Washington, Jan 3: A new research has suggested that the mammoths went extinct not because of climate change or overhunting by early humans, but a "perfect storm" of conditions.

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 long argued that climate change, an asteroid impact, or even the rise of the humans, armed with spears, may have played an important factor in their extinction.

Now, according to a report in Discovery News, Sergey Zimov of the Russian Academy of Science and a team of researchers have proposed that mammoths lived in an ecosystem as rich in life as today''s African savannah, and that all three extinction factors must have 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, of the Russian Academy of Sciences. "They lived in many different temperatures and levels of precipitation," he added.

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 have 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.

So, something other than temperature must have gone haywire.

According to the researchers, that something might be the entry of humans, who armed only with spears, and in too few numbers to kill off mammoths entirely, could have reduced the population enough to allow tundra plants to creep back into the ecosystem.

"First the animals died, then the pastures vanished," 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. (ANI)