Overview
The Northern Nail-tail Wallaby (Onychogalea unguifera), known historically as the Karrabul, is a slender, elegant macropod native to the tropical savannas of northern Australia. Famous for possessing a mysterious, fingernail-like horny spur embedded in the tufted black tip of its exceptionally long tail, it is also celebrated for its unique running style, in which it windmills its forearms while bounding away.
Biology and Physical Characteristics
The Northern Nail-tail Wallaby has a sandy-fawn to yellowish-buff coat with a pure white belly, a distinct dark brown dorsal stripe along the back, and white hip stripes. Its tail is longer than its body, terminating in a thick black brush of hair that conceals a sharp, flattened, black fingernail-like horny spur (unguis) measuring 3 to 6 mm in length.
Behavior and Ecology
Primarily nocturnal and solitary, the Karrabul shelters by day in shallow depressions scratched out beneath low shrub canopies or tall spinifex clumps. When flushed, it flees with tremendous speed, holding its arms extended and rotating them in a curious windmill-like circular motion while keeping its head low and tail arched, a locomotion style that earned the genus the nickname ‘organ grinders’.
Conservation and Human Impact
Classified as Least Concern by the IUCN, the Northern Nail-tail Wallaby is the most secure member of its genus, having avoided the catastrophic declines suffered by its southern relatives (the bridled and crescent nail-tail wallabies). Nonetheless, it faces threats from altered fire regimes that burn off dry-season grass cover and predation by feral cats and dingoes.
Interesting Factoid
The Northern Nail-tail Wallaby has a bizarre secret hidden in its tail: buried inside the fluffy black fur at the very tip is a hard, pointed black ‘fingernail’ whose biological purpose remains an evolutionary mystery to scientists.