Saltwater Crocodile

Satellite tracking upended the assumption that these are river animals with an unusual tolerance for salt. They are genuinely ocean-going, and they travel efficiently: rather than swimming against a current, a tagged crocodile will hold position in a tidal eddy for hours and then move only when the flow turns in its favour. That behaviour explains a distribution spanning from eastern India to Vanuatu without any need for a land bridge.

Australia hunted the species to an estimated few thousand animals before protecting it in 1971. The Northern Territory population has since recovered to around a hundred thousand, sustained partly by a regulated egg-harvest and ranching industry that gives landholders a financial reason to keep wetlands intact. It is one of the few large-predator recoveries substantial enough to have created a management problem rather than a conservation one.