Cretaceous terrestrial beds from the Neuquén Basin (Argentina) and their tetrapod assemblages

Abstract

The Cretaceous terrestrial strata of the Neuquén Basin (northern Patagonia, Argentina) are described together with their tetrapod records. Six local tetrapod assemblages are identified: Amargan (Barremian–Early Aptian), Lohancuran (Late Aptian–Albian), Limayan (Cenomanian–Early Turonian), Neuquenian (Late Turonian–Coniacian), Coloradoan (Santonian–Early Campanian) and Allenian [Late Campanian–Early Maastrichtian (= Alamitense = Alamitian SALMA)]. The last of these includes records from north-eastern Patagonia.

Full text

Cretaceous terrestrial beds from the Neuque
´n Basin
(Argentina) and their tetrapod assemblages
He
´ctor A. Leanza
a,
)
, Sebastia
´n Apesteguı
´a
b
, Fernando E. Novas
c
,
Marcelo S. de la Fuente
d
a
SEGEMAR & CONICET, Av. Julio A. Roca 651, 10(piso, 1322 Buenos Aires, Argentina
b
Seccio
´n de Paleontologı´a de Vertebrados, Museo Argentino de Ciencias Naturales, Av. A
´ngel Gallardo 470,
1405 Buenos Aires, Argentina
c
Laboratorio de Anatomı´a Comparada, CONICET, Museo Argentino de Ciencias Naturales, Av. A
´ngel Gallardo 470,
1405 Buenos Aires, Argentina
d
Departamento de Paleontologı´a, CONICET, Museo Municipal de Historia Natural de San Rafael,
Parque Mariano Moreno s/N(. 5600, San Rafael, Argentina
Accepted 3 October 2003
Abstract
The Cretaceous terrestrial strata of the Neuque
´n Basin (northern Patagonia, Argentina) are described together with their
tetrapod records. Six local tetrapod assemblages are identified: Amargan (BarremianeEarly Aptian), Lohancuran (Late
AptianeAlbian), Limayan (CenomanianeEarly Turonian), Neuquenian (Late TuronianeConiacian), Coloradoan (Santoniane
Early Campanian) and Allenian [Late CampanianeEarly Maastrichtian (ZAlamitense ZAlamitian SALMA)]. The last of these
includes records from north-eastern Patagonia.
Ó2004 Elsevier Ltd. All rights reserved.
Keywords: Argentina; Neuque
´n Basin; Tetrapods; Biostratigraphy; Terrestrial beds; Cretaceous
1. Introduction
The Neuque
´n Basin is perhaps the best-known
sedimentary basin of Patagonia. Its Cretaceous terres-
trial beds are some of the most fossiliferous and
stratigraphically complete worldwide. It has received
special attention since the beginning of the 20th century
due to coal and oil prospecting, as well as for providing
the first dinosaur remains from South America. This
attention has continued increasingly in recent decades
because of the abundance of Mesozoic vertebrates.
The basin is well developed in west-central Argentina
and eastern Chile between 34(and 41(S. It is exposed
in the Argentine territory in the provinces of Neuque
´n
(from which it takes the name), Mendoza, Rı
´o Negro,
and La Pampa (see Fig. 1). Between 34(and 37(S, it is
restricted to the cordilleran belt as a narrow NeS-
elongated strip. Southwards from 37(S it broadens
eastwards into an extra-Andean domain where it is
known as the Neuque
´n Embayment (see Digregorio,
1972; Digregorio and Uliana, 1980; Legarreta and
Uliana, 1991; Gulisano and Gutie
´rrez Pleimling, 1995).
A narrow belt, however, extends northwards along the
axis of the Andean Cordillera up to 31(S (San Juan
Province), where it is called the Aconcagua Basin.
The Cretaceous continental beds in this region lie
between marine beds of the Agrio and Jagu
¨el forma-
tions, forming part of the Mendoza and Malargu
¨e
Groups, respectively (see Fig. 2). The lithostratigraphic
units of this terrestrial interval are known, from older to
younger, as the La Amarga and Lohan Cura forma-
tions, the Neuque
´n Group, and the Allen Formation.
In recent years, the rate of discoveries of tetrapods in
these units has improved. Furthermore, geological
mapping carried out by the Geological Survey of
Argentina between 39(e40(Sand69(e66(30#W
www.elsevier.com/locate/jnlabr/ycres
Cretaceous Research 25 (2004) 61e87
)Corresponding author.
E-mail address: hleanz@secind.mecon.gov.ar (H.A. Leanza).
0195-6671/$ - see front matter Ó2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.cretres.2003.10.005

(Neuque
´n and Rı
´o Negro provinces) has allowed the
clarification of the stratigraphic position and regional
distribution of several Cretaceous terrestrial units
(Leanza and Hugo, 1997; Hugo and Leanza, 2001a,b).
At present, magnetic polarity information is only
available for the Anacleto Formation (Dingus et al.,
2000). Radioisotopic dating is still lacking for the
Neuque
´n Group, although we are undertaking some
studies. The estimated ages of each unit have been
mainly obtained from the ages of the superimposed
intervals limited by regional unconformities as a result
of the tectonosedimentary evolution of the Neuque
´n
Basin (Vergani et al., 1995).
The aim of this paper is to provide a brief description
of the terrestrial red-bed units exposed in the southern
Neuque
´n Basin, pointing out their main discontinuities,
areal distribution, age, and tetrapod fauna. As a result,
a more precise chronostratigraphic framework of the
tetrapod-bearing beds is proposed and six local tetrapod
assemblages are defined.
Fig. 1. Distribution of Cretaceous continental strata in west-central Argentina.
62 H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

2. Materials and methods
The absolute ages followed in the present paper are
those presented at the 31st International Geological
Congress held in Brazil by the IUGS (see Remane,
2000), in agreement with the proposal of the Cretace-
ous Subcommission of the International Commission
on Stratigraphy (ICS). The Cretaceous terrestrial
Fig. 2. Cretaceous stratigraphy of southern Neuque
´n Basin and the proposed tetrapod assemblages; absolute ages from Remane (2000).
63H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

stratigraphic chart (see Fig. 2) follows that given by
Leanza (1999) and Leanza and Hugo (2001).
The term ‘assemblage’ used in this paper refers to
tetrapod taxa discovered in the same lithostratigraphic
unit in a restricted area. Therefore, it is worth noting that
our assemblages do not refer to palaeocommunities of
tetrapods that lived together in a certain terrestrial
ecosystem. Moreover, assemblages are not considered
‘vertebrate ages’. Because of possible local variations, this
paper is restricted to the relatively well-known southern
part of the Neuque
´n Basin. In order to characterize these
assemblages we use information obtained mainly from
dinosaurs, crocodyliforms and turtles, because of the still
poor record of other taxa such as mammals and frogs.
It is not our aim to make a comprehensive phyloge-
netic review of any cited clade. However, it is necessary
to specify the classificatory schemes taken into consid-
eration for each faunal clade.
Reptilia
CheloniadPodocnemidoidea (as in Lapparent de Broin,
2000).
CheloniadChelidae (as in Gaffney, 1977; Gaffney and
Meylan, 1988; Broin and de la Fuente, 1993; Lapparent
de Broin and de la Fuente, 2001).
LepidosauriadSphenodontia (as in Reynoso, 1998).
LepidosauriadSquamata (as in Reynoso, 1998).
LepidosauriadSquamatadSerpentes (as in Rieppel
et al., 2002).
Archosauria
CrocodylomorphadMesoeucrocodyliadNotosuchia
(as in Pol and Norell, in press).
DinosauriadOrnithischiadEurypodadStegosauria
(as in Sereno, 1999).
DinosauriadOrnithischiadEurypodad
Ankylosauria (as in Sereno, 1999).
DinosauriadOrnithischiadOrnithopodad
Euiguanodontia (as in Coria and Calvo, 2002).
DinosauriadSaurischiadSauropodad
Diplodocoidea (as in Wilson, 2002).
DinosauriadSaurischiadSauropodadTitanosauria
(as in Salgado, 2003).
DinosauriadSaurischiadTheropodad
Abelisauroidea (as in Coria et al., 2002).
DinosauriadSaurischiadTheropodad
Neotetanurae (as in Sereno, 1999).
SynapsidadMammaliadCladotheria (as in Portero,
1981).
In order to analyze the faunal assemblages, we use
the names in the most accurate way we can. This way,
because Madtsoiidae is a widely used name we keep it
here but it is expressed as ‘‘Madtsoiidae’’, the quotes
meaning that we are referring to a paraphyletic assem-
blage of Gondwanan basal alethinophidian snakes
(Rieppel et al., 2002), that needs further revision.
Titanosaurs have been treated recently in several
publications. Some of these (e.g., Sanz et al., 1999;
Curry Rogers and Forster, 2001; Wilson, 2002) avoided
the use of the name Titanosauridae because of the
nomen dubium status of Titanosaurus indicus Lydekker,
1877. However, there are no comparable names in the
literature because those recently created are equivalent
to diverse titanosaur ingroup clades including a different
taxonomic content of titanosaurids. This way, we follow
Salgado et al. (1997) and Salgado (2003) in the use of
the node-based name Titanosauridae (Epachthosaurus,
Saltasaurus, their most recent common ancestor and all
of its descendants), meaning basically, titanosaurs with
procoelous caudal vertebrae.
We consider that the existence of gigantic or very
small dinosaurs in certain strata and not in others is
significant for the purposes of this paper. Saltasaurine
titanosaurs being one order of magnitude less than
a basal titanosaurid such as Argentinosaurus,we
consider the term ‘small’ for a horse-sized sauropod
(e.g., Neuquensaurus), ‘medium’ for sauropods around
10e15 m in length (e.g., Andesaurus) and ‘large’ for
sauropods that were around 20 m in length (e.g.,
Agustinia). The term ‘gigantic’ is only used for special
cases like Argentinosaurus, with a total estimated length
surpassing 35 m. In the case of theropods, the term small
refers to sizes less than 3 m in length, medium to sizes
around 4e8 m in length, and large to sizes more than
9 m in length.
3. The Cretaceous terrestrial beds and
their tetrapod records
The oldest red-bed unit in the Cretaceous of the
southern Neuque
´n Basin belongs to the Bajada Colorada
Formation, which in turn is unconformably overlain by
the marine Agrio Formation through the Catanlilican
unconformity. The Initial Miranican unconformity is
located between the transition zone (gypsum evaporites
and clays) of the Agrio Formation and the fluvial conglo-
merates of the La Amarga Formation. The Lohan Cura
Formation overlies the La Amarga Formation through
the Middle Miranican unconformity. The Neuque
´n
and Malargu
¨e groups, both forming part of the Rio-
grandican cycle of Groeber (1946), constitute the Upper
Cretaceous strata of the Neuque
´n Basin. They are
separated from the previous strata by the Main Mirani-
can unconformity.
The Neuque
´n Group was laid down during nearly
20 myr from the Cenomanian through to the Early
Campanian. It is composed of a series of wholly
continental red beds consisting of conglomerates, sand-
stones and claystones corresponding to fluvial, alluvial
and playa lake environments. They are generally
arranged in recurrent fining-upward sequences. The
64 H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

