Plesiosauria

Abstract

Patagonian plesiosaurs are among the first Mesozoic reptiles described in South America. However, they are scarcely known, and most of the findings are recent. They are scarce compared to the record of the Northern Hemisphere, but concerning the taxonomic diversity and wide temporal distribution, they are the referents of Gondwana. Jurassic and Early Cretaceous plesiosaurs come from the Neuquén Basin, a wide embayment of the Pacific Ocean on northwestern Patagonia. Those of the Late Cretaceous come from the Chilean Patagonia (Pacific Ocean), and Argentine Patagonia, which was largely overflooded by the southern Atlantic by those times. With different swimming and prey capture strategies, plesiosaurs have been the large pelagic reptiles that sailed all the seas of the world, even at high latitudes. Despite the controversial points in the phylogeny of the Plesiosauria, and consequently in biogeographic interpretations, some features on the distributions of theses reptiles can be outlined. The Patagonian rhomaleosaurid Maresaurus of the early Bajocian has close affinities with forms of the European Lias and Callovian. Likewise, forms referred to cf. Cryptoclidus and cf. Muraenosaurus entered the Neuquén Basin during the early Callovian when specimens of these genera lived in the European Tethys. Toward the end of the Jurassic plesiosauroids and pliosaurids inhabited the European Tethys. In the Neuquén Basin, only pliosaurids (Liopleurodon, Pliosaurus) have been found. The lack of plesiosauroids could be explained because the prospected areas correspond to off-shore environments. Precisely, in the same basin, but during a shallowing up stage (Valanginian-Hauterivian) only elasmosaurids are recorded. Toward the end of the Mesozoic, Patagonia was partially overflooded by the South Atlantic, becoming an archipelago. The elasmosaurids found there have a mainly South Gondwanan distribution (Aristonectes, cf. Mauisaurus, Tuarangisaurus), while the polycotylid Sulcusuchus is unknown elsewhere in the world.