Scientists once considered dinosaurs to be slow, cold-blooded creatures. At the time, research suggested that some could control their body temperature, but when and how that shift came about remained a mystery.
Now, a new study estimates that the first warm-blooded dinosaurs roamed the Earth about 180 million years ago, about halfway through the creatures' time on Earth.
Warm-blooded creatures – included birdsthat descend from dinosaurs, and humans – keep their body temperature constant regardless of whether the world around them is cold or warm. Cold-blooded animals, including reptiles such as snakes and lizards, rely on outside sources to control their temperatures: for example, sunbathing to warm up.
Knowing when dinosaurs developed their stable internal thermometer could help scientists answer other questions about how they lived, including how active and social they were.
Davide Bonadonna/University of Vigo/University College London via AP
To estimate the origin of the first warm-blooded dinosaurs, researchers analyzed more than 1,000 fossils, climate models and dinosaur family trees. They found that two major groups of dinosaurs – including Tyrannosaurus rex, velociraptors and relatives of triceratops – migrated to colder areas during the early Jurassic period, suggesting they may have evolved the ability to stay warm. A third group of dinosaurs, including brontosaurs, stuck around in warmer areas.
“If something can live in the Arctic or in very cold areas, it must be able to warm up somehow,” said Alfio Allesandro Chiarenza, author of the study and postdoctoral researcher at University College London.
The research was published Wednesday in the journal Current Biology.
Jasmina Wiemann, a postdoctoral researcher at the Field Museum in Chicago, said that a dinosaur's location is not the only way to determine whether it is warm-blooded. Research by Wiemann, who was not involved in the latest study, suggests that warm-blooded dinosaurs may have evolved closer to the start of their time on Earth, about 250 million years ago.
She said gathering clues from multiple aspects of dinosaurs' lives — including their body temperature and diet — could help scientists paint a clearer picture of when they evolved to be warm-blooded.