Neuque
´n Group comprises the Candeleros, Huincul and
Cerro Lisandro formations (Rı
´o Limay Subgroup),
Portezuelo and Plottier formations (Rı
´o Neuque
´n Sub-
group) and Bajo de la Carpa and Anacleto formations
(Rı
´o Colorado Subgroup).
Such continental sedimentary conditions together
with a large supply of coarse clastics from the west
provide evidence of the final isolation of the basin from
the Pacific Ocean. The Huantraiquican unconformity
separates the Neuque
´n Group from the Malargu
¨e
Group made up of the Allen, Jagu
¨el and Roca
formations. The continental units lying between the
Agrio and Jagu
¨el formations will be described below.
3.1. La Amarga Formation
Musacchio (1970) established this terrestrial unit. Its
type locality is the La Amarga Creek and the nearby
northern slope of the China Muerta Hill. It unconform-
ably overlies the transition zone of the marine Agrio
Formation and is overlain in the same way by the
continental Lohan Cura Formation (Fig. 3). Based on
basin analysis, stratigraphical relationships and tecto-
nosedimentary aspects, this unit may be regarded as
BarremianeEarly Aptian in age (Leanza and Hugo,
1995, 1997). The total thickness of the La Amarga
Formation is approximately 159 m. It is usually divided
into three subunits (see Fig. 4), which from base to top
are: the Puesto Antigual, the Ban
˜ados de Caichigu
¨e, and
the Piedra Parada members (Leanza and Hugo, 1995).
The Puesto Antigual Member (28.9 m) is composed of
fluvial channel sands of braided rivers with well-
developed palaeosol tops. The Ban
˜ados de Caichigu
¨e
Member (20.9 m) is composed of white to yellowish
lacustrine limestones alternating with black shales and
greenish siltstones, from which rich ostracod and
palynomorph associations were reported (Musacchio,
1970; Volkheimer, 1978). The Piedra Parada Member
(109.4 m) constitutes a thick succession of light brown
and reddish, fine- to medium-grained sandstones alter-
nating with pink, reddish and brownegreenish silt-
stones. The palaeoenvironment corresponds to alluvial
systems with well-developed fluvial channels alternating
with some swamp lenses and palaeosol tops.
3.1.1. Tetrapod content
From the Puesto Antigual Member of La Amarga
Formation, the ‘spiny’ dicraeosaurid sauropod Amarga-
saurus cazaui (Salgado and Bonaparte, 1991) was found.
This is characterized by a remarkable enlargement of the
bifid neural spines on its cervical and dorsal vertebrae.
Its most closely related species comes from the Late
Jurassic of Tanzania (Janansch, 1929; Salgado and
Bonaparte, 1991) and Chubut Province (P. Puerta, pers.
comm. 2002). Basal diplodocoid and basal titanosauri-
form teeth also come from the same quarry (pers. obs.).
Fig. 3. Stratigraphic column of the La Amarga Formation.
65H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

The Puesto Antigual Member has also yielded the
abelisauroid theropod Ligabueino andesi (Bonaparte,
1996); fragmentary remains of the first known South
American stegosaur (Bonaparte, 1996); the tremato-
champsid crocodyliform Amargasuchus minor (Chiappe,
1988) and several specimens of the cladotherian
mammal Vincelestes neuquenianus (Bonaparte, 1986b;
see also Rougier, 1993), the only mammal known for the
entire Lower Cretaceous of South America.
3.2. Lohan Cura Formation
This unit was established by Leanza and Hugo (1995)
for the continental deposits which unconformably
overlie the La Amarga Formation. It is overlain by the
Candeleros Formation (Fig. 4). The Lohan Cura
Formation is widespread in the southern portion of
the Neuque
´n Basin, extending from national road 40
along the China Muerta Creek up to the vicinity of
the Limay River. Apart from the La Amarga Forma-
tion, the Lohan Cura Formation overlies the Bajada
Colorada and Agrio formations through the Middle
Miranican unconformity. Based on tectonosedimentary
aspects and field relationships, the Lohan Cura Forma-
tion can be ascribed to the Late Aptian and Albian and
correlated in the central part of the basin with the
Rayoso Formation (Leanza, 1999, 2003).
Some years ago this unit was mistaken for the Bajada
Colorada Formation, which indeed belongs to the
Mendoza Group (see above). Leanza and Hugo (1995)
divided the Lohan Cura Formation (177 m) into two
subunits (see Fig. 4): the Puesto Quiroga and the Cullı
´n
Grande members. The Puesto Quiroga Member (85 m)
begins with a well-lithified, brown-reddish, thinning-
upwards, polymictic conglomerate 4 m thick, followed
by an alternation of 24 m of red and red-brownish
conglomeratic sandstones and siltstones. Next 57 m of
redepurple and brownegreenish shales and some
intercalations of greyegreenish and light green siltstones
follows. The Cullı
´n Grande Member (92 m) shows
a remarkable development of fluvial channels with high
angle cross-stratification with reddish conglomeratic
sandstones in alternation with brownegreenish silt-
stones showing poor stratification. The general trend of
the sedimentation pattern is fining- and thinning-
upwards and for that reason the brown and light red
siltstones and claystones become dominant.
3.2.1. Tetrapod content
In the Cullı
´n Grande Member of the Lohan Cura
Formation, in the locality of Cerro Los Leones near
Picu´ n Leufu´ , Leanza and Hugo (1997) discovered a new
fossil site of reptile bones and reported this to J. F.
Bonaparte. This resulted in the description of the basal
titanosaur Agustinia ligabuei Bonaparte, 1999 and
a new, different titanosaur, the former at least displaying
Fig. 4. Stratigraphic column of the Lohan Cura Formation.
66 H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

notable dorsal osteoderms divided into two laminae,
each of which is 0.8 m in length (see Leanza, 1999).
Rebbachisaurid sauropods were recently collected from
the same unit and area (L. Salgado, pers. comm. 2003),
but in slightly older strata (J. Bonaparte, pers. comm.
2003). Additionally, from the Rayoso Formation, pre-
sumably the Rinco
´n Member (equivalent to the Lohan
Cura Formation), comes the rebbachisaurid sauropod
Rayososaurus agrioensis (Bonaparte, 1996). This taxon
extends the record of rebbachisaurids in Patagonia back
to the Aptian (Bonaparte, 1996) while the youngest
record is Late Cenomanian to Turonian (Salgado, in
press) or Campanian according to others (e.g., Jacobs
et al., 1993).
Turtle records in the Lohan Cura Formation include
two different species of Prochelidella (Lapparent de
Broin and de la Fuente, 1999, 2001). A short-necked
chelid turtle closely related to the genus Acanthochelys is
also present.
3.3. Neuque
´n Group
Red beds containing dinosaur bones have been
known since early 19th century in west-central Argenti-
na. For a long time, they were termed by Keidel (1917)
as ‘‘Dinosaurier schichten’’ (ZEstratos con Dinosaur-
ios) or ‘‘Formacio
´n del Neuque
´n’’ (Roll, 1941). Stip-
anicic et al. (1968) were the first authors to use the name
Neuque
´n Group for these strata, which are divided from
base to top into Rı
´o Limay, Rı
´o Neuque
´n and Rı
´o
Colorado subgroups (Cazau and Uliana, 1973). The
Neuque
´n Group was deposited in a north-northwest-
oriented basin nearly 800 km long and 200e350 km
wide, including the southern Mendoza and eastern
Neuque
´n regions. It was laid down between the
Cenomanian and Early Campanian, and thus represents
a total duration of nearly 24.9 myr. It comprises
conglomerates, sandstones, siltstones, claystones and
mudrocks (see Fig. 5) predominantly deposited under
alluvial processes.
Although several discontinuity-bounded beds are
scattered within the Neuque
´n Group as a result of
changes in the relative base level, variable sediment
supply and differential accommodation rates (Legarreta
and Uliana, 1998), none of them reached the status of
the main unconformities already referred to in the
Cretaceous strata of the Neuque
´n Basin (see Fig. 2).
Anomalous behaviour in mass and heat distribution
in the Earth’s mantle during the Early Cretaceous led to
abnormal activity in the South Atlantic and Pacific mid-
oceanic ridges. This led to a maximum spreading rate in
the oceanic floors (Larson and Pitman, 1972), favouring
the separation of the Gondwanan landmasses. The
convergence rate of the plates increased during the Late
Cretaceous, making the magmatic arc migrate eastward.
This led to a flexural subsidence which allowed the
alluvial deposition of the Neuque
´n Group (Legarreta
and Uliana, 1998). Another factor contributing to the
accumulation of these beds may have been the uplift of
Fig. 5. Generalized stratigraphic column of the Neuque
´n Group.
67H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

the west Patagonian orogenic mountain belt. The strong
deformation of strata on the eastern flank of the orogene
resulted in a thrust and fold belt whose tectonic load was
responsible for flexural subsidence. As a result, a fore-
land basin was developed allowing the accumulation of
the Neuque
´n Group (Ramos, 1988).
3.3.1. Rı´o Limay Subgroup
This stratigraphical unit was established by de
Ferrarı
´is (1968) and is composed of the Candeleros,
Huincul and Cerro Lisandro formations, with a thick-
ness of at least 350 m. On the basis of basin analysis, its
age can be regarded as Cenomanian to Early Turonian.
The Rı
´o Limay Subgroup is widespread in the southern
Neuque
´n Basin and extends from the national road 40
eastwards to the Santa Lucı
´a de El Cuy region, in
northwestern Rı
´o Negro Province.
Candeleros Formation
This constitutes the basal unit of the Neuque
´n Group
(Fig. 5) and was established by Keidel (in Wichmann,
1929), its type locality being Candeleros hill situated east
of Cerro Lotena in southern Neuque
´n. It was studied
regionally by many geologists including Roll (1939),
Herrero Ducloux (1946), Leanza and Hugo (1997) and
Hugo and Leanza (2001a) among others. Its maximum
thickness is nearly 300 m. It is essentially composed of
massive coarse- and medium-grained sandstones and
conglomerates, violet, purple, dark red and brownish in
colour, deposited in a fluvial environment under braided
and meandering regimes, as well as in aeolian conditions
(Spalletti and Gazzera, 1989). Sequences are arranged in
a thinning- and fining-upward pattern. Palaeosols are
frequent in some horizons, whereas dark-brownish
siltstones and claystones are present in thin beds, some
representing swamp conditions (Cazau and Uliana,
1973; Leanza and Hugo, 1997; Hugo and Leanza,
2001a). The age of the Candeleros Formation may be
regarded as Early Cenomanian.
Tetrapod content. This unit has a remarkable faunal
record, especially with respect to dinosaurs. Among
sauropods, the taxa present include the titanosaur
Andesaurus delgadoi Calvo and Bonaparte, 1991, and
rare primitive titanosaurid sauropods from El Choco
´n
(Calvo, 1999; Simo
´n and Calvo, 2002) and Sierra Chata,
70 km north of Neuque
´n(Calvo and Salgado, 1998).
Rebbachisaurid diplodocoids, such as ‘Rayososaurus’
tessonei (Calvo and Salgado, 1995), and a closely related
form (Apesteguı
´a et al., 2001; Gallina et al., 2002) are
present and are rather abundant. From this unit near the
El Choco
´n area, the giant carcharodontosaurid thero-
pod Giganotosaurus carolinii Coria and Salgado, 1995
was discovered as were possible abelisauroid theropods
from a locality 34 km north of An
˜elo (Calvo et al., 1999)
and ‘‘La Buitrera’’ (de Valais and Apesteguı
´a, 2001).
A notable abundance of araripesuchid crocodyli-
forms, related to Brazilian and African forms, includes
Araripesuchus patagonicus Ortega, Gasparini, Buscalioni
and Calvo, 2000; and a new form with narrow snouts,
frontal nasal openings, and well-developed caniniforms,
resembling the head of a fox.
Eilenodontine sphenodontian lepidosaurs (Novas
et al. 1999a); ‘‘madtsoiid’’ snakes (Apesteguı
´a et al.,
2001), and at least two species of chelid turtles
(Lapparent de Broin et al., 1997) assigned to Procheli-
della Lapparent de Broin and de la Fuente, 2001 were
also collected.
Non-reptilian vertebrates were also recorded, in-
cluding cladotherian mammals (Apesteguı
´a et al., in
press), a primitive pipoid frog (Ba
´ez and Calvo, 1990)
and ceratodontiform fishes (Apesteguı
´a and Agnolin,
2002). Apart from these finds, footprints of different
terrestrial reptiles have been reported (Calvo, 1989)in
the bedding planes of the Candeleros Formation around
Lake Ezequiel Ramos Mexı
´a. The unit is characterized
by a diverse footprint record, including titanosauriform
sauropods, theropods, pterosaurs and large ornithopods
(Calvo, 1991).
Huincul Formation
This unit was established by Keidel (in Wichmann,
1929) and its type locality is situated in the vicinity of
Plaza Huincul from which its name is derived. It is
widespread in the southern part of the Neuque
´n Basin in
Neuque
´n Province to the east of national road 40, and in
the vicinity of Planicie de Renterı
´a and Santa Lucı
´ade
El Cuy regions in the Rı
´o Negro Province (Hugo and
Leanza, 2001a). It conformably overlies the Candeleros
Formation from which it clearly differs by its lighter
green-yellowish colours, and it is overlain conformably
by the red claystones and siltstones of the Cerro
Lisandro Formation (Fig. 5). The thickness of the
Huincul Formation varies regionally between 50 and
250 m (see Roll, 1939; Leanza and Hugo, 1997). It is
composed of yellowish and greenish fine- to medium-
grained (sometimes tuffaceous) sandstones. In the Cerro
Policı
´a region, a level of white tuff up to 2.5-m thick is
present close to its base. The age of the Huincul
Formation is probably Late Cenomanian (Hugo and
Leanza, 2001a).
Tetrapod content. The most remarkable reptile from
this unit is one of the largest sauropod dinosaurs of
them all, the basal titanosaurid Argentinosaurus huincu-
lensis Bonaparte and Coria, 1993, as well as a medium-
sized titanosaurid (Calvo and Salgado, 1998) and a new
gigantic and advanced titanosaurid, recently reported
(Simo
´n, 2001). Additional rebbachisaurid sauropod
68 H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

