Maastrichtian plesiosaurs from northern Patagonia

Zulma Gasparinia*, Leonardo Salgadob, Silvio Casadı́oc

aDpto. Paleontologı́a de Vertebrados, Museo de La Plata, Universidad Nacional de La Plata, Paseo del Bosque s/n, 1900 La Plata,
Buenos Aires, Argentina

bMuseo de Geologı́a y Paleontologı́a, Universidad Nacional del Comahue, Buenos Aires 1400, 8300 Neuquén, Argentina
cUniversidad Nacional de La Pampa, Uruguay 151, 6300 Santa Rosa, La Pampa, Argentina

Accepted 24 February 2003

Abstract

Three relatively complete elasmosaurid plesiosaurs were recently recovered from the north of Patagonia, Argentina. They were
found in the uppermost levels of the Jagüel Formation (upper Maastrichtian). One of the specimens was found only 0.3 m below
the Cretaceous/Paleogene boundary, this being the youngest record of a Mesozoic reptile in Patagonia. Two specimens are referred
to cf. Mauisaurus sp. and the other to Tuarangisaurus? cabazai sp. nov. This study has revealed that some character states, previously
regarded as mere ontogenetic variations, could be taxonomically valid. Comparison of the Upper Cretaceous elasmosaurids of
Patagonia with those from the Upper Cretaceous of central Chile, the northeastern islands of the Antarctic Peninsula, and New
Zealand reinforce the hypothesis of a south Gondwanan distribution for some pelagic reptiles.
� 2003 Published by Elsevier Ltd.

Keywords: Plesiosauria; Elasmosauridae; Maastrichtian; Patagonia; Argentina

1. Introduction

The first remains of Cretaceous plesiosaurs from
South America were found in Chile, in the lower
Maastrichtian of the Quiriquina Formation
(Stinnesbeck, 1986). Gay (1848) referred them to his
species Plesiosaurus chilensis. Almost one century later,
Cabrera (1941) described Aristonectes parvidens (upper
Maastrichtian of Chubut Province, Argentina), the first
plesiosaur from the Argentinian Patagonia, and tenta-
tively related it to the Elasmosauridae. Bardet et al.
(1991) and Gasparini et al. (in press) confirmed this
familial assignment. Both this record and studies of
Cretaceous plesiosaurs from Patagonia were scorce up
to the end of the twentieth century. Casamiquela (1969,
1980) reported plesiosaurs from southern Rı́o Negro
Province. Gasparini & Goñi (1985) described remains of

a plesiosaur from the area around Lago Pellegrini
(northwestern Rı́o Negro Province), which they referred
to Trinacomerum lafqueniaum. This specimen, and
others found later in Campanian–Maastrichtian levels
of the Allen Formation, Rı́o Negro Province, were
studied again by Gasparini & Salgado (2000) and
reinterpreted to belong to an indeterminate species of
Elasmosauridae, probably close to Elasmosaurus platy-
urus Cope, 1868. A polycotilid, Sulcusuchus erraini
Gasparini & Spalletti, 1990, from the upper
Campanian–lower Maastrichtian and the lower–middle
Maastrichtian of Chubut Province (Gasparini & de la
Fuente, 2000; Gasparini et al., 2001), and isolated
remains of elasmosaurids from the provinces of
Mendoza, Rı́o Negro and Chubut, complete the record
of Patagonian plesiosaurs from the end of the Mesozoic
(González Riga, 1999; Gasparini et al., 2001). This
synthesis shows that, except for Aristonectes parvidens,
most Patagonian plesiosaurs have been recovered from
the Campanian–middle Maastrichtian interval.

Between 1998 and 2001 Mr Héctor Cabaza and
collaborators from the Museum and the Municipality of
Lamarque, discovered the remains of three mosasaur

* Corresponding author: Dr Z. Gasparini, Dpto. Paleontologı́a
Vertebrados, Paseo del Bosque s/n, La Plata 1900, Argentina.
Tel.; +54-2214234921; fax: +54-2214257527

E-mail addresses: zgaspari@museo.fcnym.unlp.edu.ar
(Z. Gasparini), lsalgado@uncoma.edu.ar (L. Salgado),
sacasadio@hotmail.com (S. Casadı́o).

Cretaceous Research 24 (2003) 157–170

0195-6671/03/$ - see front matter � 2003 Published by Elsevier Ltd.
doi:10.1016/S0195-6671(03)00036-3

lizards and three long-necked plesiosaurs. These reptiles
were found in the central area of Rı́o Negro Province
(Fig. 1), in the uppermost levels of the Jagüel Formation
(upper Maastrichtian) (Fig. 2). One of the plesiosaurs
(MML-PV4) was found 0.3 m below the Cretaceous/
Paleogene boundary (Gasparini et al., 2002), this being
the youngest record of a Mesozoic reptile in Patagonia.

The systematics of Upper Cretaceous plesiosaurs is
not yet clear because, although they are one of the first
known tetrapod clades (Williston, 1903; Bakker, 1993),
studies based on complete specimens are comparatively
few (Welles, 1943). Several studies based on skulls have
recently been undertaken, resulting in a greater con-
sensus concerning systematic hypotheses (Carpenter,
1996, 1997, 1999; Storrs, 1999; Druckenmiller, 2002;
Gasparini et al. (in press)). However, when only the
postcranium is available, as in the specimens described
here, identification is not simple, since the postcranial
anatomy is relatively conservative and some differences
have been interpreted as ontogenetic variation (Adams,
1997; Storrs, 1999).

The three new specimens of elasmosaurid plesio-
saurs from northern Patagonia permitted an analysis
of characters previously considered to be exclusively
ontogenetic variation, conditioning taxonomic deter-
minations. The comparison of the new specimens with
those, generally more incomplete, from the Upper
Cretaceous of Patagonia, central–western Chile, the
northeastern islands of the Antarctic Peninsula, and
New Zealand, reinforces the hypothesis of a clear south
Gondwanan distribution of some pelagic reptiles (Novas
et al., 2002). Likewise, an analysis of the fossil-bearing
rocks and the biota related to the carcasses of the new
elasmosaurids from Rı́o Negro, throw light upon the

environmental conditions of northern Patagonia, just
before the end of the Cretaceous Period.

