Isotope analysis suggests Tyrannosaurus rex maintained a body temperature near that of modern elephants

A team of geochemists from the University of California, Los Angeles measured the body temperature of Tyrannosaurus rex by analyzing the isotopic composition of tooth enamel. Using clumped isotope thermometry, which records temperature independent of water composition, they examined three teeth from the Hell Creek Formation in Montana. The enamel showed no signs of post-burial alteration, allowing reliable temperature estimates.

The two teeth from a juvenile specimen yielded temperatures of 37.3 °C and 35.9 °C, while a third tooth from a different individual recorded 34.7 °C. Averaged together, the data indicate a body temperature of roughly 36.3 °C (±2.5 °C), comparable to that of modern African and Indian elephants and within the range of large flightless birds such as ostriches. By contrast, five crocodilian teeth from the same ecosystem produced an average of 30.9 °C, matching the temperature range of present-day crocodiles.

To assess ambient conditions, the researchers analyzed clumped isotopes in fossil freshwater mussels from the same formation, which reflect summer water temperatures averaging about 26 °C. Climate-model simulations of the late Cretaceous also suggest maximum summer temperatures near 33 °C and mean annual temperatures around 21 °C at the site. These findings imply that T. rex maintained a body temperature consistently above its environment.

The authors note that large body size can confer thermal inertia (inertial homeothermy), but the measured temperatures exceed predictions for a cold-blooded animal of comparable mass. They argue that the results add to growing evidence that T. rex was a homeothermic endotherm, though they acknowledge that the sample size is limited and seasonal bias cannot be completely excluded.

Using thermal tolerance data from modern mammals and birds, the team modeled potential habitat suitability across late-Cretaceous North America. The model suggests that T. rex could have inhabited a broad range of latitudes, from humid southern regions to polar northern areas, consistent with known fossil localities and recent finds in Alaska and Texas. The study concludes that, if confirmed, the dinosaur possessed physiological flexibility that allowed it to thrive across diverse climates.

“The teeth record a body temperature that is higher than the surrounding environment, supporting the view that T. rex was a warm-bodied predator,” the researchers wrote.

Future work will apply the same isotopic technique to other dinosaur taxa to determine how widespread this physiological trait was and when it first evolved.