specimens were also collected (Salgado et al., 1991;
Calvo and Salgado, 1998; Calvo, 1999). Theropods from
this unit include medium-sized abelisauroids such as
Ilokelesia aguadagrandensis (Coria and Salgado, 2000)
as well as another undetermined abelisauroid found not
far from El Choco
´n(Novas and Bandyopadhyay, 2001;
de Valais et al., 2002).
Human-sized basal euiguanodontian ornithopod
dinosaurs have been reported from the Rı
´o Limay
Subgroup (Coria, 1999b) and probably come from the
Huincul Formation. At Las Cortaderas, 15 km south of
Plaza Huincul, another iguanodontian ornithopod was
found not far from an 8-m-long adult carcharodonto-
saurid theropod and a 5-m-long abelisaurid (Coria and
Currie, 1997).
Cerro Lisandro Formation
This is the youngest unit of the Rı
´o Limay Subgroup
and was first named by Herrero Ducloux (in Fossa
Mancini et al., 1938). Its type locality is at Cerro
Lisandro, 2.5 km northwest of Senillosa in eastern
Neuque
´n Province. It is easily recognizable by massive
red siltstones and claystones, which probably represent
swamp environments (Cazau and Uliana, 1973; Leanza
and Hugo, 1997; Hugo and Leanza, 2001a). It conform-
ably overlies the yellowish sandstones of the Huincul
Formation and is overlain in the same way by the sandy
Portezuelo Formation (Fig. 5). Freshwater bivalves have
been reported. The thickness of this unit varies between
35 and 75 m. The best exposures are located around the
western foothills of the Sierra Barrosa. The age of the
Cerro Lisandro Formation can be regarded as Late
CenomanianeEarly Turonian (Hugo and Leanza,
2001a).
Tetrapod content. Fossil bones found in this unit
belong to crocodilian and pleurodiran turtles. Fresh-
water bivalves (Diplodon spp.) were also found. In levels
belonging to the Cerro Lisandro Formation at Sierra del
Portezuelo, tiny ornithischian and avialan dinosaurs
(Agnolin et al., in press) as well as lepisosteid scales were
found. At Cerro Bayo Mesa, 30 km south of Plaza
Huincul, the four specimens found of the ornithopod
Anabisetia saldiviai Coria and Calvo, 2002 were not
associated with sauropods (Coria et al., 1996) but with
freshwater taxa including fishes, turtles and crocodyli-
forms. A small abelisauroid theropod has also recently
been reported (Paulina Carabajal et al., in press).
3.3.2. Rı´o Neuque
´n Subgroup
The Rı
´o Neuque
´n Subgroup was established by
Cazau and Uliana (1973) and constitutes the middle
part of the Neuque
´n Group. It is widely distributed in
the southern part of the Neuque
´n Basin. Excellent
outcrops can be seen in the area around Sierra del
Portezuelo and Sierra Barrosa (Neuque
´n Province) and
in the Planicie de Renterı
´a region (Rı
´o Negro Province).
The subgroup embraces the sandy Portezuelo Forma-
tion below and the argillaceous Plottier Formation
above. According to new regional geological studies and
palaeontological records, the age of this subgroup may
be Late TuronianeConiacian (Leanza and Hugo, 1995,
1997; Hugo and Leanza, 2001a).
Portezuelo Formation
This unit was established by Keidel (in Wichmann,
1929) and its type locality is situated in the Sierra del
Portezuelo region just where the railroad crosses this
range. It conformably overlies the Cerro Lisandro
Formation and at its top grades into the more
argillaceous Plottier Formation (Fig. 5). The Portezuelo
Formation displays excellent exposures around Lake
Los Barreales. It is composed of yellowish and red-
brownish, medium-grained sandstones and siltstones of
a fluvial regime, alternating with light red claystones in
a fining- and thinning-upwards sequence. A frequent
feature of this unit is the presence of palaeosol tops,
which indicates stable conditions through relatively long
periods of time. According to Roll (1939) and Leanza
and Hugo (1997), the thickness of the Portezuelo
Formation varies between 95e130 m. The age of the
Portezuelo Formation is Late TuronianeEarly Con-
iacian (Hugo and Leanza, 2001a).
Tetrapod content. The palaeontological record of this
unit was substantially increased in the last decade, as
reported by Novas (1997a,b). One of the most remark-
able theropod dinosaurs is the alvarezsaurid Patagony-
kus puertai Novas, 1996, closely related to Alvarezsaurus
calvoi (Bajo de la Carpa Formation, Santonian of
Patagonia) and Mononykus olecranus (Maastrichtian of
Mongolia). Unenlagia comahuensis Novas and Puerta,
1997, a maniraptoran theropod very close to the
basalmost birds, and the large coelurosaur Megaraptor
namunhuaiquii Novas, 1997b, with sharp manual dro-
maeosaurid-like ungual phalanges on its hands, were
also collected from this unit (see also Calvo et al., 2002).
Other tetrapods of this association include another big
coelurosaur (Coria et al., 2001) and a troodontid
theropod (Novas et al., 1999b). Sauropods of the
Portezuelo Formation include both procoelian- and
amphiplatyan-tailed large titanosaurs (Salgado and
Calvo, 1993; Calvo et al., 2001a,b; Calvo, 2002).
Ornithopods still constitute an unknown component of
the Portezuelo Formation fauna although small speci-
mens (Porfiri and Calvo, 2002), human-sized individuals
(Calvo and Porfiri, in press), and 7-m-long forms (Coria,
1999b) were reported from the Rı
´o Neuque
´n Subgroup,
probably the Portezuelo Formation.
69H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

Crocodyliforms are rather scarce in the taxonomic
list for this unit, but at least a basal mesoeucrocodylian
was collected (D. Pol, pers. comm. 1998). The turtles are
more diversified here than in older strata. They are
represented by the chelid Prochelidella portezuelae de la
Fuente, 2003 and the podocnemidoid Portezueloemys
patagonica de la Fuente, 2003. These records represent
the first discovery of taxa belonging to the two main
groups of pleurodiran turtles (Chelidae and Pelomedu-
soides) in the Patagonian Upper Cretaceous. This dis-
covery confirms the coexistence of North-Gondwanan
(pelomedusoids) with South-Gondwanian (chelids)
elements during the Late TuronianeEarly Coniacian
(de la Fuente, 2003) in north-western Patagonia.
Plottier Formation
This unit was defined by Herrero Ducloux (in Fossa
Mancini et al., 1938). The type locality is north of
Plottier, in the vicinity of Neuque
´n City airport. It
conformably overlies the Portezuelo Formation with
which it interfingers, and is overlain by the Bajo de la
Carpa Formation (Fig. 5). The Plottier Formation is
hard to distinguish in the field, the only difference from
the Portezuelo Formation being the higher proportion
of argillaceous content. It is composed of light red
massive claystones with thin layers of pink siltstones. Its
maximum thickness is nearly 25 m. Its age is regarded as
Late Coniacian (Hugo and Leanza, 2001a).
Tetrapod content. Few tetrapod fossils have been
recorded from this unit. Coria et al. (2001) reported the
presence of some fossils from the top of the Portezuelo
Formation at Sierra Barrosa. However, these discoveries
were recently reassigned to the Plottier Formation
(Coria and Currie, 2002). Among them are a large basal
coelurosaur which adds support to the idea that a large
and previously unknown basal coelurosaur radiation
took place in South America by TuronianeConiacian
times (Apesteguı
´a, 2002). A fragmentary mammal jaw
and titanosaurid bones were also mentioned. Bonaparte
and Gasparini (1980) recorded cf. Antarctosaurus
giganteus from the Plottier Formation at Aguada del
Can
˜o, near Neuque
´n City.
3.3.3. Rı´o Colorado Subgroup
The Rı
´o Colorado Subgroup was established by
Cazau and Uliana (1973) and constitutes the upper third
of the Neuque
´n Group. It is widely distributed in the
southern Neuque
´n Basin. Excellent outcrops may be
seen in the area between Neuque
´n City and Sierra del
Portezuelo (Neuque
´n Province) and in the region
around Planicie de Renterı
´a (Rı
´o Negro Province). It
is divided into the sandy Bajo de la Carpa Formation
below and the argillaceous Anacleto Formation above.
According to new regional geological studies and
palaeontological records, the age of this subgroup is
considered to be SantonianeEarly Campanian (Leanza,
1999; Hugo and Leanza, 2001a,b).
Bajo de la Carpa Formation
This unit, defined by Herrero Ducloux (in Fossa
Mancini et al., 1938) is, together with the Candeleros
Formation, one of the most homogeneous and charac-
teristic units of the Neuque
´n Group. It crops out from
the Sierra del Portezuelo area in south-central Neuque
´n
to the Bajo de Santa Rosa region in the northern part of
Rı
´o Negro Province (Hugo and Leanza, 2001b). It
conformably overlies the Plottier Formation and is
overlain in the same way by the Anacleto Formation
(Fig. 5). This is the only unit of the Neuque
´n Group
which overlies to the east the Upper PermianeMiddle
Triassic (or earliest Jurassic?) plutonicevolcanic base-
ment of the North Patagonian Massif. It is composed of
coarse-grained, light violet and pink sandstones of
fluvial origin. Rain drops, chemical nodules, palaeosols
and siliceous geodes are very abundant throughout the
unit. Reddish siltstones and claystones form thin beds
between the hard sandstone layers. The Bajo de la Carpa
Formation may reach 105 m in thickness. According to
Bonaparte (1991), the age of this unit is Santonian (see
also Hugo and Leanza, 2001a).
Tetrapod content. The reptile record of this unit
comprises the chicken-sized alvarezsaurid theropod
Alvarezsaurus calvoi Bonaparte, 1991; the abelisauroid
Velocisaurus unicus Bonaparte, 1991; the enanthiorni-
thine bird Neuquenornis volans Bonaparte, 1991 and
Patagopteryx deferrariisi Alvarenga and Bonaparte,
1992. Sauropod bones are not rare but only recently,
diagnostic material was found, assigned to cf. Lap-
latasaurus (Apesteguı
´a and Gallina, in press).
The crocodyliform record is significant, although
Notosuchus terrestris Woodward, 1896, whose canini-
forms, tall maxilla, and fore-nasal openings give it
a dog-like aspect, is by far the dominant species. There
are other closely related terrestrial crocodyliforms, such
as Comahuesuchus brachybuccalis Bonaparte, 1991, with
a flat and wide snout that resembles a large toad, and
also terrestrial hunters, such as the peirosaurids (Price,
1955; Bonaparte, 1991; Gasparini et al., 1991). Around
Lake Los Barreales, crocodyliform remains referred to
as peirosaurids such as Lomasuchus palpebrosus Gas-
parini, Chiappe and Ferna
´ndez, 1991 and Peirosaurus
tommini Price, 1955 are recorded (see Gasparini et al.,
1992; Danderfer and Vera, 1992). It is uncertain whether
Cynodontosuchus rothi Woodward, 1896, came from this
unit. The Bajo de la Carpa Formation has also yielded
beautifully preserved skeletons of the primitive snake
Dinilysia patagonica Woodward, 1901. The turtles are
represented by Lomalatachelys neuquina Lapparent de
70 H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

