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Journal of Vertebrate Paleontology
ISSN: 0272-4634 (Print) 1937-2809 (Online) Journal homepage: http://www.tandfonline.com/loi/ujvp20
New rebbachisaurid cranial remains (Sauropoda,
Diplodocoidea) from the Cretaceous of Patagonia,
Argentina, and the first endocranial description for
a South American representative of the clade
Ariana Paulina Carabajal, Juan I. Canale & Alejandro Haluza
To cite this article: Ariana Paulina Carabajal, Juan I. Canale & Alejandro Haluza (2016): New
rebbachisaurid cranial remains (Sauropoda, Diplodocoidea) from the Cretaceous of Patagonia,
Argentina, and the first endocranial description for a South American representative of the
clade, Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2016.1167067
To link to this article: http://dx.doi.org/10.1080/02724634.2016.1167067
Published online: 04 May 2016.
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ARTICLE
NEW REBBACHISAURID (SAUROPODA, DIPLODOCOIDEA) CRANIAL REMAINS FROM THE
CRETACEOUS OF PATAGONIA, ARGENTINA, AND THE FIRST ENDOCRANIAL
DESCRIPTION FOR A SOUTH AMERICAN REPRESENTATIVE OF THE CLADE
ARIANA PAULINA CARABAJAL,
*,1,2
JUAN I. CANALE,
1,3
and ALEJANDRO HALUZA
3
1
CONICET–Consejo Nacional de Investigaciones Cient
ıficas y T
ecnicas, Av. Rivadavia 1917 (C1033AAJ), Buenos Aires, Argentina;
2
INIBIOMA–Instituto de Investigaciones en Biodiversidad y Medioambiente, Quintral 1250 (8400), San Carlos de Bariloche,
R
ıo Negro, Argentina, a.paulinacarabajal@conicet.gov.ar;
3
Museo ‘Ernesto Bachmann’, Dr. Natali S/N (8311) El Choc
on, Neuqu
en, Argentina, juanignaciocanale@hotmail.com;
haluzaalejandro@gmail.com
ABSTRACT—Here we report new rebbachisaurid material (MMCh-PV 71) recovered from the Candeleros Formation
(Cenomanian) of northwest Patagonia, Argentina. The cranial remains consist of a partial braincase and a right quadrate.
Fractures in the braincase exposed the endocranial cavity, allowing the first study of the brain and inner ear morphologies of
a South American rebbachisaurid. The braincase and cranial endocast both exhibit traits similar to those observed in the
Cretaceous rebbachisaurs Nigersaurus from Africa and Limaysaurus from Argentina, although in terms of osteology, the
South American taxa are highly similar. The endocast of MMCh-PV 71 is more similar to that of Nigersaurus than to those of
Diplodocus and Camarasaurus, suggesting some probable rebbachisaurid features such as the noteworthy presence of the
flocculus. The overall morphology of the quadrate shows similarities with Limaysaurus and Nigersaurus. However,
differences such as the broader posterior fossa and the shape and orientation of the head and the pterygoid process indicate
that the new specimen could represent a distinct taxon.
Citation for this article: Paulina Carabajal, A., J. I. Canale, and A. Haluza. 2016. New rebbachisaurid (Sauropoda,
Diplodocoidea) cranial remains from the Cretaceous of Patagonia, Argentina, and the first endocranial description for a
South American representative of the clade. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1167067.
INTRODUCTION
Current knowledge of diplodocoid sauropods in South
America is poor, although it has been improving in recent years
due to new discoveries, particularly in Argentina (e.g., Carbal-
lido et al., 2012; Haluza et al., 2012; Ibiricu et al., 2012, 2013;
Gallina et al., 2014). Within this clade, Rebbachisauridae is the
basal-most group of Diplodocoidea and the sister group of Flag-
ellicaudata (Diplodocidae CDicraeosauridae; Wilson, 2002;
Harris and Dodson, 2004). Their remains, which usually consist
of postcranial elements, are frequently recorded in the lower
Upper Cretaceous units (Cenomanian) of the Neuqu
en and San
Jorge basins in Patagonia (Novas, 2009). In particular, the out-
crops of the Candeleros and Huincul formations (Garrido, 2010)
surrounding the city of Villa El Choc
on and Ezequiel Ramos
Mex
ıa lake (both Neuquen Province localities) have provided
several rebbachisaurid specimens (e.g., Calvo and Salgado, 1995;
Calvo, 1999; Gallina and Apestegu
ıa, 2005; Apestegu
ıa, 2007;
Sim
on and Salgado, 2009; Haluza et al., 2012). These discoveries
have allowed a relatively good understanding of the postcranial
anatomy of this group of basal diplodocoids. However, the cra-
nial morphology is still poorly known because skull remains are
rare and braincases even rarer. As such, the complete braincase
of Limaysaurus tessonei (DRebbachisaurus tessonei; Calvo and
Salgado, 1995) represents the only rebbachisaurid braincase
described besides that of Nigersaurus (Sereno et al., 2007), and
the first described from South America. The braincase morphol-
ogy of the African rebbachisaurid Nigersaurus has been
published as a three-dimensional (3D) model that is available at
Digital Morphology (www.digimorph.org; Sereno et al., 2007).
