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

The origin of endothermy in synapsids, including the ancestors of mammals. The diagram shows the evolution of main groups through the Triassic, and the scale from blue to red is a measure of the degree of warm-bloodedness reconstructed based on different indicators of bone structure and anatomy. Mike Benton, University of Bristol. Animal images are by Nobu Tamura, Wikimedia

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. animal drawings by Jim Robins, University of Bristol

16 October 2020

Mammals and birds today are warm-blooded, and this is often taken as the reason for their great success.

University of Bristol palaeontologist Professor Mike Benton identifies in the journal Gondwana Research that the ancestors of both mammals and birds became warm-blooded at the same time, some 250 million years ago, in the time when life was recovering from the greatest mass extinction of all time.

The Permian-Triassic mass extinction killed as much as 95 per cent of life, and the very few survivors faced a turbulent world, repeatedly hit by global warming and ocean acidification crises. Two main groups of tetrapods survived, the synapsids and archosaurs, including ancestors of mammals and birds respectively.

Palaeontologists had identified indications of warm-bloodedness, or technically endothermy, in these Triassic survivors, including evidence for a diaphragm and possible whiskers in the synapsids.

“This revolution in ecosystems was triggered by the independent origins of endothermy in birds and mammals, but until recently we didn’t realise that these two events might have been coordinated.

“That happened because only a tiny number of species survived the Permian-Triassic mass extinction - who survived depended on intense competition in a tough world. Because a few of the survivors were already endothermic in a primitive way, all the others had to become endothermic to survive in the new fast-paced world.’


‘The origin of endothermy in synapsids and archosaurs and arms races in the Triassic’ by M. J. Benton in Gondwana Research.

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