Broin and de la Fuente, 2001, a chelid turtle closely
related to Chelus and a podocnemidoid pleurodiran (see
de la Fuente, 1993). Some nests containing small eggs
ascribed to a basal avian (probably Neuquenornis; see
Schweitzer et al., 2002) have also been recorded.
Anacleto Formation
The Anacleto Formation is the highest unit of the
Neuque
´n Group. This formation was defined by
Herrero Ducloux (in Fossa Mancini et al., 1938). Its
type locality is in the Aguada de Anacleto area, located
40 km west of Neuque
´n City. It conformably overlies
the Bajo de la Carpa Formation and is unconformably
overlain by the Allen Formation, which forms part of
the Malargu
¨e Group (Fig. 5). It displays a very uniform
lithology. It is composed of purple and dark red
claystones with sporadic, small siliceous light blue
geodes. The thickness of the Anacleto Formation varies
between 60 and 90 m and its age is considered to be
Early Campanian (Leanza, 1999; Dingus et al., 2000;
Hugo and Leanza, 2001a,b).
Tetrapod content. From the ‘‘Huayquerı
´a occiden-
tal’’, immediately to the west of Paso Co
´rdova (Rı
´o
Negro Province), in strata belonging to the Anacleto
Formation according to the field observations of Hugo
and Leanza (2001a),Wichmann (1916) reported the
finding of a gracile titanosaurid dinosaur later studied
by von Huene (1929) who named it Antarctosaurus
wichmannianus. Near the Cinco Saltos locality, the
rather abundant saltasaurine titanosaurid Neuquensau-
rus australis (Lydekker, 1893) was recorded from beds
belonging to this unit. This new generic name was given
by Powell (1986, 1992) to Lydekker’s Titanosaurus
australis because of the abundant differences between
this taxon and the Indian species Titanosaurus indicus.
Besides this, the gracile aspect of the titanosaurid
Laplatasaurus araukanikus (von Huene, 1929) resembles
Indian sauropods. Another titanosaurid closely related
to the saltasaurines is Pellegrinisaurus powelli Salgado,
1996. A new titanosaurid was recently reported from
Auca Mahuida, as well as possible embryos preserved
inside its eggs (Chiappe and Coria, 2000; Chiappe and
Dingus, 2001). In the Rinco
´n de Los Sauces area,
especially at Loma del Lindero (Neuque
´n), Can
˜ado
´n
Rı
´o Seco (Neuque
´n) and Arroyo Seco (Mendoza), very
complete titanosaurids were collected (Calvo et al.,
1997; Gonza
´lez Riga, 1998, 1999b; Gonza
´lez Riga and
Calvo, 2001). At the last locality, a large, gracile
titanosaurid coexisted with small, robust species. Bona-
parte (1998b) listed the theropod Abelisaurus comahuen-
sis Bonaparte and Novas, 1985, as coming from the
Allen Formation at the Cinco Saltos locality, but this
species is now considered to come from the Anacleto
Formation (Heredia and Salgado, 1999). Additionally,
the new abelisaurid theropod Aucasaurus garridoi was
reported from Auca Mahuevo (Coria and Chiappe,
2000; Chiappe and Dingus, 2001; Coria et al., 2002). A
new theropod dinosaur was recorded from Loma del
Lindero, Rinco
´n de los Sauces (Calvo and Gonza
´lez
Riga, 1998) and bird icnites from Sierra Barrosa (Coria
et al., 2001).
The ornithischian record includes the basal ornitho-
pod Gasparinisaura cincosaltensis Coria and Salgado,
1996 (see also Salgado et al., 1997). Recently, Albino
(2002) described a fragmentary lower jaw that might
belong to a teiid lizard, while Goin et al. (1986) recorded
a mammalian jaw.
3.4. Malargu
¨e Group
The Malargu
¨e Group or ‘‘Malalhueyan’’ of Groeber
(1946) forms the upper section of the Riograndican
cycle. It overlies the Neuque
´n Group through the
Huantraiquican unconformity. From base to top it is
composed of mostly fluvial and lacustrine beds (Allen
Formation), followed by an Atlantic flooding episode
(‘‘Ka
´was Sea’’; Casamiquela, 1978) represented by both
clastic (Jagu
¨el Formation) and carbonate (Roca For-
mation) sediments. The group ranges in age from Late
Campanian to Danian. It is worth noting that the
Cretaceous/Tertiary boundary in the Neuque
´n Basin
occurs in marine sediments (i.e., the Jagu
¨el Formation).
Allen Formation
This unit is equivalent to the ‘‘Senoniano Lacustre’’
(Wichmann, 1924) of northern Patagonia, but its first
mention as a stratigraphic unit was by Fossa Mancini
et al. (1938). Its type locality is on the left bank of the
Negro River close to Paso Co
´rdova (see Roll, 1939).
However, Uliana and Dellape
´(1981) have proposed
a neostratotype section at El Caracol, in the eastern part
of Bajo de An
˜elo. For many years, the Allen Formation
was regarded as the youngest unit of the Neuque
´n Group.
Based on field evidence, Uliana (1974) and Andreis et al.
(1974) later considered it as the basal unit of the Malargu
¨e
Group, lying just below the marine beds of the Middlee
Upper Maastrichtian Jagu
¨el Formation (Fig. 6). The
formation is an extremely important unit as it displays
a varied spectrum of continental sedimentary facies of
mostly fluvial and lacustrine environments. It is widely
distributed in the eastern region of Neuque
´n Province
and in the northern part of Rı
´o Negro Province.
The formation is composed mainly of a red or
yellowish lower psammitic member, a middle lacustrine
section with greyegreenish shales and an upper part with
gypsum, limestones and stromatolitic limestones (see
Andreis et al., 1974). In the Paso Co
´rdova region it is up
to 50 m thick. Hugo and Leanza (2001a) proposed
a correlation of the basal member with the Angostura
71H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

Colorada Formation (Volkheimer, 1973) and of the
middle and upper members with the Los Alamitos
Formation (Franchi and Sepu´ lveda in Bonaparte et al.,
1984) of north-eastern Patagonia. Less accurate correla-
tions with the Allen Formation could be suggested for the
Loncoche, Paso del Sapo, and the base of La Colonia
formations, exposed in Mendoza and Chubut provinces.
The age of the Allen Formation may be Late Campanian,
and it is conceivable that it may also represent the Early
Maastrichtian (see Hugo and Leanza, 2001a,b), taking
into account that the earliest foraminiferal records in the
overlying Jagu
¨el Formation are of Mid Maastrichtian
age (Nan
˜ez and Concheyro, 1996).
Tetrapod content. The reptile record of the Allen
Formation and correlative units includes rather abun-
dant saltasaurine titanosaurids such as Rocasaurus
muniozi (Salgado and Calvo, 1999; Salgado and
Azpilicueta, 2000), and the derived eutitanosaurian
Aeolosaurus (Salgado and Coria, 1993; Powell, 1986).
Ornithischians are an important component in this fauna,
as evidenced by the findings at Salitral Moreno (Powell,
1987; Salgado and Coria, 1996). Hadrosaurid ornitho-
pods (i.e., Kritosaurus australis Bonaparte et al., 1984) are
common in the Los Alamitos Formation at Los
Alamitos, the Angostura Colorada Formation at Laguna
Carri-Laufquen and the Allen Formation at Salitral
Moreno (Rı
´o Negro Province). They are also present in
the Allen Formation of the Islas Malvinas (La Pampa
Province), the La Colonia Formation at Bajada del
Diablo (Chubut Province), and the Loncoche Formation
at Buta Ranquil (northern Neuque
´n Province). An
indeterminate lambeosaurinae was also collected at
Salitral Moreno (Powell, 1987). Theropod dinosaurs
include the highly derived abelisaurid Carnotaurus sastrei
in the La Colonia Formation (Chubut Province), and the
abelisauroid Quilmesaurus curriei (Coria, 2001) and
a new maniraptoran theropod (Novas et al., in press),
both from the Allen Formation. Although ornithothor-
acean birds have been recovered from Salitral Moreno
and Los Alamitos, only those from the former locality
could be assigned with certainty to the Carinatae (Lime-
navis patagonica Clarke and Chiappe, 2001). Enantior-
nithes, so common in the Bajo de la Carpa (Neuque
´n and
Rı
´o Negro) and Lecho formations (Salta) have not
definitely been recovered from the Allen Formation.
Diverse crocodyliforms include basal mesoeucroco-
dylians and neosuchians. The turtle record shows the
presence of abundant chelids and meiolaniids (see Broin
and de la Fuente, 1993; Lapparent de Broin and de la
Fuente, 2001; de la Fuente et al., 2001). The former is
represented by new unnamed South American short and
long-necked species (see Broin and de la Fuente, 1993).
Among the long-necked chelids is Yaminuechelys
gasparinii de la Fuente et al. 2001, related to the extant
South American Hydromedusa.
Bonaparte and Novas (1985) and Bonaparte (1998a)
recorded the theropod Abelisaurus comahuensis from the
Allen Formation at Lake Pellegrini (Rı
´o Negro Province).
However, this specimen is now considered to come from
the Anacleto Formation (Heredia and Salgado, 1999).
4. The tetrapod assemblages
In the framework of the tectonosedimentary evolu-
tion of the area studied, six tetrapod assemblages can
be recognized (see Fig. 7 and Table 1). These are
Fig. 6. Generalized stratigraphic column of the Malargu
¨e Group.
72 H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

Fig. 7. Proposed tetrapod assemblages for the Cretaceous of the Neuque
´n Basin, Argentina. The tetrapod shadows have been taken or modified from
Rich (1996), Novas (1996), Wilson and Sereno (1998) and Sereno (1999).

