The body temperature of Tyrannosaurus rex.

Despite an extensive history of study, quantitative constraints on the thermophysiology of Tyrannosaurus rex remain limited. Here, we derive a thermodynamically based determination of T. rex body temperatures from clumped isotopes in tooth enamel. Measurements of three T. rex teeth from the Late Cretaceous Hell Creek Formation yield a temperature of 36.3 ± 2.5°C (1 SE), comparable to modern endotherms. Teeth of coeval Hell Creek Formation crocodilians yielded temperatures significantly lower than did those of T. rex. Comparison with proxy-derived paleotemperatures and model simulations indicates that T. rex maintained a higher body temperature than its environment. Projected habitat suitability for T. rex based on these results shows that most of the North American paleocontinent, including colder and higher latitudes, were potentially accessible to the species.