Khosla, A. and Lucas, S.G., eds., 2016, Cretaceous Period: Biotic Diversity and Biogeography. New Mexico Museum of Natural History and Science Bulletin 71.
NEW THEROPOD FAUNA FROM THE UPPER CRETACEOUS (HUINCUL FORMATION)
OF NORTHWESTERN PATAGONIA, ARGENTINA
MATÍAS J. MOTTA1, ALEXIS M. ARANCIAGA ROLANDO1, SEBASTIÁN ROZADILLA1, FEDERICO E. AGNOLÍN1, 2,
NICOLÁS R. CHIMENTO1, FEDERICO BRISSÓN EGLI1, 3 AND FERNANDO E. NOVAS1, 3
1Laboratorio de Anatomía Comparada y Evolución de los Vertebrados, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Av.
Ángel Gallardo 470, C1405DJR Buenos Aires, Argentina; 2Fundación de Historia Natural “Félix de Azara”, Universidad Maimónides, V.
Virasoro 732, 1405 Buenos Aires, Argentina; 3CONICET, Consejo Nacional de Investigaciones Cientícas y Técnicas, Argentina
Abstract—The present contribution describes theropod remains coming from the Huincul Formation (Neuquén
Group; Cenomanian-Turonian; Upper Cretaceous) at a single locality located in northwestern Río Negro
province, Patagonia, Argentina. This theropod association is composed of abelisauroids, two different-sized
carcharodontosaurid allosauroids, a coelurosaur of uncertain relationships, a megaraptoran tyrannosauroid, and a
possible unenlagiid paravian. Two new theropod genera and species are here described. The new carcharodontosaurid
is based on an isolated postorbital bone bearing a unique prominence above the orbital brow. The new megaraptoran
of uncertain afnities is described on the basis of a partially articulated tail and sacral vertebra. A new taxon is
characterized by having notably elongate and highly pneumatic sacral and caudal vertebrae. It shows a large
number of similarities with the African taxa Deltadromeus and Baharisaurus. These genera probably constitute
a still poorly known clade of megaraptoran tyrannosauroids different from the Megaraptoridae. These ndings
support that Patagonia is a key place for understanding theropod evolution in Gondwana.
Within South America, Argentina possess the richest record of
theropod dinosaurs for the Late Cretaceous, and this is especially true for
Patagonia (Novas et al., 2013). Here the group is represented by several
clades, such as Noasauridae, Abelisauridae, Carcharodontosauridae,
Megaraptoridae, Alvarezauridae, Unenlagiidae as well as basal
coelurosaurs (Novas, 2011; Novas et al., 2013). One of the better
known Upper Cretaceous formations, for its large and varied record
of vertebrate remains, is the Huincul Formation (Neuquén Group;
Cenomanian-Turonian; Garrido, 2010), which documents a high
number of shes, dipnoans, turtles, crocodiles and dinosaurs (Leanza
et al., 2004; Garrido, 2010). Among the most outstanding members
of the latter clade are the titanosaur Argentinosaurus huinculensis
(Bonaparte and Coria, 1993), the rebbachisaurid Cathartesaura
anaerobica (Gallina and Apesteguía, 2005), the carcharodontosaurid
Mapusaurus roseae (Coria and Curie, 2006) and the abelisaurids
Skorpiovenator bustingorryi and Ilokelesia aguadagrandensis (Canale
et al., 2008; Coria and Salgado, 1998). These dinosaurs are part of a
faunal composition that is characteristic of the lower part of the Upper
Cretaceous in western Gondwana (Novas, 2011; Novas et al., 2013).
This assemblage is different from the uppermost Cretaceous, where
large derived abelisaurids and megaraptorids were the apex predators,
and the gigantic titanosaurs were replaced by the smaller saltasaurine
sauropods and ornithischians, such as hadrosaurids and ankylosaurids
(Leanza et al., 2004; Novas et al., 2011).
In the present contribution, we report new theropod remains
from the Violante farm fossiliferous locality (Río Negro province,
Patagonia), where the outcrops of the Huincul Formation are exposed.
This association shows different theropod clades, including small-sized
abelisauroids, large-sized carcharondontosaurids, megaraptoran and
LOCALITY AND HORIZON
The Violante farm (39°23’52.37”S, 68°37’4.30”W) is located
southeast of the Ezequiel Ramos-Mexía lake, at the northwest of
Río Negro province, Argentina (Fig. 1). Here the Huincul Formation
(middle Cenomanian-early Turonian; Garrido, 2010) is widely
exposed. This formation is composed of yellowish and greenish ne- to
medium-grained sandstones that sometimes can be tuffaceous (Leanza
et al., 2004). Within the study area, this stratigraphic unit has been
characterized by Garrido (2000, 2010) as representing a high sinuosity
uvial system that gradually lowers its sinuosity. Overall, weather
conditions were warm with a strong seasonal regimen (Garrido, 2000,
2010; Sanchez et al., 2008).
As mentioned above, the fossil content is highly diverse. Silicied
trunks of cycads and conifers have been reported (Leguizamón and
Garrido, 2000), the latter group represented by the Araucariaceae and
Cupressaceae (Martinez, 2008, 2009b), and some basal angiosperms
(i.e., Magnoliophyta; Martinez, 2009a, b). Vertebrate remains consist
of turtles, crocodiles and sh teeth (Garrido, 2000, 2010). Among the
latter, remains of the dipnoan Ameghinoceratodus iheringi (Apesteguía
et al., 2007) have been described. The dinosaur record is extensive,
including large-sized theropods such as Mapusaurus rosae (Coria
and Currie, 2006), Ilokelesia aguadagrandensis (Coria and Salgado,
1998) and Skorpiovenator bustingorryi (Canale et al., 2008). Among
sauropods there are titanosaurids and rebbachisaurids (Bonaparte and
Coria, 1993; Gallina and Apesteguía, 2005).
Institutional Abbreviations: MPCA PV. Colección Paleontología
de Vertebrados, Museo Provincial “Carlos Ameghino”, Rio Negro,
DINOSAURIA Owen, 1842
SAURISCHIA Seeley, 1888
THEROPODA Marsh, 1881
ABELISAUROIDEA Bonaparte and Novas, 1985
Gen. et sp. indet. 1
Referred material: MPCA-Pv 800, distal end of a left quadrate
Description and comparisons: The preserved portion of the
quadrate is transversely wide, with the medial condyle projected
slightly more ventrally than the lateral one, a condition present in some
abelisauroids, such as Abelisaurus comahuensis, Carnotaurus sastrei
and Masiakasaurus knoperi (Bonaparte and Novas, 1985, Bonaparte,
1993; Sampson et al., 2001; Carrano et al., 2002, 2011; Novas et al.,
2013). The shaft is anteroposteriorly wider at its medial side and narrows
towards the lateral edge. The condyles are subovoidal in contour in
ventral view. The external condyle is broader and more anteroposteriorly
compressed than the internal one. On the other hand, the inner condyle
is transversely narrower, but anteroposterioly elongate. The condyles
are separated by a shallow and obliquely oriented intercondylar sulcus.
Posteriorly, the dorsal margin of both condyles is delimited by a low,
transverse ridge. The quadratojugal contact is represented by a shallow
posterolateral concavity. The pterygoid ange was not preserved.
Comments: The morphology of the quadrate closely matches
that of other abelisauroids, such as Carnotaurus, Majungasaurus,
Masiakasaurus and Noasaurus (Bonaparte, 1993; Sampson and
Krause, 2007; Carrano et al., 2011; Bonaparte and Powell, 1980) in
having asymmetrical condyles that are separated by an obliquely
oriented sulcus, a medial condyle that is anteroposterioly elongated and
transversely narrow, and a lateral condyle that is transversely expanded
and anteroposteriorly short. Because of its fragmentary nature, MPCA-
FIGURE 1. Detail of the area of study showing the location of the Violante farm, the geological map of the El Cuy Department (modied from
Hugo and Leanza, 2001), and a photograph showing Huincul Formation beds where the fossil specimens were found.
Pv 800 cannot be identied beyond Abelisauroidea indet.
Gen. et sp. indet. 2
Referred material: MPCA-Pv 801, nearly complete right
metatarsal IV, with the distal end lacking part of its dorsal margin (Fig.
Description and comparisons: The metatarsal is long and
relatively slender. The shaft ares laterally on its distal end. The
proximal end has a subtriangular shape in proximal view with an
anterior projection, as occurs in other abelisauroids (e.g., Aucasaurus;
Coria et al., 2003). There is a concavity on the proximomedial surface
of the shaft, probably for articulation with metatarsal III. The proximal
half of the shaft is subtriangular in cross-section, with conspicuous
at ventral and medial margins, indicating a very strong metatarsal
III as occurs in abelisauroids and coelophysoids (Gauthier, 1986). The
shaft narrows towards its distal end, as occurs in other abelisauroids
(e.g., Brissón et al., 2016). In lateral view, the shaft is nearly straight.
The shaft narrows immediately before the distal end, thus dening a
subtle neck. Only the lateral condyle of the distal end was preserved.
The lateral trochlea is low, and its ventral margin is lateroventrally
oriented. Ventrally, there is a wide space separating the condyles, as
in Aucasaurus and Masiakasaurus (Carrano et al., 2002; Coria et al.,
Comments: The isolated metatarsal reported here is very similar
to that of Masiakasaurus in gross morphology, being long and slender
and thus differing from the more massive metatarsals of abelisaurids
(Carrano et al., 2002). However, because of the absence of shared
derived traits between the material here described and the known
metatarsals IV of noasaurids (e.g. Velocisaurus, Masiakasaurus;
Bonaparte, 1991; Carrano et al., 2002) there is not enough evidence to
justify it identication beyond Abelisauroidea.
TETANURAE Gauthier, 1986
ALLOSAUROIDEA Currie and Zhao, 1993
CARCHARODONTOSAURIDAE Stromer, 1931
Taurovenator violantei gen. et sp. nov.
Etymology: The generic name derives from the Latin words
“tauro” (Bull) and “venator” (Hunter). The specic name honours Enzo
Violante, owner of the farm where the specimen was discovered.
Holotype: MPCA PV 802, isolated right postorbital (Fig. 4).
