T. rex’s teeth reveal the dinosaur’s body temperature for the first time - CNN

Scientists have suspected for nearly 60 years that Tyrannosaurus rex was warm-blooded.

When a fossilized footprint of T. rex turned up in Alaska in 2022, it added to the evidence that these predators could thrive in frigid environments, where most cold-blooded reptiles could not. Now, researchers have put a number on just how warm tyrannosaurs likely ran: about 97 degrees Fahrenheit, or 36 degrees Celsius, similar to humans.

A new study published Wednesday in the journal Science Advances provides the first direct estimate of T. rex’s body temperature, using a technique that analyzes chemical signatures preserved in fossil teeth. The finding adds a crucial piece of evidence to the decades of research suggesting the giant predator was warm-blooded and capable of maintaining an active metabolism even in cold climates.

“It’s probably the most direct and least complicated constraint on the actual body temperature of a T. rex that’s been possible before,” said study coauthor Robert Eagle, a geobiologist and associate professor at the University of California, Los Angeles.

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Having an estimated body temperature for T. rex provides a better glimpse into what life was like for the dinosaur 69 million to 66 million years ago. “This was a warm-bodied organism, which really places new constraints on its behavior, its physiology, how it interacted with other species and how much food it needed, for example,” Eagle added.

So far, the technique has been used on a handful of ancient species, including other dinosaurs, woolly mammoths and megalodons, giving scientists a clearer picture of how extinct animals regulated their body temperatures in ancient climates.

The temperature is unusually high for a reptile, but Eagle said the number itself was not surprising. Dinosaurs, while classified as reptiles, share an evolutionary link with birds. The new number reveals that T. rex sits between the two — hotter than reptiles but colder than modern avians — and allows scientists to form new hypotheses about how exactly the prehistoric predator might have moved and lived.

Eagle and a team of scientists used two small portions of teeth from Thomas the T. rex — an approximately 70% complete Tyrannosaurus rex skeleton held at the Natural History Museum of Los Angeles County — to estimate the dinosaur’s body temperature from chemical bonds preserved in its tooth enamel.

The researchers spent more than a decade perfecting the method to make the measurement possible. Over the years, their work reduced the amount of fossil material needed by roughly 90%, enabling the museum to provide tiny samples of two teeth that weren’t on display.

“Nobody can measure a T. rex tooth unless you can show them you only need a few milligrams,” said senior study author Aradhna Tripati, a climate scientist and professor of geochemistry at UCLA.

“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,” Tripati added in an email. “The enamel chemistry recorded the temperature at which it formed, and 66 million years later we can read it.”

The researchers essentially used the T. rex teeth as a prehistoric thermometer. Inside tooth enamel are different forms of the elements carbon and oxygen, called isotopes. These isotopes form bonds with one another at rates that depend on temperature — cooler temperatures produce more bonds, while warmer ones produce fewer. By drilling out a few milligrams of enamel and measuring those bonds, scientists could determine the temperature at which the enamel formed, revealing the T. rex’s body temperature.

This technique can be used on any part of the skeleton, but teeth work best because their hard enamel is less likely to change over millions of years, Eagle explained.

“We have wondered about whether dinosaurs were warm-blooded or not literally since the first time dinosaurs got their name,” said vertebrate paleontologist Thomas Holtz Jr., referring to Richard Owen’s 1842 paper, which introduced the name Dinosauria and suggested that dinosaurs might have had characteristics of warm-blooded animals.

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