New evidence suggests that changes in the North American ecosystem didn't kill the mammoth - their demise may have brought the changes about.
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SYDNEY: The extinction of mammoths in North America at the end of the last ice age was not caused by a change in the ecosystem: it's what triggered the changes, a new study suggests.
The study also elucidates a possible cause for the demise of mammoths and mastodons 15,000 years ago, and researchers say that the expanded incidence of fire in the landscape - suspected of being caused by human arrival - only appeared after the extinction.
Unmasking the last ice age
"For the first time, we have a very close linkage between this major ecological event and some evidence about the consequences of this extinction," said John Williams, a professor at the University of Wisconsin in Madison and the senior author of the study published in the U.S. journal, Science.
The researchers used fossils, pollen, charcoal and dung fungus spores, along with radiocarbon dates, to build a more accurate picture of the sequence of events at the end of the last ice age.
They found a decline of Sporormiella dung fungal spores, began around 14,800 years ago, leading to its virtual disappearence 13,700 years ago, said Jacquelyn Gill, study leader and a graduate student in Williams' lab.
Previous hypotheses
The data discounts previous hypotheses for the cause of extinction of 50% of all mammal species above 32 kg and all species above 1,000 kg in North America.
It shows that the megafaunal decline, including mammoths and mastodons, took about 1,000 years. The decline also preceded major habitat change, increased incidence of fire in the landscape, and a presumed comet or asteroid impact estimated to have occurred around 12,900 years ago.
On the other hand, the study does "not fully resolve the human versus climate debate," said Williams.
Some researchers argue that the arrival of prehistoric humans on the American continent and their voracious hunting of game, along with their widespread use of fire, helped bring about the decline of mammals in the region. Known as the Clovis people, they are thought to have arrived 13,500 to 13,000 years ago.
