Zulma Gasparini

A NEW SPECIES OF ARARIPESUCHUS (CROCODYLOMORPHA, MESOEUCROCODYLIA) FROM THE LOWER CRETACEOUS OF PATAGONIA (ARGENTINA)

Abstract A new species of the genus Araripesuchus from the Albian–Cenomanian locality of the El Chocón (Neuquén Province, Argentina) is described. The diagnosis of the genus is reviewed and its phylogenetic placement within Crocodylomorpha discussed. Araripesuchus is proposed here as being the sister taxon of Neosuchia, corroborating previous phylogenetic analysis. The new species, Araripesuchus patagonicus, differs from the type species, A. gomesii in the relationships of the prefronto-nasal and lachrymo-nasal sutures, the dermal placement of the postorbital bar on the medial side of the jugal, and the greater extension of the squamosals in the skull dorsum. The African species, “Araripesuchus” wegeneri, does not share the diagnostic traits of the genus, and its reassignment to a new genus needs to be considered. The phylogenetic context of Araripesuchus and “A.” wegeneri permits a reanalysis of the role played by their amphiatlantic distribution in the Aptian-Albian. “Araripesuchus” wegeneri and the South American forms might share a pre-Aptian common ancestor, and have been already differentiated and isolated in the African and South American continents by the time of the Aptian–Albian.

THE ELASMOSAURID PLESIOSAUR ARISTONECTES CABRERA FROM THE LATEST CRETACEOUS OF SOUTH AMERICA AND ANTARCTICA

Abstract Aristonectes parvidens Cabrera, 1941, and Morturneria seymourensis (Chatterjee and Small, 1989), two plesiosaurs from the Maastrichtian of South America and Antarctica whose phylogenetical position is controversial, are reviewed and found to be congeneric and conspecific. Most differences between the two type specimens are interpreted as related to ontogenetic growth: Morturneria is based on an immature, whereas Aristonectes is based on an adult, probably an old individual. Aristonectes exhibits an unique set of characters among Plesiosauria: a low and wide ogival skull, a paired vomero-nasal fenestra, a mandible high anteriorly with a very short and high symphysis, a homodont dentition composed of numerous, strongly outwardly directed and poorly ornamented teeth (dental formula: 10–13 premaxillary, at least 51 maxillary and probably 60–65 dentary teeth, depending upon individual ontogeny). Moreover, Aristonectes shares several synapomorphies with the elasmosaurid clade, mainly strongly binocular-shaped and platycoelous cervical centra with lateral ridges. In contrast to cryptoclidids, it retains some plesiomorphic characters (e.g., horizontal jugal and poorly ventrally excavated cheek, glenoid fossa at about the same level as the alveolar row). The dental morphology and peculiar occlusal pattern, forming an interlocking trap, suggest that Aristonectes strained a diet of small, soft organisms from the water.

Maastrichtian plesiosaurs from northern Patagonia

Three relatively complete elasmosaurid plesiosaurs were recently recovered from the north of Patagonia, Argentina. They were found in the uppermost levels of the Jaguel 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.

Reinterpretation and new denominationof Atacisaurus crassiproratus (Middle Eocene; Issel, France) as cf. Iberosuchus (Crocodylomorpha, Metasuchia)

Abstract The holotype of Atacisaurus crassiproratus Astre , 1931 (Middle Eocene; Issel, France) is herein reinterpreted and attributed to cf. Iberosuchus. The holotype of A. crassiproratus consists of a fragment of a mandible that Astre (1931) assigned to an eusuchian crocodile. However, the combination of characters that we have recognized in this mandible allows to consider it as a member of the Metasuchia clade (sensu Benton & Clark 1988 ). Furthermore, the specimen from Issel shows a similar morphology and the same combination of character states than those of several specimens from the middle Eocene site of Caenes (Duero basin, Salamanca province, Spain). We consider that both the Issel and Caenes mandibles belong to the same taxon. The mandibles of all these specimens, attributed to cf. Iberosuchus, share with other metasuchians the following combination of apomorphic traits: a dorsal prolongation of the dentary ascending behind the tooth row; the presence of a lateral depression on the dentary; robust splenials; the presence of a big slot-like foramen intramandibularis oralis;; and an anteroposteriorly elongated glenoid fossa of the articular. These specimens are also compared with the Eocene African species Eremosuchus elkoholicus Buffetaut , 1989 . The phylogenetic relationships, based on mandibular characters, of cf. Iberosuchus with other taxa previously associated to this genus, such as the Sebecosuchia Simpson 1937 (sensu Gasparini et al. 1991 ) and the Trematochampsidae Buffetaut, 1974 (sensu Buffetaut, 1986 , Buffetaut, 1988 , Buffetaut, 1989 ), as well as with other members of the Metasuchia and Neosuchia clade, are discussed.

