Mammoths wiped out by 'perfect storm?'

Image: Wooly mammoths
A team of researchers believe that the hearty mammoths were much tougher than we give them credit for. They say that the extinction of the giant animals cannot be attributed to humans or climate change alone, but to a "perfect storm" of factors. Mauricio Anton via PLoS Biology
/ Source: Discovery Channel

Mammoths were a hearty group of giants that went extinct not because of climate change or overhunting by early humans, but a "perfect storm" of conditions, according to new research.

At the height of their numbers, the elephant-like beasts roamed the northern hemisphere from France to Canada, north above the Arctic circle and south into China.

But after thriving for millions of years, they suddenly disappeared around 12,000 years ago. Scientists have argued that climate change, an asteroid impact, or even the rise of a new predator — humans, armed with spears — did them in.

Sergey Zimov of the Russian Academy of Science and a team of researchers believe the animals were far tougher than we give them credit for. In a presentation at the fall meeting of the American Geophysical Union this month, they proposed that mammoths lived in an ecosystem as rich in life as today's African savannah, and that all three extinction factors must've converged to deliver the mortal blow.

Around 12,900 years ago, temperatures in the northern hemisphere plunged abruptly, beginning 1,000 years of bitter cold known as the Younger Dryas cooling event. The shift in climate is thought to have destroyed the mammoths' ecosystem and, the theory goes, starved the giants as tundra mosses and woody scrub carpeted the frosty Earth.

"Climate change alone is not enough to kill them off," said Nikita Zimov, Sergey's son, also of the Russian Academy of Sciences. "They lived ... in many different temperatures and levels of precipitation."

For years the team has been recreating the environment around that time in a 62-square-mile paddock in Siberia they call "Pleistocene Park." They've introduced a variety of animals that used to live alongside mammoths, including reindeer, musk oxen, and moose.

They found the large mammals carve out a grassy landscape from what would otherwise be tundra. Their trampling hooves kill mosses and scrub brush, but allow room for hearty, nutritious grasses to grow.

The researchers believe that as long as mammoths and other creatures existed in abundance, they were able to maintain grasslands, even in the face of climate change. Something other than temperature must have gone haywire.

Enter humans. Though armed only with spears, and in too few numbers to kill off mammoths entirely, they could have reduced the population enough to allow tundra plants to creep back into the ecosystem.

"First the animals died, then the pastures vanished," Nikita Zimov said.

There is evidence, too, of an asteroid or comet several miles wide impacting Earth 12,900 years ago, a fact the Russian team acknowledges. They argue that the changing climate, human hunting, and the asteroid all contributed to the mammoths' extinction.

"This whole business of man causing the demise of these animals is way overstated," Richard Firestone of Lawrence Berkeley National Laboratory in California said. "Man co-existed with these animals for 100,000 years before the Younger Dryas."

More on  Mammothsextinction