The spectacular haul of 20,000 fossils from a hillside in south-west China represents the first discovery of a complete ecosystem which bounced back after life was nearly wiped off the face of the planet 252 million years ago.
The beautifully preserved remains include molluscs, sea urchins and arthropods, alongside much larger animals that occupied the top of the food chain, such as carnivorous fish and the first icthyosaurs.
Among the remnants are rare fragments of land life that survived the same period, including part of a conifer plant and the tooth of an archosaur.
The fossils were excavated from rocks formed when ocean sediments solidified many millions of years ago in what is now Luoping county in Yunnan province.
The Earth has had several mass extinctions in its 4.5billion-year history, but the event that struck at the end of the Permian period was unequalled in scale. About 96 per cent of marine species and 70 per cent of land vertebrates were lost in what has been called “the great dying”.
What caused such global havoc is still open to debate, but Michael Benton, a palaeontologist at Bristol University, England, who led the latest research, said evidence pointed to prolonged and violent eruptions from the Siberian traps, a huge region of volcanic rock. In this scenario, mass eruptions triggered environmental catastrophe by belching an overwhelming quantity of gas into the atmosphere for half a million years.
“The main follow-on was a flash warming of the Earth. That caused stagnation in the oceans, as normal circulation shut down. On land, the consequence of all the carbon dioxide and other gases appears to have been massive acid rain that killed the forests and stripped the landscape bare,” Benton said. “This was the greatest of all mass extinctions, the time when life was most nearly completely wiped out.” The life that survived became the starting point for a recovery played out over the next ten million years.
Some of these organisms clung on through sheer hardiness, coping with scarce food, wild temperature variations and little oxygen in the oceans.
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 understand how life returned from the brink.
“The recovery from mass extinction touches on current concerns ... Why do certain species go extinct? Which species come back? How do you rebuild an ecosystem and how long does it take?” The study appears in the Proceedings of the Royal Society B . The Luoping fossils show that many small organisms at the bottom of the food chain came back within 2-3 million years and other creatures that could feed on them recovered. The familiar spiralled ammonites bounced back surprisingly fast. Only later did the larger predators reappear in the oceans. The loss of so many species at the end of the Permian gave new creatures the chance to thrive.
“Part of it is a rebuilding of the ecosystem from the grim survivors, but there are also opportunities for new groups. There were no marine reptiles before the extinction but this gave them a way in.”
Palaeontologists have unearthed other fossils showing life returning from the Permian extinction but the Luoping fossils are unique in having the rich biodiversity of a fully functioning ecosystem, from plankton to carnivorous apex predators. — © Guardian Newspapers Limited, 2010
