Washington: A new research has studied how anomodonts responded after Permian mass extinction, about 252 million years ago, when as many as 90 percent of marine organisms and 70 percent of terrestrial species became extinct.
The study`s findings are surprising as much research so far suggests that the survivors of mass extinctions are often presented with new ecological opportunities because the loss of many species in their communities allows them to evolve new lifestyles and new anatomical features as they fill the roles vacated by the victims.
However, it turns out that not all survivors respond in the same way, and some may not be able to exploit fully the new opportunities arising after a mass extinction.
Dr Marcello Ruta of the University of Lincoln, with colleagues from the Field Museum of Natural History in Chicago, the Museum fur Naturkunde in Berlin and the University of Bristol, found that near the end of the Permian, a large number of anomodont species existed with a wide range of body sizes and ecological adaptations, including terrestrial plant eaters, amphibious hippo-like species, specialized burrowers, and even tree-dwelling forms.
The most successful group of anomodonts, with canine-like tusks in their upper jaws and turtle-like beaks, were the most important terrestrial herbivores of their time.
Ruta said that the number of anomodont species increased during the Permian, sharply dropped during the end-Permian extinction event, and then rebounded in the Middle Triassic Period (about 240 million years ago) before the final extinction of the group at the end of the Triassic.
He said that however, the variety of different anatomical features found in anomodonts - that is, their anatomical diversity - declined steadily over their history.
Ruta explained that even in the aftermath of the mass extinction, when there should have been a lot of empty ecological space, anomodonts did not evolve any fundamentally new features. Rather than allowing them to move to a new evolutionary trajectory, the genetic bottleneck they passed through constrained their future evolution.
The study has been published in Proceedings of the Royal Society B.