The first mammals arose in the Triassic period, over 225 million years ago and included small shrew-like animals like Morganucodon from England, Megazostrodon from South Africa, and Bienotherium from China.
They had differentiated teeth (incisors, canines, molars) and large brains and were probably warm-blooded and covered in fur - all characteristics that make them stand apart from their reptile ancestors, and which contribute to their huge success today.
New research from the University of Lincoln, the National Museum in Bloemfontein, South Africa, and the University of Bristol suggests that this array of unique features arose step-wise over a long span of time, and that the first mammals may have arisen as a result of the end-Permian mass extinction which wiped out 90 per cent of marine organisms and 70 per cent of terrestrial species.
Lead author Dr Marcello Ruta of the University of Lincoln of the study, said that mass extinctions are seen as entirely negative but in this case, cynodont therapsids, which included a very small number of species before the extinction, really took off afterwards and was able to adapt to fill many very different niches in the Triassic - from carnivores to herbivores.
Co-author Dr Jennifer Botha-Brink of the National Museum in Bloemfontein, South Africa said that during the Triassic, the cynodonts split into two groups, the cynognathians and the probainognathians.
She said that the first were mainly plant-eaters, the second mainly flesh-eaters, and the two groups seemed to rise and fall at random, first one expanding, and then the other.
Botha-Brink asserted that in the end, the probainognathians became the most diverse and most varied in adaptations, and they gave rise to the first mammals some 25 million years after the mass extinction.
The new research has been published in Proceedings of the Royal Society B.
--ANI (Posted on 29-08-2013)