Giant titanosaur (Dinosauria, Sauropoda) from the Late Cretaceous of Patagonia

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.

Full text

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