Osteology and phylogenetic relationships of Tyrannotitan chubutensis Novas, de Valais, Vickers-Rich and Rich, 2005 (Theropoda: Carcharodontosauridae) from the Lower Cretaceous of Patagonia, Argentina

Abstract

The theropod clade Carcharodontosauridae is a broadly distributed group of large allosauroid theropods. The carcharodontosaurids recorded in the Albian– Cenomanian of Gondwana are the youngest and most derived members of this clade. Tyrannotitan chubutensis, from the Cerro Castaño Member of Cerro Barcino Formation (Albian; Chubut Group), Central Patagonia, Argentina, is of prime interest among Gondwanan carcharodontosaurids as it represents the oldest record of the group. Here we offer a detailed osteological comparative description of the holotype and paratype of Tyrannotitan chubutensis together with a new diagnosis of the species. The new information results in a better understanding of this taxon and Carcharodontosauridae. Furthermore, a comparative study of the anatomy of the pectoral girdle of Giganotosaurus is reinterpreted as very similar to that of Tyrannotitan and Mapusaurus. We also present a phylogenetic analysis of Carcharodontosauridae that recovers Tyrannotitan as a derived carcharodontosaurid, being the sister group of the clade formed by Giganotosaurus and Mapusaurus, all nested in the clade Giganotosaurini.

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Osteology and phylogenetic relationships of
Tyrannotitan chubutensis Novas, de Valais,
Vickers-Rich and Rich, 2005 (Theropoda:
Carcharodontosauridae) from the Lower Cretaceous of
Patagonia, Argentina
Juan Ignacio Canaleab, Fernando Emilio Novasac & Diego Polad
a CONICET: Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina
b Museo Municipal ‘Ernesto Bachmann’, Dr. Natali S/N Villa El Chocón (8311), Neuquén,
Argentina
c Laboratorio de Anatomía Comparada y Evolución de los Vertebrados, Museo Argentino
de Ciencias Naturales ‘Bernardino Rivadavia’, Av. Ángel Gallardo 470 (C1405DJR), Buenos
Aires, Argentina
d Museo Paleontológico ‘Egidio Feruglio’, Fontana 140, 9100, TrelewChubutArgentina
Published online: 08 Jan 2014.
To cite this article: Juan Ignacio Canale, Fernando Emilio Novas & Diego Pol , Historical Biology (2014): Osteology
and phylogenetic relationships of Tyrannotitan chubutensis Novas, de Valais, Vickers-Rich and Rich, 2005 (Theropoda:
Carcharodontosauridae) from the Lower Cretaceous of Patagonia, Argentina, Historical Biology: An International Journal of
Paleobiology
To link to this article: http://dx.doi.org/10.1080/08912963.2013.861830
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Historical Biology, 2013
http://dx.doi.org/10.1080/08912963.2013.861830
Osteology and phylogenetic relationships of Tyrannotitan chubutensis Novas, de Valais, Vickers-
Rich and Rich, 2005 (Theropoda: Carcharodontosauridae) from the Lower Cretaceous of
Patagonia, Argentina
Juan Ignacio Canale
a,b
*, Fernando Emilio Novas
a,c1
and Diego Pol
a,d2
a
CONICET: Consejo Nacional de Investigaciones Cientı
´ficas y Te
´cnicas, Argentina;
b
Museo Municipal ‘Ernesto Bachmann’, Dr. Natali
S/N Villa El Choco
´n (8311), Neuque
´n, Argentina;
c
Laboratorio de Anatomı
´a Comparada y Evolucio
´n de los Vertebrados, Museo
Argentino de Ciencias Naturales ‘Bernardino Rivadavia’, Av. A
´ ngel Gallardo 470 (C1405DJR), Buenos Aires, Argentina;
d
Museo
Paleontolo
´gico ‘Egidio Feruglio’, Fontana 140, 9100 Trelew, Chubut, Argentina
(Received 1 October 2013; accepted 30 October 2013)
The theropod clade Carcharodontosauridae is a broadly distributed group of large allosauroid theropods. The
carcharodontosaurids recorded in the Albian – Cenomanian of Gondwana are the youngest and most derived members of this
clade. Tyrannotitan chubutensis, from the Cerro Castan
˜o Member of Cerro Barcino Formation (Albian; Chubut Group),
Central Patagonia, Argentina, is of prime interest among Gondwanan carcharodontosaurids as it represents the oldest record
of the group. Here we offer a detailed osteological comparative description of the holotype and paratype of Tyrannotitan
chubutensis together with a new diagnosis of the species. The new information results in a better understanding of this taxon
and Carcharodontosauridae. Furthermore, a comparative study of the anatomy of the pectoral girdle of Giganotosaurus is
reinterpreted as very similar to that of Tyrannotitan and Mapusaurus. We also present a phylogenetic analysis of
Carcharodontosauridae that recovers Tyrannotitan as a derived carcharodontosaurid, being the sister group of the clade
formed by Giganotosaurus and Mapusaurus, all nested in the clade Giganotosaurini.
Keywords: Theropoda; Carcharodontosauridae; Tyrannotitan; Patagonia; Argentina
1. Introduction proposal was recently challenged by Novas et al., which
Allosauroid theropods, and particularly carcharodontosaur- considered Megaraptora as more closely related to
ids, have been the focus of recent research (Novas et al. tyrannosauroid coelurosaur theropods (Novas et al. 2013)
2005; Coria and Currie 2006; Brusatte and Sereno 2008; than to carcharodontosaurids.
Sereno and Brusatte 2008;Brusatteetal.2009;Ortegaet al. The phylogenetic relationships within carcharodonto-
2010). Although Carcharodontosauridae was formerly saurids have been highly debated, in spite of the few
interpreted as a group of gigantic Gondwanan predatory detailed anatomical descriptions available for most
dinosaurs, this clade is now known to be present in both the carcharodontosaurids (Coria and Currie 2006; Brusatte
southern and northern hemispheres (Brusatte et al. 2009, and Sereno 2007; Eddy and Clarke 2011). Therefore, the
2012; Ortega et al. 2010). New carcharodontosaurid taxa description in detail of carcharodontosaurid remains is
have been recovered from different localities in the northern necessary in order to understand the basic osteology, as
hemisphere, such as Spain (Ortega et al. 2010) and China well as, the phylogenetic relationships of this group.
(Brusatte et al. 2009; Brusatte et al. 2012), distant from the The aim of this paper was to provide a detailed
‘classic’ localities in South America and Africa (Stromer osteological description of Tyrannotitan chubutensis
1931; Coria and Salgado 1995; Sereno et al. 1996;Sereno Novas, de Valais, Rich and Rich, 2005, including a new
and Brusatte 2008). Recently, Benson et al. (2010) and revised diagnosis of the genus and species. We also
considered that some ‘problematic’ carnivorous dinosaurs present and discuss a phylogenetic analysis of carchar-
from southern continents, including Megaraptor, Orkor- odontosaurids, including the anatomical information
aptor, Australovenator and Aerosteon (all grouped in a obtained from the study of both specimens of Tyrannotitan
clade called Megaraptora), with the European form and new data of other carcharodontosaurid taxa.
Neovenator as their sister group, constitute a monophyletic
clade that conform the sister group of Carcharodontosaur-
idae: the Neovenatoridae. In this way, these authors 2. Institutional abbreviations
established the new clade Carcharodontosauria, which BYU-VP: Brigham Young University, Vertebrate Paleon-
includes Neovenatoridae and Carcharodontosauridae. This tology collection, Provo, Utah, USA MACN-CH: Museo
*Corresponding author. Email: juanignaciocanale@hotmail.com
q 2013 Taylor & Francis
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2 J.I. Canale et al.
Argentino de Ciencias Naturales ‘Bernardino Rivadavia’,
coleccio
´n Chubut, Buenos Aires, Argentina; MCF-PVPH:
Museo Municipal ‘Carmen Funes’, Plaza Huincul,
Provincia de Neuque
´n, Repu
´blica Argentina; MMCh-PV:
Museo Paleontolo
´gico ‘Ernesto Bachmann’, coleccio
´n
Paleontologı
´a Vertebrados, Villa El Choco
´n, Provincia de
Neuque
´n, Argentina; MNN IGU: Muse
´e National du
Niger, Iguidi collection. Niger; MPEF-PV: Museo
Paleontolo
´gico ‘Egidio Feruglio’, coleccio
´n Paleontologı
´a
Vertebrados, Trelew, Provincia de Chubut, Argentina;
MUCPV: Museo de la Universidad del Comahue, Ciudad
de Neuque
´n, Provincia de Neuque
´n, Argentina; MUCPV-
Ch: Museo de la Universidad del Comahue, Coleccio
´n
Choco
´n, Villa El Choco
´n, Provincia de Neuque
´n,
Repu
´blica Argentina; NCSM: North Carolina State
Museum of Natural Sciences, Raleigh, North Carolina,
USA; SGM-Din: Ministe
´re de l’Energie et des Mines,
dinosaur collection, Rabat, Morocco; UMNH-VP: Utah
Museum of Natural History, Vertebrate Paleontology
collection, Salt Lake City, Utah, USA.
3. Anatomical abbreviations
abr, articular brace; ac, ace tabulum; acd, anterior
centrodiapophyseal lamina; af, antorbital fossa; a l,
accessory lamina; ap, acromion process; avp, anteroventral
process; bict, biceps tubercle; cf, coracoid foramen; cfu,
collateral furrow; cp, collateral pit; cprf, centroprezygapo-
physeal fossa; cprl, centroprezygapophyseal lamina; ctf,
crista tibiofibularis; dc, distal carina; df, dorsal fossa; dia,
diapophysis; dpc, deltopectoral crest; ep, epipophysis; f,
foramen; ff, fibular fossa; fh, femoral head; flf, flexor fossa;
foc, facet for occipital condyle; ft, fourth trochanter; gf,
glenoid fossa; hya, hypantrum; hys, hyposphene; idp,
interdental plates; ift, iliofibularis tubercle; il, ilium; ilped,
iliac peduncle; iprf, infraprezygapophyseal fossa; jaf,
articular facet for jugal; jpr, jugal pneumatic recess; lc,
lateral condyle; lf, lateral fossa; lmf, lateromedial furrow;
ls, ligament scar; lt, lesser trochanter; mc, mesial carina;
mco, mesial condyle; mf, Meckelian fossa; mfp, medial
fibular pocket; mg, Meckelian groove; nc, neural canal; nvf,
neurovascular foramen; nvg, neurovascular groove; on,
obturator notch; op, obturator process; paf, articular facet
for postorbital; pcd, posterior centrodiapophyseal lamina;
pec, prezygoepipophyseal crest; pf, pubic foramen; pl,
pleurocoel; po, pneumatic opening; pvp, posteroventral
process; poz, postzygapophysis; pp, parapophysis; ppdl,
paradiapophyseal lamina; pped, pubic peduncle; prz,
prezygapophysis; ps, pubic symphysis; pvp, posteroventral
process; r, ridge; rcl, ridge for cruciate ligaments; spol,
spinopostzygapophyseal lamina; spof, spinopostzygapo-
physeal fossa; sprl, spinoprezygapophyseal lamina; sprf,
spinoprezygapophyseal fossa; tp, transverse process; tub,
tuberosity; vf, ventral fossa.
4. Systematic paleontology
Dinosauria Owen, 1842
Saurischia Seeley, 1888
Theropoda Marsh, 1881
Allosauroidea Marsh, 1878
Carcharodontosauridae Stromer, 1931
Carcharodontosaurinae Stromer, 1931 (nomen
translatum Brusatte and Sereno, 2008)
Giganotosaurini Coria and Currie, 2006 (nomen
translatum Brusatte and Sereno, 2008)
Tyrannotitan chubutensis Novas, de Valais, Vickers-Rich
and Rich, 2005
4.1 Holotype
MPEF-PV 1156: Partially articulated skeleton, composed
of right dentary with two complete teeth, left dentary,
articulated dorsal vertebrae 2nd to 7th, 8th? to 11th?
dorsals, 14th? dorsal, 1st? sacral vertebra, anterior caudal
vertebra, left scapula and coracoid, right humerus, both
radii, fragments of left ilium, both ischia, both pubis, both
femora, left fibula, six haemal arches and fragments of
gastralia.
4.2 Paratype
MPEF-PV 1157: Composed by right jugal, right
quadratojugal, right dentary, two isolated teeth, 7th
cervical vertebra, 1st dorsal vertebra, 4th dorsal, 6th to
8th dorsals, 12th to 14th dorsals, isolated neural spine of a
posterior dorsal vertebra, incomplete sacrum, distal caudal
vertebra, proximal fragment of dorsal rib, right dorsal rib
14, haemal arch, right femur, left metatarsal II and left
pedal phalanges II-2, II-3, IV-2, IV-3. The specimen was
found 1 km from the holotype material.