Salt glands in a Tithonian metriorhynchid crocodyliform and their physiological significance

Our knowledge of Mesozoic tetrapods is based mainly on osteological evidence. The discussion of the evolution of any homeostatic system is highly speculative because direct non-osteological evidence is uncommon. Here we report an extraordinarily well-preserved cast of a pair of lobulated protuberances in the skull of the marine metriorhynchid crocodiliform Geosaurus from the Tithonian (Jurassic) of Patagonia (Argentina). These protuberances are interpreted as representing salt glands. Based on their topology, these glands are identified as the nasals. Optimization of this character on a phylogenetic tree permits us to infer the ancestral condition for archosaurs. The relationship between salt gland and diet is also analysed. The presence of hypertrophied salt glands in the skull of Geosaurus suggests that as early as 140 million years ago, some Mesozoic marine reptiles had evolved an extra-renal osmoregulatory system. This achievement was an important clue in the successful colonization of marine environments. Salt glands preclude the risk of lethal dehydration and allow marine reptiles to include an important amount of invertebrates in their diet.

Salt glands in the Jurassic metriorhynchid Geosaurus: implications for the evolution of osmoregulation in Mesozoic marine crocodyliforms

The presence of salt-excreting glands in extinct marine sauropsids has been long suspected based on skull morphology. Previously, we described for the first time the natural casts of salt-excreting glands in the head of the Jurassic metriorhynchid crocodyliform Geosaurus araucanensis from the Tithonian of the Vaca Muerta Formation in the Neuquén Basin (Argentina). In the present study, salt-excreting glands are identified in three new individuals (adult, a sub-adult and a juvenile) referable to the same species. New material provides significant information on the salt glands form and function and permit integration of evolutionary scenarios proposed on a physiological basis in extant taxa with evidence from the fossil record. G. araucanensis represents an advanced stage of the basic physiological model to marine adaptations in reptiles. G. araucanensis salt glands were hypertrophied. On this basis, it can be hypothesized that these glands had a high excretory capability. This stage implies that G. araucanensis (like extant pelagic reptiles, e.g. cheloniids) could have maintained constant plasma osmolality even when seawater or osmoconforming prey were ingested. A gradual model of marine adaptation in crocodyliforms based on physiology (freshwater to coastal/estuarine to estuarine /marine to pelagic life) is congruent with the phylogeny of crocodyliforms based on skeletal morphology. The fossil record suggests that the stage of marine pelagic adaptation was achieved by the Early Middle Jurassic. Salt gland size in the juvenile suggests that juveniles were, like adults, pelagic.

New Tertiary Sebecosuchia (Crocodylia: Mesosuchia) from Argentina

ABSTRACT A new sebecid from the early Eocene of Jujuy, with more generalized characteristics than Sebecus, is described. A tooth from the same formation (Lumbrera Formation, Salta Group) and age, in the province of Salta, is assigned to ?Sebecus sp. Another sebecosuchian comes from the late Eocene of Mendoza. A sebecid from the early Oligocene in Patagonia (Chubut) is the most recent record of sebecosuchians in Argentina. Certain local environments in the Tertiary of South America are inferred on the basis of presence of sebecosuchians and associated herpetofauna. Hypotheses of origin and geographical distribution of the Sebecosuchia s.l. (Langston, 1956; Sill, 1969; Steel, 1973; Buffetaut, 1980; Molnar, 1981) are analyzed. Finally, it is confirmed that ziphodonty arose several times during crocodilian history, and that in order to understand the origin and evolution of the Sebecosuchia it will be necessary to have more and better material.

