The first mammals arose in the Triassic period, more than 225 million years ago, including small shrew-like animals such as 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 stand them apart from their reptile ancestors, and which contribute to their huge success today.
“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 different niches in the Triassic - from carnivores to herbivoresm,” said Dr Marcello Ruta, lead author and evolutionary palaeobiologist from the University of Lincoln.
"During the Triassic, the cynodonts split into two groups, the cynognathians and the probainognathians," added
co-author Dr Jennifer Botha-Brink of the National Museum in Bloemfontein, South Africa. "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. 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."
"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," concluded Michael Benton, of the University of Bristol, UK, added:
The researchers concluded that cynodont diversity rose steadily during the recovery of life following the mass extinction, with their range of form rising rapidly at first before hitting a plateau. This suggests there is no particular difference in morphological diversity between the very first mammals and their immediate cynodont predecessors.
Image at the top of the page shows the fossil remains of the 10-foot (0.3-meter) predator Dinogorgon that stalked the floodplains in the heart of today's South Africa.
The paper 'The radiation of cynodonts and the ground plan of mammalian morphological diversity' by Marcello Ruta, Jennifer Botha-Brink, Steve Mitchell and Michael J. Benton is published in Proceedings of the Royal Society B 20131865 on 28th August, 2013.
The Daily Galaxy via University of Lincoln
« Will Life on Planets of Red Dwarf Stars be Older & More Evolved? (Today's Most Popular) | Main | Carbon-12 --Does Its Creation in Stars Suggest a Universe Fine-Tuned for Life? (Today's Most Popular) »