September 4, 2008

Ice Age Wooly Mammoths Migrated To Siberia

In the largest DNA study of the ancient wooly mammoths, Canadian scientists have discovered that the last Siberian wooly mammoths may actually have originated in North America.

The study also raises questions about the role climate change may have played in the mammals' demise.  They believe the mammoths likely survived through the period when the ice sheets were at their largest, even as other Ice Age mammals were wiped out.

The woolly mammoth, also known as Mammuthus primigenius, inhabited mainland Eurasia and North America during the Ice Age, until about 10,000 years ago.   It was previously believed that the last mammoths in Siberia were actually from North America, although more evidence was needed to support the theory.

Researchers led by Professor Hendrik Poinar from McMaster University in Canada collected 160 mammoth samples from across Holarctica, a region including present-day Asia, North America and Europe.

The team obtained well-preserved material between 4,000 and 40,000 years old, with DNA samples of "almost every part of the animal - even from preserved hind, skin and hair", Professor Poinar told BBC News.

The team then analyzed DNA from mitochondria, genetic material passed from mother to offspring, which can identify the ancestry of a species for many hundreds of generations.  This genetic information proved that a North American mammoth population had replaced those endemic to Asia, although the scientists said it was difficult to speculate why the North American mammoths had returned to Siberia.

"Presumably, conditions were favorable on the Bering land bridge which was more of a large filter than an open highway," Professor Poinar said, adding that the expansion of North American forests may have "pushed the mammoths along".

The Bering land bridge was a large tundra plain that connected North America and Asia, possibly enabling the migration of humans from Asia to the Americas.  At its largest, it extended about 1,000 miles from north to south, and was alternately exposed and submerged as global sea levels changed during the Plestocene era.   The land bridge was flooded and eventually became the Bering Strait about 11,000 years ago.

The native Siberian mammoths had different molar features and a "very unique DNA signature" dated to be nearly 900,000 years old.  They may have been around for much of the Middle Pleistocene, scientists said, but completely disappeared around the same time the North American forests expanded.  It is not clear if the Siberian mammoths experienced a "natural decline" or if the North American mammoths simply out-competed them.

It is possible that the endemic Siberian may not have been a true woolly mammoth, but rather a more primitive species. 

"Many people thought that this (primitive) species had become extinct way before 38,000 years ago," said Professor Poinar.

"Paleontologists were not so happy because these are the intricacies of DNA that are very difficult to discern based on mammoth tusks and teeth," he said.

Scientists are only now beginning to understand the dynamic evolutionary story of these iconic Ice Age mammals.

"This study adds to a growing body of evidence about just how dramatic and tumultuous the Pleistocene climate actually was," Dr Beth Shapiro, Penn State University scientist, told BBC News.

"With ancient DNA, we can actually go back in time and look directly at these old populations.

"Here we have evidence of local extinctions, replacements and long-distance dispersals," she said.

Their research was published in the journal Current Biology.

Image Courtesy Wikipedia


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