National Geographic blogger Ed Yong has written a highly readable account of a paper in Nature about Darwin's dognot the great naturalist's pet, but a strange doglike animal found by the first visitors to the remote Falkland Islands, off southern Argentina. The Falklands wolf, Dusicyon australis, was slaughtered to extinction in the 1800s, but Charles Darwin collected a specimen during HMS Challenger's visit in 1834. Now DNA from museum specimens have shown that D. australis shared ancestors with a mainland South American cousin, the equally extinct D. avus, just 16,300 years ago. It walked to the Falklands during a time in the ice age when the sea was exceptionally low, making it a newly documented example of land-bridge dispersal.
Land bridges used to be the paleontologist's favorite thing, invoked to explain all kinds of connections between fossil species. Then we learned that the Earth doesn't work that way: the seafloor stays deep below the sea, never rising to create a nice highway from continent to continent. Real land bridges are rather rare, and they form only when sea level is drawn down far enough. The land now drowned by the Bering Strait is the most prominent one. It allowed humans to reach the Americas during the ice age. Now we know about another one that once connected the Falklands to the mainlandwell, almost. The Nature paper argues that the lowest 20 kilometers of the bridge was thick sea ice, suitable for the wolf to cross but not any other land mammal.
Background: The rise and fall of land bridges