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Hot-blooded marine reptiles



An interesting paper by Bernard and a handful of colleagues dealing with body temperature in Mesozoic marine reptiles, with a brief summary/comment by the ichthyopterygian expert Ryosuke Motani, in the last release of Science magazine:


Bernard, A., Lecuyer, C., Vincent, P., Amiot, R., Bardet, N., Buffetaut, E., Cuny, G., Fourel, F., Martineau, F., Mazin, J.-M. & Prieur, A., 2010. Regulation of body temperature by some Mesozoic marine reptiles. Science, 328(5984), 1379-1382. 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.

Motani, R., 2010. Warm-blooded "sea dragons"? Science, 328(5984), 1361-1362.
When dinosaurs roamed the land in the Mesozoic (251 to 65 million years ago), the top predators in the ocean were reptiles. Three lineages of Mesozoic marine reptiles (plesiosaurs, ichthyosaurs, and mosasaurs) were especially successful (see the first figure). They were similar to current marine mammals in many respects. They fed on fish, cephalopods, bivalves, and other air-breathing vertebrates. Ichthyosaurs evolved dolphin-like body plans. Plesiosaurs became underwater fliers, vaguely resembling sea lions. It now appears that similarities to today's marine mammals extended further: On page 1379 of this issue, Bernard et al. report that some ancient reptiles may have been able to sustain a constant body temperature (i.e., homeothermy).