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Allosauroid (Theropoda, Tetanurae) remains from the Sierra Barrosa Formation (Middle Coniacian, Upper Cretaceous), Patagonia, Argentina.

  • Museo Municipal Argentino Urquiza, Rincón de los Sauces, Neuquén, Argentina


The Late Cretaceous theropod fauna of South America is composed of Abelisauridae, Noasauridae, Spinosauridae, Carcharodontosauridae, Megaraptora, and Coelurosauria. These groups include mostly small (Noasauridae and Coelurosauria) and medium- tolarge-sized taxa (Carcharodontosauridae, Abelisauridae, and Megaraptora). Some of these lineages are predominantly Gondwanic (Abelisauridae, Noasauridae, Carcharodontosauridae, Megaraptora) and poorly represented in Laurasian landmasses. Particularly, several theropods have been reported from Patagonia, known either due to distinct anatomical features or due to their high degree of preservation, such as Carnotaurus, Skorpiovenator, Giganotosaurus, Megaraptor, Alvarezsaurus, and Unenlagia. Here we describe a new incomplete tibia (MAU-PV-CM-653) from the Sierra Barrosa Formation (middle Coniacian, Upper Cretaceous), Patagonia, Argentina. MAU-PV-CM-653 shows an anteroposteriorly reduced cnemial crest that is strongly curved laterally. Finally, the tibia lacks a proximal extension of the fibular crest. These traits are reminiscent of tetanuran morphology and, together with the stratigraphic provenance of MAU-PV-CM-653, they allow us to assign it to an allosauroid theropod, thus improving the Allosauroidea global record for the middle Late Cretaceous.
ISSN 2469-0228
Recibido: 2 de septiembre 2021 - Aceptado: 25 de octubre 2021 - Publicado: 26 de enero 2022
Para citar este artículo: Mattia Antonio Baiano & Leonardo Sebastián Filippi (2022). Allosauroid (Theropoda, Tetanurae)
remains from the Sierra Barrosa Formation (Middle Coniacian, Upper Cretaceous), Patagonia, Argentina. Publicación
Electrónica de la Asociación Paleontológica Argentina 22 (1): 1–10.
Link a este artículo:
1. Área Laboratorio e Investigación, Museo Municipal “Ernesto Bachmann”. Dr. Natali s/n, Q8311AZA Villa El Chocón, Neuquén, Argentina.
2. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET).
3. Universidad Nacional de Río Negro (UNRN). Isidro Lobo 516, 8332 General Roca, Río Negro, Argentina.
4. Museo Municipal Argentino Urquiza. Chos Malal 1277, Q8319BFA Rincón de los Sauces, Neuquén, Argentina.
Asociación Paleontológica Argentina
Maipú 645 1º piso, C1006ACG, Buenos Aires
República Argentina
Tel/Fax (54-11) 4326-7563
Allosauroid (Theropoda, Tetanurae)
remains from the Sierra Barrosa Formation
(Middle Coniacian, Upper Cretaceous),
Patagonia, Argentina
©2022 Baiano and Filippi
1Área Laboratorio e Investigación, Museo Municipal “Ernesto Bachmann”. Dr. Natali s/n, Q8311AZA Villa El Chocón, Neuquén, Argentina.
2Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET).
3Universidad Nacional de Río Negro (UNRN). Isidro Lobo 516, 8332 General Roca, Río Negro, Argentina.
4Museo Municipal Argentino Urquiza. Chos Malal 1277, (Q8319BFA), Rincón de los Sauces, Neuquén, Argentina.
MAB: https://orc; LSF:
Abstract. The Late Cretaceous theropod fauna of South America is composed of Abelisauridae, Noasauridae, Spinosauridae,
Carcharodontosauridae, Megaraptora, and Coelurosauria. These groups include mostly small (Noasauridae and Coelurosauria) and medium- to
large-sized taxa (Carcharodontosauridae, Abelisauridae, and Megaraptora). Some of these lineages are predominantly Gondwanic (Abelisauridae,
Noasauridae, Carcharodontosauridae, Megaraptora) and poorly represented in Laurasian landmasses. Particularly, several theropods have
been reported from Patagonia, known either due to distinct anatomical features or due to their high degree of preservation, such as Carnotaurus,
Skorpiovenator, Giganotosaurus, Megaraptor, Alvarezsaurus, and Unenlagia. Here we describe a new incomplete tibia (MAU-PV-CM-653) from
the Sierra Barrosa Formation (middle Coniacian, Upper Cretaceous), Patagonia, Argentina. MAU-PV-CM-653 shows an anteroposteriorly
reduced cnemial crest that is strongly curved laterally. Finally, the tibia lacks a proximal extension of the fibular crest. These traits are reminiscent
of tetanuran morphology and, together with the stratigraphic provenance of MAU-PV-CM-653, they allow us to assign it to an allosauroid
theropod, thus improving the Allosauroidea global record for the middle Late Cretaceous.
Key words. Late Cretaceous. Neuquén Group. South America. Patagonia. Dinosauria. Allosauroidea. Tibia.
