Cynodont therapsids, small shrew-like mammals, managed to survive the end-Permian mass extinction that wiped out 90 percent of marine organisms and 70 percent of terrestrial species, they said.
"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 herbivores," Marcello Ruta of the University of Lincoln said.
Cynodonts identified from fossil remains include Morganucodon from England, Megazostrodon from South Africa and Bienotherium from China, the researchers said.
Cynodonts had large brains and were probably warm-blooded and covered in fur -- all characteristics that stand them apart from their reptile ancestors and contribute to their huge success today, the researchers said.
Cynodont diversity rose steadily during the recovery of life following the mass extinction, they said.
"We saw that when a major group, such as cynodonts, diversifies, it is the body shape or range of adaptations that expands first," Michael Benton of the University of Bristol said. "The diversity, or number of species, rises after all the morphologies available to the group have been tried out."