Its cranial endocast and inner ear were also studied using com-
puted tomography (CT) scans by Sereno et al. (2007:figs. S4–S6)
and are used here for comparisons.
In the present study, a partial braincase and right quadrate
(MMCh-PV 71) are described. They were recovered from the
Candeleros Formation (Cenomanian) at the Barda Atravesada
de Las Campanas locality, 25 km southwest from Villa El
Choc
on, Neuqu
en Province, Argentina (Fig. 1). The specimens
were found in close association with postcranial bones, including
a dorsal vertebra that shows clear rebbachisaurid synapomor-
phies, such as a petal-shaped neural spine and a festooned spino-
diapophyseal lamina (Whitlock, 2011). As mentioned above,
within rebbachisaurids the braincase of the holotype of Limay-
saurus tessonei was only briefly described (Calvo and Salgado,
1995), and its endocranial morphology was preliminarily
reported by Paulina Carabajal and Calvo (2015). The new speci-
men, MMCh-PV 71, was recovered from the same formation as
the holotype of Limaysaurus, but from a different locality.
Although the braincase morphology is notably similar in the two
specimens, the morphologies of the quadrate and some of the
postcranial remains (that are not described here) indicate that
the former could represent a new taxon.
The purpose of this study is to provide a detailed description of
the braincase and quadrate of this new rebbachisaurid, which
includes the first observations on the endocranial anatomy of a
representative of the clade from South America. The dinosaur
braincase is a rich source of phylogenetically informative data
(e.g., Rauhut, 2007; Paulina Carabajal, 2009; Balanoff et al., 2010).
*Corresponding author.
Journal of Vertebrate Paleontology e1167067 (9 pages)
Óby the Society of Vertebrate Paleontology
DOI: 10.1080/02724634.2016.1167067
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Because the discovery and description of braincase remains are
scarce across Sauropoda, new information—particularly for poorly
sampled groups such as Rebbachisauridae—will help to increase
our understanding about their anatomy and morphological varia-
tion between species.
MATERIALS AND METHODS
The braincase of MMCh-PV 71 is preserved in two halves, as
left and right lateral walls, attached to fragmentary pieces of
skull roof and basicranium (Fig. 2). There is no preserved
median connection between the left and right sides, although the
midline is recognizable at the interfrontal region and in the floor
of the endocranial cavity. A latex cranial endocast and an inner
ear cast were made by one of the authors (A.P.C.) based on the
right lateral wall of the braincase, which preserves part of the
basicranium. A complete dorsal view of the brain was recon-
structed using a specular image of the right side, as shown in Fig-
ures 3 and 4. A partial latex cast of the labyrinth of the inner ear
is shown in Figure 5. The right quadrate (Fig. 6) was found iso-
lated, 1 m distant from the braincase remains. All the cranial
remains were found in close association with part of the postcra-
nium that includes a dorsal vertebra, a partial ilium, and an
ungual phalanx, all of which were recovered in an area of no
more than 4 m
2
.
The specimen MMCh-PV 71 was compared with the holotype
of Limaysaurus, from the same stratigraphic age and formation,
and with Nigersaurus, from the Early Cretaceous (Barremian–
Albian) and thus slightly older stratigraphically than the Patago-
nian forms (Fig. 7). All three specimens represent adult individu-
als based on relative size and the lack of sutures (personal
observation of MMCh-PV 71 and MUCPv 205; Sereno et al.,
2007).
Digitally rendered 3D models of the braincase and quadrate of
Nigersaurus are available at Digital Morphology (http://digi
morph.org/specimens/Nigersaurus_taqueti).
Institutional Abbreviations—MMCh-PV, Museo ‘Ernesto
Bachmann,’ Villa El Choc
on, Argentina; MUCPv, Museo de la
Universidad Nacional del Comahue, Neuqu
en, Argentina.
SYSTEMATIC PALEONTOLOGY
SAURISCHIA Seeley, 1887
SAUROPODA Marsh, 1878
DIPLODOCOIDEA Marsh, 1884
REBBACHISAURIDAE Bonaparte, 1997
REBBACHISAURIDAE INDET.
(Figs. 2–7)
DESCRIPTION
Braincase
The braincase of the rebbachisaurid MMCh-PV 71 is pre-
served in two lateral halves (Fig. 2). Most of the basicranium
(including structures such as the occipital condyle and basiptery-
goid processes) and the median portion of the skull roof are
missing. Structures such as the nuchal crest and the paroccipital
processes are incomplete, and the margins of the foramen mag-
num are not preserved. The lateral walls of the braincase include
a partially preserved exoccipital-opisthotic complex, the prootic,
laterosphenoid, orbitosphenoid, and a dorsal fragment of the
basisphenoid.