SUPERIOR), PATAGONIA, ARGENTINA. La fauna de terópodos del Cretácico Tardío de América del Sur escompuesta por Abelisauridae,
Noasauridae, Carcharodontosauridae, Spinosauridae, Megaraptora y Coelurosauria. Estos grupos incluyen mayormente taxones de pequeño
(Noasauridae y Coelurosauria) y de mediano a gran tamaño (Abelisauridae, Carcharodontosauridae y Megaraptora). Algunos de estos linajes son
predominantemente gondwánicos (Abelisauridae, Noasauridae, Carcharodontosauridae, Megaraptora) y poco representados en los continen-
tes laurásicos. Particularmente, distintos terópodos han sido reportados desde la Patagonia, conocidos o por sus distintivas características
anatómicas o por su grado de preservación, tales como Carnotaurus, Skorpiovenator, Giganotosaurus, Megaraptor, Alvarezsaurus y Unenlagia. Aquí
describimos una nueva tibia incompleta (MAU-PV-CM-653) proveniente de la Formación Sierra Barrosa (Coniaciano medio, Cretácico Superior),
Patagonia, Argentina. MAU-PV-CM-653 muestra una cresta cnemial reducida anteroposteriormente, que está fuertemente curvada lateral-
mente. Finalmente, la tibia carece de una extensión proximal de la cresta fibular. Estos rasgos hacen recordar una morfología de tetanuro y,
junto con la procedencia estratigráfica de MAU-PV-CM-653, nos permite asignarla a un terópodo allosauroideo, y por ende mejorar el registro
global de Allosauroidea para la parte media del Cretácico Tardío.
Palabras clave. Cretácico Superior. Grupo Neuquén. América del Sur. Patagonia. Dinosauria. Allosauroidea. Tibia.
THE CRETACEOUS South American theropod record spans all
major internal taxa (e.g., Ceratosauria, Allosauroidea,
Coelurosauria), and is represented by small, medium, and
large-sized specimens (e.g., Carrano & Sampson, 2008;
Carrano et al., 2012; Novas et al., 2013). In particular, this
region is the most abundant fossil area compared to other
Gondwanan provinces, due to the strong increase in the
South American fossil record from the Cenomanian (Late
Cretaceous) onward. The abundance of remains of some
groups of theropods such as Abelisauridae, Megaraptora,
and Maniraptora in the Argentine Patagonia is remarkable,
with a large number of nominated taxa, some of which are
distinguished by their high degree of conservation (e.g.,
Novas et al., 2013).
Año 2022 - 22(1): 1–10 ARTÍCULO
©2022 Baiano and Filippi | CC BY-NC 4.0 | Acceso Abierto - Open Access
The Neuquén Group is the principal lithostratigraphic unit
regarding the theropod fossil record in northern Patagonia
(e.g., Leanza et al., 2004; Garrido, 2010), and it is subdivided in
nine formations that mainly encompass the Upper Cretaceous
(middle Cenomanian–middle Campanian) (Garrido, 2010).
However, theropod remains are scarce from the Río
Neuquén Subgroup (Portezuelo, Los Bastos, Sierra Barrosa
and Plottier formations; middle Turonian–lower Santonian),
except for the Portezuelo Formation (Novas, 1997, 1998;
Novas & Puerta, 1997; Calvo et al., 2004a; Novas & Pol,
2005). This paucity of theropods mainly affects the
allosauroid record, since only two specimens have been
recorded from the middle Late Cretaceous (Coria & Currie,
2016; Porfiri et al., 2018). However, when we take into
account the global allosauroid record (excepting Argentina),
this paucity is even worse, since no middle Late Cretaceous
(Coniacian–Santonian) specimens have been discovered
anywhere else up to now. Here, we report a new tetanuran
theropod partial tibia from the Sierra Barrosa Formation
(middle Coniacian, Upper Cretaceous) (Fig. 1) that we refer
to Allosauroidea based on several features of its
morphology and, tentatively, to Megaraptora if we consider
its stratigraphic provenance.
Institutional acronyms. MAU, Museo Municipal Argentino
Urquiza, Rincón de los Sauces, Argentina; MB, Museum für
Naturkunde, Humboldt-Universität zu Berlin, Germany;MCF,
Museo Municipal Carmen Funes, Plaza Huincul, Argentina;
MCT, Museu de Ciências da Terra do Departamento Nacional
de Produção Mineral, Rio de Janeiro, Brazil; MPCA, Museo
Provincial Carlos Ameghino, Cipolletti, Argentina; MPEF,
Museo Paleontológico Egidio Feruglio, Trelew, Argentina;
MUC, Museo Universidad Nacional del Comahue, Neuquén,
Argentina; UNPSJB, Universidad Nacional de la Patagonia
San Juan Bosco, Comodoro Rivadavia, Argentina; USNM,
National Museum of Natural History, Smithsonian Institution,
Washington, USA.
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Figure 1. Locality map showing where the specimen MAU-PV-CM-653 was found, indicated by the black star.
THEROPODA Marsh, 1881
TETANURAE Gauthier, 1986
Figures 2 and 3.1
Specimen. MAU-PV-CM-653, proximal end of the left tibia
(Tab. 1).
Geographic occurrence. MAU-PV-CM-653 was found at
Cañadón Mistringa locality, southwest of Rincón de los
Sauces city, Pehuenches Department, Neuquén Province,
Argentina (Fig. 1).
Stratigraphic occurrence. The fossil-bearing strata are
attributed to the Sierra Barrosa Formation (Coniacian, Upper
Cretaceous), Neuquén Group (Garrido, 2010), Neuquén Basin.
Description. MAU-PV-CM-653 corresponds to the proximal
end of the left tibia, including the articular surface, the pos-
terior condyles, and the cnemial crest. However, the speci-
men lacks the rest of the diaphysis, including the crista
fibularis and the distal articular end. In proximal view (Fig.
2.1), the articular surface has a comma shaped outline. The
proximal condyles are well defined and separated by a
shallow intercondylar sulcus. The medial condyle shows a
teardrop outline, whereas the lateral condyle is oval in out-
line, with an anteroposteriorly oriented major axis. Further-
more, the medial condyle is anteroposteriorly longer and
more posteriorly projected than the lateral one. Anterior to
the articular condyles there is a depression that is probably
where the femoral tibial condyle articulated. The cnemial
crest is anteroposteriorly reduced and is strongly curved
laterally. In fact, the anterior rim of the cnemial crest is
positioned at 90 degrees with respect to the main axis of
the proximal surface. The medial rim is convex due to the
lateral curvature of the cnemial crest. The lateral rim is si-
nusoidal, since the section that corresponds to the lateral
condyle is slightly convex whereas the section that corre-
sponds to the cnemial crest is concave. The lateral condyle is
separated from the cnemial crest by a deep incisura tibialis.