Diagnosis: Mid-sized carcharodontosaurid having the following
autapomorphies: 1) presence of a horn-like prominence in the orbital
brow, and 2) presence of a deep excavation in the ventral surface of the
Description and comparisons: As in other theropods this bone is
heavily constructed and T-shaped in lateral view. This element seems
to be more robust than that of Eocarcharia and Mapusaurus (Coria
and Currie, 2006; Sereno and Brusatte, 2008). In lateral view, the
orbital brow is stout and short, and, as in most carcharodontosaurids,
its posterior half is transversely thicker than the anterior half. On its
posterodorsal corner, there is a prominent and rounded process that
supercially resembles the orbital boss of Eocarcharia (Sereno and
Brusatte, 2008), but differs in being more prominent, notably rounded,
smaller, and relatively narrower. The lateral wall of the brow is nearly
smooth, but it becomes conspicuously rugose closer to its dorsal
margin, as also occurs in Giganotosaurus and Carcharodontosaurus
(Sereno and Brusatte, 2008; Fig. 5). The lateral wall is anteroventrally
projected, and reaches the orbit, forming a convex ventral margin when
viewed anteriorly, a condition reminiscent of that in Mapusaurus and
Carcharodontosaurus (Coria and Currie, 2006; Sereno and Brusatte,
2008; Fig. 5). In lateral view, the ventral margin of the lateral wall is
anteroposteriorly sigmoidal and posteriorly contacts the orbital boss.
In medial view, on its anterior margin, this brow shows the articular
surface with the frontal and posterior to it, there is the crescent-shaped
articular surface for the laterosphenoid. Posterior to the brow, this bone
shows a robust and rounded bar that is posteriorly projected. This bar
together with the squamosal constitutes the supratemporal arch.
The ventral ramus is dorsoventrally short, anteroposteriorly wide,
and transversely narrow, resulting in a subtriangular cross-section.
This ramus is anteroventrally projected and forms an acute angle
with the brow that resembles Mapusaurus and Carcharodontosaurus,
contrasting with the condition exhibited by Giganotosaurus (Coria and
Currie, 2006; Sereno and Brusatte, 2008). The lateral surface of this
ramus is decorated by abundant anastomosed and bifurcate vascular
grooves, suggesting that this region was strongly vascularized. The
ventral ramus is shorter and wider than Eocarcharia, resembling in
this aspect Mapusaurus and Carcharodontosaurus (Coria and Currie,
2006; Sereno and Brusatte, 2008). A large and subtriangular intraorbital
process is placed at the distal end of the ventral ramus, a similar process
occurs in most derived carcharodontosaurids (e.g., Mapusaurus,
Giganotosaurus, Carcharodontosaurus; Coria and Currie, 2006;
Sereno and Brusatte, 2008; Fig. 5), contrasting with the smaller and
rugose process present in Eocarcharia (Sereno and Brusatte, 2008) and
other allosauroids (e.g., Sinraptor; Currie and Zhao, 1993). In posterior
view, the articular surface for the squamosal is present in the posterior
bar. Below, the posterior surface of the ventral ramus exhibits a shallow
There is a vertical ridge that runs along the ventral ramus becoming
rugose posteriorly. A similar ridge is present in Mapusaurus and
Carcharodontosaurus, but absent in Eocarcharia (Coria and Currie,
2006; Sereno and Brusatte, 2008). This area probably represents the
articular surface for the jugal.
In Taurovenator, the postorbital bar seems to be more robust
than in Mapusaurus and Eocarcharia (Coria and Currie, 2006; Sereno
and Brusatte, 2008). Nevertheless, the posterior bar is relatively sub-
circular in cross section, which resembles Carcharodontosaurus more
than other carcharodontosaurids, in which this bar is subtriangular in
cross section (Sereno and Brusatte, 2008).
In anterior view, the articular surface for the frontal can be
observed at its medial margin. It is represented by an anteroposteriorly
short but strongly rugose surface. Near the lateral margin of the bone
there is a notably tall lacrimal articular surface, as occurs in other
members of this family (Sereno and Brusatte, 2008). Furthermore, this
articulation excludes the frontal from the orbital margin, as occurs in
derived Carcharodontosauridae (Sereno and Brusatte, 2008).
In ventral view, a very deep concavity is present in the inner
surface of the brow. This concavity is posteriorly delimited by the
ventral ramus and laterally by the ventrally projected lateral wall of
the brow. At the most posterior portion of this cavity, there is a deep
and subrectangular pit that transversely enters the bone, and is here
interpreted as a pneumatopore.
In dorsal view, the brow shows a prominent and rounded orbital
boss at its posterior margin. The roof of the postorbital is slightly rugose,
and the ornamentation increases through the laterodorsal corner of the
brow. Posterior to the orbital boss, the bone narrows caudally towards
the rounded and short posterior bar. Coria and Currie (2006) describe
the brow in Mapusaurus, as a “palpebral,” a different ossication that
is completely fused with the postorbital. In the present specimen, there
is no evidence indicating the presence of such a structure.
Remarks: Taurovenator is similar in gross morphology
to other derived carcharodontosaurids such as Giganotosaurus,
FIGURE 2. Left quadrate of Abelisauroidea indet. A, B, posterior view;
C, D, lateral view; E, F, anterior view; G, H, medial view; I, J, distal
view. Scale bar: 1 cm.
FIGURE 3. Right metatarsal IV of Abelisauroidea indet. A, B, anterior
view; C, D, posterior view; E, F, lateral view; G, H, medial view; I,
J, proximal view. Abbreviations: cpit, collateral ligamental pit. Scale
bar: 3 cm.
FIGURE 4. Right postorbital (holotype) of Taurovenator violentei gen. et sp. nov. A, lateral view; B, medial view; C, posterior view; D, dorsal
view; E, anterior view. Scale bar: 3 cm.
FIGURE 5. Right postorbital (holotype) of Taurovenator violentei gen. et sp. nov. interpretive drawing. A, lateral view; B, medial view; C,
posterior view; D, dorsal view; E, anterior view. Scale bar: 3 cm.
Carcharodontosaurus, and Mapusaurus (Coria and Currie, 2006;
Sereno and Brusatte, 2008)(Fig. 6). In spite of that, the postorbital
of Taurovenator is notably smaller than that of Mapusaurus or
Giganotosaurus (Coria and Currie, 2006; Sereno and Brusatte, 2008),
although it is proportionally more robust and transversely thicker than
in the aforementioned species.
Taurovenator shares with derived carcharodontosaurids the
1) Dorsoventrally short and anteroposteriorly wide ventral
ramus of the postorbital, that bears a short and dorsally placed
subtriangular shaped intraorbital process. A postorbital with a ventral
process anteroposteriorly broader than transversely wider is present
in most Theropoda (Holtz, 1998). In some large-sized clades, such
as abelisaurids, carcharodontosaurids and tyrannosaurids, the ventral
process is wide in lateral view and has an intraorbital process (or
suborbital ange) that supports the ventral margin of the orbit (Novas,
1997; Rauhut, 2003). This feature was acquired independently in each
lineage, according to most phylogenetic hypotheses (Holtz et al., 2004;
A dorsoventrally short ventral ramus seems to be diagnostic of
Taurovenator, Acrocanthosaurus, and derived carcharodontosaurids,
because allosaurids (e.g., Allosaurus), sinraptorids (e.g., Sinraptor) and
basal carcharodontosaurids (e.g., Eocarcharia) have a longer ventral
ramus (Fig. 6). This also results in the position of the intraorbital process
becoming more dorsally positioned in Acrocanthosaurus and derived
carcharodontosaurids, such as Mapusaurus, Carcharodontosaurus,
or Taurovenator. In a similar way, the width of the ventral process of
carcharodontosaurids is greater when compared more basal allosauroids
(e.g., Allosaurus, Sinraptor, Eocarcharia). The above mentioned
combination of characters appears to be related with the reinforcement
of the orbit and skull roof.
2) The ventral process of the postorbital forms an acute angle with
the orbital brow. The ventral ramus of the postorbital is vertical or slightly
anteroventrally directed in most theropod groups. In some taxa such
as abelisaurids or derived carcharodontosaurids this ramus is strongly
anteroventrally oriented (Novas, 1997). In more basal allosauroids,
such as allosaurids, sinraptorids, Eocarcharia, and Acrocanthosaurus
(Eddy and Clarke, 2011), the ventral ramus is vertical or forms a
90° angle with the orbital brow. In derived carcharodontosaurids and
abelisaurids, the angle between the ventral ramus and the orbital brow
is approximately 60°-70° (Sereno and Brusatte, 2008; Fig. 4).
3) A vertical ridge in the medial surface of the ventral process.
Presence of a subvertical ridge that represents the articular surface
for the laterosphenoid on its dorsal half and the articular surface for
the jugal at its ventral half. In abelisaurids (Bonaparte et al., 1990),
and selected basal tetanurans, such as spinosaurids, Allosaurus,
Acrocanthosaurus, and carcharodontosaurids (Carrano et al.,
2012), is notably ventrally projected as a rod-like process. Within
Carcharodontosauria, this structure is observed in Acrocanthosaurus,
Carcharodontosaurus, and Taurovenator (Eddy and Clarke, 2011). In
Mapusaurus, the ventral ramus is broken but a well-developed vertical
ridge is observed on the dorsal portion of the ventral ramus (Coria and
Currie, 2006). In Eocarcharia, the medial surface of the ventral ramus
is at, and a vertical ridge is absent (Sereno and Brusatte, 2008). This
might indicate that the contact for the jugal was different in derived
carcharodontosaurids when compared to the basal Eocarcharia.
4) The posterolateral wall of the orbital brow projects ventrally
and overhangs the orbit. As indicated by previous authors, the
postorbital morphology is highly diverse within Carcharodontosauria,
which is very informative taxonomically (Sereno and Brusatte, 2008).
The lateral wall of the orbital brow of Taurovenator expands ventrally
and is medially directed surrounding the orbit. This feature is present in
Taurovenator, Acrocanthosaurus, and Mapusaurus (Coria and Currie,
2006). In other allosauroids, such as Allosaurus or Sinraptor, this
feature is absent, whereas in Eocarcharia the brow expands ventrally
but does not surround the orbit (Figs. 4-5).
In conclusion, based on the features mentioned above,
we assign Taurovenator to the Carcharodontosauridae. Among
carcharodontosaurids, Taurovenator closely resembles the derived
members of the group including Carcharodontosaurus, Giganotosaurus,
and Mapusaurus, but not Acrocanthosaurus or Eocarcharia.
