When Western sailors started landing on the Falkland Islands, off the curling tip of South America, they were greeted by a bizarrely tame dog-like creature. It roamed wild across the islands, but would frequently swim out to meet the approaching boats while wagging its tail. Although some called it a fox, it became more commonly known as the Falkland Islands wolf. Its scientific name: Dusicyon australis, the foolish dog of the south.

The name was apt. The wolf’s fearlessness made it extremely easy to kill. People lured it in with meat, and either clubbed or knifed it. By 1880, it was extinct, but not before a young, twenty-something naturalist called Charles Darwin managed to see one for himself in 1834.

Darwin saw the Falkland Islands wolf not as easy meat, but as a strange biological puzzle. What was such a large predator doing on this tiny set of islands, some 460 kilometres away from the South American mainland? Deepening the puzzle, South America is a land dominated by rodents, but none of them had made it to the Falklands. In fact, the wolf was the only mammal there. Where had it come from? And why had nothing else furry followed it?

Some said that early South Americans must have partly domesticated the wolf and brought it over on their boats—hence its unfortunate tameness. Others said that the wolf sauntered across prehistoric land bridges, or rafted over on chunks of ice. “It struck me as an outstanding mystery in natural history,” says Alan Cooper from the University of Adelaide. He was keen to solve it.

Cooper’s speciality is wresting samples of ancient DNA from fossils, and sequencing these millennia-old molecules to better understand their owners. So far, he and others have filled their genetic ark with Smilodon the sabre-toothed cat, American lion, cave lion and American cheetah. They have done the massive short-faced bear, giant jaguar, cave hyena and European bison. They looked at the dodo, New Zealand’s enormous moas, elephant birds, and giant ducks. “We were running out of good ones to do,” he laments. The wolf made the cut.

View Images Illustration of Falkland Islands wolf from Zoology of the Voyage of H.M.S. Beagle. By George R. Waterhouse

In 1996, Cooper travelled to London’s Natural History Museum to check out one of only six specimens of Falkland Islands wolf that were known at the time. Darwin collected the animal himself, and his handwriting graces the label (although it’s unclear whether he actually clubbed it over the head himself, as some stories claim).

Darwin was meticulous and the skull had been thoroughly cleaned—great for museums, bad for geneticists. Cooper needed organic material that still contained DNA. He suggested to Paula Jenkins, the museum’s curator of mammals, that he could pull out a tooth, cut off part of its root, and put it back in. “Her countenance was not one that suggested this was going to happen,” says Cooper, delicately.

But Darwin had missed a spot. As Cooper turned the skull around, he noticed a tiny sinus on its face—an opening, and one that clearly had something in it. He reached in with some tweezers and pulled out a little piece of nerve and blood vessel. It was just 3 millimetres long and 1 millimetre wide. But it was enough. It was raw tissue, loaded with DNA. “I thought: This is definitely going to work,” says Cooper.

His team have since collected DNA from five of the wolves, including a 7th moth-eaten, stuffed specimen that was gathering dust in an attic at New Zealand’s Otago Museum. “Everyone figured this was a fox that had been taxidermied badly,” says Cooper. His student took a bit of its toe, sequenced it, and confirmed that it was indeed a match for the other Falkland Island wolves.

When they finally analysed their sequences, the team concluded that the Falkland Islands wolf’s closest living relative is the maned wolf, a handsome stilt-legged dog found in South America.* The two species split apart around 6.7 million years ago. That’s useful to know, but it doesn’t tell us anything about the animal’s mysterious origins.

Cooper tried again. This time, he compared the Falkland Islands wolf’s DNA with that of a close relative that lived on the mainland—the similarly extinct Duscyon avus. The DNA revealed that the two species of “foolish dogs” diverged from their common ancestor just 16,300 years ago. That gives a pretty good indication of when the wolf reached the Falkland Islands and started evolving independently from its mainland cousins.

The date ruled out the possibility that humans brought the wolf over to the islands, but it suggested an alternative.

View Images During the last Ice Age, four shallow ice terraces (numbered I to IV) spanned the ocean between Argentina and the Falklands.

At the time, Earth had just come out of an ice age. Frozen sheets covered much of the world and sea levels were dramatically lower than they are now. The ocean floor between mainland Argentina and the Falkland Islands is incredibly flat, sloping by just 0.5 degrees for 600 kilometres. “If the sea level goes down, it goes down a hell of a long way,” says Cooper.

So, 16,000 years ago, huge underwater terraces extended off the coast of Argentina, like the shallow end of a swimming pool. Meanwhile, the Falklands were about four times bigger than they are now. The gap between them and the mainland was just 20 to 30 kilometres wide, and 10 to 30 metres deep. “I’d put money on the fact that it would have frozen over at some point,” says Cooper.

Such a crossing would have been easy for the wolf’s ancestors. Perhaps it behaved like modern Arctic foxes, taking advantage of the glut of seabirds, baby animals and washed-up carcasses on the frozen shoreline. “By tracing along and using these food supplies, it would have had a high chance of hitting the Falklands,” says Cooper.

But rodents would have found the same distance far more daunting. “If you were a small rodent and looked out on 20 to 30 kilometres of ice, that wouldn’t have been a great option,” says Cooper. The ice terraces acted as an ecological filter—a opportunity for a large predator to seize, but a forbidding no-go area for smaller animals.

Reference: Austin, Soubrier, Prevost, Prates, Trejo, Mena & Cooper. 2013. The origins of the enigmatic Falkland Islands wolf. Nature Communications http://dx.doi.org/10.1038/ncomms2570

* (The maned wolf isn’t really a wolf, and neither is the Falkland Islands one. Fox would be closer, but they’re not foxes either. They belong to an independent branch of the dog evolutionary tree, and one whose members are largely extinct.)