However, the lateral condyle of MAU-PV-CM-653 lacks a
distally directed anterolateral process. The posterior rim is
w-shaped and is obliquely oriented relative to the medio-
lateral axis.
In medial view (Fig. 2.2), the preserved portion of the
tibia is triangular in outline. The dorsal rim is almost straight,
only bowing ventrally at the posterior end. In this view,
the cnemial crest is horizontal and does not exceed the ar-
ticular surface proximally. Near the posterodorsal corner,
there is a triangular depression with a rugose surface where
the muscles flexor tibialis internus 3 (FTI3) and flexor tibialis
externus (FTE) (Carrano & Hutchinson, 2002) were probably
inserted. The surface is slightly concave near the anterior
border of the cnemial crest.
In lateral view (Fig. 2.3), the medial condyle is proximally
higher and posteriorly deeper than the lateral condyle, re-
sulting in a laterodistally inclined proximal surface. The lat-
eral condyle ends distally with a marked step. The lateral
fossa of the cnemial crest is anteroposteriorly narrow with
a finger-like outline and its major axis is anteroproximally-
posterodistally oriented. The anterior rim of the cnemial crest
is slightly convex and bears a rugose bump at the proximal
end, where the muscles ambiens (AMB), femorotibialis
(FMT), and iliotibiales 1–3 (IT 1-3) would have been inserted
(Carrano & Hutchinson, 2002). The fibular crest cannot be
observed because of the poor preservation of the tibial
TABLE 1 - Measurements (in cm) of the tibia MAU-PV-CM-653
Proximodistal Length Proximodistal Length
of Cnemial Crest
Anteroposterior Length
of Proximal Surface
Anteroposterior Length
of Cnemial Crest
Mediolateral Width of
Proximal Posterior Rim
11.5* 6.6 12.7 4.3 6.8
*Asterisk indicates incomplete measurements due to missing bone.
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Figure 2. Allosauroidea indet.MAU-PV-CM-653. Tibia in 1, proximal; 2, medial; 3, lateral; 4, anterior; and 5, posterior views. Abbreviations:
cc, cnemial crest; d, depression; is, intercondylar sulcus; lb, lateral bump; lc, lateral condyle; lf, lateral fossa; mc, medial condyle; pdd,
posterodorsal depression; r, rugosity. Scale bar= 5 cm.
shaft. However, in the fragment of tibia presented, the
fibular crest does not extend proximally or anteroproximally
onto the lateral surface of the cnemial crest.
In anterior view (Fig. 2.4), the cnemial crest is laterally
directed with a thick proximal end that narrows towards the
distal end. On the medial part, the shallow medial depres-
sion is visible, delimited proximally and anteriorly by a stout
In posterior view (Fig. 2.5), the proximal rim is laterodis-
tally oriented. The medial condyle is rounded and ends dis-
tally with a convex step. The lateral condyle has a rugose
surface and is rectangular in shape, with the major axis
mediolaterally positioned. The intercondylar sulcus is deep
and distally to it there is a rugose oval area where soft tis-
sue was probably inserted (possibly the muscle flexor tibialis
internus 1, FTI1; Carrano & Hutchinson, 2002). Although the
tibial shaft has been almost completely lost, the preserved
fragment shows a lateral bowing of the element.
The MAU-PV-CM-653 tibia shows a posteriorly posi-
tioned medial condyle, a condition present more markedly
in Neovenator, Orkoraptor, and in the indeterminate tetanu-
ran MB.R.1763, but different from the condition present in
Australovenator, Fukuiraptor, Murusraptor, Phuwiangvenator,
and Vayuraptor, in which both proximal condyles reach
roughly the same distance posteriorly (Azuma & Currie,
2000; Rauhut, 2005a; Brusatte et al., 2008; Novas et al.,
2008; White et al., 2013; Coria & Currie, 2016; Samathi et al.,
2019) (Fig. 3.1, 3.6, 3.8). However, the rounded posterior end
of the medial condyle of MAU-PV-CM-653 differs from the
triangular posterior end of Neovenator and of the indeter-
minate tetanuran MB.R.1763 (Fig. 3.1, 3.6). MAU-PV-CM-
653 differs from Allosaurus, Neovenator, Australovenator,
Fukuiraptor, Murusraptor, Phuwiangvenator, Vayuraptor, and
the tetanuran MB.R.1763 since it lacks the anterolateral
projection of the lateral condyle present in the other men-
tioned taxa (Madsen, 1976; Azuma & Currie, 2000; Rauhut,
2005a; Brusatte et al., 2008; White et al., 2013; Coria &
Currie, 2016; Samathi et al., 2019) (Fig. 3.1, 3.6, 3.8). In the
same way, the absence of a ventrally oriented process of the
lateral condyle observed in MAU-PV-CM-653 is shared with
several tetanurans (e.g., Torvosaurus, Allosaurus, Sinraptor,
Fukuiraptor, Murusraptor, Orkoraptor, Vayuraptor; Madsen,
1976; Britt, 1991; Currie & Zhao, 1993; Azuma & Currie,
2000; Novas et al., 2008; Coria & Currie, 2016; Samathi et
al., 2019) (Fig. 3.1, 3.4, 3.7), but differs from Neovenator,
Australovenator, Tyrannosaurus, Phuwiangvenator, and the in-
determinate tetanuran MB.R.1763, that have a conspicuous
ventrally directed process (Brochu, 2003; Rauhut, 2005a;
Brusatte et al., 2008; White et al., 2013; Samathi et al., 2019)
(Fig. 3.5–6, 3.8).