On the other hand, Taurovenator shows two unique features that
deserve the following comments:
1) Presence of a boss on the posterodorsal margin of the orbital brow
(Fig. 4). One of the most striking traits of Taurovenator is the presence
of a horn-like structure in the orbital brow. Some large-sized theropod
groups such as Ceratosauridae, Abelisauridae, Carcharodontosauridae
and Tyrannosauridae show ornamental structures in the postorbital
region, and these cranial ornamentations are traditionally regarded as
indicative of intraspecic competition related with mating (Sereno and
Brusatte, 2008). In carcharodontosaurids the cranial ornamentation is
widely distributed (Novas, 1997), for example, prominent and rugose
lateral brows are common among carcharodontosaurids. (Coria and
Currie, 2006; Sereno and Brusatte, 2008). Furthermore, in Eocarcharia,
a big and rounded orbital boss is present in the laterodorsal margin
of the postorbital (Sereno and Brusatte, 2008). A similar but less-
developed boss is observed in Carcharodontosaurus; furthermore, the
ventral ramus of the bone shows a “pitted pyramidal projection” in the
lateral margin near the distal end of the element (Sereno and Brusatte,
2008). In spite of such diversity of cranial ornamentation, no other
carchardontosaurid shows a horn-like projection of the orbital boss at
its posterolateral margin as the one present in Taurovenator.
2) Presence of an excavation housed at the posterodorsal
surface of the eye socket (Fig. 4). This feature is not mentioned for
other carcharodontosaurids or basal tetanurans. In Majungasaurus a
neurovascular foramen is also present in the spot, but is much smaller
in size (Sampson and Witmer, 2007). In Mapusaurus (Coria and Currie,
2006) the region in which the fossa should be housed is broken, and,
thus, the condition cannot be corroborated. In Acrocanthosaurus,
Carcharodontosaurus, and Eocarcharia a deep excavation or fossa is
totally absent. In this way, we conclude that presence of such a structure
in Taurovenator should be regarded as an autapomorphy of the latter.
Gen. et sp. indet
Referred material: MPCA-Pv 803/1-803/11, associated specimen
consisting of a dorsal vertebral centrum (803/1), one fragmentary
rib (803/2), incomplete right hindlimb composed of distal tarsals III
(803/3) and IV (803/4), metatarsal II (803/5), metatarsal III (803/6)
and possible distal fragment of an indeterminate metatarsal (803/7),
pedal phalanges IV-1 (803/8) and IV-3 (803/9), and two pedal unguals
Description and comparisons: A single dorsal vertebra is
represented by a poorly preserved centrum with the base of the neural
arch (Fig. 7). It is interpreted as a posterior dorsal vertebra due to
the absence of a parapophysis on the centrum and the amphyplatic
condition of the articular surfaces. The centrum is laterally compressed
and has its posterior half dorsoventrally higher than the anterior half.
The centrum shows a ventral longitudinal keel and exhibits a strong
middle constriction as occurs in other allosauroids (e.g., Allosaurus,
Acrocanthosaurus; Holz et al., 2004). It shows notably laterally
expanded rims surrounding the anterior and posterior articular surfaces,
resulting in a spool-shaped centrum. On its lateral surface, there is a
large and deep, dorsally located pneumatic foramen that is subdivided
by an oblique septum, a condition present in posterior dorsal
vertebrae of other carcharodontosaurids (including Acrocanthosaurus
and Giganotosaurus; Harris, 1998), Torvosaurus, Megaraptoridae,
and Tyrannosauridae (Rauhut, 2003; Sereno et al., 2008). In spite
of its fragmentary nature, the spool-shaped contour in ventral view,
longitudinal ventral keel, and large subdivided pneumatic foramen are
a combination of features that indicate that MPCA-Pv 803/1 belongs to
a carcharodontosaurid theropod.
Two distal tarsals were also recovered. These elements are rarely
preserved or illustrated in the literature, so that, exhaustive comparisons
cannot be done.
Distal tarsal III is not entirely preserved and lacks its posterior
margin. Its proximal surface is convex, and the distal surface is slightly
concave, probably to contact with metatarsal III (Fig. 8). The lateral
surface shows a deep and well-dened ovoid depression that is located
at its anterior half. This concavity bears several vascular pits. The
medial surface shows a wide but shallow depression that bears a broad
and low subvertical ridge. The anterior surface shows an obliquely
oriented concavity and a laterodistally located suboval pit. The lateral
depression probably represents part of the contact with tarsal IV. Over
all, the distal tarsal III here described is similar in gross morphology to
the distal tarsal III of Sinraptor (Currie and Zhao, 1993).
Distal tarsal IV shows similar gross morphology to that of
Allosaurus and Sinraptor (Madsen 1976; Currie and Zhao 1993; Fig.
9). The lateral and distal surfaces are badly preserved. The proximal
surface shows a large and obliquely oriented concavity similar to that
present in Sinraptor (Currie and Zhao, 1993). The distal surface is
slightly concave. The medial surface shows a small subcircular pit near
its anterior end, and a large posterior concavity. A similar morphology is
FIGURE 6. Selected carcharodontosaurid left postorbitals in A-D, lateral; E-H, medial; and I-L, dorsal views. A, E, I, Eocarcharia dinops
(modied from Sereno and Brusatte, 2008); B, F, J, Carcharodontosaurus saharicus (modied from Sereno and Brusatte, 2008); C, G, K,
Mapusaurus roseae (modied from Coria and Currie, 2006); D, H, L, Taurovenator violantei nov. Not to scale.
present in Sinraptor (Currie and Zhao, 1993) and Allosaurus (Madsen,
A well-preserved right metatarsal II was recovered and only
lacks part of its distal end (Fig. 10). The bone is 43.5 cm long. This
element is robust and almost straight for most of its length, with a
lateral curvature near its distal end. In proximal view, the proximal end
shows a slightly convex medial margin and a strongly convex lateral
margin, giving the metatarsal a “D” contour when viewed proximally, a
condition present also in Sinraptor and Mapusaurus (Currie and Zhao,
1993; Coria and Currie, 2006). As occurs in Sinraptor, when viewed
proximally, the metatarsal bears a set of rugose grooves along its medial
margin, suggesting some kind of cartilage cap. There is a rounded pit
in the center of the proximal surface. In medial view, the proximal
end is roughly fan-shaped, and more anteroposteriorly expanded than
in Allosaurus (Madsen, 1976) or Neovenator (Brusatte et al., 2008),
resembling Sinraptor in this aspect (Currie and Zhao, 1993). The shaft
is stout and expands distally to form the medial hemicondyle. The
distal end shows a deep and rounded collateral pit on its medial side. In
anterior view, the distal end is laterally oriented because of the lateral
curvature of the shaft. There is a remarkable small protuberance at the
middle of the shaft, a trait also present in Acrocanthosaurus (Currie and
Carpenter, 2000). In lateral view, the proximal end bears a well dened
facet to contact metatarsal III. Moreover, there are three longitudinal
scars at the distal half of the bone that probably served as the insertion
of the M. gastrocnemius pars lateralis (Carrano and Hutchinson, 2002).
In posterior view, the distal half of the bone bears a suboval concavity
that shows a dorsoventrally oriented major axis, probably to contact the
rst metatarsal, as occurs in Allosaurus (Osborn, 1899).
The right metatarsal III is badly weathered (Fig. 11). In gross
morphology this element is similar to that Allosaurus (Madsen, 1976),
Sinraptor (Currie and Zhao, 1993), and Mapusaurus (Coria and Currie,
2006). In proximal view it is subtriangular in shape, with the anterior
half more transversely compressed than the posterior portion. The
medial border shows a slightly concave contact for metatarsal II. The
lateral border is more concave than the medial one. In gross morphology
this element is more transversely compressed and anteroposteriorly
shorter than the metatarsal II, which is proportionally more robust, a
condition widespread among allosauroids (e.g., Sinraptor, Mapusaurus,
One right pedal phalanx IV-1 was recovered (Fig. 12). It is a robust
and asymmetrical element, being strongly tilted laterally. The lateral
condyle is more robust than the medial condyle. In proximal view,
the articular surface is dorsoventrally taller than transversely wide
and shows an asymmetrical dorsal margin, as occurs in some other
allosauroids such as Neovenator (Brusatte et al., 2008). The dorsal
surface is slightly concave in lateral view and shows a well dened and
subcircular extensor pit. The collateral ligamental pits are subcircular,
the lateral one being relatively smaller, better dened, and deeper than
the medial one. The ventral surface is nearly at and shows a proximal
tubercle on its lateral margin, similar to that of Neovenator (Brusatte et
al., 2008). The distal surface shows a poorly developed intercondylar
groove that separates distal condyles, resulting in a nearly at ventral
margin, whereas in Neovenator this groove is deeper.
A pedal phalanx that probably represents phalanx IV-3 was found
(Fig. 13). This element is notably short, with a length of approximately
6 cm. In proximal view the articular surface is concave and ovoid
in contour, showing a median keel as in other allosauroids, such as
Neovenator (Brusatte et al., 2008). The ventral surface is at and wider
than the dorsal one, which is slightly concave. In this way, when viewed
dorsally, the ventral portion of the phalanx is notably exposed. Both
lateral and medial surfaces bear deep and large collateral ligamental
pits. There is a wide rim running along the laterodorsal and mediodorsal
edges of the phalanx. These rims run along the phalanx and end on
the anterior margin of each collateral ligamental pit. Other allosauroids
such as Sinraptor and Neovenator (Currie and Zhao, 1993; Brusatte
et al., 2008) show weaker rims at the sides of the phalanx. Both distal
condyles are rounded and separated by a deep intercondylar groove.
Two pedal ungual phalanges where recovered. Because they were
not found in direct articulation, and because of the homogeneity of
carcharodontosaurid claw morphology, we are unable to determine to
which digit they pertain.
The available unguals are notably similar to each other (Figs.
