Ancestors to modern North American black bears, wolverines and other animals walked here across a land bridge from Asia, an important new fossil find in the Canadian Arctic shows.
Their long journey more than five million years ago foreshadowed the eventual migration of humans from Asia to North America, says Richard Harington, a paleontologist with the Canadian Museum of Nature.
"A lot of these animals came across the Bering isthmus -- land where the Bering Strait is now -- about five million years ago." That is the same land bridge likely used by humans to arrive in North America at least 15,000 years ago.
The fossils were found in a peat deposit on Ellesmere Island, Nunavut, when a geologist noticed sticks poking out that looked as though they had been chewed by beavers. It was an ancient beaver pond, about the size of a Volkswagen Beetle, and about four million to five million years old.
Dr. Harington began peeling apart the layers of peat in 1992 to find out what was living there, and found an environment similar to a modern beaver pond -- except that many of its ancient inhabitants were distinctly Asian, including a tiny Asian badger never before found in North America, a three-toed horse about the size of a modern donkey, and small musk deer still common in parts of Asia. Similar mammals had previously been found together in northeastern China's Ushe Basin.
Most of the species were from Asia, yet North Americans would quickly recognize many, including a marten, a fisher and an early bear species.
Dr. Harington also found fossils from a wolverine similar to the modern North American animal, and probably its ancestor, he said.
He worked with Richard Tedford of the American Museum of Natural History in New York to identify the fossils. Dr. Tedford is an expert on ancient Asian carnivores. Their findings are in today's edition of Nature.
It is not clear if the Asian animals mixed with species already in the high Arctic at the time, or if new arrivals had the place to themselves. There is evidence of animals elsewhere in North America at the time, including rabbits, beavers and weasels.
Evidence also shows that species migration wasn't a one-way route. Animals from North America and Asia periodically travelled back and forth across the Bering Strait, which is relatively shallow and dries up during ice ages.
Dr. Harington has worked extensively in Yukon on fossils from giant ice-age mammals, like the mammoth or giant beaver, that died out about 10,000 years ago. Most -- about 75 per cent -- originated in Europe or Asia, he says.
But some animals, such as camels and horses, evolved in North America first and then travelled to Asia, he says.
Overall, he believes most North American species originated in Eurasia and came here across the land bridge from Asia. The animal remains found on Ellesmere Island add weight to that theory.
Dr. Harington says he isn't sure why so many animal bones were in one spot, although he also found evidence of a forest fire, and speculates animals may have come to the pond seeking a haven.
His finds fill a gap in the fossil record in the high Arctic. Researchers have found fossils from much earlier, including dinosaur bones, but nothing from four million to five million years ago.
At the time, Canada's North was far warmer than it is today. Plant fossils show larch, pine and spruce trees surrounded the pond, and birch and alder grew nearby. Today, the closest tree is 2,000 kilometres to the south.