A Tyrannosaurus rex, it turns out, may have been only slightly warmer than you are right now.
A new study estimates the dinosaur's body temperature at roughly 97 degrees Fahrenheit — a figure close to normal human body temperature and well above the surrounding environment of its time. The work, reported by Science and covered widely by outlets including CNN, The New York Times and the Los Angeles Times, used chemical signatures preserved in T. rex teeth to make the estimate.
The method relies on the way certain atomic bonds form in minerals as an animal's body develops. Those bonds carry a faint record of the temperature at which they formed, and because tooth enamel is among the hardest tissues a vertebrate produces, it can survive for tens of millions of years in a way that bone rarely does.
That makes teeth one of the few windows scientists have into the internal physiology of a long-extinct animal.
The result adds weight to a view that has been gaining ground for decades: that T. rex was not the sluggish, cold-blooded predator of older museum displays, but an animal generating much of its own heat. Popular Science described the finding as confirmation that the dinosaur was warm-blooded.
That distinction matters for how the animal lived. An animal that holds a stable internal temperature needs far more food than one that does not, which shapes how far it roams, how often it hunts and how much of a landscape it can support. It also changes what a T. rex's day looked like — and what it cost the ecosystem to keep one alive.
The study does not settle every question. Body temperature estimates from fossil chemistry come with ranges and assumptions, and scientists continue to debate how close any single number lands to the real value for a given species. What the new work offers is a direct measurement where before there was mostly inference.
Researchers involved have not claimed the case is closed. The number is an estimate, and the method is one line of evidence among several.
What happens next is a broader test: whether the same technique holds up across other dinosaurs, and whether it produces a consistent picture of which species ran hot and which did not.