Skull Roof—The skull roof is formed by the thick and robust
parietal and frontals (Fig. 2B, D). The parietal is fragmentary,
and its complete morphology remains unknown. The posterolat-
eral projection of the parietal is firmly fused to the frontal anteri-
orly and to the dorsal section of the paroccipital process
posteriorly. A foramen for the caudal middle cerebral vein,
enclosed at least externally by the parietal, is observed on the
right side (Fig. 2D). The passage of this vein has a relatively
large diameter (3.5 mm) and runs from the posterior section of
the dural expansion area of the endocranial cavity (Fig. 2C, F).
It is worth noting that this foramen is not observed in Limaysau-
rus (MUCPv 205; Paulina Carabajal and Calvo, 2015), but its
passage is reconstructed in the cranial endocast of Nigersaurus
(Sereno et al., 2007:fig. S4A; Fig. 4).
The frontal forms a more-or-less curved and smooth orbital
margin (Fig. 2B), while anteriorly, the nasal process is robust
and thick. Endocranially, the cerebral hemisphere is well marked
on the ventral aspect of the frontal, although the olfactory bulb
does not leave clear impressions (Fig. 2C).
Exoccipital-Opisthotic Complex—Most of the paroccipital pro-
cesses are missing. The preserved proximal sections indicate that the
paroccipital processes were low and posterolaterally projected
(Fig. 2B, D). Fractures on both sides of the braincase exposed cavi-
ties within the paroccipital processes, suggesting some degree of
pneumaticity for the structure, which is usually massive in sauropods
(pers. observ., A.P.C.). Although this condition could be the result
of erosion, the paired nature of the cavities within the paroccipital
processes of MMCh-PV 71 indicate a lower density of the spongy
bone compared with other sauropods.
There is a single foramen for cranial nerve (CN) XII preserved
on the right exoccipital (Fig. 2D). A single foramen is also
observed in Limaysaurus (Calvo and Salgado, 1995), whereas
there are two foramina in Nigersaurus (Sereno et al., 2007). On
the lateral side of the braincase, there are no visible sutures
between the opisthotic and the prootic. The metotic foramen (for
CNs IX–XI) is enclosed by the opisthotic posteriorly and the
prootic anteriorly, and is large and oval, as in most sauropods.
The crest that anteriorly bounds the metotic foramen (crista inter-
fenestralis) is developed as a low ridge, poorly expanded postero-
laterally, differing from the laminar condition observed in
Limaysaurus (MUCPv 205) and Nigersaurus (Knoll, pers. comm.,
2015). In Limaysaurus, the crest that bounds the metotic foramen
posteriorly (crista tuberalis) is well expanded and clearly sepa-
rates CN XII posteriorly from the metotic foramen anteriorly
(Fig. 2A). The fenestra ovalis is not observed in the lateral view
of MMCh-PV 71, because it faces posteriorly and is located within
a recess together with the metotic foramen, as in Limaysaurus.
Although the margins of the crista prootica are poorly preserved,
it seems that the foramen for CN VII opens on the anterior side
and not posterior to the ridge as in Limaysaurus, where CN VII,
CN XII, and the metotic foramen are clearly visible in posterior
view of the braincase (Calvo and Salgado, 1995:fig. 5).
Prootic—The prootic is firmly fused to the opisthotic posteriorly
and the laterosphenoid anteriorly, whereas the suture with the parie-
tal is obscured by fractures. The prootic forms at least the posterior
FIGURE 1. Location map for rebbachisaurid specimen MMCh-PV 71.
Paulina Carabajal et al.—New rebbachisaurid from Patagonia (e1167067-2)
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FIGURE 2. Braincase of rebbachisaurid specimen MMCh-PV 71 in A, right lateral view; B, left lateral view; C, right medial view, and D, posterior
view. E, detail of floor of the endocranial cavity; F, detail of right vestibular eminence (not to scale). Abbreviations:c.an, crista antotica; cap, capi-
tate process; cer.i, cerebral hemisphere impression; cmcv, caudal middle cerebral vein; c.pr, crista prootica; c.tb, crista tuberalis; dhv, dorsal head
vein; ds, dorsum sellae; endo.f, floor of endocranial cavity; f, frontal; fl.r, floccular recess; fm, foramen magnum (preserved margin); gr, groove; inf,
infundibulum; lab, labyrinth of inner ear; met, metotic foramen; or, orbital rim; p, parietal; pit.f, pituitary fossa; pop, paroccipital process; sut, suture;
vem, vestibular eminence; I–XII, cranial nerves. Scale bars equal 10 mm in A–D.InE, which is an enlarged detail, the scale bar equals 20 mm.
Paulina Carabajal et al.—New rebbachisaurid from Patagonia (e1167067-3)
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margin of the large and oval foramen for CN V, which has a maxi-
mum diameter of 9.7 mm, almost equal to the diameter of the
metotic foramen (10.7 mm). From the posterodorsal and postero-
ventral margins of the foramen for CN V, there are two impressions
left by the maxillary and mandibular branches of the trigeminal
nerve (Fig. 2A). The groove interpreted as the mandibular branch is
posteriorly oriented, whereas the groove interpreted as the maxillary
branch is posteroventrally oriented. In Limaysaurus, the mandibular
and maxillary branches also leave clear impressions, oriented poste-
riorly and ventrally, respectively (MUCPv 205). In Limaysaurus,the
foramen for CN V has a bilobate contour resulting from a ventral
projection of the crista antotica overhanging the dorsal margin of the
foramen, unlike the elliptical outline of the foramen in Nigersaurus
(Knoll, pers. comm.).
