Determining the thermoregulatory strategies of present-day and fossil marine vertebrates using oxygen isotopes: palaeoenvironmental implications

• Main Author: Séon, Nicolas
• Other Authors: Centre de Recherche en Paléontologie - Paris (CR2P), Muséum national d'Histoire naturelle (MNHN)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Muséum national d'Histoire naturelle - MNHN, Paris, Peggy Vincent, Romain Amiot, Sylvain Charbonnier
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2023
• Subjects: thermophysiology; isotopes; oxygen; cetaceans; Ichthyosauria; Plesiosauria; thermophysiologie; oxygène; Cetacea; [SDV]Life Sciences [q-bio]; Killer Whale; Orca; Orcinus orca; Killer whale
• Online Access: https://mnhn.hal.science/tel-04572084; https://mnhn.hal.science/tel-04572084/document; https://mnhn.hal.science/tel-04572084/file/Manuscrit_th%C3%A8se_SEON.pdf

Recent paleobiogeographic, osteohistological and geochemical studies indicate that Mesozoic Ichthyosauria and Plesiosauria were endothermic and probably homeothermic organisms such as Cetacea. By this thermoregulatory strategy, the oxygen isotope composition of the phosphate group of the bioapatite of their bones and teeth (δ18Op) could constitute a good proxy to trace the variations of the oxygen isotope composition of the oceans (δ18Osw) of the Mesozoic and thereby improve the estimates of paleotemperatures of the oceans of the epoch based on the thermo-dependence of the isotope fractionation of the oxygen. However, to use these marine vertebrates as biotracers of the variations of δ18Osw, it is necessary to determine what is the relationship between the oxygen isotope composition of the body water (δ18Obody water), the water from which mineralize skeletal elements and teeth, and that of the sea water (δ18Osw); but also to characterize the intra-skeletal variability of the δ18Op in order to define the skeletal elements that it is relevant to use for future paleoceanographic studies.To resolve these issues, the oxygen isotope composition of the body fluids (blood plasma and urine) of three species of extant marine vertebrates (the loggerhead turtle Caretta caretta, the common bottlenose dolphin Tursiops truncatus and the killer whale Orcinus orca) kept under controlled conditions was compared to that of their basin and their diet. The results indicate that the oxygen isotope composition of the body fluids and that of the water in which they live is largely dependent on the presence of salt glands and the type of diet. In parallel, six intra-skeletal isotope maps of the δ18Op were carried out on two species of Cetacea (two specimens of short beaked common dolphin Delphinus delphis delphis and one specimen of Commerson’s dolphin Cephalorhynchus commersonii kerguelensis), two species of Osteichthyes (one specimen of Atlantic bluefin tuna Thunnus thynnus and one specimen of swordfish Xiphias gladius) and one ...