Abbreviations. NZGS, CD, New Zealand Geological
Survey, Fossil Chordata Collection; MCS, Museo de
Cinco Saltos, Rı́o Negro, Argentina; MLP, Museo
de La Plata, Argentina; MML, Museo Municipal de
Lamarque, Rı́o Negro, Argentina; MUCPv, Museo
de la Universidad Nacional del Comahue, Neuquén,
Argentina, collection of paleovertebrates; TTU-P,
Museum of Texas Tech University, Lubbock, Texas.

2. Geological setting

One of the most significant geodynamic events that
took place in southern South America between the
Campanian and the Danian was the relative sea-level
change related to the subsidence of the Atlantic margin,
accounting for important flooding. This subsidence was
caused by lithospheric cooling and sediment loading
(Uliana & Biddle, 1988) which, in northern Patagonia,
was coeval with the development of a foreland basin in
the east of the Andes (Tunik, 2001). During the
Cretaceous/Paleogene transition, the southern tip of
South America was reduced to an archipelago in which
the central part of the Somuncurá and Deseado massifs
remained emergent (Yrigoyen, 1969; Riccardi, 1988;
Uliana & Biddle, 1988; Urien et al., 1995; Malumián,
1999). Malumián & Caramés (1995) calculated the
minimum area of the presently emerged Patagonia
that was covered by the sea during the early Danian
to be 507,000 km2. This wide, flooded surface was
important from a palaeogeographic standpoint, and it
certainly played a primary role in the climatic and

Fig. 1. Map of the study area, centre of Rı́o Negro Province, Argentina. A–C, paleontological localities.

Z. Gasparini et al. / Cretaceous Research 24 (2003) 157–170158

Fig. 2. Correlation of measured stratigraphic sections.

Z. Gasparini et al. / Cretaceous Research 24 (2003) 157–170 159

evolutionary events recorded in Patagonia and the
Antarctic Peninsula.

The transgression is recorded in the sedimentary
rocks of the Malargüe Group in the Neuquén Basin,
northwestern Patagonia; it is widely exposed in southern
Mendoza, northeastern Neuquén, western La Pampa
and the northern Rı́o Negro provinces. These rocks have
been studied by several authors since the nineteenth
century (see Camacho, 1992). In recent years, interest in
them has increased because they include the Cretaceous/
Paleogene boundary in both marine and continental
facies (Parras & Casadı́o, 1999). These rocks record
excellent examples of Upper Cretaceous ecosystems in
middle latitudes of the Southern Hemisphere.

North of the Neuquén Basin, the Malargüe Group
crops out widely along the foothills of the Andes
(Dessanti, 1973, 1975; González Dı́az, 1975; Holmberg,
1975; Ramos, 1981), and is more than 400 m thick. It is
composed, from base to top, of the Loncoche, Jagüel,
Roca, and Pircala formations. In the southeastern area,
this Group is less than 200 m thick, and comprises the
Allen, Jagüel, Roca, and Carrizo formations.

Uliana & Dellape (1981) inferred a littoral to
restricted marine environment for the Allen Formation.
Barrio (1991) pointed out that, while in the eastern
sector of the basin the facies association represents
intertidal environments, in the western sector its features
are those of a tide-dominated estuary. This difference
was attributed to different tidal rates, directly related to
the geometry of the basin. The equivalent unit in the
Andean area is the Loncoche Formation. The Allen
Formation and its equivalents are covered by marine
rocks of the Jagüel Formation, mainly shales, as well as
by its correlatives, the Coli Toro, Aguada Cecilio, and
Malargüe formations, all Maastrichtian in age (Casadı́o,
1994).

The Jagüel Formation is transitionally overlain by
mainly carbonate and regressive levels of the Roca
Formation, assigned to the Maastrichtian–Danian on
the basis of its fossil content (Casadı́o et al., 1998). The
evaporitic deposits of the Carrizo Formation overlie
the Roca Formation in the area. In the Andean region,
the Roca Formation continues transitionally into the
continental sandstones of the Pircala Formation (Parras
et al., 1998).

Differences in depositional environments between
the Andean and eastern areas lie mainly in the pre-
dominance of continental and deltaic facies, as well as in
the abundant pyroclastic material of the Andean area.
This suggests the vicinity of an emergent and volcani-
cally active zone (Digregorio, 1978; Parras et al., 1998;
Parras & Casadı́o, 1999). In addition, the eastern area
comprises mostly marine deposits, mainly shales, lime-
stones, and evaporites, suggesting a distal position with
respect to the supply area, and a proximal oceanic
relationship.

The elasmosaurids reported in this paper were found
at three localities in the depressions of Trapalcó and
Santa Rosa, central Rı́o Negro Province, on the south-
ern margin of the Neuquén Basin (Fig. 1). The plesio-
saur MML-PV3 was found at locality A (39(46#20$S,
66(40#42$W), and MML-PV4 at locality B
(39(51#37$S, 66(37#22$W); both are referred to cf.
Mauisaurus sp. Specimen MML-PV5, referred to
Tuarangisaurus? cabazai sp. nov., was found at locality
C (39(50#45$S, 66(40#40$W).

The fossils were exhumed from mudstones assigned
to the Jagüel Formation, which in the localities studied
transitionally overlies the lacustrine deposits of the Allen
Formation, and transitionally underlies the limestones
of the Roca Formation (Concheyro et al., 2002;
Gasparini et al., 2002). In the area of Trapalcó and
Santa Rosa, the Jagüel Formation is composed of olive
green mudstones, laminated in some sections (Fig. 2). It
contains scarce Maastrichtian marine bivalves, such as
Ambigostrea clarae (Ihering von, 1907) and ‘Pecten’
mahuidaensis (Weaver, 1931). This unit also bears a very
rich association of calcareous nannofossils from Zone
CC26, late Maastrichtian, the most conspicuous of
which are Arkhangelskiella cymbiformis, Biscutum mela-
niae, Cribrosphaerella daniae, Lithraphidites quadratus,
Nephrolithus frequens and Prediscosphaera stoveri
(Concheyro et al., 2002).

