs, as discussed by Welles (1984),
and seen in most basal members of the group (Galton 1999;
Scelidosaurus—BMNH 6704). Yet, this is by no means an
unknown feature among dinosaurs, and is particularly com-
mon in “ceratosaurs” (Gilmore 1920, Raath 1969, Bonaparte
et al. 1990).
First Sacral Vertebra—The centrum is broader than high,
as is its neural canal, resembling Staurikosaurus (Galton
1977), theropods (Huene 1934, Welles 1984),
sauropodomorphs (Galton 1999, Riojasaurus—PVL 3808),
and some ornithischians (Dryosaurus—MB dy II), but dif-
fering from Herrerasaurus (Novas 1994), which has more
laterally compressed sacral vertebrae. Its neural spine is not
entirely preserved, but it is clearly not as transversely broad
as that of Herrerasaurus (Novas 1994) or Staurikosaurus
(Galton 1977). Instead, it is narrow and craniocaudally elon-
gated as in most other basal dinosaurs (Raath 1969, Galton
1976, Cooper 1981; Scelidosaurus—BMNH 6704). There
are also no indications of a “spine table” and/or dorsal broad-
ening, which have been recognized in Herrerasaurus (No-
vas 1994), Eoraptor, as well as in more derived dinosaurs
(Bonaparte et al. 1990, Galton 2000b).
The first sacral vertebra has each of its ribs and corre-
sponding transverse processes fused into a single structure
with an expanding (both craniocaudally and dorsoventrally)
lateral portion. Laterally expanding transverse processes/
ribs are also present in basal dinosauromorphs (Sereno and
Arcucci 1993, 1994), as well as in Herrerasaurus (Novas
1994) and some “prosauropods” (Galton 1999). On the
contrary, the “primordial” first sacral vertebra of most other
basal dinosaurs (Raath 1969, Galton 1981, Welles 1984)
has derived transverse processes/ribs, which are much nar-
rower in dorsal aspect.
Although fused, the sacral ribs and transverse processes
of Saturnalia can be distinguished from one another by
their position and morphology. This is based on compari-
son with some specimens of Plateosaurus (SMNS F65), in
which both elements are not completely fused together. In
these forms (contra Galton 2000b), as in Saturnalia, the
craniodorsal margin of the structure is not formed by the
cranial margin of the transverse process, but by the dorsal-
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 3
Fig. 1. Sacrum and ilium of Saturnalia tupinquim (MCP 3944-PV). Scale bar = 2 cm. A. Dorsal aspect of sacral vertebrae and
right ilium. B. Left lateral aspect of sacral vertebrae. C. Lateral aspect of right ilium. Abbreviations: ac, acetabulum; an,
antitrochanter; brfo, brevis fossa; csa, articulation area for the “caudosacral” vertebra; fteo, flexor tibialis externus origin; ftio,
flexor tibialis internus origin; icr, iliac preacetabular ridge; ifco, iliofemoralis cranialis origin; ito, iliotibialis origin; ns, neural spine;
po, postzygapophysis; pp, pubic peduncle; pr, prezygapophysis; sac, supracetabular crest; srtp, sacral rib and transverse process.
most portion of the rib, which contacts the cranial-most tip
of the iliac ala. Caudal to this, each transverse process arises
from the lateral surface of the respective neural arch to form
a horizontal platform. Like in other basal saurischians (Huene
1926, Raath 1969, Novas 1994), the space between the ilia
and the first sacral vertebra is “roofed” by the transverse
processes. However, unlike Herrerasaurus and theropods,
but similarly to some “prosauropods” (Cooper 1981, fig.
12b, “tp”; Plateosaurus—SMNS F65), the bony part of the
transverse process does not contact the ilium, and the lat-
eral-most part of the “roofing” was probably completed by
cartilage. These structures together (craniodorsal margin of
4PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
the rib plus transverse process) are fan-shaped in dorsal as-
pect, articulating with the dorsomedial margin of the ilium,
from its cranial tip as far as the level of the ischial peduncle.
The rib of the first sacral vertebra expands from the
craniodorsal corner of the centrum, and is composed of
two main parts: an inclined ventral platform, and a cranial
vertical wall. These give the rib an “L-shaped” lateral out-
line, which is apomorphic for Dinosauria, because the sac-
ral ribs of basal dinosauromorphs (Sereno and Arcucci 1993,
1994, Novas 1996) and most basal archosaurs (Ewer 1965,
Romer 1972, Chatterjee 1978) are simple plate-like struc-
tures. The ventral platform of the first sacral vertebra of
Saturnalia is fan-shaped, expanding lateroventrally and cau-
dally to form the “floor” of the space between the ilium
and the first sacral vertebra (see Novas 1994 for a similar
condition in Herrerasaurus). It articulates with the internal
surface of the ilium, from the caudal margin of the
preacetabular embayment to the cranial part of the ischial
peduncle, at a level corresponding to the supracetabular crest
on the external surface of the bone. The vertical wall, on
the other hand, bridges the gap between the cranial mar-
gins of the transverse process and the ventral platform of
the rib, forming the entire cranial portion of the vertebral
articulation to the ilium. It inserts along the cranial and
ventral parts of the medial surface of the preacetabular ala.
The depth of this vertical wall (representing the depth of
the entire rib/transverse process) distinguishes Saturnalia
from forms such as Staurikosaurus (Galton 1977) and
Herrerasaurus (Novas 1994), the first sacral of which has a
much deeper rib.
The transverse process/rib of the first sacral of Saturnalia
has a “C-shaped” lateral outline. This is formed by the ven-
tral platform and the cranial wall of the rib and the “roofing”
transverse process. This configuration is also seen in
Herrerasaurus (Novas 1994), as well as in some
“prosauropods” (Benton et al. 2000, Galton 2000b, fig.
6a). A transverse process that “roofs” the space between
the ilium and the fist sacral vertebra is also present in the
primordial first sacral of several theropods (Gilmore 1920,
pl. 8, “d” of s3, Raath 1969) and in “prosauropods” with a
sacral added from the trunk series (Young 1941a, Cooper
1981). The vertical wall and ventral platform of the rib are,
on the other hand, also known in Staurikosaurus (Galton
1977) and ornithischians (Janensch 1955, abb. 23, “sw3”).
Second Sacral Vertebra—Its centrum is almost identical
to that of the first sacral vertebra, and the dimorphism seen
in Herrerasaurus (Novas 1994) and Staurikosaurus (Galton
1977) is not present. The neural arches are also similar, but
the two vertebrae differ significantly in the morphology of
their transverse processes/ribs. As is also seen in
Herrerasaurus (Novas 1994), these have an “inverted C-
shaped” lateral outline, composed of dorsal and ventral hori-
zontal platforms, and a cranioventrally to caudodorsally
inclined caudal wall.
Each dorsal platform is fan-shaped in dorsal aspect and,
based on the comparison to some “prosauropods”
(Plateosaurus—SMNS F65; Riojasaurus—PVL 3805), it
seems to be composed mainly of the transverse process. It
expands laterally from the lateral border of the neural arch,
forming an extensive articulation with most of the mediodor-
sal surface of the iliac postacetabular ala, closely resembling
the condition in Herrerasaurus (Novas 1994). The dorsal
platform of the second sacral vertebra of Saturnalia is, how-
ever, more craniocaudally elongated, correlating with its
much longer iliac postacetabular ala. In addition, it “roofs”
the space between the cranial part of the second sacral ver-
tebra and the ilium, as seen in Herrerasaurus and some
theropods (Gilmore 1920, Raath 1969). Unlike these forms,
however, its cranial margin is not in contact with the trans-
verse process of the first sacral. This “roofing” seems to
represent a derived feature among dinosaurs, since only the
caudal wall and ventral platform are recognizable in the sec-
ond sacral of basal dinosauromorphs (Sereno and Arcucci
1994).
In Saturnalia, the caudal wall and ventral platform of
each pelvic articulation of the second sacral vertebra is formed
only by the rib, which circumscribes ventrally and caudally
the space between the cranial part of that vertebra and the
ilium. The caudal wall extends from the mid-cranial portion
of the centrum, where it contacts the caudal-most part of
the dorsal platform attachment, to insert along the
medioventral surface of the cranial part of the iliac
postacetabular ala, medial to the insertion area for the M.
caudofemoralis brevis (M. caudofem. brevis; see below). The
ventral platform, on the other hand, bridges the cranial-
most part of the centrum to the medial surface of the iliac
body, just cranial to the postacetabular embayment. As in
most dinosaurs (Huene 1926, Janensch 1955, Novas 1994,
Galton 2000b), its craniolateral margin contacts the
caudolateral part of the ventral platform of the first sacral
rib, and an open space is left medial to this articulation.
The articulation between the ilium and the second pri-
mordial sacral of most other dinosaurs, including
Staurikosaurus (Galton 1977), Herrerasaurus (Novas 1994),
“prosauropods” (Galton 1973, Cooper 1981, fig. 13, Benton
et al. 2000), theropods (Gilmore 1920), and ornithischians
(Forster 1990, fig. 4, third sacral), also present a caudal wall
and ventral platform. In various forms that show caudal ver-
tebrae added to the sacrum, however, the caudal wall is less
developed and often perforated (Gilmore 1920, Janensch
1955, Galton 1976, 2000b).
?Caudosacral Vertebra—The vertebral element caudal to
the second main sacral of Saturnalia is not completely pre-
served, but it seems to represent a sacral vertebra added
from the caudal series. Its centrum is about the same length
as that of sacral vertebrae 1 and 2, but only slightly nar-
rower. The transverse processes/ribs are fused to the middle
part of the centrum and neural arches, at the level of the
neurocentral joint. In dorsal aspect, the transverse possesses
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 5
seem to extend perpendicularly to the column, and to ex-
pand laterally. Their distal-most portions are, however, oblit-
erated. Yet, a striated area is seen in the mediocaudal margins
of the right iliac ala and second sacral transverse process
(Fig. 1A), where signals of osseous attachments are present.
Most probably, this indicates the articulation area of the
caudosacral transverse process.
Most dinosaurs possess at least one caudosacral vertebra.
These are present in all theropods (Raath 1969, Welles 1984)
and ornithischians (Galton 1999, Scelidosaurus—BMNH
6704), and apparently also in Staurikosaurus (Langer 2003).
On the contrary, Herrerasaurus (Novas 1994) and Eoraptor
(Sereno et al. 1993) do not have caudosacral vertebrae. This
condition is apparently also present in most basal
sauropodomorphs with a three-vertebrae sacrum, such as
Massospondylus (Cooper 1981), Riojasaurus (PVL 3808),
Yunnanosaurus (Young 1942), and Lufengosaurus (Young
1941a). Plateosaurus, on the contrary, does present a
caudosacral vertebra (Galton 1999, 2000b, Yates 2003a), a
condition that it might be also present in Thecodontosaurus
(Benton et al. 2000), and Ammosaurus (Galton 1999).
The “caudosacral” vertebra of Saturnalia differs from
the cranial-most caudal vertebra of Herrerasaurus (Novas
1994) in that its centrum is not axially shortened, and the
transverse processes not so caudally directed. Indeed, the
latter condition seems to be related to the peculiar com-
pression seen in the vertebrae of the sacral area of
Herrerasaurus, which cranially displaced the caudal centra.
Moreover, the transverse processes/ribs of the second sac-
ral vertebra of Herrerasaurus entirely occupy its short
postacetabular iliac alae, leaving no space for the articula-
tion of a caudosacral vertebra. The caudosacral vertebra of
Staurikosaurus (Galton 2000a) more closely resembles that
of Saturnalia. Compared to the first caudal vertebra of
Herrerasaurus, it is not so axially shortened, and the trans-
verse processes/ribs not so caudally projected. Yet, the iliac
articulations of both the second sacral and the caudosacral
vertebrae are not as craniocaudally expanded as in Saturnalia,
fitting the short postacetabular alae of that dinosaur.
Among basal sauropodomorphs, the “caudosacral” ver-
tebra of Saturnalia is not comparable to the putative one of
Ammosaurus (Galton 1976), which presents a bulged cen-
trum and much thinner transverse processes, but resembles
more those of Plateosaurus (Galton 1999, 2000b, Yates
2003b, SMNS 5715). However, the transverse processes of
the second sacral vertebra are not so distally expanded (fan-
shaped) in these forms as in Saturnalia, while those of the
caudosacral vertebra articulate to a larger area on the medial
surface of the ilium. In Saturnalia, on the other hand, they
only directly contact the ilia in a very short area, which might
correspond to an equally short free space (caudal to the
articulation of the second sacral transverse process) seen on
the iliac alae of Efraasia specimens with putative two-verte-
brae sacrum (Galton 1999; fig. 1F). In fact, the lateral ar-
ticulation of the caudosacral of Saturnalia is very peculiar.
The cranial part of the transverse processes articulate to the
mediocaudal margin of the second sacral vertebra transverse
processes, and not only to their caudal margin as in
Plateosaurus.
In some aspects, the sacrum of Saturnalia is intermedi-
ary between those of Herrerasaurus and “prosauropods”
with a caudosacral. As in Herrerasaurus, the transverse pro-
cesses of the second sacral are large and fan shaped, but
those of the caudosacral also articulates to the expanded
postacetabular iliac alae (as in Plateosaurus). A caudosacral
that articulates to the transverse processes of the second
sacral and to the mediocaudal margin of the ilia might also
be present in Thecodontosaurus (Benton et al. 2000), and
represent the ancestral condition among sauropodomorphs.
Pelvic Girdle
Ilium (Figs. 1A, C)—Both alae are strongly developed,
but the postacetabular ala is much more elongated. The
dorsal iliac crest forms a continuous line in dorsal aspect,
the cranial half of which is concave laterally. This is formed
by a marked depression on the lateral surface of the bone
(see below), and is supposed to represent a primitive feature
among dinosaurs, since similar structures are present in
Marasuchus (Sereno and Arcucci 1994), Herrerasaurus
(Novas 1994), “Caseosaurus” (Long and Murry 1995), and
Thecodontosaurus (Benton et al. 2000). The dorsal iliac crest
of other dinosaurs is also laterally concave, but the concav-
ity is usually not as strong (Raath 1969, Thulborn 1972;
Scelidosaurus—BMNH 6704; Liliensternus—MB.R. 2175),
or it is placed more caudally (Galton 1973, 1976, 2000b).
The preacetabular ala of Saturnalia (PVL 3845PV) is
very short, and does not extend cranial to the pubic pe-
duncle as in basal theropods (Huene 1934, Raath 1969,
Welles 1984) and basal ornithischians (Thulborn 1972,
Charig 1972, Santa Luca 1980). Moreover, it presents a
truncated cranial margin that, among dinosaurs with a short
preacetabular ala, is more similar to that of Herrerasaurus
(Novas 1994), Staurikosaurus (Colbert 1970),
“Caseosaurus” (Long and Murry 1995, Hunt et al. 1998),
and Thecodontosaurus (Benton et al. 2000, fig 15c), than to
those of most “prosauropods” (Bonaparte 1972, Galton
1976, Cooper 1981), which are pointed and more elon-
gated. Accordingly, there is no evidence for a cranial carti-
laginous extension, as suggested for Massospondylus (Cooper
1981), and the rugose area on the craniodorsal surface of
the preacetabular ala seems to be related to muscle attach-
ments. In fact, this rugosity is continuous with the rest of
the dorsal iliac crest, although significantly wider. A similar
wider area is seen in Herrerasaurus (Novas 1994),
“Caseosaurus” (Long and Murry 1995), and “prosauropods”
(Riojasaurus—PVL unnumbered; Plateosaurus—SMNS
13200b), as well as in ornithischians (Romer 1927), sauro-
pods (Romer 1923a), and theropods (Perle 1985). As sug-
gested for ornithischians (Romer 1927, Thulborn 1972),
this area possibly marks the origin of the M. iliotibialis
6PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
cranialis (M. iliotib. cran. = avian M. sartorius, Vanden Berge
and Zweers 1993), indicating a division in the iliotibialis
musculature (Fig. 8). From that muscle insertion area, a
robust lateral ridge extends caudoventrally, bordering the
caudal margin of the preacetabular embayment, to reach
the craniodorsal border of the acetabulum. A similar ridge
is seen in various dinosaurs (Romer 1923a, Thulborn 1972,
Novas 1994, Long and Murry 1995, Benton et al 2000;
Liliensternus - MB.R. 2175), as well as in more basal
archosaurs such as Ornithosuchus (Walker 1977) and
poposaurids (Galton 1977). However, in Saturnalia this
ridge is more robust than that of basal ornithischians
(Thulborn 1972) and “prosauropods” (Cooper 1981), ap-
proaching the condition of Staurikosaurus (MCZ 1669),
Herrerasaurus (PVL 2566), and some theropods
(Liliensternus MB.R. 2175, Romer 1923a).
Caudal to the aforementioned rugose area and ridge, the
lateral surface of the ilium of Saturnalia presents a marked
sub-triangular concavity. This area is most probably related
to the origin of part of the iliofemoral musculature, based
on topographic correlation with crocodiles (Romer 1923b).
Differing from those reptiles, however, but resembling birds
(Rowe 1986), Saturnalia might have had two branches of
the M. iliofemorale (M. iliofem.), judging from their dis-
tinct insertions on the femur (see below). This concavity
appears to mark the origin of the largest branch, i.e. the
avian M. iliofemoralis cranialis (M. iliofem. cran. = M.
iliotrochantericus posterius, McGowan 1979). A similar
concavity can also be seen in “prosauropods” (Cooper 1981;
fig. 85 “ife”), theropods (Huene 1934, Welles 1984), and
ornithischians (Thulborn 1972, Santa Luca 1980). As in
birds, the origin of this branch is cranially expanded in all
dinosaurs compared to the condition in crocodiles (Romer
1923b; fig. 2), as is the preacetabular ala. This modification
seems to be related to the increase in the importance of this
muscle in medial rotation of the femur, together with a small
role in the protraction of the bone (Vanden Berge 1975,
McGowan 1979). This trend is particularly clear in
theropods, in which the origin of the M. iliofem. cran. oc-
cupies most of the lateral surface of their extremely enlarged
preacetabular ala (Romer 1923a, Padian 1986).
It has been suggested (Russell 1972) that a vertical ridge
extending through the lateral surface of the ilium of some
theropods (Osborn 1916, Osmólska et al. 1972, Galton and
Jensen 1979, Bonaparte 1986, Barsbold and Maryanska
1990, Cuny and Galton 1993) marks the division between
the origins of the two branches of the M. iliofem. Such a
ridge is not clearly seen in most dinosaurs, but Saturnalia
presents a faint elongated convexity extending caudodorsally
from the caudal half of the acetabulum. Contra Russell
(1972), it is here proposed that this ridge separates the ori-
gin areas of the M. iliofem. (most probably the M. iliofem.
cran. alone), cranially, and M. iliofibularis (M. iliofib.), cau-
dally, as suggested by Walker (1977). The very similar ridge
of some birds (McGowan 1979, fig. 2) also separates the
origins of these two groups of muscles (Vanden Berge 1975).
