UCLA scientists reported Wednesday they have determined the body temperature of Tyrannosaurus rex for the first time, using fossilized teeth to calculate that the dinosaur had a temperature of about 97 degrees Fahrenheit — roughly comparable to humans.
The findings, published in the journal Science Advances, provide further evidence that T. rex was warm-blooded and support theories that tyrannosaurs were active animals capable of surviving in climates too cold for many reptiles.
“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 Celsius (97 Fahrenheit), 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.”
Modern cold-blooded reptiles have body temperatures of about 82 to 86 degrees Fahrenheit, while most birds have temperatures of about 104 to 109 degrees, according to the researchers.
UCLA researchers developed a method about a decade ago to determine whether extinct animals were warm- or cold-blooded by measuring chemical bonds preserved in fossils. But testing the method on T. rex initially required more fossil material than museums were willing to provide.
Researchers subsequently refined the technique, reducing the amount of material needed by about 90%.
The Natural History Museum of Los Angeles County then provided portions of two teeth from Thomas the T. rex, the most complete of the tyrannosaur skeletons displayed in the museum’s dinosaur hall, officials said.
The researchers drilled enamel from the teeth and analyzed bonds formed by rare isotopes of carbon and oxygen. The number of those bonds varies with temperature, allowing scientists to estimate the temperature at which the tooth enamel formed.
“That’s the basis of using the isotopes as a thermometer,” Eagle said. “In theory, we can make measurements using any part of the skeleton, but the bones in our body are constantly being remodeled and dissolved and replaced. Tooth enamel has large crystalline structures that are extremely durable, making it the part of the skeleton that most resists chemical alteration by the environment over the eons.”
The scientists compared the T. rex results with ancient crocodilian fossils from the same Hell Creek site in Montana. The crocodilian registered a body temperature of about 86 degrees, compared with 97 degrees for T. rex, helping researchers rule out the possibility that geological processes had altered the fossils to produce the temperature reading.
Researchers said T. rex’s ability to regulate its body temperature would have supported an active metabolism and allowed the animal to live across a broad range of climates.
Fossils of Tyrannosaurus have been found in Cretaceous-era Alaska, while fossils of cold-blooded reptiles such as lizards, turtles and crocodiles have not been found there, according to the researchers.
“Now we have empirical evidence using this geologic thermometer,” study co-author Alessandro Chiarenza, a paleontologist at University College London, said. “Using paleoclimate models of the past, we were able to reconstruct a range in North America 66 million years ago that stretched from Mexico to Alaska, based on where T. rex could have survived with a 97 F body temperature.”
Senior author Aradhna Tripati, a UCLA isotope geochemist and climate scientist, said knowing the dinosaur’s body temperature provides insight into its behavior, geographic range and metabolism.
“For an animal this famous, it is remarkable how little we actually knew,” Tripati said. “Thermal physiology drives behavior, range, energy budget and how a species responds to a changing climate. Without it, you don’t really have an understanding of the animal. The teeth tell us T. rex was warmer than the environment around it. A warm-blooded T. rex can go almost anywhere on the continent, including the Arctic.”
The research was supported in part by grants from the National Science Foundation.