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We report the discovery of a new titanosaurian taxon, Puertasaurus reuili gen. et sp. nov., from Maastrichtian beds of SW Patagonia. Four vertebrae were recovered (i.e., cervical 9, dorsal 2, and two mid-caudals). The new form is diagnosed on the basis of an inflated neural spine on cervical vertebra, and extremely short second dorsal vertebra, among other features. Puertasaurus is one of the largest known sauropod dino-saurs, with dorsal vertebra 2 measuring 168 cm in transverse width. This is the first time that a cervical verte-bra is reported for a giant titanosaur, giving a new insight on neck anatomy of neosauropod dinosaurs.
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Novas et al.: Giant titanosaur from Patagonia.37
Rev. Mus. Argentino Cienc. Nat., n.s.
7(1): 37-41, 2005
Buenos Aires, ISSN 1514-5158
Giant titanosaur (Dinosauria, Sauropoda) from
the Late Cretaceous of Patagonia
Fernando E. NOVAS1,2, Leonardo SALGADO3, Jorge CALVO4 & Federico AGNOLIN2
1CONICET-2Laboratorio de Anatomía Comparada, Museo Argentino de Ciencias Naturales «Bernardino
Rivadavia», Av. Angel Gallardo 470, Buenos Aires (1405), Argentina-3Museo de Geología y Paleontología,
Universidad Nacional del Comahue, Buenos Aires 1400, (8300) Neuquén, Argentina-4Centro Paleontológico
Lago Barreales, Universidad Nacional del Comahue, Ruta Prov. 51, km 65. Neuquén.
Abstract: We report the discovery of a new titanosaurian taxon, Puertasaurus reuili gen. et sp. nov., from
Maastrichtian beds of SW Patagonia. Four vertebrae were recovered (i.e., cervical 9, dorsal 2, and two mid-
caudals). The new form is diagnosed on the basis of an inflated neural spine on cervical vertebra, and extremely
short second dorsal vertebra, among other features. Puertasaurus is one of the largest known sauropod dino-
saurs, with dorsal vertebra 2 measuring 168 cm in transverse width. This is the first time that a cervical verte-
bra is reported for a giant titanosaur, giving a new insight on neck anatomy of neosauropod dinosaurs.
Key words: Sauropoda, Titanosauria, Cretaceous, Patagonia.
____________
The Titanosauria is a diverse and geographi-
cally widespread clade of Cretaceous neosauro-
pods, abundant in Upper Cretaceous rocks of
South America (Salgado et al., 1997; Powell,
2003; Wilson & Upchurch, 2003). Many titano-
saurs were large, but just a few (e.g., the Ceno-
manian Argentinosaurus huinculensis and the
Turonian «Antarctosaurus» giganteus; Huene,
1929; Bonaparte & Coria, 1993) are known to have
attained truly gigantic sizes (up to 35 meters long
and around 80 tons). Because known specimens of
these giant sauropods are incomplete, many aspects
of their anatomy and systematics remain obscure.
Here we report the discovery of a new Patagonian
sauropod, Puertasaurus reuilli gen et sp. nov., one of
the largest of these giant tetrapods. This is the first
time in which a cervical vertebra is reported for a
giant titanosaur, making it possible to compare it
with smaller members of the clade.
We follow the taxonomy proposed by Salgado
(2003).
SYSTEMATIC PALEONTOLOGY
Sauropoda Huene, 1932
Titanosauriformes Salgado, Coria & Calvo, 1997
Titanosauria Bonaparte & Coria, 1993
Titanosauridae Lydekker, 1893
Puertasaurus reuili gen et sp. nov.
Etymology. In honor to Pablo Puerta and
Santiago Reuil, remarkable fossil-hunters who
discovered and prepared the specimen.
Holotype. MPM (Museo Padre Molina, Río
Gallegos, Santa Cruz) collection number 10002,
consisting of four disarticulated vertebrae, in-
cluding most of a cervical vertebra, a complete
dorsal 2, and the centra of two caudal vertebrae.
Locality and Horizon. Cerro Los Hornos, La
Leona, Santa Cruz Province, Argentina. Pari Aike
Formation, early Maastrichtian (Kraemer & Riccardi,
1997; Novas et al., 2004a). Vertebrae were found in
situ in a fine, gray sandstone lens, containing highly
carbonized plant remains classified as cycads and
conifers on the basis of cuticular morphology (L. Villar
de Seoane, pers comm.). Dinosaurs recorded in the
Pari Aike Formation are the basal iguanodontian
Talenkauen santacrucensis (Novas et al., 2004a) and
a large, yet undescribed, derived tetanuran theropod
(Novas et al., 2004b).
