Humans have been blamed for slaughtering woolly mammoths and other large ice-age animals into extinction, but new evidence from Yukon suggests this isn't the case.
Moose were to blame, at least in part, says Dale Guthrie, a researcher at the University of Alaska.
He has found evidence that the climate in Yukon and Alaska was warming between 13,000 and 10,000 years ago, around the time a wave of human hunters moved into North America from Asia.
The North was changing from a grassland to a boreal forest and tundra, he says. Moose also arrived, and were better adapted to digest the new, woodier plants that were taking over.
A close examination of the fossil record suggests moose and other browsers probably competed against the mammoths and other ice-age grazers for food, Guthrie says.
In a May edition of the British journal Nature, he makes the argument for a less bloody ending to the mystery of what happened to the mammoths, mastodons, camels, giant sloths, horses and beavers as big as black bears that once lived in North America.
They disappeared from the continent around the same time adept hunters known as the Clovis people moved in. Many scientists argue that the timing was not a coincidence.
The blitzkrieg theory, put forward in the 1960s, argued that people quickly destroyed the naive beasts unaccustomed to attacks from humans.
Guthrie says his evidence doesn't support the idea that animals died in a bloodbath. But it does back up a competing, although less popular, theory that says the warming climate led to their demise.
He examined more than 600 bones in Alaska and the Yukon territory, sifting through them to get several dozen from the period when the Clovis began populating North America.
He found that three animals bison, an elk-like creature called a wapiti and moose all increased their numbers during human colonization.
As people moved in from Asia, Guthrie's fossil finds show that moose moved with them. They were better at digesting the available food than mammoths and horses.
Horses, he says, were already decreasing in both size and number in the North before the Clovis people arrived.
The horses disappeared before the mammoths, which is a blow to the keystone theory of the extinctions.
It says that mammoths were a key species because they ripped out growing forests and kept the land more open for other grazers. Humans hunted them to extinction, which led to the demise of other herbivores. But if the horses died first, the theory doesn't stand, Guthrie says.
He also says that many large animals, including camels, giant beavers, ground sloths, mastodons, short-faced bears and saber-tooth cats all disappeared from the fossil record in the North before the Clovis people arrived.
His work suggests that humans are not to blame for the fact that North America has so few big animals compared with Africa. The North is where the encroaching humans first encountered the large beasts.
If they didn't kill them in Yukon and Alaska, he says, it doesn't makes sense that they exterminated the same animals as they slowly moved further south.
But others aren't so sure. Researchers have proposed that disease carried by humans may have jumped to their dogs, and then to wild animals.
Anthony Barnosky, a paleobiologist at the University of California in Berkeley, argues that both humans and the shifting climate were to blame.
Further south on the continent, the extinction of the large animals happened later, during a period when there is solid evidence humans were hunting them.
Distributed by Scripps Howard News Service.