July 24 (UPI) -- Fresh fossil analysis suggests the earliest warm-blooded species emerged during the Late Permian period, between 252 and 259 million years ago.
The adaptation -- a feature of all modern mammals, including humans -- may have helped the species survive the Permian-Triassic extinction event that wiped out 96 percent of all marine species and 70 percent of terrestrial vertebrate species 252 million years ago.
The ability to generate body heat, called endothermy, and maintain a stable internal temperature, homeothermy, first emerged among therapsids, a group of mammal-like reptiles. Therapsids consisted of six subgroups, including cynodonts, the group that yielded the earliest mammalian lineages during the Triassic period.
In an effort to pinpoint the origins of warm bloodedness, paleontologists at the French National Center for Scientific Research collected several dozen therapsid fossils, comprising 22 different species, from South Africa, Lesotho, Morocco and China. By measuring ratios of oxygen isotopes, scientists were able to discern the metabolic characteristics of each species' remains.
By comparing the metabolism of different species, researchers were able to differentiated between warm- and cold-blooded species. Their analysis -- detailed last week in the journal eLife -- revealed warm bloodedness in eight species from two different therapsid lineages predating the Permian-Triassic extinction event.
It's possible, researchers hypothesize, that the adoption of endo-homeothermy among therapsid species may have enabled their resistance to rapid and dramatic climate change and helped them survive the P-T extinction event.