Diagnosis. Puertasaurus reuili is diagnosed
on the basis of the following combination of char-
acters: gigantic size; cervical neural spine con-
siderably inflated, being transversally wider than
the vertebral centrum and bearing strong dorso-
lateral ridges; caudal cervicals with spinoprezy-
gapophyseal laminae transversely thick and dor-
soventrally deep; cranial dorsal vertebrae ex-
tremely short, more so than in other sauropods
(e.g., centrum width/centrum length:1; in all
other titanosauriforms, this ratio is less than 1).
Description. For the first time a cervical ver-
tebra of a giant titanosaur is documented (Fig.
1). The neck vertebra (presumably cervical 9) is
118 cm long (between pre- and postzygapophyses)
and although mid-cervicals of the Early Creta-
Revista del Museo Argentino de Ciencias Naturales, n. s. 7 (1), 2005
38
ceous brachiosaurid Sauroposeidon (Wedel et al.,
2000) are longer than the cervical of the new
titanosaur, the latter one is exceptionally wide
with a transverse width of 140 cm (including
fused ribs). The neural spine bears deep and wide
pre- and postspinal fossae for cradling well-de-
veloped interspinous ligaments, as well as a con-
siderably inflated distal end, suggesting a pow-
erful neck ligament and cervical muscles. Such
characters are insinuated in smaller titanosaurs,
but they reach an extreme development in the
new form. The dorsal enlargement of the neural
spine is derived with respect to the transversely
narrower neural spine of all other titanosau-
riforms (e.g., Brachiosaurus, Euhelopus, Neu-
quensaurus; Fig. 3), and sharply differs from the
bifid spines of diplodocoids. This peculiar neural
spine is associated with a set of titanosaurian
features (e.g., Upchurch, 1999), such as laterally
projecting diapophyses and parapophyses, and a
low neural arch with a high neural spine. In the
new specimen, the zygapophyseal articulations
are positioned low on the neural arch, and the
centrum is even more depressed than in other
titanosaurids (e.g., Saltasaurus). Consequently,
the system of bony struts on the sides of the ver-
tebra (and the pneumatic fossae they define) are
dorsoventrally flattened. The cervical vertebra
is poorly pneumatized and lacks pleurocoels.
The available dorsal (dorsal 2) vertebra is
craniocaudally short, in sharp contrast with the
cervical described above (Fig. 2). The centrum is
strongly opisthocoelous and proportionally
shorter than in other Titanosauridae. Hypos-
phene-hypantrum articulations are absent. Al-
though the lack of these structures is diagnostic
of Titanosauridae (Salgado et al., 1997; Bonaparte,
1999), their absence in Puertasaurus may be due
to the cranial position of this vertebra.
Dorsal 2 of Puertasaurus is 106 cm in height
but 168 cm from the ends of the wing-like trans-
verse processes, thus exceeding by nearly 45 cm
Fig. 1. A-D, Puertasaurus reuili gen. et sp. nov. (MPM-10002, Río Gallegos), cervical 9 in cranial (A),
lateral (B), dorsal (C), and ventral (D) views. Scale bar 50 cm.
Novas et al.: Giant titanosaur from Patagonia.39
dorsal 4? of Argentinosaurus huinculensis, con-
sidered to be one of the biggest dinosaurs
(Bonaparte & Coria, 1993; Paul, 1994). This dor-
sal is considerably wider (in absolute terms) than
in other known sauropod. Transverse processes
are dorsoventrally deep at their bases, resulting
in a wing-like appearance in cranial view (Fig.
