The crescent nail-tail wallaby, also known as the worong (Onychogalea lunata), was a small species of marsupial that grazed on grasses in the scrub and woodlands of southwestern and central Australia.

The species was extremely timid and would flee to a hollow log if disturbed at their daytime resting places, a small patch of sand cleared near a large shrub or tree.

The first description and specimens of the animal were presented by John Gould to the Linnean Society of London in 1840 and published in its Proceedings in 1841, assigning the new species to the genus Macropus and the epithet derived from the Latin lunatus, meaning "of the moon", for its crescent-shaped marks.

[3] When Gould completed his second volume of Mammals of Australia (1849) he provided a lithograph depicting a male and female by Henry C. Richter and named the species as Onychogalea lunata, allying it to a genus established by George Waterhouse.

[4] The systematic revision of Australian mammals by Oldfield Thomas in 1888 recognised Gould's description as one of three species of the genus, and re-examined specimens from western and southern Australia that were held at the British Museum.

A local term by settlers, kangaroo rabbit, was recorded by Gilbert, explained as the resemblance of the animal's soft fur and long ears to the exotic species.

[8] Variants on the name throughout the southwest of Australia, recorded by Gilbert and most subsequent historical sources from Nyungar informants, was regularised for common usage with the spelling "worong" or "wurrung" and syllabic pronunciation "wo'rong".

[11] The species was hunted for food by the English settlers of southwest Australia, who described the flesh as white, resembling chicken and having a flavour similar to rabbit.

John Gilbert's report to Gould in the early 1840s was quoted in his Mammals of Australia,[2] "[t]he Waurong is found in the gum forests [eucalypt woodlands] of the interior of Western Australia, where there are patches of thick scrub and dense thickets, in the open glades intervening between which it is occasionally seen sunning itself, but at the slightest alarm immediately betakes itself to the shelter of the thick scrub; the dogs sometimes succeed in driving it out to the open spots, when, like the Kangaroo rats, it runs to the nearest hollow log, and is then easily captured.

[6] The behaviour was well known to the Aboriginal peoples of the central deserts, where the species persisted after their disappearance from the semi-arid regions, and were able to provide information some forty years since their last sighting in the mid twentieth century.

[2] A South African curator and collector employed by the British Museum, Shortridge conducted what was the only major field survey of mammalian fauna in that period, and noted the absence of previously reported mammal species from the southern and western coastal regions.

[13][2] Shortridge's second field report on 18 specimens from "Woyaline, east of Pinjelly", published by Oldfield Thomas in 1907, was to be amongst the last descriptions of the declining population: "More local than Macropus eugenei and seeming to prefer lower and more scrubby thickets than that animal.

[15] A specimen was collected at the Everard Ranges by Richard Helms, one of the few mammals returned by an expedition passing through central regions of Australia at a similar time to Leake's report.

[16] Localised extinctions appear to have preceded the arrival of cats and foxes to some regions, often regarded as major threatening factors in the collapse of mammalian fauna in Australia.

[17] A news report of this and other small mammal species sudden disappearance at a road connecting Esperance and the Fraser Range, constructed in 1875, is consistent with modeling of the primary factor in the populations demise as disease.

The epizootic theory includes secondary and tertiary causes for the extinction of the worong, the clearing for pastoralism that has also been proposed as the primary factor, and the remnants of the population being finally extirpated by hunting.

[2] The species appears in palaeontological records dated to the Pleistocene and Holocene, found in local fauna of fossil sites from New South Wales to Western Australia.