The second branch of the avian M. iliofem., the M.
iliofemoralis externus (M. iliofem. ext. = M. gluteus medius
et minimus), originates immediately dorsal to the
antitrochanter, either at the dorsal margin of the ilium
(McGowan 1979), or at the sulcus antitrochantericus
(Vanden Berge and Zweers 1993). Various authors (Romer
1927, Coombs 1979) have suggested that this muscle origi-
nated from the so-called “antitrochanter” of some ornithis-
chians. In fact, there has always been a discussion of whether
the M. iliofem. ext. of ornithischians originated at the mid-
cranial lateral surface of the dorsal iliac crest (Walker 1977)
or at the “antitrochanter,” while the M. iliotrochantericus
caudalis originated at the aforementioned part of the dorsal
iliac crest (Galton 1969, Norman 1986). Rowe (1986) pro-
posed that these two muscles are derived from the reptilian
M. iliofemoralis. Based on this assumption, it is clear that,
as in birds, the M. iliofem. cran. (= avian M. iliotrochantericus
caudalis) of dinosaurs originated on the mid-cranial lateral
surface of the dorsal iliac crest, while the M. iliofem. ext.
originated somewhere caudal to it, but cranial to the M.
iliofib. No clear origin area for the M. iliofem. ext. is seen
on the ilium of Saturnalia, and it might have been fleshy as
suggested for Thescelosaurus (Romer 1927, p. 264). A pos-
sible origin, however, is the dorsal border of the acetabu-
lum, just caudal to the supraacetabular crest. This area bears
clear indications of muscle insertion, and it is both dorsal to
the antitrochanter and caudal to the origin of the M. iliofem.
cran., as expected for the origin of the M. iliofem. ext. Like-
wise, no sign of the origin of the M. iliotrochanterici (M.
iliotroc.), sensu Rowe 1986, is seen on the pelvis of
Saturnalia. This might indicate that this muscle had its ori-
gins on the caudalmost presacral vertebrae, as is the case in
crocodiles (= M. puboischiofemoralis internus pars dorsalis;
Walker 1977).
The postacetabular ala of Saturnalia is longer than the
space between the preacetabular and postacetabular
embayments of the ilium, a condition shared by most
eusaurischians (Huene 1934, Raath 1969, Welles 1984,
Padian 1986, Benton et al. 2000; Guaibasaurus—MCN PV
2355) and two marked ridges extend through its ventral
portion. The medial one (“pv” in Novas 1996; fig. 8) ex-
tends caudodorsally from the caudal border of the ischial
peduncle, where its ventral margin is more ventrally pro-
jected than that of the second (lateral) ridge. More cau-
dally, the ventral portion of this ridge deflects medially to
form a horizontal platform, which extends to the end of the
ala. The lateral ridge, on the other hand, extends caudally
from near the caudodorsal margin of the acetabulum, and
its caudal two thirds (“bs” in Novas, 1996; fig. 8) over-
hangs the medial ridge/platform laterally and ventrally. At
the cranial portion of the postacetabular ala, the lateral and
medial ridges define a ventrally concave surface - the brevis
fossa (see Novas 1996)—that corresponds to the large ori-
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 7
gin area of the M. caudofem. brevis (Gatesy 1990). More
caudally, the origin of this muscle expands into the much
broader ventral surface of the platform formed by the cau-
dal part of the medial ridge, which is laterally bound by the
lateral ridge.
Several muscle scars are seen in the dorsal and lateral
surfaces of the postacetabular iliac ala of Saturnalia. The
most marked of these is a craniocaudally elongated rugose
area, which is continuous with the dorsal iliac crest. Ac-
cordingly, its craniodorsal portion is thought to mark the
origin of part of the M. iliotibialis, which also extends cra-
nially along the dorsal iliac crest (Romer 1923b). More cau-
dally, the rugose area enters the lateral surface of the ala,
expanding ventrally and occupying most of its caudal por-
tion. Based on the comparison with the crocodile (Romer
1923b, 1927), it is suggested that this ventrally expanded
area represents the origin of the M. flexor tibialis externus
(M. flex. tib. ext.), while the M. flexor tibialis internus (M.
flex. tib. int.) had its origin at the caudal-most part of the
lateral surface of the ala (fig. 1C). Birds also present a simi-
lar arrangement, with the M. flexor cruris lateralis (= semi-
tendinosus) originating caudal to the origin of the M.
iliotibialis (Vanden Berge 1975, McGowan 1979). A similar
rugose area is found in several dinosaurs, including
“Caseosaurus” (Long and Murry 1995), Herrerasaurus
(Novas 1994), basal ornithischians (Janensch 1955, Abb. 3,
Santa Luca 1980, fig. 17, 1984, fig. 12), and “prosauropods”
(Galton 1976, fig. 26e, Plateosaurus—GPIT skeleton 1;
Efraasia—SMNS 12389). In theropods, on the other hand,
this rugose area is restricted to a more caudal portion of the
ala (Gilmore 1920, pl. 10.2, Raath 1969; Liliensternus—
MB.R. 2175).
As already discussed, the smooth area between the rug-
ose origin of the M. flex. tib. ext. and the ridge that marks
the caudal margin of the M. iliofem. cran. origin probably
corresponds to the origin area of the M. iliofib. This is cor-
roborated by the fact that in birds, the origin of this muscle
is also between the origins of the M. caudofem. brevis (=
M. piriformis) and M. iliotibialis (Vanden Berge 1975,
McGowan 1979). As reconstructed for various other dino-
saurs (Gregory 1923, Romer 1923a, Galton 1969, Russell
1972, Coombs 1979, Norman 1986, Dilkes 2000), the ori-
gin of the reptilian M. iliocaudalis (Romer 1923b) was prob-
ably at the caudal surface of the postacetabular ala and its
medial platform.
The dorsalmost part of the internal surface of the
postacetabular ala of Saturnalia bears strong striations, which
are also present on the dorsal surface of the transverse pro-
cess of the second sacral vertebrae. As discussed by Dilkes
(2000), this probably corresponds to the origin of the M.
longissimus, or of less differentiated dorsal muscles (Romer
1923b). Ventral to this, the rib/transverse process of the
second sacral vertebra articulates with the medial border of
the platform that forms the caudal part of the brevis fossa.
Further cranially, this vertebral articulation is bounded ven-
trally by a ridge, which extends cranially along the internal
surface of the ilium. This ridge is continuous with the plat-
form itself, and it is also seen in several other dinosaurs
(Long and Murry 1995, fig. 181b, Galton 2000b;
Liliensternus—MB.R. 2175; Efraasia—SMNS 12389). Need-
less to say, this ridge has nothing to do with either of the
two ridges mentioned above, which mark the medial and
lateral boundaries of the brevis fossa.
The body of the ilium of Saturnalia is slightly longer
than deep, proportions also seen in basal theropods (Huene
1934, Raath 1969, Padian 1986), basal ornithischians
(Thulborn 1972), and some “prosauropods” (Galton 1973,
Benton et al. 2000). This differs from the iliac body of ro-
bust “prosauropods” (Bonaparte 1972, Cooper 1981) and
Herrerasaurus (Novas 1994), which are deeper than long.
The pubic peduncle of Saturnalia bears a straight dorsal
margin at about 45˚ to the horizontal plane, and a sub-
triangular robust pubic articulation, which is broader medi-
ally and tapers laterally. This differs from the pubic peduncle
of basal ornithischians, which is shorter and tapers ventrally
(Thulborn 1972, Charig 1972), and is also distinct from
those of basal theropods, which are much shorter and broader
(Raath 1990, Cuny and Galton 1993; Liliensternus—MB.R.
2175). Right on the laterodorsal part of its articulation area,
the pubic peduncle of Saturnalia presents a series of stria-
tions. Thulborn (1972) suggested that similar scars in
Lesothosaurus indicate the presence of cartilaginous tissues
binding the ilium to the pubis. However, as seen in
Maiasaura (Dilkes 2000), it is likely that such scarring cor-
responds to the origin of either the M. ambiens (see below)
or the M. puboischiofemoralis internus pars medialis (M.
pub. isch. fem. int. med. = avian M. iliofemoralis internus;
Walker 1977). Indeed, the medial surface of the pubic pe-
duncle of Saturnalia presents faint muscular scars leading
ventrally, which most probably are not associated with the
origin of a crocodilian-like M. ambiens and/or M. pub.
isch. fem. int. med. (see Romer 1923b, Walker 1977).
The iliac acetabulum of Saturnalia is longer than high,
and deeper in its caudal part. It is almost fully closed, with
the ventral border of the well-developed medial acetabular
wall preserved as an almost straight margin. This suggests
that the acetabular aperture, if present, would be rather re-
duced, and restricted to a small craniocaudally elongated
gap between the ventral part of the iliac medial wall and the
acetabular incisure of the pubis and ischium. Such a well-
developed iliac medial wall approaches that of Marasuchus
(Sereno and Arcucci 1994, Novas 1996), and the only other
basal dinosaurs known to have such a closed acetabulum are
Guaibasaurus (Bonaparte et al. 1999) and Scelidosaurus
(BMNH 6704). In addition, as in most dinosaurs, Saturnalia
has a well-developed supraacetabular crest.
The medial acetabular wall of Saturnalia shows a differ-
ent texture in its central area, which is almost exactly in the
position of the acetabular aperture of various basal dino-
saurs (Bonaparte 1972, Novas 1994). It is suggested that
8PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
this area, which is perforated in more derived dinosaurs,
represents one of the articulation surfaces of the femoral
head. A second main articulation area for the femoral head
in the acetabulum is the antitrochanter (see Fraser et al.
2002), which occupies its caudoventral portion. It most
closely resembles the antitrochanter of Marasuchus (Sereno
and Arcucci 1994), Herrerasaurus (Novas 1994),
“Caseosaurus” (Long and Murry 1995), and basal theropods
(Raath 1969, Padian 1986; Liliensternus—MB.R. 2175).
“Prosauropods” such as Efraasia (SMNS 12667) and
Plateosaurus (GPIT skeleton 1), also have the antitrochanter
in a similar position, but it is not so prominent as in the
forms mentioned above. The antitrochanter of ornithischians,
on the other hand, is usually more dorsally placed (Thulborn
1972, Maryanska and Osmólska 1974, Charig 1972), also
facing more ventrally in some forms (Santa Luca 1980).
Obviously, the so-called “antitrochanter” of several derived
ornithischians (Romer 1927, Weishampel and Horner 1990,
Dodson 1996) is not homologous to the articular area dis-
cussed here.
The short and robust ischial peduncle of Saturnalia is
divided into two portions: the acetabular area, which is mainly
occupied by the antitrochanter; and a caudal portion, the
lateral surface of which is somewhat continuous with the
brevis fossa. In lateral aspect, the caudal portion tapers ven-
trally, and does not contribute significantly to the ischial
articulation, which is almost entirely below the area of the
antitrochanter. This seems to represent a plesiomorphic fea-
ture for dinosaurs, since it is present in Marasuchus (PVL
3870), Staurikosaurus (Colbert 1970), Guaibasaurus
(Bonaparte et al. 1999), basal ornithischians (Charig 1972,
Santa Luca 1984), and some “prosauropods” (Efraasia—
SMNS 12667). Robust basal dinosaurs, such as
Herrerasaurus (PVL 2566) and various “prosauropods”
(Bonaparte 1972, Van Heerden 1979), also retain this char-
acter, but the caudal part of the peduncle is much broader.
In theropods, on the other hand, the ischial articulation
faces caudoventrally, rather than ventrally, and the caudal
part of the pubic peduncle is expanded (Raath 1990;
Liliensternus—MB.R. 2175).
The articular facet of the ischial peduncle of Saturnalia
is sub-rectangular, rounded laterally, but more angled me-
dially. This contrasts with the sub-triangular and narrower
articulation of Lesothosaurus (BMNH RUB17),
Staurikosaurus (MCZ 1669), and Herrerasaurus (Novas
1994), but approaches the more derived condition seen in
“prosauropods” (Young 1942, Galton 1973), theropods
(Liliensternus—MB.R. 2175), and most ornithischians
(Maryanska and Osmólska 1974, Galton 1981;
Scelidosaurus—BMNH 6704).
Pubis (Fig. 2)—It is composed of a robust proximal body
and an elongated shaft. The main axis is about 70˚ to the
horizontal plane, a much higher angle than that of basal
Dinosauriformes (Arcucci 1987, Sereno and Arcucci 1993,
1994), basal theropods (Huene 1934, Raath 1990), and
“prosauropods” (Bonaparte 1972, Galton 1976, 1990, but
see Galton 1984, fig.1e). Together with that of
Staurikosaurus (Galton 1977), the pelvis of Saturnalia ap-
proaches a derived opisthopubic condition, as seen in
Herrerasaurus (Novas 1994), but especially ornithischians
(Seeley 1887) and some derived theropods (Perle 1979,
1985). Like Pseudolagosuchus (PVL 4629) and all basal di-
nosaurs, but different from more basal dinosauriforms
(Sereno and Arcucci 1993, 1994), the pubis of Saturnalia
is also much longer than half the length of the femur.
The body of the pubis in Saturnalia is composed of a
robust cranial portion, a small caudal process, and the ob-
turator plate. The boundaries between these three areas are
clearly seen in lateral aspect. The ischio-acetabular groove
(Sullivan and Lucas 1999) marks the separation between
the cranial portion and the caudal process, which are clearly
distinguished from the obturator plate because of their more
robust construction. Their medial surfaces, on the other
hand, are less differentiated, and are continuous with those
of the pubic peduncle and the medial acetabular wall of the
ilium.
The portion of the pubic body craniodorsoal to the ischio-
acetabular groove is very robust, bearing a large and flat
dorsocaudally facing proximal surface, the cranial two thirds
of which is entirely in articulation with the pubic peduncle
of the ilium. A flat acetabular incisure occupies the caudal
third of that surface, forming the cranial-most part of the
acetabular floor. Its medial margin is bounded cranially by
the cranialmost part of the iliac medial acetabular wall, and
caudally by the ischio-acetabular groove.
The ischio-acetabular groove was first described for the
basal theropod Eucoelophysis (Sullivan and Lucas 1999), but
it also constitutes a peculiar feature on the pubis of
Saturnalia. It consists of a strong elongated concavity that
excavates the proximal surface of the bone, and is entirely
open towards the acetabulum. It also opens externally, pierc-
ing the lateral surface of the bone at its proximal margin.
From that point it extends craniomedially, separating the
pubic acetabular floor (craniolaterally) from the short con-
tribution of the bone to the medial acetabular wall
(caudomedially). Its medial end is, however, difficult to de-
termine. It does not directly pierce the medial acetabular
wall, but it might be connected to the inner part of the
body by the main acetabular aperture. A much fainter ischio-
acetabular groove is also seen on the pubis of some
“prosauropods” such as Plateosaurus (Huene 1926, tafel V,
fig. 3a,c) and Efraasia (SMNS 12354).
The function of this structure is uncertain, and it might
represent only an incisure derived from the rearrangement
of the proximal pubic articulation. It seems more likely,
however, that it marks the position of a particular soft-tis-
sue element, or represents the pathway of a vascular struc-
ture crossing the pelvis through the acetabular aperture.
Sullivan and Lucas (1999) suggested that it might corre-
spond to a branch of the ischial artery, but I am unaware of
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 9
any living diapsid with a major blood vessel penetrating the
acetabular aperture (O’Donoghue 1920, Baumel 1975).
Some basal theropods (Camp 1936, Raath 1969, Rowe and
Gauthier 1990, Carpenter 1997), as well as some basal
archosaurs (Walker 1961, Ewer 1965), have two pubic aper-
tures, which have been related to the obturator foramen
and the “thyroid fenestra” (Romer 1956, Walker 1961, Raath
1969). Yet, these are placed on the obturator plate and nei-
ther seems to be homologous to the ischio-acetabular groove.
The obturator foramen of basal theropods is in an abso-
lutely corresponding position to that of Saturnalia. The
extra aperture is, however, placed ventral to the ridge that
marks the dorsal border of the main branch of the M.
puboischiofemoralis externus (M. pub. isch. fem. ext.),
whereas the ischio-acetabular groove is dorsal to it.
Caudal to the ischio-acetabular groove lies the caudal
process of the proximal pubis. Its caudal margin forms a
mediocaudally facing subtriangular convex articulation facet,
which fits into a corresponding concavity on the craniolateral
corner of the ischium. Laterally, the process has two in-
clined surfaces converging to an elongated raised central
area. The dorsal surface forms the mediocaudal border of
the ischio-acetabular groove, and also a small part of the
cranioventral portion of the medial acetabular wall, where it
is connected to the iliac part of the wall. The ventral surface
of the process is continuous with the obturator plate.
Fig. 2. Pubis of Saturnalia tupinquim (MCP 3944-PV). Scale bar = 2 cm. Right pubis in (A.) cranial, including cross section at
the middle of the shaft and distal outline, and (B.) lateral aspects. C. Medial aspect of left pubis. Abbreviations: “ap,” “ambiens”
process; iag, ischio-acetabular groove; obf, obturator fenestra; obp, obturator plate; pai, pubic acetabular incisure; pcb, pubic cra-
nial butress; piaf, ischiadic articular facet on pubis; pilaf, iliac articular facet on pubis; pmdl, pubic mediodistal lamina.
10 PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
The obturator plate forms the thin ventral part of the
pubic body, expanding from the medial margin of its more
robust proximal portion. It extends distally as a medially
concave flange for about one quarter of the length of the
pubis. At this point its ventral border is mediodorsally
deflected to form the thin medial part of the pubic shaft,
which composes the entire symphyseal area of the bone.
Differing from basal theropods (Rowe and Gauthier 1990)
a single aperture is present in the obturator plate, which is
the obturator foramen. Its size is comparable to that of most
basal dinosaurs, though it is smaller than that of some
“prosauropods” (Huene 1926, Cooper 1981).
The body of the pubis possesses several indications of
muscle attachments. Its craniodorsal rim forms a broad stri-
ated ridge that is continuous with the similarly striated dor-
sal margin of the pubic peduncle of the ilium. In the lateral
surface of the bone, a series of strong striations radiate from
the cranial margin of the acetabulum, at the pubis-ilium
contact. More ventrally, two longitudinal ridges are seen.
The first ridge extends from the caudal part of the acetabu-
lar incisure, entering the pubic shaft to form the ventrolat-
eral corner of its proximal portion. Dorsally to the middle
of this ridge, a very strong protuberance is seen, which is
somewhat continuous with the broad ridge on the dorsal
part of the bone. The second ridge is fainter and extends
sub-parallel and ventral to the previous one. It originates
from the striated caudal process of the iliac body, and also
extends cranially.
As in Saturnalia, the dorsal rim of the pubis of most
dinosaurs is somewhat salient, a feature much more marked
in certain sauropods (Gillette 1991). In an arrangement simi-
lar to that of the crocodile (Romer 1923b), several authors
reconstructed the origin of the M. ambiens in this area,
both in sauropods (Romer 1923a, Borsuk-Bialynicka 1977)
and other dinosaurs (Romer 1927, Perle 1985, Dilkes 2000).
This might also have been the case in Saturnalia, but the
more distal “pubic tubercle” (Hutchinson 2001b) also seems
to represent a suitable origin area for that muscle, as sug-
gested for several other dinosauromorphs (Galton 1973,
1984, Bonaparte 1986, Arcucci 1987, Novas 1994, Sereno
and Arcucci 1993, 1994, Bonaparte et al. 1999, Sullivan
and Lucas 1999). Although the M. ambiens has a single
head in birds (McGowan 1979), it is suggestive that croco-
diles have a second head, which originates on the internal
surface of the pubic body (Romer 1923b). Accordingly, it
is possible that basal dinosaurs had a double-headed M.
ambiens (Fig. 8), originating on the dorsal rim of the pubis
and on the more distal lateroventral protuberance. Indeed,
both areas are nearly continuous in some basal dinosaurs
(Galton 1984, Sereno and Wild 1992).