Endocranially, a notable feature is the presence of a small and
oval floccular recess on the anterior side of the vestibular emi-
nence (Fig. 2C, F). This structure is also present in Nigersaurus
(Sereno et al., 2007), Giraffatitan (Knoll and Schwarz-Wings,
2009), and Dicraeosaurus (D‘fossa subarcuata’ in Janensch,
1935), although it is absent in most sauropods.
Laterosphenoid—There are no visible sutures between the lat-
erosphenoid and the surrounding bones, except with the frontal
dorsally. The postorbital process of the laterosphenoid
(Dcapitate process) and/or crista antotica is preserved only at its
base, indicating a low and markedly thin, crescentic process
(Fig. 2A). In Limaysaurus, the postorbital process of the lateros-
phenoid is blade-like, anteroposteriorly short, and markedly pro-
jected posteriorly (Calvo and Salgado, 1995).
The laterosphenoid bounds the foramen for CN V anteriorly
and the foramina for CNs III and IV posteriorly. These latter
two cranial nerves probably indicate the laterosphenoid-orbito-
sphenoid contact. Cranial nerve III is large and located within a
shallow recess posterior to CN II and anterior to CN V. The
opening of the foramen for CN III faces posteriorly. The fora-
men for CN IV is small and opens anterodorsally to CN III and
dorsally to CN II (Fig. 2A, C). The shape, size, and disposition
of CN III and CN IV are similar to those observed in Limaysau-
rus, but unlike the condition in Nigersaurus (Sereno et al., 2007:
fig. S4A), where CN III and CN IV share a single exit foramen
(Fig. 4).
Endocranially, the laterosphenoid does not form a marked pil-
lar protruding into the endocranial cavity (Fig. 2C), unlike the
condition observed in titanosaurid sauropods (e.g., Paulina Cara-
bajal, 2012; Knoll et al., 2013, 2015). There are no visible sutures
to indicate if the laterosphenoid forms the dorsal-most section of
the dorsum sellae (Fig. 2E).
Orbitosphenoid—The orbitosphenoid is a relatively large ele-
ment, contacting the laterosphenoid posterodorsally. The suture
with the frontal observed on the right side dorsal to CN II, is proba-
bly the laterosphenoid-frontal suture, although the most anterior sec-
tion may correspond to the orbitosphenoid-frontal contact. The
foramen for CN II is large (7.4 mm), rounded, and separated from its
counterpart by a septum of bone. The foramen indicated in Figure 2
as CN I corresponds to the passage for the olfactory tract, enclosed
by the orbitosphenoid and frontal (Fig. 2A).
The orbitocerebral fenestra present in Nigersaurus dorsal to
CN II (Sereno et al., 2007:fig. S4A) is absent in MMCh-PV 71
and Limaysaurus (Figs. 2A, 4A). This might suggest that the two
Argentinean taxa form a natural grouping relative to Nigersau-
rus (Knoll, pers. comm).
Basisphenoid—Only the anterodorsal section of the basisphe-
noid is preserved on the right side of the floor of the endocranial
cavity (Fig. 2C, E). The dorsum sellae is a thin wall that is ante-
rodorsally projected, formed by the basisphenoid and probably
by median projections of the laterosphenoids. The foramen for
CN VI is small in diameter (1.7 mm), as is usual in sauropods
(Knoll et al., 2006), and located far behind the top of the dorsum
sellae (Fig. 2E). The passage of CN VI is short and runs laterally
to the pituitary fossa to exit through a small foramen located
ventral to CN V (Fig. 2A). This condition resembles that
observed in Limaysaurus (MUCPv 205) and titanosaur sauro-
pods and is different from that observed in Flagellicaudata,
where CN VI usually penetrates the pituitary fossa (e.g., Paulina
Carabajal, 2012:table 1, and references therein).
Endocranially, the preserved walls of the infundibulum indi-
cate an oval shape for this opening when complete, with the
main axis mediolaterally oriented. The internal foramen for CN
III is level with the infundibulum (Fig. 2C). The right lateral wall
of the pituitary fossa is preserved (Fig. 2E), indicating that it was
large and strongly posteroventrally oriented (Fig. 3A, C).
Cranial Endocast
The complete right side of the endocranial cavity was cast
(Fig. 3A, B), and the left side of the complete brain was recon-
structed using a specular image (Fig. 3D). The cranial endocast
is subhorizontal, with laterally expanded cerebral hemispheres,
and the pituitary is markedly enlarged and posteroventrally ori-
ented (Fig. 4C). The specimen MMCh-PV 71 shares with Niger-
saurus the general shape of the cranial endocast, particularly in
dorsal view (Fig. 4B, C). By contrast, in lateral view (Fig. 4A),
the dorsal expansion—which was occupied by the dorsal venous
longitudinal sinus (Witmer et al., 2008)—is more anteriorly
developed than in Nigersaurus (Sereno et al., 2007).
