A 66-Million-Year-Old Tooth Shows T. Rex Ran Almost as Warm as a Human Body

The champion thermometer for Tyrannosaurus rex whitethorn person been successful its mouth. A survey published connected 9/16/2026 successful Science Advances utilized chemic signatures locked wrong fossil bony enamel to estimation however blistery the predator ran, landing astatine astir 97 degrees Fahrenheit, astir a quality assemblage temperature. “No one’s been capable to marque a somesthesia measurement similar this before,” UCLA geobiologist Robert A. Eagle said, aft the squad drilled tiny enamel samples, dissolved them successful phosphoric acid, and work the resulting state successful a wide spectrometer. The UCLA radical says the teeth constituent to an carnal that stayed warmer than its surroundings, strengthening the long-running lawsuit for warm-blooded tyrannosaurs.

Unearthing a dinosaur’s temperature

One of the astir amazingly “modern” numbers successful subject landed this fall: 97 degrees Fahrenheit. A survey published connected September 16, 2026, successful Science Advances utilized chemic signatures locked wrong fossil teeth to enactment a nonstop estimation connected however lukewarm Tyrannosaurus rex apt ran successful life, astir matching a quality body.

For decades, researchers person argued implicit whether large dinosaurs were warm-blooded oregon much reptile-like. This enactment is notable due to the fact that it moves beyond inference and into measurement, the benignant of step-change you usually spot erstwhile caller laboratory techniques mature and yet get applied to an old, stubborn question.

What bony enamel tin store for 66 cardinal years

The survey was led by UCLA geochemists Randon J. Flores and Robert A. Eagle, who analyzed three T. rex teeth to estimation assemblage temperature. Two of those teeth came from a skeleton nicknamed “Thomas,” held astatine the Natural History Museum of Los Angeles County and preserved to astir 70% completeness.

The halfway trick: bony enamel preserves uncommon “clumped” bonds betwixt c and oxygen isotopes, and the abundance of those clumps rises successful cooler temperatures and falls successful warmer ones. Enamel’s big, durable crystals defy chemic alteration implicit millions of years amended than bony does, making it an unusually reliable archive for this benignant of forensic chemistry.

The laboratory enactment down the header number

To work that somesthesia signal, Flores and Eagle utilized a dental drill to cod tiny enamel samples, dissolved the pulverization successful phosphoric acid, past measured the c dioxide state with a wide spectrometer. Eagle summed up the infinitesimal plainly: “No one’s been capable to marque a somesthesia measurement similar this before.”

The effect landed astatine astir 36°C, oregon 97°F. Eagle enactment it adjacent much directly: “We recovered T. rex was 36°C (97°F), astir the aforesaid arsenic humans.” The authors noted they could not wholly regularisation retired seasonal bias, though samples from antithetic parts of the Thomas teeth produced statistically indistinguishable temperatures.

Warm-blooded, but not bird-hot

That 97°F estimation sits supra modern cold-blooded reptiles, which typically tally astir 82 to 86°F, but beneath birds, which often timepiece 104 to 109°F adjacent though they’re evolutionary descendants of dinosaurs. The mediate crushed matters, due to the fact that it suggests tyrannosaurs generated important interior vigor without needfully operating similar today’s high-octane birds.

UCLA prof and co-author Aradhna Tripati connected the physiology to geography: “What the teeth archer america is that T. rex was warmer than the situation astir it,” and “A warm-blooded T. rex is simply a T. rex that tin spell astir anyplace connected the continent, including the Arctic.” The survey adds to cold-tolerance grounds similar a T. rex footprint recovered successful Alaska successful 2022.