14-15). They are robust, and the shaft is almost straight, without a
pronounced lateral compression as occurs in the pedal phalanx of many
large theropods such as Neovenator, Tyrannosaurus and Allosaurus
(Madsen, 1976; Brochu, 2002; Brusatte et al., 2008). In proximal view
the proximal end tapers dorsally, resulting in a subtriangular proximal
contour. The proximal articular surface shows two bumps at the ventral
margin and lacks the median subvertical crest, in contrast with the pedal
unguals of other theropods (e.g., abelisaurids, coelurosaurs; Ostrom,
1969; Carrano et al., 2002), but resembling other allosauroids (e.g.,
Neovenator: Brusatte et al., 2008; Sinraptor: Currie and Zhao, 1993)
in this regard. The dorsal surface of the claw is rounded and smooth. It
is proximally expanded, forming a notable posteriorly expanded dorsal
lip. This thick lip has a concave dorsal margin, and is located more
ventrally than the dorsal edge of the ungual blade. This condition is
uniquely present in allosauroids such as Neovenator, Allosaurus, and
Sinraptor, being absent in other theropods such as Tyrannosaurus or
Australovenator (Brochu, 2003; Hocknull et al., 2009). Presence of such
an unique proximal lip may represent a unique feature of allosauroids, a
hypothesis that needs to be further studied.
There is a single and deep longitudinal groove along the lateral
and medial sides of the claw, the medial one being more dorsally
placed, wider, and with less well dened edges than the lateral one. This
condition is shared with other theropods, including allosauroids such as
Neovenator, Sinraptor and Mapusaurus (Currie and Zhao, 1993; Coria
and Currie, 2006; Brusatte et al., 2008), and contrasts with abelisaurids,
which show a distinctive bifurcated groove in each side of the claws
that usually delimits a notable lateral bump (Coria and Salgado, 1998;
Carrano et al., 2002; Novas et al., 2005).
These phalanges lack a exor tubercle, a condition shared with
abelisaurids and carcharodontosaurids (Currie and Zhao, 1993;
Carrano et al., 2002; Coria and Currie, 2006; Brusatte et al., 2008). The
specimens MPCA-Pv 810 and 811 show a at ventral surface, without
any sign of a longitudinal groove or keel, in contrast with abelisaurids
(e.g., Masiakasaurus; Noasaurus; Bonaparte and Powell, 1980; Novas
et al., 2005), that have a exor fossa on their ventral surfaces, but being
similar to other allosauroids (e.g., Neovenator, Sinraptor, Mapusaurus;
Currie and Zhao, 1993; Brusatte et al., 2008). There is a posteroventral
rugosity that represents the area for the insertion of M. exor digitorum
In sum, the presence of a very large, dorsally concave and
ventrally oriented proximal lip, and ventral surface lacking a exor
tubercle are features that may be useful to diagnose allosauroid pedal
unguals. Furthermore, the total absence of a proximal subvertical keel
and presence of two proximal ventral bumps may be diagnostic of
Carcharodontosauridae. The synapomorphic condition of each trait,
as well as its distribution, should be corroborated by future numerical
FIGURE 7. Centrum of dorsal vertebra of Carcharodontosauridae
indet. A, left lateral; and B, ventral views. Scale bar: 10 cm.
FIGURE 8. Distal tarsal III of Carcharodontosauridae indet. in: A, B,
anterior view; C, D, proximal view; E, F, medial view; G, H, lateral
view. Scale bar: 3 cm.
COELUROSAURIA Huene, 1914
Gen. et sp. indet.
Referred material: MPCA-Pv 806/1-806/11, associated
individual composed of three incomplete caudal vertebral centra
(806/1-3), incomplete anterior cervical vertebra (806/4), incomplete
distal caudal vertebra (806/5), incomplete distal metapodial (806/6),
incomplete proximal ungual phalanges of the hand (806/7-8) (Figure
Description and comparisons: The specimen (Fig. 16) represent
a single individual of small-sized coelurosaur having notably slender
proportions. In spite of its poor preservation, the fused neural arches
indicate that it was probably a skeletally mature individual. The
presence of ferruginous covering of the material precludes the detailed
description of most recovered bones.
The available cervical vertebra is very poorly preserved. The
centrum has a strongly parallelogram-shaped contour, and is ventrally
smooth. The neural arch was dorsoventrally low. The neural spine is
dorsoventrally low and anteroposteriorly extended.
The caudal vertebrae are long and gracile. They show subovoid
anterior and posterior articular surfaces that are wider than tall. The
ventral surface is at, having a shallow longitudinal groove surrounded
FIGURE 9. Distal tarsal IV of Carcharodontosauridae indet. in: A, B,
proximal view; C, D, distal view; E, F, medial view. Scale bar: 3 cm.
FIGURE 10. Rigth metatarsal II of Carcharodontosauridae indet. in: A,
B, medial view; C, D, anterior view; E, F, proximal view; G, H, lateral
view; I, J, posterior view; K, L, distal view Scale bar: 15 cm.
by two feebly developed ridges that are restricted to the anterior third
of the centrum. The neural canal is small. The prezygapophyses are
robust, but are too incomplete to allow a more detailed description
and comparisons. The neural spine is transversely narrow and
The ungual phalanges are poorly preserved. They are notably
dorsoventrally tall and transversely compressed, and the proximal
end shows an acute and well-developed subvertical ridge. There is no
proximodorsal lip. The exor tubercle is represented by its base; in
spite of that is appears to be very well-developed.
Comments: In spite of its fragmentary nature, the present
specimen may be referred to Coelurosauria mainly on the basis of
elongate cervical vertebrae, lacking ventral grooves or a keel and
retaining a relatively well-developed and anteroposteriorly long neural
spine (see Agnolin and Martinelli, 2007). Further, the caudal vertebrae
show notably small neural spines, a feature considered as typical of
coelurosaurs (Rauhut, 2003). In addition, the strongly compressed and
acute ungual phalanges are also different from that known in noasaurid
abelisauroids (Agnolin and Chiarelli, 2010).
Within coelurosaurs, the afnities of the present specimen are
far from certain. In spite of that, it is worth mentioning that it differs
from unenlagiids and dromaeosaurids (e.g., Buitreraptor, Deinonychus;
Ostrom, 1969; Gianechini and Apesteguía, 2010) in having caudal
vertebrae lacking strong lateral and ventral grooves and ridges, and
in having transversely wide and ovoid anterior and posterior articular
surfaces (rather than box-like; Norell and Makovicky, 1997). Further,
it differs from troodontids in lacking caudal vertebrae with a dorsally
excavated neural arch (Averianov and Sues, 2016). In this way, the
present specimen is determined as a non-paravian coelurosaurian of
TYRANNOSAUROIDEA Osborn, 1905
MEGARAPTORA Benson, Carrano and Brusatte, 2010
Aoniraptor libertatem gen. et sp. nov.
Etymology: Aoni from the Tehuelche language, which means
south, and raptor, Latin word for thief; libertatem, from the Latin,
meaning “independence,” due to the 200 years anniversary of 9th July
1810, which led to the declaration of independence of Argentina from
the Spanish government, thus constituting one of the most important
chapters in the history of this South American country.
FIGURE 11. Right metatarsal III Carcharodontosauridae indet. in: A,
proximal view; and B, lateral view. Scale bar: 10 cm.
FIGURE 12. Right pedal phalanx IV-1 of Carcharodontosauridae indet.
in: A, C, dorsal view; B, D, medial view; E, G, ventral view; F, H,
lateral view; I, J, proximal view; K, L, distal view. Scale bar: 3 cm.
Diagnosis: Megaraptoran theropod diagnosable on the basis of
the following autapomorphies: (1) anterior mid-caudal vertebrae with
fan-shaped prezygapophyses lacking a discernible articular surface
for contacting the postzygapophyses; (2) presence of a blunt and thick
process on the lateral surface of the prezygapophyses of anterior mid-
caudal vertebrae; and (3) mid-posterior caudals with a pair of non-
articular at surfaces located on the posterodorsal corner of the centrum.
Holotype: MPCA-Pv 804/1 to 804/25, incomplete vertebral series
represented by the last sacral vertebra, 6 proximal caudal vertebrae, 4
mid-caudal vertebrae, and 5 haemal arches.
Description: The available vertebrae indicate that Aoniraptor was
a mid-sized theropod with an estimated length of 6 meters. The neural
arches are not fused to the centra, indicating a skeletally immature
individual. The centra are elongate, amphicoelous, and highly
All available vertebrae that are in articulation show an element
separating each other that probably represents the intervertebral disc.
These elements approximately represent one tenth the total length of
each corresponding vertebra and each is about 1 cm of length.
The rst sacral is slightly deformed and has an incompletely
preserved neural arch (Fig. 17). The centrum is relatively elongate,
transversely narrow, and is highly pneumatized. The anterior articular
surface is subcircular in outline, being dorsoventrally lower than the
posterior articular surface. This results in a roughly paralellogram-
shaped centrum. Its surface is rugose, indicating a strong attachment
with a preceding sacral. The posterior surface is suboval, having a
dorsoventrally oriented major axis. The articular surface shows a well-
developed striated rim of bone along its perimeter. In lateral view, the
ventral margin of the centrum is strongly concave, and, in ventral view,
is at, lacking any sign of a keel or groove.
Pneumatic traits along the vertebral series are notably variable
within and among vertebrae in Aoniraptor. In this regard, the rst sacral
has at the dorsal half of the centrum a large but shallow fossa, ventrally
delimited by a rounded and mound-like shelf of bone. Within this fossa,
in right lateral view, there is a large and deep pneumatic foramen that is
anteriorly and posteriorly delimited by thin subvertical ridges of bone.
These ridges delimit two smaller and shallow fossae. On the left lateral
side, the pneumatization is different in that there are four small fossae
that are separated by subvertical ridges of bone.
The neural arch is deformed and difcult to interpret, being
also posteriorly displaced. However, the main anatomical details are
still discernible. The neural arch is strongly pneumatized, showing a
camerate internal structure. The neural spine is only represented by
its incomplete base, but it shows that it was transversely compressed
and anteroposteriorly long. It is laterally bounded by two narrow and
acute laminae that are obliquely oriented and diverge posterolaterally.
These laminae are separated from the neural spine by deep fossae. The
transverse process is strongly pneumatized, being of camerate internal
structure. It is strongly anteroposteriorly expanded and shows a roughly
subtriangular contour when viewed laterally. It shows a longitudinal
shallow groove that is ventrally delimited by an acute ridge. Within
this groove there is a large number of longitudinal striations, probably
related to its anchoring with the ilium. At the inner surface of the
anterior expansion of the sacral articulation the transverse process
shows a subtriangular and deep fossa that is anterolaterally delimited
by a strong ridge of bone that runs to the base of the neural spine. It is
worth mentioning that the transverse process and neural arch show a
large number of dispersed pneumatic fossae and foramina.
The rst caudal vertebra is very similar to the rst sacral (Fig. 17).
