T. Rex Body Temperature Measured for the First Time

Nobody has ever taken a Tyrannosaurus rex’s temperature, for obvious reasons. A new study found a way to do it anyway, 66 million years after the animal died.

Reading a Temperature From 66-Million-Year-Old Teeth

Researchers led by biogeochemist Aradhna Tripati and geobiologist Robert Eagle, both at UCLA, along with paleontologist Alfio Alessandro Chiarenza of University College London, analyzed three fossilized teeth housed at the Natural History Museum of Los Angeles County. Two of the teeth came from a T. rex nicknamed Thomas, one of the most complete skeletons of the species ever found. The team drilled tiny holes into the teeth and examined the powder for chemical bonds between specific forms of carbon and oxygen preserved in the enamel. Colder formation temperatures produce more of these bonds, giving researchers a way to calculate body temperature directly from fossilized tissue. The findings appeared September 16 in the journal Science Advances.

Checking the Result Against a Cold-Blooded Neighbor

The analysis produced a body temperature of about 97 degrees Fahrenheit for Thomas, remarkably close to the average human temperature. To rule out the possibility that local geology had altered the chemical signal rather than reflecting a real biological temperature, the team also examined five teeth from an ancient crocodilian recovered from the same site in Montana. If geology alone explained the readings, both animals should have produced similar results. Instead, the crocodilian’s teeth pointed to a noticeably cooler temperature of 88 degrees, supporting the conclusion that the T. rex measurement reflects the animal’s actual internal temperature rather than an artifact of its burial environment.

Where T. Rex Sits Between Reptiles and Birds

According to the study, T. rex’s temperature sat well above that of modern reptiles, which typically run between 82 and 86 degrees, and below that of birds, dinosaurs’ living descendants, which maintain internal temperatures around 104 to 109 degrees. That places Thomas squarely between the two groups, consistent with an animal capable of actively regulating its own body heat rather than depending entirely on its surroundings.

A Warm Body Opened Up a Much Bigger Range

Study co-author Robert Eagle noted that higher metabolic rates come with higher food demands, but also allow more sustained activity and access to colder environments. Fossils of tyrannosaurids have turned up in modern-day Alaska, alongside a conspicuous absence of reptile fossils from the same Cretaceous rock layers, even though Cretaceous temperatures ran roughly 11 to 25 degrees warmer than today. The researchers used paleoclimate simulations to map where T. rex’s measured body temperature would have allowed the species to live across North America 66 million years ago, and the resulting range extended from Alaska all the way down to Mexico.

Sources

This report draws on original coverage by Smithsonian Magazine of the study published in Science Advances.