Forebrain—In MMCh-PV 71, the olfactory bulbs did not leave
a well-defined impression on the ventral surface of the frontal
and therefore they are not clearly visible in the endocast
(Fig. 3D). The olfactory tracts are clearly discernible from the
olfactory bulbs, with both structures at least as long as the cere-
bral hemispheres (Fig. 3D). This condition is the same in Niger-
saurus, which has relatively small dural sinuses over the
cerebrum (Sereno et al., 2007:fig. 1F), unlike the almost nonexis-
tent olfactory tract observed in titanosaurs (e.g., Paulina Caraba-
jal, 2012). The olfactory tract and bulbs of MMCh-PV 71 are
slightly ventrally projected, as in Nigersaurus, rather than antero-
dorsally projecting as in Diplodocus and Camarasaurus (Sereno
et al., 2007:fig. 1G).
The maximum width of the endocast is at the level of the cere-
bral hemispheres, and is approximately 46 mm (Fig. 3D). The
cerebral hemispheres are rounded and laterally expanded,
although the fissura inter-hemispherica is obscured by the devel-
opment of the dorsal longitudinal sinus and the dura, as in most
sauropsids. In Nigersaurus (Sereno et al., 2007) and MMCh-PV
71, the dural sinus is small, allowing the view of the anterior end
of the brain, including the olfactory tract, cerebrum, and cerebel-
lar region. In most non-titanosaurians, such as Apatosaurus (Bal-
anoff et al., 2010), Brachiosaurus (Janensch, 1935; Knoll and
Schwarz-Wings, 2009), Spinophorosaurus (Knoll et al., 2012),
and dicraeosaurids (Janensch, 1935; Knoll et al., 2014; Paulina
Carabajal et al., 2014a), and the cast of these structures obscures
the dorsal surface of the forebrain.
The pituitary is a long structure, strongly projected postero-
ventrally from the ventral aspect of the cranial endocast
(Fig. 3A, C). The distal end of the pituitary is missing, including
the entrances for the internal carotid arteries. Part of the canal
of the internal carotid artery is observed in the left side of the
basicranium, indicating that the external foramen for this blood
vessel was located ventral to the metotic foramen, similar to the
condition in Limaysaurus (Paulina Carabajal and Calvo, 2015).
Midbrain—The root of CN II is subcircular in cross-section,
short, and laterally projected. It is located anterodorsal to the
base of the infundibulum (Fig. 3A, C). The two CN II openings
are relatively more separated from each other than in Nigersau-
rus, in which they seem to be confluent on the midline and origi-
nating from the base of the infundibulum (Sereno et al., 2007:
fig. S4C). Cranial nerve III is located posteroventrally relative to
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CN II and is confluent with the posterior aspect of the infundibu-
lar stalk. The small passage anterodorsal to CN II belongs to a
separate CN IV, as in Limaysaurus, but unlike Nigersaurus
where both nerves leave the endocranial cavity through a single
large foramen (Sereno et al., 2007:fig. S4A).
Hindbrain—The posterior-most dorsal section of the medulla
oblongata is not preserved (Fig. 3A). The dural expansion is a
well-defined but small dorsal protuberance (Fig. 4A, C), slightly
more marked than that in Nigersaurus (Sereno et al., 2007). The
caudal middle cerebral vein is located at the posterior section of
the dural expansion. The passage for this vein is relatively large
in diameter. It is closely related to a transverse lateral sinus that
leaves a half-moon–shaped protuberance on the endocast
(Fig. 3A, C). This transverse sinus has a ventral branch that runs
towards the root of CN V and probably corresponds to the ante-
rior middle cerebral vein that leaves the endocranial cavity
through the trigeminal foramen. In both MMCh-PV 71 and
Nigersaurus (Sereno et al., 2007:fig. S4A), this lateral sinus is
well marked.
The floccular process of the cerebellum is located dorsal to CN
V and ventral to the caudal middle cerebral vein (Fig. 3A, C), as
in Nigersaurus (Fig. 4C). The presence of a developed flocculus
that leaves an impression on the anterior wall of the vestibular
eminence (floccular recess) is uncommon in sauropods, having
been identified in only a few taxa such as the dicraeosaurid
Dicraeosaurus (Janensch, 1935:pl. XIII, 7) and the titanosauri-
form Giraffatitan (“Brachiosaurus” in Janensch, 1935:pl. XIII,
1a; Knoll and Schwarz-Wings, 2009).
The root of CN V is large and oval in cross-section (Fig. 3A,
C). It is positioned level with CN II and CN III. As in other sau-
ropods, the passage for this nerve is short and laterally projected.
The passage of CN VI has a small diameter (3 mm), and its
root is located posteroventral to CN V, on the ventral side of
the hindbrain (Fig. 3A, C). The passage for this nerve runs
anteroventrally through the basisphenoid lateral to the pituitary
fossa and exits the braincase through a small foramen on the
basisphenoid (Fig. 2A), as in Limaysaurus (Paulina Carabajal
and Calvo, 2015) and Nigersaurus (Sereno et al., 2007:fig. S4B).