The anteroposteriorly reduced and strongly laterally
curved cnemial crest of the MAU-PV-CM-653 tibia is a fea-
ture that is also observed in several large (e.g., Allosaurus,
Sinraptor, Murusraptor, Tyrannosaurus; Madsen, 1976; Currie
& Zhao, 1993; Brochu, 2003; Coria & Currie, 2016) and
small-sized tetanurans (MB.R.1763; Rauhut, 2005a) (Fig.
3.1, 3.4–5), but that differs from the more open and more
anteroposteriorly developed cnemial crest of the tibiae of
non-averostran theropods (e.g., Dilophosaurus; Marsh &
Rowe, 2020), ceratosaurs (e.g., Ceratosaurus, Eoabelisaurus,
Velocisaurus, Quilmesaurus, Xenotarsosaurus, Genusaurus,
Aucasaurus; Gilmore, 1920; Martínez et al., 1986; Accarie et
al., 1995; Madsen & Welles, 2000; Coria, 2001; Coria et al.,
2002; Pol & Rauhut, 2012; Ibiricu et al., 2021; MCF-PVPH-
236; MPCA-PV-100; MPEF PV 3990; MUCPv-41; UNPSJB-
PV 184) and basal tetanurans (e.g., Piatnitzkysaurus; Rauhut,
2005b) (Fig. 3.1–3.3). The extension of the cnemial crest of
MAU-PV-CM-653 is reduced when compared with Aerosteon
(Aranciaga Rolando et al., 2021) and Australovenator (White
et al., 2013), but similar to the development observed in
Phuwiangvenator (Samathi et al., 2019). Moreover, MAU-PV-
CM-653 shows a cnemial crest almost horizontally pro-
jected in lateral view, as in the Murusraptor tibia but unlike
the dorsally directed crest of Aerosteon. The lack of a proxi-
mal and an anteroproximal extension of the fibular crest
onto the lateral cnemial crest and the absence of a connec-
tion between the fibular crest and the proximal rim ob-
served in MAU-PV-CM-653 is a condition shared with
tetanuran theropods (e.g., Allosaurus, Sinraptor, Murusraptor,
Tyrannosaurus; Madsen, 1976; Currie & Zhao, 1993; Brochu,
2003; MCF-PVPH-411) (Fig. 3.1, 3.4–5, 3.7). Whereas,
coelophysoids and ceratosaurs have a fibular crest strongly
developed, both proximally and anteroproximally, reaching the
proximal rim (e.g., Ceratosaurus, Quilmesaurus, Ekrixinatosaurus,
Aucasaurus; Madsen & Welles, 2000; Rauhut, 2003; Calvo
et al., 2004b; MCF-PVPH-236; MPCA-PV-100; MUCPv-294)
(Fig. 3.2–3.3). The bump where musclesambiens, femorotibialis,
and iliotibiales 1–3would have been inserted is less developed
than the one observed in several ceratosaurs (e.g., Ceratosaurus,
Eoabelisaurus, Xenotarsosaurus, Aucasaurus; Madsen & Welles,
2000; MCF-PVPH-236; MPEF PV 3990; UNPSJB-PV 184),
some megaraptorans (Australovenator, Murusraptor; White
et al., 2013; Coria & Currie, 2016), and large tetanurans (e.g.,
Allosaurus, Asfaltovenator, Torvosaurus, Tyrannosaurus;
Madsen, 1976; Britt, 1991; Brochu, 2003; Rauhut & Pol,
2019). The posterior intercondylar sulcus in MAU-PV-CM-
653 as well as in Australovenator (White et al., 2013) and
Phuwiangvenator (Samathi et al., 2019), is shallower than the
intercondylar sulcus of Murusraptor (MCF-PVPH-411). The
posterior rugose area distal to the intercondylar sulcus is
well marked, as in an indeterminate abelisauroid from
Brazil (Abelisauroidea indet. MCT 1783-R; Machado et al.,
2013). The posterior morphology of both condyles differs
from the triangular medial condyle and the rounded lateral
condyle observed in several ceratosaurs (e.g., Aucasaurus,
Abelisauroidea indet. MCT 1783-R; Machado et al., 2013;
Taxa belonging to several theropod clades have been
discovered in the cretaceous layers from Patagonia (e.g.,
Coria, 2007; Novas, 2009; Novas et al., 2013), thus yielding
the most comprehensive fossil record from Gondwana
(Novas et al., 2013). The affinity of MAU-PV-CM-653 with
Patagonian tetanurans, and the marked differences between
this specimen and all known ceratosaur tibiae means it prob-
ably belonged to some tetanuran group (Megalosauroidea,
Allosauroidea, or Coelurosauria; Rauhut et al., 2016). South
American megalosauroid remains are mainly from Brazil,
where several spinosaurid taxa have been discovered (e.g.,
Kellner et al., 2011; Carrano et al., 2012). In contrast, only a few
isolated teeth have been reported from Patagonia (Canudo
et al., 2004; Canale et al., 2017). Moreover, Megalosauroidea
is a clade distributed mainly in the Jurassic (Megalosauridae;
Rauhut et al., 2016) and throughout the Early Cretaceous up
to the Cenomanian (Spinosauridae; Kellner et al., 2011;
Malafaia et al., 2020a, 2020b). The Allosauroidea fossil
record from the Late Cretaceous of Patagonia is mainly
composed of carcharodontosaurian taxa, although carchar-
odontosaurids disappeared globally after the Turonian (e.g.,
Canale et al., 2009; Delcourt & Grillo, 2018), with the last
presence of this family documented in Asia (Brusatte et al.,
2009). However, a possible non-Carcharodontosauria al-
losauroid has been reported from the late Turonian–early
Coniacian of Patagonia (Paulina Carabajal & Coria, 2015).
