T. rex teeth show the enormous predatory dinosaur was warm-blooded

The world’s most famous dinosaur, Tyrannosaurus rex, was probably warm-blooded like birds and mammals, new evidence, obtained from 66-million-year-old tooth enamel, suggests, adding weight to previous findings.

Scott Persons at South Carolina State Museum, who wasn’t involved in the new study, says the research means “the opening to the last Jurassic World flick was one big pile of Hollywood bunk”.

“That film premised that dinosaurs could not survive in the modern world, except near the equator,” says Persons. “Not so. The evidence indicates that a Tyrannosaurus would be comfortable in subtropical and even mild climates.”

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Robert Eagle at the University of California, Los Angeles, and his colleagues analysed the chemistry in the enamel of three T. rex teeth and compared them with five similarly aged fossilised crocodile teeth.

The researchers also compared their results with data from mammals such as elephants and mammoths to try to determine whether T. rex was also an endotherm – an animal that can regulate its body heat through its metabolism. Ectothermic, or so-called cold-blooded animals like crocodiles, often warm up by basking in the sun instead.

Endothermy is common in large animals and even some fish, says Eagle, allowing them to move around and exhibit more sustained activity to find food and migrate, and to live in colder environments. It has long been thought that many dinosaurs, including T. rex, were also warm-blooded.

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“It comes at a cost though – higher metabolic rates mean higher food requirements and potentially more active hunting to acquire it,” he says.

Within the enamel chemistry, the researchers focused on the abundance of bonds between rare heavy isotopes of carbon and oxygen, known as carbon-13-oxygen-18 bonds. These bonds are more abundant in minerals that form at cold temperatures than minerals that form at warm temperatures.

“Therefore, in a very old tooth we can measure carbon-13-oxygen-18 bond abundance and figure out whether it formed in a hot or cold body.”

He says T. rex had a body temperature of around 36°C, similar to large modern mammals but below many modern birds.

“We also found that the reconstructed temperature of T. rex was significantly elevated compared to temperatures derived from crocodile teeth from the same geological formation – Hell Creek in Montana,” Eagle says.

The researchers also say that T. rex body temperatures were higher than the ambient temperatures in prehistoric Montana, reconstructed both from isotopic estimates and climate models.

“Using thermal performance curves and climate modelling based on these results, we found that the entire North American continent would have been habitable for T. rex in the Cretaceous Period,” he says.

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Persons says there was already extensive evidence that T. rex was warm-blooded, including bone growth rates and predator-prey ratios – with energy-hungry endotherms requiring much more prey per predator than ectotherms – and a “slew of anatomical traits consistent with high-performance athleticism”.

Thomas Carr at Carthage College in Wisconsin says the new work is an “example of science in action, converging upon a single, robust hypothesis, which in this case reveals T. rex as an active top predator”.

The researchers “make the case for a wide geographic distribution for T. rex, showing that it could tolerate cool temperatures in the north of its range and tolerate the tropical temperatures in the south”, says Carr. “And in both cases, T. rex‘s body temperature is higher than the average air temperature. That result is consistent with the hypothesis that T. rex might have migrated from Asia into North America at high latitudes.”

Science Advances DOI: 10.1126/sciadv.aeb7653