Tyrannosaurus rex was likely a warm-blooded predator, according to new evidence drawn from the chemical composition of 66-million-year-old tooth enamel. The finding adds weight to a growing body of research suggesting that the iconic dinosaur regulated its own body temperature through metabolism, much like modern birds and mammals.
Robert Eagle of the University of California, Los Angeles, and his colleagues analysed the enamel of three T. rex teeth and compared it with five fossilised crocodile teeth of similar age. They also compared their results with data from large mammals such as elephants and mammoths to determine whether T. rex was an endotherm — an animal capable of regulating its body heat internally.
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 common in minerals that form at cold temperatures than in those that form in warm conditions. «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,» Eagle said.
The analysis indicates that T. rex maintained a body temperature of around 36°C, similar to that of large modern mammals but below that of many modern birds. The reconstructed temperature was significantly higher than temperatures derived from crocodile teeth found in the same geological formation — Hell Creek in Montana. It was also higher than the ambient temperatures of prehistoric Montana, as reconstructed from both 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,» Eagle said. That conclusion challenges a premise of the opening scene of the film Jurassic World, which suggested dinosaurs could not survive outside tropical regions in the modern world.
Scott Persons of the South Carolina State Museum, who was not involved in the study, said the research means «the opening to the last Jurassic World flick was one big pile of Hollywood bunk». He added that the evidence indicates a Tyrannosaurus would have been comfortable in subtropical and even mild climates.
Endothermy is common among large animals and even some fish, Eagle noted. It allows them to move around and sustain activity to find food and migrate, and to live in colder environments. But it comes at a cost: higher metabolic rates mean higher food requirements and potentially more active hunting to acquire it.
Persons said extensive evidence already pointed to T. rex being warm-blooded, including bone growth rates, predator-prey ratios — with energy-hungry endotherms requiring far more prey per predator than cold-blooded animals — and a slew of anatomical traits consistent with high-performance athleticism.
Thomas Carr of Carthage College in Wisconsin described the work as an example of science in action, converging on a single, robust hypothesis that reveals T. rex as an active top predator. The researchers make the case for a wide geographic distribution for T. rex, he said, showing that it could tolerate cool temperatures in the north of its range and tropical temperatures in the south. In both cases, its body temperature was higher than the average air temperature — a result consistent with the hypothesis that T. rex might have migrated from Asia into North America at high latitudes.
The study, published in Science Advances, adds to decades of debate over dinosaur metabolism. While crocodiles and other ectotherms often warm up by basking in the sun, endotherms generate heat internally. The new isotopic evidence places T. rex firmly in the latter category, reinforcing its image as an active, wide-ranging predator rather than a sluggish, cold-blooded reptile.