Lunar and Planetary Institute
Ninety percent of all life was killed during the Permian mass extinction 250 million years ago. But the pig-sized animal Lystrosaurus curvatus and other species apparently survived by burrowing underground.
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updated 10/5/2009 12:12:59 PM ET 2009-10-05T16:12:59

When the going gets tough, putting your head in the sand isn't always a bad idea. According to a new study, that's exactly how a group of animals living 250 million years ago survived the worst mass extinction of all time.

In a series of new fossil discoveries in South Africa, researchers have uncovered a slew of petrified burrows, many of them a foot wide and a 3.3 feet or more deep.

Many of the shelters coincide with the end of the Permian era, a time when the region suddenly shifted from a moist, balmy river delta environment to parched, sweltering badlands.

Ocean life, land animals and plants perished around the world during this intense climatological shift. Some estimates suggest up to 90 percent of all organisms on Earth were snuffed out over a period of several hundred thousand years.

But Roger Smith of the Iziko South African Museum in Capetown and Jennifer Botha of the South African National Museum believe that the pig-sized animal Lystrosaurus curvatus and several other species weathered the apocalypse by simply hiding underground. During the worst of the heat and dry season, they may have hibernated, and fossil skeletons show that multiple species sometimes shared the same burrow.

Smith presented the discovery at the Society for Vertebrate Paleontology annual meeting in Bristol, United Kingdom last week.

In some ways, the discovery helps explain why the humble, plodding Lystrosaurus overran Pangea after the extinction. Their fossils have also been found in Antarctica, Russia, China, and India.

But other burrowing animals like the small, proto-mammal Diictodon didn't survive the extinction.

For Robert Reisz of the University of Toronto, that calls into question just how beneficial burrowing was, and whether it was a reaction to extreme conditions or a holdover from old behavioral habits.

"Lots of animals that did not burrow made it through," Reisz said. He wasn't involved in the study. "Lystrosaurus had large claws. It's more likely that they were natural burrowers. Such a dramatic change in their behavior is not likely."

So did Lystrosaurus and its fellow subterranean denizens just get lucky? Reisz questions whether the extinction was really as disastrous as many people like to believe.

"There are clearly major shifts in climate and fauna," he said. "But the evidence from large animals seems to indicate this wasn't the catastrophe it's generally thought to be."

© 2012 Discovery Channel

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