4.3 Referred material
MPEF-PV 10821: 19 isolated teeth found in this locality,
which are housed at the MPEF collections but have not
been assigned to the holotype or paratype. Only two
isolated teeth have been catalogued as part of the paratype
(MPEF-PV 1157; see above).
4.4 Locality and horizon
‘La Juanita’ farm, 28 km north-west of Paso de Indios
town, Chubut Province, Argentina (Figure 1). Precise GPS
data of the fossiliferous localities are deposited at the
MPEF collection and available upon request. Cerro
Castan
˜o Member, Cerro Barcino Formation, Albian
(Musacchio and Chebli 1975; Codignotto et al. 1978;
Rich et al. 2000; Marveggio and Llorens 2013).
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3 Historical Biology
Figure 1. Tyrannotitan chubutensis (Novas et al. 2005) locality map: (A) Argentina and (B) detail of Chubut province with the
Tyrannotitan locality indicated by a star.
Cerro Barcino Formation is the upper unit of the Chubut
Group and its age has been regarded as Hauterivian to
Senonian (Campanian?) in age (Page et al. 1999), and is
subdivided into several members. The basalmost member is
Puesto La Paloma and is characterised by pyroclastic and
fluvial sediments, with dunes intercalated deposited under
arid conditions. This unit contains chelid and meiolaniform
turtles (Gaffney et al. 2007; de la Fuente et al. 2011; Sterli
et al. 2013), as well as abelisaurid theropod and
titanosauriform sauropod dinosaurs (Rich et al. 2000;
Rauhut et al. 2003). Overlying La Paloma Member is the
Cerro Castan
˜o Member, formed mainly by fluvia l
sediments. Sedimentological evidence indicates that during
deposition of the Cerro Castan
˜o Member, a return to wetter
conditions occurred over the previous unit. Apart from
Tyrannotitan (Novas et al. 2005), this member has provided
a variety of vertebrate remains, including crocodiles
(Leardi and Pol 2009), sphenodontians (Apesteguı
´a and
Carballido in press), sauropod eggs (Argaran
˜az et al. 2013)
and possibly the ceratosaur theropod Genyodectes serus
(Rauhut et al. 2003;Rauhut 2004). Cerro Barcino
Formation culminates with Bayo Overo Member, in
which the titanosauriform sauropod Chubutisaurus insignis
was found (Del Corro 1975; Carballido et al. 2011).
4.5 Emended diagnosis
A carcharodontosaurid theropod diagnosed by the follow-
ing autapomorphic characters: teeth with bilobated
denticles in the mesial carinae; dentary with an
anteroventrally-posterodorsally symphyseal margin in
lateral view; second and third dorsal vertebrae with well-
developed accessory lamina connecting anterior and
posterior centrodiapophyseal laminae; fibular fossa
extended over the proximal end of the crista tibiofibularis
in the femoral shaft; proximomedial fossa of the fibula
with posteriorly projected anterior border. Modified from
Novas et al. (2005) (see Section 6).
5. Description
5.1 Jugal
The right jugal of the paratype (MPEF-PV 1157) is well
preserved, but lacks a fragment of its anterior portion, the
surface for the maxilla/lacrimal contact surface and the
quadratojugal processes (Figures 2 and 7).
The jugal is a transversely flattened bone that has an
anterior projectio n for articulation with the maxilla, a
dorsal process to contact the postorbital and a double
posterior projection for articulation with the quadratoju-
gal. In lateral view the ventral margin of the bone is
straight to slightly convex (Figure 2), as in Carchar-
odontosaurus saharicus (SGM-Din 1) and Mapusaurus
(MCF-PVPH 108,167), but differing from that of
Allosaurus (UMNH-VP 9085, UMNH-VP 9086) where
the ventral margin is sigmoid in lateral view, with a strong
convexity ventral to the level of the postorbital process. In
ventral view, the jugal has a sigmoidal shape, with the
anterior region laterally concave and the posterior portion
laterally convex.
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4 J.I. Canale et al.
Figure 2. Tyrannotitan chubutensis right jugal (MPEF-PV 1157) photographs and line drawings in (A) lateral view and (B) medial view.
Note: Scale bar is 10 cm; see text for abbreviations.
The anterior end of the jugal is thin and laminar,
incompletely preserved in some areas, and bears on its
lateral surface the posteroventral corner of the antorbital
fossa (Figure 2(A)). The edge of this fossa is curved, with a
similar position and morphology to that of Mapusaurus
(MCF-PVPH 108.167) and Allosaurus (Madsen 1976). A
large jugal pneumatic recess is also present, and is as
expanded as in Mapusaurus (MCF-PVPH 108.167) and
Acrocanthosaurus (NCSM 14345).
A prominent horizontal ridge runs along most of the
lateral surface of the jugal, which extends from the notch
between the two quadratojugal processes towards few
centimetres anteriorly to the anterior margin of the
postorbital process. This crest, also present in Mapusaurus
(MCF-PVPH 108.167), was probably an insertion area for
the m. pterygoideus ventralis (Holliday 2009).
Ventrally to the ventral edge of the orbital margin, the
jugal is pierced by a foramen of about 1 cm in diameter,
which penetrates into the bone internal structure (Figure 2
(A)). Posteriorly to this foramen, there is a much smaller
and rounded blind depression.
The postorbital process of jugal is triangular in lateral
view, with the anterior margin nearly straight and
subvertically oriented. In cross section this process has a
rounded and robust anterior end and tapers posteriorly
becoming a thin lamina at its posterior margin. The base of
this process is anteroposteriorly long, as in Mapusaurus
(MCF-PVPH 108.167-168), but differing from the con-
dition of Carcharodontosaurus saharicus (SGM-Din 1) in
which the process is anteroposteriorly short. On the anterior
margin the oblique and anterolaterally oriented postorbital
facet occupies the dorsal three-quarters of the postorbital
process (Figure 2(A)). The laminar posterior margin of the
process bears a slight depression, corresponding to the
anterior edge of the infratemporal fossa.
The articulation for the quadratojugal is forked into
dorsal and ventral quadratojugal processes. Both processes
have their posterior end broken, being the ventral process
the most completely preserved. The latter is subcircular in
cross-section and bears a dorsal concavity. The dorsal
process is laminar in cross-section. The posterior region of
the jugal of Tyrannotitan lacks, both laterally and
medially, a third medial process or accessory prong
(contra Eddy and Clarke 2011), as was described for
Acrocanthosaurus (Eddy and Clarke 2011), Sinraptor
(Currie and Zhao 1993) and Mapusaurus (MCF-PVPH
108 168).
5.2 Quadratojugal
The right quadratojugal has been preserved in MPEF-PV
1157 (Figures 3 and 7). The jugal process is dorsoventrally
high, and becomes narrower towards its anterior end. The
squamosal process has a fairly constant anteroposterior
width along the dorsoventral axis throughout its entire
length. In lateral view, the height of the jugal process is
larger than the anteroposterior width of the squamosal
process, unlike Allosaurus (UMNH-VP 8944, UMNH-VP
8946) and Acrocanthosaurus (NCSM 14345) in which an
inverse relationship is present. In the posteroventral
corner, this bone has a posterior process similar to that of
other theropods. In medial view, a shallow depression is
present at the dorsal sector of the jugal process. This
depression represents the area for the articulation of the
posterodorsal process of the jugal.
5.3 Dentary
The three available dentaries are preserved in a fairly good
condition, lacking only the posteriormost portion that
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5 Historical Biology
Figure 3. Tyrannotitan chubutensis right quadratojugal (MPEF-PV 1157) photographs and line drawings in (A) lateral view and (B)
medial view. Note: Scale bar is 10 cm; see text for abbreviations.
contacts the postdentary bones. The following description
is based on the three elements.
In dorsal view, the dentary is transversely compressed,
and slightly widens anteriorly towards the symphyseal
area (Figure 4(C)). This feature is reminiscent to that of
other allosauroids, such as in Giganotosaurus (MUCPV-
Ch 1), Acrocanthosaurus (NCSM 14345), Allosaurus
(UMNH-VP 9351), but differs from abelisaurids (e.g.
Carnotaurus (MACN-CH 894), Ekrixinatosaurus
(MUCPV-294), Skorpiovenator (MMCh-PV 48) in
which the den tary has a constant transverse width
throughout its entire length. The dentary of Tyrannotitan
is nearly straight along most of its length, showing a slight
medial curvature near its anterior end, at the level of the
anterior edge of the third alveolus. In Giganotosaurus
(MUCPV-Ch 1, MUCPV 95), the medial curvature of the
anterior region is more marked and starts more posteriorly,
approximately at the anterior border of the sixth alveolus,
whereas in Acrocanthosaurus (NCSM 14345), the dentary
is straight and in Allosaurus (UMNH-VP 9351) the
dentary is gently curved medially along its entire length. In
lateral view, the dentary is posteriorly high and
Figure 4. Tyrannotitan chubutensis left dentary (MPEF-PV 1156) photographs in (A) lateral view, (B) medial view, (C) dorsal view and
(D) detail of the symphysis in medial view. Note: Scale bar is 10 cm in A–C and 2 cm in D; see text for abbreviations.
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6 J.I. Canale et al.
Figure 5. Tyrannotitan chubutensis right dentary (MPEF-PV 1157) photographs and line drawings in (A) lateral view and (B) medial
view. Note: Scale bar is 10 cm; see text for abbreviations.
progressively tapers anteriorly, but has a dorsoventrally
higher anterior end, creating a constriction at its central
portion (Figures 4 and 5). This condition is als o found in
Giganotosaurus (MUCPV-Ch 1, MUCPV 95) and
Mapusaurus (Coria and Currie 2006). In Acrocantho-
saurus (NCSM 14345), Allosaurus (UMNH-VP 9351,
UMNH-VP 6476) and the purported carcharodontosaurid
Kelmayisaurus petrolicus (Brusatte et al. 2012), the
dorsoventral dentary height is nearly homogeneous along
the entire length of the bone. In Tyrannotitan the minimum
height of the dentary occurs at the level of the seventh
alveolus. The dentary has 15 alveoli, the anteriormost of
which is subcircular while all others are ellipsoidal and
anteroposteriorly elongated; a morphology that is more
pronounced in the posterior alveoli. This contrasts with the
condition of Neovenator and in most ceratosaurs, in which
the alveoli have a subrectangular outline (Sereno et al. 2004;
Brusatte et al. 2008;Canaleetal. 2009). Anterior alveoli are
arranged obliquely to the anteroposterior axis of the dentary.
The anterior end of the dentary has a subrectangular contour
in lateral view, with the angle between the anterior end of
the ventral margin and the symphyseal edge nearly straight.
The same subrectangular outline is present in Giganoto-
saurus (MUCPV-Ch 1, MUCPV-95), Carcharodontosaurus
iguidensis (MNN IGU 5), Acrocanthosaurus (NCSM
14345) and in a large specimen of Allosaurus (UMNH-
VP 6476). However, in Tyrannotitan the symphysea l
anterior edge is completely vertical with respect to its
ventral margin. Moreover, the anteroventral end is more
anteriorly projected than the anterodorsal margin, so
that the symphyseal edge has a slight anteroventral –
posterodorsal orientation, which constitutes an autapo-
morphy of Tyrannotitan. In the anterior end of the
ventral margin, there is a ventral process (‘chin’) that is
also present in Giganotosaurus (MUCPV-Ch 1),
Carcharodontosaurus iguidensis (MNN IGU 5),
Acrocanthosaurus (NCSM 14345) and Mapusaurus
(Coria and Currie 2006). This character is only present
in the dentary of the paratype specimen, and has not
been preserved in remaining available dentaries of
Tyrannotitan (Figure 5).
The anterior margin of the dentary in lateral view bears
large and rounded neurovascular foramina. Some of these
foramina are located within a longitudinal neurovascular
groove, which is located dorsally on the lateral surface of
the dentary at its anterior region. This groove bends
ventrally at the level of the fourth and fifth alveoli, and
more posteriorly it curves dorsally (reaching the alveolar
margin at the level of the posteriormost alveolus, (Figure 5
(A)). Therefore, the groove follows a sigmoidal pattern, a
feature considered as diagnostic of carcharodontosaurids
by Sereno and Brusatte (2008). A similar pattern is present
not only in Carcharodontosaurus iguidensis (MNN IGU 5),
Giganotosaurus (MUCPV-Ch 1, MUCPV-95) and Acro-
canthosaurus (NCSM 14345), but also in Allosaurus
(UMNH-VP 6476). In Sinraptor (Currie and Zhao 1993),
the lateral neurovascular groove is relatively straight and is
located more dorsally than in the above-mentioned taxa. In
Tyrannotitan, this lateral neurovascular groove follows the
same path and is similarly positioned to a groove located on
the medial surface of the dentary, where the ventral ends of
the fused dental plates are placed.