2), as in the basal titanosauriform Euhelopus
(Wiman, 1929). In Puertasaurus the transverse
processes of dorsal 2 are perpendicular to the
axial plane (Fig. 2D), as is the case in Argenti-
nosaurus and Euhelopus, instead of being
laterocranially oriented as in more derived
titanosaurids (e.g., Saltasaurus, Titanosauridae
indet. «Series B»; Powell, 2003). The neural spine
is dorsoventrally low but transversely expanded,
as usually found among Titanosauridae (Powell,
2003). The neural spine is vertically oriented,
being perpendicular in respect to the craniocaudal
axis of centrum, thus resembling Argenti-
nosaurus, for example. The system of laminae in
the neural arch is reduced but robust, and it shows
pre- and postspinal laminae diagnostic of
titanosaurs (Upchurch, 1999). The pre- and
postspinal fossae of Puertasaurus are wider and
deeper than in more derived titanosaurids (e.g.,
Saltasaurus, Opisthocoelicaudia; Powell, 2003;
Borsuk-Bialynicka, 1977), resembling in this fea-
Fig. 2. A-D, Puertasaurus reuili gen. et sp. nov. (MPM-10002, Río Gallegos), dorsal 2 in cranial (A), left
lateral (B), caudal (C), and dorsal (D) views. Scale bar 50 cm.
Revista del Museo Argentino de Ciencias Naturales, n. s. 7 (1), 2005
40
ture basal titanosauriforms such as Euhelopus and
Brachiosaurus (Bonaparte, 1999).
Two mid-caudal centra are preserved. They
are procoelous, a common feature among Tita-
nosauridae (Salgado et al., 1997).
Discussion. Puertasaurus reuili exhibits the
following synapomorphic features of Titanosau-
riforms: 1) deep and wide pre- and postspinal
fossae in cervical and dorsal vertebrae; 2) very
elongated cervical centra (Wilson, 2002); 3) re-
duced cervical neural arch lamination; and 4)
presence of prespinal laminae in dorsal vertebrae
(Salgado et al., 1997). Puertasaurus is referred to
Titanosauria because it shows the following de-
rived features: 1) cervicals with laterally project-
ing diapophyses and parapophyses (Upchurch,
1999); 2) low neural arch with a relatively high
neural spine (Salgado et al. 1997; Bonaparte,
1999); and 3) dorsal vertebrae with robust pre-
and postspinal laminae (Upchurch, 1999).
Puertasaurus exhibits two titanosaurid features:
1) neural spines of dorsal vertebrae dorsoven-
trally low and transversally expanded (Salgado
et al. 1997; Bonaparte, 1999); and 2) procoelous
mid-caudal vertebrae. Moreover, the new taxon
bears a well developed prespinal lamina in dor-
sal 2, a feature interpreted as diagnostic of
Eutitanosauria (Salgado, 2003). Nevertheless,
Puertasaurus lacks some of the synapomorphies
of Titanosauridae: for example, cranial dorsals
of the new taxon retained vertical neural spines
and transverse processes that are perpendicularly
oriented, and neural arches that lack the com-
plex system of laminae and pneumatic depres-
sions characteristic of derived titanosaurids. In
conclusion, Puertasaurus is interpreted as a pos-
sible basal titanosaurid.
Puertasaurus and Argentinosaurus are the
largest known sauropods. However, Puertasaurus
differs from the latter one in having dorsal ver-
tebrae with large, wing-like transverse processes,
lower neural spine, thick postspinal laminae, and
cranial dorsals craniocaudally shorter. We con-
sider such distinctions enough to distinguish both
taxa, a conclusion that is in agreement with the
stratigraphical provenance of these dinosaurs:
Puertasaurus comes from Maastrichtian beds,
while Argentinosaurus is Cenomanian in age.
The evidence at hand suggests that basal
titanosaurian clades were prone to attain big
sizes. In contrast, more derived Titanosauridae
include not only medium sized members, but also
the smallest adult known sauropods (e.g.,
Neuquensaurus, Saltasaurus, Magyarosaurus;
Jianu & Weishampel, 1999). It was suggested
(Bonaparte & Coria, 1993) that in South America
sauropods attained their maximum sizes between
Aptian and Coniacian times. The discovery of
Puertasaurus in Maastrichtian beds demon-
strates that gigantic sizes of South American sau-
ropods endured up to the end of the Mesozoic
Era, an interpretation that is in agreement with
other findings of big sauropod bones in the Pari
Aike Formation (Lacovara et al., 2004). Exepting
Fig. 3. Comparison among cervical and dorsal vertebrae of some selected sauropods. A, B, D, Puertasaurus
reuili gen. et sp. nov., cervical 9 in lateral (A), cranial (B), and dorsal (D) views. C, Puertasaurus reuili gen.
et sp. nov., dorsal 2 in cranial view; E, Brachiosaurus brancai, cervical vertebra in cranial view (Janensch,
1950); F, Argentinosaurus huinculensis, dorsal 4? in cranial view (modified from Bonaparte & Coria,
1993). Scale 50 cm.
