T. rex had body temperature similar to humans, study finds

Chemical clues preserved in Tyrannosaurus rex teeth have provided evidence that the massive predator was warm-blooded, with a body temperature close to that of humans, a finding researchers say could fundamentally change perceptions of the famous dinosaur, Reuters reported, citing a study published Wednesday in the journal Science Advances, CE Report quotes AGERPRES.

The chemical composition of enamel from three T. rex teeth discovered in Montana indicated that the dinosaur had a body temperature of 36.3 degrees Celsius, plus or minus 2.5 degrees, according to the researchers. The average human body temperature is around 37 degrees Celsius.

More relevant comparisons may be the average body temperature of an elephant, the largest living land animal, at about 36 degrees Celsius, and an ostrich, the largest living bird, at around 39 degrees Celsius. Tyrannosaurus was among the largest carnivorous dinosaurs.

The new evidence that T. rex was warm-blooded challenges older depictions of the animals as sluggish, opportunistic predators.

“It stops being a reptile in the way people imagine reptiles,” said UCLA geologist Aradhna Tripati, lead author of the study. “An animal with a body temperature of 36 degrees Celsius is not waiting for the sun to warm it up. It is thermally independent of the environment and, in that sense, closer to an elephant or an ostrich than to a crocodile.”

Tyrannosaurus inhabited western North America during the Cretaceous Period around 66 million years ago, near the end of the age of dinosaurs. Its fossils have been found as far north as the Canadian provinces of Alberta and Saskatchewan and south through the US states of Montana, Wyoming and the Dakotas to New Mexico and Texas.

Tripati said climate modeling suggests Tyrannosaurus could have inhabited much of the continent, “including cold environments where it would have experienced freezing.”

“This is a much more mobile and adaptable animal than people imagine,” she said.

Warm-blooded animals, also known as endotherms, are able to generate and retain internal metabolic heat. This provides physiological advantages including sustained energy and endurance, as well as the ability to thrive in both warm and cold climates.

Cold-blooded animals, or ectotherms, depend on external heat sources to warm their bodies, as seen in animals such as crocodiles and snakes.

“Endothermy is common in large animals and even in some fish. However, it comes at a cost,” said UCLA geobiologist and study co-author Robert Eagle.

“Higher metabolic rates mean greater food requirements and potentially more active hunting to obtain it. An endothermic T. rex would have needed to acquire much more food to maintain its higher metabolic rate, but it would also have been capable of more sustained activity to find food and migrate, and to live in colder environments,” Eagle said.

Birds and mammals are endothermic. All carnivorous dinosaurs belong to a lineage known as theropods, which also includes birds, which evolved from small feathered dinosaurs. Today’s small flying birds have body temperatures of around 42 degrees Celsius.

“Our temperature for T. rex falls at the lower end of the endothermic range,” Tripati said.

Teeth were key to the study because tooth enamel forms inside an animal at its body temperature.

“Tooth enamel forms inside the animal at body temperature, so the chemistry of the enamel is like a thermometer,” Tripati explained.

The ratio of certain carbon and oxygen isotopes in enamel can reveal body temperature. Researchers used a minimally destructive technique involving a low-speed rotary drill with a tungsten carbide tip to extract around five milligrams of enamel powder — less than a pinch of salt — from each tooth.

The Natural History Museum of Los Angeles County provided the teeth. Two came from a well-preserved young adult T. rex nicknamed Thomas, while the third was a partially isolated tooth from another Tyrannosaurus. Both specimens were found at the same location in Carter County, Montana.

Researchers also applied the technique to five similarly aged crocodilian teeth from the same rock formation. They found average body temperatures of 30.9 degrees Celsius, consistent with modern crocodiles and notably lower than those recorded for Tyrannosaurus.

“Many dinosaurs, but not necessarily all, are thought to have been warm-blooded,” Eagle said. “However, even among warm-blooded organisms, there are questions about the degree of endothermy.”

Some animals may have relatively low levels of endothermy, while birds generally have higher metabolic rates than mammals, he explained.

Tripati cautioned against applying the findings to all dinosaurs.

“This is a single species, and the evidence across dinosaurs points to a range of strategies rather than a single answer,” she said.

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