The symphyseal area is only well preserved in the right
dentary of MPEF-PV 1156. It has two smooth concavities
separated by a central ridge at its mid-height. In the ventral
concavity there is a small rounded process; also observed
in Carcharodontosaurus iguidensis (‘articular brace’ sensu
Brusatte and Sereno 2007)(Figure 4(D)). The symphyseal
surface is set at a wide angle with respect to the medial
surface of the dentary, observable in dorsal view. This
angle gives a rounded appearance to the symphyseal
region of the dentary, but not as rounded as in
Carcharodontosaurus iguidensis (Brusatte and Sereno
2007). Dorsal to the symphysis a small anterodorsal
process is present, as in Carcharodontosaurus iguidensis
(MNN IGU 5).
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7 Historical Biology
Along the medial face of the dentary of Tyrannotitan,
a thickened bar of bone is present, being more prominent
in the anterior sector. This bar forms the dorsal limit of
the Meckelian groove and is dorsally limited by a deep
neurovascular groove that receives the ventral edge of the
dental plates. This medial groove, as mentioned above,
follows a similar path as the neurovascular groove of the
lateral surface of the dentary. Within this groove, it can
be observed in dorsal view two foramina located
approximately at the level of the sec ond and third
alveoli, as in Carcharodontosaurus iguidensis (MNN
IGU 5). The dental plates are fused together, and have
variable height along the dentary. Its maximum height is
located at the level of the central constriction of the
dentary, decreasing both anteriorly and posteriorly
(Figure 5(B)).
The Meckelian groove in Tyrannotitan, as in other
carcharodontosaurids, is deep and well defined. As in
Carcharodontosaurus iguidensis (MNN IGU 5) and
Giganotosauurs (MUCPV-Ch 1, MUCPV-95), the Meck-
elian groove in Tyrannotitan ends anteriorly at the level of
first and second alveoli, whereas in Acrocanthosaurus
(NCSM 14345) it ends more posteriorly, at the level of
third and fourth alveoli. Anteriorly to the Meckelian
groove, the dentary bears an anteroposteriorly elongated
oval fossa that is preceded anteriorly by a small round
foramen (Figure 5(B)). At the level of the dorsoventral
constriction of the dentary, the Meckelian groove expands
ventrally, forming a broad and subtriangular Meckelian
fossa, which receives the anterior process of the splenial.
Dorsally to this fossa, the medial surface of the dentary is
smooth and flat, as also occurring in Tyrannosaurus
(Brochu 2003), whereas anteriorly this surface is gently
convex. This transition occurs at the level of the 9th to 10th
alveoli.
5.4 Teeth
The right dentary of the holotype (MPEF-PV 1156) has the
sixth and seventh teeth preserved in their alveoli. The
collected materials also include 21 isolated teeth, 2 of
which had been referred to the paratype specimen (MPEF-
PV 1157). The following description is based on the
general characteristics present in all the available teeth.
The teeth are transversely compressed, with a crown
base ratio (crown base width/crown base length) that
varies between 0.33 and 0.63 (values taken from 13 teeth)
(Appendix S4, Table 2). The mesial margin is convex and
the distal is in general straight, except for a few teeth that
have concave distal margin (Figure 6(D)). In eight of the
teeth recovered, the mesial and distal carinae are centrally
located, giving the tooth crown a symmetrical cross
section. These teeth may have occupied a middle-posterior
position in the toothrow. In the remaining seven teeth that
Figure 6. Tyrannotitan chubutensis isolated teeth (MPEF-PV
10821) photographs in (A) lateral view, (B) mesial view and (C)
distal view of a ‘anterior’ tooth, (D) lateral view, (E) mesial view
and (F) distal view of a ‘middle-posterior’ tooth. Note: Scale bar
is 5 cm; see text for abbreviations.
have preserved both carinae, the mesial and distal carinae
are displaced from the mesiodistal axis, giving the tooth
crown an asymmetrical cross section. Probably these teeth
were positioned at the anterior region of the toothrow. The
specific position of the isolated teeth (i.e. whether they
represent upper or lower teeth, left or right) is difficult to
determine, given the variation observed in other
theropods. For example, in the abelisaurid Majungasaurus
crenatissimus (Fanti and Therrien 2007), the anterior teeth
have both carinae lingually displaced. However, in the
dentary of Giganotosaurus (MUCPV-Ch 1), the anteriorly
located teeth have their carinae labially displaced, creating
a greater convexity on the lingual surface of each tooth.
For this reason, in the case of the isolated teeth of
Tyrannotitan, we have decided not to use the carinae
displacement as a parameter to assign the teeth of
asymmetric cross section to a particular placement of the
toothrow (left or right side), except for identifying them as
positioned anteriorly or middle-posteriorly in the tooth-
row. The complete teeth, which have preserved their crown
and root, have a sigmoid shape when observed in anterior
or posterior view (Figure 6(C)), as in Giganotosaurus
(MUCPV-Ch 1), Mapusaurus (MCF-PVPH 108.9) and
Carcharodontosaurus saharicus (SGM-Din 1).
The denticles are ‘chisel-like’ (Currie et al. 1990), with
poorly developed blood-grooves. In the central sector of
both carinae, there are two denticles per mm, as in
Giganotosaurus (MUCPV-Ch 1), Carcharodontosaurus
saharicus (SGM-Din 1), Carcharodontosaurus iguidensis
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8 J.I. Canale et al.
Figure 7. Reconstruction of the lateral side of the skull of
Tyrannotitan chubutensis based on elements of the paratype
(MPEF-PV 1157). Note: Scale bar is 10 cm.
(MNN IGU 6), but differing from Acrocanthosaurus
(Currie and Carpenter 2000) that has three denticles per
mm. Close to the base the denticles are smaller, and the
denticle density raises to three per mm. Of the 23 teeth
studied, only 5 have preserved a complete mesial carina.
Out of those five teeth, only three have bilobulated
denticles (the sixth tooth of the right dentary of the
holotype plus two isolated teeth). In one of the isolated
teeth, the mesial carina extends only over the apical half of
the crown. Its ventral half has a smooth and rounded
mesial border, lacking a carina or denticles.
At least five teeth have preserved enamel wrinkles,
which are present in a wide variety of theropod species
(Brusatte et al. 2007; Canale et al. 2009). In Tyrannotitan
chubutensis, the wrinkles occur variably in each tooth,
being located on the mesial carina, on the distal carina or
in both carinae. The four teeth preserving the root have a
constriction on both the labial and lingual sides, creating
an eight-shaped cross section of the root.
5.5 Vertebral column
Combining the vertebral elements of both specimens
recovered, the available material of Tyrannotitan contains
representatives of all sections of the vertebral column.
Novas et al. (2005) identified a cervical vertebra of the
paratype of Tyra nno titan as the ninth cervical. Through
comparisons with the cervical series of Giganotosaurus
(MUCPV-Ch 1), this element is reinterpreted here as the
seventh cervical vertebra, given the presence of characters
such as a marked opisthocoely of the centrum, a transverse
process directed more ventrally than laterally and a neural
arch anteroposteriorly extended. Novas et al. (2005)also
identified a sequence of articulated vertebrae of the holotype
(MPEF-PV 1156), exposed only on its right lateral side, as
the segment of third to eighth dorsals. Here, this series is
reinterpreted as the sequence of second to seventh dorsals,
based on comparison of the neural arch of the first of these
articulated elements with the dorsal series of Allosaurus
(Madsen 1976). The transverse process of this neural arch is
laterally directed, making its dorsal surface visible in lateral
view. This is consistent with the morphology of the second
dorsal of Allosaurus (Madsen 1976), whereas in the third
dorsal of this taxon, the transverse process has a slight dorsal
orientation, so that its dorsal surface is not exposed in lateral
view. Another character that supports this interpretation is
the locationof the parapophysisin the middle of the centrum,
as in the second dorsal of Allosaurus (Madsen 1976),
whereas in the third dorsal the parapophysis is located on the
base of the neural arch (Figure 7).
5.5.1 Atlas
The atlas (MPEF-PV 1157) is an anteroposteriorly short
element. In anterior view, the vertebral body has a square
contour at its ventral half. The anterior surface of the
centrum has a deep concavity that articulates with the
occipital condyle. Within this concavity, the dorsal sector
bears an oval perforation separated from the neural canal
by a thin bridge of bone (Figure 8(A),(C)). In posterior
view, the centrum is dorsally concave and ventrally
convex. The dorsal concavity corresponds to the articula-
tion with the odontoid process of the axis. The neural arch
is as high as the centrum. Anteriorly and laterally to the
neural canal there is a pair of rounded prominences.
Ventrally to each postzygapophysis, the neural arch bears
Figure 8. Tyrannotitan chubutensis atlas (MPEF-PV 1157) photographs in (A) anterior view, (B) right lateral view, (C) posterior view
and (D) left lateral view. Note: Scale bar is 10 cm; see text for abbreviations.
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9 Historical Biology
Figure 9. Tyrannotitan chubutensis seventh cervical vertebra (MPEF-PV 1157) photographs and line drawings in (A) anterior view, (B)
right lateral view, (C) posterior view and (D) left lateral view. Note: Scale bar is 10 cm; see text for abbreviations.
a rounded and well-marked fossa. The postzygapophyses
are oriented medioventrally (Figure 8(C)). The epipo-
physes are well developed (Figure 8), as in Torvosaurus
(BYU-VP 725/4884), Majungasaurus (O’Connor 2007)
and Acrocanthosaurus (NCSM 14345).
5.5.2 Seventh cervical
The centrum of this vertebra (MPEF-PV 1157) is strongly
opisthocoelic, having a hemispherical anterior articular
surface (Figure 9), as in Giganotosaurus (MUCPV-Ch 1),
but unlike that of Allosaurus (UMNH-PV 8354) in which
the opisthocoely is less developed. The ventral surface is
concave in lateral view. The parapophysis is large and
rounded, and located at the anteroventral corner of the
lateral surface of the centrum, immediately behind the
anterior articular face. This vertebra has two pleurocoels on
its lateral surface (Figure 9(B)), as in Carcharodontosaurus
saharicus (NCSM 18166) and Giganotosaurus (MUCPV-
Ch 1). The anterior pleurocoel is located dorsally to the
parapophysis, is larger than the posterior pleurocoel and is
separated from the posterior pleurocoel by a thin oblique
sheet of bone. The posterior surface of the centrum is nearly
circular, except for its flattened dorsal margin below the
neural canal. The prezygapophyses are wide and dorsome-
dially oriented. The medial edge of each prezygapophysis is
ventrallycurved forming a rudimentary hypantrum (Figure 9
(A)), which is not as developed as in the dorsal vertebrae.
The diapophysis is triangular in lateral view (Figure 9
(B),(D)), as in Giganotosaurus (MUCPV-Ch 1), Mapu-
saurus (MCF-PVPH 108.90) and Carcharodontosaurus
saharicus (NCSM 18166), and is lateroventrally directed.
The prezygodiapophyseal lamina is supported by two
accessory laminae: the anterior of which is more developed.
In posterior view, dorsal to the neural canal, there is a small
vertical lamina that supports the base of the ‘U-shaped’
hyposphene. On each side of this lamina, over the neural
canal, the neural arch bears small circular fossae that are
bounded laterally by a curved lamina, which comes from the
vertebral centrum and connects to the lateral wall of the
hyposphene (Figure 9(C)). Dorsal to postzygapophyses, a
rhomboid deep depression occupies the entire posterior
surface of the neural spine, at the centre of which is
distinguished the ligament scar. The epipophyses are pointed
and well developed on the dorsal surface of each
postzgapophysis (Figure 9(D)). The robust neural spine has
a quadrangular cross section at its base, as in Giganotosaurus
(MUCPV-Ch 1) and Mapusaurus (MCF-PVPH 108.90). At
the base of its anterior surface there are ligament scars.
5.5.3 First dorsal
The centrum of the first dorsal (MPEF-PV 1157) is larger
but less opisthocoelic than in the seventh cervical. The
kidney-shaped parapophyses are located anteroventrally
on the lateral sides of centrum. Dorsally to each
parapophysis, the centrum bears a large oval pleurocoel
(Figure 10(B),(D)). The posterior surface of the centrum
has a perfectly circular outline. The ventral surface is
concave in lateral view. The neural arch is higher and
anteroposteriorly shorter than that of the seventh cervical
vertebra. The neural canal is oval, being higher than wide.
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10 J.I. Canale et al.
Figure 10. Tyrannotitan chubutensis first dorsal vertebra (MPEF-PV 1157) photographs and line drawings in (A) anterior view, (B) right
lateral view, (C) posterior view and (D) left lateral view. Note: Scale bar is 10 cm; see text for abbreviations.
The prezygapophyses are dorsally positioned, on the
neural arch, with a wide hypantrum developed ventral to
them (Figure 10(A)). The neural spine is robust, with a
square-shaped base in cross section. The transverse
processes are more laterally than ventrally directed. The
prezygapophyses, as the postzygapophyses, face dorsally
as in the rest of the dorsa l vertebrae. The hyposphene is
well developed and has a short medial lamina at its ventral
end that extends down to the dorsal edge of the neural
canal. On both sides of the above-mentioned lamina, deep
fossae are present. These are laterally bounded by a pair of
curved laminae that have a similar disposition to that
described of the seventh cervical, but are proportionally
more robust (Figure 10(C)). These same laminae are
present in Mapusaurus (MCF-PVPH 108.82) but in this
taxon they are less developed than in Tyrannotitan.