Carcharodontosauria also includes megaraptorans (Benson
et al., 2010), extending the biochron of this lineage until the
Maastrichtian (Novas et al., 2008; Méndez et al., 2012). Fi-
nally, Patagonian coelurosaurs are generally smaller sized
theropods, some of them recovered as basal forms within
Coelurosauria and others recovered deeply nested within
Paraves (e.g., Novas et al., 2013; Motta et al., 2020). Inter-
estingly, an alternative scenario proposes Megaraptora as a
member of Tyrannosauroidea (Novas et al., 2013; Porfiri et
al., 2014; Aranciaga Rolando et al., 2019), which implies a
re-evaluation of Tetanurae internal relationships.
Taking into account the morphology of MAU-PV-CM-
653, plus the stratigraphic and geographic data from the
records of some tetanuran clades (e.g., Megalosauroidea,
Tyrannosauroidea), we assign it to Tetanurae, possibly to a
less inclusive allosauroid group such as Megaraptora. The
allosauroid record is globally scarce after the Turonian age,
since it only includes megaraptoran taxa and several post-
Cenomanian carcharodontosaurid teeth that have been re-
evaluated as belonging to Abelisauridae (see Canale et al.,
2009 and references therein). From Argentina proceed the
Cenomanian–Turonian Aoniraptor and two unnamed speci-
mens (Motta et al., 2016; Lamanna et al., 2020), the late
Turonian–early Coniacian Megaraptor namunhuaiquii (Novas,
1998; Porfiri et al., 2014), the middle Coniacian Murusraptor
barrosaensis (Coria & Currie, 2016), and the Santonian
Tratayenia rosalesi (Porfiri et al., 2018). From the Campanian
of Argentina, Aerosteon riocoloradensis (Sereno et al., 2008),
Orkoraptor burkei (Novas et al., 2008), and several recently
described unnamed megaraptorans (e.g., Novas et al., 2019;
Ibiricu et al., 2020) have been reported. In contrast, from
Brazil, only an indeterminate specimen has been communi-
cated (Martinelli et al., 2013). For the Maastrichtian, the
Allosauroidea record is also represented uniquely by
megaraptorans known from Argentina and Brazil (Méndez
et al., 2012; Casal et al., 2019). With the exception of the
Argentine and Brazilian specimens for the Coniacian-
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Maastrichtian period, no other allosauroid dinosaurs are
known globally. When the middle Late Cretaceous (Coniacian–
Santonian) is considered, only two taxa, i.e., Murusraptor
and Tratayenia, and one specimen, MAU-PV-CM-653, are
Despite the incompleteness of MAU-PV-CM-653 and
the lack of the peculiar traits that characterize the Late
Cretaceous allosauroids of South America, this specimen
could represent a new theropod taxon. In this case, the find-
ing presented here increases the theropod fauna for the
Sierra Barrosa Formation that currently only includes the
megaraptorid Murusraptor barrosaensis (Coria & Currie,
2016). The morphology of MAU-PV-CM-653 also differs
from the tibia of Aerosteon riocoloradensis (Sereno et al.,
2008) that was recovered in the same geographical area but
in a different stratigraphic horizon (Anacleto Formation,
Figure 3. Comparison of theropod tibiae in proximal (top) and lateral (bottom) views. 1, Allosauroidea indet., MAU-PV-CM-653; 2, Ceratosaurus
nasicornis (USNM 4735); 3, Quilmesaurus curriei (MPCA-PV-100; reversed); 4, Murusraptor barrosaensis (MCF-PVPH-411; reversed); 5,
Tyrannosaurus rex (after Brochu, 2003); 6, Neovenator salerii (after Brusatte et al., 2008); 7, Allosaurus fragilis (after Madsen, 1976); and 8,
Australovenator wintonensis (after White et al., 2013). Abbreviations: alp, anterolateral process; apfc, anteroproximal extension of the fibular
crest; cc, cnemial crest; is, intercondylar sulcus; lc, lateral condyle. Image not to scale.
lower Campanian). Moreover, the allosauroid fossil record
from the Coniacian to the Santonian is globally scarce, with
some exceptions in South America (e.g., Coria & Currie, 2016;
Porfiri et al., 2018). Therefore, we consider MAU-PV-CM-
653 important to fill the paucity of this clade in the middle
Late Cretaceous.
We are thankful to S. Palomo, technician of the Museo Municipal
Argentino Urquiza (MAU), who found the specimen MAU-PV-CM-
653. We are also grateful to the Municipalidad de Rincón de los
Sauces for the logistical support provided during fieldwork. We are
grateful to CONICET, Universidad Nacional de Río Negro (UNRN), and
Municipalidad de Plaza Huincul for institutional support. We thank A.
Méndez, an anonymous reviewer and PE-APA editorial board for
their detailed comments and suggestions, which greatly improved
the manuscript. L. Herbert ( assisted with
English editing. We also thank A. Méndez for providing us with the
photographs of the Aerosteon tibia.