Table 1
Tetrapod assemblages of the Cretaceous of the Neuque
´n Basin
Tetrapod assemblages Composition
Amargan
Age: BarremianeEarly Aptian
Definition: ‘Spiny’ dicraeosaurid neosauropods; rebbachisaurid diplodocoids;
basal tit anosauriforms; basal abelisauroid theropods; Kentrosaurus-lik e
stegosaurian ornithischians.
Main stratigraphic units: La Amarga Formation
SauropodadDicraeosauridaedAmargasaurus cazaui Salgado and Bonaparte, 1991.
SauropodadRebbachisauridae indet. (SA, pers. obs.).
SauropodadTitanosauriformesdbasal form (SA, pers. obs.).
TheropodadAbelisauroideadLigabueino andesi Bonaparte, 1996.
OrnithischiadStegosauridae indet. (Bonaparte, 1996).
CrocodyliformesdTrematochampsidaedAmargasuchus minor Chiappe, 1988.
MammaliadCladotheriadVincelestes neuquenianus Bonaparte, 1986b.
Lohancuran
Age: Late AptianeAlbian
Definition: Large, gracile non-titanosaurid titanosaurs with broad tooth crowns,
amphiplatyan entire series of caudal vertebrae and elongate osteoderms;
rebbachisaurid diplodocoids (shared with Limayan); large carcharo-
dontosaurid theropods at San Jorge Basin and isolated teeth in Neuque
´n
Basin (shared with Limayan); small primitive chelid turtles related to
Acanthochelys (shared with Limayan).
Main stratigraphic units: Lohan Cura and Rayoso formations
SauropodadTitanosauriadAgustinia ligabuei Bonaparte, 1999.
SauropodadRebbachisauridaedRayososaurus agrioensis Bonaparte, 1996; Rayoso Formation, Neuque
´n.
CheloniadChelidaedProchelidella spp.
Limayan
Age: CenomanianeEarly Turonian
Definition: Medium-sized, gracile non-titanosaurid titanosaurs with broad tooth
crowns, and a large number of amphiplatyan caudal vertebrae; large to gigantic
titanosaurids with procoelous caudal vertebrae, broad tooth crowns and true
hyposphenes or parallelized structures on dorsal vertebrae; rebbachisaurid
diplodocoid sauropods (shared with Lohancuran); abundant and large
carcharodontosaurid theropods (probably shared with Lohancuran); small to
medium-sized abelisauroid theropods (shared with Neuquenian); abundant
medium-sized euiguanodontian ornithopods (AFNP); araripesuchid mesoeu-
crocodylians and rare neosuchians; large eilenodontine sphenodontians;
medium-sized limbed ‘‘Madtsoiid’’ snakes; small South-Gondwanan chelid
turtles related to Acanthochelys (shared with Lohancuran and Neuquenian).
Main stratigraphic units: Candeleros, Huincul, Cerro Lisandro formations
SauropodadTitanosauriadAndesaurus delgadoi Calvo and Bonaparte, 1991.
SauropodadTitanosauridaedArgentinosaurus huinculensis Bonaparte and Coria, 1993.
Sauropodadprimitive Titanosauridae from El Choco
´n fauna (Calvo, 1999; Simo
´n, 2001; Simo
´n and Calvo,
2002).
SauropodadTitanosauridae indet. from Sierra Chata (Calvo and Salgado, 1998).
SauropodadDiplodocoideadRebbachisauridaedRayososaurus tessonei (Calvo and Salgado, 1995) and
allied (Calvo and Salgado, 1998) as well as La Buitrera rebbachisaurid (Gallina et al., 2002).
TheropodadCarcharodontosauridaedGiganotosaurus carolinii Coria and Salgado, 1995.
Theropodad8-m-long indet. Carcharodontosauridae from Las Cortaderas (Coria and Currie, 1997).
TheropodadAbelisauroideadIlokelesia aguadagrandensis Coria and Salgado, 2000.
Theropodad5-m-long Abelisauroidea indet. from El Choco
´n area (Novas and Bandyopadhyay, 2001; de
Valais et al., 2002); 34 km north of An
˜elo (Calvo et al., 1999); a 5-m-long specimen from Las Cortaderas
(Coria and Currie, 1997) and a small one from Cerro Bayo Mesa (Paulina Carabajal et al., in press).
TheropodadCoelurosauria indet.d(Apesteguı
´a et al., unpublished).
OrnithischiadEuiguanodontiadAnabisetia saldiviai (Coria, 1999a; Coria and Calvo, 2002).
OrnithischiadEuiguanodontiadcf. Gasparinisaura sp. (Coria, 1999a).
OrnithischiadEuiguanodontia indet., from Cerro Bayo Mesa (Coria et al., 1996) and Las Cortaderas (Coria
and Currie, 1997).
CrocodyliformesdMesoeucrocodyliadAraripesuchus patagonicus Ortega, Gasparini, Buscalioni and Calvo,
2000.
CrocodyliformesdMesoeucrocodyliadAraripesuchus sp. (Apesteguı
´a et al., 2001; Pol et al., 2001;
Carignano et al., 2002).
CrocodyliformesdNeosuchia indet. (Carignano et al., 2002).
Crocodyliformes indet. (Coria et al., 1996).
LepidosauriadSphenodontiadEilenodontinae indet. (Novas et al., 1999a; Apesteguı
´a et al., 2001).
‘‘Madtsoiidae’’ indet. (Apesteguı
´a et al., 2002).
CheloniadChelidaedProchelidella spp. (Lapparent de Broin et al., 1997; Lapparent de Broin and de la
Fuente, 1999, 2001).
74 H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

CheloniadChelidae indet. from Cerro Bayo Mesa (Coria et al., 1996).
MammaliadCladotheria closely related to Dryolestoidea (Apesteguı
´a et al., 2002, in press).
AnuradPipoidea indet. Ba
´ez and Calvo, 1990.
Anurad? ‘‘Leptodactylidae’’ indet. (SA pers. obs.).
Neuquenian
Age: Late TuronianeConiacian
Definition: Large and robust titanosaurid sauropods with mostly procoelous
caudal vertebrae (some rare amphiplatyan), with mostly slender but also broad
tooth crowns and devoid of hyposphenes on dorsal vertebrae; alvarezsaurid
theropods (shared with Coloradoan); large basal coelurosaurian theropods;
small South-Gondwanan pleurodiran chelids (shared with Lohancuran and
Limayan); North-Gondwanan podocnemidoid pleurodirans (AFNP).
Main stratigraphic units: Portezuelo, Plottier formations
SauropodadTitanosauriadamphiplatyan-tailed specimens (Salgado and Calvo, 1993).
Sauropodadgigantic indeterminate titanosauridd(Calvo et al., 2001a,b).
SauropodadTitanosauridaedAntarctosaurus giganteus von Huene, 1929.
SauropodadTitanosauridaedMendozasaurus neguyelap Gonza
´lez Riga, 2003.
TheropodadCoelurosauriadMegaraptor namunhuaiquii Novas, 1997b; (Calvo et al., 2002).
TheropodadLarge basal coelurosaur (Coria et al., 2001; Coria and Currie, 2002).
TheropodadManiraptorad? DromaeosauridaedUnenlagia comahuensis Novas and Puerta, 1997.
TheropodadManiraptorad? Dromaeosauridae (Poblete and Calvo, in press).
TheropodadTroodontidae indet. (Novas et al., 1999b).
TheropodadCarcharodontosauridae (Veralli and Calvo, in press).
TheropodadAlvarezsauridaedPatagonykus puertai Novas, 1996.
OrnithopodadSmall, medium-sized and up to 7-m long (Coria, 1999a; Porfiri and Calvo, 2002; Calvo and
Porfiri, in press).
Mesoeucrocodylia indet. (D. Pol, pers. comm. 2003).
CheloniadChelidaedProchelidella portezuelae de la Fuente, 2003.
CheloniadPodocnemidoideadPortezueloemys patagonica de la Fuente, 2003.
Mammalia indet. from Plottier Formation at Sierra Barrosa (Coria et al., 2001).
Coloradoan
Age: SantonianeEarly Campanian
Definition: Small, robust and armoured saltasaurine titanosaurid sauropods
(AFNP); large, gracile non-saltasaurine eutitanosaurs; large carnotaurine
abelisauroid theropods (AFNP); alvarezsau rid theropods (shared with
Neuquenian); velocisaurid abel isauroids; enantiornithine birds (AFNP);
small-sized basal euiguanodontian ornithopods; notosuchian crocodyliforms;
chelidae turtles closely related to Chelus; podocnemidoid turtles (shared with
Neuquenian and Allenian); dinilysidae snakes; ?teiid lizards.
Main stratigraphic units: Bajo de la Carpa, Anacleto formations
SauropodadTitanosauridaedAntarctosaurus wichmannianus von Huene, 1929.
SauropodadTitanosauridaedLaplatasaurus araukanikus (von Huene, 1929) Powell, 1986.
Sauropodadtitanosaurid from Auca Mahuevo, Anacleto Formation (Chiappe and Dingus, 2001).
Sauropodadtitanosaurids from Loma del Lindero, Rinco
´n de los Sauces (Calvo et al., 1997; Gonza
´lez Riga,
1998).
Sauropodadtitanosaurids from Can
˜ado
´nRı
´o Seco, Neuque
´n(Gonza
´lez Riga and Calvo, 2001).
Sauropodadlarge gracile titanosaurid from Arroyo Seco, Mendoza (Gonza
´lez Riga, 1998, 1999a).
Sauropodadsmall robust titanosaurid from Arroyo Seco, Mendoza (Gonza
´lez Riga, 1998, 1999a).
SauropodadEutitanosauriadPellegrinisaurus powelli Salgado, 1996.
SauropodadTitanosauridaedSaltasaurinae Neuquensaurus australis (Lydekker, 1893) Powell, 1992.
TheropodadAbelisauridaedAbelisaurus comahuensis Bonaparte and Novas, 1985.
TheropodadAbelisauridaedCarnotaurinaedAucasaurus garridoi Coria et al., 2002 (see also Coria and
Chiappe, 2000; Chiappe and Dingus, 2001).
TheropodadAbelisauroidea indet. (Calvo and Gonza
´lez Riga, 1998).
TheropodadAbelisauroideadVelocisauridaedVelocisaurus unicus Bonaparte, 1991.
TheropodadAlvarezsauridaedAlvarezsaurus calvoi Bonaparte, 1991.
TheropodadAvialaedPatagopteryx deferrariisi Alvarenga and Bonaparte, 1992.
TheropodadAvialaedEnantiornithesdNeuquenornis volans Bonaparte, 1991.
TheropodadAvialaedichnites from Sierra Barrosa (Coria et al., 2001).
OrnithopodadGasparinisaura cincosaltensis Coria and Salgado, 1996.
CrocodyliformesdNotosuchiadNotosuchus terrestris Woodward, 1896.
CrocodyliformesdNotosuchiadComahuesuchus brachybuccalis Bonaparte, 1991.
CrocodyliformesdBaurusuchidaedCynodontosuchus rothi Woodward, 1896.
CrocodyliformesdPeirosauridaedLomasuchus palpebrosus Gasparini et al., 1991.
CrocodyliformesdPeirosauridaedPeirosaurus tominni Price, 1955.
SquamatadTeiidae? (Albino, 2002). (continued on next page)
75H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

