250 million years ago there was a world wide extinction event where 96% of all marine species were exterminated. Most of this event is unknown. Only one in every ten species survived, and these formed the basis for the recovery of life in the subsequent time period, called the Triassic. A new fossil site — at Luoping in Yunnan Province — provides a new window on that recovery, and indicates that it took about 10 million years for a fully-functioning new ecosystem to develop. During that time window, the new ecosystem evolved and changed until it stabilized.
Marine invertebrates suffered the greatest losses during the Permian extinction. In the intensively-sampled south China sections at the Permian boundary, for instance, 280 out of 329 marine invertebrate genera disappear within the final 2 sedimentary zones containing conodonts from the Permian.
The Permian had great diversity in insect and other invertebrate species, including the largest insects ever to have existed. The end-Permian is the only known mass extinction of insects, with eight or nine insect orders becoming extinct and ten more greatly reduced in diversity.
The spectacular haul of 20,000 fossils from a hillside in southwestern China represents the first discovery of a complete ecosystem which bounced back after life was nearly wiped off the face of the planet 252m years ago.
The small town of Luoping in China lies in the relatively underdeveloped eastern part of Yunnan province. Luoping is dominated by karst features with small basins among mountain ranges. This area was a sea in Permian times.
"The Luoping site dates from the Middle Triassic and contains one of the most diverse marine fossil records in the world," said Professor Benton. "We can tell that we’re looking at a fully recovered ecosystem because of the diversity of predators, most notably fish and reptiles. It’s a much greater diversity than what we see in the Early Triassic — and it’s close to pre-extinction levels."
By studying the fossils, Benton and his colleagues at the Chengdu Institute of Geology and Mineral Resources and the University of Western Australia, hope to piece together how life can come back from the brink. "The recovery from mass extinction touches on current concerns about biodiversity and conservation. Why do certain species go extinct? Which species come back? How do you rebuild an ecosystem and how long does it take?" said Benton.
Reinforcing this conclusion is the complexity of the food web, with the bottom of the food chains dominated by species typical of later Triassic marine faunas — such as crustaceans, fishes and bivalves — and different from preceding ones.
Just as important is the debut of new predators — such as the long-snouted bony fish Saurichthys, the ichthyosaur Mixosaurus, the sauropterygian Nothosaurus and the prolacertiform Dinocephalosaurus.
"The fossils at Luoping have told us a lot about the recovery and development of marine ecosystems after the end-Permian mass extinction," said Professor Benton. "There’s still more to be discovered there, and we hope to get an even better picture of how life reasserted itself after the most catastrophic global event in the history of our planet."
For further information: http://www.bristol.ac.uk/news/2010/7398.html