5.5.4 Second dorsal
In the second dorsal vertebra, only the neura l arch has been
preserved (MPEF-PV 1156), lacking neural spine. The
transverse process is laterally directed, so that its dorsal
surface is exposed in lateral view. The centroprezygapo-
physeal lamina is subvertically oriented and merges with
the anterior centrodiapophyseal lamina. The resultant
lamina extends along the neural arch towards the
parapophysis (Figure 11), as in the second dorsal of
Acrocanthosaurus (Harris 1998), Allosaurus (Madsen
1976) and in an anterior dorsal of Mapusaurus (MCF-
PVPH 108.82). The parapophysis is located at mid height
of the neural arch. The centroprezygapophyseal fossa
(sensu Wilson et al. 2011) is shallower than in more
posterior dorsal vertebrae. The posterior centrodiapophy-
seal lamina is more robust than the anterior centrodiapo-
physeal lamina and is vertically oriented. Both laminae
delimit a triangular and deep centrodiapophyseal fossa. At
the ventral region of this fossa there is a low accessory
lamina that runs anteroposteriorly (Figure 11).
5.5.5 Third dorsal
In this vertebra (MPEF-PV 1156) only the neural arch and
part of the centrum have been preserved. The neural arch is
anteroposteriorly longer than that of the second dorsal, in
part because the transverse process becomes more
posterodorsally oriented and the prezygapophysis is
more anteriorly projected, surpassing the anterior border
of the vertebral centrum. This trend among the transverse
processes and prezygapophysis is accentuated in sub-
sequent vertebrae. Consequently, along this series the
centroprezygapophyseal fossa becomes progressively
wider and deeper in posterior dorsal vertebrae. The
parapophysis is located at the base of the neural arch. As in
the second dorsal, the anterior centrodiapophyseal lamina
merges with the centroprezygapophyseal and the resultant
lamina extends over the neural arch dorsal to the
parapophysis. The accessory lamina is more prominent
and better defined than in the second dorsal (Figure 11).
This lamina is absent in the anterior dorsal vertebra of
Mapusaurus (MCF-PVPH 108.82) and Allosaurus
(UMNH-VP 8334). In Acrocanthosaurus (SMU-74646 4-
17: Harris 1998), there are two thin accessory laminae in
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11 Historical Biology
Figure 11. Tyrannotitan chubutensis articulated second dorsal to seventh dorsal vertebrae (MPEF-PV 1156) photographs and line
drawings in right lateral view. Note: Scale bar is 10 cm; see text for abbreviations.
the third dorsal vertebra, which resemble that of
Tyrannotitan, although they are much less developed.
The parapophysis is dorsoventrally elongated.
5.5.6 Fourth dorsal
The fourth dorsal vertebra is represented by fragments of
the centrum and neural arch in both holotype and paratype
(Figures 11 and 12). The centrum is tall, with flat and
ovoid articular surfaces, dorsoventrally elongated and with
a concave margin under the neural canal. The centrum is
spool shaped, ventrally concave in lateral view and
without a ventral keel. The centrum bears two pleurocoels
on its lateral surface, which are anteroposteriorly aligned
and separated by a thin oblique lamina (Figure 12), as in
Giganotosaurus (MUCPV-Ch 1) and Acrocanthosaurus
(Harris 1998). The neural canal is dorsoventrally
elongated. The prezygapophysis faces dorsomedially.
The hypantrum is thin walled, and delimits the medial
margin of the deep centroprezygapophyseal fossae. These
fossae are laterally limited by the centroprezyga pophyseal
laminae (Figure 12(A)). The neural arch has the same
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12 J.I. Canale et al.
Figure 12. Tyrannotitan chubutensis fourth dorsal vertebra (MPEF-PV 1157) photographs in (A) anterior view, (B) right lateral view,
(C) posterior view and (D) left lateral view. Note: Scale bar is 10 cm; see text for abbreviations.
height as the centrum. The centroprezygapophyseal
lamina is shorter and more robust than in the preceding
vertebrae. The anterior centrodiapophyseal lamina reaches
the dorsal border of the parapophysis and does not merge
to the centroprezygapophyseal lamina. Therefore, in the
fourth dorsal (and in more posterior vertebrae), this lamina
is referred as parapodiapophyseal lamina (Figure 11). In
this vertebra, and in the subsequent dorsal vertebrae, there
is no evidence of the accessory laminae described for the
second and third dorsals. The centroprezygapophyseal
fossa is wider than the centrodiapophyseal fossa, whereas
in the second dorsal both fossae are similarly developed.
This trend is accentuate d in the subsequent posterior
vertebrae. The parapophysis is dorsoventrally elongated
and is located at the anterior border of the neural arch.
5.5.7 Fifth dorsal
The fifth dorsal vertebra lacks the neural spine (MPEF-PV
1156) (Figure 11). It has two aligned pleurocoels on each
lateral side of the centrum. In lateral view, the tip of the
transverse process surpasses the posterior border of the
centrum. The centroprezygapophyseal lamina is as robust
as the same in the fourth dorsal, expanding to the base of
the prezygapophysis. As in the precedent vertebrae, the
centrodiapophyseal lamina is vertically oriented. The
parapophysis has a circular outline.
5.5.8 Sixth dorsal
Two centra with part of the neural arch have been preserved
of the sixth dorsal, belonging to holotype and paratype
(Figures 11 and 13). The centrum is tall, amphyplatyan and
ventrally concave in lateral view. Both pleurocoels are
anteroposteriorly elongated and located on the dorsal
region of the lateral surface of the cent rum. The neural canal
is dorsoventrally elongated. The prezygapophysis faces
dorsally and below them there are two deep cenotroprezy-
gapophyseal fossae, limited laterally by the robust
centroprezygapophyseal laminae and medially by the
hypantrum walls (Figure 13(A)). Over the anterior border
of the prezygapophysis there are two rounded pneumatic
pits, which are also present in Giganotosaurus (MUCPV-
Ch 1), Mapusaurus (MCF-PVPH 108.84) and Allosaurus
Figure 13. Tyrannotitan chubutensis sixth dorsal vertebra (MPEF-PV 1157) photographs in (A) anterior view, (B) right lateral view, (C)
posterior view and (D) left lateral view. Note: Scale bar is 10 cm; see text for abbreviations.
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13 Historical Biology
Figure 14. Tyrannotitan chubutensis eighth dorsal vertebra (MPEF-PV 1157) photographs in (A) anterior view, (B) right lateral view,
(C) posterior view, (D) left lateral view of the isolated neural spine and (E) anterior view of a fragment of the neural arch. Note: Scale bar
is 10 cm; see text for abbreviations.
fragilis (UMNH-VP 10108). The hyposphene – hypantrum
facets are well developed and dorsoventrally elongated.
The parapophysis is located at the anteroventral border of
the neural arch (Figure 11 ). The centrodiapophyseal lamina
is robust and the parapodiapophyseal is very reduced. The
transverse process is strongly posterodorsally directed.
5.5.9 Seventh dorsal
Remains of the seventh dorsal have been preserved on both
the holotype and the paratype. The transverse process is
more posterodorsally oriented and the centroprezygapo-
physeal lamina is shorter and more robust than in the sixth
dorsal vertebra (Figure 11). The parapodiapophyseal
lamina is weakly developed in comparison with the
posterior centrodiapophyseal lamina. The neural spine is as
high as the centrum plus the neural arch. The neural spine
has strongly developed ligament scars on the dorsal region
of its anterior surface, as in Mapusaurus (MCF-PVPH 108)
and Acrocanthosaurus (Harris 1998). The centrum bears
two pleurocoels on the dorsal region of its lateral surface.
5.5.10 Eighth? dorsal
An isolated neural spine (MPEF-PV 1156) (Figure 14(A) –
(D)) and part of a neural arch (MPEF-PV 1157) (Figure 14
(E)) were assigned with doubts to the eighth dorsal
vertebra. The centroprezygapophyseal fossae are strongly
reduced and restricted to the base of the parapophysis
(Figure 14(E)). The hypantrum is rhomboid shaped, being
wider at its central sector than in the sixth dorsal. The
parapophysis is laterally directed, and has a pointed
projection at its dorsal end. The neural spine is
subrectangular in lateral view, with a central anteroposter-
ior and lateromedial constriction. The ligament scars are
strongly developed, having rounded anterolateral projec-
tions and being restricted to the dorsal half of the neural
spine. The spinoprezygapophyseal laminae ventrally
delimit a wide spinoprezygapophyseal fossa (Figure 14
(A),(C)). The posterior ligament scars are not as developed
as those of the anterior surface.
5.5.11 Ninth? dorsal
An isolated neural spine (MPEF-PV 1156) was assigned
with doubts to the ninth dorsal vertebra. The overall
morphology is very similar to that assigned to the eighth
dorsal vertebra, but is higher and more slender. The
pneumatic openings are well developed under each
prezygapophysis. The right spinoprezygapophyseal lam-
ina has a bifurcation with a small anterolateral lamina. The
transverse process is dorsally oriented, but only a fragment
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14 J.I. Canale et al.
of this process has been preserved. The anterior ligament
scar is strongly developed and restricted to the dorsal half
of the spine.
5.5.12 Tenth dorsal
The 10th dorsal vertebra has been almost completely
preserved (MPEF-PV 1156) (Figure 15). The centrum is
spool shaped and bears two ovoid pleurocoels. These are
anteroposteriorly aligned and, unlike in the anterior dorsals,
located within a deep and anteroposteriorly elongated
fossa. The transverse process is laterally directed, as in the
last dorsal vertebra of Allosaurus (Madsen 1976). The
posterior centrodiapophyseal lamina is robust and reaches
the anterior margin of the postzygapophysis. The lateral
border of the postzygapophysis is ventrally curved,
covering laterally the prezygapophysis of the subsequent
vertebra (preserved in articulation), as in Giganotosaurus
(MUCPV-Ch 1), Acrocanthosaurus (Harris 1998), Majun-
gasaurus (O’Connor 2007) and Carnotaurus (MACN-CH
894). The morphology of the neural spine is very similar to
that of the preceding dorsal vertebrae.
5.5.13 Eleventh dorsal
The 11th dorsal vertebra (MPEF-PV 1156) is almost
completely preserved and articulated with the 10th dorsal
(Figure 15). In posterior aspect, the articular surface has a
subcircular outline as in the posterior dorsal vertebrae of
Giganotosaurus (MUCPV-CH 1) and Allosaurus (Madsen
1976). As in the 10th dorsal, the pleurocoels are located
within a deep and anteroposteriorly elongated fossa. The
parapophyses are dorsoventrally elongated. The transverse
processes are laterally directed. The centroprezygapophy-
seal lamina is short and robust. The parapodiapophyseal
lamina is an oblique and very thin sheet of bone. The
posterior centrodiapophyseal lamina is vertically oriented
and thinner than in the 10th dorsal. The postzygapophysis
has its lateral margin ventrally curved, as in the 10th
dorsal. The spinopostzygapophyseal laminae are markedly
robust at their base, and both delimit a deep spinopostzy-
gapophyseal fossa. Between both postzygapophyses, only
a fragment of the hyposphene has been preserved in this
vertebra.
5.5.14 Twelfth dorsal
Only an isolated vertebral cent rum is known from the 12th
dorsal vertebra (MPEF-PV 1157). The posterior articular
surface has a circular contour. The anterior pleurocoel is
larger than the posterior pleurocoel. The left side of the
centrum has preserved the base of an oblique anterior
centrodiapophyseal lamina and a vertical posterior
centrodiapophyseal lamina. Unlike the more anterior
dorsal vertebrae, this vertebra has a wide ventral furrow.
Figure 15. Tyrannotitan chubutensis articulated 10th and 11th dorsal vertebrae (MPEF-PV 1156) photographs and line drawings in right
lateral view. Note: Scale bar is 10 cm; see text for abbreviations.
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15 Historical Biology
Figure 16. Tyrannotitan chubutensis 14th dorsal vertebra (MPEF-PV 1157) photographs in (A) anterior view, (B) right lateral view, (C)
posterior view and (D) left lateral view. Note: Scale bar is 10 cm; see text for abbreviations.
5.5.15 Thirteenth dorsal
Only the isolated centrum of the 13th dorsal vertebra has
been preserved (MPEF-PV 1157). As in the 12th dorsal
vertebra,the articularsurfaceshave a subcircular outline, the
anteriorpleurocoel is more developed than the posterior, and
the centrum has a wide ventral furrow. The neural canal is
rounded, instead of being dorsoventrally elongated as in the
most anterior dorsal vertebrae.