Table 1 (continued )
Tetrapod assemblages Composition
AlethinophidiadDinilysidaedDinilysia patagonica Woodward, 1901.
CheloniadChelidaedLomalatachelys neuquina Lapparent de Broin and de la Fuente, 2001.
CheloniadPodocnemidoidead?Podocnemididae indet (de la Fuente, 1993; Broin and de la Fuente, 1993).
Mammalia indet.dGoin et al., 1986.
Allenian
(= Alamitense = Alamitian SALMA)
a
Age: Late CampanianeEarly Maastrichtian
Definition: Armoured small saltasaurine titanosaurids (shared with Coloradoan);
large and advanced non-saltasaurine eutitanosaurs (SA, pers. obs. at Salitral
Moreno); highly derived and large carnotaurine abelisauroid theropods (shared
with Coloradoan); ornithure (AFNP) and non-ornithure ornithothoracine
birds; hadrosaurid and ankylosaurian ornithischians (AFNP); high
crocodyliform diversity including both mesoeucrocodylians and neosuchians;
‘Madtsoiidae’ snakes; non-eilenodontine sphenodontians (pers. obs. at Los
Alamitos); teiid and indeterminate iguanian lizards (pers. obs. at Los Alamitos);
highest Cretaceous diversity of chelid turtles; meiolaniid turtles (AFNP); dryo-
lestoids, symmetrodonts, gondwanatheres, australosphenid and probably
triconodont mammals.
Main stratigraphic units: Allen, Angostura Colorada, Loncoche, Los Alamitos
and La Colonia formations (although the last two are not in the Neuque
´n Basin)
SauropodadTitanosauridaedAeolosaurus sp. (Powell, 1986; Salgado and Coria, 1993) and related
species /Angostura Colorada Formation.
SauropodadTitanosauridaedAeolosaurus-like species /Loncoche Formation (Gonza
´lez Riga, 1999a).
SauropodadTitanosauridaedRocasaurus muniozi (Salgado and Azpilicueta, 2000).
TheropodadAbelisauridae?dQuilmesaurus curriei Coria, 2001.
TheropodadAbelisauridaedCarnotaurus sastrei Bonaparte, 1985/La Colonia Formation.
TheropodadAvialaedOrnithothoraces indet. (Chiappe, 1992).
TheropodadAvialaedCarinataedLimenavis patagonica Clarke and Chiappe, 2001.
OrnithopodadHadrosauridaedKritosaurus australis Bonaparte et al., 1984, and Hadrosaurinae indet. /
Los Alamitos Formation, Angostura Colorada Formation, Loncoche Formation, La Colonia Formation.
OrnithopodadHadrosauridaedLambeosaurinae indet. (Powell, 1987).
AnkylosauriadNodosauridae indet. (Salgado and Coria, 1996).
CheloniadChelidaedshort-necked chelids closely related to Phrynops, long-necked chelids related to Chelus
and the group composed by Chelodina +Hydromedusa (Broin and de la Fuente, 1993).
CheloniadChelidaedPalaeophrynops patagonicus Lapparent de Broin and de la Fuente, 2001.
CheloniadChelidaedlong-necked chelid related to Hydromedusa and Yaminuechelys gasparinii de la Fuente
et al., 2001.
CheloniadMeiolaniidaedcf. Niolamia sp. (Broin, 1987; Broin and de la Fuente, 1993).
Serpentesd‘Madtsoiidae’dAlamitophis argentinus Albino, 1986 /Los Alamitos Formation.
Serpentesd‘Madtsoiidae’dPatagonophis parvus Albino, 1986 /Los Alamitos Formation.
Serpentesd‘Madtsoiidae’dRionegrophis madtsoioides Albino, 1986 /Los Alamitos Formation.
Serpentesd‘Madtsoiidae’ indet. /Loncoche Formation (Gonza
´lez Riga, 1999b).
MammaliadTriconodontadAustrotriconodon mckennai Bonaparte, 1986b.
MammaliadTriconodontadAustrotriconodon sepulvedai Bonaparte, 1992.
MammaliadGondwanatheriadFerugliotherium windhauseni Bonaparte, 1986b.
MammaliadGondwanatheriadGondwanatherium patagonicum Bonaparte, 1986b.
MammaliadSymmetrodontadBondesius ferox Bonaparte, 1990.
MammaliadDryolestoideadGroebertherium stipanicicia Bonaparte, 1986b.
MammaliadDryolestoideadGroebertherium novasi Bonaparte, 1986b.
MammaliadDryolestoideadLeonardus cuspidatus Bonaparte, 1990.
MammaliadDryolestoideadMesungulatum houssayi Bonaparte and Soria, 1985.
MammaliadDryolestoideadReigitherium bunodonta Bonaparte, 1990.
MammaliadDryolestoideadCasamiquelia rionegrina Bonaparte, 1990.
MammaliadDryolestoideadRougietherium tricuspes Bonaparte, 2002.
MammaliadDryolestoideadAlamitherium bishopi Bonaparte, 2002.
AnuradPipidae indet. (Ba
´ez, 1987)/Los Alamitos Formation.
Anurad‘Leptodactylidae’ indet. /Los Alamitos (Ba
´ez, 1987) and Loncoche Formation (Gonza
´lez Riga,
1999b).
a
The synonymy with previously proposed ‘tetrapod ages’ is only partial.
/arrows mean that data are from units outside the Neuque
´n Basin sensu stricto. AFNP (all following, not previously) means that the taxon first appears in this faunal assemblage and is present in
all of the following assemblages.
76 H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

considered here to be tetrapod remains discovered in the
same lithostratigraphic unit within a restricted area (see
also Section 5).
4.1. Amargan tetrapod assemblage
The Amargan tetrapod assemblage is commonly
found in rock units constrained between the transition
zone of the marine Agrio Formation below and the
Lohan Cura Formation above. The age of the tetrapod-
bearing units is probably BarremianeEarly Aptian.
4.1.1. Characterization
This assemblage is characterized by the co-occurrence
of Late Pangaean members. This implies elements of
clades distributed along Pangaea during the Jurassic
(e.g., basal neosauropods, basal neotetanurans, basal
neoceratosaurians, eurypodans and basal iguanodon-
tians). However, most of the taxa present are not
recorded outside Gondwana in coeval deposits, suggest-
ing some degree of incipient Gondwanan endemism.
These latter include non-diplodocid diplodocoids such
as dicraeosaurids (Salgado and Bonaparte, 1991) and
rebbachisaurids (SA, pers. obs.); basal diplodocoids,
basal titanosauriforms (teeth, pers. obs.); basal abeli-
sauroid theropods and Kentrosaurus-related stegosaurs.
Most of the Amargan fauna has been used to suggest
certain similarities with the Late Jurassic African fauna
(Bonaparte, 1986a; Salgado and Bonaparte, 1991).
Although trematochampsid crocodyliforms and well-
preserved cladotherian mammals were also found, the
lack of taxonomic accuracy for the former or compa-
rable records for the latter make it difficult to use them
for characterizing this assemblage.
The presence in Central Patagonian basins of latest
Jurassic and Early Cretaceous basal titanosauriforms
(Rauhut et al., 2001; Apesteguı
´a and Gime
´nez, 2001)
and dicraeosaurids (P. Puerta, pers. comm. 2003), makes
it highly probable that both groups constituted part of
the Late Pangaean fauna, represented here by the
Amargan assemblage. Following poor and conflicting
data from other Gondwanan regions for the Early
Cretaceous, other possible members of Gondwanan
assemblages of the same age but yet to be recorded
could be basal ornithomimosaurs, oviraptorosaurs,
basal neoceratopsians (according to Albian records of
Australia; Rich, 1996), and basal tyrannoraptorans
(according to Aptian records of Brazil).
4.2. Lohancuran tetrapod assemblage
The Lohancuran tetrapod assemblage is commonly
found in rock units constrained between the Middle
Miranican unconformity below and the Main Miranican
unconformity above. The age of the tetrapod-bearing
units can be regarded as Late AptianeAlbian.
4.2.1. Characterization
This assemblage is characterized by the co-occurrence
of typical Early Gondwanan lineages. Among sauro-
pods, this involves basal titanosaurs and rebbachisaur-
ids. Among the former, the large non-titanosaurid basal
titanosaur sauropods exhibit amphiplatyan caudal
vertebrae, gracile, elongate forearms and sometimes
spine-like dermal armour. The other sauropod compo-
nents are basal diplodocoids such as rebbachisaurids.
Theropod dinosaurs are still unreported from this
assemblage, but the presence of carcharodontosaurids
and basal titanosaurians of the same age in Central
Patagonia suggests that such theropods could be
present. An isolated tooth shows a morphology that
resembles carcharodontosaurids (SA, pers. obs.).
Crocodyliforms have not been found in the Neuque
´n
Basin, but basal mesoeucrocodylians are present in
Aptian rocks from Central Patagonia (D. Pol, pers.
comm. 2003). The Lohancuran turtles are small and
smooth-shelled pleurodirans (about 25 cm in length), the
oldest unarguable members of Chelidae (see Lapparent
de Broin and de la Fuente, 2001), closely related to the
extant South American genus Acanthochelys.
Although the findings are scarce, the different types
of dinosaurs recorded in the Neuque
´n Basin possess
spiny projections on their backs. In the case of
Amargasaurus (Amargan assemblage), they are expan-
sions of bifid neural spines; in Agustinia they are long
osteoderms, and in Rayososaurus, as in all rebbachi-
saurids, they are remarkably tall neural spines, about
seven times the centrum height. The possession of these
non-homologous features, especially noteworthy in
sauropods, but also in Early to ‘mid’ Cretaceous African
theropods and ornithopods (e.g., Spinosaurus,Ourano-
saurus), suggests non-phylogenetic causes such as special
devices to cope with environmental conditions. These
taxa form part of the Lower Cretaceous ‘Spiny Fauna’
(Apesteguı
´a, 2002). Furthermore, although widespread
in the Jurassic of Pangaea, the only ornithischian found
was a stegosaur, a group characterized by the develop-
ment of bony projections on their backs.
4.3. Limayan tetrapod assemblage
The Limayan tetrapod assemblage is commonly
found in rock units constrained between the Main
Miranican unconformity at its base and the Portezuelo
Formation above, the main units involved being the
Candeleros, Huincul and Cerro Lisandro formations.
The age of these rocks is probably Cenomaniane
Early Turonian. The tetrapod assemblage is partially
equivalent to the ‘AlbianeCenomanian association’ of
Bonaparte (1998b).
77H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