The top of the Jagüel Formation lies at the base of the
first level of coquina formed by Pycnodonte (Phygraea)
burckhardti (Böhm, 1903) and Gryphaeostrea callophyla
(Ihering von, 1903). In this area, the Cretaceous/
Paleogene boundary is in the Jagüel Formation (Fig. 2).

Concheyro et al. (2002) pointed out that in the lower
section of the Jagüel Formation at locality A, an inner-
platform foraminiferal association underlies another
association, probably of middle-platform origin,
suggesting a transgressive pulse during the late
Maastrichtian. This has also been observed at other
localities in northern Patagonia (Casadı́o, 1994; Parras
et al., 1998; Parras & Casadı́o, 1999).

The plesiosaur MML-PV3 was found 1.5 m below the
Cretaceous/Paleogene boundary, MML-PV4, 0.3 m and
MML PV5, 5 m below this boundary. The level in which
MML-PV5 was found is enclosed within ‘intervalo A’ of
Concheyro et al. (2002). These authors proposed a
shallow inner-platform environment for this interval
because of the occurrence of a high percentage of
agglutinated foraminifers and the absence of planktonic
foraminifers. A continuous bed 0.2 m thick composed of
medium-grained bioclastic limestone with hummocky
cross stratification is recognized at this level of the
section over the entire area. This bed lies 3 m below the
level with specimen MML-PV5.

MML-PV3, collected at locality A, was preserved at
the base of the ‘Intervalo B’ of Concheyro et al. (2002).
These authors recognized an increase in diversity of

Z. Gasparini et al. / Cretaceous Research 24 (2003) 157–170160

planktonic foraminifers as well as an increase in the
planktonic/benthic ratio that, together with the size of
the planktonic foraminifers, suggest a deepening with
respect to the previous level to a middle platform level.
These conditions are similar to those at the level from
which specimen MML-PV4 was collected at locality B.
In all of these cases, the absence of invertebrates is
puzzling. Only a few specimens of bivalves assigned to
‘Pecten’ mahuidaensis and Ambigostrea clarae were col-
lected. Very few levels show lamination, which may be
owning to a low gradient of water temperature rather
than to the activity of benthic organisms.

The three plesiosaurs are relatively complete.
MML-PV3 includes a mandibular fragment and a large
number of associated gastroliths, suggesting that the
animal was still complete when it reached the bottom.
MML-PV4 is a trunk fragment with an articulated
paddle. The skull and neck of MML-PV5 were not
preserved, but the rest of the body was articulated.

3. Systematic Paleontology

3.1. Taxon 1

Plesiosauria de Blainville, 1835
Plesiosauroidea (Gray, 1925) Welles 1943
Elasmosauridae Cope, 1869
Mauisaurus Hector, 1874

cf. Mauisarus sp.
Figs. 3 and 4

Material. Remains of two incomplete specimens.
MML-PV3 (Fig. 3A–C, Fig. 4B): right mandibular
fragment, prefrontal, four incomplete cervical vertebrae
(one anterior, one medial and two posterior), two
incomplete dorsal, one sacral and four caudal vertebrae;
right femur, ten phalanges of a single (?) paddle, one
indeterminate tarsal, rib fragments, several gastroliths.
MML-PV4 (Fig. 3D–G, Fig. 4A, G): one incomplete
cervical vertebra, 13 incomplete dorsals, three sacrals, 24
caudals, two ilia and the left anterior paddle (humerus,
radius, ulna, proximal and distal carpals and phalanges).

Locality and horizon. MML-PV 3, Locality A
(39(46#20$, 66(40#42$); MML-PV 4, Locality B
(39(51#37$, 66(37#22$) (Fig. 1). Upper part of the
Jagüel Formation (upper Maastrichtian) (Fig. 2).

Description
As MML-PV3 and MML-PV4 are considered to be a

single taxon, the following description encompasses
both specimens.

Mandible (Fig. 3C). Right mandibular fragment,
60 mm long, with three incomplete alveoli for functional
teeth and two complete alveoli for replacement teeth. As
in all plesiosaurs, the alveoli for replacement teeth are
located posteromedial to the alveoli for functional teeth
(Edmund, 1960). The external alveoli for functional

teeth are very close to each other and the antero-
posterior diameter is approximately 10 mm. No teeth
have been found in situ or isolated.

Cervical vertebrae (Fig. 3A, B). The body of the
anterior cervical of MML-PV3 is wider (56 mm) than
long (47 mm), and longer than high (33 mm). There are
two foramina in ventral view on both sides of the
longitudinal keel. The measurements of the most com-
plete posterior cervical vertebra of MML-PV3 are simi-
lar to those the anterior cervical (width, 112 mm; length,
87 mm; height, 68 mm). It is kidney-shaped in anterior
view, with the ventral notch characteristic of elasmosau-
rids. The lateral horizontal crest that characterizes the
elasmosaurids is observed (Fig. 3B), but it is only
slightly developed, as in usual is the posterior cervicals
(Bardet & Godefroit, 1995). MML-PV4 has half a
centrum, which is very deteriorated, and probably a
middle to posterior cervical. The centrum is longer than
high, and a slight horizontal crest crosses the lateral side.

Fig. 3. cf. Mauisaurus sp. A–C, MML-PV3 and D–G, MML-PV4.
Anterior cervical vertebra in anterior (A) and right lateral (B) views. C,
right mandibular fragment in dorsal view. Posterior dorsal vertebra in
right lateral (C) and anterior (D) views. E, sacral vertebra in anterior
view. F, caudal vertebra in anterior view. cer, base the cervical rib;
cr, caudal rib; fa, alveoli for functional teeth; lc, lateral crest;
prz, prezygapophysis; ra, alveoli for replacement teeth; sr, sacral rib.
Scale bars represent 50 mm.