5.5.16 Fourteenth dorsal
The isolated vertebral centrum of the 14th vertebra has
been preserved (MPEF-PV 1157) (Figure 16), as well as an
isolated neural spine (MPEF-PV 1156) (Figure 17). The
centrum is anteroposteriorly shorter than in the 12th and
13th vertebrae. Both anterior and posterior articular
Figure 17. Tyrannotitan chubutensis articulated neural spines
of 14th dorsal vertebra and 1st sacral vertebra (MPEF-PV 1156)
photographs in left lateral view. Note: Scale bar is 10 cm; see text
for abbreviations.
surfaces are rounded, but the posterior one is smaller,
which matches the size of the first sacral centrum. There is
only one rounded pleurocoel on each lateral surface of the
centrum (Figure 16(B),(D)). The posterior centrodiapo-
physeal lamina (only preserved on the left side) is
anterodorsally directed, as in the 14th dorsal of Allosaurus
(Madsen 1976)(Figure 16(B)). The hypantrum is well
developed and dorsomedially elongated. The neural spine
is anteroposteriorly shorter than that of the 10th and 12th
dorsal vertebrae, as in Allosaurus (Madsen 1976) and
Tyrannosaurus (Brochu 2003). The anterior ligament scar
is strongly developed in this vertebra. The neural spine is
anterodorsally oriented (Figure 17), as in the 14th dorsal
vertebra of Allosaurus (Madsen 1976), Sinraptor (Currie
and Zhao 1993) and Aerosteon (Sereno et al. 2008).
5.5.17 Sacrum
A neural spine, found in articulation with the neural spine
of the 14th dorsal (MPEF-PV 1156) (Figure 17), has been
preserved from the sacrum of the holotype, as well as two
fragments of fused sacral centra of the paratype (MPEF-
PV 1157) (Figure 18).
The lateral surface of the neural spine is partially
covered by a fragment of the left ilium. The spine is
anteroposteriorly wider than in the 14th dorsal and has the
posterior ligament scar strongly developed. As in
Giganotosaurus (MUCPV-Ch 1), there is no evidence of
fusion between the sacral neural spines.
The two preserved sacral fragments of the paratype
include the left half of the first and a small part of the
second sacral centrum, which are fused and have clear
evidence of deformation, and a fused sequence of the third,
fourth and fifth sacral centra. The sacrum is ventrally
concave and medially compressed, as in Giganotosaurus
(MUCPV-Ch 1), Carnotaurus (MACN-CH 894) and
Ceratosaurus (Gilmore 1920)(Figure 18(A) –(C)). The
lateral surface of the first sacral centrum bears a medial
longitudinal ridge. The base of the neural arch has been
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16 J.I. Canale et al.
preserved and is located over the posterior half of the mation at the tip of its neural spine. This element is
centrum. This vertebra lacks pleurocoels, but it has a interp reted as belonging to the series between the 5th and
pneumatic recess and small opening at the base of the 10th caudal vertebrae, giving the size difference between
neural arch (Figure 18(A)). The ventral surf ace, although its centrum and that of the last sacral and the orientation of
incomplete seems to be transversely compressed. The third the zygapophyses.
centrum is the smallest of the sacral series. The contact The centrum is amphyplatyan. The margins of its
between the third and fourth centra is the lateromedially articular surfaces are not complete, and they likely were
narrowest contact of the sacral series. The fourth sacral has more expanded than preserved, creating a spool-shaped
the posterior surface expanded with respect to the anterior centrum. There are anteroposteriorly elongated depressions
surface and has a pleurocoel on the posterodorsal region of (‘pleurocoelic fossae’) on the dorsal region of its lateral
the left lateral surface of the centrum (located within a surface, as in Giganotosaurus (MUCPV-Ch 1) and
anteroposteriorly elongated fossa) (Figure 18(A)). Sacral Mapusaurus (MCF-PVPH 108.81). This differs from the
pleurocoels are known also in Mapusaurus (MCF-PVPH condition of Carcharodontosaurus saharicus (Stromer
108.209) and Giganotosaurus (MUCPV-Ch 1). The fifth 1931), which have actual pleurocoels in the anterior caudal
sacral vertebra is the highest of the sacral series; its vertebrae. The prezygapophyses face dorsomedially, at an
posterior articular surface is also expanded, and has a angle of approximately 45th from the horizontal plane
conspicuous pleurocoel on its lateral surface (as in the (Figure 19(A)). The spinoprezygapophyseal fossa is
fourth sacral). The postzygapo physis preserved in this shallow between both spinoprezygapophyseal laminae.
sacral centrum faces ventrally (Figure 18(D)). Over the dorsal half of the anterior surface of the neural
spine, there is a ligament scar, which is less developed than
in the posterior dorsal vertebrae. The transverse processes
5.5.18 Anterior caudal are robust and posterolaterally oriented. The anterior
There is an almost complete anterior caudal vertebra surface of the transverse process bears a longitudinal wide
(MPEF-PV 1156) (Figure 19), whi ch has slight defor- fossa, as in the anterior caudal vertebrae of Giganotosaurus
Figure 18. Tyrannotitan chubutensis sacrum (MPEF-PV 1157) photographs and line drawings in (A) left lateral view, (B) right lateral
view, (C) ventral view and (D) posterior view. Note: Scale bar is 10 cm; see text for abbreviations.
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17 Historical Biology
Figure 19. Tyrannotitan chubutensis anterior caudal vertebra (MPEF-PV 1156) photographs in (A) anterior view, (B) right lateral view,
(C) posterior view and (D) left lateral view. Note: Scale bar is 10 cm; see text for abbreviations.
(MUCPV-Ch 1). The postzygapophyses faces ventrolat-
erally. Dorsal to the postzygapophyses and between both
spinopostzygapophyseal laminae there is a deep spino-
postzygapophyseal fossa, limited dorsally by a ligament
scar, which is much more developed than the anterior scars
(Figure 19(B),(D)). The neural spine is twice as tall as the
centrum. There is no preserved hypantrum in this element,
but there is a small hyposphene between the postzygapo-
physes, as in Giganotosaurus (MUCPV-Ch 1) and possibly
in cf. Veterupristisaurus (MB R 1940: Rauhut 2011).
5.5.19 Distal caudal
There is a fragmentary and isolated distal caudal vertebra
preserved (MPEF-PV 1157) (Figure 20). Based on
Figure 20. Tyrannotitan chubutensis distal caudal vertebra
(MPEF-PV 1157) photographs in (A) anterior view and (B) right
lateral view. Note: Scale bar is 10 cm; see text for abbreviations.
comparisons with the caudal series of Allosaurus (Madsen
1976), this element was interpreted as belonging to the
series between the 30th and 35th caudal vertebrae. The
centrum is laterally compressed, ventrally concave in
lateral view and expanded at its articular surfaces. The
anterior articular surface (the only one preserved) is wider
than high. The lateral surface of the centrum bears an
anteroposteriorly long depression. The preserved right
prezygapophysis is laterodorsally projected and seems to
have the spinoprezygapophyseal lamina extending as
anteriorly as in Veterupristisaurus (to the midwidth of the
base of the prezygapophysis; Rauhut 2011). In addition,
the lamina that extends over the lateral surface of the
prezygapophysis, which characterises Veterupristisaurus
(Rauhut 2011), is absent in Tyrannotitan. The neural spine
is low and anteroposteriorly extended.
5.5.20 Ribs
Several ribs, mostly fragments, were recovered. They have
no major differences with those of Giganotosaurus
(MUCPV-Ch 1) and Allosaurus (Madsen 1976).
A proximal fragment of an anterior dorsal rib (MPEF-
PV 1157) lacks evidence of pneumatisation, as in
Mapusaurus (Coria and Currie 2006) and Sinraptor
(Currie and Zhao 1993). A complete posterior dorsal rib
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18 J.I. Canale et al.
Figure 21. Tyrannotitan chubutensis left scapulocoracoid (MPEF-PV 1156) photographs in (A) lateral view and (B) medial view. Note:
Scale bar is 10 cm; see text for abbreviations.
was recovered (MPEF-PV 1157), probably the 14th dorsal
rib, based on the comparisons with Allosaurus (Madsen
1976). It is a short and recurved element with a flattened
shaft. The capitulum is also flattened and its dorsomedial
margin is formed by a lamina that connects to the
subcylindrical tuberculum.
5.5.21 Haemal arches
Seven haemal arches have been recovered from both the
holotype and paratype specimens, five anterior and two
distal. They are proximodistally long and laterally
compressed elements. The haemal arch interpreted as the
most anterior element is straight in lateral view, whe reas
the rest are posteriorly concave. The haemal canal is
triangular in anterior view, and occupies approximately
less than one-fifth of the total height of the bone, differing
from the condition of the first 10 haemal arches of
Tyrannosaurus in which the canal occupies at least one-
fourth of their height (Brochu 2003). The haemal canal is
dorsally closed by two oblique articular facets for the
caudal vertebrae. Over the anterior and posterior margins
of both proximal rami, there are rounded proce sses. The
posterior process occupies a more distal position over the
ramus than the anterior process.
5.6 Scapulocoracoid
A left coracoid with the proximal third of the scapula fused
was preserved (MPEF-PV 1156). Although this element is
damaged, it has preserved the subcircular outline of the
coracoid (Figure 21). The coracoid is a robust bone near
the glenoid cavity, and becomes thinner towards the
anterior and dorsal margins. The posteroventral process is
well developed, as in Giganotosaurus (MUCPV-Ch 1),
Allosaurus (UMNH-VP 9822), Piatnitzkysaurus (Bona-
parte 1986) and Carnotaurus (MACN-CH 894). The
anteroventral sector of the lateral surface of the coracoid
bears a long biceps tubercle (Figure 21(A)), as in
Tyrannosaurus (Brochu 2003). This tubercle is represented
by a straight low crest of about 9 cm long, being more
pronounced at its posterodorsal end. The coracoid foramen
is large and rounded, positioned in a central position on the
lateral surface of the coracoid, as in Giganotosaurus
(MUCPV-Ch 1), but unlike Mapusaurus (MCF-PVPH
108.71) in which the foramen is located near the glenoid
cavity. This foramen perforates the bone obliquely, so that
the medial opening is more posteriorly positioned than the
lateral one. A broad fossa occupies most of the anterior
region of the medial surface of the coracoid. This fossa is
subdivided in two smaller fossae: one located dorsally and
another located ventrally, being separated from each other
by a low anteroposterior crest (Figure 21(B)).
Only the proximal scapula part was preserved, which,
unlike Mapusaurus (MCF-PVPH 108.50; MCF-PVPH
108.71), is completely fused to the coracoid. The acromial
process projects abruptly forming a straight angle with the
dorsal margin of the scapular blade, as in Mapusaurus
(Coria and Currie 2006), Acrocanthosaurus (Harris 1998)
and most non-avian theropods. The anterolateral region of
the acromion process is occupied by the subacromial fossa.
The preserved portion of the scapular blade has a wide and
rounded ventral border and a sharp dorsal margin.
5.7 Humerus
Only the distal half of a right humerus has been preserved
(MPEF-PV 1156). The distal end is preserved of the
deltopectoral crest at the proximal end of the preserved
anterior surface, which is anteromedially oriented as in
Mapusaurus (MCF-PVPH 108.45). In contrast, Allosaurus
(UMNH-VP 8157) and Acrocanthosaurus (NCSM 14345)
have an anteriorly projected distal end of the deltopectoral
crest. The humerus is lateromedially expanded at its distal
end (Figure 22(A),(C)). At the medioventral region of the
anterior surface, the humerus bears the proximal end of the
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19 Historical Biology
Figure 22. Tyrannotitan chubutensis right humerus (MPEF-PV 1156) photographs in (A) anterior view, (B) lateral view, (C) posterior
view and (D) medial view. Note: Scale bar is 10 cm; see text for abbreviations.
fossa located between the radial and ulnar condyles
(Figure 22(A)). This fossa has a triangular outline, as in
Mapusaurus (MCF-PVPH 108.45) and Torvosaurus
(BYU-VP 2002). In lateral view, it can be seen that the
distal articular condyles are anteriorly projected (Figure 22
(B),(D)).
5.8 Radius
The right ulna cited by Novas et al. (2005) is reinterpreted
here as a right radius, based on comparisons with
Acrocanthosaurus (NCSM 1434 5) and Allosaurus
(Madsen 1976; UMNH-VP unnumbered). In addition, a
fragment of left radius has been preserved in the holotype.
The radius is a short and robust bone that is strongly
curved, being posteriorly concave (Figure 23), as in
Acrocanthosaurs (NCSM 14345) and Mapusaurus (MCF-
PVPH-108.46), but unlike that of Allosaurus (Madsen
1976; UMNH-VP unnumbered). In anterior view the
radius is straight. The shaft is subcircular in cross section
and the proximal end is expanded. The proximal articular
surface, although partially eroded, has preserved an
ovoidal contour, as in Acrocanthosaurus (NCSM 14345)
and Mapusaurus (MCF-PVPH 108.46). The proximal
expansion is laterally projected. The region of the radius
on the medial surface where the ulna articulates is smooth
and slightly depressed. The distal of the radius end is only
moderately expanded.
