And a new study find that the ancestors of both mammals and birds became warm-blooded at the same time.Endothermy, warm-bloodedness, is the ability to regulate body temperature using metabolism rather than relying on outside nature. Animal images are by Nobu Tamura, Wikimedia.Palaeontologists had identified indications of warm-bloodedness. including evidence of a diaphragm and whiskers in the synapsids, while bone structure of both synapsids and archosaurs of the Triassic tshowscharacteristics of warm-bloodedness. Today, warm-blooded animals can live all over the Earth, even in cold areas, and they remain active at night. Because a few of the survivors were already endothermic in a primitive way, all the others had to become endothermic to survive.