This condition is also present in titanosaurs, although in most
Flagellicaudata (derived diplodocoids) CN VI penetrates the
pituitary fossa (e.g., Paulina Carabajal, 2012:table 1, and refer-
ences therein).
The root of CN VII is just posterior to the root of CN V, and
both are connected to the transverse venous sinus (Fig. 3A, C).
The passage for CN VII has a small diameter (4 mm), and
although not reconstructed in the endocast, it is possible to fol-
low it through the prootic (Fig. 2A), as in Limaysaurus (Calvo
and Salgado, 1995). Cranial nerve VIII is not preserved on the
endocast of MMCh-PV 71.
The cast of the metotic passage (for the branches of CNs IX–
XI) is large in diameter (13 mm high and 7 mm wide) and oval
(Fig. 3C). It is slightly posteroventrally oriented. At the base of
the metotic passage, a smaller passage connects anteriorly with
the vestibulum of the inner ear, corresponding to the fenestra
pseudorotunda (Fig. 3C), as observed in Nigersaurus (Sereno
et al., 2007:fig. S5A).
There is single root for all the branches of CN XII in the endo-
cast, and a single foramen is observed in the braincase (Figs. 2D,
3C). The same condition is observed in Limaysaurus (Calvo and
Salgado, 1995), but there are two roots for this nerve in Nigersau-
rus (Sereno et al., 2007).
Inner Ear—A partial endocast of the left inner ear was
obtained, including the lagena, the lateral semicircular canal,
and partial anterior and posterior semicircular canals (Fig. 5).
The inner ear is 35 mm long and approximately 27 mm wide (at
the level of the anterior and posterior ampullae). Although the
posterior semicircular canal is missing, the angle formed between
it and the anterior semicircular canal is approximately equal to
or less than 90in dorsal view (Fig. 5C). In turn, the lateral semi-
circular canal is oriented upwards, forming an angle with the
anterior semicircular canal that is strongly acute (Fig. 5A). This
disposition of the lateral semicircular canal is also present in
Nigersaurus (Sereno et al., 2007:fig. S5A). In MMCh-PV 71, the
anterior semicircular canal is subtriangular in shape and has a
diameter (of the canal) of approximately 3.4 mm. The lateral
semicircular canal is oval in shape and has a diameter of 3.0 mm
(Fig. 5). The fenestra ovalis is partially preserved and indicates
the limit between the lagena and the vestibulum (Fig. 5). The
FIGURE 3. Latex cranial endocast of rebbachisaurid specimen MMCh-
PV 71 in A, right lateral view and B, dorsal view. Line drawings of recon-
structed cranial endocast in C, lateral view and D, dorsal view. Abbrevia-
tions:cer, cerebral hemisphere; cmcv, caudal middle cerebral vein; de,
dorsal expansion; floc, flocculus; fpr, fenestra pseudorotunda; ie, inner
ear; met, metotic passage (for CNs IX–XI); ob, olfactory bulb; ot, olfac-
tory tract; pit, pituitary; I–XII, cranial nerves. Scale bar equals 10 mm.
Paulina Carabajal et al.—New rebbachisaurid from Patagonia (e1167067-5)
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lagena is simple and conical, and, as in Nigersaurus (Sereno
et al., 2007:fig. S5A), is notably short.
The morphology of the inner ear of MMCh-PV 71 strongly
resembles that of Nigersaurus, except for the more triangular
shape of the anterior semicircular canal. In Nigersaurus, the
inner ear morphology supports the hypothesis that the skull was
held inclined downward in life.
Quadrate
The right quadrate is almost complete. It lacks the head and
the dorsal third of the posterior fossa (Fig. 6). The quadrate shaft
is relatively robust above the articular region and up to the
beginning of the lateral expansion of the quadrate fossa. Dorsal
to this point, the shaft is reduced to thin plates of bone, including
the pterygoid wing anteriorly, the inner wall of the quadrate
fossa laterally, and a small ventral portion of the posterior pro-
jection. In MMCh-PV 71, the quadrate fossa is deep as in other
rebbachisaurids, Giraffatitan, Brachiosaurus, and Camarasaurus
(Tschopp et al., 2015). In macronarians such as Camarasaurus,
Brachiosaurus, and non-rebbachisaurid diplodocoids such as
Diplodocus and Apatosaurus, the quadrate fossa is mediolater-
ally slender (Janensch, 1935; Berman and McIntosh, 1978; Mad-
sen et al., 1995). The specimen MMCh-PV 71 has a broad lateral
expansion of the quadrate fossa, which is approximately 30%
larger than in Limaysaurus (Fig. 7) and Nigersaurus (Sereno
et al., 2007), although in all three rebbachisaurid specimens this
expansion is relatively larger than in other sauropods. This con-
dition may constitute a synapomorphy of rebbachisaurids.
