T. rex was as warm as an elephant, tooth analysis reveals

When people think of dinosaurs, they tend to picture reptiles — creatures like lizards or crocodiles that bask in the sun to warm up and retreat to the shade to cool down. T. rex was long assumed to regulate its body temperature in much the same way.

New research suggests otherwise. A study analyzing chemical traces preserved in T. rex teeth has calculated the dinosaur's body temperature at 36.3 degrees Celsius — roughly as warm as a modern elephant.

A reptile and a Tyrannosaurus rex. [AI-generated image]

Whether dinosaurs were cold-blooded ectotherms or warm-blooded endotherms capable of generating their own body heat has been debated for decades. Studies examining bone growth patterns and the energy demands of locomotion have pointed toward endothermy, though some researchers have argued that not all dinosaurs fit that profile. T. rex, despite being the most extensively studied dinosaur, remained an open question when it came to body temperature.

A research team led by Landon Flores and Robert Eagle at UCLA published findings in Science Advances, Vol. 12, No. 38, reporting a calculated body temperature for T. rex based on analysis of the dinosaur's teeth.

A Tyrannosaurus rex tooth used in this study to calculate body temperature. [S. Abramowicz/Dinosaur Institute, Natural History Museum of Los Angeles County, Science Advances Vol. 12, No. 38]

T. rex body temperature: 36.3 degrees Celsius

The method centered on examining tooth enamel, the hard outer layer of a tooth.

Enamel contains carbonate minerals, and within them, the rate at which heavy carbon and heavy oxygen bond together as neighbors varies with the temperature at which the tooth formed. The lower the temperature, the more frequently the two elements bond. By measuring that bonding ratio, the researchers were able to work backward and calculate the temperature.

Estimated body temperature measurements from the study. [Science Advances Vol. 12, No. 38]

The analysis used three T. rex teeth recovered from the Hell Creek Formation in Montana. Two came from a young adult nicknamed "Thomas," an individual estimated to have weighed more than 3 metric tons when alive. The third tooth belonged to a separate specimen.

The average temperature calculated across all three teeth was 36.3 C — a figure reflecting body temperature at the time the teeth were forming, not the present day.

For comparison, Indian elephants average 36.0 C and African elephants 36.2 C. Ostriches and emus range between 37 C and 39 C. The figure was lower than the 41.6 C average recorded in small flying birds.

For comparison, the team applied the same method to five crocodilian teeth recovered from the same geological formation. The crocodiles averaged 30.9 C, with individual readings ranging widely from 27.7 C to 38.2 C.

The team also estimated the ambient temperature of the environment T. rex inhabited. Shell samples from the same formation yielded an average environmental temperature of 25.9 C, while climate model simulations placed Late Cretaceous summer temperatures between 24.9 C and 33.4 C, depending on the assumed concentration of atmospheric carbon dioxide.

That T. rex's body temperature exceeded the ambient environment suggests the animal was most likely an endotherm rather than an ectotherm — heat from its surroundings alone would not have been sufficient to produce such a reading.

A map of the North American continent in the Late Cretaceous showing areas where T. rex could have survived. Lighter green indicates more habitable zones; darker blue indicates less hospitable ones. Orange dots mark locations where T. rex fossils have been found. [Science Advances Vol. 12, No. 38]

Could have survived even in frigid Alaska

Using the calculated body temperature as a baseline, the team modeled how far across the continent T. rex could have ranged.

Drawing on the thermal tolerances of living animals, the researchers set a comfort zone of 34.7 C to 37.3 C and defined survival limits spanning minus 13 C to 43.6 C. They then overlaid those parameters onto a climate model of Late Cretaceous North America.

The results showed that most of the North American continent would have been habitable for T. rex — a finding consistent with the actual fossil record.

Bones from juvenile tyrannosaurs have been found in northern Alaska, a region that would have corresponded to roughly 85 degrees latitude at the time and experienced below-freezing winters. Surviving year-round in such conditions would have required a body capable of tolerating significant cold.

However, the team acknowledged limitations: only three teeth were analyzed, two of them from the same individual. Samples were also taken only from areas of the teeth least likely to have suffered damage, meaning the measurements may reflect enamel that formed during a specific season rather than across the full year.

The team also cautioned that a high body temperature does not automatically indicate a high metabolic rate. In large-bodied animals, heat dissipates slowly, meaning body temperature can remain elevated even with a relatively low metabolism.

Reference

DOI: 10.1126/sciadv.aeb7653

R.J. Flores, R.A. Eagle, R.B. Trayler, G. Larocca Conte, S.L. Kim, A.A. Chiarenza, A. Farnsworth, P.J. Valdes, L. Chiappe, & A. Tripati, "The body temperature of Tyrannosaurus rex," Sci. Adv. 12 (2026) eaeb7653.

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