4.3.1. Characterization
The assemblage is characterized by the co-occurrence
of Early Gondwanan lineages. Among sauropods, the
abundance of basal diplodocoids (i.e., rebbachisaurids)
is characteristic. These constitute the last indubitable
record of a diplodocoid sauropod (Calvo and Salgado,
1995, 1998; Salgado et al., 1991; Calvo, 1999; Apeste-
guı
´a et al., 2001; Gallina et al., 2002). Their extinction or
diminution in younger strata was related to the mid
Cretaceous global extinction of sauropod dinosaurs
(Gallina et al., 2002; Salgado, in press; Salgado et al., in
press). Only a lower jaw related to the Coloradoan
assemblage was proposed to be part of this group
(Jacobs et al., 1993) but recent titanosaurid findings
(SA, in prep.) demonstrate that purported diplodocoid
features are also present in titanosaurids.
Titanosaurs also form part of this assemblage.
Medium-sized non-titanosaurid titanosaurian sauro-
pods are relatively common (Calvo and Bonaparte,
1991; Bonaparte and Coria, 1993; Calvo, 1999; Simo
´n,
2001). The first gigantic titanosaurids also occur
(Salgado et al., 1991; Calvo and Salgado, 1998; Calvo,
1999; Simo
´n, 2001; Simo
´n and Calvo, 2002) and show
procoelous caudal vertebrae and several primitive fea-
tures such as amphiplatyan tail vertebrae, hyposphenee
hypantrum vertebral articulations and broad tooth
crowns.
Abundant, gigantic and medium-sized basal neo-
tetanuran theropods such as carcharodontosaurids
(Coria and Salgado, 1995; Coria and Currie, 1997) also
form part of this assemblage, as well as medium-sized
neoceratosaurs such as abelisauroids (Coria and Currie,
1997; Calvo et al., 1999; Coria and Salgado, 2000;
Novas and Bandyopadhyay, 2001; de Valais and
Apesteguı
´a, 2001; Coria, 2001; de Valais et al., 2002;
Paulina Carabajal et al., in press). Small non-avialan
maniraptoran theropods are also present (Apesteguı
´a
et al., 2001), but until their phylogenetic position can be
clarified they are not useful to characterize the
assemblage. Medium-sized basal euiguanodontian orni-
thopods (Coria et al., 1996; Coria and Currie, 1997;
Coria, 1999b) can also be included as part of the
Limayan assemblage.
Araripesuchid basal mesoeucrocoylians are also re-
corded (Ortega et al., 2000), as well as some scarce and
quite large unnamed putative neosuchians (Carignano
et al., 2002). Among lepidosaurians is the first record
from anywhere in the world of a Late Cretaceous
sphenodontian lepidosaur, belonging to the large
eilenodontines. Furthermore, it represents a unique
Gondwanan eilenodontine sphenodontian. A new basal
alethinophidian (or ‘‘madtsoiid’’) snake is remark-
ably abundant at some levels (Novas et al., 1999a;
Apesteguı
´a et al., 2001). Small, freshwater chelid turtles
closely related to Acanthochelys are present, but are not
especially diverse (Lapparent de Broin et al., 1997;
Lapparent de Broin and de la Fuente, 1999, 2001); they
also occur in the Lohancuran assemblage. Dryolestoid-
derived mammals (Apesteguı
´a et al., in press) and pipoid
anurans (Ba
´ez and Calvo, 1990) are also recorded.
4.4. Neuquenian tetrapod assemblage
The Neuquenian tetrapod assemblage is commonly
found in rock units belonging to the Neuque
´n Subgroup
(Portezuelo and Plottier formations). The Santa Lucı
´a
de El Cuy Formation (Hugo and Leanza, 2001a) is also
equivalent to this interval. The age of these rocks is Late
TuronianeConiacian. The assemblage is partially equiv-
alent to the ‘TuronianeConiacian association’ of
Bonaparte (1998b). It is also necessary to clarify here
that the ‘Neuqueniense’ Vertebrate Age of Bonaparte
(1991), also includes the whole fauna of the Bajo de la
Carpa Formation, here included in the Coloradoan
tetrapod assemblage.
4.4.1. Characterization
The Neuquenian assemblage is characterized by the
establishment of a distinctive South American Late
Cretaceous fauna (Apesteguı
´a, 2002), although it is
theoretically possible that similar faunas could have
been living in Africa by that time. The Neuquenian
tetrapod assemblage includes the co-occurrence of
typical North-Gondwanan lineages, such as podocne-
midoid turtles and, perhaps, large non-Neoceratosau-
rian theropods (especially coelurosaurs). The latter are
abundant when compared to abelisauroids, a ratio that
abruptly changes in the overlying Coloradoan assem-
blage. Although the absence of taxa cannot characterize
an assemblage, the absence of diplodocoids in the
Neuquenian assemblage, related by some authors to
the Laurasian extinction of sauropods, is at least as
significant as the abundance of non-saltasaurine eutita-
nosaurs. The latter includes medium-sized and some-
times gigantic eutitanosaur (with procoelous mid-caudal
vertebrae) and a few andesauroid (amphiplathyan mid-
caudals) sauropods, including gracile and robust taxa
(Bonaparte and Gasparini, 1980; Salgado and Calvo,
1993; Calvo et al., 2001a,b; Calvo, 2002). Narrow tooth-
crowned taxa are more abundant than broad tooth-
crowned taxa (Calvo and Grill, in press).
Theropods include non-avialan maniraptorans (No-
vas and Puerta, 1997), such as possible dromaeosaurids,
troodontids, alvarezsaurids (Novas, 1996; Chiappe and
Coria, 2003) and large basal coelurosaurs that seem to
constitute an endemic radiation (Novas, 1997b; Coria
et al., 2001; Coria and Currie, 2002; Calvo et al., 2002).
Carcharodontosaurid theropods were still present
(Veralli and Calvo, in press; SA, pers. obs.) but not
abundant. A few possible neornithe remains were also
recorded (Agnolin et al., in press).
78 H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

Although an increasing quantity of small (Porfiri and
Calvo, 2002; SA, pers. obs.), medium-sized (Calvo and
Porfiri, in press) and up to 7-m-long basal iguanodon-
tian ornithopods (Coria, 1999b) are also present, the
phylogenetic resolution is still too poor to permit an
assemblage characterization. The same can be said for
some still poorly known mesoeucrocodilians (D. Pol,
pers. comm. 1998).
The turtles include at least two groups: short-necked
chelids (related to extant Acanthochelys) and podocne-
midoids (Lapparent de Broin and de la Fuente, 2001; de
la Fuente, 2002, 2003), confirming the presence of
North-Gondwanan pelomedusoids together with South-
Gondwanan chelids. The mammalian history remains
poorly known, the discovery of a mammal jaw being the
only record for this unit (Coria et al., 2001).
4.5. Coloradoan tetrapod assemblage
(= Greater Gondwanan Endemic Dinosaur Domain,
Apesteguı
´a, 2002)
The Coloradoan tetrapod assemblage is typically
found within the Rı
´o Colorado Subgroup (Bajo de la
Carpa and Anacleto formations). The age of these rocks
can be regarded as SantonianeEarly Campanian. It is
necessary to clarify that the ‘Neuqueniense’ Vertebrate
Age of Bonaparte (1991) includes, among other remains,
the whole fauna of the Bajo de la Carpa Formation, here
considered as Coloradoan.
4.5.1. Characterization
The Coloradoan assemblage is characterized by the
highest known diversity of Gondwanan titanosaurid
sauropods and abelisauroid theropods. The abundant
titanosaurids include the first appearance in Patagonia
of small, robust and armoured saltasaurines (Lydekker,
1893; Powell, 1992), as well as large and gracile basal
eutitanosaurs (von Huene, 1929; Powell, 1986; Salgado,
1996; Calvo et al., 1997, 1999; Gonza
´lez Riga, 1998,
1999a; Chiappe and Dingus, 2001; Gonza
´lez Riga and
Calvo, 2001). Putative saltasaurines were also reported
from the Cenomanian Itapecuru´ Formation in Brazil
(Medeiros, 2002). If this is correct, Patagonian salta-
saurines could constitute a second migratory wave
completing the faunal mixture with northern Gond-
wanan forms already detected for the Neuquenian
assemblage. However, the recent report of hadrosaurids
from the Itapecuru´ Formation (Avilla et al., 2003) might
indicate possible taxonomic misidentification, or strati-
graphic uncertainty in the provenance horizon.
Different lineages of abelisauroid theropods such as
abelisaurines (Bonaparte and Novas, 1985), carnotaur-
ines (Coria and Chiappe, 2000; Chiappe and Dingus,
2001), velocisaurids (Bonaparte, 1991) and indetermi-
nate medium-sized taxa are present (Calvo and Gonza
´-
lez Riga, 1998), showing perhaps the largest known
abelisauroid diversity. Additionally, maniraptoran
theropods include derived alvarezsaurids (Bonaparte,
1991) and enantiornithine birds (Alvarenga and Bona-
parte, 1992; Bonaparte, 1991; Coria et al., 2001), but no
large forms. The rise of saltasaurines (previously
restricted to north-eastern Brazil), the probable loss
of large endemic coelurosaurs and the diversifica-
tion of abelisauroid theropods could be related events
(Apesteguı
´a, 2002). Small, closely related basal euigua-
nodontian ornithopods are not rare (Coria and Salgado,
1996; Salgado et al., 1997).
Crocodyliforms are remarkable, not only in their
diversity but also in their quantity (Woodward, 1896;
Price, 1955; Bonaparte, 1991; Gasparini et al., 1991).
They include a good sample (representing more than
60% of reported tetrapods from the assemblage) of
mammal-toothed notosuchian crocodyliforms (basal
mesoeucrocoylians). Dinilysid snakes (Woodward,
1901) represent a local radiation of basal alethino-
phidians that is also accompanied by an endemic radia-
tion of teiid lizards (Albino, 2002). Podocnemidoid
pleurodiran turtles and chelids closely related to Chelus
(Broin and de la Fuente, 1993; de la Fuente, 1993;
Lapparent de Broin and de la Fuente, 2001), also form
part of this rich assemblage. Although the single
mammal recorded from this unit was thought to
represent a metatherian, its affinities remain uncertain
(Goin et al., 1986; Marshall and de Muizon, 1988)and
thus is not significant in characterizing the assemblage.
4.6. Allenian tetrapod assemblage
(= Alamitense Bonaparte, 1991 = Alamitian SALMA
Flynn and Swisher, 1995)
The Allenian tetrapod assemblage occurs in strata
constrained between the Huantraiquican unconformity
at its base and the marine Jagu
¨el Formation above. The
age of these units is Late CampanianeEarly Maastrich-
tian. The Allenian tetrapod assemblage is partially
equivalent to the Alamitense of Bonaparte (1986b), the
‘CampanianeMaastrichtian association’ of Bonaparte
(1998b) and to the Alamitian SALMA of Flynn and
Swisher (1995). The main stratigraphic unit of the
Neuque
´n Basin yielding this tetrapod assemblage is the
Allen Formation. However, the equivalent units in
north-eastern Patagonia (the Angostura Colorada and
Los Alamitos formations) represent similar environ-
ments, age and faunas, so their taxa are also included to
give a more accurate picture of the Allenian assemblage.
Together, these formations contain a variety of extraor-
dinary fossils. New findings in Southern Mendoza and
La Pampa provinces, both at the northern limits of the
Neuque
´n Basin, also help to understand some faunal
clues from the Allen Formation and equivalent units.
Contrary to the view of Powell (1986), the tetrapod taxa
found around Cinco Saltos and the Lago Pellegrini area
79H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