In conclusion, the well-developed bump on the dorsal
rim of the pubis of some derived sauropodomorphs and
theropods (Romer 1923a, Perle 1985, Gillette 1991) is not
homologous to the more distal lateroventral protuberance
of basal dinosauromorphs, and other basal archosaurs (Walker
1961, 1964). Accordingly, this last structure seems to have
been progressively lost in various dinosaur lineages (Gilmore
1920, Cooper 1981, 1984, Welles 1984). If basal dinosaurs
had a single-headed M. ambiens, the dorsal rim of the pu-
bis could mark the insertion of a branch of the abdominal
muscles, or the origin of the M. pub. isch. fem. int. med.
(Romer 1923b, Walker 1977, Dilkes 2000). Alternatively, as
discussed by Hutchinson (2001b), the “pubic tubercle”
might be related to pelvic ligaments or the abdominal mus-
culature.
As in most saurischians (Cooper 1981, 1984, Sereno and
Wild 1992, Novas 1994), the proximal portion of the pubic
symphysis of Saturnalia is formed by the dorsomedially
deflected ventral margin of the distal part of the obturator
plate. From that point, the symphysis continues distally along
almost the entire medial margin of the shaft. This situation
is distinct from that of ornithischians, the pubic symphysis
of which is restricted to the distal end of the bone, as is that
of their ischium (Ostrom and McIntosh 1966). In addi-
tion, the shaft of the highly derived ornithischian pubis is
narrow and rod-like, usually lacking a medial lamina (but
see Thulborn 1972). The pubic shaft of Saturnalia, on the
other hand, presents an extensive medial lamina, which ex-
pands from the mediodorsal corner of the more robust lat-
eral border to form the pubic symphysis. This condition is
thought to be primitive for dinosaurs, because it occurs in
basal dinosauriforms (Sereno and Arcucci 1993, 1994;
Pseudolagosuchus - PVL 4629) as well as in Herrerasaurus
(Novas 1994), Staurikosaurus (MCZ 1669), Guaibasaurus
(Bonaparte et al. 1999), “prosauropods” (Huene 1926,
Galton 1973), and basal theropods (Huene 1934, Raath
1969, Carpenter 1997). In addition, in Saturnalia,
Guaibasaurus, and basal theropods, the lateral margin of
the pubis extends ventrally, giving the shaft a transversely
concave ventral surface.
The pubis of Saturnalia is swollen at its distal end, a
feature unknown in basal ornithischians (Thulborn 1972,
Charig 1972). Herrerasaurus (PVSJ 373), Staurikosaurus
(MCZ 1669), basal theropods (Huene 1926, Welles 1984,
Padian 1986, Carpenter 1997), and “prosauropods” (Huene
1926, Bonaparte 1972, Galton 1973), also present a swol-
len distal end of the pubis, a feature considered plesiomorphic
for dinosaurs because it is also present in Pseudolagosuchus
(PVL 4629). Besides, in all non-ornithischian basal dino-
saurs, and possibly also in Pseudolagosuchus (PVL 4629),
the thin medial flange that composes most of the pubic
symphysis is slightly proximally deflected, and does not con-
tact its counterpart at the distal end of the bone. In
“prosauropods” this space is occupied by the distal bulging
of the bone, which is medially extended and meets its coun-
terpart in the symphyseal area. Their symphysis, therefore,
reached the distal end of the pubis, which shows an “apron-
like” shape (Huene 1926, Galton 1973, 1990) that is char-
acteristic of the group. On the contrary, the swollen area of
the distal pubis of Saturnalia is not medially extended, and
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 11
a small gap appears between the distal end of the pubic
shafts, which is also seen in basal theropods (Padian 1986,
Carpenter 1997), Pseudolagosuchus (PVL 4629), and
Herrerasaurus (PVSJ 373), but is particularly marked in
Staurikosaurus (Novas 1994). Yet, in the last two forms the
distal bulging of the pubis is much more transversely exten-
sive, approaching the condition of “prosauropods,” and dif-
fering from that of the other taxa mentioned above, which
are narrow in distal outline. However, they still do not con-
tact the counterpart (Staurikosaurus—Novas 1994), or this
contact is cranially restricted (Herrerasaurus—PVSJ 373).
This last arrangement seems to be also present in some basal
theropods such as Coelophysis (Padian 1986) and Gojirasaurus
(Carpenter 1997). Other members of the group (Huene
1934, Sereno and Wild 1992), however, present an arrange-
ment more similar to that of Saturnalia and Staurikosaurus,
and their pubic symphysis is restricted to the medial thin
flange of the bone.
The main muscle attached to the pubic shaft of Saturnalia
is the M. pub. isch. fem. ext. (Fig. 8). Its part 1 (Romer
1923b) originated on the cranial surface of the distal half of
the bone, and extended proximally, bounded dorsally by a
lateroventral protuberance (“ambiens process”) and the
dorsalmost longitudinal ridge of the lateroventral part of
the pubic body. The origin of part 2 of the muscle was on
the caudal surface of the pubic shaft. Its proximal part ex-
tended ventral to part 1, covering the obturator plate,
bounded dorsally by the ventral-most ridge of the
lateroventral part of the pubic body. The caudal process of
the pubic body was also covered by part 1 of the M. pub.
isch. fem. ext., and its striated lateral surface might have
marked a separated branch of this muscle, as seen in the
crocodile (Romer 1923b). In the modified pubis of
Herrerasaurus, the lateral surface of the distal half is equiva-
lent to the cranial surface of that of Saturnalia. Accord-
ingly, the extensive longitudinal ridge seen on that surface
marks the dorsomedial border of the origin of
puboischiofemoralis part 1. A similar muscle arrangement
on the pubis was probably present not only in Marasuchus
and Staurikosaurus, but also in more derived theropods with
a marked distal “boot” (contra Romer 1923a).
The pubic shaft of Saturnalia and “prosauropods”
(Bonaparte 1972, Galton 1973) presents a lateral expansion
in the distal half of its lateral border. The proximal margin
of this expansion probably marks the passage of the part 1
of M. pub. isch. fem. ext., extending proximally from its
origin at the cranial surface of the pubis. A similar concavity
is seen in Herrerasaurus (Novas 1994) but not in basal
theropods (Gilmore 1920, Colbert 1989, Sereno and Wild
1992, Carpenter 1997), which present a mainly straight lat-
eral margin of the pubis that converges medially towards
the distal end. This arrangement might indicate that part 1
of their M. pub. isch. fem. ext. originated from a more
restricted area on the distal pubis and extended more ven-
tral to the shaft, a condition likely to have been also present
in Guaibasaurus (Bonaparte et al. 1999).
Ischium (Fig. 3)—Its body is composed of a robust dor-
sal portion and the thin obturator plate. The medial surface
of the dorsal portion is flat to slightly convex, whereas the
lateral surface is markedly convex. The obturator plate is a
sigmoid flange, convex laterally and concave medially in its
proximal portion, but convex medially and concave laterally
in its distal portion. The proximal surface of the ischium is
almost flat, lacking an excavated acetabular incisure as seen
in most basal dinosaurs (Santa Luca 1984, Raath 1990).
The caudomedial portion of that surface is occupied by the
Fig. 3. Left ischium of Saturnalia tupinquim (MCP 3944-PV) in (A.) lateral, including distal outline, and (B.) ventral aspects.
Scale bar = 2 cm. Abbreviations (see also Figs. 1 and 2): ado, abductor dorsalis origin; ifo, ischifemoralis origin; ipaf, ischiadic ar-
ticular facet for pubis; oo, obturatorius origin.
12 PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
articulation with the ischial peduncle of the ilium, the
ventrocaudal corner of which is covered by the upturned
caudal margin of the ischial body. Cranial to this, the
antitrochanter of Saturnalia occupies the entire acetabular
incisure. It presents strongly expanded lateral borders, and
reaches the pubic articulation at its cranial end. This differs
from the condition in Marasuchus (Novas 1996),
Herrerasaurus (Novas 1994), “prosauropods”
(Plateosaurus—IGPT skeleton 1; SMNS F-07), and basal
theropods (Huene 1934, Welles 1984, Raath 1990), the
ischial antitrochanter of which is restricted to the caudal
part of the acetabular incisure. The condition in theropods
is even more distinct from that of Saturnalia, because their
ischium bears a strong concavity at the cranial part of the
acetabular incisure. Ornithischians, on the other hand, have
a distinct antitrochanter, which does not enter the ischium
(Maryanska and Osmólska 1974, Charig 1972, Santa Luca
1980, Sereno 1991a).
No other basal dinosaur presents an ischial antitrochanter
as large as that of Saturnalia. Such a well-developed struc-
ture is thought to represent an autapomorphic reversal in
this taxon, since it is otherwise known only in more basal
archosaurs (Walker 1964, Ewer 1965, Chatterjee 1978),
including the dinosauromorph Lagerpeton (Sereno and
Arcucci 1993). Moreover, the ischial antitrochanter of
Saturnalia is craniomedially bounded by the medial acetabu-
lar wall of the ilium, though the ischium itself does not
contribute to that wall. This arrangement is also
plesiomorphic, since it is unknown in dinosaurs with a par-
tially closed acetabulum (Novas 1994), but it is present in
Lagerpeton (Sereno and Arcucci 1993) and Marasuchus
(Novas 1994).
In the ischium of Saturnalia, the pubic articulation is
placed cranioventral to the antitrochanter. Its main part is
formed by a laterocranially facing concavity, which receives
the caudal process of the pubis. The thin sheet of bone that
forms its medial surface is continuous with the obturator
plate, and overlaps the caudal process of the pubis medially.
The obturator plate itself is incompletely preserved but,
contrary to the condition in some other dinosaurs (Huene
1926, Novas 1994), it does not seem to contribute
significantly to the pubo-ischial articulation. However, it was
certainly ventrally extensive, occupying the entire
cranioventral margin of the ischial body. This condition seems
to be apomorphic within dinosaurs, since the cranial mar-
gin of the ischium of Marasuchus (Sereno and Arcucci 1994)
apparently does not have such a well-developed thin ventral
expansion. This condition seems to have been retained in
ornithischians, because the pubic peduncle of their ischium
either lacks (Ostrom and McIntosh 1966, Colbert 1981;
Scelidosaurus—BMNH 6704) or presents a very reduced
obturator plate (Santa Luca 1980, Forster 1990, Sereno
1991a). In Herrerasaurus (Novas 1994), Staurikosaurus
(Colbert 1970), “prosauropods” (Bonaparte 1972, Galton
1984), and basal theropods (Janensch 1925, Huene 1934,
Welles 1984, Raath 1990), on the other hand, a thin ven-
tral flange forms at least half of the depth of the pubic pe-
duncle, corresponding to a well-developed obturator plate.
In various theropods, this plate is caudally displaced (Osborn
1916, Ostrom 1969, Barsbold et al. 1990, Barsbold and
Maryanska 1990) to a position similar to that of the so-
called “obturator process” of ornithopods (Galton 1974,
1981, Forster 1990), which is not homologous to the struc-
ture dealt with here (see below).
Each obturator plate of Saturnalia meets its counterpart
on its caudoventral margin, where it forms the short cra-
nial-most portion of the ischial symphysis. Caudal to that,
as in all basal saurischians, the obturator plate merges into
the shaft, and the rest of the symphysis is formed by the
rod-like distal part of the bone (Gilmore 1920, Janensch
1925, Huene 1926, 1934, Young 1941a, b, Raath 1969,
Bonaparte 1972, 1982, Galton and Jensen 1979, Van
Heerden 1979, Cooper 1981, 1984, Welles 1984, Galton
1984 Novas 1994, 1996, Bonaparte et al. 1999; Eoraptor—
PVSJ 512; Staurikosaurus—MCZ 1669). That portion of
the symphysis marks the caudal border of the pubo-ischial
fenestra, the ischial part of which is well-developed in
Saturnalia, as it is in most basal dinosauriforms, except
Lagerpeton (Sereno and Arcucci 1993). Yet, this part of the
fenestra seems to be apomorphically less extensive in forms
that, like Saturnalia, present an enlarged obturator plate
(Huene 1926, Raath 1969, Novas 1994). On the contrary,
the ischial symphysis of Marasuchus (Bonaparte 1975) is
restricted to the caudal part of the shaft, and the ventrome-
dial lamina of the bone forms the caudal margin of a larger
pubo-ischial fenestra. Similarly, a major excavation forming
the caudolateral margin of the pubo-ischial fenestra is seen
in the craniomedial surface of the ischium of Lesothosaurus
(Thulborn 1972). Indeed, a distally restricted ischial sym-
physis seems to be a general ornithischian feature (Ostrom
and McIntosh 1966). In addition, the ischium of
Lesothosaurus (Thulborn 1972; BMNH RUB17) presents a
ventromedial lamina expanding from the lateral border of
its caudal half. This is probably homologous to the so-called
“obturator process” of some derived ornithopods (Romer
1927, Galton 1974), which seems to represent a remnant of
it.
The caudal two thirds of the rod-like ischial shaft of
Saturnalia is sub-triangular in cross section. Such an ar-
rangement is given by its flat medial, dorsal, and lateroventral
margins. In fact, the medial margin is not completely flat,
but bears a longitudinal groove, as seen in some theropods
(Gilmore 1920, Raath 1969). The dorsal margin, on the
other hand, is slightly inclined, giving the dorsal surface of
the joined ischia a concave outline, and joins the lateroventral
margin to form a marked lateral ridge. This ridge is one of
the major features of the ischial shaft of Saturnalia, and a
similar structure has been recognized in most other basal
dinosaurs, including Guaibasaurus (MCN 2355),
Herrerasaurus (PVL 2566; PVSJ 373), “prosauropods”
(Bonaparte 1972, Galton 1984), basal theropods (Gilmore
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 13
1920, Janensch 1925, Huene 1926, Raath 1969), and basal
ornithischians (Thulborn 1972, Charig 1972, Santa Luca
1984; Dryosaurus—MB mounted skeleton). In Saturnalia,
the cranial part of the ridge enters the lateral surface of the
ischial body, where it is dorsally deflected, extending as far
as the caudal part of the antitrochanter. This arrangement is
different from that of dinosaurs with a strong acetabular
incisure (Raath 1969, Santa Luca 1980, 1984, Cooper 1984,
Bonaparte 1986; Liliensternus—MB.R. 2175), in which this
ridge usually bifurcates along the body of the ischium. In
Saturnalia, such a bifurcation can only be hinted at by the
presence of a feeble secondary ridge, extending cranially and
ventral to the main ridge. Caudally, the main lateral ridge
forms the dorsolateral corner of the ischial shaft. This con-
dition is similar to that of Herrerasaurus (PVSJ 373),
Guaibasaurus (MCN 2355), and “prosauropods” (Huene
1926, Cooper 1981). In basal theropods, on the other hand,
the lateral ridge is more ventrally placed. As a result, the
cross section of the ischial shaft is semicircular rather than
sub-triangular (Raath 1969, Padian 1986; Liliensternus—
MB.R. 2175), a condition apparently also present in
Staurikosaurus (MCZ 1669). In Saturnalia, the lateral ridge
is dorsally deflected in the distal third of the ischium. In
addition, it meets its counterpart medially, defining the caudal
border of the concave dorsal surface of the conjoined ischial
shafts.
As in all basal eusaurischians (Huene 1926, 1934, Young
1942, Galton and Jensen 1979, Bonaparte 1972, 1982, Jain
et al. 1975, Van Heerden 1979, Welles 1984, Padian 1986,
Bonaparte et al. 1990, 1999, Raath 1990), but distinct from
other basal dinosauromorphs (Ostrom and McIntosh 1966,
Colbert 1970, Santa Luca 1980, Novas 1994, Sereno and
Arcucci 1993, 1994, Sereno et al. 1993; Scelidosaurus—
BMNH 6704; Lesothosaurus—BMNH RUB17), the distal
end on the ischium of Saturnalia is dorsoventrally expanded.
In addition, the dorsal end of the shaft is slightly upturned
and more distally projected than the ventral end. A similar
form of the distal end of the ischium is seen in
“prosauropods” (Huene 1926, Bonaparte 1972), basal
theropods (Huene 1926, Padian 1986), Guaibasaurus
(MCN 2355), and also Herrerasaurus (PVL 373). The is-
chium of basal ornithischians, on the contrary, has its distal
surface forming straight angles to the dorsal and ventral
margins (Charig 1972, Galton 1974, Sereno 1991a, Peng
1997).
The distal aspect of the ischium of Saturnalia is incom-
pletely known, because its dorsolateral corner is not well
preserved in any of the available specimens. It seems, how-
ever, that the lateral ridge reaches the distal border of the
bone at its dorsal-most portion. This condition is also seen
in “prosauropods” (Buffetaut et al. 1995), Guaibasaurus
(MCN 2355), Herrerasaurus (Novas 1994), and most basal
ornithischians (Thulborn 1972, Galton 1981, Colbert 1981),
but not in basal theropods (Gilmore 1920, Padian 1986)
and some other ornithischians (Scelidosaurus—BMNH
6704), in which the distal part of the crest is more ventrally
placed. Yet, the caudodorsal surface of the ischium of
Saturnalia is not as broad and flat as that of some
“prosauropods” (Young 1941a, 1942, Van Heerden 1979,
Buffetaut et al. 1995). Instead, it approaches more the con-
dition of other members of the group (Huene 1926, Galton
1976; ?Massospondylus—BPI 4693), as well as that of basal
theropods (Padian 1986), Herrerasaurus (PVSJ 373) and
Guaibasaurus (MCN 2355), in which the dorsocaudal sur-
face of the ischium is narrower and dorsally convex.
The lateral ridge of the ischium is the main muscle-re-
lated feature of this bone in Saturnalia. It marks the sepa-
ration between the areas of origin of the M. ischiofemoralis
(M. ischiofem. = M. ischiotrocantericus; Romer 1923b,
Dilkes 2000) mediodorsally, and those of the M. pub. isch.
fem. ext. part 3 (= avian M. obturatorius) and dorsal branch
of the M. adductor (M. add. = avian M. puboischiofemorale),
lateroventrally. This ridge apparently corresponds with the
entire dorsal surface of the ischium of non-dinosaurian
archosaurs (Romer 1956, Walker 1964, Chatterjee 1978,
Sereno and Arcucci 1993, 1994), which separates the origin
area of the aforementioned muscles. In birds, like in dino-
saurs, this separation is placed on the lateral surface of the
ischium, rather than at its dorsal border (Feduccia 1975,
McGowan 1979).
The striations related to the origin of the M. obturatorius
(M. obt.) occupy all the lateroventral surface of the ischial
shaft of Saturnalia. Therefore, different from the recon-
structions of Romer (1923a) for saurischians, it is suggested
that the origin of this muscle was not restricted to the ob-
turator plate, but extended along almost the entire ischial
shaft (see also Gregory 1923, Russell 1972, Borsuk-
Bialynicka 1977). From that area the muscle extended proxi-
mally, lateral to the obturator plate, in the direction of the
femoral head (Fig. 8). Similar relations for the M. obt. were
also reconstructed by Romer (1927) for Thescelosaurus, and
probably represent the condition for most basal dinosaurs.