5.9 Ilium
Two fragments of the left ilium were preserved (MPEF-
PV 1156). One of them, preserved attached to the
posteriormost dorsal and first sacral neural spines
(Figure 17), corresponds to part of the preacetabular
blade. The other fragment is interpreted here as the lateral
wall of the postacetabular blade, which is lateromedially
narrow. The posterior sector of this fragment is ventrally
directed.
Figure 23. Tyrannotitan chubutensis right radius (MPEF-PV 1156) photographs in (A) anterior view, (B) lateral view, (C) posterior view
and (D) medial view. Note: Scale bar is 10 cm; see text for abbreviations.
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20 J.I. Canale et al.
5.10 Pubis
Both pubic shafts have been preserved, lacking their
proximal end and distal foot (MPEF-PV 1156) ( Figure 24).
The pubic shafts are straight in lateral view (Figure 24(B)),
as in Giganotosaurus (MUCPV-Ch 1), but unlike
Carcharodontosaurus saharicus (Stromer 1931)and
Acrocanthosaurus (Harris 1998) in which these elements
are anteriorly curved. In anterior or posterior view the pubic
shaft has a sigmoid shape (Figure 24(A),(C)). The pubic
symphysis is laminar and occupies the central third of the
preserved region of the pubis. Distally to the symphysis and
proximally delimited by pubic foot, a proximodistally
enlarged pubic foramen is present. Proximal to the pubic
symphysis the medial margins of the shaft are sharp, giving
a tear-shaped cross section to this region of the pubic shaft.
The distance between both iliac processes of both pubes and
both ischia is approximately 40 cm, indicating the width of
the hip in the holotype of Tyrannotitan.
5.11 Ischium
Both ischia have been almost completely preserved and
articulated along their shafts (MPEF-PV 1156) (Figure 25).
The ischia are not fused to each other, but in some parts the
limit between the left and right element is not clear
because of their poor preservation. The iliac peduncles,
although incomplete, have a rectangular outline at their
base. Based on the available material, it cannot be
confirmed whether they had the pocket for the isquiatic
peduncle of the ilium, as in Giganotosaurus (MUCPV-Ch
1) or Mapusaurus (Coria and Currie 2006). The pubic
process is subrectangular, lateromedially compressed and
has the distinct ‘neck’ between the ischial body and the
articular surface for the pubis, a feature also present in
Sinraptor (Currie and Zhao 1993), Allosaurus (UMNH-VP
40-273) and Carcharodontosaurus saharicus (Rauhut
1995). The obturator processes are incompletely preserved
on both ischia, but it can be observed that they were
prominent and distally expanded, as in Allosaurus fragilis
(UMNH-VP 40-273). The ischia also have preserved the
obturator notch that separates the distal end of the
obturator process and the ischiatic shaft (Figure 25(A),
(C)), cited by Rauhut (1995) for Sinraptor, Allosaurus,
Carcharodontosaurus saharicus and basal theropods.
Distally to the obturator processes, the ischiatic shafts
are parallel to each other, as in Allosaurus fragilis
(UMNH-VP 40-273), but unlike Giganotosaurus
(MUCPV-Ch 1) in which the contact between both ischia
is restricted to their distal ends. The ischiatic shaft is
subcircular in cros s section, and slightly expanded at its
distal end. Tyrannotitan, however, lacks the distinct
ischiatic foot present in Neovenator (Brusatte et al.
2008), Concavenator (Ortega et al. 2010) and Acro-
canthosaurus (Harris 1998).
5.12 Femur
The femur is known by both femora of the holotype, and
the right femur of the paratype. The femur is robust,
straight in anterior view and anteriorly convex in lateral
view (Figure 26). The femoral head is strongly upturned
dorsomedially, as in Giganotosaurus (MUCPV-Ch 1),
Carcharodontosaurus saharicus (Stromer 1931)and
Mapusaurus (MCF-PVPH 108.203). The lesser trochanter
Figure 24. Tyrannotitan chubutensis articulated pubes (MPEF-PV 1156) photographs in (A) anterior view, (B) right lateral view and (C)
posterior view. Note: Scale bar is 10 cm; see text for abbreviations.
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21 Historical Biology
Figure 25. Tyrannotitan chubutensis articulated ischia (MPEF-PV 1156) photographs in (A) left lateral view, (B) anterior view and (C)
right lateral view. Note: Scale bar is 10 cm; see text for abbreviations.
is proximally projected, but does not surpass the level of
the greater trochanter (Figure 26(A)), as in Concavenator
(Ortega et al. 2010) and Carcharodontosaurus saharicus
(Stromer 1931). In contrast, the lesser trochanter of
Giganotosaurus (MUCPV-Ch 1) is strongly reduced. Both
lesser and greater trochanters are separated by a deep
vertical notch. The lesser trochanter has a similar
morphology to that of Allosaurus fragilis (UMNH-VP
12231), being subtriangular in lateral view and laterome-
dially robust. Distal to the lesser trochanter there is a
rugose surface, probably for insertion of the ilifemoralis
muscle. Distal to that surface there is a low pyramid-
shaped elevation: the ‘trochanteric shelf’ sensu Brochu
(2003). The femoral shaft is lateromedially wider than
anteroposteriorly long. The fourth trochanter is placed on
the upper half of the posterior surface of the femoral shaft
(Figure 26(B)), being a well-developed proximodistally
elongated crest that is posteromedially projected. The
fourth trochanter is more posteriorly projected and
proximodistally longer than in Mapusaurus (MCF-PVPH
108.203) and Giganotosaurus (MUCPV-Ch 1), in which
the fourth trochanter is reduced to a low crest. In
Tyrannotitan, the fourth trochanter delimits posteriorly a
distinct ovoid and proximodistally elongated fossa; the
Figure 26. Tyrannotitan chubutensis right femur (MPEF-PV 1157) photographs and line drawings in (A) anterior view, (B) medial view,
(C) posterior view, (D) lateral view, (E) proximal view and (F) distal view. Note: Scale bar is 10 cm; see text for abbreviations.
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22 J.I. Canale et al.
Figure 27. Tyrannotitan chubutensis left fibula (MPEF-PV 1157) photographs in (A) anterior view, (B) lateral view, (C) posterior view,
(D) medial view and (E) proximal view. Note: Scale bar is 10 cm; see text for abbreviations.
insertion point of the M. caudifemoralis longus (Coria and
Currie 2006).
Almost one-fourth of the anteri or surface of the distal
end of the femur is occupied by a well-developed
mediodistal crest, as in Mapusaurus (Coria and Currie
2006) and Giganotosaurus (MUCPV-Ch 1), bounded by a
low and wide depression with a medial projection. The
fibular fossa, delimited by the lateral tibial condyle and the
tibiofibular crest, extends proximally over the femoral
shaft up to the proximal limit of the tibiofibular crest. This
wide and shallow fossa has not been reported in other
allosauroid theropods. In distal view, the posterior
projections of the medial condyle and the tibiofibular
crest are rounded (Figure 26(F)), differing from the
pointed posterior project ions of Mapusaurus (MCF-PVPH
108.55). The extensor fossa is shallow and broad, as in
Mapusaurus (MCF-PVPH 108.55), and different from the
narrow and deep fossa of Allosaurus (UMNH-VP 12231)
and Acrocanthosaurus (Harris 1998; Currie and Carpenter
2000). The flexor fossa has a low ridge for the attachment
of the cruciate ligaments, as in Allosaurus (UMNH-VP
12231) and Acrocanthosaurus (Harris 1998; Currie and
Carpenter 2000). The lateral condyle is strongly developed
and has a circular outline, as in Mapusaurus (MCF-PVPH
108.55). The lateral condyle and the tibiofibular crest are
separated by a deep and very narrow fibular fossa as in
Mapusaurus (MCF-PVPH 108.55), a condition absent in
other allosauroid theropods.
5.13 Fibula
The preserved left fibula lacks its distal end (MPEF-PV
1156) (Figure 27). The proximal end is anteroposteriorly
expanded, although the posterior projection is less
developed than in Giganotosaurus (MUCPV-Ch 1) and
Mapusaurus (Coria and Currie 2006: fig. 30; right fibula
figured as left). The proximal articular surface is smooth,
as in Giganotosaurus (MUCPV-Ch 1). The proximomedial
fossa is subovoid and tear-shaped, resembling the
condition of Giganotosaurus (MUCPV-Ch 1), Mapu-
saurus (Coria and Currie 2006) and Allosaurus fragilis
(UMNH-VP 6400). The anterior margin of the proximo-
medial fossa is posteriorly projected, covering a small part
of the fossa (Figure 27(E)), a character absent in other
allosauroids. The fibular shaft has a D-shaped cross
section, with a flat medial surface. The iliofibularis
tubercle is located on the distal region of the dorsal half of
the anterior surface of the fibula (Figure 27(B),(D)). This
tubercle is a proximodistally elongated ridge, resembling
that condition of Giganotosaurus (MUCPV-Ch 1). Distal
to the iliofibularis tubercle the anteroposterior width of the
fibular shaft is constant.
5.14 Metatarsal II
Only the distal half of the left metatarsal II was preserved
(MPEF-PV 1157) (Figure 28). This element is robust and
has and expanded distal e nd, similar to that of Allosaurus
(UMNH-VP 10142). The shaft has a subcircular cross
section, with a slightly flattened medial surface for the
contact with metatarsal III. On the ventral surface, the
trochlea is separated from the shaft by a distinct
lateromedial furrow (Figure 28(B)). Proxi mal to this
furrow there are two tuberosities, a rounded distal
tuberosity andanelongated proximal tuberosity. The
collateral pits are deep and well delimited (Figure 28(D),
(E)). The medial pit is deeper than the lateral pit, and is
located at the distal sector of a marked fossa that occupies
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23 Historical Biology
Figure 28. Tyrannotitan chubutensis left II metatarsal (MPEF-PV 1157) photographs in (A) dorsal view, (B) ventral view, (C) distal
view, (D) lateral view and (E) medial view. Note: Scale bar is 10 cm; see text for abbreviations.
the entire lateral surface of the trochlea. The flexor fossa
is deep and laterally displaced ( Figure 28(C)), as in
Allosaurus fragilis (UMNH-VP 10142) and Sinraptor
(Currie and Zhao 1993), but unlike in Torvosaurus
(BYU-VP 5147) in which this fossa is much shallower.
5.15 Pedal phalanges
We have reinterpreted the identity of the four preserved
pedal phalanges of Tyrannotitan (see Novas et al. 2005)as
the phalanges II-2, II-3, IV-2 and IV-3, all of which belong
to the left pes of the paratype specimen (Figure 33).
5.15.1 Phalanx II-2
This phalanx is robust and proximally expanded
(Figure 29). The proximal articular surface is higher than
wide and has a pronounced medial vertical sulcus. The
ventral surface is flat and is separated from the trochlea by
a transversal and laterally extensive furrow. On the
proximal region of the lateral surface, there are two
subcircular depressions, one dorsal and another ventral.
The colateral ligamental pits are deep and located centrally
on the lateral surfaces of the trochlea. In dorsal view, the
lateral hemicondyle is more developed and distally
projected than the medial hemicondyle.
5.15.2 Phalanx II-3
This phalanx is a robust and recurved ungual that lacks
the distal tip and part of the proximodorsal tubercle
(Figure 30). It is asymmetrical in anterior view: the
medial surface is located slightly dorsally with respect
to the lateral surface. The ventral surface is mostly flat,
except for the pres ence of a transverse elongated
furrow located on its proximal region. The collateral
grooves are well marked, with the lateral g roove more
ventrally positioned than the medial one. These
grooves run parallel to the ventral margin of the
phalanx until the proximal third of this element, in
which they are abruptly deflected ventrally. There is no
evidence of proximal bifurcation of the colateral
Figure 29. Tyrannotitan chubutensis phalange II-2 (MPEF-PV
1157) photographs in (A) medial view, (B) lateral view, (C)
ventral view, (D) dorsal view, (E) proximal view and (F) distal
view. Note: Scale bar is 10 cm; see text for abbreviations.
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24 J.I. Canale et al.
Figure 30. Tyrannotitan chubutensis phalange II-3 (MPEF-PV
1157) photographs in (A) lateral view, (B) medial view, (C)
proximal view, (D) dorsal view and (E) ventral view. Note: Scale
bar is 10 cm; see text for abbreviations.
grooves, contrasting with the condition of abelisaurids
(Novas and Bandyopadhyay 2001). The proximal
articular surface is subcircular and bears a rounded
proximodorsal tubercle.
5.15.3 Phalanx IV-2
This phalanx is short and robust and lacks part of the
trochlea (Figure 31). The proximal articular surface is
almost twice as wide as high. The ventral surface has a
marked transversal furrow just proximal to the trochlea.
