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Thermophysiologies des reptiles marins mésozoïques révélées par la composition isotopique de l'oxygène des tissus phosphatés

Abstract : There are currently about a hundred species of marine reptiles (snakes, turtles, crocodile and Galapagos iguana). With the exception of some turtles, all of these organisms live in the intertropical zones where they absorb heat from their environment in order to increase their body temperature, mainly through behavioral regulation. During the Mesozoic (from -252 to -66 Million years), the specific diversity of marine reptiles was at least five times greater than today, with taxa such as Ichthyosauria, Plesiosauria, Mosasauroidea but also Crocodylomorpha and Testudinata (turtles). Fossil remains of Plesiosauria and Ichthyosauria were found in strata deposited at low to subpolar paleolatitudes, suggesting they had a thermophysiology allowing them to live in cold waters. In addition, histological studies of long bone sections of Ichthyosauria, Plesiosauria and Crocodylomorpha have revealed rapid rates of bone growth followed by strong remodeling suggesting high metabolism. To study the thermophysiology of marine reptiles of the Mesozoic from another perspective, the isotopic oxygen composition of the hydroxyapatite constituting dental enamel and bone has been analyzed in order to estimate the body temperatures of these organisms. These temperatures have then been compared to those of poikilothermic ectotherms (Chondrichthyes and Osteichthyes) found in the same deposits. Body temperature estimates indicate that Ichthyosauria and Plesiosauria had high and constant temperatures, in contrast to those of Metriorhynchidae and Mosasauroidea that appeared to vary with those of their living environment. Consequently, Ichthyosauria and Plesiosauria were supposed to be homeothermic endotherms while Metriorhynchidae and Mosasauroidea were poikilothermic endotherms. Teleosauridae seem to have an ectothermic thermophysiology coupled with a behavioral regulation linked to their semi-aquatic ecology. The presence of endothermy involving temperature independence from the environment probably conferred a significant adaptative advantage for these organisms to colonize high-latitude environments and to survive cooling episodes of the Mesozoic.
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Submitted on : Friday, November 20, 2020 - 12:04:36 PM
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  • HAL Id : mnhn-03016214, version 1

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Nicolas Séon, Romain Amiot, Peggy Vincent. Thermophysiologies des reptiles marins mésozoïques révélées par la composition isotopique de l'oxygène des tissus phosphatés. Bulletin de l’Association paléontologique de Villers-sur-Mer, A paraître, Actes du premier colloque de l’APVSM, « Paléontologie et Archéologie en Normandie », 1 (1). ⟨mnhn-03016214⟩

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