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Wednesday, May 22, 2013

The Mystery of the Falkland's Island Wolf


IT IS not often that we can pinpoint the exact spot where a species went extinct, but Shallow Bay on the remote north coast of West Falkland is such a place. There, in 1876, a very peculiar animal – the last of its kind – was mercilessly slain. Chances are it was quick. The creatures were known to be unafraid and easy to kill. And so, as Charles Darwin himself had predicted, the Falkland Islands wolf went the way of the dodo.
It hadn't taken long. Half a century earlier, the islands were largely uninhabited and the wolf was abundant. Then people began to arrive – shepherds from Scotland and gauchos from Argentina. They did not take kindly to having a voracious predator in their midst. When fur trappers arrived from America, it was only a matter of time.
In 1914, taxonomist Oldfield Thomas of the Natural History Museum in London dealt the wolf a final, posthumous insult by naming it Dusicyon australis: foolish dog of the south.
And that might have been that, except for the fact that the wolf presented a biological mystery par excellence. The Falklands are 500 kilometres off the coast of Patagonia and the wolf was their only native land mammal. How did it get there? Even Darwin was baffled. ...

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Until a few thousand years ago, South America was home to a much more diverse group of canids than it is today. Among the now-extinct species was a fox-like animal called Dusicyon avus, which died out just 1600 years ago. Perhaps, Cooper thought, this was the missing link between the Falklands wolf and its closest living relative. He went in search of specimens, eventually tracking down six in museums in Argentina and Chile.
"We got DNA and found that it was incredibly closely related to the Falkland Islands wolf," he says. That explains the wolf's origins, Cooper suggests: it split away from Dusicyon avus about 16,000 years ago (Nature Communications, doi.org/mcb).
It was no coincidence, says Cooper, that the wolf diverged from its mainland cousin then. This was when the last ice age was at its peak and sea levels were very low; the South American coastline extended much farther out than it does today.
"There's a series of terraces off the coast of Argentina that mark where the shoreline sat for some time," Cooper says. The one indicating the coastline at the glacial maximum is 150 metres underwater and stretches almost to the Falklands (see map).
When at its narrowest, the strait between the mainland and the islands was roughly 20 kilometres wide and 10 to 30 metres deep, says Cooper – so shallow that it almost certainly froze over from time to time. It seems the wolves' ancestors could simply have walked across the ice.
This could also explain why no other land mammals made it. The ice bridge was a kind of ecological filter that large terrestrial carnivores were able to cross, but excluded omnivores and herbivores. "Twenty kilometres of ice is not a great place to be for a rodent," says Cooper.

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