Novas et al.: Giant titanosaur from Patagonia.41
southernmost Patagonia, the remaining Maas-
trichtian fossil sites with sauropods in South
America (Powell, 2003), Madagascar (Curry-Rogers
& Forster, 2001), and Europe (Jianu & Weishampel,
1999), the documented titanosaurs are consider-
ably smaller than Puertasaurus.
Up to now, the biggest Cretaceous dinosaurs
(e.g., Argentinosaurus huinculensis, «Antarcto-
saurus» giganteus, and Puertasaurus reuili) were
documented in South America. Why such gigan-
tic vertebrates evolved in this continent is puz-
zling. We suggest that this may reflect the evolu-
tion in progressive isolation of sauropods on this
continent during the Cretaceous.
The discovery of Puertasaurus demonstrates
that disparity in neck anatomy among sauropod
dinosaurs is greater than suspected (Fig. 3). The
low and wide titanosaurian cervicals differ from the
deep cervicals of the remaining neosauropods (e.g.,
diplodocids, Brachiosaurus, and Euhelopus) in that
the latter exhibit rounded articular surfaces of the
centra, ribs mostly ventrally oriented, and zygapo-
physes occupying an elevated position with respect
to the centrum (Fig. 3E). Such anatomical distinc-
tions, not recognized before, remain unexplored
from mechanical, postural and movemental points
of view, and may have important consequences for
functional studies of sauropod necks (Wedel et al.,
2000; Stevens & Parrish, 1999).
ACKNOWLEDGEMENTS
Thanks to Eduardo Vidal and his family for the
logistic support received during field exploration.
Pablo Puerta, Santiago Reuil, Juan Canale,
Alejandro Haluza, Gastón Lo Coco, Juan Goroso,
and Daniel Hauk for their work in the field. Greg
Paul, Mike Parrish, Olivier Rauhut, and Rodolfo
Coria for their valuable comments on our manu-
script. Drawings were executed by Gabriel Lío, and
photographs by Hernán Canutti. Field work and
study was supported by the National Geographic
Society, Conicet, Agencia Nacional de Promoción
Científica y Tecnológica, Vialidad Nacional,
Akapol SA, and Renault Argentina (Buenos Aires).
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Recibido: 16-XII-2005
Aceptado: 01-VIII-2005
... They also mentioned that there are six caudal vertebrae (not seven) and did not include the presence of haemal arches. Together with Puertasaurus (Novas et al. 2005), Dreadnoughtus is the only giant titanosaur found in the upper part of the Upper Cretaceous deposits of Gondwana. Both taxa were found in the same formation, and although the remains of Puertasaurus are very fragmentary, Dreadnoughtus represents one of the most complete large titanosaur known to date. ...
... Locality and Age Cerro Los Hornos, La Leona, Santa Cruz Province, Argentina (Leanza 1972;Arbe 2002;Novas et al. 2005;Egerton 2011;Varela et al. 2012;Sickmann et al. 2018) (Fig. 1). Cerro Fortaleza Formation (=Pari Aike Formation), Magallanes-Austral Basin, Campanian (Upper Cretaceous). ...
... (3) caudal cervicals with spinoprezygapophyseal laminae transversely thick and dorsoventrally deep; (4) cranial dorsal vertebrae extremely short (shorter than in other sauropods) (Novas et al. 2005). ...
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... Dicha asociación comprendía series ontogenéticas excepcionalmente conservadas, nidos y huevos, lo que permitió desarrollar líneas de investigación que tienen que ver no solo con la anatomía y las relaciones de parentesco de esta especie (Pol y Powell, 2007;Otero y Pol, 2013), sino también con la biología del desarrollo (Cerda et al., 2012Norell et al., 2020;Otero y Pol, en prensa) y la locomoción (Otero et al., 2017(Otero et al., , 2019 raptórido Orkoraptor burkei Novas et al., 2008 (Fig. 5.3-5.4) y el posible abelisauroideo Austrocheirus isasii Ezcurra et al., 2010, 2005, 2008Ezcurra et al., 2010). ...
