New research estimates when first warm-blooded dinosaurs roamed the Earth

Scientists once thought of dinosaurs as sluggish, cold-blooded creatures. Then 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 may have roamed the Earth about 180 million years ago, about halfway through the creatures’ time on the planet.

Warm-blooded creatures — including birds, who are descended from dinosaurs, and humans — keep their body temperature constant whether the world around them runs cold or hot. Cold-blooded animals, including reptiles like snakes and lizards, depend on outside sources to control their temperature: For example, basking in the sun to warm up.