Z. Gasparini et al. / Cretaceous Research 24 (2003) 157–170 161

Dorsal vertebrae (Fig. 3D, E). These are best pre-
served in MML-PV4, which has 13 dorsal vertebrae. The
centra are wider than high and than long, the transverse
processes are compressed, directed upward and
expanded at their distal ends. The prezygapophyses are
long, and deeply concave (Fig. 3D, E). The neural
spines, complete from the sixth to the ninth, are very
high and compressed, and the neural arch (spine
included) is twice the height of the vertebral centrum.
The dorsals of MML-PV3 and MML-PV4 are identical
to those of some undetermined elasmosaurids from the
Upper Cretaceous of New Zealand (Wiffen & Moisley,
1986, figs. 51–52).

Sacral vertebrae (Fig. 3F). MML-PV3 has the
complete body of a sacral vertebra, without the ribs
attached. The body is wider (100 mm) than high
(74 mm) and higher than long (65 mm). The facet for the
articulation of the rib is oval, occupying almost all of the
lateral side of the vertebral body. The ventral side is flat,
with two nutrition foramina. MML-PV4 has three
sacrals whose centra are similar in morphology and
dimensions to those of MML-PV3. The sacral ribs are
compressed with a conspicuous posterior depres-
sion. Distally there are two faces; the ilium probably
articulated with one of them.

Caudal vertebrae (Fig. 3G). MML-PV3 has four
centra of caudal vertebrae. These are wider than high

and relatively short. The anterior and posterior facets
for the articulation with hemapophyses are well defined.
The ventral side of the centrum is flat. MML-PV4 has 18
caudal vertebrae in different degrees of preservation.
The caudal ribs are long and compressed. The bases of
the ribs are not well developed dorso-ventrally, unlike
the sacral ribs. The neural spines are narrower antero-
posteriorly than in the dorsals, and they are more
backwardly directed.

Paddles (Fig. 4). The left fore paddle of MML-PV4 is
almost complete (Fig. 4C). The humerus is short and
robust, without a conspicuous neck; the capitulum and
tuberosity are scarcely distinguishable because of the
poor preservation of this area. The distal part is wide
with two articulating surfaces relatively well marked.
The humerus lacks the knee or posterior expansion of its
distal end, as in most elasmosaurs, except for Hydralmo-
saurus (Carpenter, 1999). The morphology of the
humerus is similar to that of Mauisaurus haasti Hector
1874 (Welles & Gregg, 1971, fig. 7) from the uppermost
Cretaceous of New Zealand.

The radius is approximately rectangular and slightly
larger than the ulna; both form the epipodial foramen.
The ulna is irregularly hexagonal. The radiale and the
ulnare are of similar size. Between them, the inter-
medium is an irregular hexagon, the longest sides
of which articulate proximally with the ulna, and
distally with carpals 2 and 4. The contact between
the intermedium and the radius is less than with the
ulna.

The longest finger of MML-PV4, the fifth, develops
on the concave margin of the paddle, being clearly
posterior and linked to the ulna. Carpal 1 articulates
with metacarpal I and has a facet for metacarpal II.
Carpal 2 articulates distally with metacarpal II, and with
metacarpal III through a posterodistal facet. Likewise,
carpal 4 (third carpal element; see Welles & Bump, 1949,
p. 528) articulates proximally with the intermedium and
ulnare through a facet, each approximately equal in size.

Phalanges of MML-PV3 and 34 phalanges of
MML-PV4 have been preserved. They are flat, spool-
shaped, with very expanded ends and relatively flat
articular surfaces (Fig. 3C). The expansion of the ends is
approximately one and a half times the transverse
diameter of the phalange on its middle part. Phalanges
of MML-PV3 probably belong to the hind limb, while
those of MML-PV4, to the left forelimb. In both cases,
the distal phalanges are shorter and more cylindrical
than the proximal ones.

MML-PV3 preserves the proximal and distal ends
of the right femur (Fig. 3B). A convex condyle and a
flat trochanter are located on different planes of the
proximal end. An isthmus of periosteal tissue that
normally separates both articular surfaces is not yet
developed. The areas for the insertion of the retrac-
tion muscles of the femur are only just visible on the

Fig. 4. cf. Mauisaurus sp. A, C, B, MML-PV4 and MML-PV3. A,
ilium, and B, right femur in dorsal view; C, left anterior paddle in
ventral view. c1–c5, distal carpals; af, articular facets; co, condyle;
h, humeurs; I, intermedium; p, pisciform; ph, phalanges; r, radius;
ra, radiale; tr, trochanter; u, ulna; ul, ulnare; I–V, metacarpals. Scale
bars represent: 50 mm.

Z. Gasparini et al. / Cretaceous Research 24 (2003) 157–170162

posteroventral side of the femur. Unlike the humerus
(preserved in MML-PV4), the neck of the femur is well
defined, as in Mauisaurus haasti (Hector, 1874, pl. 29,
fig. a). The articular surfaces for the tibia and fibula are
concave and relatively well defined.

As for the metapodials, MML-PV3 preserves the
intermedium of the hind limb. It is pentagonal, similar in
shape to that of the holotype of Mauisaurus haasti
(Hector, 1874, pl. 29, fig.a), but different from that of
the anterior paddle (preserved in MML-PV 4), which is
hexagonal. This difference in the number of sides of the
anterior and posterior intermedium has been seen in
other elasmosaurids (Welles, 1952, 1962, fig. 15).

Ilium (Fig. 4A). MML-PV4 has both ilia. Each ilium
is compressed, and its proximal end contacts the sacrum.
It is thin and sharp, with three well-defined sides, while
the opposite end, which dorsally closes the acetabulum,
is slightly expanded. The morphology and propor-
tions are similar to those of the Patagonian elasmosaur
illustrated by Gasparini & Goñi (1985), pl. II, 1).

