Hot-blooded marine reptiles

[Jocelyn Falconnet <j.falconnet@gmail.com>]

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).