New technology developed by US researchers should shed light on whether dinosaurs were cold-blooded or warm-blooded animals, a study released Monday said.
California Institute of Technology (Caltech) researchers unveiled what they said was the first method for direct measurement of the body temperatures of large extinct vertebrates using analyses of isotopes in animals' bones, teeth, and eggshells.
The findings were published in the early edition of the Proceedings of the National Academy of Sciences (PNAS).
"This is not quite like going back in time and sticking a thermometer up a creature's back end," said researcher John Eiler, a geochemistry professor Caltech. "But it's close."
To study changes in temperature regulation in extinct animals requires knowing what their body temperatures once were. The team's method looks at the concentrations of two rare isotopes -- carbon-13 and oxygen-18.
"Heavy isotopes like to bond, or clump together, and this clumping effect is dependent on temperature," said lead author Robert Eagle, a Caltech postdoctoral scholar.
"At very hot temperatures, you get a more random distribution of these isotopes, less clumping. At low temperatures, you find more clumping."
After proving their method on living elephants and sharks, the team turned to the extinct.
They examined a 12-million-year-old fossil from a relative of the rhinoceros, as well as from a cold-blooded member of the alligator family tree. "We found we could measure the expected body temperature of the rhino-like mammal, and could see a temperature difference between that and the alligator relative, of about six degrees centigrade," Eagle explained.
"When we look at tooth enamel, for instance, what we get is a record of the head temperature of the animal when the tooth grew," Eiler said. But "if you want to know what his big-toe temperature was two years later, too bad."
With an accurate paleothermometer working, the researchers want to look further back at body temperatures of less-known vertebrates.
"Before mammals and birds," Eagle said, "we have no good idea what physiology these ancient creatures had."
Now it is the dinosaurs' turn to get a closer temperature look.
"We're looking at eggshells and teeth to see whether the most conspicuous dinosaur species were warm- or cold-blooded," Eiler explained.