Remember when Darwin visited the Falkland Islands, and he noted a "wolf-like fox" as the only large native quadruped? It was about the size of a coyote, peculiar to the island, and apparently very tame, to the point of going into gauchos' tents at night to steal meat. Darwin thought that the tameness indicated that they had been brought over as pets when humans travelled to the island, and before leaving, predicted (correctly) its imminent extinction because it was so easy to kill (and then facilitated the process, of course, by taking samples). Recently, researchers at UCLA have looked at mitochondrial DNA from these samples and other samples, and determined that it was indeed a separate species, its closest relatives being South American canids. But it wasn't brought over by people, because the 5 samples they looked at had a common ancestor (one that was already speciated into their current form) 70,000 years ago, and people didn't even arrive in the New World until 13,000 years ago. Furthermore, the South American canids that it shares an ancestor with (the "toaster-like" bush dog and the maned wolf) separated off about 6 million years ago-- which is before dogs even show up in South America (2.5 mya). So apparently the ancestors of all three species (and some other ones, incluing a Patagonian canid) evolved in North America and then migrated south. Somewhat annoyingly, though, no fossils that look like the Falklands fox-wolf lineage have been found in North America.
As to how it got to the Islands: since the Falkland Islands were never connected with South America, the researchers think it must have floated over from the mainland on an iceberg, surviving the journey and subsequent stay on seals, penguins, seabirds, etc.
Apparently Darwin's notebooks associate the wolves with some of his first thoughts on evolution, since he mentions them in conjunction with the Galapagos finches and his idea that species change over time.