By studying portions of Tyrannosaurus rex teeth, scientists from the University of California, Los Angeles (UCLA) have pinned down the dinosaur’s body temperature for the first time ever – placing it at around 36 degrees Celsius (97 degrees Fahrenheit).
The findings were published in the journal Science Advances.
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When picturing the large prehistoric reptile we know as Tyrannosaurus rex, you may assume it was cold-blooded. All modern living reptiles are – but, as it turns out, T. rex was surprisingly warm, running at a temperature comparable to a human.
Experts have suspected that T. rex might have been warm-blooded for a while, especially considering that palaeontologists have found T. rex fossils in Alaska. Temperatures in Cretaceous Alaska would’ve been too low for cold-blooded reptiles to survive, and paleontologists haven’t found any fossils of lizards, turtles, crocodiles or other reptiles in the region dating to this period.
Studying T. rex teeth
To determine the dinosaur’s body temperature, scientists used fossils provided by the Natural History Museum of Los Angeles County (NHM). The two teeth came from Thomas the T. rex, the most complete of the tyrannosaur skeletons inside the museum’s dinosaur collection, unearthed in 2003 from a dig site at Hell Creek, Montana, USA.
The key to taking T. rex’s temperature lies in a chemical bond – inside tooth enamel, rare isotopes of carbon and oxygen form bonds together. The number of those bonds depends on the internal temperature, with a warm-blooded animal having fewer of these chemical bonds in their teeth than a cold-blooded animal.
“That’s the basis of using the isotopes as a thermometer,” explains Robert Eagle, a geobiologist at UCLA and one of the study’s co-authors. “In theory, we can make measurements using any part of the skeleton, but the bones in our body are constantly being remodelled 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.”
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The researchers used a dental drill to remove the enamel from the fossils and dissolved the powder in phosphoric acid to release carbon dioxide gas containing the isotope bonds. Then, they measured the gas with a mass spectrometer, which revealed the isotope ratios.
These tests revealed that the T. rex’s body temperature is more comparable to a furry, warm-blooded mammal than a cold-blooded reptile. A modern reptile runs about 28-30 degrees Celsius, while most birds – T. rex’s evolutionary descendants – often run much warmer at 40-43 degrees Celsius.
Years in the making
UCLA researchers developed their prehistoric thermometer method a decade ago, using bones to measure whether extinct animals were warm-blooded or cold-blooded. But testing it on a T. rex required more bone than any museum was willing to part with.
So over that decade, the scientists perfected the method, cutting the amount of material needed by roughly 90 per cent. This was enough to convince the NHM to part with portions of two teeth from Thomas the T. rex.
“We’re asked for fossils for use in destructive analysis all the time,” says Luis Chiappe, curator of the NHM’s Dinosaur Institute and head of research and collections.
“The museum contains tens of millions of specimens of minerals, animals and fossils that are irreplaceable. We have to make decisions that balance the damage to the specimen against gaining knowledge about the natural world. Sacrificing small portions of two teeth to learn about T. rex’s body temperature is definitely worth the trade-off.”
Read the full findings here.
Top image: illustration of a T. rex. Credit: Roger Harris/Science Photo Library/Getty Images
