The whole-body endothermy seen in modern birds and mammals is long held to have evolved independently in each group, a reasonable assumption when it was believed that its earliest appearances in birds and mammals arose many millions of years apart. According to the new research, the evolutionary origin of endothermy could have occurred nearly 300 million years ago. An artist’s impression of the likely-endothermic Dimetrodon grandis, an early synapsid...