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doi: 10.5710/PEAPA.25.10.2021.396
Recibido:2 de septiembre 2021
Aceptado: 25 de octubre 2021
Publicado: 26 de enero 2022
Publicación Electrónica - 2022 - Volumen 22(1): 1–10
Abelisaurids are medium–large-sized theropod dinosaurs that were predominant in the carnivorous fauna during the Late Cretaceous of Gondwana. These predators are abundant in the Cretaceous fossil strata of Patagonia, which yield the best record for this group. In the Late Cretaceous, abelisaurids appear in almost all regions of Gondwana and in all stages, except for the Coniacian, in which they are globally unknown. Here we describe a new abelisaurid, Elemgasem nubilus gen. et sp. nov., from the Portezuelo Formation (Turonian–Coniacian), Patagonia, Argentina. The palaeohistology of the appendicular bones of Elemgasem shows that the holotype was a subadult individual, but had achieved sexual maturity. This taxon is based on several axial and appendicular elements, and is diagnosed by the presence of a marked pattern of rugosity on the lateral surface of the fibula and a dorsoventrally deep lateral wall of the calcaneum. Moreover, the posterior caudal vertebrae have a morphology slightly different from any other abelisaurid. Elemgasem nubilus is recovered as an unstable taxon within Brachyrostra, given that it was recovered as sister taxon of Furileusauria or in several positions within this clade. Despite the problematic phylogenetic relationships of Elemgasem nubilus, it is important because it is the first abelisaurid from the Turonian–Coniacian interval and it increases the diversity of this theropod family at a time of marked turnover in the tetrapod fauna of South America, global climate change, and mass extinction events recorded worldwide in the marine realm.
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We describe two partial postcranial skeletons belonging to the enigmatic theropod dinosaur clade Megaraptoridae from the Upper Cretaceous (lower Cenomanian-upper Turonian) Bajo Barreal Formation of southern Chubut Province, central Patagonia, Argentina. The specimens are assigned to Megaraptoridae due to their possession of multiple anatomical features that are considered synapomorphies of that predatory dinosaur group, such as a greatly enlarged, laterally compressed ungual of manual digit I that possesses asymmetrical lateral and medial vascular grooves. Overlapping elements of the two skeletons are nearly identical in morphology, suggesting that they probably represent the same taxon, a large-bodied theropod that was previously unknown from the early Late Cretaceous of southern South America. The Bajo Barreal specimens constitute the most ancient unquestionable records of Megaraptoridae from that continent, and exhibit particularly strong osteological resemblances to penecontemporaneous megaraptorids from the Winton Formation of Australia. Phylogenetic analysis recovers the unnamed Bajo Barreal taxon as the earliest-diverging South American megaraptorid and the oldest-known representative of this clade that likely attained a body length of at least seven meters and a mass of at least one metric ton. Overall, the balance of the evidence suggests that megaraptorids originated in eastern Gondwana (Australia) during the Early Cretaceous, then subsequently dispersed to western Gondwana (South America) during the mid-Cretaceous, where they attained substantially larger body sizes, ultimately coming to occupy the apex predator niches in their respective habitats.
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The fossil record of spinosaurid theropods from the Lower Cretaceous of the Iberian Peninsula is relatively abundant, but not very informative. This record, as generally occurs in other geographic areas, is mainly represented by isolated teeth, probably due to the distinctive features of the dentition of these theropods. However, cranial and postcranial elements attributed to spinosaurids have been described and reported from different Iberian fossil sites. The currently known record of these theropods spans from the upper Hauterivian to the lower Aptian of the Cameros and Maestrazgo basins in Eastern Spain whereas it is early Barremian in age in the Lusitanian Basin of Western Portugal. Spinosaurid remains from the Iberian fossil record were traditionally attributed to Baryonyx, firstly described in the upper Barremian–lower Aptian of United Kingdom. However, the recent description of a specimen collected in the locality of Santa Águeda (Vallibona, Castellón), from sediments of the Morella Formation, implies the presence of a new taxon with a combination of derived features more closely related with some Gondwanan spinosaurines than with Baryonyx. Therefore, the currently known Iberian spinosaurid record would be made up of at least three taxa: Baryonyx (or a closely related baryonychine), the spinosaurine Vallibonavenatrix cani, and possibly Camarillasaurus cirugedae, which was recently re-interpreted as belonging to a megalosauroid tentatively related with spinosaurids. This faunal diversity is also compatible with the assortment of spinosaurid tooth morphotypes (distinguished mostly by the presence or absence of serrated mesial carina) that has been described in the Lower Cretaceous of the Iberian Peninsula.
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Dilophosaurus wetherilli was the largest animal known to have lived on land in North America during the Early Jurassic. Despite its charismatic presence in pop culture and dinosaurian phylogenetic analyses, major aspects of the skeletal anatomy, taxonomy, ontogeny, and evolutionary relationships of this dinosaur remain unknown. Skeletons of this species were collected from the middle and lower part of the Kayenta Formation in the Navajo Nation in northern Arizona. Redescription of the holotype, referred, and previously undescribed specimens of Dilophosaurus wetherilli supports the existence of a single species of crested, large-bodied theropod in the Kayenta Formation. The parasagittal nasolacrimal crests are uniquely constructed by a small ridge on the nasal process of the premaxilla, dorsoventrally expanded nasal, and tall lacrimal that includes a posterior process behind the eye. The cervical vertebrae exhibit serial variation within the posterior centrodiapophyseal lamina, which bifurcates and reunites down the neck. Iterative specimen-based phylogenetic analyses result in each of the additional specimens recovered as the sister taxon to the holotype. When all five specimens are included in an analysis, they form a monophyletic clade that supports the monotypy of the genus. Dilophosaurus wetherilli is not recovered as a ceratosaur or coelophysoid, but is instead a non-averostran neotheropod in a grade with other stem-averostrans such as Cryolophosaurus ellioti and Zupaysaurus rougieri. We did not recover a monophyletic ‘Dilophosauridae.’ Instead of being apomorphic for a small clade of early theropods, it is more likely that elaboration of the nasals and lacrimals of stem-averostrans is plesiomorphically present in early ceratosaurs and tetanurans that share those features. Many characters of the axial skeleton of Dilophosaurus wetherilli are derived compared to Late Triassic theropods and may be associated with macropredation and an increase in body size in Theropoda across the Triassic-Jurassic boundary.