belong to the Anacleto Formation and not to the Allen
Formation (see Heredia and Salgado, 1999). On the
other hand, although Carnotaurus sastrei was originally
regarded as from the AptianeAlbian Cerro Barcino
Formation in Chubut Province, Ardolino and Franchi
(1996) noted that it came from the La Colonia
Formation.
4.6.1. Characterization
The Allenian assemblage is characterized by the co-
occurrence of highly derived members of typical
Gondwanan lineages and probable immigrants from
the Northern Hemisphere. Among the former, there are
small, armoured saltasaurine titanosaurs (Salgado and
Azpilicueta, 2000), closely related large and advanced
eutitanosaurs (Powell, 1986 and SA, pers. obs. at
Salitral Moreno and Bajo Santa Rosa) and large, highly
derived Carnotaurus-like abelisaurid theropods (after
the record from the La Colonia Formation, continuous
at that time with the easternmost Neuque
´n Basin;
Bonaparte, 1985; Bonaparte et al., 1990), as well as
some other lesser indeterminate abelisauroids. Onithure
and non-ornithure ornithothoracean birds are also
found together.
Among the immigrants, there are hadrosaurine and
lambeosaurine allochthonous hadrosaurid ornithopods
(Bonaparte et al., 1984; Powell, 1987; Gonza
´lez Riga,
1999a; Gonza
´lez Riga and Casadı
´o, 2000) and ankylo-
saurian ornithischians (Salgado and Coria, 1996). It
may become possible to add other Laurasian taxa, but
only after a careful taxonomic revision of the abundant
but fragmentary bones already collected, and/or the
discovery of better preserved specimens. Furthermore,
several supposedly Laurasian taxa have a possible
Gondwanan counterpart, making it difficult to de-
termine the allochtonous condition of some taxa
(e.g., Tyrannoraptora, Ceratopsia, Ornithomimosauria,
Dromaeosauridae, Ankylosauridae; see Rich, 1996;
Novas et al., in press).
Non-dinosaurs include fragmentary materials of
a diverse array of crocodyliforms, a high diversity of
‘‘madtsoiid’’ snakes (Albino, 1986), lizards (teiids and
indeterminate iguanians?), and non-eilenodontine sphe-
nodontians. Turtles comprise the most diverse chelid
assemblage of the whole Cretaceous. The latter includes
different groups of South American short and long-
necked (related to Hydromedusa) chelids, and the first
appearance of meiolaniids (Broin, 1987; Broin and de la
Fuente, 1993; Lapparent de Broin and de la Fuente,
1999, 2001; de la Fuente et al., 2001). A remarkable
record of mammals has also been reported, especially
including dryolestoids, but also symmetrodonts, gond-
wanatheres, and perhaps triconodonts and australos-
phenids (Bonaparte and Soria, 1985; Bonaparte, 1986b,
1990, 1992), as well as pipoid and ‘leptodactylid’ frogs,
both from the Los Alamitos (Ba
´ez, 1987) and the
Loncoche (Gonza
´lez Riga, 1999b) formations.
5. Discussion and significance of the
tetrapod assemblages
Knowledge of Neuque
´n Basin tetrapods has accu-
mulated during the last century and particularly in the
last 20 years. It has allowed us to associate them with
different stratigraphical units displaying some common
faunistic patterns that we term tetrapod assemblages.
Evolution is not static but also is not homogeneous.
The different components of a biota have distinct
evolutionary patterns and rhythms that restrict its
stratigraphic utility. As knowledge of rock units and
the record of their fossil contents is increased, faunal
assemblages become better known, allowing recognition
of successional patterns. The discovery of an enantior-
nithine bird in red beds is not evidence enough to assign
it to the Bajo de la Carpa Formation, but when it is
found in association with the crocodyliform Notosuchus,
the snake Dinilysia and small alvarezsaurid theropods,
the risk of making a wrong assumption is relatively low.
However, the use of vertebrate, tetrapod or reptile ages
should be avoided because of their informal biochrono-
logical meaning and the very limited record and low
reliability that tetrapods provide for comparing rock
units. Accordingly, tetrapod assemblages are considered
here as tetrapod remains discovered in the same
lithostratigraphic unit within a restricted area.
From the palaeontological aspect, it is worth noting
that Ameghino (1903) recognized a number of faunistic
sequences in the Cenozoic of Argentina based on the
‘‘evolutive grade’’ of their components. In the past 35
years, his ideas have been adapted by other authors and
have given rise to well-known ‘‘Mammal Ages’’ (Pascual
et al., 1965) or, more recently, to the South American
Land Mammal Ages (SALMA) of Flynn and Swisher
(1995).
Bonaparte (1986b, 1987, 1990, 1991, 1992) began to
use ‘Vertebrate Ages’ for the Cretaceous of South
America, pointing out that what actually defines them
is in fact their whole vertebrate content, especially the
reptiles (Bonaparte, 1992). In this way, he criticized the
‘Alamitian’ (‘Alamitense’) biochron of Ortı
´z Jaureguizar
and Pascual (1989) because it was based only on
mammals; the same was said of the ‘Amargan’
(‘Amarguense’) biochron. Accordingly, Bonaparte
(1991) created the following two ‘Vertebrate Ages’
(VA) for the Cretaceous of South America, as follows:
Alamitian V. A. (= Edad Vertebrado Alamitense
Bonaparte, 1986b): includes the tetrapod fauna from
the Middle section of the Los Alamitos Formation
(Rı
´o Negro Province), the upper section of the
80 H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

Loncoche Formation (Mendoza Province) and the
Allen Formation (Rı
´o Negro and Neuque
´n provinces)
(see Bonaparte, 1986b, 1987, 1990, 1992).
Neuquenian V. A. (= Edad Vertebrado Neuqueniense
Bonaparte, 1991): includes the tetrapod fauna from the
Bajo de la Carpa Formation (Bonaparte, 1991).
More recently, Bonaparte (1998b) has concluded that
there are three main successive faunistic assemblages of
land tetrapods in the Cretaceous of South America:
AlbianeCenomanian Assemblage, whose faunal content
in the present scheme is restricted to the Neuque
´nBasin,
and partiallybelongs to our Limayan tetrapod assemblage.
TuronianeConiacian Assemblage (ZNeuquenian V. A.
Bonaparte, 1991), whose faunal content in the present
scheme is restricted to the Neuque
´n Basin, and partially
belongs to our Neuquenian tetrapod assemblage.
CampanianeMaastrichtian Assemblage (ZAlamitian
V. A. Bonaparte, 1991), whose faunal content in the
present scheme is restricted to the Neuque
´n Basin, and
belongs to our Allenian tetrapod assemblage.
Similarly, Novas (1997c) noted four ‘Major Intervals’
of the Cretaceous of South America: Hauterivian (La
Amarga), AptianeAlbian, CenomanianeSantonian (all
Neuque
´n Group), and Maastrichtian.
Apesteguı
´a (2002) recently characterized a series of
three main evolutionary stages and domains for tetra-
pod faunas, based on dinosaurian faunas.
First (Earliest CretaceouseEarly Aptian): with de-
rived relics of widespread global Jurassic faunas, mainly
basal neosauropods, basal neotetanuran theropods,
basal neoceratosaurs (inferred from Late Jurassic faunal
lists from Central Patagonia; Rauhut and Puerta, 2001;
Rauhut et al., 2001; Rauhut, 2002) and stegosaurian
ornithischians.
Second (= Gondwanan) (Late AptianeEarly Cam-
panian): constituted faunas in which the isolation from
Laurasia originated endemisms at generic and some-
times family level. It is divided into three domains:
(1) Early Gondwanan (Late AptianeMid Cenomanian),
mainly represented by carcharodontosaurid theropods,
basal titanosaur and diplodocoid sauropods; (2) South
American (Late CenomanianeConiacian), mainly re-
presented by endemic coelurosaurs, titanosaurid sauro-
pods and basal euiguanodontian ornithopods. At this
level, the record shows the loss of dominance of basal
titanosaurs, diplodocoid sauropods and carcharodonto-
saurid theropods, together with the diversification of
titanosaurids and large endemic coelurosaurs; (3)
Greater Gondwanan (SantonianeEarly Campanian),
mainly represented by abelisauroid theropods and sal-
tasaurine titanosaurs. The rise of saltasaurines (pre-
viously restricted to northern Brazil) is evident, as is the
probable loss of large endemic coelurosaurs and the
diversification of abelisauroid theropods.
Third (Late CampanianeEarly Maastrichtian): the
establishment of land connections between Gondwana
and Laurasia produced mixed faunas in several regions,
as evidenced by the contact of North America with
South America; and the abundant Gondwanan fauna in
the Maastrichtian of Europe and Asia.
The late survival of plesiomorphic clades (e.g.,
temnospondyls from the Cretaceous of Australia;
ceratodontiform dipnoans from the Upper Cretaceous
of South America); and the theoretical appearance
because of the presence of its sister group and the early
appearance in the fossil record of highly derived groups
must be taken into account in order to discuss fossil
faunal associations and their characterization.
Because of their weaker dispersal barriers, marine
faunas are spread more easily and widely than terrestrial
faunas. As a result, it is possible to consider a single
index fossil as an age indicator. However, because
terrestrial environments can be conditioned by the
isolation of a particular area, provinciality can arise
more easily, allowing the survival of ‘archaic’ elements
in isolated refugia. Furthermore, the random nature of
the fossil record, and the strong biases produced by
terrestrial palaeoenvironmental conditions, in contrast
with marine environments, means that the assignation of
a certain rock with its faunal content to some particular
age, should not be based on a single index fossil. To
prevent further possibilities of error, several taxa should
be considered simultaneously. In this way, the error is
substantially reduced.
Changes of tetrapod assemblages in an area represent
major events that transformed the biotic composition
(e.g., environmental changes, volcanism, transgressive
events, evolution). Some of these are indicated in the
geological record by regional unconformities.
6. Conclusions
Present knowledge of terrestrial fossil biotas in the
Neuque
´n Basin is still poor, restricting the possibility of
building a reliable database. However, some peculiari-
ties of the tetrapod faunas seem to be evident enough to
allow us to formulate a brief characterization of the
Cretaceous continental strata of the southern part of
the basin and their dominant tetrapod assemblages. The
term assemblage refers to tetrapod taxa coming from
the same lithostratigraphic unit within a certain region.
As a result, six tetrapod assemblages are recognized
here: Amargan (BarremianeEarly Aptian); Lohancuran
(Late AptianeAlbian); Limayan (CenomanianeEarly
Turonian); Neuquenian (Late TuronianeConiacian);
Coloradoan (SantonianeEarly Campanian) and Alle-
nian [Late CampanianeEarly Maastrichtian (= Alami-
tense = Alamitian SALMA)]. As discussed in this
paper, tetrapod assemblages cannot be used in order
81H.A. Leanza et al. / Cretaceous Research 25 (2004) 61e87

to determine the age of a certain stratigraphic unit.
However, by defining them locally and within a concise
stratigraphical framework, such assemblages could pro-
vide the basis for developing a useful tool for addressing
inter-regional correlations.
Acknowledgements
This paper is dedicated to Jose
´F. Bonaparte (Museo
Argentino de Ciencias Naturales). His intensive and
brilliant work through several decades made possible
approaches like that in our paper. We are also deeply
indebted to Carlos A. Hugo and David Repol (both
from the Argentine Geological Survey) for field obser-
vations and geotectonic comments on the Cretaceous
stratigraphic chart included here. Diego Pol (American
Museum of Natural History) made useful comments on
crocodyliform phylogeny. We also thank the anony-
mous reviewers who offered diverse information and
constructive comments that greatly improved the
original manuscript.
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