Study estimates Tyrannosaurus rex body temperature at about 97°F

Researchers have estimated the body temperature of Tyrannosaurus rex at roughly 97 degrees Fahrenheit (36 degrees Celsius), a level comparable to that of present-day humans. The finding, published in Science Advances, derives from chemical analysis of tooth enamel taken from a nearly complete T. rex skeleton housed at the Natural History Museum of Los Angeles County.

The team, led by geobiologist Robert Eagle of UCLA and climate scientist Aradhna Tripati, measured carbon and oxygen isotopes in milligram samples of two teeth. These isotopes form bonds at rates that vary with temperature, allowing the scientists to infer the temperature at which the enamel formed about 66 million years ago.

"It's probably the most direct and least complicated constraint on the actual body temperature of a T. rex that's been possible before," Eagle said.

The estimated temperature is higher than that of contemporary cold-blooded reptiles, which typically range from 82°F to 86°F, and falls within the range observed in modern warm-blooded mammals and birds. The researchers argue that such a temperature would have enabled T. rex to remain active for longer periods and to inhabit a wide geographic range, from present-day Mexico to Alaska, even in cooler climates.

"A warm-blooded T. rex is a T. rex that can go almost anywhere on the continent, including the Arctic," Tripati noted.

Vertebrate paleontologist Thomas Holtz Jr. said the results add confidence to the hypothesis that tyrannosaurs were endothermic, though he cautioned that the method has yet to be applied to other dinosaur groups. Future work may extend the technique to species such as Triceratops and Stegosaurus to assess whether warm-bloodedness was widespread among dinosaurs.

The study also highlights the potential of tooth-based thermometry to investigate metabolic traits in extinct organisms, ranging from other dinosaurs to mammoths and megatooth sharks.