T. rex teeth suggest a body temperature of 36°C, close to the human average

Tyrannosaurus rex had a body temperature of about 36°C (97°F), roughly the same as an average human, according to a study published in Science Advances on September 16, 2026. The UCLA-led team estimated the temperature from chemical signatures in the enamel of two teeth from one of the most complete T. rex skeletons known.

The paper is titled "The body temperature of Tyrannosaurus rex."

A chemical thermometer in tooth enamel

The researchers used a technique that measures how often rare isotopes of carbon and oxygen bond together in the mineral of tooth enamel. Warmer body temperatures produce fewer of these bonds than cooler ones, so the bonds act as a thermometer that records conditions while the tooth formed, according to UCLA.

To run the analysis, the team drilled small amounts of enamel from the fossils, dissolved the powder in phosphoric acid and measured the carbon dioxide gas released with a mass spectrometer, Phys.org reports. A refinement of the method over the past decade has cut the amount of material needed by roughly 90 percent.

"No one's been able to make a temperature measurement like this before. We found T. rex was 36 Celsius (97 Fahrenheit), about the same as humans," said Robert Eagle, a UCLA geobiologist and co-author of the study.

Teeth from Thomas the T. rex

The teeth came from "Thomas the T. rex," a skeleton at the Natural History Museum of Los Angeles County that was excavated from the Hell Creek area of Montana. The sampled teeth are not on public display.

Luis Chiappe, a curator at the museum, said: "Sacrificing small portions of two teeth to learn about T. rex's body temperature is definitely worth the trade-off."

To check that the signal was biological rather than the result of changes to the fossil over time, the team also measured an ancient crocodilian from the same site. It came out at 30°C (86°F), consistent with a cold-blooded animal, according to UCLA.

Between reptiles and birds

The T. rex result sits between the two groups most closely related to dinosaurs. Modern cold-blooded reptiles typically have body temperatures of 28 to 30°C (82 to 86°F), while modern birds run at 40 to 43°C (104 to 109°F).

Alessandro Chiarenza, a paleontologist at University College London, said: "Now we have empirical evidence using this geologic thermometer."

According to Phys.org, the findings support the idea that T. rex was warm-blooded, which fits with active predation and scavenging and with the ability of tyrannosaurs to survive cooler winters in Cretaceous Alaska.

Why it matters

Whether dinosaurs were warm-blooded, cold-blooded or somewhere in between has been debated for decades, largely on indirect evidence such as bone growth and anatomy. This study offers a direct temperature estimate for the most famous dinosaur, using a method checked against a cold-blooded animal from the same rocks. It adds measured evidence to the picture of T. rex as an active, warm-bodied animal.

Sources

This article was drafted with AI assistance and checked against the sources above. Company claims are reported as claims. Cover image is AI-generated.