... Estas expediciones produjeron diversos hallazgos, incluyendo restos vertebrales de un abelisáurido(Martínez et al., 2004; Fig. 1), y una serie de hallazgos en niveles de la Formación Cerro Fortaleza (Campaniano) en el Cerro de los Hornos, costa sur del Lago Viedma(Fig. 1), tales como el ornitópodo Talenkauen santacrucensisNovas et al., 2004, el saurópodo gigantePuertasaurus reuili(Novas et al., 2005), el terópodo mega-Figura 5. El registro paleoherpetológico de la provincia de Santa Cruz. 1, Cráneo de ejemplar juvenil del sauropodomorfo basal Mussaurus patagonicus (MPM-PV 1813/4), escala= 5 cm. 2, Cráneo del ejemplar adulto de la misma especie (MPM-PV 1868), escala= 5 cm. ...
... The centrum is opisthocoelous and slightly wider than tall in anterior and posterior views, as in Futalognkosaurus, Mendozasaurus and Puertasaurus Novas et al., 2005Novas et al., 2005;Calvo et al., 2007). In ventral view, the lateral margins of the centrum are anteroposteriorly concave, hence the centrum is hourglass shaped (Fig. 8A, B). ...
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Rinconsaurus caudamirus, from the Bajo de la Carpa Formation (Santonian), Río Negro, Argentina, is represented by several axial and appendicular elements from, at least, four specimens. The axial skeleton of this taxon was described in detail in a recent contribution, pending a complete analysis and description of its appendicular skeleton. This contribution focuses on the description of the appendicular skeleton of Rinconsaurus and its phylogenetic relationships, considering the new information provided here. Rinconsaurus clearly differs from other titanosaurs for the presence of several autapomorphic characters and for a unique association of characters, some of which are also present in lognkosaurians, aeolosaurines and saltasaurines titanosaurs, and by having a scapula with a scapular blade angled 65° with respect to the coracoid articulation, similar to that of Bellusaurus, Dreadnoughtus and Muyelensaurus. Equations for estimating body mass in sauropods based on long bone circumference suggest a body mass of at least 3-5 tonnes for the largest individuals of Rinconsaurus, being lighter than saltasaurines, but heavier than aeolosaurines. Rinconsaurus was incorporated into an expanded version of a phylogenetic data matrix along with several ontemporary South American titanosaurs. The resulting data matrix comprises 102 taxa scored for 431 characters, and our phylogenetic analysis retrieves Rinconsaurus as a member of the clade Rinconsauria. For its part, the clade Rinconsauria, in which Aeolosaurini is nested, is recovered within a diverse Lognkosauria. When the resulting trees are time calibrated and taking into account the position of Ninjatitan within Rinconsauria, there results that the possible origin of the clades Lognkosauria and Rinconsauria (among other titanosaur clades) could have occurred towards the beginning of the Early Cretaceous.
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Most taphonomy studies of South American sauropodomorphs have addressed extrinsic factors such as sedimentary environments, bone dispersal, and mineralogical processes that occurred during fossil diagenesis. These studies provide important data on the taphonomic modes which are associated with bone accumulations in different paleoenvironmental contexts. However, these analyses have generally not considered intrinsic factors like the shape, size, and structural integrity of the skeletal elements, variables that can produce some taphonomic bias. Sauropodomorphs include dinosaurs of highly varied sizes, ranging from small (less than 8 m long) to remarkably giant forms (around 30 m long). In the largest sauropods, such as the huge titanosaurs, very incomplete skeletons are commonly found and most notably skull and articulated pedes rarely are preserved. We focus here on some intrinsic anatomical factors as they relate to articulation in some key parts of the skeletons. Further, this study suggests that the preservation of fragile portions of sauropodomorph skeletons was possible only under specific combinations of sedimentological and biological processes.
