Researchers at the University of California, Los Angeles have measured Tyrannosaurus rex's body temperature by analysing fossilised teeth, finding it ran at approximately 36.3°C—comparable to modern elephants. This discovery provides evidence that T. rex was warm-blooded and actively regulated its body temperature, settling a long-standing palaeontological debate about whether the dinosaur possessed the physiology to sustain the active, predatory lifestyle suggested by fossil evidence and modern reconstructions.

The team used a technique called clumped isotope thermometry, which measures how rare heavy isotopes of carbon and oxygen bond together in tooth enamel, a process dependent on formation temperature. They analysed three teeth from Montana's Hell Creek Formation, yielding readings of 37.3°C, 35.9°C, and 34.7°C. For context, Indian and African elephants maintain roughly 36°C, whilst modern crocodilians average 30.9°C and small flying birds exceed 41°C. The researchers verified that 66 million years underground had not altered the chemical composition of the enamel, validating their findings.