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Scientists from UCLA measured the chemistry of three Tyrannosaurus rex teeth found in Montana, estimating a body temperature of 36.3°C, with a variance of 2.5 degrees either way. The result, published in Science Advances, indicates that the dinosaur was warm-blooded, like birds and mammals.
The chemistry of three Tyrannosaurus rex teeth uncovered in Montana, USA, indicated that the dinosaur had a body temperature of 36.3°C, with a variation of 2.5 degrees either way. This value is close to the human average of 37°C.
The study was published in the scientific journal Science Advances on Wednesday and reported by Reuters on September 18, 2026. According to the authors, this discovery could fundamentally change how the public perceives the predator.
Tooth Enamel Functions as a Body Thermometer
The key to the study lies in the formation of teeth. “Tooth enamel forms within the animal at body temperature; therefore, the chemical composition of the enamel functions as a thermometer,” explained UCLA geoscientist Aradhna Tripati, a senior author of the research.
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The reading is taken from the ratio of certain forms of carbon and oxygen isotopes present in the material. The method used is called “clustered isotopes.”
Drill Extracted 5 Milligrams of Powder from Each Tooth
To avoid destroying the fossils, researchers used a minimally destructive technique, employing a low-speed rotary drill with a tungsten carbide tip.
From each tooth, about 5 milligrams of enamel powder, a quantity smaller than a pinch of salt.
Teeth Came from “Thomas” and a Second Tyrannosaurus
The Natural History Museum of Los Angeles County provided the analyzed material. Two teeth belonged to a well-preserved young adult specimen, nicknamed Thomas.
The third was a partial isolated tooth from a second Tyrannosaurus. The two animals came from the same site in Carter County, Montana.
Temperature of 36.3°C Falls Between That of Elephants and Ostriches
The human average is 37°C, slightly above the estimated value for T. rex. Among current animals, the elephant, the largest living terrestrial animal, has a body temperature of about 36°C.
Meanwhile, the ostrich, the largest existing bird, hovers around 39°C. The tyrannosaurus was among the largest carnivorous dinosaurs that ever existed.
Crocodiles from the Same Rock Formation Had a Body Temperature of 30.9°C
Researchers applied the same technique to five similarly aged crocodilian teeth extracted from the same rock formation.
The result was an average body temperature of 30.9°C, aligning with modern crocodiles and below that recorded for the tyrannosaurus.
“It Stops Being a Reptile,” Says the Study Author
According to Tripati, the number changes the image of the animal. “It stops being a reptile in the way people imagine reptiles. An animal at 36° Celsius doesn’t just wait for the Sun to warm it up,” she stated.
The researcher claims that T. rex is “thermally independent of its surrounding environment” and, in that aspect, is closer to an elephant or an ostrich than to a crocodile.
Warm-Bloodedness is the Ability to Generate and Conserve Heat
Endothermy, the technical term for being warm-blooded, is the ability to generate and conserve internal metabolic heat. It provides sustained energy and resilience, allowing survival in both hot and cold climates.
Cold-blooded animals, or ectotherms, rely on external heat sources to warm their bodies. This includes crocodiles and snakes.
Accelerated Metabolism Comes at the Cost of Needing More Food
Maintaining a warm body has its costs. “Endothermy is common in large animals and even in some fish. However, it comes at a price,” said Robert Eagle, geobiologist at UCLA and co-author of the study.
According to him, “an endothermic T. rex would have to obtain significantly more food to sustain its higher metabolic rate, but would also be capable of sustained activity to find food, migrate, and live in colder environments.”
Predator Lived 66 Million Years Ago in Western North America
The tyrannosaurus roamed western North America during the Cretaceous Period, around 66 million years ago, at the end of the dinosaur era.
Fossils of the species have been found from the Canadian provinces of Alberta and Saskatchewan, through Montana, Wyoming, and the Dakotas, down to New Mexico and Texas.
Climate Models Suggest It Could Withstand Freezing Cold
According to Tripati, climate models indicate that the tyrannosaurus would have been able to inhabit most of the continent.
This includes, in her words, “cold environments where it would have faced freezing temperatures.” The researcher states that it is “a much more mobile and adaptable animal than people imagine.”
Results Debunk the Image of a Slow and Clumsy Creature
Evidence of warm-bloodedness refutes the outdated notion that the tyrannosaurus was a slow and clumsy creature.
Still, the temperature value found is not among the highest. “Our temperature estimate for T. rex falls at the lower end of the range for endotherms,” said Tripati. Small flying birds today, for example, hover around 42°C.
Birds Are Part of the Same Lineage as Carnivorous Dinosaurs
Birds and mammals are endothermic. All carnivorous dinosaurs belong to a lineage called theropods.
Birds are also in this group: they evolved from small feathered dinosaurs, which brings the Tyrannosaurus closer to today’s warm-blooded animals.
Scientists Urge Caution Before Extending the Conclusion to Other Dinosaurs
Eagle notes that there are different degrees of warm-bloodedness. “It is believed that many dinosaurs, but not necessarily all, were warm-blooded,” he stated, referencing the low-level endothermy of sloths and anteaters to that of birds, which have metabolic rates higher than those of mammals.
Tripati makes the same caution about generalizing the result. “This is a single species, and the evidence among dinosaurs points to a variety of strategies rather than a single answer,” he said.
In your opinion, do discoveries like the 36.3°C body temperature of Tyrannosaurus rex change the way movies and books depict dinosaurs? Leave your thoughts in the comments.
