World’s greatest mass extinction triggered switch to warm-bloodedness

Posture shift at the end of the Permian, 252 million years ago. Before the crisis, most reptiles had sprawling posture; afterwards they walked upright. This may have been the first sign of a new pace of life in the Triassic. Credit: animal drawings by Jim Robins, University of Bristol. Mammals and birds today are warm-blooded, […]