First Direct Measurement: T. rex Ran at 97°F, Matching Human Body Temperature

Key points

• Researchers used clumped isotope paleothermometry on three T. rex teeth from the Hell Creek Formation in Montana to determine body temperature.
• The analysis revealed an average body temperature of 36.3°C, comparable to Indian and African elephants, and significantly higher than the 30.9°C found in contemporary crocodilians.
• The warm-blooded physiology allowed T. rex to thrive in a wider range of latitudes, including colder northern regions where cold-blooded reptiles could not survive.
• The findings support the theory that large theropods were active predators with high metabolic rates, distinct from modern reptiles and slightly cooler than modern birds.

Background

Previous studies, including a 2022 analysis, suggested dinosaurs had varied metabolisms, but lacked direct temperature measurements. This study builds on that by providing precise thermal data, confirming long-standing hypotheses about dinosaur endothermy.

How outlets are covering it

All three sources agree on the 36.3°C finding and its implication for T. rex being warm-blooded. Sci.News and Scientific American emphasize the novelty of the measurement technique, while Smithsonian Magazine highlights the broader implications for T. rex's geographic range, noting it could extend from Alaska to Mexico. Scientific American also notes that T. rex was cooler than modern birds, aligning with previous 2022 studies that placed T. rex on the lower end of endothermy.

Why it matters

This study provides direct evidence for the warm-blooded nature of T. rex, reshaping our understanding of dinosaur physiology, behavior, and habitat. It confirms that large theropods were active, high-metabolism animals capable of surviving in diverse climates, bridging the gap between reptilian ancestors and modern birds.

What to watch

Researchers plan to apply the same isotope analysis technique to avian dinosaurs and ancient mammalian ancestors to further map the evolution of endothermy. The method may also be used to determine the body temperatures of other extinct species, providing insights into their lifestyles and environments.