Tyrannosaurus rex may have been far warmer than its reptilian appearance suggests. Scientists examining fossil tooth enamel estimate the dinosaur's average body temperature at approximately 36.3°C, remarkably close to that of modern humans.
The research offers one of the clearest direct measurements yet of dinosaur physiology. While rapid growth, active behavior and fossils found across varied climates had long indicated that many dinosaurs generated internal heat, the new analysis provides a precise temperature estimate for the iconic theropod.
A chemical record preserved in teeth
The team analyzed enamel from three T. rex teeth using clumped-isotope thermometry. This method measures how often heavier carbon and oxygen isotopes bond within the mineral structure of a tooth. Those pairings vary predictably according to the temperature at which enamel formed, allowing researchers to reconstruct an animal's internal conditions millions of years later.
Researchers used samples from two teeth belonging to "Thomas," a young adult T. rex from Montana's Hell Creek Formation, along with a third isolated tooth. The results consistently pointed to a temperature of 36.3°C. By comparison, crocodilian teeth from the same geological formation averaged 30.9°C, while fossil bivalves indicated warmer-season environmental temperatures near 25.9°C.
Scientists at UCLA refined the process over about a decade to require only tiny enamel samples, helping preserve rare museum fossils while opening the method to wider study.
What a warmer T. rex could mean
A body temperature near 36°C supports the view of T. rex as an energetically active animal capable of producing and retaining substantial metabolic heat. Such physiology could have enabled it to remain mobile across a broad range of climates, including cooler northern environments during the Late Cretaceous.
The researchers note that body size may also have helped T. rex retain heat, so temperature alone cannot define every aspect of its metabolism. Still, the evidence adds an important data point to the growing picture of dinosaurs as diverse, dynamic animals with sophisticated ways of managing body heat.
Published in Science Advances, the study demonstrates how minute chemical signals in fossils can reshape our understanding of prehistoric life. As this technique is applied to more species, it could build a richer map of how dinosaurs adapted to changing environments and evolved across deep time.