As already discussed, the lateral ridge has a faint side branch
extending cranially along the ventral portion of the ischial
body, dorsal to the obturator plate. This possibly marks the
ventral edge of the origin area of the dorsal branch of the
M. add., which has been reconstructed in approximately
the same position in various other dinosaurs (Romer 1923a,
1927, Dilkes 2000).
In the crocodile (Romer 1923b), two other muscles origi-
nate at the lateral surface of the cranioventral portion of the
ischium: the M. puboischiotibialis and the ventral branch of
the M. add. The presence of such muscle attachment areas
in Saturnalia is unclear, due to incomplete preservation of
the obturator plate. However, a rugose sub-triangular scar
is seen at the ventral margin of the caudal part of the plate,
just dorsal to the area where it forms the cranial part of the
ischial symphysis. Such a rugose area is also seen in other
basal dinosaurs such as Megapnosaurus (QVM QG1) and
Efraasia (SMNS 12354), and it might be related to the
origin of the ventral branch of the M. add.
14 PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
The ischium of Saturnalia bears a marked laterodorsally-
facing groove, which extends along the dorsal surface of the
cranial part of the bone, and is continuous with the dorsal
platform that occupies most of the shaft. This is the main
muscle attachment area medial to the lateral ridge of the
ischium, and it surely corresponds to the origin of the M.
ischiofem. (Fig. 3A). A similar groove is known in various
basal dinosaurs including Guaibasaurus (MCN 2355), basal
sauropodomorphs (Huene 1926, Cooper 1981, 1984), basal
theropods (Gilmore 1920, Janensch 1925—Liliensternus—
MB.R. 2175), and basal ornithischians (Thulborn 1972,
Santa Luca 1984; Dryosaurus—MB mounted skeleton). In
all these forms, the marked dorsomedial border of the is-
chium, the cranial portion of which rises above the lateral
ridge itself, borders the groove medially. This seems to rep-
resent a neomorphic structure of dinosaurs, since it is ab-
sent in other archosaurs, in which the origin of the M.
ischiofem. is restricted to the medial surface of the bone
(Romer 1923b). On the contrary, in dinosaurs, as in birds
(McGowan 1979), the origin of this muscle is partially on
the lateral surface of the ischium. In some derived ornithis-
chians (Romer 1927, Galton 1969, Santa Luca 1980,
Norman 1986), the caudal portion of the lateral ridge is
lateroventrally deflected, entering the lateral surface of the
shaft. In these forms, the entire laterodorsal surface of the
bone is occupied by the M. ischiofem. An analogous situa-
tion is also seen in basal theropods (Raath 1969, Padian
1986), the lateral ridge of which is placed more ventrally on
the lateral surface of the shaft. In Saturnalia, in particular,
the M. ischiofem. does not occupy only the dorsal groove,
but also spreads onto the flat dorsomedial surface of the
caudal part of the bone.
In the crocodile (Romer 1923b), two branches of the
M. flex. tib. int. (= avian M. flexor cruris medialis) have
their origins on the ischium. The more caudal origin has
been recognized in Piatnitzkysaurus (Bonaparte 1986), and
different authors have also associated it with different struc-
tures on the lateral surface of the ischium of ornithischians
(Romer 1927, Thulborn 1972, Coombs 1979, Dilkes 2000).
In Saturnalia, a small rugose area is seen on the caudal part
of the lateral ridge, between the areas of origin of M. obt.
and M. ischiofem. Its position is almost the same as that of
the “knob-like” structure described by Novas (1994) on
the ischium of Herrerasaurus. This probably corresponds
to the origin of the caudal part of the M. flex. tib. int., the
caudal position of which is thought to be primitive amongst
dinosaurs.
The origin of the dorsal part of the M. flex. tib. int., has
been related to a rugose area on the caudal part of the is-
chial body of some saurischians (Romer 1923a, Borsuk-
Bialynicka 1977). Indeed, the M. flexor cruris medialis has
its origins in a very similar position on the avian pelvis
(Vanden Berge 1975, Dilkes 2000). In Saturnalia, the cau-
dal part of the ischial body has a striated caudal surface,
which is continuous with the protuberant caudomedial mar-
gin of the bone. Various basal saurischians (Gilmore 1920,
Bonaparte 1986; Herrerasaurus—PVL 2566; Efraasia—
SMNS 12354) have a concavity just cranial to that caudal
border, while the caudal border itself is particularly well
developed in Riojasaurus (Bonaparte 1972). Both the con-
cavity and/or the border could be associated with the ori-
gins of the M. flex. tib. int.
The poor preservation of the distal end of the ischium of
Saturnalia does not allow the recognition of muscle scars,
but their position can be partially inferred based on the
general shape of that area. Norman (1986) reconstructed
the insertion of the M. rectus abdominis on the cranial sur-
face of the distal end of the ischial shaft of Iguanodon. It is
likely that such an insertion was also present on the
ventrocranial corner of the expanded distal ischium of vari-
ous basal dinosaurs (Huene 1926, 1934, Bonaparte 1972,
Padian 1986; Herrerasaurus—PVSJ 373), including
Saturnalia. Similarly, the distally expanded caudodorsal part
of the end of the ischium of these forms (Galton 1984,
Padian 1986, Raath 1990, Bonaparte et al. 1999) probably
corresponds with the origin of the reptilian M. ischiocaudalis
(Romer 1923b), as also reconstructed for other members
of the group (Romer 1923a, Russell 1972, Dilkes 2000).
According to Dilkes (2000), both the M. ischiocaudalis and
M. iliocaudalis of reptiles correspond to the avian M.
pubocaudalis (Vanden Berge and Zweers 1993).
Pelvic Limb
The hind limb of Saturnalia is more than twice the esti-
mated length of the forelimb. A similar proportion is also
found in theropods (Huene 1926, Raath 1969, Welles 1984),
bipedal ornithischians (Thulborn 1972, Santa Luca 1980),
and it was also estimated for Herrerasaurus (Novas 1994,
Sereno 1994). Most “prosauropods,” on the other hand,
have relatively long forelimbs (Cooper 1981, Galton 1976,
Bonaparte and Pumares 1995), which are more than half
the hind limb length. Various authors (Romer 1966, Coo-
per 1981) have used these ratios as indicative of bipedal or
quadrupedal gait in dinosaurs. Based solely on this approach,
Saturnalia would be placed within the bipedal group.
Femur (Fig. 4)—It shows a “sigmoid” aspect both in
cranial and lateral views. As discussed by Hutchinson
(2001b), however, the dinosaur “sigmoid” femur results from
the combination of an inturned head and a bowed shaft. In
the case of Saturnalia, the femoral shaft is bowed both
cranially and medially. The cranial bowing is a common fea-
ture of the archosaur femur, which is retained
plesiomorphically in most early dinosaurs (Hutchinson
2001b). The medial bowing is also plesiomorphic for dino-
saurs, since it is present in Lagerpeton (PVL 4619) and
Pseudolagosuchus (PVL 4629).
The proximal surface of the femoral head of Saturnalia
is flat, and articulates entirely with the acetabulum. It bears
a distinct groove, which extends along its long axis. This
groove fits into a faint ridge in the dorsal part of the ac-
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 15
etabulum, and divides the femoral head into mediocaudal
and laterocranial areas, which articulated respectively with
the body of the ilium and the supracetabular buttress (see
also Cooper 1981, fig. 64). A similar groove is present in
various basal dinosaurs, including Staurikosaurus (Galton
1977), Herrerasaurus (PVL 2558), Scelidosaurus (BMNH
6704), Coelophysis (Padian 1986; fig. 5.4c, “gr1”),
Liliensternus (MB.R. 2175), Anchisaurus (Galton 1976),
and Massospondylus (Cooper 1981). In ornithopods and
advanced theropods (Galton 1981, Forster 1990, Barsbold
Fig. 4. Right femur of Saturnalia tupinquim (MCP 3944-PV) in (A.) cranial, (B.) lateral, (C.) proximal, (D.) distal, (E.) medial,
and (F.) caudal aspects Scale bar = 2 cm. Abbreviations: cflf, fossa for caudofemoralis longus; dlt, dorsolateral trochanter; faa, facies
articularis antitrochanterica; fc, fibular condyle; fclil, femoral caudolateral intermuscular line; fcmil, femoral caudomedial intermus-
cular line; fcril, femoral cranial intermuscular line; fdms, muscle scar on laterocranial distal femur; ffna, foramen for nutritive artery
on femur; fhls, ligament sulcus on femoral head; fhmt, medial tuber on femoral head; ft, fossa trochanteris; lc, lateral condyle; lccf,
facet for Lig. cruciatum craniale; lt, lesser trochanter; mc, medial condyle; oi, obtutarorius insertion; si, sulcus intercondilaris; ts,
trochanteric shelf; 4t, fourth trochanter.
16 PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
et al. 1990, Russell and Dong 1993), on the other hand,
this groove is highly modified into the well-developed con-
stricted area that separates their elevated “greater trochanter”
from the inturned medial part of the head. This arrange-
ment is also seen in birds (Baumel and Witmer 1993), which
have a trochanteric fossa (fossa trochanteris) separating the
greater trochanter (trochanter femoris) from the inturned
head (collum and caput femoris). Accordingly, the “greater
trochanter” of early dinosaurs is not restricted to the
laterocaudal corner of the femoral head, as often suggested
(Welles 1984, Padian 1986, Rowe 1989, Novas 1994). In-
stead, it encompasses the entire lateral surface extending
from that corner to the craniolateral ridge (“r” in Padian
1986, fig. 5.4c).
In birds (McGowan 1979), the lateral surface of the
greater trochanter bears the insertion area of the M. iliotroc.
(sensu Rowe 1986). This was probably also the case in
Saturnalia, in which an array of cavities and bumps are seen
on the lateral surface of the head, in an arrangement very
similar to that of Herrerasaurus (Novas 1994). Among these
muscle scars, one deserves special attention for its wide-
spread distribution among dinosaurs. In Saturnalia, it rep-
resents a crescent structure situated on the laterocaudal
corner of the femoral head, as also seen in Staurikosaurus
(Galton 1977, Fig 5c), Guaibasaurus (“dlt” in Bonaparte
et al. 1999, fig. 8), ornithischians (Galton 1974, fig 54a,
Galton and Jensen 1973, fig. 5a, Norman 1986, fig 79d),
“prosauropods” (Galton 1984, pl. 4), and basal theropods
(“Tg” in Raath 1990, fig. 7.7k; Liliensternus—MB.R. 2175).
As suggested by Galton (1969) and Norman (1986), this is
an insertion point for a branch of the M. iliotroc. that, judg-
ing by the orientation of the muscle scars and structure of
the ridge, extended cranially.
An obturator ridge, like that of coelophysoid theropods
(Raath 1990), is not present in the femur of Saturnalia.
However, the caudal part of the medial surface of the femo-
ral head bears a small proximodistally oriented ridge that
seems to represent the insertion area for the external
puboischiofemoral musculature, including its part 3 (= avian
M. obt.; see Romer 1923b, Walker 1977, Dilkes 2000). As
in birds, in which the impreciones obturatorae (Baumel and
Witmer 1993) mark the mediocaudal border of the greater
trochanter, the “greater trochanter” of Saturnalia is also
limited caudally by the aforementioned ridge. Cranial to this,
a longitudinal groove extends through the mediocaudal part
of the head, entering the proximal surface of the bone as a
faint concavity. In some dinosaurs, this groove is continu-
ous with the trochanteric fossa. Yet, it clearly served for the
articulation of the antitrochanter, and is considered here as
homologous to the avian facies articularis antitrochanterica
(Baumel and Witmer 1993).
Novas (1996; fig. 3c, “pd”) erroneously considered the
proximal part of the facies articularis antitrochanterica of
Herrerasaurus as its single correlate to the avian trochant-
eric fossa. This is probably because in some specimens of
that taxon (PVSJ 373) this articular area is so enlarged that
it merges with the trochanteric fossa itself, and is not clearly
distinguishable from it. In addition, Novas (1996) also
claimed that such a structure was not for the articulation
with the antitrochanter, because Lagerpeton, which has an
antitrochanter, lacks a corresponding element. However,
Lagerpeton has a facies articularis antitrochanterica, but be-
cause the antitrochanter of this dinosauromorph is placed
more ventrally (Sereno and Arcucci 1993), it does not ex-
tend onto the proximal femur, but is restricted to the me-
dial surface of the bone (see Novas 1996; fig. 3a,d).
The femoral head of Saturnalia has a medially projected
portion, which is bounded caudally by the facies articularis
antitrochanterica, and laterally and cranially by the trochan-
teric fossa. This is homologous to the collum end caput
femoris of birds (Baumel and Witmer 1993), and a longitu-
dinal ridge on its mediocaudal part leads proximally to the
so-called medial tuber (see Novas 1996). More cranially,
the femoral head forms a rounded articulation, which projects
further medially. It articulates dorsally and medially with
the cranial part of the iliac acetabulum, and cranially, dis-
tally, and laterally to the pubic acetabulum. This area is not
as projected in basal dinosauromorphs (Marasuchus—PVL
3870; Pseudolagosuchus—PVL 4629) as it is in Saturnalia
and other dinosaurs, and its further development seems to
represent a derived feature of the group. Strong cavities,
which border this projection distally and mediocaudally, are
probably for the insertion of ligaments of the caput femo-
ris—Lig. iliofemorale and pubofemorale (see Baumel and
Raikow 1993). In various dinosaurs (Galton 1981, Barsbold
et al. 1990, Scelidosaurus—BMNH 6704), these ligaments
insert smoothly onto proximally expanded concavities, both
cranial and caudal to the medial projection. In Saturnalia,
and in a series of other basal dinosaurs (Colbert 1970, Galton
1976, Cooper 1981, Bonaparte et al. 1990, Raath 1990,
Novas 1994, Madsen and Welles 2000; Liliensternus—MB.R.
2175), the insertion area of the cranial ligament is restricted
to the distal part of the head, and lateroproximally bordered
by a step border.
Based on the homology hypothesis for the femoral struc-
tures presented here, the achievement of a fully inturned
femoral head within dinosaurs must be reviewed. In
Saturnalia, as well as in most basal dinosaurs (Huene 1926,
Galton 1977, Welles 1984, Raath 1990, Sereno 1991a, No-
vas 1994), the femoral head is slightly inturned and the
“greater trochanter” faces laterocranially. This is a derived
condition if compared to the femoral head of basal
dinosauriforms such as Marasuchus (Sereno and Arcucci
1994) and Pseudolagosuchus (Arcucci 1987), in which it is
almost not inturned, and possesses a laterally facing “greater
trochanter.” A fully inturned head, on the other hand, is
derived for dinosaurs, and most previous studies argued that
this condition was acquired via the medial rotation of the
proximal elements of the bone (Gauthier 1986, Carrano
2000, Hutchinson 2001b). In some dinosaur groups this
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 17
seems to have been the case, as in various tetanuran theropods
(Osmólska et al. 1972, Madsen 1976, Currie and Zhao 1993)
and derived “prosauropods”—Melanorosaurus (Van Heerden
and Galton 1997) and Ruehleia (Galton 2001a, b)—which
have a mainly cranially facing “greater trochanter.” In
ornithopods (Galton 1981, Norman 1986, Forster 1990)
and more derived tetanurans (Ingenia—Barsbold et al. 1990;
Alxasaurus—Russell and Dong 1993; Saurornithoides—
Currie and Peng 1993), on the other hand, the “greater
trochanter” faces laterally, a condition that seems to have
been retained in birds (McGowan 1979). These forms seem
to have acquired an inturned femoral head via the extreme
elongation of its medial part, rather than via its medial rota-
tion.
Distal to the insertion area for the M. iliotroc., the lat-
eral surface of the femur of Saturnalia presents a “S-shaped”
insertion area for the iliofemoral musculature (sensu Rowe
1986). It begins in the laterocranial corner of the bone, as a
proximally projecting, but not strongly developed trochanter
(“lesser trochanter”). From the base of that trochanter, a
protuberant ventrally arched shelf (“trochanteric shelf”) ex-
tends caudally along the entire lateral surface of the bone.
At the caudolateral corner of the femur, it curves distally
and merges into the shaft. Similar structures are described
for Herrerasaurus (Novas 1994) and basal theropods
(Andrews 1921, Padian 1986, Rowe 1989, Raath 1990,
Madsen and Welles 2000), and it is here suggested that the
“trochanteric shelf” and “lesser trochanter” correspond re-
spectively to the insertion of the M. iliofem. ext. (M. glu-
teus medius et minimus, in McGowan 1979) and M. iliofem.
cran. (see Walker 1977). Marasuchus (Sereno and Arcucci
1994) and Staurikosaurus (MCZ 1669) also show similar
insertions for the iliofemoral musculature. However, their
trochanter and shelf are not protuberant, and only a “S-
shaped” scar is present. A different version of this muscle
insertion is seen in other dinosaurs such as Thecodontosaurus
(BRSUG various specimens), Liliensternus (MB.R. 2175),
and various ornithischians (Galton 1974, Novas 1996;
Scelidosaurus—BMNH 6704; Lesothosaurus—BMNH
BUB17). Most of these forms present a more expanded
“lesser trochanter,” while the shelf is reduced to a caudal
scar and/or faint bump. Birds, on the other hand, differ
from most dinosaurs because the lesser trochanter is fused
to the femoral head to form a “true” trochanter femoris
(“lesser” plus “greater trochanter”). This is a structure that,
therefore, receives the insertion not only of part of the M.
iliofem., but also of the M. iliotroc. In conclusion, the pres-
ence of a protuberant insertion for the iliofemoral muscula-
ture seems to represent a dinosaur apomorphy.
The fourth trochanter of Saturnalia is a pronounced el-
ement whose midpoint is located at one third of the way
along the femur from its proximal end. It starts as a faint
ridge on the caudal surface of the femur, distal to the inser-
tion area for the M. obt., and extends medially to the pos-
teromedial corner of the bone. At this point, it curves distally,
extending in that same direction as a vaguely “S-shaped,”
pronounced crest. The fourth trochanter is sub-rectangular
in outline, resembling that of Herrerasaurus (Novas 1994)
and “prosauropods” (Galton 1990). Extensive scarring is
seen in its mediocaudal surface, where the M. caudofem.
brevis inserted. Romer (1927) suggested that distally ex-
tending muscles—a proximal branch of the M. gastrocne-
mius (M. gastroc.), according to Galton (1969)—also
attached to that element, which accounted for its pendant
shape in ornithischians. Such a musculature might have also
been present in Saturnalia, Herrerasaurus, and
“prosauropods,” the fourth trochanters of which show a
sharply angled distal margin. This hypothesis is corrobo-
rated by the presence of somewhat distinct scars on the
distal inflection of the fourth trochanter of Saturnalia, and
by its pendant shape in some specimens of Massospondylus
(Cooper 1981, fig. 59).
The femur of Saturnalia has a marked oval concavity
cranial to the fourth trochanter, which corresponds to the
insertion of the M. caudofemoralis longus (M. caudofem.
long.). It is craniodistally bounded by a ridge, which ex-
tends cranioproximally from the distal end of the fourth
trochanter. This ridge, based on a topographic comparison
with the crocodile (Romer 1923b), is for the insertion of a
branch of the M. pub. isch. fem. int. med. (= avian M.
iliofemoralis internus; Walker 1977, Rowe 1986). An osteo-
logical correlate of the M. ischiofem. is not found in the
femur of Saturnalia. It is suggested, however, that it in-
serted somewhere between the proximal end of the fourth
trochanter and the caudal part of the trochanteric shelf.
