Were some gigantic Jurassic sea creatures warm-blooded?

In ancient Mesozoic seas, the biggest predators might not have been entirely cold-blooded killers. Rather, a new studysuggests some of these rapacious reptiles might have been able to regulate their own body temperature, thereby expanding their hunting ranges. 

Some modern aquatic reptiles, including leatherback turtles, as well as some sharks and tuna are able to keep their body temperatures relatively stable compared to the fluctuating water temperatures around them. But just when and how many times this ability emerged in the evolutionary past has remained up for debate, shrouding many questions about the impact of ancient environmental changes on adaptation and hunting strategies.

The new study, published online June 10 in Science, proposes that ichthyosaurs, plesiosaurs and, perhaps to a lesser extent, mosasaurs, were all able to maintain relatively stable body temperatures in tropical and frigid waters alike some 251 to 65 million years ago.

By analyzing oxygen isotopes in the fossil teeth of these extinct animals, researchers were able to assess the creature’s body temperature when the teeth were growing—even for teeth that protruded from the mouth. And comparing isotope ratios among animals that presumably lived in the same time and place, the team determined the reptiles’ different internal temps—and different temperature regulation systems.

The researchers, led by Aurélien Bernard, of Paléoenvironnements et Paléobiosphère at the University of Lyon, found that these extinct marine behemoths were able to keep their internal temperatures between about 35 degrees Celsius and 39 degrees C (normal human body temperature is 37 C) regardless of ambient water temperature. And smaller fish that were found nearby in the same fossil beds, whose body temperatures were assumed to be closer to the water temperature, had much more variable stats.

Continued:  http://blogs.scientificamerican.com/observations/2010/06/10/were-some-gigantic-jurassic-sea-creatures-warm-blooded/