Two hundred and fifty million years ago an egg-laying mammal-like reptile the size of a German shepherd dominated land ecosystems. "It doesn't really look like the guy you would bet on for being the champion survivor," said Jessica Whiteside, assistant professor of geological sciences.
But this now-extinct species, called Lystrosaurus, was able to survive the end-Permian mass extinction, the most severe in Earth's history. During this event, 78 percent of all land-dwelling vertebrates went extinct, Whiteside and co-author Randall Irmis from the University of Utah and the Utah Museum of Natural History reported Tuesday in the Proceedings of the Royal Society B.
Before this study, the impact of the end-Permian mass extinction on terrestrial species was highly debated — some scientists said land vertebrates were devastated and others said they were not affected at all, Whiteside explained. Though it was known that marine taxa took a huge hit, with somewhere between 70 and 80 percent going extinct, no studies had looked closely at the effects on land.
So Whiteside and Irmis set out to settle the debate. They looked at 70,000 specimens from two of the best-preserved locations in the fossil record, one in South Africa and one in Russia. Their analysis revealed the impact on land was similar to that at sea.
The end-Permian extinction was likely tied to major eruptions from fissures in the Earth's crust, Whiteside said. These eruptions threw lava over a kilometer into the air, releasing greenhouse gases into the atmosphere. A dramatic change in climate likely ensued, she said.
It took five to 10 million years for the planet to recover its biodiversity, the study reports. During that period, two "disaster taxa"— the Lystrosaurus and a reptile that might be related to the turtle — dominated land ecosystems.
"What's interesting is they weren't dominant members of the ecosystem during the Permian," Whiteside said. "It was only after their way was paved" that these species took over, possibly because they were not particular about foraging conditions.
The long recovery period was caused by the low number of species, making the food web more susceptible to perturbations like climate change, Whiteside explained. Just as an ecosystem was starting to recover, "it gets hit by something that should be relatively minor," leading to a series of "boom-and-bust-cycles," she said.
During this period of low diversity, the carbon cycle was unstable, hinting that climate change may be affected by ecosystem stability. Climate change is not a purely physical process, the research suggests. "The carbon cycle has wild swings because diversity itself is low," Whiteside said.
"The effects of an extinction last for a really long time, on the order of five to 10 million years," Whiteside said. Current extinction rates mimic those of previous mass extinctions, she said, and some biologists suggest that the Earth's sixth mass extinction is currently underway.
"Unfortunately, in that aspect (the study) paints a dismal picture," she said. Just look at the long, lonely reign of Lystrosaurus and his turtle-like companion.
