T. rex Had a Body Temperature Similar to Humans, Study of Fossilized Teeth Reveals

Scientists have successfully measured the body temperature of a Tyrannosaurus rex for the first time, discovering that the iconic apex predator maintained an internal temperature remarkably similar to that of modern humans and elephants. The findings, published Wednesday in the journal Science Advances, offer new insight into the biology and ecology of one of history's most famous dinosaurs.

For generations, early paleontologists viewed dinosaurs as sluggish, cold-blooded reptiles dependent on their external environment for warmth. Decades of subsequent research challenged that assumption, leading many scientists to conclude that large dinosaurs were warm-blooded and capable of regulating their internal temperatures. However, determining an exact core temperature for an extinct creature that vanished millions of years ago remained a significant challenge.

"We can't just use a thermometer to do that," noted Jasmina Wiemann, a paleobiologist at Johns Hopkins University who was not involved in the new research. Previous attempts to calculate dinosaur body temperatures relied on indirect clues, such as analyzing growth rates or examining bone structure, but a definitive numerical reading had previously eluded researchers.

To overcome this obstacle, the study's authors turned to chemical analysis of the predator's fossilized teeth. The research team discovered that atoms within tooth enamel clump together in distinct patterns that directly reflect an animal's body temperature while the enamel was forming.

"We figured out how warm the most famous animal of all, a T. rex, was," said co-author Aradhna Tripati, a geochemist at the University of California, Los Angeles.

By taking readings from three preserved T. rex teeth, the researchers calculated an average body temperature of approximately 97 degrees Fahrenheit, or 36 degrees Celsius. This measurement aligns closely with the body temperatures of modern elephants and falls just under the typical human range of 97 to 99 degrees Fahrenheit (36 to 37 degrees Celsius).

The measurement surprised some experts in the field. Wiemann stated that she initially anticipated a higher internal temperature, closer to 100 degrees Fahrenheit or more, which would have mirrored modern birds—the direct living descendants of dinosaurs.

Understanding the precise thermal biology of the Tyrannosaurus rex helps researchers reconstruct how the animal lived, hunted, and interacted with its environment. According to Tripati, maintaining a stable internal temperature of 97 degrees Fahrenheit would have allowed the T. rex to thrive across diverse regions of prehistoric North America, giving it a reliable internal thermostat whether it roamed cooler northern latitudes or hotter southern habitats. Furthermore, understanding the metabolic rate of the predator helps scientists model the caloric intake and prey requirements necessary to sustain such a massive creature.

Following this breakthrough, the research team emphasizes the need to apply the tooth-enamel analysis method to a broader array of dinosaur species. Investigating other prehistoric animals could reveal whether a body temperature around 97 degrees Fahrenheit was common among giant theropods or if it played a unique role in establishing the T. rex's ecological dominance during the age of dinosaurs.

"There's lots of interesting, charismatic species that could be explored using this," said study co-author Robert Eagle, a geobiologist at UCLA.