For more than a century, Tyrannosaurus rex has often been portrayed as a giant, cold-blooded reptile that depended on the heat of its surroundings. A new study now adds a striking piece of evidence to the growing case that the dinosaur was anything but sluggish.
Scientists have estimated that T. rex had an average body temperature of about 36.3°C (97.3°F)—remarkably close to humans and comparable to the temperature of modern elephants. The findings were published Sept. 16, 2026, in Science Advances.
The research provides what scientists describe as the first direct numerical estimate of T. rex’s body temperature, rather than relying solely on indirect evidence about its metabolism.
Scientists found the answer hidden inside T. rex teeth
The research team, led by scientists associated with UCLA, examined chemical signatures preserved in the enamel of three T. rex teeth recovered from Montana’s Hell Creek Formation.
The key was a technique known as clumped-isotope thermometry. Certain carbon and oxygen isotopes form chemical bonds in tooth enamel in temperature-dependent patterns. By measuring those patterns, researchers can estimate the temperature at which the enamel formed—and therefore gain a window into the animal’s internal temperature.
Only about 5 milligrams of enamel was required from each tooth, allowing researchers to study museum specimens while minimizing damage to irreplaceable fossils. Two of the analyzed teeth came from a well-preserved young adult T. rex known as Thomas, housed at the Natural History Museum of Los Angeles County.
The number was close to human temperature—but not exactly the same
The study calculated an average T. rex temperature of 36.3°C, with an uncertainty of about ±2.5°C. Humans average around 37°C, although normal human body temperature varies among individuals and circumstances.
The researchers said the result is also comparable to modern elephants, which have body temperatures around 36°C. By contrast, many modern reptiles generally have lower body temperatures and rely much more heavily on environmental heat.
The result is particularly important because temperature regulation is closely connected to metabolism, activity, geographic range and energy requirements.
A T. rex that could stay warm without waiting for the sun
The findings add to previous evidence suggesting that tyrannosaurs were endothermic, meaning they could generate and maintain substantial internal heat through metabolism.
That matters because an endothermic animal is less dependent on external temperatures. Researchers’ climate modeling indicates that a T. rex maintaining an internal temperature around 36°C could potentially have occupied a broad portion of prehistoric North America, including colder regions.
T. rex fossils are known from areas extending from parts of western Canada through Montana, Wyoming and the Dakotas and farther south into New Mexico and Texas. Evidence of tyrannosaurs in northern regions has long been part of the broader discussion about their ability to function in cooler environments.
Researchers tested the result against ancient crocodilians
One particularly useful part of the study was the comparison with five crocodilian teeth from the same Hell Creek Formation.
The crocodilian teeth produced an estimated average temperature of approximately 30.9°C (87.6°F)—substantially lower than the T. rex measurements and consistent with expectations for ectothermic reptiles.
That comparison helped researchers argue that the T. rex result was not simply caused by geological alteration of the fossils after the animals died.
Warm-blooded did not necessarily mean “bird-hot”
The study does not mean T. rex had the same physiology as a modern bird.
Researchers place its estimated temperature toward the lower end of the range associated with endothermic animals. Modern birds generally maintain substantially higher body temperatures, often around 40–43°C.
And scientists caution against applying the T. rex result to every dinosaur.
The dinosaur group was extraordinarily diverse, and researchers say different species may have used different strategies for controlling body temperature. The new study therefore provides an important measurement for T. rex specifically, rather than proving that all dinosaurs were equally warm-blooded.
There was a trade-off to being warm-blooded
Maintaining a relatively high internal temperature would have had advantages—but it would also have required substantial energy.
A higher metabolic rate means greater food requirements. For a giant predator such as T. rex, that could have translated into a greater need to obtain food while providing the physiological capacity for sustained activity and movement across different environments.
This helps explain why the new temperature estimate is more than a fascinating dinosaur trivia fact.
Body temperature affects how scientists reconstruct an extinct animal’s entire lifestyle—from its energy budget and activity level to its potential habitat.
Why this discovery matters
For decades, scientists have gradually moved away from the simplistic image of dinosaurs as oversized, sluggish reptiles.
Evidence from anatomy, growth patterns, fossil distribution and the evolutionary relationship between dinosaurs and modern birds has already contributed to a more complicated picture of dinosaur metabolism. The new T. rex temperature measurement provides another piece of empirical evidence.
Most importantly, scientists now have a measurable physiological estimate rather than simply an inference.
And that could open the door to something even bigger: using the same technique on other dinosaur species to determine just how different their thermal biology really was.