Although this element is incompletely preserved, it can be
determined that the medial hemicondyle was more
developed than the lateral hemicondyle, as in Allosaurus
(Madsen 1976) and Sinraptor (Currie and Zhao 1993).
5.15.4 Phalanx IV-3
This phalanx is extremely short and lacks almost all the
trochlea (Figure 32). The proximal articular surface has a
straight ventral margin and continuous and curved lateral,
medial and dorsal margins. As in the other non-terminal
phalanges, it has ventral and dorsal transversal furrows
that separate the trochlea from the rest of the phalanx.
6. Discussion
The combined elements of both holotype and paratype
specimens of Tyrannotitan chubutensis (MPEF-PV 1156;
MPEF-PV 1157) offer new information about the anatomy
of this taxon and its diagnostic features, which improves
Figure 31. Tyrannotitan chubutensis phalange IV-2 (MPEF-PV
1157) photographs in (A) medial view, (B) lateral view, (C)
ventral view, (D) dorsal view, (E) proximal view and (F) distal
view. Note: Scale bar is 10 cm; see text for abbreviations.
our knowledge about poorly known anatomical regions in
derived carcharodontosaurids. In this section we first
discuss the diagnostic characters of Tyrannotitan, then we
discuss the new data on the axial skeleton and the scapular
girdle of carcharodontosaurids, and finally we present a
phylogenetic analysis of Carcharodontosauridae
(Figure 33).
6.1 Diagnostic features of Tyrannotitan
Novas et al. (2005) diagnosed Tyrannotitan based on three
characters, only one of which is left in the emended
diagnosis. These three characters are first discussed here,
followed by a discussion of the four new autapomorphies
found in this study.
6.1.1 Characters in the original diagnosis
6.1.1.1 Teeth with bilobated denticles in the mesial
carinae. This condition occurs in the teeth preserved in the
holotype material of Tyrannotitan (MPEF-PV 1156)
(Figure 34(A)) and some of the isolated teeth recovered
at the site. Bilobated denticles are not present in all
Tyrannotitan teeth and, therefore, this condition should be
regarded as polymorphic among the available material.
The reasons for this polymorphism could be intraspecific
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25 Historical Biology
Figure 32. Tyrannotitan chubutensis phalange IV-3 (MPEF-PV
1157) photographs in (A) medial view, (B) lateral view, (C)
ventral view, (D) dorsal view and (E) proximal view. Note: Scale
bar is 10 cm; see text for abbreviations.
variation or it could represent a pathologic feature of the
holotype. Although we consider further material is needed
to determine the degree of variation of this character in
Tyrannotitan, we have left for the moment this feature
among the autapomorphies of Tyrannotitan following
previous authors (Novas et al. 2005; Sereno and Brusatte
2008; Carrano et al. 2012), given that this condition has
not been recorded in any other known theropod.
6.1.1.2 Deep mental groove on the dentary.The
morphology, depth and orientation of the anterior end of
the Meckelian groove in Tyrannotitan do not significantly
differ from those of other theropod species, such as
Carcharodontosaurus iguidensis (MNN IGU 5), Gigan-
otosaurus carolinii (MUCPV-Ch 1) or Allosaurus fragilis
(UMNH-VP 9351) (Appendix S1: Figure 1:A-B).
Therefore, we have excluded this feature as an
autapomorphy of Tyrannotitan, in contrast to previous
proposals (Novas et al. 2005; Carrano et al. 2012).
6.1.1.3 Posterior dorsal vertebrae with strongly devel-
oped ligament scars on neural spines.In Tyrannotitan, the
neural spines of the posterior dorsal vertebrae have well-
developed ligament scars, ornamented with rounded and
anterolaterally oriented projections. This character,
originally noted in a preliminary study of Tyrannotitan
Figure 33. Reconstruction of the left foot of Tyrannotitan
chubutensis based on elements of the paratype (MPEF-PV 1157).
(Rich et al. 2000), was considered as an autapomorphy of
this genus by Novas et al. (2005). However, the same
condition was described for Acrocanthosaurus atokensis
(Harris 1998), and is present in Mapusaurus roseae (MCF-
PVPH 108) and Giganotosaurus carolinii (MUCPV-Ch 1)
(Appendix S1: Figure 1: C-D). In consequence, this
character has been excluded from the emended diagnosis
of Tyrannotitan.
6.1.2 New autapomorphic characters of Tyrannotitan
Based on observations made in this study, four new
characters were identified as autapomorphic features of
Tyrannotitan.
6.1.2.1 Symphyseal margin of dentary with anteroven-
tral–posterodorsal inclination in lateral view. Several
allosauroids have a characteristic squared anterior end and
subvertical symphyseal margin in the dentary (Sereno and
Brusatte 2008). However, in Tyrannotitan the anteroventral
corner of the symphyseal margin is slightly anterior to the
anterodorsal corner, which gives a very slight anteroven-
tral – posterodorsal inclination to this margin (Figure 34
(B)). This condition is absent in other theropods, including
all known carcharodontosaurids (Brusatte and Sereno
2007; Sereno and Brusatte 2008), and is present in both the
holotype and the paratype specimens of Tyrannotitan.
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26 J.I. Canale et al.
Figure 34. Autapomorphic characters of Tyrannotitan chubutensis. (A) detail photograph of the teeth with bilobated denticles, (B)
photograph of the left dentary in lateral view, showing the vertical symphyseal margin, (C) photograph and line drawing of the second and
third dorsal vertebrae in lateral view, showing the accessory laminae, (D) photograph of the right femur in medial view with a detail of the
fibular fossa extended on the shaft and (E) photograph of the left fibula in medial view with a detail of the anterior border of the fibular
fossa posteriorly projected. Note: Scale bar is 1 mm in (A) and 10 cm in (B) – (E).
6.1.2.2 Second and third dorsal vertebrae with well-
developed accessory laminae connecting anterior and
posterior centrodiapophyseal laminae. This character is
also present in Acrocanthosaurus atokensis (Harris 1998),
although in Tyrannotitan this is a very well-developed
lamina. This character has been preserved only in the
holotype, given that the paratype has not preserved these
dorsal vertebrae (Figure 34(C)).
6.1.2.3 Fibular fossa extended over the proximal end of
the crista tibiofibularis in the femoral shaft.In
Tyrannotitan the fibular fossa is laterally delimited by
the lateral tibial condyle and the crista tibiofibularis, as
occurring in most theropods. However, in Tyrannotitan
this fossa extends proximally in the form of a groove that
approaches the proximal margin of the tibiofibular crest in
the femoral diaphysis (Figure 34(D)). This character is a
unique feature of Tyrannotitan, and is present in both
holotype and paratype.
6.1.2.4 Proximomedial fossa of the fibula with poster-
iorly projected anterior border.In Tyrannotitan the
anterior edge of the proximomedial fossa is developed as
a posteriorly oriented projection, covering part of the fossa
in medial view (Figure 24(E)). In allosauroids, such as
Allosaurus (UMNH-VP 6400), Neovenator (Brusatte et al.
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27
2008), Giganotosaurus (MUCPV-Ch 1) and Mapusaurus
(MCF-PVPH 108.202), this margin is smooth and lacks
any type of projection or well-developed margin.
6.2 Remarks on carcharodontosaurid anatomy
6.2.1 Vertebral anatomy
The vertebral anatomy of carcharodontosaurids has not
been fully analysed yet. For instance, the derived
carcharodontosaurid Giganotosaurus carolinii (Coria and
Salgado 1995) has preserved a complete vertebral series,
but these remains are still undescribed in detail. The study
of the vertebrae of Tyrannotitan revealed striking
similarities with those of Giganotosaurus, Carcharodon-
tosaurus and Mapusaurus, and to a lesser degree with the
vertebrae of Acrocanthosaurus.
The cervical vertebrae in Tyrannotitan are strongly
opisthocoelic, with the anterior articular face subspherical,
as in Giganotosaurus (MUCPV-Ch 1) and Carcharodon-
tosaurus (NCSM 18166). The neural spines are robust and
‘pyramid-shaped’ in anterior view, a feature that can also
be seen in Giganotosaurus (MUCPV-Ch 1) and Mapu-
saurus (MCF-PVPH 108.90). The cervical centra have two
pleurocoels on their lateral sides, as in Giganotosaurus
(MUCPV-Ch 1), Carcharodontosaurus (NCSM 18166)
and Acrocanthosaurus (Harris 1998). At least the posterior
cervicals have rudimentary hyposphene –hypantrum
accessory articulations, resembling the condition of
Giganotosaurus (MUCPV-Ch 1) and Carcharodonto-
saurus (NCSM 18166). All the dorsal vertebrae also bear
two pleurocoels on each side of the centrum (except for
dorsal 14, which has a single pleurocoel) and the
prezygapophyses have pneumatic openings or pits on
their anterior borders as in Mapusaurus (MCF-PVPH
108.80) and Giganotosaurus (MUCPV-Ch 1). The neural
spines are high, robust and rectangular in cross section,
with strongly developed and prominent ligament scars and
spinopre- and spinopostzygapophyseal fossae below them,
as in Acrocanthosaurus (Harris 1998), Mapusaurus (MCF-
PVPH 108.80) and Giganotosaurus (MUCPV-Ch 1). The
sacrum is composed of five fused vertebrae, ventrally
concave in lateral view, laterally compressed at its
anteroposterior midpoint, and with unfused neural spines,
as in Giganotosaurus (MUCPV-Ch 1). The posterior sacral
centra have a single pleurocoel on each lateral side as in
Giganotosaurus (MUCPV-Ch 1) and Mapusaurus (MCF-
PVPH 108.209). Finally, the anterior caudal vertebrae only
have pneumatic depressions (lacking true pleuroco els) on
the lateral surfaces of their centra, as in Giganotosaurus
(MUCPV-Ch 1) and Mapusaurus (MCF-PVPH 108.81).
The absence of pleurocoels in the first sacral centrum
and the presence of pleurocoels in the last dorsals and in
the fourth and fifth sacral vertebrae suggest the presence of
a caudosacral pneumatic hia tus (Wedel 2009). A
Historical Biology
pneumatic hiatus is an apneumatic portion of the vertebral
column bracketed between pneumatic vertebrae, which
has been interpreted as indicative of different air sacs or
diverticula that pneumatise different parts of the skeleton.
In the case of Tyrannotitan, the position of the hiatus
suggest that different diverticula of the abdominal air sac
pneumatised the last dorsals and the last sacral vertebrae
independently. This interpretation is reinforced by the
presence of only one pleurocoel in the posteriormost
dorsal vertebra compared with the double opening of the
preceding dorsal vertebrae, suggesting that the source of
the presacral pneumatisation is not completely expanded
posteriorly. The presence of this hiatus has not been
previously reported in theropods but has been described
for the sauropod Haplocantosaurus (Wedel 2009). Its
presence provides further evidence for inferring the
development of abdominal air sacs with different
diverticula, in addition to the cervical and clavicular air
sacs in theropods, as occurring in birds (Wedel 2009).
6.2.2 Scapular girdle
The study of the scapulocoracoid in Tyrannotitan allows
reinterpreting the morphology of this anatomical region in
the closely related Giganotosaurus (Coria and Salgado
1995; Calvo 1999; Calvo et al. 2004; Novas et al. 2005;
Novas 2009). In the original description, Coria and
Salgado (1995) cited the following character as part of the
diagnosis of Giganotosaurus: ‘proximal end of the scapula
forwardly projected over the coracoid’. In the description
of the specimen they detailed that ‘the coracoid is small
and hook shaped with an externally open coracoid
foramen’. This particular morphology was cited in
subsequent contributions (Calvo 1999; Calvo et al. 2004,
Novas et al. 2005) as a derived condition of Gigan-
otosaurus that was absent in related forms.
A detailed comparison between the scapulocoracoid of
Tyrannotitan and Giganotosaurus reveals that in the
coracoid of the holotype of Giganotosaurus, the dorsal and
anterior borders are damaged and only the sector over the
glenoid cavity is preserved. The scapula of the type
specimen of Giganotosaurus also has the acromial process
broken, which was previously interpreted as a low
acromial process (Calvo et al. 2004). The character
‘externally open coracoid foramen’ is also produced by a
misinterpretation of the type material of this taxon. The
coracoid foramen is present, but in a fragment of the left
coracoid that is fused and preserved attached to the scapula
(Figure 35(A)). This fragment of the coracoid was
interpreted as part of the scapula by previous authors,
but the suture scar between the coracoid and scapula is
visible in the type material. The position of the coracoid
foramen is almost the same as in Tyrannotitan, located
centrally on the lateral surface of coracoid. The
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28 J.I. Canale et al.
