T. Rex Body Temperature Matched Elephants, Study Finds

A new chemical analysis of Tyrannosaurus rex teeth puts the animal's body temperature at roughly 36 degrees Celsius, close to that of a modern elephant, according to a study reported by Ars Technica. The finding adds physical evidence to a decades-long debate over whether the predator generated its own body heat.

The work was led by Randon J. Flores and Robert A. Eagle, geochemists at the University of California, Los Angeles, Ars Technica reported.

What did the researchers measure?

The team used a method called clumped isotope thermometry to read temperature signals locked inside fossil tooth enamel. Carbonate minerals in enamel contain rare heavy isotopes of carbon and oxygen. How often those isotopes bond together depends on the temperature at which the mineral formed, Ars Technica reported. Because enamel forms inside a living animal, the bonding pattern effectively records body temperature at the time the tooth grew.

Why not just use older methods?

Earlier attempts relied on oxygen isotope ratios alone, a technique that depends on the chemistry of water inside the animal's body — a variable no one can pin down for a creature extinct for 66 million years, according to Ars Technica. Clumped isotope thermometry sidesteps that problem because it measures how isotopes bond to each other rather than their raw ratios, removing the water-chemistry variable. Eagle introduced the technique to dinosaur research more than a decade ago in studies of Jurassic sauropods, Ars Technica reported.

"This dental thermometer read about 36° Celsius — roughly the body temperature of a modern elephant."

Which fossils were tested?

Researchers analyzed three T. rex teeth supplied by the Natural History Museum of Los Angeles County, all recovered from Montana's Hell Creek Formation, a rock unit that preserves the final stretch of time before the asteroid impact, according to Ars Technica. Two of the teeth came from a young adult T. rex estimated to have weighed more than 3 tons; the third was an isolated partial tooth from a separate individual. For comparison, the team also tested five teeth from crocodilians that lived in the same rivers and floodplains, Ars Technica reported.

How did scientists confirm the teeth weren't altered underground?

Before trusting the temperature readings, the researchers had to rule out chemical changes accumulated over 66 million years in the ground. They focused on enamel, which resists alteration better than bone or dentin, and ran several checks, according to Ars Technica. Enamel and dentin from the same teeth showed different isotopic signatures — a pattern unlikely to survive if burial chemistry had reset the samples. Infrared spectroscopy showed the fossil enamel resembled that of a modern alligator, and its carbonate content matched living reptilian enamel. Carbon isotopes also carried the dietary signal expected of a predator, Ars Technica reported.

What does a 36-degree reading suggest about T. rex?

A body temperature in that range sits closer to warm-blooded mammals such as elephants than to cold-blooded reptiles that depend on external heat sources. The result does not settle every question about dinosaur physiology — different lineages may have used different thermal strategies, Ars Technica noted — but it gives researchers a direct chemical measurement to weigh against decades of inference from bone growth rings and geographic range.

For the full methodology and additional isotope data, see the original report at Ars Technica.

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