Discussion
Following Welles (1952), MML-PV3 may be inter-

preted as an immature individual (Brown, 1981)
because of the presence of an isthmus of periosteal
bone at the proximal end of the femur. However, this
interpretation cannot be accepted because the different
elements of the vertebrae are fused. MML-PV3 and
MML-PV4 probably represent adult specimens whose
estimated body length is between 9 and 11 m. Cervical
vertebrae with a horizontal crest on the lateral side of
the body suggest their referral to the Elasmosauridae
(Brown, 1981).

Humerus proportions, the shape of radius and ulna,
and the pentagonal hind limb intermedium match those
of Mauisaurus haasti (Welles & Gregg, 1971) from the
upper Maastrichtian of New Zealand. In Styxosaurus
snowi (Carpenter, 1999) the posterior intermedium is
also pentagonal, but the anterior, though hexagonal as
in MML-PV4, has parallel sides, while the hexagon of
the Patagonian specimen is irregular (Fig. 4C), as shown
in the description above.

Welles & Gregg (1971) referred several New Zealand
specimens to Mauisaurus on the basis of very incomplete
material. Wiffen & Moisley (1986) described and
referred materials to Mauisaurus haasti based on some
diagnostic characters of this species, among them, a
central pit on the articular face of the dorsal vertebrae
centrum. A similar structure may be observed in speci-
mens from Seymour Island, Antarctic Peninsula, related
to Mauisaurus (Fostowicz-Frelik & Gazdzicki, 2001).
This pit is not found in the Patagonian specimens.

In MML-PV4, the contact between the intermedium
and the radius is less than with the ulna, unlike other
elasmosaurids such as the Jurassic species Muraeno-
saurus beloclis (Brown, 1981, p. 293), and Cretaceous

forms such as Styxosaurus snowi (=Alzadasaurus
pembertoni Welles, 1962, fig. 15; Welles & Bump, 1949,
fig. 5a), Alzadasaurus colombiensis (Welles, 1962, fig. 6),
A. riggsi (Welles, 1962, fig. 10), Morenosaurus stocki
(Welles, 1962, fig. 22) and Aristonectes parvidens
(Cabrera, 1941, fig. 6). In this sense the metapodials of
MML-PV4 are most similar to those of cf. ‘Cimolio-
saurus’ andium (Broili, 1930, fig. 1). The ulnare has a
wide articulation surface for the pisciform, similar in
extension to that of cf. ‘Cimoliosaurus’ andium (Broili,
1930, fig. 1) and Styxosaurus snowi (=Alzadasaurus
pembertoni Welles, 1962, fig. 15). This facet is less well
developed in other elasmosaurs (Aphrosaurus furlongi,
Welles, 1962, fig. 18; Alzadasaurus riggsi, Welles, 1962,
fig. 10; Morenosaurus stocki Welles, 1962, fig. 22) or
almost absent (Aristonectes parvidens, Cabrera, 1941,
fig. 6). Another difference from the Patagonian species
is that in Aristonectes parvidens the distal facets of
the ulnare for carpals 4 and 5 are equal, whereas in
MML-PV4 the facet for the carpal 4 is somewhat larger
than that for carpal 5.

So far there is no definitive definition of this taxon;
consequently MML-PV3 and MML-PV4 are referred to
cf. Mauisaurs sp. Broili (1930), referred a paddle found
in the Quiriquina Formation, (upper Maastrichtian;
Stinnesbeck, 1986) of central-southern Chile to cf.
‘Cimoliosaurus’ andium. From the new evidence reported
in this paper the anterior paddle illustrated by Broili
(1930), fig. 1) appears to be very similar to that of
MML-PV4 and the Central 4 (C3 of Broili) is wrongly
orientated. When the location of this element is cor-
rected, both paddles are similar, and consequently the
elasmosaurid from Quiriquina is also referred to cf.
Mauisaurus sp.

Chatterjee & Small (1989) briefly described several
remains of the Elasmosauridae from the uppermost
section of the López de Bertodano Formation, close
to the Cretaceous/Paleogene boundary, on northern
Seymour Island (northeastern Antarctic Peninsula).
The specimen TTU-P 9217 was identified as a posterior
paddle. However, the hexagonal-shaped intermedium
suggests that it is an anterior paddle. Likewise, the
humerus of this specimen seems longer and more
slender because it is reconstructed from two pieces.
When these fragments are put together, the humerus is
identical in shape and proportions to that of MML-
PV4. In addition, MML-PV4 and TTU-P 9217 are
similar in other ways, namely in the shape of ulna and
radius, the hexagonal intermedium with irregular
margins, and the general architecture of the paddle.
Because of this, TTU-P 9217 is also referred to cf.
Mauisaurus sp. Coincidentally, when referring to the
dorsal vertebrae of another specimen (TTU-P 9221),
Chatterjee & Small (1989) pointed out that they show
similar features to those of Mauisaurus (Wiffen &
Moisley, 1986).

Z. Gasparini et al. / Cretaceous Research 24 (2003) 157–170 163

3.2. Taxon 2

Tuarangisaurus? Wiffen & Moisley 1986

Tuarangisaurus? cabazai sp. nov.
Figs. 5–7

Derivation of name. The species is dedicated to
Mr Héctor Cabaza, who has discovered numerous Cre-
taceous animals and plants in Rio Negro Province and
promoted the foundation of the Museo Municipal de
Lamarque.

Holotype. MML-PV5. An incomplete specimen with-
out skull and neck, with 17 dorsal vertebrae, 30 caudals,
ribs and gastralia, incomplete anterior and posterior
limbs, left coracoid and fragments of the right scapula,
complete ischium and pubis.

Locality and horizon. Locality C (39(50#45$S,
66(40#40$W). Upper part of the Jagüel Formation
(upper Maastrichtian) (Figs. 1 and 2).

Diagnosis. Elasmosaur with thick postcranial ele-
ments and rounded external. Relatively high and short
vertebral centra, with low and thick neural spines, and
short prezygapophyses. Coracoid with robust posterior
process. Ischium short and narrow.