Ventrally, the lateral surface of the quadrate exhibits a shallow
sulcus for the quadratojugal. This scar continues dorsally over the
oblique ventrolateral margin of the posterior fossa of the quad-
rate. Over the dorsal end of this sulcus and covering the lateral
margin of the quadrate, a rugose surface is present that is here
interpreted as the articular area for the squamosal. In lateral
view, the pterygoid process is moderately anteriorly projected
and has a rounded outline, whereas in Limaysaurus this process is
subtriangular in shape and more anteriorly projected (Fig. 7). A
small dorsoventrally oriented pterygoid scar is located on the
anteromedial margin of the shaft, ventral to the beginning of the
pterygoid process and in the same position as, but smaller than,
that of Rapetosaurus (Curry Rogers and Forster, 2004).
The articular surface of the quadrate is crescent-shaped in ven-
tral view (Fig. 6E), another synapomorphic trait of Rebbachi-
sauridae (Whitlock, 2011; Tschopp et al., 2015). The quadrate
condyle is subdivided by an anteroposterior sulcus, with a medial
hemicondyle at least two times mediolaterally larger than the
FIGURE 4. Brain and inner ear of rebbachisaurid specimen MMCh-PV 71 in A, right lateral view and B, dorsal view. Brain and inner ear of
Nigersaurus in C, right lateral view and D, dorsal view (after Sereno et al., 2007). Abbreviations:cer, cerebral hemisphere; cmcv, caudal middle cere-
bral vein; de, dorsal expansion; floc, flocculus; ie, inner ear; met, metotic passage for CNs IX–XI; ob, olfactory bulb; ocf, orbitocerebral fenestra; pit,
pituitary; I–XII, cranial nerves. Not to scale.
FIGURE 5. Partial left inner ear latex endocast of rebbachisaurid speci-
men MMCh-PV 71. A, lateral view; B, anterior view; C, dorsal view.
Abbreviations:asc, anterior semicircular canal; lag, lagena; lsc, lateral
semicircular canal; psc, posterior semicircular canal. Scale bar equals
10 mm.
Paulina Carabajal et al.—New rebbachisaurid from Patagonia (e1167067-6)
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lateral one. In Limaysaurus (MUCPv 205), the condyle is subdi-
vided but the hemicondyles are subequal in size. A different con-
dition is seen in some macronarians such as Nemegtosaurus,
where the articular condyle is undivided (Wilson, 2005).
DISCUSSION
Specimen MMCh-PV 71 consists of cranial (present study) and
postcranial (currently under analysis) remains that show clear
rebbachisaurid features. These include the large lateral expansion
of the quadrate fossa and a crescent-shaped articular condyle of
the quadrate in ventral view, characters shared with Limaysaurus
and Nigersaurus (Calvo and Salgado, 1995; Sereno et al., 2007).
The lateral expansion of the quadrate in MMCh-PV 71, however,
is 30% larger than in Limaysaurus (Calvo and Salgado, 1995) and
Nigersaurus (Sereno et al., 2007), likely representing an autapo-
morphy of MMCh-PV 71 together with the unequally subdivided
articular condyle (see Table 1). The braincase has several non-
titanosaurian characters such as a markedly curved orbit vault
and a short and laminar crista antotica. Endocranially, there is no
pillar of the laterosphenoid, but there is a floccular recess, a well-
developed transverse sinus and caudal middle cerebral vein, and a
poorly developed dorsal expansion; all these characters shared
with Limaysaurus and Nigersaurus (Sereno et al., 2007). Finally,
rebbachisaurid characters present in the postcranial elements of
MMCh-PV 71 are the ‘petal-shaped’ neural spine and a
‘festooned’ spinodiapophyseal lamina (Calvo and Salgado, 1995;
Wilson, 2002; Whitlock, 2011; Tschopp et al., 2015).
The external braincase morphology of MMCh-PV 71 is very
similar to that of Limaysaurus (MUCPv 205), showing the same
general distribution of cranial and vascular foramina, including
the well-marked grooves formed by the maxillary and mandibular
branches of the trigeminal nerve, and separate foramina for CNs
III and IV (Fig. 2A). Also, CN VI does not penetrate the pituitary
fossa, which is an uncommon trait within non-titanosaurid sauro-
pods, suggesting that it is a derived trait of Rebbachisauridae
(together with the strongly laterally expanded posterior fossa of
the quadrate). The differences with Nigersaurus are that the Afri-
can taxon possesses an orbitocerebral fenestra that is absent in
the Patagonian rebbachisaurids, and that CNs III and IV share a
single exit foramen (Fig. 4A, C). However, minimal differences
are observed between Limaysaurus and MMCh-PV 71, including
a less expanded crista prootica in the latter specimen (whereas in
Limaysaurus the crista prootica is large and the foramen for CN
VII opens on the posterior side of the crest).
