UCLA study estimates Tyrannosaurus rex body temperature at about 97°F

A team of scientists at the University of California, Los Angeles has measured the body temperature of a Tyrannosaurus rex by analyzing isotopic ratios in tooth enamel. The study, published in Science Advances, reports an average temperature of 97.3°F (±4.5°F), comparable to that of present-day mammals. The researchers say the finding supports the hypothesis that T. rex was warm-blooded and capable of sustained activity, rather than a cold-blooded ambush predator.

The method relies on differences in the bonding of heavy and light carbon and oxygen isotopes, which vary with temperature during mineral formation. Improvements to the technique now allow accurate readings from very small enamel samples, enabling the team to sample teeth from the Natural History Museum in Los Angeles without causing significant damage.

"The isotopic composition of the enamel indicates a body temperature consistent with endothermy," the study’s lead author said.

The results contrast with measurements from ancient crocodile teeth, which showed temperatures around 88°F, typical of ectothermic reptiles. The researchers note that a warm-blooded metabolism would have allowed T. rex to inhabit a broader geographic range, including higher latitudes, and to sustain higher levels of activity.

The study adds to recent discoveries about T. rex locomotion, including trackways in North Dakota suggesting walking speeds of 3.5–4.5 mph and biomechanical models indicating that smaller individuals could run short distances faster than a human sprinter. However, the authors caution that the data do not resolve whether the dinosaur was primarily a predator, a scavenger, or both.

The findings illustrate how advances in fossil chemistry can provide new insights into the physiology of extinct species.