Evidence that dinosaur body temperatures varied between different groups has been presented this week in Nature Communications. Analyses of fossil eggshells show body temperatures were quite different between large sauropods and the more bird-like oviraptors, but no clear warm-blooded or cold-blooded signatures were seen.

Studying the body temperatures of extinct animals is difficult, but Robert Eagle and colleagues show that the isotopic composition in the carbonate of fossil eggshells can be used to determine the body temperatures of females during periods of ovulation. Eggshells are produced deep within the body, in the lower oviduct, and therefore reflect core body temperatures. The authors tested the isotopes of a suite of modern bird and reptile eggshells to see how they compared with measured body temperatures. This matrix was then used to assess the body temperature of Upper Cretaceous (roughly 70-80 million-year-old) dinosaur eggshells from long-necked titanosaurs and small oviraptors, both of which yielded unexpected results, with high body temperatures for the sauropods and low body temperatures for the oviraptors.

High body temperatures in sauropods may be due to the size of the animals; for example, some large modern leatherback turtles are known to have elevated body temperatures as a result of their size. The oviraptors were evidently not warm-blooded as in modern birds, but more work needs to be done to assess whether all dinosaurs had body temperatures different to those of modern birds.