This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: When picturing a scaled, toothy Tyrannosaurus rex stomping across North America, building nests and eating other dinosaurs, it's easy to forget that scientists have gleaned everything we know about T. rex from clues left more than 60 million years ago. While the presence of fossils in Alaska suggested that this prehistoric ancestor of birds was already on the evolutionary path from cold-blooded reptile to warm-blooded avian, there wasn't a way to take T. rex's temperature—until now.
UCLA scientists have perfected a method to measure a dinosaur's temperature from its teeth and found that T. rex was a relatable 97°F (36°C)—almost the same as humans. The finding, using fossils from the Natural History Museum of Los Angeles County, confirms the "King of the Tyrant Lizards" would have been a fast-moving predator or scavenger—not a sun-basking slowpoke—that was able to survive in chilly climates deadly to other reptiles. UCLA researchers developed their prehistoric thermometer method a decade ago, using bones to measure whether extinct animals were warm-blooded or cold-blooded.
Testing it on a T. rex, however, required more bone than any museum would part with. Over that decade, however, the UCLA team refined the process, cutting the amount of material needed for ancient dental testing by roughly 90%. It was enough to convince L.A.'s Natural History Museum to provide portions of two teeth from Thomas the T. rex, the most complete of the towering tyrannosaur skeletons inside NHM's dinosaur hall.
Though scientists have found increasing evidence that T. rex was warm-blooded in recent years, the study published Sept. 16 in Science Advances marks the first time scientists have had an actual number. "No one's been able to make a temperature measurement like this before," UCLA geobiologist and study co-author Robert Eagle said. "We found T. rex was 36°C (97°F), about the same as humans.
The temperature is about what I would have guessed—higher than a reptile or a slow mammal like a sloth, but lower than an avian." Though still a scaly, egg-laying reptile, T. rex's 36°C body temperature is comparable to a furry, warm-blooded mammal's. Modern, cold-blooded reptiles run about 28–30°C (82–86°F), while most birds—T. rex's evolutionary descendants—often run much warmer at 40–43°C (104–109°F), Eagle said. The key to taking T. rex's temperature lies in a chemical bond, Eagle said.
Inside tooth enamel, rare isotopes of carbon and oxygen form bonds together. The number of those bonds between those isotopes increases in cooler temperatures and decreases in warmer temperatures. A warm-blooded animal will have fewer of these chemical bonds in its teeth than a cold-blooded animal.
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