Several longitudinal intermuscular lines are seen on the
femoral shaft of Saturnalia. The most pronounced of them
extends through its cranial surface, from the lesser trochanter
to the distal third of the bone. This line (termed here “cra-
nial line”) is probably homologous with the avian linea
intermuscularis cranialis (Baumel and Witmer 1993), and
was also described for other dinosaurs, such as Hypsilophodon
(Galton 1969, fig 10), Massospondylus (Cooper 1981, fig
84), Iguanodon (Norman 1986, fig 70a), and Herrerasaurus
(Novas 1994, fig. 7 “q”). A second intermuscular line is
seen on the caudolateral corner of the femur. It extends
distally from the caudal part of the “trochanteric shelf,” and
bifurcates into two branches on the distal half of the bone.
The cranial branch extends onto the lateral surface of the
distal femur, while the caudal branch enters the popliteal
fossa. This line (termed here “caudolateral line”) is approxi-
mately in the same position as the avian linea intermuscularis
caudalis (Baumel and Witmer 1993), and might be homolo-
gous to it. A similar intermuscular line was described for
Massospondylus (Cooper 1981, fig. 84), Hypsilophodon
(Galton 1969, fig. 10), and Iguanodon (Norman 1986, fig.
70a). A third and fainter line is seen on the caudomedial
part of the femur. It extends from distal of the insertion
area for the M. caudofem. long. to the lateral part of the
18 PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
medial condyle. This line (termed here “caudomedial line”)
was also described for Hypsilophodon (Galton 1969, fig. 10).
Based on the position of the intermuscular lines, it is
possible to reconstruct the musculature extending along the
femoral shaft of Saturnalia. Regarding the M. femorotibialis,
crocodiles have only two branches of this muscle—M.
femorotibialis internus and externus (Romer 1923b). Birds,
on the other hand, have three branches—M. femorotibialis
lateralis, intermedius and medialis (Vanden Berge and Zweers
1993). In addition, both crocodiles (Romer 1923b) and
birds (McGowan 1979) have the M. adductor femoris (=
avian M. puboischiofemoralis; Vanden Berge and Zweers
1993) inserting along the femoral shaft, usually on its cau-
dal surface. Saturnalia shows four potential areas for these
muscles: the first area occupies most of the medial surface
of the shaft, between the cranial and the caudomedial lines;
while the other three are on the lateral surface of the shaft,
the larger of them between the cranial and the caudolateral
lines, and smaller areas between the caudolateral line and
the fourth trochanter, and between the two diverging
branches of the caudolateral line. Most of these areas were
also described for other dinosaurs (Galton 1969, Cooper
1981, Norman 1986; see table 5.1), but their relation to
the bird and crocodile muscles is not clear.
Given the homology between the cranial intermuscular
line of Saturnalia and the linea internus cranialis of birds, it
follows that the musculature extending medial to this struc-
ture along the femur of Saturnalia corresponds to both the
avian M. femorotibialis intermedius and M. femorotibialis
medialis. Indeed, a faint line extends proximally from the
medial condyle along the medial surface of the femur of
Saturnalia, which might represent the incipient division
between these two muscles. These correspond to the M.
femorotibialis internus of crocodiles (contra Hutchinson
2001b; but see Norman 1986, p. 344), which is the single
branch of the femorotibial musculature that extends through
the dorsal and cranial surfaces of the femur (Romer 1923b).
Accordingly, the M. femorotibialis externus (M. fem. tib.
ext. = avian M. femorotibialis lateralis) and the M. add. are
associated with the three areas on the lateral part of the
femur of Saturnalia. It is suggested that the distal head of
the M. fem. tib. ext. (Vanden Berge 1975, McGowan 1979)
inserted in the area between the two diverging branches of
the caudolateral line, while its main body extended proxi-
mally along the large lateral surface of the bone. This ar-
rangement also accounts for the modifications involving the
insertion of the iliofemoral musculature in dinosaurs, which
shifted from a more distal position on the femoral shaft, as
in crocodiles (Romer 1923b), to a more proximal position,
as in birds. As a result, the laterocranial surface of the femur
was abandoned by the M. iliofem., and occupied by the
lateral shift of the M. fem. tib. ext. In this scenario, the
space between the caudolateral line and the fourth trochanter
is most probably related to the insertion of the M. add.
This is also the area where the nutritive artery of the proxi-
mal femur, a branch of the ischial artery (Baumel 1975),
becomes interosseous, perforating the femur.
Other muscle scars are seen on the distal part of the
femur of Saturnalia. The clearest of them is circular in shape
and placed craniodistal to the scar for the distal head of the
M. femorotibialis lateralis. A similar scar was described for
Herrerasaurus (Novas 1994, fig. 7, “ms”), and is probably
associated with the origin of the proximal arm of the ansa
M. iliofib. (Vanden Berge and Zweers 1993). Further down
the shaft, the M. flexor digitorum longus probably origi-
nated on the truncated caudoproximal part of the tibiofibular
crest, while the accessory part of the M. flexor cruris lateralis
originated on the ridge proximal to it.
The medial condyle occupies the entire medial surface of
the distal femur, and articulates with the internal condyle of
the proximal tibia. It is pinched caudally, and its flat medial
surface might have hosted various muscle insertions (see
Dilkes 2000). The cnemial crest of the tibia articulates with
the sulcus intercondilaris, a faint craniocaudally-oriented
groove that laterocranially bounds the medial condyle. Yet,
contrary to the condition in most dinosaurs (Galton 1976,
fig. 8, Forster 1990, fig. 19, Currie and Zhao 1993, fig.
22d), this groove is not proximally extended, and does not
excavate the cranial surface of the distal femur. Instead,
Saturnalia retains a primitive flat craniodistal femoral mar-
gin, as also seen in basal dinosaurs such as Herrerasaurus
(Novas 1994), Staurikosaurus (Galton 1977), Liliensternus
(MB.R. 2175), and Lesothosaurus (Thulborn 1972). Cau-
dal to the sulcus intercondilaris, a strong concavity is present
on the distal surface of the femur. It differs from that of
basal theropods (Padian 1986, fig. 5.4 “inc”; Liliensternus—
MB.R. 2175) because it is separated from the strong caudal
incision of the bone by a caudal elevation. This concavity
might have hosted the insertion of the Lig. cruciatum
caudalis, whereas the caudal incision represents the pathway
of the Lig. cruciatum cranialis, also forming the caudalmost
separation between the lateral and medial condyles (Baumel
and Raikow 1993). The laterocranial part of the distal fe-
mur is occupied by the broad fibular condyle (Novas 1994),
which articulates with the proximal fibula. Caudal to this
surface a groove extends caudolaterally from the medial con-
cavity, cranially bordering the small lateral condyle. Its lat-
eral expression forms the trochlea fibularis, onto which the
caudoproximal part of the fibula articulates. The lateral
condyle is parallelogram-shaped, and the medial part of its
distal area articulates with the fibular condyle of the tibia.
Tibia (Figs. 5A–D, G–H)—It is a straight bone, with a
craniocaudally elongated proximal end, and a sub-quadran-
gular distal end. It is subequal in length to the femur, as
seen in Eoraptor (PVSJ 512), Staurikosaurus (MCZ 1669),
Guaibasaurus (Bonaparte et al. 1999), and most basal
theropods (Gilmore 1920, Camp 1936, Huene 1934, Welles
1984, Padian 1986, Colbert 1989). This condition is also
present in Pseudolagosuchus (Arcucci 1987), and considered
primitive for dinosaurs in general. Most basal
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 19
sauropodomorphs (Galton 1976, 1984, Cooper 1981, 1984,
Bonaparte and Pumares 1995), on the other hand, have a
tibia that is significantly shorter than the femur, as also seen
in Herrerasaurus (Novas 1994).
The proximal articulation of the tibia of Saturnalia shows
well-developed internal and fibular condyles, as well as a
pronounced cnemial crest. The internal condyle occupies
most of the mediocaudal part of that articulation, and its
medial and caudal surfaces present indication of muscle at-
tachments. These might correspond to the origin for the
M. plantaris, or the insertion of the M. puboischiotibialis
and/or M. flex. tib. ext. (McGowan 1979, Dilkes 2000).
The fibular condyle of Saturnalia does not extend as far
caudally as the internal condyle, as seen in most basal dino-
Fig. 5. Right tibia and fibula of Saturnalia tupinquim (MCP 3944-PV). Scale bar = 2 cm. Tibia in (A.) medial, (B.) lateral, (C.)
cranial and (D.) caudal aspects. Fibula in (E.) lateral and (F.) medial aspects. Tibia and fibula in (G.) proximal and (H.) distal as-
pects. Abbreviations: cn, cnemial crest; faap, articular facet for the astragalar ascending process; faf, fibular articular facet; fnta, fo-
ramen for the nutritive tibial artery; fta, tibial articulation on fibula; ftfl, facet for the tibiofibular ligament; ic, internal condyle; ifi,
iliofibularis insertion; tdp, tibial descending process; tfc, fibular condyle of tibia; tmdg, tibial mediodistal groove.
20 PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
saurs (Novas 1994, Galton 1977; Pisanosaurus—PVL 2577;
Eoraptor—PVSJ 512), and most basal theropods (Huene
1934, Welles 1984, Padian 1986, Carpenter 1997;
Megapnosaurus rhodesiensis—QVM QG 691, 792). Instead,
it is placed at the center of the lateroproximal corner of the
bone, as in most basal sauropodomorphs (Bonaparte 1972,
Galton 1976, Cooper 1984, Benton et al. 2000), and orni-
thischians (Thulborn 1972, Santa Luca 1980; Scelidosaurus—
BMNH 1111). In addition, a clear cleft separates the caudal
margins of the fibular and internal condyles, a condition
shared with most dinosaurs, but apparently absent in
Staurikosaurus (Galton 1977) and Herrerasaurus (Novas
1994).
A faint transverse groove on the proximal surface of the
tibia of Saturnalia marks the caudal limit of the cnemial
crest. This groove is somewhat continuous with the insisura
tibialis (Currie and Zhao 1993), which extends distally to
separate the cnemial crest from the fibular condyle. The
cnemial crest itself projects laterocranially from the shaft,
but not dorsally, and it is almost level with the caudal sur-
face of the proximal tibia. In this respect Saturnalia re-
sembles forms such as Heterodontosaurus (Santa Luca 1980)
and Herrerasaurus (Novas 1994), differing from most basal
saurischians, in which the cnemial crest is well projected
dorsally (Huene 1934, Raath 1969, Galton 1976, Cooper
1981). It also differs from Staurikosaurus (Galton 1977),
Pisanosaurus (Bonaparte 1975), and Lesothosaurus
(Thulborn 1972), in which the proximal projection of the
crest is even more restricted. In addition, as in Herrerasaurus
(Novas 1994) and “prosauropods” (Cooper 1981, Benton
et al. 2000), the cnemial crest of Saturnalia is not very
elongated, and does not extend for more than one third of
the tibial length. In basal theropods (Liliensternus—MB.R.
2175; Megapnosaurus—QVM QG1), some ornithischians
(Thulborn 1972, Galton 1981), and Guaibasaurus (MCN
PV2355), on the other hand, the faint excavation that ex-
tends lateral to the cnemial crest can be traced for the entire
proximal half of the bone. Scars for muscle attachments are
seen both lateral and medial to the cnemial crest. The me-
dial scars might correspond to the origin of the tibial head
of the M. gastroc., while the lateral scars possibly hosted
the origin of the M. tibialis cranialis (M. tib. cran.) more
proximally and the M. extensor digitorum longus (M. ext.
dig. long.) more distally (McGowan 1979, Dilkes 2000).
The lateral surface of the tibia of Saturnalia bears a strong
rugosity extending distally from the cranial part of the fibular
condyle. This is for the articulation of the fibula and the
attachment of the Lig. tibiofibularis, representing a feeble
version of the fibular crest of theropods. Indeed, as in those
dinosaurs, the tibial rugosity fits into a corresponding ridge
on the medial surface of the fibula. When articulated, the
distal part of the fibular ridge joins the proximal end of the
tibial rugosity, to form a “single” connected structure. Other
sauropodomorphs (Plateosaurus—SMNS F65; Masso–
spondylus—Cooper 1981) show an oval scar on the lateral
tibia, distal to the fibular condyle, which might represent a
modified version of the rugosity seen in Saturnalia. Caudal
to the distal end of this rugosity, the lateral surface of the
tibia of Saturnalia presents a vascular related structure. It
starts proximally as a canal, leading distally to a foramen
that penetrates the bone. A similar foramen was described
for other dinosaurs (Cooper 1981, Novas 1994, Currie and
Zhao 1993), and it is probably related to the nutritive tibial
artery, which represents a branch of the A. tibialis cranialis
(Baumel 1993).
Two intermuscular lines extend along the tibial shaft.
The first of them starts at the cnemial crest and extends
distally to the mediocranial border of the bone. The second
crest starts cranial to the foramen for the nutritive tibial
artery, and extends distally to the laterocranial part of the
tibia. These lines probably mark the lateral and medial bound-
aries of the origin of the M. ext. dig. long. (Vanden Berge
and Zweers 1993).
While the lateral border of the tibia remains approximately
the same width throughout the shaft, its medial border be-
comes more robust towards its distal end, which bears
strongly marked mediocranial and mediocaudal corners. This
is clearly seen in the distal aspect of the bone, which is
wider medially than laterally, as seen in most basal dinosaurs
(Thulborn 1972, Padian 1986, Bonaparte et al. 1999, Benton
et al. 2000; Liliensternus—MB.R. 1275; Megapnosaurus
rhodesiensis—QVM QG 691, 792; Pisanosaurus—PVL 2577
Scelidosaurus—BMNH 1111) but not in Herrerasaurus
(Novas 1994), Staurikosaurus (Novas 1989), and Eoraptor
(PVSJ 512). In addition, as in Herrerasaurus (Novas 1994)
and Staurikosaurus (Galton 1977), the mediocaudal corner
of the distal tibia of Saturnalia forms a right angle, differ-
ing from other basal dinosaurs—Pisanosaurus (PVL 2577),
Guaibasaurus (Bonaparte et al. 1999), Lesothosaurus
(Thulborn 1972), Megapnosaurus (QVM QG792),
Liliensternus (MB.R. 2175), and “prosauropods” (Novas
1989)—in which that corner forms an obtuse angle.
Similar to Herrerasaurus (Novas 1994), Staurikosaurus
(MCZ 1669), and “prosauropods” (Novas 1989), the dis-
tal surface of the tibia of Saturnalia has a flat medial articu-
lation for the astragalus. Laterally, this articulation is more
complex. It bears a large cranial surface which is
lateroproximally inclined to receive the astragalar ascending
process. In addition, the laterocranial corner of the tibia is
slightly projected laterally in its distal part. This feature is
also present in most other basal dinosaurs (Padian 1986,
Novas 1994, Bonaparte et al. 1999, Benton et al. 2000),
but absent in ornithischians (Thulborn 1972, Galton 1981,
Colbert 1981), including Pisanosaurus (PVL 2577).
The laterocaudal part of the distal tibia of Saturnalia
forms a wall-like descending process. It overlaps the caudal
surface of the astragalar ascending process and fits into a
concavity caudal to it. Indeed, the presence of tibial articu-
lation caudal to the astragalar ascending process is a dino-
saur apomorphy. The descending process of Saturnalia is
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 21
slightly more distally projected than the rest of the distal
tibia. It also projects laterally from the shaft, as in most
basal dinosaurs (Pisanosaurus—PVL 2577; Eoraptor—PVSJ
512; Guaibasaurus—MCN PV 2355), including most basal
sauropodomorphs (Galton 1976; Thecodontosaurus—
BRSUG 23623, 23624) and some basal theropods (Padian
1986, Carpenter 1997; Liliensternus—MB.R. 1275), but not
as much as in basal ornithischians (Thulborn 1972, Colbert
1981; Scelidosaurus—BMNH 1111), and in various
theropods (Gilmore 1920, Bonaparte 1986, Raath 1990).
A faint groove on the distal surface of the tibia of
Saturnalia separates its descending process from the articu-
lar surface for the ascending process of the astragalus, and it
leads into a cleft on the laterodistal corner of the bone. This
cleft expands proximally along the lateral surface of the tibia,
forming a groove with steep borders. This divides the later-
ally projecting laterocranial and laterocaudal (descending
process) corners of the bone, and was suggested as an
apomorphic feature of Dinosauriformes (Novas 1996).
Fibula (Figs. 5E–H)—It is long and thin, flat medially,
and with a rounded lateral border. The proximal end is
craniocaudally expanded, and its central portion articulates
medially with the fibular condyle of the tibia. Its cranial
part overhangs the insisura tibialis laterally, but does not
articulate with it. The caudal part, on the other hand, bears
an internal ridge extending craniodistally from its
caudoproximal corner. Similar scarring for the articulation
with the tibia was described for other dinosaurs (Cooper
1981, Novas 1994), and it is a common feature of the group.
Distal to this area, despite their close position, no direct
contact between tibia and fibula is seen.
At about one third of its length from the proximal end
of the fibula, a marked rugosity is present in the laterocranial
border of the bone. This structure was also observed in
several other dinosaurs such as Herrerasaurus (Novas 1994),
Dilophosaurus (Welles 1984), Sinraptor (Currie and Zhao
1993), Plateosaurus (GPIT skeleton 1), Massospondylus
(Cooper 1981), and Maiasaura (Dilkes 2000), and corre-
sponds to the insertion of the M. iliofib. In Saturnalia,
however, a second rugosity is seen proximal to that, on the
mediocranial corner of the bone. The fibular shaft is kinked
between these two structures, so that its distal part is later-
ally displaced, as seen in modern birds (McGowan 1979). A
similarly kinked fibula is seen in Guaibasaurus (Bonaparte
et al. 1999).
A closer contact between tibia and fibula is present at
their distal ends, where abundant scarring indicates the pres-
ence of a strong ligamentous attachment between the two
bones. The flat medial surface of the distal fibula faces slightly
mediocaudally, matching the also slightly cranially inclined
lateral surface of the distal tibia. The cranial and caudal bor-
ders of that surface are marked by a pair of ridges, which
match the laterally expanded laterocaudal and laterocranial
corners of the tibia, as also described for Herrerasaurus
(Novas 1994).
The fibula extends slightly more distally than the tibia.
Its distal end is swollen and mediocranially to laterocaudally
expanded. As a result, its long axis forms an angle of ap-
proximately 40° with that of the proximal end of the bone.
Its cranial part articulates medially with the lateral surface
of the astragalar ascending process, while the laterocaudally
extended part matches the shape of the calcaneal tuber, as
described for Herrerasaurus (Novas 1994). Differently from
this form, however, the distal surface of the fibula of
Saturnalia in not inclined, but mainly horizontal with a
slightly more distally expanded laterocaudal corner. The lat-
eral part of its distal surface articulates with the calcaneum,
while its mediocranial expansion and medial border articu-
late distally with the laterocranial and laterocaudal processes
of the astragalus.