Figure 35. Scapulocoracoids in lateral view of (A) Giganotosaurus carolinii (MUCPV-Ch 1) and (B) Tyrannotitan chubutensis (MPEF-
PV 1156). Note: Scale bar is 10 cm; see text for abbreviations.
interpretation of the fragment of the coracoid as part of the
scapula led previous authors to postulate the autapo-
morphic character of Giganotosaurus ‘proximal end of the
scapula forwardly projected over the coracoid’ (Coria and
Salgado 1995) or, as expressed by Calvo et al. (2004), the
‘articular margin of the scapula – coracoid oblique with
respect to the long axis of the scapula’.
In sum, the pectoral girdle of the type material of
Giganotosaurus (Coria and Salgado 1995) is incompletely
preserved and led to a misinterpretation of its anatomy. We
interpret the scapula and coracoid of Giganotosaurus as
similar to that of Tyrannotitan (Novas et al. 2005) and
Mapusaurus roseae (Coria and Currie 2006), having a
wide coracoid, well-developed coracoid foramen, scapula
and coracoid fused, and the contact between these two
elements is oriented perpendicular to the long axis of
scapula. Although the acro mion is only partially preserved
in the holotype of Giganotosaurus, the available remains
suggest its morphology did not differ from that of
Tyrannotitan.
6.3 Phylogenetic analysis
The phylogenetic position of Tyrannotitan chubutensis
within Carcharodontosauridae has been debated in recent
phylogenetic analyses (Novas et al. 2005; Brusatte and
Sereno 2008; Sereno and Brusatte 2008; Smith et al. 2008;
Eddy and Clarke 2011). Previous analyses have retrieved
Tyrannotitan as a basal carcharodontosaurid (Novas et al.
2005; Brusatte and Sereno 2008; Eddy and Clarke 2011)or
in a polytomy with other derived carcharodontosaurids
(Brusatte et al. 2008; Carrano et al. 2012). Probably this
lack of agreement came from the limited anatomical
information available, given the lack of a detailed
anatomical description of this taxon. The study of cranial
and postcranial remains of Tyrannotitan chubutensis and
comparisons with other carcharodontosaurids provided
valuable information, which allows us testing more
thoroughly their phylogenetic relationships.
The phylogenetic relationships of the clade Allosaur-
oidea, and in particular Carcharodontosauridae, have been
the subject of intense research and debate, counting with
more than 15 phylogenetic analyses published in recent
years (Sereno et al. 1996; Harris 1998; Forster 1999;
Currie and Carpenter 2000; Holtz 2000; Allain 2002;
Coria and Currie 2002; Rauhut 2003; Holtz et al. 2004;
Novas et al. 2005; Coria and Currie 2006; Smith et al.
2007; Brusatte and Sereno 2008; Sereno and Brusatte
2008; Smith et al. 2008; Brusatte et al. 2009; Benson 2010;
Benson et al. 2010; Ortega et al. 2010; Eddy and Clarke
2011; Carrano et al. 2012; Cau et al. 2012a, 2012b; Novas
et al. 2013). Here we present a phylogenetic analysis of
Carcharodontosauridae based on the original data-set of
Canale (2010), expanding the character sampling regime
and changing some previous scorings (Table S1: Character
re-scoring table). This data-set is an updated version of
that presented in a recent review by Novas et al. (2013).
The data matrix includes 16 taxa scored across 169
anatomical characters, 106 of which are cranial and 63
postcranial (Appendix S2: List of Anatomical Characters
and S3: Data Matrix). The data matrix was analysed with
TNT v1.1 (Goloboff et al. 2008). A heuristic search was
carried out with 1000 replicates of Wagner trees (using
random addition sequence) followed by tree bisection and
reconnection (TBR) branch-swapping, saving 10 trees per
replication, to find the most parsimonious trees (MPTs).
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29 Historical Biology
Figure 36. Strict consensus tree of the two MPTs obtained from the phylogenetic analysis.
A final round of TBR was applied to the best trees found in
the replicates to ensure that all MPTs were found. Twelve
MPTs of 308 steps were recovered (CI ¼ 0.633;
IR ¼ 0.726).
6.3.1 Giganotosaurini
The strict consensus tree places Tyrannotitan in a derived
position within Carcharodontosauridae, it being the sister
group of Giganotosaurus and Mapusaurus (Figure 36).
These three taxa form the clade Giganotosaurini, as also
noted by Novas et al. (2013). In this phylogenetic analysis,
the clade Giganotosaurini is diagnosed by three two
unambiguous synapomorphies.
The first of these is the presence of a postorbital
process of the jugal with a wide base (char. 60:0), a
character recently recognised by Novas et al. (2013). In
Allosaurus (UMNH-VP 9085), Monolophosaurus (Zhao
and Currie 1993), Sinraptor (Currie and Zhao 1993),
Acrocanthosaurus (NCSM 14345) and Carcharodonto-
saurus saharicus (SGM-Din1), the postorbital process of
the jugal is rod-like, its height being equal or more than
twice the anteroposterior length of its base. In Mapusaurus
(MCF-PVPH 108.168) and Tyrannotitan (MPEF-PV
1157), the postorbital process of jugal is subtriangular in
lateral view, its height being less than twice the length of
its base (Figure 37).
The second synapomorphy of Giganotosaurini is the
presence of a shallow and broad extensor groove on distal
femur (char. 161:1). This character was originally
proposed by Harris (1998) and later Coria and Currie
(2006) considered state 1 as a synapomorphy that unites
Giganotosaurus and Mapusaurus. A shallow and broad
extensor groove is also present in Tyrannotitan (MPEF-PV
1156) (Appendix S1: Figure 2).
The clade Giganotosaurini has minimal Bremer
support values (BS ¼ 1); however, this is mainly due to
the unstable behaviour of Carcharodontosaurus iguidensis
in suboptimal trees. When the alternative positions of the
highly incomplete Carcharodontosaurus iguidensis (76%
missing data) are ignored among the suboptimal trees, the
Figure 37. Illustration of character 60. Right jugals of (A)
Allosaurus fragilis (UMNH-VP 9085) and (B) Tyrannotitan
chubutensis (MPEF-PV 1157). Note: Scale bar is 10 cm.
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30 J.I. Canale et al.
monophyly of the clade Giganotosaurini is only rejected in
trees that are three steps longer than the MPTs (BS ¼ 3).
This demonstrates that despite the uncertainties on the
phylogenetic position of Carcharodontosaurus iguidensis
due to its fragmentary nature, the clustering of the three
South American taxa (Tyrannotitan, Mapusaurus and
Giganotosaurus) to the exclusion of Carcharodontosaurus
saharicus and other carcharodontosaurids is moderately
well supported.
Tyrannotitan is placed basally within Giganotosaurini
(Figure 36) because it lacks two derived features present in
the femur of Mapusaurus and Giganotosaurus, which are
interpreted in the context of this analysis as unam biguous
synapomorphies of the clade formed by these two taxa.
These are the strongly reduced fourth trochanter on femur
(char. 160:1) and the absence of the ridge for cruciate
ligaments in flexor groove of femur (char. 162:0).
6.3.2 Carcharodontosaurinae
Giganotosaurini and the African genus Carcharodonto-
saurus are retrieved as sister taxa (Figure 36), forming the
clade Carcharodontosaurinae: a group of giant-sized,
derived, gondwanan carcharodontosaurids. The mono-
phyly of this clade is supported by the four cranial
characters proposed in previous studies that are interpreted
here as unambiguous synapomorphies: the maxilla with
only promaxillary foramen on the antorbital fossa (char.
7:3), external sculpturing of maxilla covering the main
body of the bone (char. 13:1), strong rugosities and
projections over the anterior half of the nasal (char. 25:1)
and interorbital septum present and well ossified (char.
77:1). It is worth noting that the condition of Tyrannotitan
for these four cranial synapomorphies is unknown.
However, the support for the inclusion of this taxon
deeply nested within Carcharodontosaurinae comes from
the derived features shared with Mapusaurus and
Giganotosaurus noted above (see Giganotosaurini; chars.
60, 161).
The support value for Caracharodontosaurinae is
higher than that for the clade Giganotosaurini within the
context of the analysed data matrix. In trees that are three
to seven steps longer than the most parsimonious topology,
both Shaochilong and Eocarcharia get nested within this
clade, but not other carcharodontosaurid taxa. This
indicates that despite the uncertainties on the position of
Shaochilong and Eocarcharia (both of which are
fragmentary and with large amounts of missing data in
this data-set), the clade Carcharodontosaurinae has strong
character support within Carcharodontosauridae.
The monophyly of this Gondwanan clade of giant
theropods and its internal divergence between the clades
Carcharodontosaurus (recorded in the Cenomanian of
northern Africa) and Giganotosaurini (recorded from the
Albian to the Cenomanian in southern South America) are
compatible with a vicariant explanation of their distri-
bution, given that the separation between both continents
was apparently effective at some point during the Aptian –
Albian (Gheerbrant and Rage 2006).
6.3.3 Carcharodontosauridae
The monophyly of Carcharodontosauridae is supported by
18 synapomorphies: maxilla with fully co-ossified
posterior interdental plates (char. 14:1), squared anterior
margin of maxillary antorbital fossa (char. 20:1), maxilla
with sinuous shape of ridge across interdental plates in
medial view (char. 22:1), nasals parallel sided throughout
its length in dorsal view (26:1), frontals co-ossified (char.
35:1), frontals co-ossified with parietal (char. 36:1), paired
frontals mediolaterally wider than 4/3 of frontal length
(char. 37:2), lacrimal and postorbital in contact (char.
41:1), transversely broad interlocking suture between
postorbital and squamosal (char. 42:1), postorbital with
suborbital flange (char. 43:1), postorbital with bulbous
swelling extensively overhanging the orbit (char. 46:1),
postorbital with vascular groove present and limited to
anterior half of dorsal boss (char. 49:1), postorbital with
expansion of supratemporal fossa close to posterior margin
of main body in dorsal view (char. 50:1), large axial
epipophyses (char. 109:1), cervicals with interior structure
of centrum camellate (char. 118:2), dorsal vertebrae with
hyposphene laminae parallel and sheet like (char. 122:1),
ischium with a boot-shaped distal expansion (absent in
more derived forms) (154:2) and tibial lateral malleolus
distal extension beyond medial malleolus more than 5%
tibial length (char. 167:1).
7. Conclusions
The carcharodontosaurid theropod Tyrannotitan chubu-
tensis is here described improving our knowledge of the
anatomy, the phylogenetic position of this taxon and the
internal relationships of carcharodontosaurid dinosaurs.
The original diagnosis of the species was revised and
emended with four new autapomorphic characters. The
available material of Tyrannotitan has provided new
information on the axial skeleton, allowing a comparison
with related forms on vertebral anatomy. The presence of a
pneumatic hiatus in the sacrum of Tyrannotitan adds
evidence to the presence of abdominal air sacs; with
different diverticula pneumatising different parts of the
skeleton, in addition to the cervical and clavicular air sacs,
as occurring in birds. Tyrannotitan shares several derived
characters with Giganotosaurus and Mapusaurus, and to a
lesser degree, with Carcharodontosaurus (for which there
is limited vertebral information) and Acrocanthosaurus.
The analysis of the pectoral girdle of Tyrannotitan allowed
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31
a reinterpretation of the scapula and coracoid anatomy of
the related carcharodontosaurid Giganotosaurus.
Features of the latter genus previously interpreted as a
derived morphology actually respond to misinterpreta-
tions of broken surfaces. The new anatomical infor-
mation on Tyrannotitan and related forms was
incorporated in a phylogenetic analysis that reinforces
the hypothesis of Tyrannotitan being a derived
carcharodontosaurid. In our results, this taxon is
depicted as the sister group of Giganotosaurus plus
Mapusaurus, forming the South American clade
Giganotosaurini. The close affinities of Tyrannotitan
with other South America forms and the position of the
African Carcharodontosaurus as their sister group are
concordant with previous hypotheses on the vicariant
pattern of southern dinosaurs that resulted from the break
up of Gondwana during the Cretaceous.
Acknowledgements
The authors would like to thank Eduardo Ruigo
´ mez (MEF),
Rodolfo Coria (MCF), Jorge Calvo (MUC), Alejandro Kramarz
(MACN), Mike Getty (UMNH), Vince Schneider (NCSM), Paul
Sereno (University of Chicago, USA), Rodney Scheetz (BYU)
for allowing access to specimens under their care. Federico
Agnolı
´n made comments on early drafts of the manuscript. We
also thank Andrea Cau (Museo Geologico ‘Giovanni Capellini’,
Bologna, Italy) and an anonymous reviewer for their improving
and useful comments on the manuscript, especially Dr Cau for his
suggestions about axial pneumaticity. Miguel O. Mancen
˜ido
helped with taxonomic and nomenclatural aspects.
Funding
Travel finance to carry out this work was provided by the Jurassic
Foundation (to JIC). The program TNT is made freely available,
thanks to a subsidy by the Willi Hennig Society.
Notes
1. Email: fernovas@yahoo.com.ar
2. Email: dpol@mef.org.ar
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