Body temperatures of modern and extinct vertebrates from 13C-18O bond abundances in bioapatite. 2010. R. A. Eagle, et al. PNAS published online before print May 24.
The technique the team has developed to measure body temperature in extinct vertebrates looks at the concentrations of two rare isotopes—carbon-13 and oxygen-18. "These heavy isotopes like to bond, or clump together, and this clumping effect is dependent on temperature," says Robert Eagle. "At very hot temperatures, you get a more random distribution of these isotopes, less clumping. At low temperatures, you find more clumping."
In living creatures, this clumping can be seen in the crystalline lattice that makes up bioapatite—the mineral from which bone, tooth enamel, eggshells, and other hard body parts are formed. "When the mineral precipitates out of the blood—when you create bone or tooth enamel—the isotopic composition is frozen in place and can be preserved for millions of years," he adds.
"This is not quite like going back in time and sticking a thermometer up a creature's back end," says John Eiler, "but it's close." link