Within rebbachisaurids, only the endocranial morphology of
Nigersaurus has been studied in detail, whereas a preliminary
study has been recently made on the holotype of Limaysaurus
using CT scans (Paulina Carabajal and Calvo, 2015). So far, it
has not been possible to identify a floccular process on the CT
scan of Limaysaurus, although its presence in MMCh-PV 71 and
Nigersaurus suggests that it may be characteristic of rebbachi-
saurids. Development of this cerebellar structure to such an
extent that it leaves an impression on the endocranial cavity
(floccular recess) is uncommon in sauropods—as discussed
above, it has been identified also in Giraffatitan (Janensch, 1935;
Knoll and Schwarz-Wings, 2009) and Dicraeosaurus (Janensch,
1935). Within ornithischians, the flocculus has been identified in
even fewer taxa, including some ankylosaurids (Miyashita et al.,
2011; Paulina Carabajal et al., 2014c) and Stegosaurus (Galton,
FIGURE 7. Comparison of quadrate morphology of the South
American rebbachisaurids. MMCh-PV 71 in A, lateral view and B, poste-
rior view. Limaysaurus (MUCPv 205) in C, lateral view and D, posterior
view. Not to scale.
FIGURE 6. Right quadrate of rebbachisaurid specimen MMCh-PV 71. A, anterior view; B, lateral view; C, posterior view; D, anterior view; E, distal
view. Abbreviations:ac, articular condyle; ptp, pterygoid process; pt.s, pterygoid scar; qf, quadrate fossa; qj.as, articular surface for quadratojugal; sq.
as, articular surface for squamosal. Scale bar equals 10 cm.
Paulina Carabajal et al.—New rebbachisaurid from Patagonia (e1167067-7)
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2001). However, the paleobiological implications of the develop-
ment of the flocculus in quadrupedal dinosaurs or in other non-
archosaurian reptiles remain unknown (e.g., Paulina Carabajal
et al., 2014b; von Baczko et al., 2015).
Taxonomic Implications—The holotype of Limaysaurus tesso-
nei and the specimen MMCh-PV 71 were both collected from
outcrops of the Candeleros Formation, approximately 3 km
apart. Comparisons of the neuroanatomy are restricted to the
external aspect because the endocranial cavity remains unpre-
pared and filled with sediment in Limaysaurus, and has been
only preliminarily studied using CT scans (Paulina Carabajal and
Calvo, 2015). The quadrate of MMCh-PV 71 shows strong differ-
ences with Limaysaurus, including the more expanded lateral
edge of the quadrate fossa, and the more rounded outline and
anteroposteriorly shorter pterygoid process (Figs. 6, 7). As men-
tioned, the braincase shows few differences. Taking into account
the fact that the postcranium of MMCh-PV 71 (including a dor-
sal vertebra still under analysis) also shows strong differences
with Limaysaurus, we assume that these differences do not cor-
respond to ontogeny or sexual dimorphism, and therefore the
new specimen could represent a new taxon. However, further
phylogenetic analyses will be crucial to evaluate the distribution
of some of the characters presented here to determine if they are
systematically informative.
CONCLUSIONS
The braincase, cranial endocast, and quadrate of MMCh-PV
71 share a number of features with Limaysaurus and Nigersau-
rus, suggesting that some endocranial traits, particularly the pres-
ence of a large lateral sinus, dorsal head vein, and presence of a
floccular recess, together with the laterally expanded quadrate
fossa, are characteristic of rebbachisaurids. Although the new
specimen comes from the same stratigraphic age and formation
as Limaysaurus, it exhibits strong differences from Limaysaurus
in the quadrate and postcranium, suggesting that it may repre-
sent a new rebbachisaurid taxon, thereby increasing the sauro-
pod diversity known from the lower Upper Cretaceous of
northern Patagonia.
ACKNOWLEDGMENTS
We thank A. Kamman for access to his land, help during the
field work, and support for our activity at the Ernesto Bachmann
Museum. We thank Rita and Bernardo, field managers, for mak-
ing us always feel welcome. We thank the technicians R. Zapata,
C. Albornoz, M. Negron, M. Ripoll, G. Gonzalez, M. Soto, A.
Moretti, and J. Ochoa for their help during field work and fur-
ther laboratory preparation. The editor R. Butler and two
reviewers, F. Knoll (University of Manchester) and J. L. Carbal-
lido (Museo ‘Egidio Feruglio,’ Trelew), provided valuable com-
ments that greatly improved the manuscript. Financial support
was provided by the Municipality of Villa El Choc
on.
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TABLE 1. Braincase and quadrate character variation within the studied rebbachisaurids.
Character Rebbachisaurid MMCh-PV 71 Limaysaurus (MUCPv 205) Nigersaurus
*
Braincase characters
cmcv Present Not visible Present
*
Crista Prootica Low ridge Well developed Well-developed
CN VII, foramen Anterior to c.pro Posterior to c.pro Posterior to c.pro
a
CN V, shape Oval Bilobate Oval
CN XII, foramina One One Two
floccular process Present ? Present
CN III and CN IV Separate foramina Separate foramina Single exit
Orbitocerebral fenestra Absent Absent Present
Quadrate characters
Lateral expansion Extremely broad Broad Broad
Pterygoid process Short and tall Subtriangular in shape,
more rostrally projected
Short and tall
Distal hemicondyles Medial hemicondyle
at least two times larger
Subequal hemicondyles Medial hemicondyle at
least two times larger
*
Sereno et al. (2007).
a
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Abbreviations:cmcv, caudal middle cerebral vein; c.pro, crista prootica.
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Handling editor: Richard Butler.
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