Description
Dorsal vertebrae (Fig. 5A–C). MML-PV3 has 17

dorsal centra. They are short and wide (length approxi-
mately 60% of the height). Measurements of one of the
vertebrae (Fig. 5A–C) are: length 31 mm; height 51 mm;
width 69 mm. Most vertebrae show a central depression
on the anterior and posterior sides of the body. In every
dorsal vertebra the neural arch is not fused, suggesting
that the specimen may be a subadult (Brown, 1981). The

Fig. 5. Tuarangisaurus? cabazai sp. nov. MML-PV5, holotype, axial
skeleton. Dorsal centrum in dorsal (A), anterior, with the articulated
neural arch (B) and lateral (C) views; sacral centrum in anterior (D)
and lateral (E) views; caudal centrum in anterior (F), lateral (G) and
ventral (H) views. naf, facets for the neural arch; ns, neural spine; prz,
prezigapophyses; srf, facet for the sacral rib; tp, transverse process.
Scale bars represent 50 mm.

Fig. 6. Tuarangisaurus? cabazai sp. nov. MML-PV5, holotype,
appendicular skeleton. Scapula fragment in lateral (A) and proximal
(B) views; left coracoid in dorsal (C) and medial (D) views; E, left ilium
in dorsal view; F, left pubis in dorsal view; G, left ischium in dorsal
view. ac, acetabulum; icv, intercoracoid vacuity; pif, pubo-ischiatic
fenestra; scm, area for the subcoracoid muscle. Scale bar represents
50 mm.

Fig. 7. Tuarangisaurus? cabazai sp. nov. MML-PV5, holotype,
appendicular skeleton. Propodials. Humerus in proximal (A), lateral
(B) and distal (C) views; femur in proximal (D), lateral (E) and distal
(F) views. Scale bar represents 50 mm.

Z. Gasparini et al. / Cretaceous Research 24 (2003) 157–170164

articulation surface of the neural arch has a central
subquadrangular scar that occupies the entire body
length. Coincidentally, the articular faces of the neural
arch are subquadrate. The neural spines are thick, very
low, with the distal end markedly convex (Fig. 5B). The
prezygapophyses are extremely short. The transverse
processes are very short, subcylindrical, without an
expanded distal end.

Sacral vertebrae (Fig. 5D, E). Only one centrum of
sacral vertebra has been recovered. It is short, and
quadrangular in anterior view. The lateral side of the
centrum shows depressions for ribs, which do not
occupy the whole length of the body and are higher than
long.

Caudal vertebrae (Fig. 5F–H). The 30 caudal ver-
tebrae recovered are also short. There are two foramina
on the flat ventral side, and only one on the floor of the
neural canal. The facets for the hemapophyses are
slightly marked and in some they are not evident.

Pectoral girdle (Fig. 6). The left coracoid is complete,
and notably robust (Fig. 6 C, D). The medial lamina,
through out the right coracoid contacts, is very thick
anteriorly, while it narrows distally or posteriorly.
No antero-medial process suggests the existence of a
pectoral bar in the coracoid.

The postero-medial margin of the coracoid is little
expanded and suggests that the intercoracoid vacuity
was wide posteriorly. On the visceral side of the coracoid
of MML-PV5 there is a slight prominence dividing two
slightly concave surfaces. The smaller posterior one is
interpreted as the area for the insertion of the sub-
coracoid muscle (Fig. 6C, D). The area of the glenoid
cavity of the scapula has been preserved (Fig. 6A, B).

Pelvic girdle (Fig. 6E–G). As for the coracoid, the
elements of the pelvic girdle are notably thick. In this
sense, they are very different from other Patagonian
elasmosaurids (Gasparini & Salgado, 2000). The ischium
is short and the pubis is subcircular, with the anterior
margin strongly convex. The acetabular articulation is
very robust and, unlike in MCS-4, there is no pelvic bar.
The pubo-ischiatic fenestra is transversely elongate. The
different pelvic bones do not seem to be fused. The
pubes are closely comparable to those of NZGS, CD429
(aff. Tuarangisaurus keyesi) (Wiffen & Moisley, 1986,
fig. 30).

The ilia are short, with very thick acetabular portions,
even thicker than in MML-PV4 (Fig. 6E), and MCS-4
and MLP 71-II-13-1 (Gasparini & Goñi, 1985, pl. II, 1).
The dorsal end of the ilium is slightly compressed, and
the three planes observed in MML-PV4 (referred to
cf. Mauisaurus sp.), are not evident (Fig. 6E).

Paddles (Fig. 7). The humeri and femora are short
and very robust. The humerus is slightly longer
(193 mm) than the femur (186 mm). The condyle and the
tuberosity are not clearly distinguishable at the proximal
end of the humerus. Likewise, the condyle cannot be

differentiated from the trochanter in the femur. In both
the humerus and the femur the distal sector is very thick
and lacks defined articulation faces to contact with the
epipodials.

The mesopodials include subcircular and oval ele-
ments of the fore and hind paddles (Fig. 7G). These
series are incomplete, and the lack of articular faces
render it impossible to determine their homology and
topological location.

The phalanges are very short, spool like and subcir-
cular in section, and the central area is little compressed,
which makes them different from MML-PV3 and
MML- PV4 referred to cf. Mauisaurus sp. The phalanges
of these latter forms are elongate, compressed, and with
strangled central and expanded distal areas.

The ribs and gastralia are represented by numerous
fragments. They are robust and circular to subcircular in
section.

Discussion
Some authors (e.g., Brown, 1981) have stated that

certain characters depend on whether or not the speci-
men is juvenile. Among these are short and flat vertebral
bodies, unfused neural arches, short neural spines,
absence of a pectoral bar, rounded anterior margin of
the pubis, absence or little development of a pelvic
bar, tuberosity/trochanter not separated by a condylar
isthmus, and poor definition of the articular facets of the
propodials and mesopodials. MML-PV5 shows some of
these characters, consequently one could presume that
several of the characters interpreted as diagnostic of
Tuarangisaurus? cabazai may be owing to its juvenile
condition. However, to determine the juvenile condition
of a particular specimen, an ontogenetic series of the
species must be known, and in the case of plesiosaurs,
immature specimens of known taxa are very scarce
(Carpenter, 1999).

