A new analysis of Tyrannosaurus rex teeth indicates the ancient predator maintained a body temperature of about 36.3 degrees Celsius (97.3 degrees Fahrenheit), close to that of Indian and African elephants and far warmer than its cold-blooded reptile neighbors.
Tyrannosaurus rex holotype specimen at the Carnegie Museum of Natural History, Pittsburgh, the United States. Image credit: Scott Robert Anselmo / CC BY-SA 3.0.
“Tyrannosaurus rex is perhaps the most intensely studied dinosaur owing to a relatively well-sampled record, earning it the status of an exemplar organism that is commonly referenced in studies of vertebrate paleontology,” said University of California-Los Angeles geobiologist Robert Eagle and his colleagues.
“Aspects of the biology and ecology of Tyrannosaurus rex, which provide evidence for an endothermic thermophysiology, include locomotor costs, growth rates, and geographic distribution, yet confident estimates of body temperature are lacking.”
Using a technique called clumped isotope paleothermometry, the authors analyzed three Tyrannosaurus rex teeth collected from the Late Cretaceous Hell Creek Formation from a site southeast of Ekalaka, Carter County, Montana.
The technique measures the bonding patterns of carbon and oxygen atoms in tooth enamel to determine the temperature at which the mineral formed.
The results pointed to an average body temperature of about 36.3 degrees Celsius, comparable to living large mammals such as Indian and African elephants with reported body temperatures of 36 and 36.2 degrees Celsius.
“No one’s been able to make a temperature measurement like this before,” Dr. Eagle said.
“We found Tyrannosaurus rex was 36 degrees Celsius, about the same as humans.”
“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.”
By contrast, teeth from crocodilians that lived alongside Tyrannosaurus rex in the same Late Cretaceous ecosystem yielded significantly cooler temperatures, averaging around 30.9 degrees Celsius (87.6 degrees Fahrenheit) — consistent with the cold-blooded, Sun-basking lifestyle of modern crocodiles.
The gap between predator and reptile suggests Tyrannosaurus rex was maintaining a body temperature well above its surroundings, a hallmark of warm-blooded physiology.
“A thermoregulated Tyrannosaurus rex supports theories that tyrannosaurs were active animals, chasing or scavenging food to fuel their fast metabolisms,” Dr. Eagle said.
“It also adds to the timeline, showing how much this ancestor of modern, very warm-blooded birds had already diverged from cold-blooded dinosaurs.”
The researchers also modeled how such thermal tolerance might have shaped where Tyrannosaurus rex could live.
Using paleoclimate simulations of the Maastrichtian-age North American continent, they found that a wide range of latitudes — including colder, higher-latitude regions — would have been habitable for the dinosaur, aligning with fossil evidence of tyrannosaurs found as far north as Alaska’s North Slope.
The findings add to a growing body of evidence that at least some dinosaurs, particularly large theropods, were warm-blooded animals capable of generating and regulating their own body heat, rather than relying solely on external conditions, as reptiles do today.
“A toasty Tyrannosaurus rex also was able to survive in a cooler habitable range, stretching into territory where cold-blooded animals would have faltered,” said Dr. Alessandro Chiarenza, a paleontologist at University College London.
“The warm-blooded reptile would have adapted over millions of years to the hot-house conditions of the Cretaceous period, one of the warmest periods in Earth’s history.”
“But even in the baking heat of the Cretaceous period, winter in Alaska would have been too frigid for a cold-blooded dinosaur.”
The team’s results appear in the journal Science Advances.
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Randon J. Flores et al. 2026. The body temperature of Tyrannosaurus rex. Science Advances 12 (38); doi: 10.1126/sciadv.aeb7653