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The fossil record of basal paravians in Gondwana is still poorly known, being limited to the Cretaceous unenlagiids from South America and the problematic Rahonavis from Madagascar. Here we report on a new paravian from the Cenomanian-Turonian (Late Cretaceous) of Río Negro province, NW Patagonia, Argentina. The new taxon exhibits a derived bird-like morphology of the forelimbs (e.g., robust ulna with prominent, anteriorly oriented, and proximally saddle-shaped radial cotyle and wide medial flange on metacarpal I) and a plesiomorphic foot with a raptorial pedal digit II. Phylogenetic analysis recovers the new taxon in a monophyletic clade with Rahonavis, being the sister group of the remaining Avialae and more derived than other non-avian dinosaurs. Both exhibit derived forelimb traits in opposition with their plesiomorphic hind limbs. The position of the new taxon and Rahonavis as stem avialans indicates that Gondwanan basal paravians are represented by two different clades, at least. The new taxon probably constitutes a previously unknown grade in the avian-line theropods in which some flight-related adaptations of the forelimbs are present in cursorial taxa. The present discovery sheds light on the acquisition of flight-related traits in non-avian dinosaurs and on the still poorly known paravian radiation in Gondwana.
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Tetanurae, the most successful clade of theropod dinosaurs, including modern birds, split into three major clades early in their evolutionary history: Megalosauroidea, Coelurosauria, and Allosauroidea. The oldest tetanurans occur in the earliest Middle Jurassic, but the early fossil record of the clade is still poor. Here we report one of the oldest known and most complete pre-Late Jurassic tetanuran, the probable allosauroid Asfaltovenator vialidadi gen. et sp. nov., which has an unusual character combination, uniting features currently considered to be apomorphic of different tetanuran lineages. A phylogenetic analysis resulted in a monophyletic Carnosauria (Allosauroidea + Megalosauroidea), and the inclusion of the new taxon significantly changes topology within carnosaurs. The analysis shows concentrated homoplasy in proximal nodes at the base of Tetanurae, and a temporal peak at the Pliensbachian-Toarcian extinction event, recently identified as a potential driver of tetanuran radiation. These results highlight the complex morphological evolution in the early radiation of tetanuran theropods, in which convergences and parallelisms were extremely common. This pattern seems to be a common feature in rapid radiation events of major clades of vertebrates and might explain the common difficulties to unravel phylogenetic relationships of important lineages at the base of major clades.
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The first fossil remains of vertebrates, invertebrates, plants and palynomorphs of the Chorrillo Formation (Austral Basin), about 30km to the SW of the town of El Calafate (Province of Santa Cruz), are described. Fossils include the elasmarian (basal Iguanodontia) Isasicursor santacrucensis gen. et sp. nov., the large titanosaur Nullotitan glaciaris gen. et sp. nov., both large and small Megaraptoridae indet., and fragments of sauropod and theropod eggshells. The list of vertebrates is also composed by the Neognathae Kookne yeutensis gen. et sp. nov., two isolated caudal vertebrae of Mammalia indet., and isolated teeth of a large mosasaur. Remains of fishes, anurans, turtles, and snakes are represented by fragmentary material of low taxonomical value, with the exception of remains belonging to Calyptocephalellidae. On the other hand, a remarkable diversity of terrestrial and freshwater gastropods has been documented, as well as fossil woods and palinological assemblages. The Chorrillo Formation continues south, in the Las Chinas River valley, southern Chile, where it is called Dorotea Formation. Both units share in their lower two thirds abundant materials of titanosaurs, whose remains cease to appear in the upper third, registering only elasmarians (Chorrillo Formation) and hadrosaurs (Dorotea Formation). Above both units there are levels with remains of invertebrates and marine reptiles. It is striking that the dinosaurs of the lower two thirds of the Chorrillo and Dorotea formations are represented by large basal titanosaurs and Megaraptoridae coelurosaurs, being the Saltasaurinae and Aeolosaurinae sauropods and Abelisauridae theropods totally absent. In contrast, these taxa are dominant components in sedimentary units of central and northern Patagonia (e.g., Allen, Los Alamitos, La Colonia formations). Such differences could reflect, in part, a greater antiquity (i.e., late Campanian-early Maastrichtian) for the Chorrillo fossils, or, more probably, different environmental conditions. Thus, knowledge of the biota of the southern tip of Patagonia is expanded, particularly those temporarily close to the K-Pg boundary.
