T. rex teeth reveal dinosaur had a body temperature of 97 degrees

The Tyrannosaurus rex was warm-blooded, carrying a body temperature of 97 degrees Fahrenheit (36 degrees Celsius) that was strikingly similar to our own.

Scientists have suspected for years that the iconic predator was more than a sluggish, cold-blooded reptile. But a study published in the journal Science Advances provides the first direct chemical measurement of a T. rex's body heat, effectively ending the debate.

A research team, led by scientists at the University of California, Los Angeles (UCLA), achieved the breakthrough by analysing the fossilised tooth enamel of a T. rex known as Thomas, which is housed at the Natural History Museum of Los Angeles County. They found that the dinosaur's internal temperature sat comfortably above that of modern cold-blooded reptiles, yet remained below the 104 to 109 degrees Fahrenheit typical of modern birds, which are the T. rex's evolutionary descendants.

How the temperature was measured

To take a dinosaur's temperature from 66 million years ago, the researchers used a technique called clumped isotope geochemistry. Inside tooth enamel, rare heavy isotopes of carbon and oxygen form bonds. Because these bonds form more frequently at colder temperatures and less frequently at warmer ones, they act as an ancient, locked-in thermometer.

While scientists have used this method on bones before, testing a T. rex required a massive sample that museums were unwilling to sacrifice. Over a decade of research, the UCLA team, including geobiologist Robert Eagle and geochemist Aradhna Tripati, managed to reduce the required sample size by 90 per cent. This allowed them to scrape just a few milligrams of powder using a dental drill.

"Nobody hands you a T. rex tooth unless you can show them you only need a few milligrams," Tripati said.

The researchers dissolved the powder in phosphoric acid to release carbon dioxide gas, which was then pressurised and analysed using a mass spectrometer to reveal the isotope ratios.

Proving the results were real

To make sure their readings were accurate and not just a quirk of millions of years in the dirt, the team also analysed fossilised crocodile teeth found in the same Hell Creek geological formation in Montana.

The ancient crocodiles registered a cooler 86 degrees Fahrenheit (30 degrees Celsius). Had the fossils been chemically altered by the surrounding environment over the eons, both animals would have returned the same temperature.

What this tells us about T. rex

This difference in temperature explains how the T. rex lived. A body temperature of 97 degrees Fahrenheit supports the theory that the T. rex was an active, fast-moving hunter with a high metabolism, rather than an animal that needed to bake in the sun to gather energy.

It also explains the dinosaur’s vast geographic range. Alessandro Chiarenza, a paleontologist at University College London who co-authored the study, noted that while cold-blooded reptiles like crocodiles and turtles are entirely missing from the fossil records of Cretaceous-era Alaska, T. rex fossils have been found there.

With an internal temperature comparable to a mammal, the T. rex could tolerate the freezing winters of the far north just as easily as the heat of the south. Using climate models, the researchers determined that the entire North American continent would have been habitable for the dinosaur.