How do you take T. rex's temperature? These scientists did it

Thomas the Tyrannosaurus rex can be seen at the Natural History Museum of Los Angeles County. Two of his teeth were used in this analysis to determine the body temperature of T. rexes. (Dinosaur Institute, Natural History Museum of Los Angeles County)Social SharingScientists have long discussed whether and which dinosaurs were warm-blooded. Now, researchers say they have used chemistry to take the temperature of two T. rexes. 

It wasn't easy, acknowledged Aradhna Tripati, a professor and geochemist at the University of California, Los Angeles. She co-authored the research published Wednesday in the journal Science Advances, and explained it to CBC's Quirks & Quarks ahead of an interview with host Bob McDonald.

"You would not want to go to a T. rex and stick a thermometer in its mouth or in its armpit or in its butt, you know, the way you might take temperature in a person or most other animals."

Nor could you, considering they went extinct about 66 million years ago.

Instead, scientists used a technique that relies on chemistry that varies with temperature, and leaves signals in certain hard tissues such as tooth enamel and eggshells.

Those materials contain a mineral called bioapatite, where carbon atoms bond with oxygen. A heavier kind of carbon atom (carbon-13, which has one more neutron than carbon-12)  bonds preferentially with a heavier, rarer kind of oxygen atom (oxygen-18, rather than oxygen-16). This is more prevalent at lower temperatures, where the bonds are more stable.

By comparing the amount of "isotope clumping" in living animals with different body temperatures, scientists can estimate the body temperature of extinct animals, including dinosaurs.

In fact, UCLA scientists did that a decade ago using eggshells from titanosaurs and oviraptors, and concluded that they were both warm-blooded.

They had also analyzed teeth from some plant-eating dinosaurs, such as brachiosaurs, which have thick enamel for grinding plants. 

But tyrannosaurs have very thin tooth enamel, Tripati said, so getting enough tooth enamel for the analysis was tricky.

The researchers worked on the technique with more common teeth from the megalodon, an ancient giant shark, until they could successfully do the analysis with very small samples.

Study author and UCLA Professor Robert Eagle holds one of the T. rex teeth used to measure the body temperature of T. rex. Tooth provided by the Natural History Museum of Los Angeles County. (UCLA)Then they requested some tooth enamel from Thomas the tyrannosaur, a young adult T. rex skeleton displayed at the L.A. County Natural History Museum.

"They wouldn't let us pull a tooth off and just, you know, destroy it," Tripati recalled. But the scientists were permitted to shave a little bit off the sides of two teeth – "a pinch of salt amount."

They also managed to get a T. rex tooth fragment from a specimen identified only by a number.

By analyzing the three teeth, the researchers estimated T. rex's body temperature at between 33.8 C and 38.8 C – similar to that of large mammals such as elephants and large and possibly flightless birds such as ostriches (which have temperatures between 38.1 C and 39.7 C), but lower than that of smaller birds that can fly, which tend to have body temperatures between 41.1 C and 42.1 C.

Tripati says an animal's body temperature affects its behaviour and where it can live. 

"A warm blooded T. rex is ... a T. rex that can go almost anywhere on the continent, including the Arctic. That's a very different animal from a sun-basking reptile."

Anthony Fiorillo, a paleontologist who described a tiny tyrannosaur in Alaska a decade ago, said while predators like T. rex were speculated to have warmer body temperatures, "this paper makes a solid and compelling case." Fiorillo, executive director of the New Mexico Museum of Natural History, added in an email that it provides "food for thought" about how dinosaurs may have adapted to life in the far north.

François Therrien, curator of dinosaur paleobiology at the Royal Tyrrell Museum in Alberta, was part of a team that used isotope clumping to analyze the eggshells of small, meat-eating dinosaurs called troodons, and found they were as warm-blooded as birds with body temperatures more than 40 C.

He said researchers knew that tyrannosaurs grew fast and weren't just sluggish, cold-blooded animals, but this study provides a more precise, confident measure of body temperature.

The fact that it had such a warm body temperature suggests T. rex could be active during the day, at night and in winter, said Therrien, and explains how tyrannosaurs could range from Mexico to Alaska, and could have crossed the Bering Strait between Asia and North America in the far north, as there's evidence they did.

However, Therrien is not sure T. rex had quite the same kind of warm-blooded metabolism as modern mammals and birds do, which may have required more food than the ecosystem could support, given their size: "That's still subject to debate."

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