The world's largest living reptile, the saltwater crocodile is found in brackish and freshwater habitats extending east-west from East India to Fiji and north-south from southern China to northern Australia (see a map of the region).

(Related: "Eating Crocodile Helped Boost Early Human Brains?")

Despite being found on several islands across this range, different crocodile groups haven't evolved into completely unique species—the way Darwin's finches evolved on the Galápagos Islands.

That suggests the crocodiles are somehow island hopping, keeping the overall gene pool well mixed. But until now, no one was sure just how the crocs were traveling, as they're