Postcranial morphology of Aristonectes (Plesiosauria, Elasmosauridae) from the Upper Cretaceous of Patagonia and Antarctica

Abstract A partial, postcranial skeleton of a juvenile individual referred to Aristonectes cf. parvidens from the upper Maastrichtian López de Bertodano Formation, Isla Marambio (Seymour Island), Antarctica, is described. Additionally, two juvenile specimens, also referred to A. cf. parvidens from the Allen Formation (upper Campanian–lower Maastrichtian) and Jagüel Formation (upper Maastrichtian) (Río Negro province, Argentina), are redescribed. The analysis of the systematic value of the cervical centrum proportions of juvenile specimens of Elasmosauridae suggests that these elements can be used to differentiate juvenile specimens of A. cf. parvidens from juveniles of other Elasmosauridae. On this basis, the specimens described are referred to A. cf. parvidens. Based on the proportion of the cervical centra, the first South American plesiosaur described by Gay in 1848 is here referred to A. cf. parvidens. The coracoid of Aristonectes is described for the first time showing a cordiform fenestra, a feature only recorded in the Elasmosauridae among the Plesiosauria, therefore, these new data support the inclusion of Aristonectes within the Elasmosauridae. With the new material described in this paper, Aristonectes is one of the most frecuently recorded genera of Late Cretaceous plesiosaurs in the Southern Hemisphere.

A metriorhynchid crocodyliform braincase from northern Chile

ABSTRACT A three-dimensionally preserved metriorhynchid braincase from the Oxfordian of northern Chile is described. The specimen is referred to the metriorhynchid Metriorhynchus cf. M. westermanni. The excellent preservation provides clear sutures and a detailed description, and X-ray computed tomographic (CT) scanning provides internal anatomical details. The general pattern of the orbitotemporal region is consistent with that of the basal thalattosuchian Pelagosaurus typus as described recently. The specimen from northern Chile shares with other metriorhynchids (e.g., Cricosaurus araucanensis, Metriorhynchus westermanni, M. casamiquelai, and Dakosaurus andiniensis) a dorsally exposed laterosphenoid, a laterosphenoid-prootic suture forming a blunt crest separating the supratemporal fenestra into two fossae for muscular attachment, and the quadrate incompletely sutured to the braincase. Thus, these features characterize not only basal but derived Thalattosuchia, as suggested by previous authors. The main difference in the orbitotemporal region is that in the specimen described herein, and in the other metriorhynchids examined, the trigeminal fossa is developed mainly caudal to the trigeminal foramen, whereas in P. typus the fossa is developed rostral and caudal to the trigeminal foramen. CT scanning indicates the presence of enlarged dorsal dural venous sinuses overlying the brain, as it has been described recently in Steneosaurus pictaviensis, and a well-developed sinus within the quadrate. The large foramen ventrolateral to the occipital condyle, which characterizes metriorhynchids, is confirmed as the entry for the internal carotid artery.

Tithonian Marine Reptiles of the Eastern Pacific

Publisher Summary This chapter presents an up-to-date analysis of the South American Tithonian reptile fauna in a biogeographical context and interprets the pattern of the marine reptile distribution during the Late Jurassic. The temporal sequence of the Tithonian marine reptiles record begins in the early Tithonian levels of Cerro Lotena. All the Tithonian thalattosuchians from the eastern Pacific are Metriorhynchidae. It is found that in spite of their relative abundance, the diversity of ichthyosaurs in the Tithonian of South America is low. The Tithonian marine reptiles of the Neuquen Basin are distributed in sedimentary facies assigned to basinal environments. In European Tithonian basins, turtles, teleosaurids, and metriorhynchid crocodiles are characteristic of nearshore and lagoonal environments. During the Late Jurassic, probably before, and during the Middle Jurassic, exchange events between reptiles from the Andean region and the West Tethys were favored by the opening of the Hispanic Corridor. Callovian crocodiles in Chile and southwestern Mexico, Callovian plesiosaurs in the Neuquen Basin, and Oxfordian plesiosaurs and crocodiles in Cuba support this hypothesis. The links to the Tethyan fauna could also be favored during the Late Jurassic by the opening of a new seaway between South America, Africa, and Antarctica. The discovery of ichthyosaur remains and fishes from the Upper Jurassic outcrops in the northeast of the Antarctic Peninsula is the first evidence of marine vertebrates in this seaway.