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STRATIGRAPHY OF THE PATAGONIAN ANDES BETWEEN ARGENTINO AND VIEDMA LAKES (49 40¨S . 50 10 ´S.L.) SANTA CRUZ PROVINCE. - The stratigraphy of the Patagonian Andes between Argentino and Viedma lakes is reviewed using 16 measured surface sections, containing 14 fossiliferous levels (n1 to n14) and reflection seismic profiles and well data. The oldest unit, the Bahia de la Lancha Formations, consists of Upper Paleozoic sedimentary rocks containing trace fossils (n1). It is unconformably covered by the Middle-Late Jurassic volcanic El Quemado Complex. The Springhill Formation of late Early Tithonian and Middle Tithonian age (n2 and n3) is correlated with a seismic sequence (S1) which is bounded by the d1 and d2 uconformities and related to a Late Jurassic rifting stage. The platform deposits of the Rio Mayer Formation of Late Berriasian- Early Valanginian (n4 and n5) to Albian age are correlated with seismic sequence S2 bounded by the d2 and d3 unconformities. The Rio Mayer Formation is related to the thermal relaxation phase of the basin. The overly Cerro Toro Formation is divided into two members. The lower one of Late Albian-Early Cenomanian to Early Coniacian age (n6 n7 and n8) is correlated with seismic sequence S3 bounded by the d3 and d4 unconformities, and the upper member of Middle Coniacian (n9-10) to Late-Early Campanian age (n11) is correlated with seismic sequence S4 bounded by the d3 and d4 unconformities. The d4 unconformity of Coniacian age is related to a pulse of tectonic reactivation of the basin. The Alta Vista Formation of Early Campanian age (n13 and n14) is correlated with seismic sequence S5. Late Jurassic normal faulting with subsequent positive inversion suggests that the geological evolution of the region was strongly influenced by the primary structures of the basin.
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Sauroposeidon proteles is a large brachiosaurid sauropod recently described from the Antlers Formation (Aptian-Albian) of southeastern Oklahoma. Sauroposeidon represents the culmination of brachiosaurid trends toward lengthening and lightening the neck, and its cervical vertebrae are characterized by extensive pneumatic structures. The elaboration of vertebral air sacs during sauropod evolution produced a variety of internal structure types. We propose a new classification system for this array of vertebral characters, using computed tomography (CT) of pneumatic internal structures. Comparisons with birds suggest that the vertebrae of sauropods were pneumatized by a complex system of air sacs in the thorax and abdomen. The presence of a thoraco-abdominal air sac system in sauropods would dramatically affect current estimates of mass, food intake, and respiratory requirements. Sauroposeidon was one of the last sauropods in the Early Cretaceous of North America; sauropods disappeared from the continent by the early Cenomanian. The demise of sauropods in the Early Cretaceous of North America predates significant radiations of angiosperms, so the decline and extinction of this dinosaur group cannot be linked to changes in flora.
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Abstract. We report the discovery of an almost complete skeleton of a new iguanodontian dinosaur, Talenkauen santacrucensis n. gen. et sp., from Maastrichtiano rocks of southwestern Patagonia. Talenkauen is odd in the presence of plate-like structures on both sides of the thorax, which are better interpreted as uncinate processes than dermal armor. Talenkauen and the also Maastrichtian Thescelosaurus neglectus Gilmore from North America, represent the only two ornithischians in which this peculiar feature is currently known. Some derived features unite Talenkauen with other Gondwanan ornithopods, but all the evidence does not offer enough support for an iguanodontian clade endemic from the Southern Hemisphere. Small- to medium-sized ornithischians appear to have been the dominant plant-eating dinosaurs in Antarctica and Australia during the Cretaceous, in contrast with the outstanding abundance of médium sized to giant sauropods in central Gondwana (e.g., South America, Africa, India).
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The phylogenetic relationships of the Late Cretaceous Mongolian sauropods Nemegtosaurus and Quaesitosaurus are controversial. Previous studies have interpreted nemegtosaurids as members of the Diplodocoidea or Titanosauroidea. The conflicting character sets, which support these alternative hypotheses, are examined and critically evaluated. Only two derived states are unique to nemegtosaurids and one or more titanosauroid taxa. At least five synapomorphies (e.g., transverse narrowing of the rostral end of the premaxilla, elongation of the subnarial foramen, and extreme retraction of the external nares) support the inclusion of the nemegtosaurids within the Diplodocoidea, but the presence of the plesiomorphic state cannot always be confirmed in higher titanosauroids. Cladistic analysis supports the hypothesis that nemegtosaurids are the sister-group to a clade containing Rebbachisaurus, dicraeosaurids and diplodocids. Antarctosaurus wichmannianus, a problematic taxon from the Late Cretaceous of Argentina, is placed within the Diplodocoidea (as the sister-taxon to the Nemegtosauridae) by the analysis. Several lines of evidence suggest, however, that the holotype of A. wichmannianus is composed of an amalgam of different sauropod taxa and does not represent a reliable operational taxonomic unit. The distribution of derived states indicates a considerable amount of convergence between the skulls of diplodocoids and higher titanosauroids. Contrary to previous suggestions, many of the apomorphic features of the diplodocoid skull were acquired gradually and do not represent a single complex character.