The survival of the cynodont therapsids during Earth's greatest mass extinction that took place 252 million years ago paved the way for the rise of modern mammals, a recent study suggests.
The Permian-Triassic extinction, informally known as the Great Dying was an extinction event that occurred 252 million years ago. The first mammals arose in the Triassic period, more than 225 million years ago. These included shrew-like animals, such as the Morganucodon from England and the Megazostrodon from Africa and the Bienotherium from China. They had very different characteristics from their reptile ancestors and were probably warm-blooded and covered in fur, which may be the reason why the continued to thrive after cataclysmic events.
According to researchers the University of Lincoln, the National Museum in Bloemfontein, South Africa, and the University of Bristol, survival of the cynodont therapsids during Earth's greatest mass extinction paved the way for the rise of modern mammals. Over time, these mammals developed differentiated teeth (incisors, canines, molars) and large brains.
"Mass extinctions are seen as entirely negative. However, in this case, cynodont therapsids, which included a very small number of species before the extinction, really took off afterwards and were able to adapt to fill many very different niches in the Triassic - from carnivores to herbivores," said Dr Marcello Ruta of the University of Lincoln, lead author of the study in a press statement.
The end-Permian mass extinction wiped out 90 per cent of marine organisms and 70 per cent of terrestrial species. Late Permian saw the rise of cynodonts that thrived and diversified during the Triassic. Cynodonts are considered to be the missing link between reptiles and mammals. During the Triassic, the cynodonts split into two groups--cynognathians and probainognathians. The first were mainly plant-eaters while the second were mainly flesh-eaters. These two groups seemed to rise and fall at random, but also gave rise to the first mammals about 25 million years after the mass extinction.
"We saw that when a major group, such as cynodonts, diversifies it is the body shape or range of adaptations that expands first. The diversity, or number of species, rises after all the morphologies available to the group have been tried out," co-author Professor Michael Benton of the University of Bristol said.