It differs in that both anterior and posterior articular surfaces are at the
same level and are subequal in size and morphology, and in that the
vertebral centrum is dorsoventrally taller. In addition, there is a small
rugose surface located at the posteroventral corner of the centrum that
articulates with the haemal arches. In ventral view the centrum shows
a small posteroventral attened surface that is absent in the sacral
vertebra. Further, the posterior margin of the neural arch of the last
sacral ends at the same level as the posterior articular surface of the
centrum, whereas in the caudal vertebrae the neural arch ends anterior
to the posterior margin of the vertebral centrum.
The anterior and posterior articular surfaces are suboval in contour.
In right lateral view the centrum lacks any sign of pneumatization, with
the exception of a very shallow depression, whereas on the left side
there is a large fossa that bears a large pneumatic foramen, delimited by
anterior and posterior, small and acute ridges of bone.
The neural arch is highly incomplete and distorted. It shows a
camerate internal structure. The right prezygapophysis and the base
of the transverse process have been preserved. The prezygapophysis is
relatively large, and subvertically oriented. The base of the transverse
process shows two well-dened buttresses that bound presumably
FIGURE 13. Right pedal phalanx IV-3 of Carcharodontosauridae indet. in: A, B, dorsal view; C, D, ventral view; E, F, lateral view; G, H, medial
view; I, J, distal view; K, L, proximal view. Scale bar: 3 cm.
pneumatic fossae. The base of the transverse process indicates that it
was laterodorsally oriented.
Other anterior caudal vertebrae are represented by centra and
incomplete neural arches. The vertebrae 2 and 3 are represented by
the centra, whereas anterior neural arches where found dissarticulated
The vertebral centra are similar in size, morphology, and
proportions to that of the rst caudal vertebra (Fig. 17). The anterior
articular surface is more deeply excavated than the posterior one. In this
regard, the intervertebral disc on these vertebrae is anteroposteriorly
thick, and shows a more strongly convex posterior surface. In ventral
or dorsal views, the anterior expansion of the articular surface is
transversely wider than the posterior one. The centra lack pneumatic
fossae. In dorsal view, approximately at the mid-length of the suture
between the neural arch and centrum there is a large subcircular internal
foramen on each side that penetrates within the centrum. In this way,
possibly the pneumatization of the vertebral centrum was probably due
to the invasion of the pneumatic system coming from the neural arch.
The ventral surface of the centrum shows a attened ellipsoidal
surface. This surface is larger in the third vertebra than in the rst or
Regrettably, the only two available anterior neural arches were
found disarticulated, incomplete, and weathered (Fig. 18). However, a
large number of interesting features may be recognized. The transverse
processes are notably elongate and are posterolaterally oriented, having
only a subtle dorsal orientation. In dorsal and ventral view they are
paddle-shaped, being slightly distally expanded on the anteroposterior
axis. The transverse processes are remarkably dorsoventrally low and
sublaminar in cross-section. In ventral view, at the proximal half of
the centrum there are posterior and anterior laminae that run from the
transverse process to the base of the neural arch, probably representing
part of the buttresses present in anterior and mid-vertebrae. The anterior
margin of the transverse process shows an anterior lamina that connects
it with the prezygapophysis, and a shallower posterior one, that contacts
with the postzygapophysis. There is a large and deep subtriangular
pneumatic fossa delimited laterally by the lamina running from the
transverse process to the prezygapophyses and ventrally by the anterior
The prezygapophyses are relatively robust and short,
being dorsomedially oriented. There is a well-developed
spinoprezygapophyseal lamina. The postzygapophyses are very small-
sized, having a subcircular articular surface. There is a small notch
separating the postzygapophyses from the transverse process.
In dorsal view, in the area of contact between the base of the neural
spine and the transverse process, there is a shallow, albeit notably wide,
There are eight nearly complete mid-vertebrae preserved. They
differ from more anterior vertebrae in having a notably low neural spine
and relatively short transverse processes.
Three anterior mid-neural arches were found in articulation. These
arches are very poorly preserved, and are represented only by their left
lateral half (Figs. 19-20). In gross morphology they resemble anterior
caudals. They are notably elongate and probably occupied the entire
length of the vertebral centrum. The neural spine has been completely
preserved in a single vertebra. It is subrectangular in contour, having
an anteroposteriorly elongate main axis. Its dorsal margin is gently
FIGURE 14. Right pedal ungual phalanx of Carcharodontosauridae
indet. A, B, ventral view; C, D, dorsal view; E, F, medial view; G, H,
lateral view; I, J, proximal view. Scale bar: 3 cm.
FIGURE 15. Right pedal ungual phalanx of Carcharodontosauridae
indet. A, B, dorsal view; C, D, ventral view; E, F, lateral view; G, H,
medial view; I, J, proximal view. Scale bar: 3 cm.
FIGURE 16. Coelurosauria indet. A, cervical vertebra in dorsal view; B, distal end of indeteminate metapodial; C, lateral view of manual ungual
phalanx; D, lateral view of incomplete vertebral centrum; E-H, nearly complete caudal vertebra in: E, anterior, F, left lateral, G, dorsal, and H,
ventral views. Abbreviations: ft, exor tubercle; ns, neural spine; pas, proximal articular surface; prz, prezygapophysis; tr, distal trochlea; vg,
ventral groove. Scale bar: 1 cm.
concave, resulting in a roughly saddle-shaped contour when viewed
from the sides. It is located on the posterior half of the vertebral
centrum. The posterior margin of the neural spine has preserved a
notably expanded ligamentary lamina for interspinal scars. As occurs
in anterior caudal vertebrae, there is a wide and well-dened fossa on
the area of contact between the neural spine and the transverse process.
The spinoprezygapophyseal and the prezygapophyseal/transverse
process laminae are present as in the anterior caudal, but in this case,
they are more developed and more acute. The spinoprezygapophyseal
lamina denes a very wide and deep prespinal fossa. The transverse
process are notably posteriorly oriented and are subrectangular in
contour when viewed dorsally. They are slightly distally expanded,
and are shorter than in more anterior caudals. The base of the laminar
transverse process shows two robust and short buttresses that are
separated from each other by means of a wide but shallow blind fossa.
These buttresses are delimited by anterior and posterior deep and wide
pneumatic fossae. The anterior fossa is anteroposteriorly elongate and
is bounded posteriorly, anteriorly, and ventrally by a rounded mound-
like lamina of bone. The posterior fossa is smaller than the anterior one
but is notably deeper and subcircular in contour. The prezygapophyses
are anteromedially oriented; they are notably expanded transversely
and fan-shaped. The articular surface of the prezygapophyses is not
discernible at all in any anterior mid-caudal vertebrae, a condition not
known in any other theropod. Laterally, the prezygapophysis shows a
blunt and thick process. As in the case of the anterior caudal vertebrae,
the postzygapophyses are notably small.
The centra are longer and lower than in more anterior caudals.
Furthermore, the centra are much more transversely compressed,
especially at mid-length. The ventral surface is narrower and sharper
than more anterior vertebrae. Notably these, as well as more posterior
mid-caudal vertebrae, lack any sign of pleurocoels or fossae, but show
a camerate centrum. It is worth mentioning that a vertebral centrum has
an attached crocodyliform tooth that partially penetrates it.
Five articulated and nearly complete posterior mid-caudal
vertebrae are preserved (Fig. 22). They are similar in gross morphology
to the other described caudals. The anteriormost element of the series
retains a robust and anterodorsally facing prezygapophysis. The
prezygapophyseal-transverse process lamina is reduced when compared
with more anterior caudals. The buttresses below the transverse process
are nearly absent, and the fossae delimited by these elements are also
reduced, but an anterior small fossa is retained. The transverse processes
are notably short and paddle-shaped, having a notable expansion on the
posterior margin. They are slightly ventrally oriented. The fossa shared
by the base of the neural arch and the transverse process is subtle to
The centrum has a pair of at surfaces located on its posterodorsal
corner, a trait that is present in all other mid-posterior caudals. This
surface is not known in any other theropod described to the date.
Because the vertebrae are articulated it can be observed that this surface
lacks any contact with other osseous structures.
The remaining posterior mid-caudal vertebrae are very similar to
that described above (Figs. 22-23). They show even more reduced fossae
and buttresses at the base of the transverse process, that disappear in the
most posterior element preserved. The transverse processes are slightly
more ventrally oriented than in the anterior vertebrae, and, in the case
of the last three preserved vertebrae, this process is notably shortened.
The distal end of these processes is notably expanded on its anterior
and posterior margins. The neural spines are notably dorsally concave
and saddle-shaped in contour. The posterior dorsal margin of the neural
spines shows a well-developed but blunt process that is posteriorly
oriented. The anterior dorsal corner of the neural spine shows a notch.
It is possible that both processes were in contact by some kind of soft
The prezygapophyses are notably different in the last three
preserved vertebral elements. They are notably elongate and are not
dorsally projected as in more anterior vertebrae. The prezygapophyses
show a well-developed and suboval articular surface, that contact
with the small postzygapophyses. The prezygapophyses show a well-
developed, thick and nger-like anteriorly pointed process that is not
present in other vertebrae. The elongation of the prezygapophyses
results in a remarkably expanded and elongate prespinal fossa. In all
available vertebrae there is a subtle prezygopostzygapophyseal lamina.
In ventral view, in all available posterior mid-caudal vertebrae
there is no longitudinal keel, groove or attened surface. The centra
are transversely narrower than anterior ones. In the case of the latter
two preserved elements the centrum is notably low and wide, being
subequal in width and height.
There are ve preserved haemal arches. Three of them belong to
anterior vertebrae, and the remaining two come from posterior mid-
caudal vertebrae. All haemal arches are relatively elongate and lack a
deep posterior curvature. They show a closed haemal canal.
The proximal haemal arches (Fig. 25) are very long and slender.
The proximal articular surface is saddle shaped and transversely
expanded. The anterior processes are laminar, moderately extended
FIGURE 17. Aoniraptor libertatem (holotype). Last sacral and rst
caudal vertebrae in: A, C, left lateral; B, D, right lateral; F, H, dorsal;
G, I, ventral; J, K, posterior; and L, M, anterior views. Abbreviations:
cd, rst caudal vertebra; hf, haemal facet; id, possible intervertebral
disc; pl, pleurocoel; sv, last sacral vertebra; tp, transverse process.
Scale bar: 3 cm.
