Mammals and Birds Were Not Warm-Blooded Not Until the Greatest Mass Extinction

The Permian-Triassic mass extinction has killed 95% of life on Earth and those left have to struggle with the dire conditions of the world due to global warming and ocean acidification. But two tetrapod groups survived, including synapsids and archosaurs, as well as the ancestors of mammals and birds.

According to Mike Benton, a paleontologist, and professor at the University of Bristol, the ancestors of both mammals and birds became warm-blooded around 250 million years ago, when the world is still recovering from the greatest mass extinction ever.

Since then, mammals and birds are warm-blooded and have successfully survived thanks to this evolution. Benton's study was published in the journal Gondwana Research.

Warm-Blooded Mass Extinction Survivors

Science Daily reported that paleontologists had discovered characteristics of being a warm-blooded in the surviving animals, like evidence for the diaphragm and possible whiskers in synapsids. It is similar to recent research that found evidence of the origin of feathers in dinosaur and bird ancestors.

Experts have suspected for a long time that Triassic survivors had feathers, but archosaurs having feathers from 250 million years ago is something new that they discovered. Also, the paleontologists found out that the bone structure of both synapsids ad archosaurs shows warm-blooded characteristics.

But in 2009 they found a hint that these animals were warm-blooded at the time of Permian-Triassic mass extinction when Tai Kubo was still a student of Masters in Palaeontology at Bristol. According to Professor Benton, the medium size and large tetrapods switch to an erect posture from sprawling right at the greatest mass extinction.

They studied the fossilized footprints of the said animals, and both Kubo and Benton were surprised to see that the posture shift instantly happened and not for millions of years as was once suggested by previous studies. It happened all at once to the animals not just by group, which marks the beginning of the arms race.

Being Warm-Blooded Helped Mammals and Birds Survive

Professor Benton said that animals being warm-blooded and having an erect posture helped mammals and birds run faster and further than those with sprawled feet. However, being warm-blooded also means that these animals have to eat more than their cold-blooded counterpart to fuel their internal temperature control.

Warm-blooded animals today can live all over the world, even those in cold environments and they can also remain active during the night. Additionally, mammals and birds also show maternal care for their young, like teaching them complex and smart behavior needed for survival.

That behavior gives them an edge against amphibians and reptiles, which allowed them to rule many parts of the world, Astrobiology reports.

"The Triassic was a remarkable time in the history of life on Earth. You see birds and mammals everywhere on land today, whereas amphibians and reptiles are often quite hidden," Professor Benton said.

Since only a number survived the greatest mass extinction of all time, this has made the revolution in the ecosystem possible. Those who survived depended on intense competition and had to adapt the endothermic way of survival in the new fast-paced world, Professor Benton added.