A Tooth Pinpoints T. rex’s Body Temp

A T. rex tooth has preserved something paleontologists never had before: an actual number for the animal's body temperature.

Scientists analyzed portions of two teeth from Thomas, one of the most complete tyrannosaur skeletons at the Natural History Museum of Los Angeles County. They measured chemical bonds between rare carbon and oxygen isotopes in the enamel using a technique UCLA researchers spent more than a decade refining until it required only a few milligrams of fossil material.

The result: about 36 degrees Celsius, or 97 degrees Fahrenheit. Roughly human body temperature.

That reading sits below modern birds, which typically run between 104 and 109 degrees Fahrenheit (40 to 43 degrees Celsius), but supports T. rex as an endothermic, warm-bodied animal. That helps explain how tyrannosaurs could range from Mexico to Alaska. Paleontologists have found their fossils in Cretaceous Alaska, where winters would have been difficult territory for a cold-blooded predator.

Geobiologist Robert Eagle, who has worked on the question for 15 years, says the finding recasts T. rex as a genuinely warm-bodied animal, one that reshapes assumptions about its behavior, physiology, how it interacted with other species and how much food it needed to survive.

Sixty-six million years in the ground, and the teeth still remembered.

Read the full story at UCLA Newsroom, September 16, 2026

Hot Take: Somewhere, a paleontologist is humming ‘Hot Blooded,’ T. rex clocked in at 97 degrees.