FIGURE 18. Aoniraptor libertatem (holotype). Third caudal vertebral
centrum in: A, B, ventral; C, E, right lateral; D, F, left lateral; G, H,
anterior; and I, J, posterior views. Abbreviations: hf, haemal facet.
Scale bar: 2 cm.
FIGURE 19. Aoniraptor libertatem (holotype). Neural arch of
anterior caudal vertebra in A, B, right lateral; C, D, posterior; and
E, F, dorsal views. Abbreviations: f, fossa; ls, ligamental scar; pos,
postzygapophysis; prz, prezygapophysis; tp, transverse process. Scale
bar: 2 cm.
anteriorly and extend to the ventral level of the haemal canal. The
posterior processes are thicker than the anterior ones, and their proximal
margins are more clearly separated from the proximal end of the haemal
arch. They are notably extended ventrally and distally join each other
at approximately half of the haemal arch. The haemal canal is ovoid in
contour, with a main dorsoventral axis that becomes narrower distally.
In posterior view, the base of the haemal canal is strongly pneumatized.
In the anteriormost preserved haemal arch there is a distinct and deep
pneumatic foramen that is located immediately below the opening of
the canal. In the other preserved proximal haemal arch, this fossa is
shallower and smaller. In anterior view the base of the haemal canal
shows a small blind concavity of subtriangular contour.
The blade of the haemal arches is strap like, and notably
transversely compressed. They are anteroposteriorly narrow and
show a slight posterior curvature that is even more evident toward the
distal end. The anterior margin is surrounded by two longitudinal and
The posterior mid-caudal neural arches (Fig. 26) are very similar
to the anterior ones. However, they differ in that the anterior process
is proximally located, reaching the level of the proximal articular
surface of the haemal arch, and in that the posterior processes are more
prominent. The proximal end lacks pneumatic features, as also occurs
FIGURE 20. Aoniraptor libertatem (holotype). Neural arch of anterior
mid-caudal vertebra in A, B, dorsal; C, D, right lateral; E, F, posterior;
and G, H, anterior views. Abbreviations: ns, neural spine; pnp,
pneumatic excavation; pz, prezygapophysis; tp, transverse process; vb,
ventral buttresses. Scale bar: 3 cm.
FIGURE 21. Aoniraptor libertatem (holotype). Anterior mid-caudal
vertebra in A, C, left lateral; B, D, right lateral; E, F, dorsal; G, H,
posterior; and I, J, anterior views. Abbreviations: pz, prezygapophysis;
tp, transverse process. Scale bar: 3 cm.
in posterior mid-caudal vertebrae. The posterior process is laminar and
very well developed. They show a subtriangular contour when viewed
from the sides, having a posteriorly located apex. The blade of these
haemals is more posteriorly curved than in the most anterior haemal
Discussion and comparisons: In spite of its incomplete nature,
Aoniraptor shows a large number of traits that allow recognition of
its phylogenetic afnities. In Aoniraptor the last sacral vertebra
and rst anterior caudal show large pleurocoels on the sides of the
centra, a feature distributed in a handful of theropod groups, namely
Carcharodontosauridae (i.e., Carcharodontosaurus; South American
members of this clade show only shallow blind fossae; Méndez
et al., 2012), Therizinosauria; Oviraptorosauria, Tyrannosauridae,
Torvosaurus and Megaraptora (Stromer, 1931, 1933; Barsbold et al.,
1990; Britt, 1993; Brochu, 2002; Calvo et al., 2004; Novas et al., 2005;
2008; 2013; Benson et al., 2011; Brusatte et al., 2012). Among these
clades, only the Megaraptora (e.g. Aerosteon, Megaraptor; Mendez
et al., 2012; Martinelli et al., 2013) show a set of septa dividing the
pleurofossae. In members of the Oviraptoridae and Therizinosauria,
the pleurofossae are single and extend distally in the caudal series,
the neural spines are dorsoventrally taller and the middle to posterior
chevrons show a well-developed boat-shaped contour (Barsbold et al.,
1990; Xu et al., 2007).
In the same way, Aoniraptor resembles megaraptorans (e.g.,
Aerosteon, Megaraptor; Sereno et al., 2009; Porri et al., 2014) in
the internal structure of its vertebrae (Martinelli et al., 2013). These
have a camerate internal structure consisting of a large number of
small chambers (Britt, 1993). This condition is present also in some
ceratosaurs (Carrano and Sampson, 2008) and some allosauroids (e.g.
Acrocanthosaurus, Neovenator; Harris, 1998; Brusatte et al., 2008).
Further, Aoniraptor shows a megaraptorid synapomorphy that is the
presence of ventral buttresses on each transverse process of the most
anterior elements, that delimit a pair of pneumatic fossae (Benson et
al., 2010; Novas et al., 2013). In addition, Aoniraptor shows notably
elongate and subrectangular-shaped neural spines on mid-caudal
vertebrae, a derived feature shared by most coelurosaurs (Rauhut,
2003), and absent in allosauroids and abelisaurids.
In the present contribution we recognize a set of anatomical features
that may help to elucidate the phylogenetic position of Aoniraptor
libertatem. In this regard, Aoniraptor shows several traits that resemble
caudal vertebrae of tyrannosaurid theropods (Fig. 27). For example,
in Aoniraptor the neural spines of mid-caudal vertebrae are strongly
saddle-shaped in lateral view. This condition is present in Tyrannosaurus
and Alioramus (Brochu, 2003; Brusatte et al., 2012). This differs
from Ceratosaurus (Madsen and Welles, 2000) and basal tetanurans
such as Allosaurus and Torvosaurus (Madsen, 1976; Britt, 1991), in
which the neural spine is notably elongate and has an anterior spike-
like process (Rauhut, 2003). In Aoniraptor libertatem, the mid-caudals
retain well-developed laminae along the anterior and posterior margins
of the neural spines, indicating the anchoring of large interspinous
ligaments. Furthermore, the top of the neural spines show small anterior
and posterior processes. These conditions are present in some derived
tyrannosauroids such as Tarbosaurus, Tyrannosaurus and Alioramus
(Brochu, 2003; Brusatte et al., 2010), and we are unaware of its presence
in any other theropod clade. In addition, Aoniraptor shows very large
and notably elongate and distally spreading prezygapophyses on mid-
caudal vertebrae. This combination of features results in a prespinal
fossa that is notably wide, deep, and elongate. This derived trait is
absent in most theropods, with the exception of derived tyrannosauroids
such as Alioramus and Tyrannosaurus (Brusatte et al., 2012). Further,
in Aoniraptor the mid-caudals show a thick spinoprezygapophyseal
lamina present along the dorsal margin of the prezygapophyses, being
continuous with a nger-like non-articular anterior process that curves
ventrally in the prezygapophysis. This combination of features is also
shared by Tyrannosaurus, Albertosaurus, Tarbosaurus, and Alioramus
(Brusatte et al., 2012). In other theropods these well-developed laminae
FIGURE 22. Aoniraptor libertatem (holotype). Posterior mid-caudal
vertebrae in A, C, dorsal; B, D, ventral; E, G, right lateral; F, H, left
lateral; I, J, posterior; and K, L, anterior views. Abbreviations: hf,
haemal facet; id, intervertebral disc; nas, non-articular at surface; nsp,
additional anterior and posterior processes of neural spines. Scale bar:
2 cm. FIGURE 23. Aoniraptor libertatem (holotype). Posterior caudal
vertebra in A, B, right lateral; C, D, left lateral; E, F, dorsal; G, H,
ventral; I, J, posterior; and K, L, anterior views. Abbreviations: ns,
neural spine; pz, prezygapophysis; tp, transverse process. Scale bar:
and non-articular process are feebly developed or absent. The presence
of a prezygopostzygapophyseal lamina on mid-caudal vertebrae was
previously indicated by Brusatte et al. (2010) as a shared derived
character of advanced tyrannosauroids.
A conspicuous feature of Aoniraptor is the presence of large ovoid
pockets located on the posteroventral side of the haemal canal. This
condition has been previously reported in the derived tyrannosauroid
Alioramus by Brusatte et al. (2012), and is also probably present in
Megaraptor (MCF-PVPH 79). This pocket penetrates the bone and
very probably constitutes a pneumatic feature, as expressed by Brusatte
et al. (2010). It is worth mentioning that the presence of such a structure
may imply that part of the respiratory system, probably the abdominal
air sacs, invaded the anterior and mid-portion of the tail in these taxa, a
condition unusual among non-avian dinosaurs.
In sum, Aoniraptor libertatem has a combination of features that
indicates it belongs to Megaraptora, and several traits that indicate it
may be well-nested among derived tyrannosauroids. In spite of that,
Aoniraptor shows several traits that distinguish it from megaraptorids
such as Megaraptor and Aerosteon. First, Aoniraptor lacks the ventral,
thick longitudinal keel along caudal vertebrae present in these taxa, a
feature considered as typical of megaraptorids by Méndez et al. (2012).
Further, Aoniraptor differs in the different proportions of the centrum,
having very elongate anterior caudal centra, whereas in Aerosteon
and Megaraptor proximal caudal vertebrae are nearly as long as tall
(Calvo et al., 2004; Sereno et al., 2008). In addition, in Aoniraptor the
vertebral centrum of all caudals, with the exception of the rst one,
lacks any sign of pleurocoels or deep penumatic fossae. This differs
from the extensive pneumatization seen in megaraptorids such as
Aerosteon and Megaraptor, in which pleurocoels are present in all
available anterior and mid-caudal vertebrae (Calvo et al., 2004; Sereno
et al., 2008; Méndez et al., 2012; Martinelli et al., 2013). Furthermore,
in Aoniraptor the buttresses located below the transverse processes of
anterior caudals are not so thick and prominent as in Megaraptor and
Orkoraptor (Calvo et al., 2004; Novas et al., 2008).
As indicated above, Aoniraptor shares a large number of features
with derived tyrannosauroids such as Alioramus, Tarbosaurus, and
Tyrannosaurus. However, it has conspicuous features to differentiate
it, including the presence of pleurocoels on its rst caudal vertebra, and
the straight and long haemal arches, contrasting with the boat-shaped
condition of tyrannosauroids (Rauhut, 2003). Aditionally, the elongate
proportions of the centrum in Aoniraptor are very different from the
shorter and more robust elements of tyrannosauroids.
