The musky rat-kangaroo feels so at home in its tropical rainforest environment that it hasn't left it -- for some 20 million years.
New fossils of the animal, extremely rare finds for this kind of tiny marsupial, indicated to researchers from The University of Queensland and The University of New South Wales that multiple species of musky rat-kangaroo once existed, though today there is only one.
But the creature never diversified into other, more temperate, environments, and the scientists warn that its stationary ways put it at risk, if its home is not protected.
Largely unchanged over tens of millions of years, and considered for that reason a kind of "living fossil," the musky rat-kangaroo makes its living on the rainforest floor in Northern Queensland, Australia.
Not only is it the world's smallest kangaroo, but it also displays some curiously non-kangaroo features, such as a prehensile tail and a fifth, opposable, digit on its hind feet. It carries more than one youngin' in its pouch and even moves more like a shuffling bunny than an ordinary kangaroo.
And did we mention small? Let's do it again, with some numbers. They're only about 6-8 inches long (tack on another 5-6 inches for the tail) -- not what you usually think of, when you imagine a big kangaroo (such as this pugislistic hopper, which made headlines last year when it decided to beat up an Australian politician).
The little kangaroo is "too specialized to be relocated elsewhere," said Dr. Kenny Travouillon, from The University of Queensland's School of Earth Sciences, noting that it and possibly other species "will have nowhere else to go" if the rainforest in which it has enjoyed living for millions of years is not closely watched.