Geoscientist Online

Recovering from the mother of all mass extinctions took 30 million years, say scientists at Bristol University. Dwain Eldred reports.

Geoscientist Online 18 January 2008

The full recovery of ecological systems, following the most devastating extinction event of all time, took at least 30 million years, according to new research from the University of Bristol.

About 250 million years ago, at the end of the Permian, a major extinction event killed over 90% of life on earth, including insects, plants, marine animals, amphibians, and reptiles. Ecosystems were destroyed worldwide, communities were restructured and organisms were left struggling to recover. This was the nearest life ever came to being completely wiped out.

Previous work indicates that some life bounced back quite quickly, but mostly in the form of 'disaster taxa' (opportunistic organisms that fill the empty ecospace), such as the hardy Lystrosaurus (picture), a barrel-chested herbivore, about the size of a pig.

The most recent research, conducted by Sarda Sahney and Professor Michael Benton at the University of Bristol (see this week's Proceedings of the Royal Society B) indicates that specialised animals and complex ecosystems with high biodiversity, complex food webs and a wide variety of niches, took much longer to reappear. In this way, recovery after a mass extinction is comparable to ecological succession, and recovery can be said to be complete when the new ecosystem is stable – a "climax community" in ecological terms.

Sahney says: "Our research shows that after a major ecological crisis, recovery takes a very long time. So although we have not yet witnessed anything like the level of the extinction that occurred at the end of the Permian, we should nevertheless bear in mind that ecosystems take a very long time to fully recover."

Sahney and Benton looked at the recovery of tetrapods – four-legged vertebrate animals, such as amphibians and reptiles - and found that although globally tetrapods appeared to recover quickly, the dramatic restructuring that occurred at the community level was not permanent and communities did not recover numerically or ecologically until some 30 million years later.

Benton says: "Diversity is most commonly assessed by tallying the number of taxa on a global scale - but these studies are subject to the vagaries of sampling. By examining well-preserved and well-studied faunas, the taxonomic and ecological recovery of communities after the Permian extinction event can be examined more accurately, and the problems of geological bias are largely avoided."

The end-Permian extinction occurred in three waves, the largest being at the boundary between the Permian and Triassic periods, 251 million years ago. This was the most devastating ecological event of all time, thought to be caused by large-scale volcanism in Russia which produced the 'Siberian Traps', which covered over 200,000 square kilometres of the Earth's surface in lava.