Tyrannosaurus Rex Was a Warm-Blooded Dinosaur, With a Body Temperature Similar to That of Humans, Study Suggests

A tooth analysis hints that the fearsome predator ran at a toasty 97 degrees Fahrenheit. Maintaining that internal temperature may have allowed it to inhabit a range stretching from modern-day Alaska to Mexico during the Cretaceous period

Margherita Bassi | Daily Correspondent

September 18, 2026 11:59 a.m.

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Knowing whether an animal is warm-blooded or cold-blooded can tell researchers a lot about the species’ behavior and geographic range. While warm-blooded creatures, called endotherms, such as humans, can regulate their own body temperatures, cold-blooded animals, or ectotherms, rely on the environment, limiting where they can live.

Until the early 2000s, researchers thought dinosaurs resembled modern-day reptiles, which are mostly cold-blooded. But mounting evidence over the past couple of decades has challenged that idea.

Now, scientists have revealed the first precise body temperature measurement for one of the world’s most iconic dinosaurs: Tyrannosaurus rex. The fearsome predator ran at a toasty 97 degrees Fahrenheit, around the same temperature as modern-day humans, according to a study published September 16 in the journal Science Advances. The findings further suggest that the beast was indeed warm-blooded, allowing experts to infer a host of information regarding the long-extinct creature.

“For an animal this famous, it is remarkable how little we actually knew. We had guesses about T. rex metabolism, mainly from bone and biomechanics. We did not have a temperature,” study co-author Aradhna Tripati, a biogeochemist at the University of California, Los Angeles, tells CNN’s Taylor Nicioli.

Measuring a live animal’s temperature usually requires a simple thermometer, but collecting that data from a giant that’s long gone is significantly more complicated. The team turned to three fossilized dinosaur teeth from the Natural History Museum of Los Angeles County, two of which came from a T. rex named Thomas, one of the most complete skeletons of the species ever found.

Drilling tiny holes in the teeth and collecting the powder allowed the researchers to analyze the chemical bonds between certain forms of carbon and oxygen in the enamel. The number of these bonds increases as temperature decreases, so a warm-blooded animal has fewer of these bonds than a cold-blooded animal.

“The enamel chemistry is truly recording the temperature at which it formed, and 66 million years later, we can read it using those measurements on a mass spectrometer,” a tool that examines a sample’s chemical properties, Tripati tells Scientific American’s Mary Randolph. “It’s the next best thing to sticking a thermometer up a T. rex’s ‘butt,’ which we wouldn’t have wanted to do anyway.”

To demonstrate that the results were not distorted by geology, the team also investigated the body temperature of an ancient crocodilian from the same site in Montana where the sampled T. rex skeletons had been found. Had geology messed with the fossils’ molecular compositions, both species would have yielded similar temperature measurements, study co-author Robert Eagle, a geobiologist at the University of California, Los Angeles, explains in a statement. But their temperatures were different; five teeth from the crocodilian suggested the animal ran at a cooler 88 degrees.

Warm-blooded animals have faster metabolisms and higher activity levels than cold-blooded creatures, so the results bolster previous proposals that T. rex could expend lots of energy.

“Higher metabolic rates mean higher food requirements and potentially more active hunting to acquire it,” Eagle tells Reuters’ Will Dunham. “An endothermic T. rex would have ‌had to acquire ⁠significantly more food to sustain its higher metabolic rate, but would also be capable of more sustained activity to find food and migrate, and live in colder environments.”

At a stable internal temperature of 97 degrees, T. rex would have been able to inhabit regions too chilly for cold-blooded animals. In fact, Alaska has yielded tyrannosaurid fossils, but not reptile fossils from the Cretaceous period, some 66 million to 145 million years ago, says study co-author Alfio Alessandro Chiarenza, a paleontologist at University College London, in the statement. The Cretaceous was around 11 to 25 degrees warmer than modern-day temperatures, but Alaska’s winters would have still been inhospitable to a cold-blooded dinosaur.

The implications go beyond just Alaska. The team used paleoclimate simulations to reconstruct where T. rex’s body temperature would have allowed the animals to live in North America 66 million years ago, and the range reached all the way down to Mexico.

“All of these habitats would have been viable from a physiological perspective,” Jasmina Wiemann, a molecular paleobiologist at Johns Hopkins University who was not involved in the study, tells the New York Times’ Carolyn Y. Johnson. “It really reshapes our way of asking questions of habitat preference.”

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.