Carbon-oxygen isotope bonds in the enamel of three T. rex teeth from Montana placed the animal's body temperature near 36°C. Teeth from crocodilian relatives in the same formation yielded lower and more variable values. The result fits internal heat production, but three teeth cannot by themselves settle the metabolism of the entire species.
Carbon-oxygen isotope bonds in the enamel of three T. rex teeth from Montana's Hell Creek Formation yielded a body-temperature estimate of 36.3°C, with uncertainty of plus or minus 2.5°C. UCLA summarized the result as about 36°C. Because enamel formed while the animal was alive and does not remodel continuously like bone, it served as a chemical record capable of preserving ancient body temperature.[1], [2]
For comparison, researchers also measured five teeth from crocodilian relatives found in the same geological formation. Those samples averaged 30.9°C and varied more widely than the T. rex teeth. Consistent with living crocodilians' greater dependence on environmental temperature, the comparison supported the view that the T. rex result did not arise only from a giant body retaining heat. Temperature alone still cannot reveal every part of an animal's energy use.[2]
A value near 36°C fits the interpretation that T. rex stayed warmer than a typical reptile relying on environmental heat and produced heat internally. It is also close to the range of large living mammals. The measurement, however, rests on three teeth from two individuals. It does not show that every T. rex lived at the same temperature, that all dinosaurs shared one thermal strategy, or that its metabolic rate matched that of modern mammals.[1], [2]