Comparison of different developmental stages among
taxa may lead to mistakes as these characters do not
vary in the same way during the ontogeny of different
species. For example, the pectoral bar is absent (or
incompletely formed) in juvenile specimens of some
plesiosaurs that display it in adult stages (Carpenter,
1999), but most plesiosaurs definitely lack bars. Like-
wise, juveniles of different taxa vary significantly from
each other. For instance, juvenile specimens of Aphro-
saurus furlongi Welles, which are of similar size to
juvenile specimens of Fresnosaurus drescheri Welles,
1943, display very different propodials. The first taxon
has well-defined articular faces and coracoid with an
anterior projection, and a posterior process that is
somewhat expanded (Welles, 1952, fig. 23).

In MML-PV5, low neural spines or short vertebral
centra are not necessarily a consequence of its juvenile
condition. The robustness of the whole postcranium,
and the flange on the visceral side of the coracoid for the

Z. Gasparini et al. / Cretaceous Research 24 (2003) 157–170 165

insertion of strong subcoracoid muscles suggest that
MML-PV5 had passed the juvenile stage and was
subadult or a young adult.

It is unlikely that such marked differences as those
observed between MML-PV5 and MML-PV3 and
MML-PV4, will have decreased during ontogeny. In the
same way, the Elasmosauridae found on Seymour Island
(Chatterjee & Small, 1989), undoubtedly a juvenile,
shows strong differences from MML-PV5, being closer
to adult forms of other elasmosaurids. These arguments
undoubtedly suggest that MML-PV5 is not a juvenile of
cf. Mauisaurus sp. Coincidentally, Wiffen & Moisley
(1986), p. 221) did not find similarities between the same
elements of the juvenile they referred to aff. Tuarangi-
saurus keyesi (NZGS, CD429), and juvenile forms of
Mauisaurus haasti. Finally, MUCPv-131 from north-
western Rı́o Negro Province (Gasparini et al., 2001),
here considered as Tuarangisaurus sp., has vertebrae,
mesopodials and phalanges that are identical to those
of MML-PV5, but larger. This supports the hypoth-
esis that some characters, supposedly indicative of
immaturity, do not vary significantly during ontogeny
and are, therefore, taxonomically useful.

When MML-PV5 is compared with polycotilids, they
differ because the coracoids do not form an intercora-
coid vacuity and ischia are strongly elongate backwards
(Carpenter, 1996). Although the ischia of very juvenile
polycotilids are short as in elasmosaurids, the coracoids
of MML-PV5 are clearly different, since in both
Dolichorhynchops Williston, 1903 and Trinacromerum
Cragin, 1888, even in juveniles, a wide contact between
coracoids does not leave a vacuity between them
(Carpenter, 1996, fig. 3). They also differ because the
propodials of MML-PV5 are thick, with as unexpanded
distal margin, while those of polycotilids are thin and
distally expanded.

Despite the fact that MML-PV5 lacks a skull and
cervical vertebrae, it is provisionally referred to the
Elasmosauridae because of the short ischium and the
morphology of the coracoid. The general anatomy of
MML-PV5 coincides with that of the specimens referred
by Wiffen & Moisley (1986) to cf. T. keyesi (NZGS,
CD427), aff. T. keyesi (NZGS, CD428), aff. Tuarangi-
saurus keyesi (NZGS, CD429), and Plesiosaurus austra-
lis (Owen 1862) (Hector, 1874, pl. 27, fig. A), from the
upper Maastrichtian of New Zealand. Welles & Gregg
(1971) considered the last of those to be a juvenile
Mauisaurus haasti. Although we agree with Welles &
Gregg (1971) that it is not Plesiosaurus, a genus from the
Lower Jurassic (Storrs, 1997), it is unlikely to be a
juvenile specimen of Mauisaurus because the characters
of this latter genus are also observed in adults of
MUCPv-131. Tuarangisaurus is defined on the skull and
cervical vertebrae; consequently Wiffen & Moisley
(1986) tentatively refered other incomplete specimens to
this genus. We follow this criterion here, differentiating

the new species Tuarangisaurus? cabazai on the basis of
the shorter neural spines and the somewhat elongate
ischia compared to the specimens referred to the type
species.

4. Elasmosaurids from southern Gondwana

Until a few years ago, the record of marine reptiles
from the Upper Cretaceous of Patagonia was scarce,
and generally not determinable below family rank
(Gasparini et al., 2001). Currently, it is known that the
marine herpetofauna was diverse and, although domi-
nated by elasmosaurids (Aristonectes, cf. Mauisaurus sp.,
Tuarangisaurus? cabazai, and other indeterminate taxa),
there were also polycotilids, including the longirostran
Sulcusuchus (Gasparini & de la Fuente, 2000), and
mosasaurine mosasaurs (Gasparini et al., 2001).

Plesiosauroids, and particularly elasmosaurids, were
slow swimmers (compared with pliosaurs) (Massare,
1997). This is compatible with a recent study of their
ecomorphology in which it is stated that the long-necked
taxa were generally specialized for efficiency and cruising
(O’Keefe, 2001), and also with the hypothesis that some
taxa may have had a very wide geographic distribution.
It is noteworthy that fragmentary and isolated remains
(teeth or postcrania) of marine reptiles from the
Upper Cretaceous of southern Gondwana are frequently
assigned to taxa from the Northern Hemisphere.
However, more complete skeletons demonstrate that,
although they are referable to families recorded in
Laurasian seas, there were differences at generic or
specific level. This is the case for the polycotilid
Sulcusuchus erraini of Patagonia, the elasmosaurid
Aristonectes (=Morturneria) of Patagonia, Chile, and the
Antarctic Peninsula (Gasparini et al., in press), and a
new tylosaurine mosasaur (Novas et al., 2002) of Ross
Island, northeastern Antarctic Peninsula.

