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.
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