Astragalus (Figs. 6A–F)—It is a robust and transversely
elongated bone. The medial part is more craniocaudally ex-
panded than the lateral, and it has a broad faint concavity
extending craniocaudally through its proximal surface. The
medial part of the distal tibia fits onto this surface, the cra-
nial part of which extends laterally to form the flat proximal
articulation of the ascending process. The ascending pro-
cess itself is a wedge-shaped element, low medially, but higher
laterally and caudally. It is also wider towards its lateral por-
tion, where it forms a broad table-like structure, with a flat
proximal surface and steep cranial, medial, and caudal bor-
ders. In its general shape, it resembles the ascending pro-
cess of Herrerasaurus (Novas 1989) and “prosauropods”
(Cooper 1981, Novas 1989), differing markedly from those
of theropods (Liliensternus—MB.R. 2175, Megapnosaurus—
QVM QG792) and most ornithischians (Galton 1981,
Colbert 1981), whose astragali are much narrower, and lack
a well-developed flat proximal surface.
The astragalar ascending process of Saturnalia is bounded
cranially by a feeble platform, which separates it from the
main cranial margin of the bone as seen in basal theropods
(Huene 1934, Welles and Long 1974, Raath 1990, Britt
1991, Madsen and Welles 2000), and “prosauropods”
(Huene 1926, Cruickshank 1980, Novas 1989, Galton and
Van Heerden 1998), but not in basal dinosauriforms (No-
vas 1996) and ornithischians (Galton 1974, 1981, Colbert
1981; Scelidosaurus—BMNH 1111; Pisanosaurus—PVL
2577). Caudally, the ascending process is bordered by a
well-developed concavity—the dorsal basin of Novas (1989),
which articulates with the descending process of the tibia.
This concavity is separated from the ascending process by a
nearly vertical steep border, the lateral portion of which forms
a strong column-like corner. At the medial end of the as-
cending process, the border extends caudally, and separates
the dorsal basin from the medial articular surface of the
astragalus. This characterizes the “interlocking” tibial-as-
tragalar articulation that is typical of Herrerasaurus (Novas
1989) and “prosauropods” (Young 1951, pl. V, Cooper
1981, fig. 71, Novas 1989). On the contrary, in other basal
dinosaurs (Gilmore 1920, Colbert 1981, Welles 1984, Britt
22 PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
1991; Guaibasaurus—MCN PV 2356; Liliensternus—MB.R.
2175; Pisanosaurus—PVL 2577; Scelidosaurus—BMNH
1111; Megapnosaurus rhodesiensis—QVM QG 174, 786, 792,
CT6), the articular area caudal to the ascending process is
continuous with that on the medial part of the astragalus.
The fibula articulates with the concave proximal surface
of the lateral part of the astragalus, as well as with the lateral
surface of the ascending process. In this respect Saturnalia
differs from most ornithischians (Galton 1974, Colbert
1981), except Pisanosaurus (PVL 2577), the astragalus of
which bears no articular facet for the fibula. Saturnalia is
also plesiomorphic in relation to most basal
sauropodomorphs, in which the lateral part of the astraga-
lus is very reduced, and the fibula articulates mainly to the
lateral surface of the ascending process (Huene 1926, Sereno
1999).
In the astragalus of Saturnalia, the base of the fibular
articulation is formed by its laterocranial and laterocaudal
processes. The former receives the calcaneum at its
laterodistal surface, which includes two flat articulation ar-
eas corresponding to the two medial processes of that bone.
The caudal articulation area is more medially expanded, and
cranially borders an articulation-free groove—the “posterior
groove” of Sereno (1991b). These two structures together
form a concavity on the ventral part of the astragalus termed
the “lateroventral depression” by Novas (1989). A third ar-
ticular facet, for the calcaneum, is seen caudal to the “pos-
terior groove,” in the craniodistal surface of the laterocaudal
process of the astragalus, and it fits into the proximal sur-
face of the mediocaudal calcaneal process. This
astragalocalcanar articulation is plesiomorphic in compari-
son to that of most dinosaurs. The astragalus retains well-
Fig. 6. Right proximal tarsals of Saturnalia tupinquim (MCP 3944-PV). Scale bar = 2 cm. Astragalus in (A.) proximal, (B.) caudal,
(C.) medial, (D.) lateral, (E.) distal and (F.) cranial aspects. Calcaneum in (G.) proximal and (H.) distal aspects. Abbreviations:
aap, astragalar ascending process; aca, calcaneum articulation on astragalus; acrp, astragalar cranial platform; adb, astragalar dorsal
basin; afa, fibular articulation on astragalus; aldt, articulation for the lateral distal tarsal; alvd, lateroventral depression on astragalus;
amdt, articulation for the medial distal tarsal; caa, astragalar articulation on calcaneum; cfa, fibular articulation on calcaneum; clg,
lateral groove on calcaneum; ct, calcaneal tuber.
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 23
developed lateral processes, as well as the “lateroventral de-
pression,” elements common to basal dinosauriforms (No-
vas 1989, Sereno and Arcucci 1994), and basal dinosaurs
such as Herrerasaurus (Novas 1989), Guaibasaurus (MCN
PV 2356), and Alwalkeria (Chatterjee 1987), but reduced
or absent in most members of the group.
Medial to the laterocaudal process, the central part of
the astragalus is thin, and its smooth distal surface probably
corresponds to a pathway for the M. gastroc. Cranially and
medially, however, the bone is more robust, and its
craniodistal surface bears three large articulation areas, sepa-
rated from each other by faint grooves. The medialmost of
them forms a flat area, which probably served for the articu-
lation of the metatarsal II. Proximally, the borders of the
mediocranial corner rises steeply, forming an acute and ar-
ticulation-free proximal surface. The articulation for the
medial distal tarsal lies medially to that of metatarsal II. It is
sub-circular in shape, and does not enter the cranial surface
of the astragalus. More laterally, the rounded articulation
facet for the medial portion of the lateral distal tarsal bounds
the calcaneal articulation medially on the laterocranial as-
tragalar process, and extends onto the cranial surface of the
bone. The robust medial margin of the astragalus bears
strong striations, which might correspond to the insertion
of joint ligaments to the medial surface of the tibia.
Calcaneum (Figs. 6G–H)—It is a proximodistally flat,
triradiate bone, with well-developed mediocranial and
mediocaudal processes, and a laterocaudally oriented tuber.
This format is similar to that of basal dinosauromorphs
(Novas 1989, Sereno and Arcucci 1994), and Herrerasaurus
(Novas 1989), but is primitive among dinosaurs in general,
the calcaneal projections of which are less marked (Huene
1926, Galton 1974, Cooper 1981, Welles 1984, Novas 1989;
Dryosaurus—HNN mounted skeleton; Liliensternus—MB.R.
2175, Scelidosaurus—BMNH 1111; Megapnosaurus
rhodesiensis—QVM QG174). The fibular articulation occu-
pies most of the proximal surface of the bone, except that
of its mediocaudal process. Its cranial part forms a shallow
obliquely elongated concavity, the curved shape of which
accompanies the laterocranial border of the bone. Caudally,
on the proximal surface of the tuber, there is a depressed
facet, which articulates with the slightly more distally ex-
panded laterocaudal corner of the distal fibula.
The medial border of the calcaneum articulates entirely
with the laterodistal part of the astragalar laterocranial pro-
cess. Its concave surface is composed of two inclined articu-
lar facets on the internal part of its medial processes, and a
vertical facet between them. In addition, the proximal sur-
face of its mediocaudal process articulates with the
craniocaudal surface of the astragalar laterocaudal process.
This articulation facet is broader at its lateral portion, where
it articulates with the tip of the astragalar laterocaudal pro-
cess. Medially, it extends along the process as a much thin-
ner articulation area. Cranial to it, a small knob-like element
fits between the lateral astragalar processes when articulated.
Unlike its proximal surface, the distal part of the calca-
neal tuber of Saturnalia bears no articular facets. It seems
to correspond to the insertion area for the M. peroneus
longus (Dilkes 2000), and forms, together with the caudal
surface of the bone, an articulation-free area on the flexor
aspect of the tarsus. The distal and cranial surfaces of the
mediocranial process, on the other hand, bear a clear ar-
ticular facet for the lateral part of the lateral distal tarsal.
Caudal to it, a small concavity is seen in the center of the
bone, which might represent the articulation of the
lateroproximal tip of the metatarsal V. An elongated groove
extends along the lateral and cranial surfaces of the bone,
which separates the tuber and the fibular articular area from
the distal articular facets for the lateral distal tarsal and meta-
tarsal V. A similar groove was described for Herrerasaurus
(Novas 1989), and “prosauropods” (Cooper 1981, Novas
1989), but seems to be absent from the highly modified
calcaneum of ornithischians and theropods. Its function is
unknown, and it might represent the pathway of a vascular
element, or even the separation between the calcaneum and
a incompletely fused distal tarsal.
Distal Tarsals (Figs. 7A–D)—Only two ossified distal tar-
sals are observed in Saturnalia (MCP 3845-PV). This same
count is known in basal dinosauromorphs (Novas 1996),
Herrerasaurus (Novas 1994), “prosauropods” (Huene
1926), most ornithischians (Galton 1974, Forster 1990),
and most theropods (Ostrom 1969, Welles 1984), and seems
to represent the primitive condition for dinosaurs. How-
ever, a third ossified distal tarsal, medial to these two ele-
ments, is known in some basal theropods (Rowe 1989,
Colbert 1989) and ornithischians (Santa Luca 1980).
The medial distal tarsal of Saturnalia (MCP 3845-PV)
is proximodistally flat, parallelogram-shaped, with rounded
corners. It articulates with the lateral distal tarsal via the
deeper caudal part of its lateral border, the cranial part of
which bears a socket-like articular facet. Its proximal surface
is slightly convex, and articulates with the astragalus. On
the opposite side, the bone has a concave distal surface,
which covers the entire proximal surface of the metatarsal
III. Its caudal end is deeper than the rest of the bone, and
expands distally to accommodate the caudoproximal corner
of that metatarsal. Most basal dinosaurs (Huene 1926, Novas
1996) have a medial distal tarsal of similar proportions, but
theropods (Padian 1986, Raath 1990) and ornithischians
(Galton 1974, Forster 1990), show a much larger element.
Also different from some theropods and ornithischians, the
medial distal tarsal of Saturnalia is not fused to metatarsal
III, and does not cover part of metatarsal II.
The lateral distal tarsal of Saturnalia is an elongated bone,
the long axis of which forms an angle of about 35˚ to the
transverse line of the metatarsals. As in basal
dinosauromorphs (Sereno and Arcucci 1993, Novas 1996),
it is markedly constricted in its midline, formed by strong
laterocaudal and medial concavities, which divide the bone
into a laterocranial portion and a mediocaudally pointed
24 PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
projection. The medial concavity occupies the entire medial
surface of the bone, and its cranial two thirds articulate with
the medial distal tarsal. The laterocaudal concavity, on the
other hand, is smaller, and forms a proximodistally-elon-
gated groove. This groove articulates with the mediocaudal
ridge of metatarsal V, while the surface cranial to it receives
the mediocranial ridge of that metatarsal. The laterocaudal
portion of the medial distal tarsal is subrectangular and flatter
than the mediocaudal projection. Its distal surface presents
a hemicylindrical articular facet, with a concave middle part
and expanded lateral and medial borders. This articulation
extends proximally, and forms the cranial border of the bone,
which articulates with the upturned cranioproximal corner
of the metatarsal IV. The lateral border of this articulation
is strong and scarred, possibly representing the insertion
area for a joint ligament to the proximal tarsus.
The proximal surface of the lateral distal tarsal is slightly
concave, and its lateral portion articulates with the calca-
neum. The medial part, on the other hand, forms a crescen-
tic facet, which extends along all the proximal surface of the
Fig. 7. Distal tarsals and pes of Saturnalia tupinquim. Scale bar = 2 cm. Right lateral distal tarsal of MCP 3944-PV in (A.) ventral
and (B.) medial aspects. Left medial and lateral distal tarsals of MCP 3945-PV in (C.) proximal and (D.) distal aspects. E. Right
metatarsals I, II, III, and V of MCP 3944-PV, and metatarsal IV of MCP 3946-PV in cranial aspect, with respective distal outline.
F. Composite reconstruction of the right foot of Saturnalia in flexor aspect, with proximal outline of the metatarsals. Abbrevia-
tions: mcp, mediocaudal process of lateral distal tarsal; mdta, medial distal tarsal articulation on lateral distal tarsal; msa, medial dis-
tal tarsal socket articulation; vc, ventral crest of lateral distal tarsal.
mediocaudal projection, and articulates with the base of the
laterocranial process of the astragalus. As in other dinosaurs
(Huene 1926, Padian 1986, Novas 1989), the mediocaudal
projection presents a slightly upturned caudal margin, which
caudally bounds its articulation with the astragalus.
Extending distally from its upturned margin, the
mediocaudal projection bears a large and smooth laterocaudal
border, which forms a somewhat continuous surface with
the caudodistal part of the astragalus. Distally, the
mediocaudal projection forms a strong crest, which is also
present in basal dinosauromorphs (Sereno and Arcucci 1993,
Novas 1996), but is reduced or absent in most other basal
dinosaurs (Huene 1926, Padian 1986, Novas 1994). Its lat-
eral tip articulates with the upturned caudoproximal corner
of metatarsal IV. From that point, a faint ridge expands
cranially, and articulates with the medial part of the proxi-
mal surface of metatarsal IV. It is uncertain, based on the
available specimens, whether this element also articulated
with the caudal-most part of metatarsal III.
The general morphology of the lateral distal tarsal of
Saturnalia is intermediate between those of basal
dinosauromorphs and other dinosaurs. As in Lagerpeton
(Sereno and Arcucci 1993) and Marasuchus (Novas 1996),
it is elongated and strongly constricted, but also somewhat
sub-triangular like those of Herrerasaurus (Novas 1994)
and “prosauropods” (Huene 1926, Cooper 1981). This sub-
triangular shape is given by the combined enlargement of
the cranial border of the bone and the shift in the orienta-
tion of its mediocaudal projection. In basal dinosauromorphs,
this projection is proximally convex, forming a caudally di-
rected articulation-free heel on the flexor aspect of the tar-
sus (Sereno and Arcucci 1994, Novas 1996). In Saturnalia
and other dinosaurs, on the other hand, it is proximally
concave, mediocaudally directed, and articulates cranially with
other elements of the tarsus. In particular, Saturnalia pre-
sents a long mediocaudal projection, if compared to those
of Herrerasaurus (Novas 1989) and “prosauropods” (Huene
1926). In theropods (Padian 1986, Raath 1990) and orni-
thischians (Galton 1974, Forster 1990), this projection is
even more reduced; a condition probably related to the in-
crease in size of the medial distal tarsal. The lateral margin
of the laterocranial portion is also more elongated in the
lateral distal tarsal of Saturnalia, “prosauropods” (Huene
1926), and Herrerasaurus (Novas 1989), than in that of
theropods (Padian 1986, Raath 1990) and ornithischians
(Galton 1974, Santa Luca 1980, Forster 1990) that, prob-
ably due to the reduction of the calcaneum, also reduced
the lateral expansion of this bone.
Metatarsals (Figs. 7E-F)—The pes of Saturnalia is com-
posed of five metatarsals, of which metatarsals I and V are
the shortest and narrowest. Accordingly, as suggested for
most dinosauromorphs, only the three central pedal digits
acted as weight-supporting structures. The three central
metatarsals of Saturnalia form a more slender unit (width
about 40% of its length) than those of most “prosauropods”
(Bonaparte 1972, Galton 1976; Thecodontosaurus—BMNH
P24) and Herrerasaurus (Novas 1994). This resembles the
condition in Guaibasaurus (Bonaparte et al. 1999), the
metatarsus of which is also not as gracile as that of basal
dinosauromorphs (Sereno and Arcucci 1993, 1994), basal
theropods (Huene 1934, Raath 1969) and basal ornithis-
chians (Thulborn 1972, Santa Luca 1980). In addition, the
maximum length of the metatarsus of Saturnalia is about
50% of its tibial length, a condition only significantly sur-
passed by Pisanosaurus (Bonaparte 1976) and coelophysoids
(Raath 1969, Colbert 1989) among basal dinosaurs.
The shafts of metatarsals I-IV of Saturnalia are “twisted,”
so that the long axis of their proximal end angles about 40˚
to the plantar surface of their distal articulations. As a re-
sult, there is an overlapping of the proximal part of these
elements, with the articulation facets for the medially adja-
cent element facing mediocranially and those for the lateral
elements facing laterocaudally. This arrangement was sug-
gested to be apomorphic for saurischians (Sereno 1999),
because it is present in Herrerasaurus (Novas 1994),
“prosauropods” (Thecodontosaurus—BMNH P24, Huene
1926, Cooper 1981), Guaibasaurus (MCN PV 2355), and
theropods (Huene 1934, Welles 1984), but absent in basal
ornithischians (Santa Luca 1980, 1984, Galton 1981, Forster
1990; Scelidosaurus—BMNH 1111). However, a similar
condition also seems to be present in basal dinosauromorphs
(Bonaparte 1975).
Metatarsal I of Saturnalia is about 60% of the length of
metatarsal II, and 55% of that of metatarsal III. This rela-
tive length is greater than that of basal dinosauromorphs
(Sereno and Arcucci 1994) and theropods (Raath 1969,
Welles 1984), but less than that of Herrerasaurus (Novas
1994), Guaibasaurus (MCN PV 2355), and most
“prosauropods” (Huene 1926, Galton 1976;
Thecodontosaurus—BMNH P24).
The proximal part of the bone is elliptical in outline,
lateromedially compressed, and craniocaudally expanded. It
is slightly concave medially, and laterally flat, where it ar-
ticulates with metatarsal II. Proximally, the bone reaches
the same level as metatarsals II-IV, and apparently articu-
lates with the tarsus. This articulation is, however, not very
extensive. It does not occupy the entire proximal surface of
the bone, and leaves no clear scar on the astragalus. A simi-
larly restricted proximal articulation is seen in Herrerasaurus
(Novas 1994), and seems to represent a derived condition
among dinosaurs, because those of basal dinosauromorphs
(Bonaparte 1975), and “prosauropods” (Thecodontosaurus—
BMNH P24; Riojasaurus—PVL skeleton no. 6;
Plateosaurus—SMNS 13200), are clearly larger. Among or-
nithischians, although some basal forms have a proximally
compressed metatarsal I (Thulborn 1972, Galton and Jensen
1973), a relatively broad tarsal articulation (Forster 1990;
Scelidosaurus—BMNH 1111) seems to represent the primi-
tive condition for the group (Sereno 1991a). The very de-
rived metatarsal I of theropods, on the other hand, is
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 25
proximally pinched and fails to reach the tarsus (Raath 1969,
Welles 1984).
Unlike Herrerasaurus (Novas 1994), no clear scars for
muscle attachments are seen on the shaft of metatarsal I of
Saturnalia. Its distal articulation is composed of two
condyles, which are separated by a groove on the plantar
surface of the bone. The lateral condyle is, however, much
larger in all dimensions, as is the respective pit for the col-
lateral ligaments. Accordingly, the further distal projection
of the medial condyle promotes the medial displacement of
the phalanges of the first digit. This condition is also seen
in Herrerasaurus (Novas 1994), Guaibasaurus (MCN PV
2355), “prosauropods” (Galton 1976; fig. 29), and
theropods (Currie and Zhao 1993), but apparently not in
ornithischians (Forster 1990; Lesothosaurus—BMNH
RUB17; Scelidosaurus—BMNH 1111). Instead, the latter
group presents a medially curved distal part of the metatar-
sal, which produces an analogous medial projection of the
digit (Santa Luca 1980, Sereno 1991a).
