from The Century Dictionary.
- Having a horny excrescence on the end of the tail: as, the nail-tailed kangaroo, Macropus unguifer.
Sorry, no etymologies found.
Not that every Australian can tell you what a bettong or a tammar or even a nail-tailed wallaby is.
There are swamp wallabies, rock wallabies, brush wallabies, the nail-tailed wallaby with a naillike horny protuberance, of uncertain function, on its tail, and others.