Gilbert's potoroo ("Potorous gilbertii") is an Australian marsupial, sometimes called a rat-kangaroo. It has a pointed face and it is about the size of a rabbit. Once thought to be extinct, it is listed as being critically endangered.It is the most endangered mammal and marsupial in the whole of Australia. There are only about 40 of the animals now left in the world. Gilbert's potoroo is one of the world's rarest mammals.