Posted on behalf of Richard A. Lovett
Some of the largest reptiles roaming the sea during the time of the dinosaurs may have been warm-blooded, a new study finds. In this week’s issue of Science, Aurélien Bernard and a team of French and Dutch colleagues looked at oxygen isotopes in the teeth of three large marine reptiles: ichthyosaurs, plesiosaurs, and mosasaurs.
Oxygen comes in two stable isotopes, Oxygen-16 and Oxygen-18, with their relative abundances in teeth and bones dependent on the temperature at which an animal grew.
The scientists compared the teeth of fish and reptiles that shared the same oceans at a variety of locations, ranging from tropical (30°-35° C) to cold (10°-12° C). Because fish don’t regulate their body temperatures, their isotope levels reflected ocean temperature. But the reptiles’ isotopes didn’t vary. “That means their body temperatures remained constant, independent of where they lived,” says study coauthor Christophe Lécuyer, of Paléoenvironnements et Paléobiosphère, Université Lyon, France.
The data indicate that these reptiles had body temperatures of 35°-39°, compatible with the high metabolic rates of fast-moving, wide-ranging predators.
But the ability of these animals to range far and wide means that their isotopes may not reflect the environments in which they died, says Robert Eagle, of the Division of Geological and Planetary Sciences at California Institute of Technology, in Pasadena.
Another problem, he says, is that isotope ratios in teeth are dependent not only on body temperature, but on the levels of the oxygen isotopes in the animals’ bloodstreams when their teeth were growing — something that might vary among species due to dietary and physiological differences. In a study published last month in the Proceedings of the National Academy of Sciences (see: Teeth tell temperature tales), Eagle and colleagues presented an alternative analysis, based on a combination of oxygen and carbon isotopes, which they believe to be less affected by factors other than temperature. “It would be interesting to see if we get the same answer,” he says.
Image: Platypterygius kiprjianovi / Dmitry Bogdanov