The Bramble Cay Melomys (Melomys rubicola) has one of the most unusual and precarious distributions of all Australian mammals. The melomys is restricted to an unstable 4-5 hectare coral cay in the eastern Torres Strait, off the tip of northern Australia.

 

This little known rodent, related to rats and mice, is morphologically and genetically distinct from Australian and known New Guinean species.

It is nocturnal and shelters in burrows or under debris where there’s vegetation. It is likely vegetarian, as the melomys have frequently been observed feeding on the fleshy herbs found on the cay.

 

Just how the species became isolated on such a remote coral cay remains a mystery. Given its close relatedness to Australian melomys, it’s been suggested it is a result of stranding by rising sea levels as ice melted following the Last Glacial Maximum.

 

Alternately, it could have come from an unknown population somewhere in the Fly River region of southern New Guinea. Bramble Cay is located only 50km from the mouth of the river, and logs and debris are regularly flushed out and deposited on the shoreline of the cay. We don’t have many records of mammals from the Fly River, so it remains a distinct possibilitythat the Bramble Cay Melomys or a closely related species could be found there.