In conclusion, based on the aforementioned combination of
characters, Aoniraptor libertatem is regarded as a non-megaraptorid
megaraptoran tyrannosauroid (sensu Novas et al., 2013; Porri et al.,
2014), a hypothesis that should be tested by a numerical phylogenetical
Comments on isolated remains previously referred to as
Megaraptoridae: Based on the recognition of some anatomical features,
especially the presence of pleurocoels, several authors sustained the
presence of megaraptorids in different South American localities based
on isolated caudal vertebral centra. For example, Martinelli et al. (2013)
and Méndez et al. (2012) sustained the presence of megaraptorids in
Brazil on the basis of isolated caudal elements. Méndez et al. (2012)
described an isolated centrum from the Bauru Group (Maastrichtian;
Late Cretaceous). As pointed out by Méndez and collaborators, this
element differs from megaraptorids such as Aerosteon and Megaraptor
in that the ventral surface lacks a middle longitudinal keel as well as in
its more elongate proportions. These features, together with a greatly
rugose anterior articular surface, suggest that this vertebra is likely a
sacral vertebrae. In the same line, Martinelli et al. (2013) described an
isolated centrum from the Bauru Group (Campanian; Late Cretaceous)
as belonging to Megaraptoridae. Although the centrum was identied
as a caudal vertebra, the rugose texture of its anterior articular surface,
as well as the anteroposteriorly expanded transverse processes, indicate
that this may represent a posterior sacral vertebra.
As in the case of Aoniraptor both elements show pleurocoels
and notably elongate and dorsoventrally low centra. This contrasts
FIGURE 25. Aoniraptor libertatem (holotype). Anterior haemal arch
in A, B, anterior; C, D, posterior; E, F, left lateral; G, H, right lateral
views. Abbreviations: hc, haemal canal; pnp, pneumatic pocket. Scale
bar: 3 cm.
with Megaraptor, which shows notably robust and dorsoventrally tall
sacral vertebral centra (Porri et al., 2014). In this aspect, the elements
reported by Méndez et al. (2012) and Martinelli et al. (2013) may be
identied as belonging to a form more nearly related to Aoniraptor than
to Megaraptor, but only more complete elements from Brazil could
Aoniraptor libertatem and comments on the phylogenetic
position of some African theropods: Resemblances between the
tail anatomy of Aoniraptor and the Early Cretaceous African taxa
Bahariasaurus ingens (Stromer, 1934) and Deltadromeus agilis (Sereno
et al., 1996) are noteworthy. Stromer (1934, 1935) originally described
a large number of scattered specimens as referable to Bahariasaurus,
coming from different localities. Because the specimens were found
in different localities and stratigraphic units, the referral to a single
taxon should be regarded as problematic. In this way, based on the
work of Sereno et al. (1996), the holotype and only known specimen
of Bahariasaurus only includes two caudal vertebrae (determined
as dorsals by Stromer in the original description, but the absence
of parapophyses indicates that may be better interpreted as caudal
elements), a neural arch, three sacral centra, pubes and a proximal
ischium (all illustrated and described by Stromer, 1934, but lost during
the Second World War). The remaining specimens were referred by
Sereno et al. (1996) to Deltadromeus, including pubes, femur, bula,
and proximal tibia (Stromer, 1922, pl. 2, gs. 4,15; pl. 3, gs. 3,5,6).
In spite of noticing minor differences between both taxa, Sereno et
al. (1996) did not deny the close similarities between the materials of
Deltadromeus and Bahariasaurus, as originally pointed out by Stromer
The then poor knowledge of theropod Gondwanan faunas,
together with the incomplete and peculiar nature of the available
specimens of Bahariasaurus and Deltadromeus, as well as the loss of
the former’s holotype during the Second World War, conspired against
recognizing the phylogenetic afnities of both taxa. Because of these,
Bahariasaurus was considered as Ceratosauria (Bonaparte, 1991), as
Carnosauria of uncertain afliation (Molnar et al., 1990), as Allosauria
(Paul, 1984; Rauhut, 1995), and as possible Tyrannosauridae (Chure,
2000). On the other hand, Deltadromeus was proposed as having
coelurosaurian (Sereno et al., 1996; Rauhut, 2003) or ceratosaurian
(Wilson et al., 2003; Carrano and Sampson, 2008) afnities. In spite of
these opinions, we were not able to nd clear derived ceratosaurian or
allosauroid features shared with Bahariasaurus or Deltadromeus.
In the case of Bahariasaurus, the caudal anatomy is highly
reminiscent of Aoniraptor in several features. For example, elongate
anterior caudal centra, anterior caudals with buttresses at the base of
neural arch, anterior caudals (and also sacral vertebrae) with deep
pneumatic fossae on the sides of its centrum, whereas these are absent
in more posterior caudals, subrectangular elongate neural spines with
deep laminae indicating the anchoring of interspinal ligaments, deep
and wide prespinal fossa, and a well-developed lamina contacting the
prezygapophyses with the transverse processes (see illustrations and
description in Stromer, 1934) are derived features shared by both taxa.
The same seems to be true also for Deltadromeus. Available
illustrations of the original description of the specimen (Sereno et al.,
1996) indicate that this taxon shares with Aoniraptor subrectangular,
elongate and robust rectangular neural spines on anterior mid-caudal
FIGURE 24. Aoniraptor libertatem (holotype). Posterior caudal vertebra
in A, C, dorsal; B, D, ventral; E, G, right lateral; F, H, left lateral; I,J,
posterior; and K, L, anterior views. Abbreviations: ha, haemal arch;
ns, neural spine; pf, prespinal fossa; prz, prezygapophysis. Scale bar:
vertebrae (considered as autapomorphic for this taxon by Sereno and
collaborators in the original description), strong ligamental scars in
anterior neural spines, presence of a prezygopostzygapophyseal lamina
on mid-caudal vertebrae, anterior mid-caudals having a fossa in the
area of contact between the neural arch and the transverse processes,
and thick spinoprezygapophyseal laminae. This latter feature is absent
in remaining theropods, including the tyrannosauroids Alioramus and
Tyrannosaurus, and appears to be a character exclusively shared by
Deltadromeus and Aoniraptor.
Wilson et al. (2003) cited the reduction of distal condyles of
metatarsal IV in Deltadromeus as indicating that this genus should
be included within noasaurid ceratosaurians. However, this condition
is widely present in basal coelurosaurs, such as ornithomimids and
tyrannosaurids, as early noted by Rauhut (2003), and is also present in
the megaraptorans Megaraptor and Australovenator (Calvo et al., 2004;
Hocknull et al., 2009). In this way, the presence of reduced condyles of
distal metatarsal IV is an ambiguous trait uniting Deltadromeus with
Noasauridae, and no clear synapomorphic features may include this
genus among abelisauroid theropods. Based on strong anatomical
similarities of vertebral elements, we consider that Aoniraptor,
Deltadromeus agilis, and Bahariasaurus ingens, conform to a clade of
non-megaraptorid megaraptoran theropods.
In spite of the strong similarities noted above, important
differences between Deltadromeus and Bahiasaurus, on one hand,
and megaraptorids, including Megaraptor and Aerosteon, on the
other, exist. For example, the African taxa show a complex distal end
of the femur having an additional anterior expansion of the medial
distal condyle, a narrow and poorly expanded distal pubic boot, and
a notably narrow pubic shaft. On the other hand, the megaraptorid
Australovenator has a simpler distal end of the femur (Hocknull et al.,
2009), and Megaraptor and Aerosteon have robust pubes with a notably
anteroposteriorly expanded pubic boot (Benson et al., 2010). Additional
distinctive features, noted solely for Deltadromeus, include humerus
with reduced deltopectoral crest and bulbous head, and radius and ulna
proximally featureless (Sereno et al., 1996). In contrast, megaraptorids
such as Megaraptor and Australovenator have robust forelimbs, a
humerus with attened humeral head and large deltopectoral crest, and
a proximal end of the ulna complex and with an enlarged olecranon
(Agnolin et al., 2010; White et al., 2012). In this way, Aoniraptor,
Deltadromeus and Bahariasaurus differ from megaraptorids in a large
number of features, which may indicate the presence of another, still
poorly known megaraptoran clade in Southern landmasses. If this
hypothesis is corroborated, the name Bahariasauridae Huene, 1936 may
be employed to group these taxa, highlighting the distinctiveness of its
Finally, Apesteguía et al. (2013) reported the presence of a
Deltadromeus-like theropod having a bulbous humeral head in the Late
Cretaceous of Patagonia, which reinforces the idea that this clade was
probably diverse and widespread in Gondwana. The presence of two
ngers in this unpublished specimen (Apesteguía et al., 2013) adds an
additional similarity between these taxa and tyrannosaurids.
MANIRAPTORA Gauthier, 1986
PARAVES Sereno, 1997
?UNENLAGIIDAE Bonaparte, 1999
Gen. et sp. indet.
Referred materials: MPCA-Pv 805/1-805/6, non-articulated,
associated specimens including three caudal vertebrae (805/1-3); a
distal end of a right metacarpal I (805/4); and fragmentary right pedal
digit ungual II (805/5).
Description and comparisons: Two of the preserved vertebrae
are likely mid-caudals (Fig. 28). These elements are anteroposteriorly
long and laterally compressed, with feebly developed neural spines
and transverse processes. The transverse processes are posterolaterally
oriented and subtriangular in contour in dorsal view. In addition, the
transverse processes are located on the posterior half of the centrum.
A posteriorly positioned transverse process is present in Buitreraptor
(Makovicky et al., 2005), Rahonavis (Forster et al., 1998) and Mahakala
(Turner et al., 2011). The ventral surface of the centrum is transversely
compressed, bearing a ventral longitudinal ridge. This ventral ridge is
FIGURE 27. Comparissons of mid caudal vertebrae of selected
theropods in right lateral view. A, Aoniraptor libertatem nov.; B,
Deltadromeus agilis (redrawn from Sereno et al., 1996); C, Alioramus
altai (redrawn from Brusatte et al., 2012); D, Tyrannosaurus rex
(redrawn from Brochu, 2003); E, Ceratosaurus nasicornis (redrawn
from Madsen and Welles, 2000); and F, Allosaurus fragilis (redrawn
from Madsen, 1976). Not to scale.
FIGURE 26. Aoniraptor libertatem (holotype). Mid-haemal arch in A,
B, posterior; C, D, anterior; E, F, left lateral; G, H, right lateral; and I,
J, proximal views. Abbreviations: ap, anterior process; as, proximal
articular surface; hc, haemal canal; pf, pneumatic pocket; pp, posterior
process. Scale bar: 3 cm.