In Saturnalia, the proximal articulation of metatarsal II
is flat and parallelogram-shaped. Its cranial border is straight,
bearing marked lateral and medial corners, whereas the cau-
dal border is narrower and bears rounded corners. Its lateral
border is flat, for the reception of metatarsal III, while the
smaller medial articulation for metatarsal I is slightly con-
cave. This proximal outline resembles that of Herrerasaurus
(Novas 1994) and some ornithischians (Galton and Jensen
1973), but differs from that of “prosauropods,” which are
typically “hourglass-shaped” (Young 1941a, Cooper 1981),
as well as from that of theropods (Huene 1934, Welles 1984),
which are medially rounded because of reduction of the proxi-
mal part of metatarsal I. Furthermore, because the proxi-
mal articulation of metatarsal II of Saturnalia is subequal
to that of the metatarsal III, it is primitive in comparison to
that of some ornithischians (Galton and Jensen 1973, Galton
1981; Scelidosaurus—BMNH 1111) and “prosauropods”
(Huene, 1926, Cooper, 1981), in which the proximal meta-
tarsal II is much larger.
The proximal part of the shaft of metatarsal II matches
the shape of its proximal surface, and is flatter cranially and
more rounded caudally. A strong concavity is seen at the
proximal end of its dorsal surface, as well as in that of meta-
tarsal III (MCP 3845-PV), probably corresponding to in-
sertion areas for the M. ext. dig. long. (Dilkes 2000). More
distally, in the laterocranial corner of the shaft, another
muscle scar is seen. It faces a similar but stronger scar on
the mediocranial surface of metatarsal III (MCP 3845-PV),
and both are thought to represent the insertion of the M.
tib. cran. (Dilkes 2000). Distally, metatarsal II expands to
form an articulation with two condyles. These are subequal
in size, but the lateral condyle is slightly more distally ex-
tended. Like those of metatarsal I, the condyles are sepa-
rated by a groove on their plantar surface, and clear collateral
ligament pits are present. From the lateral pit, however, a
strong ridge extends proximally through the lateral part of
the plantar surface of the bone, which is probably related to
a ligamentous attachment.
Metatarsal III is the longest in the series. Similar to meta-
tarsal II, its proximal articulation is flatter cranially, but tapers
caudally in a rounded border. The distal articulation is also
like that of metatarsal II, but the condyles are equally pro-
jected distally. The muscle-related features of the bone were
discussed together with those of metatarsal II.
Metatarsal IV of Saturnalia is about 90% the length of
metatarsal III. This relative length is roughly the same in all
basal dinosaurs, but metatarsal IV is significantly longer in
basal dinosauromorphs (Sereno and Arcucci 1993, 1994).
In Saturnalia, its proximal articulation is cranially flat, but
proximally projected in its caudal portion. It is sub-triangu-
lar in outline, with marked mediocaudal and lateral projec-
tions. The mediocranial border of the mediocaudal projection
forms a flat articular surface for metatarsal III, while the
cranial border of the lateral projection forms a rugose free
edge on the extensor surface of the pes. Laterocaudally, the
proximal part of the bone bears a slightly concave surface,
which articulates with metatarsal V.
In most basal dinosaurs, the proximal surface of metatar-
sal IV is sub-triangular. However, its mediocaudal process is
reduced in ornithischians (Galton and Jensen 1973, Galton
1981; Lesothosaurus—BMNH RUB17; Scelidosaurus—
BMNH 1111), the proximal metatarsal IV of which have
the mediocaudal and mediocranial corners equally projected
medially. In this respect, Saturnalia resembles more
Herrerasaurus (Novas 1994), “prosauropods” (Huene 1926,
Cooper 1981), and basal theropods (Huene 1934, Welles
1984), in which the mediocaudal process is well developed.
Differing from these forms, the lateral projection of the
proximal metatarsal IV is truncated in theropods.
The proximal two thirds of the lateral surface of metatar-
sal IV articulates with metatarsal III. This portion of the
bone is flat and bears articulation scars. Distal to this, the
shaft is sub-circular in cross section, and laterally kinked as
in most basal dinosaurs. Further distally, a muscle scar is
seen on the lateral border of its plantar surface, which is
probably for the insertion of a branch of the M. gastroc.
Dilkes (2000) noted that metatarsals II and III of Maiasaura
bear similar scarred areas for the insertion of other branches
of the M. gastroc. These are, however, not visible in
Saturnalia. In addition, the distal articulation of metatarsal
IV of Saturnalia is both deeper than wide and asymmetri-
cal, with the medial condyle larger and more distally pro-
jected than the lateral.
Metatarsal V of Saturnalia is about 45% of the length of
metatarsal III. This proportion matches that of Guaibasaurus
(MCN PV 2355) and some basal “prosauropods” (Galton
1976; Thecodontosaurus—BMNH P24), but it is greater than
that of most ornithischians (Galton and Jensen 1973, Galton
1974; Scelidosaurus—BMNH 1111) and basal theropods
(Camp 1936, Raath 1969), and less than that of
Herrerasaurus (Novas 1994). In proximal aspect the meta-
26 PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
tarsal is “L-shaped,” bearing a long mediocaudal process
and marked lateral and mediocranial corners. This outline is
similar to that of Marasuchus (Bonaparte 1975),
Herrerasaurus (Novas 1994), and “prosauropods” (Huene
1926, Cooper 1981), although the mediocaudal process is
much more developed in the latter group. On the contrary,
in theropods (Welles 1984, Currie and Zhao 1993) and
ornithischians (Galton and Jensen 1973), the mediocaudal
process is absent, and the proximal outline of the bone is
rounded to sub-triangular.
Metatarsal V articulates proximally with the calcaneum,
via the margin between its lateral and mediocranial corners.
It is, therefore, placed further proximally in relation to the
other metatarsals. Both corners, together with the
mediocaudal process, extend as ridges down the shaft of
the bone, the proximal half of which is sub-triangular in
cross section. At that point, the medial articulation of the
bone is formed between its two medial ridges, which articu-
late with the lateral margin of the lateral distal tarsal, more
proximally, and to the laterocaudal surface of metatarsal IV,
more distally. The bone is, therefore, also slightly displaced
caudally in relation to the other metatarsals. Moreover, the
mediocaudal process projects distally as a plate-like articula-
tion area, which extends through half the length of the bone,
and fits into the laterocaudal concavity of the lateral distal
tarsal. More distally, it extends as a ridge along the entire
bone, forming, together with the lateral ridge, the borders
of the elliptical cross section of the distal half. The
mediocranial ridge, on the other hand, does not enter the
distal half of the metatarsal.
At its distal third the metatarsal is “twisted,” deflecting
the lateral ridge caudally and the medial ridge cranially. Its
distal end is a simple rounded articulation, elliptical in cross
section. It is surrounded by muscle scars, which extend fur-
ther onto the cranial surface of the bone and for most of its
lateral ridge. These scars could be related to the insertion of
either the M. peroneus brevis, or a branch of the M. gastroc.
(Dilkes 2000).
Pedal Digits (Fig.7F)—The pedal phalangeal formula of
Saturnalia is ?-3-4-5-0 (MCN PV 2355), and the presence
of two phalanges in its digit 1 can be suggested as a “level
1'” inference under a phylogenetic bracket approach (see
Witmer 1995, Hutchinson 2001a), based on comparison
with other basal dinosaurs. Digits 2–4 bear the number of
phalanges common to all basal dinosaurs, but the absence
of these elements in the fifth digit is curious. Pedal digit 5
of both the holotype and MCP 3845-PV were carefully ex-
tracted from the bearing rocks in order to recognize small
elements, which might represent vestigial phalanges. De-
spite the overall fine and articulated preservation, nothing
was recovered, and the lack of phalanges in pedal digit 5 is
not believed to represent a taphonomic artifact. Indeed,
because Herrerasaurus and most “prosauropods” have pha-
langes in that digit (Huene 1926, Galton 1976, Novas 1994),
this condition was suggested to be plesiomorphic for
saurischians (Gauthier 1986, Benton 1990). Yet, consider-
ing that Saturnalia, together with basal dinosauromorphs
(Sereno and Arcucci 1993, 1994), ornithischians (Galton
1974, Galton and Jensen 1973, Forster 1990), and theropods
(Raath 1969, Welles 1984, Colbert 1989), lack such ele-
ments, it is more parsimonious to consider that they were
ancestrally lost in dinosaurs, and reacquired in Herrerasaurus
and derived sauropodomorphs.
As in most basal dinosaurs (Huene 1926, Galton 1976,
Santa Luca 1980), the first phalanx is the longest in the
pedal digits of Saturnalia. In addition, caudal to their distal
articulation, the dorsal surfaces of most phalanges bear well-
developed pits for the extensor ligaments. Pits for the col-
lateral ligaments are also present on all the recovered
non-ungual phalanges, and are approximately of the same
depth on both sides of the bones. As reported for Sinraptor
(Currie and Zhao 1993), these pits are more dorsally placed
in the penultimate phalanges of the digits. Collateral scars
for the insertion of the collateral ligaments are also present
on the plantar-proximal corner of all recovered phalanges,
including the unguals. The plantar insertions of the M. flexor
digitorum brevis (Dilkes 2000) are, however, not visible in
the available material.
The unguals are sub-triangular in cross-section and slightly
curved, but elongated and non-raptorial. Their proximal
articulations are biconcave, and present a dorsoproximal
prong, the dorsal surface of which bears scars for the at-
tachment of a possibly combined M. extensor digitorum
longus and brevis. Clear scars for the M. flexor digitorum
longus (see Dilkes 2000) are seen on the proximal part of
the plantar surface of all unguals.
HIND LIMB FUNCTION
The hind limb and pelvic girdle anatomy of Saturnalia is
representative of a general construction shared by basal
dinosauriforms such as Marasuchus and Pseudolagosuchus,
basal dinosaurs, including Herrerasaurus, Staurikosaurus,
and Guaibasaurus, as well as basal sauropodomorphs, and
some basal theropods and ornithischians (Carrano 2000;
Hutchinson 2001b, c). Accordingly, various of the consid-
erations presented here regarding the hind limb function of
Saturnalia are believed to be applicable to most basal dino-
saurs, and to represent the locomotion model involved in
the origin and early diversification of the group.
As asserted by Gatesy (1990) for other dinosaurs, the
femur of Saturnalia was mainly vertically oriented, not show-
ing a bird-like more horizontal position. This is evident by
its hip and knee articulation, because the maximum angle
of femoral protraction is about 55˚ to the vertical, while
the epipodium did not reach a flexion of much more than
90˚. In addition, it is suggested that, despite the lack of a
fully open acetabulum and an inturned femoral head, the
hind limb of Saturnalia, like those of several other
dinosauromorphs bearing similar morphological features
(Arcucci 1989, Carrano 2000), was fully erect during loco-
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 27
motion. This inference is partially based on the very deep
acetabulum (see Bonaparte 1984, Parrish 1986) and the
presence of a marked supracetabular crest, which indicates
that the pelvis of Saturnalia was constructed to support a
strictly dorsally directed pressure derived from the weight
of the animal (Charig, 1972; fig. 8). Indeed, the flat proxi-
mal articulation of the femoral head reflects this arrange-
ment, fitting perfectly below the dorsal roof of the
acetabulum.
It is clear that the femoral articulation to the dorsal roof
of the acetabulum defines the axis for the fore-and-aft swing
of the limb. As discussed by Walker (1977; fig. 7), this is
different from the condition of various dinosaurs with both
a well-developed collum and caput femoris and a fully opened
acetabulum (Galton 1981, Norman 1986, Forster 1990,
Barsbold et al. 1990, Currie and Peng 1993). In these forms,
the axis of femoral rotation was at the center of the head,
rather than at its proximal margin. In addition, the femoral
abduction was severely restricted in these dinosaurs, because
of the close articulation of their hip joint. In Saturnalia, on
the contrary, a significant degree of abduction was possible,
which was indeed an integral part of the proposed hind
limb movement. However, the hip-joint construction of
Saturnalia did not allow a full sprawling position to be
adopted. Accordingly, the complete resting position of the
animal would most probably have involved lying on the lat-
eral surface of the body.
Before further analyzing the limb movements in
Saturnalia, it is necessary to examine the structure of its
knee and ankle joints. The knee mainly operated with a simple
fore-and-aft movement, as few possibilities of rotation and/
or lateral movements are present. Yet, the main axis of the
proximal surface of the tibia forms an angle of about 60° to
the femoral intercondylar line. Accordingly, its cranial part
is laterally displaced, and the cnemial crest protrudes crani-
ally at the level of the lateral femoral condyle. Because of a
slight “twisting” along the tibial shaft, however, the trans-
verse axis of the distal epipodium is almost parallel to the
femoral intercondylar line. In addition, the articular surface
of the distal femur and that of the proximal tibia are in-
clined. The medial femoral condyle is more distally pro-
jected than the lateral, while that of the tibia projects more
proximally. As a result, the long axis of the epipodium of
Saturnalia is inclined (about 20°) in relation to that of the
femur, and its distal part shows a markedly lateral displace-
ment.
As in other dinosaurs, the ankle-joint movements of
Saturnalia were mainly related to those between the proxi-
mal tarsals and the distal tarsals-metatarsals. As with the
knee, the main ankle movement was simply that of a fore-
and-aft flexion-extension, although some rotation and lat-
eral movement seems to have also taken place. Interestingly
enough, the axis of the main fore-and-aft movement does
not seem to have been parallel to a sagittal section through
the epipodium. Instead, in its preferential angle of articula-
tion, the metatarsus was slightly inturned, so that its cranial
surface was more medially directed than that of the
epipodium.
The step cycle of Saturnalia
As a starting point for the discussion of the step cycle of
Saturnalia, a resting position for its hind limb is defined,
with the femur conformably set into the acetabulum. Ac-
cordingly, the proximal surface of the femoral head sits at
the dorsal roof of the acetabulum, with its longitudinal
groove (fossa trochanteris) fitting into the corresponding
ridge on the acetabular roof, and the articulation between
the antitrochanter and the trochanteric fossa at its maximal.
In this position, the femoral shaft bows both laterally and
cranially, so that the flexor surface of the knee is inturned,
forming an angle of about 45° to the sagittal line. This
implies that, when articulated, the epipodium would extend
both medially and caudally, with the extensor surface of the
ankle facing caudomedially. In this arrangement, the pes
would naturally extend craniolaterally. However, because of
its inwards rotation, it extends almost cranially. As a result,
the propodium plus epipodium form a craniolaterally-
inflected arch, whereas the epipodium plus metapodium
inflect caudomedially.
It is unclear whether Saturnalia would have abducted
the hind limb during motionless periods or not, as the hip-
joint articulation would allow the femoral head to form an
angle of some 35° to the vertical (see Van Heerden 1979).
Yet, the advantage of a more vertical limb posture is obvi-
ous (Charig 1972), and it was most probably adopted by a
“quietly-standing” Saturnalia. Such an “improved” posi-
tion seems to have been possible despite the fact that the
distinct functional parts of its hind limb (femur, tibiotarsus,
and pes) do not align in a parasagittal plane. This is because
of the relative slope of each of those parts, with the hind
limb experiencing a perfect counterbalance of the medially
and laterally directed transverse forces. This condition, rather
than the parasagittal alignment of each limb part, is the
fundamental characteristic of a fully erect gait (Charig 1972;
p.132). Accordingly, during a preferential “fore-and-aft”
movement, the long axis of the leg of Saturnalia would
travel in a parasagittal plane, although that of each of its
parts would not.
During the propulsive phase (Fig. 8), the femur of
Saturnalia was retracted, while its knee and ankle were ex-
tended, and the metatarsal-phalangeal joints flexed. A large
array of muscles appears to have helped in the retraction of
the femur, including: M. caudofem. brevis, M. ischiofem.,
M. add., and the caudal part of the M. obt. (= M. pub.
isch. fem. ext. part 3). As suggested by Gatesy (1990) for
other non-avian dinosaurs, however, the M. caudofem. long.
is believed to represent the main femoral retractor of
Saturnalia. Galton (1969, see also Romer 1923b) proposed
that the forward pull given by the contraction of the M.
iliotroc. also promoted femoral retraction. However, as dis-
28 PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
Fig. 8. Pelvic girdle, and partial hindlimb of the holotype of Saturnalia tupiniquim (MCP-3844PV) articulated as in (A.) the final
stages of the propulsive phase (depicting main muscles acting on the femoral retraction, knee and ankle extension, and flexion of
the metatarsal-phalangeal joints) and as in (B.) the final stages of the protractive phase (depicting main muscles acting on the femo-
ral protraction, leg elevation, knee and ankle flexion, and extension of the metatarsal-phalangeal joints). Scale bar = 10 cm. Abbre-
viations: M. add., M. adductor; M. ambiens, M. ambiens; M. caudofem. brevis, M. caudofemoralis brevis; M. caudofem. long.,
M. caudofemoralis longus; M. ext. dig. long., M. extensor digitorum longus; M. fem. tib. intermed., M. femorotibialis interme-
dius; M. fem. tib. lat., M. femorotibialis lateralis; M. flex. dig. long., M. flexor digitorum longus; M. flex. tib., M. flexor tibiale;
M. gastroc., M. gastrocnemius; M. iliofem. cran., M. iliofemoralis cranialis; M. iliofib., M. iliofibularis; M. iliotib. cran., M.
iliotibialis cranialis; M. iliotib. lat., M. iliotibialis lateralis; M. ischiofem., M. ischiofemoralis; M. obt., M. obturatorius; M. pub.
isch. fem. int. med., M. puboischiofemoralis internus pars medialis; M. tib. cran., M. tibialis cranialis.
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 29
cussed by Walker (1977; fig. 7), since the femur of Saturnalia
was mainly held against the upper part of the acetabulum,
the forward pull of any muscle placed distal to that articula-
tion (as is the case of the M. iliotroc.) played no role in
femoral retraction (see also Coombs 1979), and was not
significant in promoting the forward stroke of the leg. In
addition, knee extension in Saturnalia seems to have been
mainly promoted by the contraction of the M. ambiens, M.
iliotibiale, and M. femorotibialis lateralis, and intermedius,
all of which probably inserted on the cnemial crest via the
patellar ligament. The M. gastroc., on the other hand, was
probably the main ankle extensor, whereas the flexion of
the pedal articulations was promoted by the M. flexor
digitori.
Because the insertion point of the M. caudofem. long. is
on the medial surface of the femur, the contraction of this
muscle, while promoting the retraction of that bone, also
medially rotated the hind limb, so that the surface that was
cranially directed would be medially directed. In this con-
text, the primary action of the M. iliotroc. is clarified, since
its contraction was surely also related to femoral medial ro-
tation. Accordingly, this medial rotation lead to a complete
change in the position of the limb, in relation to its resting
position. At maximal retraction, the insertion point of the
M. caudofem. long. would be shifted caudally to face its
origin area, which is on the lateral surface of the caudal
vertebrae. As a result, the long axis of the femoral head
would then be perpendicular to the sagittal line, and the
shaft of the bone bowed cranially and medially. Moreover,
the caudal surface of the epipodium would face
laterocaudally, the propodium plus epipodium forming a
mediocranial arch, and the epipodium plus metapodium
arching laterocaudally. As a result, the distal part would be
more laterally placed than the proximal part, the knee joint
being placed slightly medially to the acetabulum, and the
ankle slightly lateral to it. This arrangement would lead to a
medial to craniomedial orientation of the extensor surface
of the inturned pes, making evident the importance of some
rotational movement of the ankle joint to turn the foot out-
ward, in order for a more cranial orientation to be achieved.
