Some Dinosaurs Evolved to Be Warm-Blooded 180 Million Years Ago, Study Suggests

Two major groups of dinosaurs may have been warm-blooded—having evolved the ability to regulate their body temperatures—around 180 million years ago, according to a new study.

Scientists used to think that all dinosaurs were cold-blooded, meaning that, like modern lizards, their body temperatures were dependent on their surroundings. While scientists have since discovered that some dinosaurs were actually warm-blooded, they haven’t been able to pinpoint when this adaptation evolved, according to a statement from University College London.

The new findings suggest that theropods, a group of mostly carnivorous dinosaurs including Tyrannosaurus rex and Velociraptor, as well as the ornithischians, which include the mostly plant-eating relatives of Stegosaurus and Triceratops, may have both developed warm-bloodedness in the early Jurassic Period. This change might have been prompted by global warming that followed volcanic eruptions, according to the results published Wednesday in the journal Current Biology.

The study is the “first real attempt to quantify broad patterns that some of us had thought about previously,” Anthony Fiorillo, executive director of the New Mexico Museum of Natural History & Science who was not involved in the work, tells CNN’s Katie Hunt. “Their modeling helps create a robustness to our biogeographical understanding of dinosaurs and their related physiology.”

Warm-blooded animals, which include mammals and birds, use energy from food to maintain a constant body temperature. Their bodies can shiver to generate heat, and they may sweat, pant or dilate their blood vessels to cool off. As a result, these animals can live in a wide range of environments.

On the other hand, cold-blooded creatures must move to different environments to control their body temperature. They might lie in the sun to warm up and move under a rock or into the water to cool off.

Previous work had uncovered evidence of warm-bloodedness in both theropods and ornithischians, such as feathers that trap body heat, according to the university’s statement. In the new study, the researchers studied the geographic spread of dinosaurs during the Mesozoic Era, which lasted from 230 million to 66 million years ago, by examining 1,000 fossils, climate models and dinosaur evolutionary trees.

They found that theropods and ornithischians lived in wide-ranging climates, and during the early Jurassic, these two groups migrated to colder areas. This suggested they had developed the ability to generate their own heat.

“If something is capable of living in the Arctic, or very cold regions, it must have some way of heating up,” Alfio Allesandro Chiarenza, a co-author of the study and a paleontologist at University College London, tells Adithi Ramakrishnan of the Associated Press (AP).

Long-necked sauropods, on the other hand, which include the Brontosaurus, seemed restricted to areas with higher temperatures. The team suggests this means sauropods could have been cold-blooded.

“It reconciles well with what we imagine about their ecology,” Chiarenza says to CNN. “They were the biggest terrestrial animals that ever lived. They probably would have overheated if they were hot-blooded.”

At around the same time, volcanic eruptions led to global warming and the extinction of some plant species.

“The adoption of endothermy, perhaps a result of this environmental crisis, may have enabled theropods and ornithischians to thrive in colder environments, allowing them to be highly active and sustain activity over longer periods, to develop and grow faster and produce more offspring,” Chiarenza says in the statement.

Jasmina Wiemann, a paleobiologist at the Field Museum of Natural History who was not involved in the new research, published a study in 2022 that came to a different conclusion: Based on oxygen intake in dinosaur fossils, she found that ornithischians were more likely cold-blooded, while sauropods were more likely warm-blooded.

She tells the AP that considering information on dinosaurs’ body temperatures and diets, not just their geographic distribution, can help scientists understand when dinosaurs evolved to be warm-blooded.

Will Sullivan | | READ MORE

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.