T. rex Teeth Reveal a Human-Like Body Temperature

Scientists have produced the first direct estimate of Tyrannosaurus rex’s body temperature, finding that the giant predator ran at about 36.3 degrees Celsius, or 97 degrees Fahrenheit. That is close to human body temperature and unusually warm for a reptile, adding strong evidence that T. rex was warm-blooded rather than dependent on sunshine for heat.

The estimate comes from a few milligrams of enamel taken from two fossil teeth. Researchers measured temperature-sensitive bonds between rare forms of carbon and oxygen that became locked into the enamel as the teeth formed. Because fewer of these bonds form at higher temperatures, the chemical pattern works as a prehistoric thermometer. Tooth enamel is especially useful because its durable crystal structure can resist chemical changes over millions of years.

The team spent more than a decade refining the technique and reduced the amount of fossil material required by roughly 90 percent. That advance persuaded a Los Angeles museum to provide tiny samples from teeth that were not on display.

A warm body would have supported an active metabolism and helped T. rex remain energetic in cooler conditions. Combined with reconstructions of the late Cretaceous climate, the result suggests the dinosaur could have inhabited a broad area of North America, potentially from present-day Mexico to Alaska, while needing substantial food to fuel its metabolism.