In this context, the overlapping pattern of the metatarsals
of Saturnalia and other basal dinosaurs is also of impor-
tance. In these forms, distal parts of the more medial meta-
tarsals are displaced cranially, so that even were the cranial
surface of the proximal part of the metatarsus to face more
medially, the flexor surface of the pes itself would be more
cranially directed.
The protractive phase (Fig. 8) is believed to resemble
that of other tetrapods (Brinkman 1980) with an initial
flexion of knee and ankle joints, and the lift and forward
movement of the limb, followed by its lowering and the
extension of those joints. The scarring associated with the
insertion of the M. pub. isch. fem. int. med. (= avian M.
iliofemoralis internus) and M. pub. isch. fem. ext. (parts 1
and 2) indicate that these were probably the main femoral
protractors, and responsible for the forward movement of
the limb. In dinosaurs with a large iliac preacetabular ala,
the M. iliofem. cran. seems also to represent an important
femoral protractor (Russell 1972, Carrano 2000; see also
Coombs 1979). Similarly, in forms such as ornithopods
(Walker 1977, Norman 1986) with well-developed collum
and caput femoris and fully opened acetabulum, the con-
traction of the M. iliofem. cran. seems to have promoted
some femoral protraction. However, in the case of
Saturnalia, and other basal dinosaurs with a short iliac
preacetabular ala and a less derived hip joint, the action of
the M. iliofem. cran. in femoral protraction was much less
significant (see Carrano 2000). In addition, some knee ex-
tensors such as the M. iliotib. cran. probably helped the
final stages of the femoral protraction, by promoting the
elevation of the bone. The flexion of the knee and ankle
were, on the other hand, mainly promoted by the contrac-
tion of M. iliofib. and M. flexor tibiale, and M. tib. cran.,
respectively. Moreover, the forward travel of the leg was
also accompanied by the extension of the pedal articula-
tions promoted mainly by the M. extensor digitori.
As discussed by Charig (1972) for the crocodile, the M.
iliofem. cran. of Saturnalia seems to have acted mainly in a
transverse plane, having been primarily involved in femoral
abduction. Yet, because of the cranial position of the “lesser
trochanter,” the contraction of that muscle would also have
had secondary importance in femoral protraction. Indeed,
this conjoined action was probably important in the final
stages of femoral protraction, when the abduction promoted
by the M. iliofem. cran. would alleviate the “femur-knock-
ing-on-the-pubis” problem (Charig 1972), allowing that
bone to pass forward of the level of the pubis, and reach its
maximum protraction of about 60° to the vertical plane. As
in birds (Vanden Berge 1975), the M. iliofem. ext., on the
other hand, was probably a postural muscle related to the
rotation of the femur on the acetabulum.
During the initial stages of the protractive phase, the
hind limb was also laterally rotated, coming back from the
maximum medial rotation achieved at the end of its retrac-
tion. This is because the main muscles responsible for femoral
protraction were inserted on the medial surface of the bone,
and their contraction turned the cranial surface of the bone
laterally. Due to this lateral rotation, the knee performed an
inward arching movement during protraction, while the foot
was displaced laterally. At maximum protraction, the long
axis of the femoral head would approach a parasagittal plane.
This is just slightly more medially rotated than that of the
resting position, and the foot would touch the ground with
its extensor surface cranially directed.
Osteological evidence for these hind-limb movements is
scarce. Yet, a few signs of some of the particular phases are
observed in the skeleton of Saturnalia. In particular, a very
distinct and rugose texture is seen at the ventral portion of
its iliac medial acetabular wall, cranial to the antitrochanter.
This is a topological correlate of the portion of the acetabu-
30 PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
lum that is perforated in several basal dinosaurs, including
most “prosauropods” (Huene 1926, Galton 1984), basal
theropods (Huene 1934, Welles 1984, Raath 1990), and
basal ornithischians (Thulborn 1972, Santa Luca 1984), and
it is believed to represent the part of the medial acetabular
surface in which the medial tip of the femoral head swung
during its lateral-medial rotation, also rotating due to its
protraction-retraction. Accordingly, at the beginning of the
propulsive phase, while the femoral head was almost aligned
to the parasagittal plane, its medial tip articulated with the
cranial portion of the rugose area. During retraction/me-
dial rotation, this part of the head would move backwards
along the rugose area, to the cranial margin of the
antitrochanter, where the medial “tip” of the perpendicu-
larly oriented head would articulate with the caudal part of
the rugose area.
In addition, the shape of the proximal surface of the fe-
mur also provides some hints regarding its movements in
the acetabulum. Its articular area is more distally expanded
in its cranial portion, especially between the laterocranial
ridge (“r” in Padian 1986; fig. 5.4) and the mediocranial
tip of the head. This area is thought to face the cranial
surface of the acetabulum during the resting period, but to
articulate to its “roof” at maximum protraction. In this
position, only the mediocranial part of the head was in con-
tact with the acetabulum, with the proximal extension of
the laterocranial ridge articulating with the top of the ac-
etabular roof, just below the central part of the supracetabular
ridge.
According to the model proposed above, it is clear that
movements at the hip joint of Saturnalia were not simply a
rotation in the parasagittal plane as suggested for various
dinosaurs (Wade 1989, Padian and Olsen 1989, Carrano
2000). Instead, it is more likely that, similar to the proposi-
tion of Christian et al. (1996; see also Van Heerden 1979)
for Plateosaurus, lateral movements of the hind limb played
an important role in the locomotion of Saturnalia.
Ichnological evidence and final considerations
Some of the inferences regarding the limb movements of
Saturnalia listed above are interestingly supported by stud-
ies of dinosaur footprints in general. The positive—inwards—
rotation of the pes, for instance, is a well-known feature of
various dinosaur trackways, especially those of bipedal forms
(Padian and Olsen 1989, Thulborn 1990). This indicates
that the foot was inturned during the kick-off phase (see
Thulborn and Wade 1989). Indeed, this phase corresponds
to the final part of hind-limb retraction in the step cycle of
a dinosaur. In the case of Saturnalia, as already discussed,
because of the medial rotation associated with the retrac-
tion of the leg, this phase is characterized by a marked
inturning of the pes.
Thulborn (1989) observed that, in semibipedal basal or-
nithischians (see Ellenberger 1974, Thulborn 1990; p. 187,
fig. 9.14), locomotion tended to be faster when the animals
shifted from a quadrupedal to a bipedal gait. Accordingly,
as is typical of faster locomotion, the pace angulation and
the stride length increased, while the imprints of the more
proximal parts of the pes became less marked. More impor-
tantly, the positive rotation of the pes was also more pro-
nounced. Again, this change can be explained based on the
functional analysis of the hind limb of Saturnalia. Indeed,
as proposed by various authors (Alexander 1976, Demathieu
1984), an increase in speed is partially related to a higher
gait angle. As discussed above, the more retracted the fe-
mur of Saturnalia is, the more medially rotated it is. There-
fore, during the kick-off phase, the pes is expected to have
been more inturned in a faster than in a slower pace. This
condition is highlighted by the fact that, during fast loco-
motion, the durations of footfalls are reduced (Brown and
Yalden 1973). Accordingly, the touch-down and weight-
bearing phases (Thulborn and Wade 1989) are abbreviated,
whereas the kick-off phase becomes more prominent. In-
deed, it is exactly during the kick-off phase that the leg of
Saturnalia was more medially rotated, and its foot more
inturned.
During a slower pace, because of the smaller gait angle
involved, the protraction and retraction of the leg in
Saturnalia were reduced. Accordingly, the inwards rotation
of its pes was less marked. Indeed, in most quadrupedal
trackways—including those attributed to “prosauropods”
(Thulborn 1990; fig. 6.22)—the pes usually shows a nega-
tive (outwards) rotation. The pes of Saturnalia would have
shown an equivalent position during the final phases of limb
protraction, and initial phases of its retraction, when the
femur was maximally rotated laterally. Indeed, during a slower
pace, the fore-and-aft movement of the leg would have been
much more restricted, and the inturning of the foot much
less marked.
Thulborn (1990) related footprint rotation to the differ-
ent gaits of dinosaurs, either quadrupedal or bipedal. How-
ever, it seems that, at least when it comes to basal dinosaurs,
the footprint rotation might also have been related to the
higher gait angle of fast locomotion. Further ichnological
evidence of the proposed locomotory strategy of Saturnalia
comes from the craniolaterally extended scrape-marks com-
monly found in some dinosaur footprints—including some
possibly related to a “prosauropod” walking bipedally
(Thulborn 1990; p. 261, fig. 6.23). These have previously
been related to an arc-like outwards movement of the limb
(Thulborn 1990). These marks might instead be related to
the outwards rotation of the foot during the initial phase of
leg protraction, as in the reconstructed gait of Saturnalia.
Basal dinosauromorphs, as well as basal ornithischians
and theropods, were all primarily or obligatorily bipeds
(Padian 1997), while all sauropods were quadrupeds (McIn-
tosh 1990). The gaits of “prosauropods” are, however, more
controversial. Very large forms, such as the melanorosaurids,
are usually accepted as quadrupeds (Weishampel and
Westphal 1986, Galton 1990, Upchurch 1997). Typical
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 31
“prosauropods,” on the other hand, have alternatively been
considered fully bipedal (Cooper 1981) or obligately qua-
drupedal (Van Heerden 1979, Wellnhofer 1994). More com-
monly, these forms are presented as having possessed an
intermediate mode of locomotion (Galton 1976, 1990,
Galton and Cluver 1976, Upchurch 1997). It is evident,
therefore, that regardless of the exact moment at which it
occurred, a trend towards a locomotion more dependent
on the forelimb action was present during the early evolu-
tion of sauropodomorphs. Accordingly, the study of the
locomotion of basal members of the group, such as
Saturnalia and Thecodontosaurus, is relevant to understand-
ing this transition.
Several skeletal features of Saturnalia, such as its long
distal limb elements and short muscle lever arms in the hind
limb, indicate that it was more cursorial than any typical
sauropodomorph (Coombs 1978, Carrano 1999), with the
possible exception of Thecodontosaurus (see Benton et al.
2000). In addition, Saturnalia has the hind limb elonga-
tion necessary to achieve bipedal locomotion (see Christian
et al. 1994). As discussed by those authors, modern reptiles
switch to a bipedal gait when the advantages of faster loco-
motion compensate for higher instability. Yet, as already dis-
cussed, Saturnalia possesses an “improved” hind limb
construction in comparison to that of “sprawling” forms
such as lizards (Charig 1972). This would probably alleviate
the problems related to instability. It is very likely, there-
fore, that Saturnalia adopted a bipedal posture more often
than modern lizards do, most probably for fast locomotion.
Given that Saturnalia was capable of bipedal locomo-
tion, would it have been an obligatory biped, or would it
sometimes have walked on all fours? It has often been pro-
posed (Galton 1990, Upchurch 1997) that Thecodontosaurus,
and “thecodontosaurids,” were bipeds. Indeed, Galton
(1990) considered Thecodontosaurus a full biped, because
its trunk to hind limb ratio is equivalent to that of other
bipedal dinosaurs. Yet, most of the relevant anatomical data
available for Thecodontosaurus is misleading, and figures on
the trunk to hind limb proportion are highly uncertain. The
only nearly complete skeleton of the taxon (Kermack 1984)
lacks its trunk series (Benton et al. 2000), and the cranial
part of that specimen (skull, cervical vertebrae, and partial
humerus) may not belong with the caudal part (most pelvic
girdle, hind limb, and caudal vertebrae). Kermack (1984)
believed that this was the case and scaled the caudal part,
producing the reconstruction used by Galton (1990) in sup-
port of his hypothesis of a bipedal Thecodontosaurus.
It is possible to calculate a confident estimate of the trunk
to hind limb ratio of Saturnalia, and this is of the order of
1.0 to 1.1. This ratio is less than that of obligatorily bipedal
dinosaurs, but higher than that of typical quadrupeds (see
Galton 1970). In fact, it is also higher than that of most
“prosauropods,” a possible exception being Massospondylus
(Galton 1976, Cooper 1981). In fact, the gait of Saturnalia
was probably somewhere between that of a fully bipedal
dinosaur like Coelophysis and that of forms such as
Plateosaurus, which were mainly quadrupedal, becoming
bipedal only at high speeds (see Christian and Preuschoft
1996). Saturnalia would have used a bipedal gait more of-
ten than other “prosauropods,” probably to escape from
predators, but also for active hunting of small prey, when
relatively fast locomotion was advantageous. However, it
was probably not an obligatory biped. During a slower pace—
perhaps while moving through areas with vegetation that
could be eaten (Upchurch 1997)—it is likely that Saturnalia
walked on all fours, a position possibly also adopted during
resting periods.
ACKNOWLEDGMENTS
This work is part of my Ph.D. thesis, supervised by Dr.
Mike Benton at the University of Bristol, UK. It was par-
tially supported by an Overseas Student Award from the
CVCPUUK, to which I express my gratefulness. I am in-
debted to Drs. Jeter Bertoleti and Cláudia Malabarba
(PUCRS, Porto Alegre) and to the DNPM-RS for allowing
me to study the specimens under their responsibility, and to
the people that helped in the field trips that unearthed
Saturnalia: Martha Richter, Fernando Abdala, José
Bonaparte, Jorje Ferigo, and Cláudia Malabarba. Drs. Adam
Yates, Peter Galton and Mike Benton provided many impor-
tant comments that significantly improved the paper. I thank
the following for permission to examine specimens and help
during this work: Judith Babot and Jaime Powell (Fundacíon
Miguel Lillo, Tucumán), José Bonaparte (Museo Argentino
de Ciencias Naturales, Buenos Aires), Sandra Chapman and
Angela Millner (Natural History Museum, London), Jorje
Ferigolo and Ana Maria Ribeiro (Fundação Zoobotânica
do Rio Grande do Sul, Porto Alegre), Alex Kellner (Museu
Nacional, Rio de Janeiro), Ricardo Martinez (Universidad
Nacional de San Juan), Bruce Rubidge and Mike Raath
(Bernard Price Institute for Paleontological Research,
Johanesburg), Rainer Schoch (Instutut für Geologie und
Paläontologie, Tübingen), Dave Unwin (Humboldt Mu-
seum für Naturkunde, Berlin) and Rupert Wild (Staatlisches
Museum für Naturkunde, Stuttgart). This work is dedicated
to Dr. Martha Richter, for everything that goes without
saying.
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LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 37
Table 1. Measurements (mm) of the sacral vertebrae of the holotype of Saturnalia tupiniquim (MCP 3844-PV).
Table 2. Measurements (mm) of the pelvic girdle of Saturnalia tupiniquim. Abbreviation: () = estimated.
MCP 3844-PV MCP 3845-PV
Right Left Left
Ilium
Maximum depth — 49 60
Maximum length — (90) 83
Depth of the acetabulum — 25 —
Maximum length of the acetabulum — 37 —
Width of the supracetabular crest — 14 —
Length of the preacetabular ala — — 7
Length of the postacetabular ala — 45 60
Maximum width of the postacetabular ala —
Inter-embayment length — 40 —
Length of the pubic peduncle — 24 27
Pubis
Maximum length 121 127 (102)
Distal extension of the obturator plate 42 — —
Proximal depth 41 35 —
Distal depth 11 10 —
Ischium
Maximum length 132 121 (96)
Length of the antitrochanter — 22 —
Distal depth — 22 —
Distal extension of the obturator plate 32 33 —
APPENDIX
First sacral vertebra
Length of the centrum 23
Cranial width of the centrum 22
Cranial height of the centrum 14
Cranial width of the neural canal 8
Cranial height of the neural canal 4
Length of the neural spine 25
Length of the right transverse process 22
Height of the left rib 21
Second sacral vertebra
Length of the centrum 25
Caudal width of the centrum 19
Caudal height of the centrum 19
Length of the neural spine 19
Length of the right transverse process 20
Height of the left rib 11
Third sacral/first caudal vertebra
Length of the centrum 26
Cranial width of the centrum 17
Cranial height of the centrum 19
Caudal width of the centrum 18
Caudal height of the centrum 23
38 PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003
Table 3. Measurements (mm) of the propodium and epipodium of Saturnalia tupiniquim. Abbreviation: () = estimated.
MCP 3844-PV MCP 3845-PV
Right Left Right Left
Femur
Maximum length 157 152 — 156
Maximum width of the head 36 35 — —
Maximum width middle of the shaft 17 17 16 17
Width of medullary canal in the middle of the shaft — 8 10 12
Lateromedial width of the distal end 35 34 28 29
Tibia
Maximum length — 158 — 155
Craniocaudal width of the proximal end — 41 — —
Lateromedial width of the proximal end — 27 — 21
Maximum width at middle of the shaft — 12 14 12
Width of medullary canal at the middle of the shaft — — 7 6
Maximum craniocaudal width of the distal end — 21 — 19
Maximum lateromedial width of the distal end — 18 — 20
Fibula
Maximum length — 154 — 154
Maximum proximal width — 27 — 24
Maximum width at middle of the shaft — 10 9 8
Width of medullary canal at the middle of the shaft — 3 — 4
Maximum caudal width — 19 — 19
Astragalus
Craniocaudal length on lateral border — 16 15 —
Craniocaudal length on medial border — 20 20 —
Width at caudal border — 24 15 —
MCP 3844-PV
Maximum craniocaudal width of the distal end of the right tibia 15
Maximum lateromedial width of the distal end of the right tibia 21
Maximum width of the distal fibula 18
LANGER—PELVIC AND HINDLIMB ANATOMY OF SATURNALIA 39
Table 5. Measurements (mm) of the phalanges of Saturnalia
tupiniquim (MCP 3845-PV).
Length of ungual of digit II 22
Length of phalanx 1 of digit III 24
Length of phalanx 2 of digit III 19
Length of phalanx 3 of digit III 15
Length of ungual phalanx of digit III (20)
Length of phalanx 1 of digit IV 14
Length of phalanx 2 of digit IV 10
Length of phalanx 3 of digit IV 9
Length of phalanx 4 of digit IV 11
Length of ungual phalanx of digit IV (17)
Table 4. Measurements (mm) of the metatarsals of Saturnalia tupiniquim.
MCP 3844-PV MCP 3845-PV MCP 3846-PV
Right Right Left Right
Length of metatarsal I 46 — — —
Proximal depth of metatarsal I 10 — 8- —
Distal depth of metatarsal I 8 — — —
Distal width of metatarsal I 9 — — —
Length of metatarsal II 70 — — —
Proximal depth of metatarsal II 17 — 15 —
Distal depth of metatarsal II 10 — — —
Distal width of metatarsal II 12 11 — —
Length of metatarsal III 84 — — —
Proximal depth of metatarsal III 20 — 15 —
Distal depth of metatarsal III 10 — — —
Distal width of metatarsal III 14 — — —
Length of metatarsal IV 74 — — 73
Proximal depth of metatarsal VI (21) — 15 16
Distal depth of metatarsal VI 11 10 — 12
Distal width of metatarsal VI 10 9 — 8
Length of metatarsal V 38 40 — —
40 PALEOBIOS, VOL. 23, NUMBER 2, JULY 2003