Aerosteon riocoloradensis represents one of the most complete megaraptorans yet discovered. This theropod comes from Anacleto Formation (Campanian) of Mendoza Province, Argentina. The aims of this contribution are: to present a detailed, bone by bone description of this specimen with figures of each bone; provide comparisons to other closely related theropods; revise the original assignation and diagnosis of such taxa. Three bones were re-assigned and almost all the autapomorphies of Aerosteon were modified. Features in the vertebral columns, which are shared with other megaraptorans, show that these theropods shared features with basal coelurosaurs. Anatomical Abbreviations ACDL: Anterior centrodiapophyseal lamina; CDF: Centrodiapophyseal fossa; CPAL: Centroparapophyseal lamina; CPRL: Centroprezygapophyseal lamina; CPRF: Centroprezygapophyseal fossa; CPR-CDF: Centroprezygapophyseal-centrodiapophyseal fossa; Hye: Hyposphene; Hym: Hypantrum; ILT: Intervertebral ligament tuberosity; IPOL: Infrapostzygapophysela lamina; IZL: Intrazygapophyseal lamina; PADL: Paradiapophyseal lamina; PAD-CDF: Paradiapophyseal-centrodiapophsyeal fossa; PCDL: Posterior centrodiapophyseal lamina; POEL: Postzygaepipophysela lamina; PODL: Postzygadiapophyseal lamina; POSF: Postspinal fossa; POCDF: Postzygapophsyeal-centrodiapophyseal fossa; Poz: Postzygapophysis; PRDL: Prezygadiapophyseal lamina; PRPAF: Prezygaparapophyseal fossa; PRPAL: Prezygaparapophyseal lamina; PRSF: Prespinal fossa; PRSL: Prespinal lamina; PRD-CDF: Prezygadiapophyseal-centrodiapophyseal fossa; PRD-PADF: Prezygadiapophyseal-paradiapophyseal fossa; PRD-PODF: Prezygadiapophyseal-postzygadiapophyseal fossa; PRCDF: Prezygapophyseal-centrodiapophyseal fossa; Prz: Prezygapophyses; SDF: Supradiapophsyeal fossa; SDL: Supradiapophyseal lamina; SPOF: Spinopostzygapophyseal fossa; SPOL: Spinopostzygapophyseal lamina; SPRF: Spinoprezygapophyseal fossa; SPRL: Spinoprezygapophyseal lamina; SR(number): Sacral rib; STP(number): Sacral transverse process
Xenotarsosaurus bonapartei was the third abelisaurid theropod dinosaur to be named from Argentina. The holotype comprises two partial anterior dorsal vertebrae and a complete right hind limb from the Upper Cretaceous (lower Cenomanian–upper Turonian) Bajo Barreal Formation, central Patagonia, Argentina. The materials display morphological features that undoubtedly position Xenotarsosaurus within Abelisauroidea. Moreover, detailed comparisons with members of that theropod group confirm the close relationship of this taxon to abelisaurids. Here we provide an emended diagnosis of Xenotarsosaurus bonapartei that includes five newly recognized autapomorphies: (1) anterior dorsal vertebrae with large, strongly dorsoventrally developed parapophyses; (2) anterior dorsal vertebrae with well-developed centroprezygapophyseal fossae that are taller dorsoventrally than wide mediolaterally; (3) fibular condyle of femur triangular in shape and projecting posteriorly; (4) well-marked groove on the anterolateral corner of the proximal fibula; and (5) iliofibularis tubercle of fibula distally interrupted by a hook-like shaped concavity. To determine its systematic position within Abelisauroidea, we incorporated Xenotarsosaurus into a phylogenetic analysis, recovering this theropod as a non-carnotaurine abelisaurid more derived than Eoabelisaurus mefi. Xenotarsosaurus displays several plesiomorphic traits when compared with penecontemporaneous abelisaurids from the Neuquén Group. Similarly, other non-avian dinosaur taxa from the Bajo Barreal Formation are frequently postulated as more phylogenetically basal than coeval forms from northern Patagonia. This scenario suggests the potential existence of provincialism in early Late Cretaceous continental vertebrate faunas of southern South America. The present study increases knowledge of abelisaurid systematics, evolution, and paleobiogeography and augments our understanding of the Late Cretaceous dinosaur assemblage of central Patagonia.
In this paper, we present an updated revision of fossil vertebrates from the Chubut Group, Golfo San Jorge Basin, while also describing some new remains. Extensive exposures of both Lower and Upper Cretaceous sedimentary sequences are present in central Patagonia. These outcrops have, over the past several decades, yielded a varied vertebrate fauna, including fishes, turtles, crocodyliforms, pterosaurs, and dinosaurs, currently herein characterized and described. Although vertebrate diversity in the Chubut Group in central Patagonia is remarkable, the most abundant vertebrates recovered are dinosaurs. The Matasiete Formation (Hauterivian?–Albian) is markedly less prolific in terms of fossils discoveries than either the Bajo Barreal Formation (Cenomanian–early Turonian) or the recently recognized Lago Colhué Huapi Formation (Coniacian–Maastrichtian). The Bajo Barreal fauna is, at a high level, typical of coeval Gondwanan faunas. However, interestingly, several taxa occupy a basal position within their respective groups. The Lago Colhué Huapi Formation has produced a more derived vertebrate fauna, again similar to those from other Gondwanan regions. Finally, in a broad context, the new materials described augment our understanding of Cretaceous terrestrial vertebrate assemblage of central Patagonia and add to the generally meager record of vertebrate in the Cretaceous of the Southern Hemisphere.
A new medium-sized theropod dinosaur from the Arcillas de Morella Formation (upper Barremian) in Vallibona (Castellón, Spain) is described based on a partial skeleton. Vallibonavenatrix cani, gen. et sp. nov., is diagnosed by five autapomorphies: moderately high dorsal neural spines relative to the centrum height, the presence of deep pleurocoelous fossae and pneumatic foramina in the sacral vertebrae, a strongly pneumatic ilium with large internal cameras, the presence of a broad and flat platform on the ventromedial surface of the postacetabular blade of the ilium, and the strong ventral torsion of the ischium diaphysis. Phylogenetic analysis recovered Vallibonavenatrix cani as a spinosaurid megalosauroid and revealed that the new Iberian form is more closely related to Gondwanan spinosaurines, such as Spinosaurus, Irritator or Angaturama and the Asian taxon Ichthyovenator than it is to its synchronic contemporary European taxon Baryonyx walkeri. The Gondwanan or Asian affinities of Vallibonavenatrix indicate a complex palaeobiogeographic pattern and may be interpreted simultaneously as evidence for contact between Europe and North Africa and between Europe and Asia before the Aptian. This specimen is currently the most complete evidence of a spinosaurid theropod known in the fossil record of the Iberian Peninsula.