The distribution of Patagonian plesiosaurs, now
including cf. Mauisaurus sp., Tuarangisaurus? sp., and
Tuarangisaurus? cabazai, supports the hypothesis of
Novas et al. (2002) in suggesting a more marked
taxonomic differentiation between marine reptiles of the
Northern and Southern Hemispheres by the end of the
Cretaceous Period. The Gondwanan distribution of
some taxa is more evident when considered in relation
to Southern Gondwana (Fig. 8). The elasmosaurid
Morturneria seymouriensis Chatterjee & Small (1989)
from the Campanian–Maastrichtian of Seymour Island
is a juvenile of Aristonectes parvidens Cabrera
(Gasparini et al., in press); Mauisaurus of the upper
Maastrichtian of New Zealand shows affinities with
cf. Mauisaurus from the upper Maastrichtian of Ross
Island and probably the lower Maastrichtian from
Seymour Island (Fostowicz-Frelik & Gazdzicki, 2001),
in addition to cf. Mauisaurus sp. from the lower
Maastrichtian of Quiriquina (Chile) and cf. Mauisaurus

Z. Gasparini et al. / Cretaceous Research 24 (2003) 157–170166

sp. from northern Patagonia (MML-PV3 and MML-
PV4) (this paper). Moreover, there are remarkable simi-
larities between several specimens assigned to aff.
Tuarangisaurus keyesi and cf. T. keyesi from the upper
Maastrichtian of New Zealand with Tuarangisaurus? sp.
from the Campanian?–Maastrichtian from northwestern
Patagonia (MUCPv-131), and Tuarangisaurus? cabazai
(MML-PV5), from the uppermost Maastrichtian of
north-central Patagonia.

The distribution of other elements of the biota from
Patagonia and the Antarctic Peninsula, such as molluscs
and crustaceans, changed both in time (Campanian–late
Maastrichtian) and latitudinally (northern Patagonia–
Antarctic Peninsula). Molluscs from the Maastrichtian–
Danian in northern Patagonia show a significant degree
of endemism at species level, but generically they show
(according to Camacho, 1992) Weddellian and Tethyian
associations, with northern Patagonia being a tran-
sitional biogeographic area. This agrees with the distri-
bution of foraminifers, for which Austral, Transitional
and Tethyian provinces have been recognized pre-
viously (Sliter, 1977; Huber, 1990, 1991). The Malvinas

(Falklands) Plateau may have been the boundary
between the Austral and Transitional provinces during
the Maastrichtian (Ciesielski et al., 1977; Sliter, 1977;
Huber, 1990; Malumián & Náñez, 1996).

According to Casadı́o et al. (1998) and Feldmann
et al. (1997), the southward displacement of Tethyian
organisms between the Maastrichtian and Danian
may have resulted from a counter-clockwise oceanic
circulation pattern in the South Atlantic.

5. Conclusions

One of the most significant of the geodynamic
phenomena that occurred in southern South America
between the Campanian and Danian was the relative
sea-level change related to subsidence of the Atlantic
margin, which led to major flooding. During the period
of the Cretaceous/Paleogene transition, the southern tip
of South America was an archipelago in which the
central part of the Somuncurá and Desado massifs
remained emerged (Malumián, 1999). The marine trans-
gression is recorded in sediments of the Malargüe

Fig. 8. Upper Cretaceous elasmosaurid plesiosaurs in the South Gondwana. 1, Mauisaurus haasti; 2, cf. Mauisaurus sp.; 3, Tuarangisaurus keyesi;
4, cf. Tuarangisaurus keyesi; 5, Tuarangisaurus? cabazai sp. nov.; 6, Aristonectes (see Wiffen & Moisley, 1986; Chatterjee & Small, 1989; Gasparini
et al. (in press); Base map modified from Smith et al., 1981 and Scotese et al., 1988).

Z. Gasparini et al. / Cretaceous Research 24 (2003) 157–170 167

Group, which are widely exposed in northern Patagonia.
In the centre of the Rı́o Negro Province, at the top of
the Jagüel Formation, three long-necked plesiosaurs
(Elasmosauridae) were found, one of them (MML-PV4)
only at 0.3 m below to the Cretaceous/Paleogene
boundary. This latter specimen, referred to cf.
Mauisaurus sp., is the youngest record of a Mesozoic
reptile in Patagonia.

The new specimens are referred to cf. Mauisaurus sp.
(MML-PV3 and MML-PV4) and to the new species
Tuarangisaurus? cabazai (MML-PV5). Some of the char-
acters observed in the postcranium of MML-PV5, such
as the short neural spines, propodials and meso-
podials with poorly defined articular facets, and the
absence of pelvic and pectoral bars, were previously
thought to be related to a juvenile condition. However,
after an examination of all of the evidence, these are here
considered to be taxonomically valid.

The Upper Cretaceous elasmosaurids in Patagonia
are closely related to those of the Maastrichtian of
central Chile, the northeastern island of the Antarctic
Peninsula and New Zealand, which reinforces the
hypothesis of a southern Gondwanan distribution for
some pelagic reptiles (Novas et al., 2002).

Acknowledgements

We thank Héctor Cabaza, Daniel Cabazza, the
staff of the Museo Municipal de Lamarque and the
Municipality of Lamarque for technical and logistical
support. We are grateful for the constructive comments
of the two referees Dr David Batten (University of
Whales) and Dr Leslie Noe (University of Cambridge).
The study was in part possible thanks to funds received
from the Consejo Nacional de Investigaciones
Cientı́ficas y Técnicas of Argentina (CONICET)-PIP
062-98. The English grammar was corrected by Cecilia
Deschamps (Museo de la Plata), Dr R. Feldmann (Kent
State University) and David Batten.

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Maastrichtian plesiosaurs from northern Patagonia
Introduction
Geological setting
Systematic Paleontology
Taxon 1
Taxon 2

Elasmosaurids from southern Gondwana
Conclusions
Acknowledgements
References