In 1690 John Strong, the captain of the H.M.S. Welfare, discovered two uninhabited islands some 460 kilometers off of Argentina’s coast. These islands were home to many species of birds and marine mammals, some found nowhere else on earth. Yet it could claim no native tree, reptile, or amphibian species. Only one organism was native to the islands-- a terrestrial mammal, a furry wolf-like creature. He named the place Falkland Islands. (Discover more about the Falkland Islands and it's history at the Falkland Islands Museum & National Trust.)
Visitors after that were sometimes intrigued, sometimes terrified of the four to five foot long canid (a mammal family including dogs, wolves, foxes, and coyotes) that had no fear of humans and would run out to meet boats as they came in. Their pelts were valued for their rich fur and coloring; red with dark rings around their tails and white tips. Settlers on the island feared their attacks on herds of sheep and began to poison them. The animals were reported to be so fearless that they could be killed by luring them with a chunk of meat in one hand and stabbing them with a knife held in the other.
When Darwin visited the islands on the H.M.S. Beagle over 100 years later he found the mysterious fox-wolf population already on the verge of extinction. The species died out not long after due to humans hunting it. (Read Darwin's account of his encounter with the Falkland Islands wolves in his Voyages of the Adventure and Beagle.) However, Darwin still had time to puzzle out a mystery that would continue to plague biologists for hundreds of years: how did such a large mammal get to an island so far out to sea? Even more perplexing: how did it become the only one that did?
460 kilometers is a long way for a land animal to swim or even to float on debris blown from land during a storm. It is not impossible that early seafaring human beings could have brought some Falkland Islands wolves to the islands on boats and left them there. However, if these canids were able to swim, float, or be carried to the islands then why were no rats, rabbits, or other mammals on the islands?
The mysterious and now extinct canid was dubbed Dusicyon australis. The next item on the agenda was to determine which species were closest to the Falkands Islands wolf. If its closet relative was known, it would be a good hint as to how long Dusicyon australis had been living on the Falkland Islands and how it got there.
An illustration of Dusicyon australis from Darwin's The Zoology of the H.M.S. Beagle.
Jeremy J. Austin and Julien Soubrier, both from the Australian Centre for Ancient DNA at the University of Adelaide, and their associates, have done just that. In their study published this month in the journal Nature Communications, the DNA found in fossilized teeth of another mainland dwelling canid, Dusicyon avus, was compared with that of Dusicyon australis, collected from a skull retrieved by Darwin and kept in a museum.
Not only were Austin and Soubrier able to tell that D. avus was the closest relative of D. australis, they also learned that the two diverged around 16,000 years ago. This was exactly the clue they needed. Around the same time, the Southern Hemisphere was experiencing the Last Glacial Maximum--a period of teim about 25-18,000 years ago when the sea levels were at record lows.
A knowledge of geology provided the last piece of the puzzle. A narrow strait had been found under the ocean off the coast of Argentina; evidence that shallower water existed between the islands and the mainland that probably froze solid for short periods during the periods of lowered sea levels. Dusicyon australis probably followed their prey--seals and penguins--across the narrow ice bridge during one of these times and found itself on the Falkland Islands. Smaller or herbivorous mammals such as rats and rabbits would not have been able to make the journey.
Sadly, Dusicyon australis probably only ate penguins, seals, and other bits of seaside food and was mostly likely no danger at all to the herds of sheep it was poisoned to protect.
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