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Plesiosaurus tournemirensis Sciau, Crochet and Mattei, based on a nearly complete skeleton with skull from the Upper Toarcian (Lower Jurassic) of Tournemire (Aveyron Department, southern France), is here redescribed and reinterpreted. Comparisons with other plesiosaurs indicate that it belongs to a new genus, Occitanosaurus. O. tournemirensis is characterized mainly by its spatulate premaxillae with short facial process, very high postorbital broadly contacting posterior ramus of the maxilla, trapezoidal jugal excluded from orbital margin, orbit diagonally oriented, temporal fenestra with a sigmoidal anterior margin, 43 cervical vertebrae, powerful interclavicle-clavicle complex and coracoids with a pointed protuberance on lateral border and expanded posterolateral cornua. Cranial and cervical vertebra features show that this new genus is undoubtedly a representative of the Elasmosauridae. A preliminary cladistic analysis of long-necked plesiosaurs reveals that, within Elasmosauridae, Occitanosaurus is a close relative of Microcleidus and Muraenosaurus. Institutional abbreviations. CMNH, Colorado MuseumType genus. Elasmosaurus Cope, 1868.Emended diagnosis. Weakly excavated ventral cheek margin; palate without anterior pterygoid vacuities; platycoelous vertebral articular surfaces; more than 40 cervical vertebrae; cervical centra longer than high; lateral keel in mid-anterior cervical vertebrae. For a characterization of elasmosaurids see Brown (1993). Genus OCCITANOSAURUS gen. nov.Derivation of name. From Occitania, the area where the Occitan language is spoken (currently includes most of southern France, Val d'Aran of Spain and several Piedmont valleys of Italy) and Sauros (Greek): lizard. Sciau, Crochet and Mattei, 1990 Diagnosis. As for type and only species of the genus, Occitanosaurus tournemirensis (Sciau, Crochet and Mattei, 1990). Type species. Plesiosaurus tournemirensis

Despite their profound adaptations to the aquatic realm and their apparent success throughout the Triassic and the Jurassic, ichthyosaurs became extinct roughly 30 million years before the end-Cretaceous mass extinction. Current hypotheses for this early demise involve relatively minor biotic events, but are at odds with recent understanding of the ichthyosaur fossil record. Here, we show that ichthyosaurs maintained high but diminishing richness and disparity throughout the Early Cretaceous. The last ichthyosaurs are characterized by reduced rates of origination and phenotypic evolution and their elevated extinction rates correlate with increased environmental volatility. In addition, we find that ichthyosaurs suffered from a profound Early Cenomanian extinction that reduced their ecological diversity, likely contributing to their final extinction at the end of the Cenomanian. Our results support a growing body of evidence revealing that global environmental change resulted in a major, temporally staggered turnover event that profoundly reorganized marine ecosystems during the Cenomanian.

What the body temperature and thermoregulation processes of extinct vertebrates were are central questions for understanding their ecology and evolution. The thermophysiologic status of the great marine reptiles is still unknown, even though some studies have suggested that thermoregulation may have contributed to their exceptional evolutionary success as apex predators of Mesozoic aquatic ecosystems. We tested the thermal status of ichthyosaurs, plesiosaurs, and mosasaurs by comparing the oxygen isotope compositions of their tooth phosphate to those of coexisting fish. Data distribution reveals that these large marine reptiles were able to maintain a constant and high body temperature in oceanic environments ranging from tropical to cold temperate. Their estimated body temperatures, in the range from 35 degrees +/- 2 degrees C to 39 degrees +/- 2 degrees C, suggest high metabolic rates required for predation and fast swimming over large distances offshore.

Marine reptiles are an adaptive assemblage including a mosaic of forms with fully marine groups (ichthyosaurs, "nothosaurs", plesiosaurs, placodonts, thalattosaurs and hupehsuchians), as well as groups containing continental representatives (turtles, crocodiles, lizards and snakes) Forty-six families of marine reptiles are recorded during the Mesozoic The fossil record of marine reptiles is punctuated by two major extinctions at the Middle-Late Triassic transition (loss of 64 % of families) and at the Cretaceous-Tertiary boundary ( 36 % of families died out) The Ladinian-Carnian boundary event coincides with an important regressive phase and affects essentially coastal forms. The K/T boundary is characterized by selective extinctions among marine reptiles, probably linked with a break in the food chain.

During the Mesozoic, various groups of reptiles underwent a spectacular return to an aquatic life, colonizing most marine environments. They were highly diversified both systematically and ecologically, and most were the largest top-predators of the marine ecosystems of their time. The main groups were Ichthyosauria, Sauropterygia, Thalattosauria, and several lineages of Testudinata, Crocodyliformes, Rhynchocephalia and Squamata. Here we show that the palaeobiogeographical distribution of these marine reptiles closely followed the break-up of the supercontinent Pangaea and that they globally used the main marine corridors However, if large faunal interchanges were possible at a global scale following a dispersal model, some provinces, such as the Mediterranean Tethys, were characterized by a peculiar faunal identity, illustrating an absence of migration with time despite the apparent lack of barriers. So, if Continental Drift enabled global circulations and faunal interchanges via dispersals among Mesozoic marine reptiles, others parameters, such as ecological and biological constraints, probably also played a role in the local endemic distribution of some of these marine groups, as they do today.

BackgroundIchthyosaurs are reptiles that inhabited the marine realm during most of the Mesozoic. Their Cretaceous representatives have traditionally been considered as the last survivors of a group declining since the Jurassic. Recently, however, an unexpected diversity has been described in Upper Jurassic–Lower Cretaceous deposits, but is widely spread across time and space, giving small clues on the adaptive potential and ecosystem control of the last ichthyosaurs. The famous but little studied English Gault Formation and ‘greensands’ deposits (the Upper Greensand Formation and the Cambridge Greensand Member of the Lower Chalk Formation) offer an unprecedented opportunity to investigate this topic, containing thousands of ichthyosaur remains spanning the Early–Late Cretaceous boundary.Methodology/Principal FindingsTo assess the diversity of the ichthyosaur assemblage from these sedimentary bodies, we recognized morphotypes within each type of bones. We grouped these morphotypes together, when possible, by using articulated specimens from the same formations and from new localities in the Vocontian Basin (France); a revised taxonomic scheme is proposed. We recognize the following taxa in the ‘greensands’: the platypterygiines ‘Platypterygius’ sp. and Sisteronia seeleyi gen. et sp. nov., indeterminate ophthalmosaurines and the rare incertae sedis Cetarthrosaurus walkeri. The taxonomic diversity of late Albian ichthyosaurs now matches that of older, well-known intervals such as the Toarcian or the Tithonian. Contrasting tooth shapes and wear patterns suggest that these ichthyosaurs colonized three distinct feeding guilds, despite the presence of numerous plesiosaur taxa.Conclusion/SignificanceWestern Europe was a diversity hot-spot for ichthyosaurs a few million years prior to their final extinction. By contrast, the low diversity in Australia and U.S.A. suggests strong geographical disparities in the diversity pattern of Albian–early Cenomanian ichthyosaurs. This provides a whole new context to investigate the extinction of these successful marine reptiles, at the end of the Cenomanian.