FIGURE 28. Mid-caudal vertebra of ?Unenlagiidae indet. in: A, C,
dorsal view; B, D, ventral view; E, H, lateral view; I, J, anterior view;
K, L, posterior view. Scale bar: 1 cm.
also present in Buitreraptor (Makovicky et al., 2005) and Rahonavis
(Forster, et al. 1998) mid caudals, but not in Deinonychus (Ostrom,
1996) and Velociraptor (Norell and Makovicky, 1997).
Another caudal vertebra is likely a posterior caudal (Fig. 29).
It is anteroposteriorly long and dorsoventrally low, with concave
lateral surfaces when viewed ventrally. As in distal caudals of most
paravians (e.g., Buitreraptor, Deinonychus, Rahonavis, Mahakala and
Microraptor (Ostrom, 1996; Makovicky et al., 2005; Hwang et al.,
2002; Turner et al., 2011) the transverse processes are represented by
smooth and long lateral ridges (Ostrom, 1969). The articular surfaces
are rounded and slightly platycoelous, as in other paravians such as
Deinonychus (Ostrom, 1969). Ventrally, the centrum presents two
longitudinal ridges that dene a medial longitudinal groove. This
feature is common among paravians, such as Deinonychus (Ostrom,
1996) and Buitreraptor (Gianechini and Apestguía, 2010). The distal
vertebrae lack any pneumatic features, as in other paravians (Ostrom,
A right metacarpal one is preserved, but lacks most of its proximal
end (Fig. 30). The metacarpal exhibits some interesting features,
including a stout and notably asymmetric shaft, which contrasts with
most paravians (e.g., Deinonychus, Velociraptor; Ostrom, 1969; Norell
and Makovicky, 1999), which have slightly and poorly asymmetric
shafts. The proximal end possesses a sub-triangular cross-section
that results in three different surfaces (lateral, dorsomedial and
ventral) that constitute the main body of the metacarpal, a widespread
condition among theropods. The metacarpal has a laterodorsal ridge
that originates on the dorsal margin of the lateral condyle and extends
proximally probably until the (not preserved) proximodorsal end of
the bone. The laterodorsal ridge forms a smooth edge that probably
overlapped metacarpal II laterally. A laterodorsal ridge is present in
Buitreraptor, albeit less developed, whereas it is absent in Deinonychus
or Velociraptor (Ostrom, 1969; Norell and Makovicky, 1999). The
distal end bears well-developed distal condyles separated by a deep
groove, thus this element is strongly ginglymoid as in other paravians
(e.g., Velociraptor; Norell and Makovicky, 1999). In distal view the
condyles diverge ventrally, contrasting with other paravian theropods
such as Deinonychus or Buitreraptor (Ostrom, 1969; Makovicky et
al., 2005) in which both condyles are subparallel to each other. This
divergence is due to the ventral portion of the medial condyle, which
is strongly aring medially. The medial condyle is stouter and more
posterodorsally positioned than the lateral one. In medial view, there is
a strong ventral rim that contacts the trochlea of the medial condyle and
projects proximally along the medioventral surface of the bone, resulting
in a continuous ange of bone, not present in other theropods. In distal
view the lateral condyle has a small depression on its laterodorsal
portion that probably served for articulation with the metacarpal II. The
lateral condyle lacks any trace of a ligamental pit, whereas the medial
condyle bears a small, albeit well-dened ligamental pit on the ventral
portion of the condyle, a condition shared with Buiteraptor. Dorsally,
the two condyles are united by a transverse ridge of bone.
A right pedal ungual phalanx of digit II was found (Fig. 31). It
is well preserved, missing only the distal tip. As in most theropods,
the claw is laterally compressed and ventrally curved. The proximal
articular surface is large and ovoid, with a median keel separating the
two articular concavities, as is typical in deinonychosaurian sickle-
claws (Werner and Rauhut, 1995). On the proximodorsal corner of the
claw, there is a well-developed, proximally projected process, which
is continuous with the dorsal margin of the blade. This morphology
resembles the pedal unguals of paravians such as Deinonychus and
Buitreraptor (Ostrom, 1969; Senter, 2007). As in these taxa, the medial
articular concavity is larger than the lateral one, indicating that this
element pertains to the right pes. A well-developed exor tubercle
projects ventral to the proximal articular surface. As in paravians
such as Deinonychus and Buitreraptor, the exor tubercle is placed
immediately distal to the articular surface (Ostrom, 1969). The ventral
surface of the ungual is represented by a ventromedial sharp ridge
that runs along the entire ventral surface of the claw. This feature is
FIGURE 29. Posterior caudal vertebra of ?Unenlagiidae indet. in: A,
C, dorsal view; B, D, ventral ridge; E, H, lateral view; I, J, posterior
view. Scale bar: 1 cm.
present in other paravians, for example Deinonychus, Velociraptor and
Buitreraptor (Ostrom, 1969; Norell and Makovicky, 1999; Makovicky
et al., 2005). The lateral and medial sides show shallow longitudinal
grooves; the lateral one is placed in a higher position than the medial
one, as in other paravians (Kirkland et al., 1993; Rauhut and Werner,
Discussion: Although fragmentary, the recovered materials
bear some features that are worth discussion. The specimens show a
combination of characters shared with other paravians (e.g., transverse
processes of the distal caudals represented by slight and long ridges;
rounded and slightly platycoelous articular faces on caudal vertebrae;
two longitudinal grooves separated by a ridge in the ventral surface
of caudal centra; proximal end of metacarpal I with a triradiate
contour; sickle-claw ungual II, having well-developed exor tubercle,
a ventromedialy located sharp edge, and asymmetrical longitudinal
grooves on medial and lateral sides of the blade) that are indicative of
the paravian afnities of the specimens.
The position of MPCA-Pv 805/1- 805/6 within paravians is more
FIGURE 30. Right metacarpal one of ?Unenlagiidae indet. in: A, B, dorsal view; C, D, ventral view; E, F, lateral view; G, H, medial view; I, J,
distal view. Scale bar: 1 cm.
difcult to assess due to the fragmentary and isolated nature of the
specimens; however, some features might indicate unenlagiid afnities.
In this regard, the vertebral centra show a series of lateral grooves
and ridges, that, together with the presence of a ventral ridge on the
mid-caudal centra, are traits that are also recorded in Buitreraptor
(Makovicky et al., 2005), Mahakala (Turner et al. 2011) and Rahonavis
(Forster, et al. 1998), and are absent in troodontids and dromaeosaurids
(e.g., Gobivenator, Deinonychus, Velociraptor, Linheraptor; Osborn,
1924; Ostrom, 1969; Xu et al., 2010; Tsuihiji et al., 2014) in which the
lateral surface is smooth, and the ventral surface shows a longitudinal
medial groove. On the other hand, the preserved metacarpal bears a
well-developed laterodorsal ridge that is not present in troodontids or
derived dromaeosaurids (e.g., Sinornithoides, Deinonychus; Ostrom,
1969; Currie and Dong, 2001) but is present in a yet undescribed
Buitreraptor specimen (Agnolin and Novas, 2013) and might turn out
to be an unenlagiid synapomorphy. Based on the above mentioned
traits, geographic and temporal location, MPCA-Pv 805/1-805/6 is
likely to represent an unenlagiid theropod, but this should be considered
cautiously, due to the fragmentary nature of the specimens.
Present ndings provide insights about the Upper Cretaceous
theropod diversity in northwestern Patagonia. The abelisauroids here
described are reminiscent of the poorly known group Noasauridae, but
due to the isolated nature of these elements, a precise determination was
not possible. Nevertheless, the only previously reported abelisauroids
from the Huincul Formation were large-sized abelisaurids (see Canale
et al., 2006). The new abelisauroid material allows us to recognize the
presence of small abelisauroids together with large abelisaurids.
Among the newly collected material, large elements pertaining
to two carcharodontosaurid individuals were found. A partial right
foot represents a gigantic sized theropod that is comparable in size
with Mapusaurus roseae, known from the same stratigraphic unit.
Due to the incomplete nature of the specimens here described a
referral to Mapusaurus cannot be sustained, although it cannot be
dismissed as well. The new material improves the knowledge of
carcharodontosaurid foot anatomy. Moreover, an isolated postorbital is
the basis for recognition of the new medium-sized carcharodontosaurid
Taurovenator violantei, which increases the diversity of the clade.
This new species shows some conspicuous features such as a horn-
like orbital boss and a pneumatic foramen in the ventral side of the
orbital brow that are unique for this taxon and distinguish it from other
carcharodontosaurids. Furthermore, it indicates the coexistence of very
large and medium sized carcharodontosaurids at the same fossiliferous
Here we report for the rst time the presence of megaraptoran
and paravian theropods from the Huincul Formation. In this regard,
the new megaraptoran, namely Aoniraptor libertatem, constitutes the
oldest member of this clade known in South America. It represents
the most complete caudal remains for this group and thus sheds light
on megaraptoran caudal anatomy. A large number of traits present in
Aoniraptor are found in derived tyrannosauroid taxa and support the
hypothesis that megaraptorans are members of Tyrannosauroidea
(Novas et al., 2013; Porri et al., 2014). Further, the shared features of
Aoniraptor with African taxa such as Bahariasaurus and Deltadromeus
indicate that these three forms may constitute a still poorly known clade
of derived Gondwanan tyrannosauroids.
Finally, the paravian remains show a caudal vertebral morphology
with features similar to some unenlagiid taxa. However, the metacarpal
shows some anatomical peculiarities that may indicate it belongs to a
new, unnamed form.
The presence of at least six theropod species in a single fossiliferous
locality, belonging to abelisauroids, allosauroids, tyrannosauroids, and
paravians, probably represents the taxonomically richest theropod
association found in Patagonia. Furthermore, it supports the idea that
Patagonia is a key place (Novas et al., 2013) that provides important
information for the understanding of theropod evolution in Gondwana.
We thank Gabriel Lio for useful comments and support during the
making of this work. We also thank the technicians Marcelo P. Isasi,
Carlos H. Alsina, Ricardo Stoll and Germán Stoll for helping with the
preparation of the materials. Ariel Méndez kindly lent photographs
and information on Brazilian specimens. Special thanks to Mr. Enzo
Violante, who allowed eld trips and paleontological investigation on
his own farm. We are indebted to the comments and corrections to the
manuscript made by the reviewers, A.G. Martinelli and A.H. Méndez.
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