Scientists Finally Measure T. rex Blood Temperature — and It Was as Hot as Ours

Tyrannosaurus rex was a hot-blooded beast, and scientists finally have a number for it. A new analysis of three T. rex teeth puts the king of the dinosaurs’ body temperature at 97.3 degrees Fahrenheit, roughly the same as a human or an elephant.

The finding comes from studying the bonds between rare isotopes of carbon and oxygen in the teeth. Those bonds form differently depending on temperature, allowing researchers to estimate body heat directly. The result, published Wednesday in the journal Science Advances, confirms what previous studies had suggested: T. rex was warm-blooded, capable of regulating its own temperature without basking in the sun like most modern reptiles.

Teeth as Thermometers

The team studied three teeth from specimens found in the Hell Creek Formation in Montana. By dissolving tiny samples and measuring the bonds in the carbon dioxide released, they could estimate where on the animal temperature scale T. rex sat.

Cold-blooded animals, which rely on their environment for warmth, have more of these bonds in their teeth. Warm-blooded animals, which can raise their body temperature through internal processes, have fewer. The T. rex teeth showed a pattern consistent with a warm-blooded metabolism.

The temperature matches what you’d expect from an active predator or scavenger. Cold-blooded reptiles tend to run about 82-86 F (28-30 C). Most birds, descended from T. rex’s branch of dinosaurs, sit even warmer at 104-109 F (40-43 C). T. rex falls in the middle, closer to the human and elephant range.

What the Temperature Means

A warm-blooded T. rex would have been an energetic, active animal. It chased or scavenged food to fuel its fast metabolism rather than basking in the sun to gain energy. That lifestyle explains a lot about where the dinosaur lived.

During the Cretaceous period, one of the warmest periods in Earth’s history, the planet was about 11-25 F (6-14 C) warmer than today. That meant T. rex could survive across most of the North American continent, from what is now Mexico up to chilly climates where cold-blooded reptiles wouldn’t have survived.

One example stands out. A tyrannosaur fossil has been found in the Kikak-Tegoseak Quarry in Alaska. There is no trace of other reptiles like lizards, turtles or crocodiles from that period in the region. The warm-blooded T. rex could handle the cold; the cold-blooded ones couldn’t.

The ability to inhabit cooler, high latitudes also aligns with recent evidence that tyrannosaurs crossed the Bering Land Bridge between Asia and North America, the authors note.

The Team Behind the Study

Randon Flores, a geobiologist at the University of California, Los Angeles (UCLA), led the research. His colleagues included Robert Eagle, a geobiologist at UCLA, and others whose names appear on the published paper.

Eagle offered a plain assessment of the finding. “The temperature is about what I would have guessed — higher than a reptile or a slow mammal like a sloth, but lower than an avian,” he said in a statement.

The paper, titled “The Body Temperature of Tyrannosaurus rex,” appears in Science Advances. The full reference includes the authors Flores, Eagle, Trayler, Conte, Kim, Chiarenza, Farnsworth, Valdes, Chiappe, and Tripat.

The Big Picture

This isn’t just a curiosity about a dead dinosaur. It adds a piece to the puzzle of T. rex’s lifestyle.

A warm-blooded predator can hunt in colder climates. It doesn’t need to wait for the sun to warm it up before moving. That flexibility likely explains why T. rex fossils have turned up in places like Alaska, where cold-blooded reptiles simply wouldn’t have survived.

The study also supports the idea that T. rex was a fast, energetic hunter and scavenger. Its metabolism required constant fuel. The finding fits with broader evidence that tyrannosaurs moved between continents.

Key Facts Box

• Body temperature: 97.3 F (36.3 C)
• Comparison:
• Cold-blooded reptiles: 82-86 F (28-30 C)
• Most birds: 104-109 F (40-43 C)
• Period: Cretaceous, 143.1 million to 66 million years ago
• Location: Hell Creek Formation, Montana
• Publication: Science Advances, Sept. 16, 2026
• Fossil sites: Kikak-Tegoseak Quarry, Alaska; Hell Creek Formation, Montana

The temperature is a number, but it opens a door. It lets us imagine T. rex as an active, mobile creature rather than a sun-soaked lizard. That’s a king of the dinosaurs we can picture hunting across the continent, from Mexico to Alaska.

body temperature · dinosaur · isotopes · palaeontology · T. rex · warm-blooded