The New Guinean genus Dorcopsis is represented by many species, all living in tropical rain forest and none larger than a fox terrier. These are short-footed forms with rather short, partly naked tails, long heads and exceptionally long sectorial premolars. They are most closely allied to the tree-climbing kangaroos (Dendrolagus) of the rain forests of New Guinea and north-eastern Queensland. The tree kangaroos are about the same size as Dorcopsis but have shorter ears than any other kan garoos and longer, thinner tails and less disproportion between the fore and hind limbs, the toes of which are all provided with sharp, curved claws. The soles of the feet are broad and underlaid by a heavy pad of fat, modifications for climbing.
The pademelons (Thylogale) are stocky little animals resembling Dorcopsis except in their much shorter head. The sectorial teeth are also much smaller than in Dorcopsis and Dendrolagus and the third upper incisor tooth is grooved at the posterior edge. They range from New Britain, New Ireland, New Guinea and the Aru islands to eastern Australia, Tasmania and south-western Aus tralia in places where there is suitable forest.
The next group (Protemnodon), sometimes referred to as the large wallabies, contains numerous species, most of which are primarily grass-land forms but others transitional in habitat, feed ing at night in the open grass-lands and resting during the day in dense scrubs. They resemble the true kangaroos in their propor tions and many of the species are commonly called kangaroo rather than wallaby, the name by which most of the smaller forms are known. Protemnodon is characterized by a long, taper ing tail, moderately long feet, large ears, cheek and hip stripes, palatal vacuities and a groove on the external face of the third upper incisor that divides the tooth into anterior and posterior halves. Some fossil species are larger than any living kangaroos.
The typical kangaroos of the genus Macropus are all large forms with long, narrow hind feet. The best known are the great gray kangaroo of the grassy plains of the open Eucalyptus forests, the wallaroo, whose build is more robust and who prefers grass covered, stony ridges, while the red kangaroo inhabits the interior of the continent where most of the terrain is level and the vegeta tion sparse. The rock wallabies (Petrogale and Peradorcas), which are as specialized in foot structure as the large kangaroos, usually spend their days among the crevices of rocks on ridges and beside gullies, as a rule near water-courses. They feed on grass, much of which they obtain at night. The nail-tailed walla bies (Onychogale) are among the most beautiful of the kangaroos. These small, graceful creatures of the semi-arid country are highly specialized in tooth and foot structure and have a peculiar, horny growth on the end of the tail resembling a nail. Palorchestes, the
Pleistocene giant kangaroo, probably weighed as much as a small horse and to judge by its dentition also resembled a horse in feeding habits.
Branching off in another direction from a primitive type some what similar to Hypsiprymnodon there developed several genera of small size popularly known as rat-kangaroos. The most primitive of these is the potoroo (Potorous), about the size of Hypsiprymnodon. It has, however, lost its great toe or hallux. Apart from Hypsiprymnodon it is the only member of the family with the primitive plantar pads. The three more specialized genera (Caloprymnus, Bettongia and Aepyprymnus) inhabit more open country but still may be called thicket-living. The banded wal laby (Lagostrophus) and the hare wallaby (Lagorchestes) avail themselves of much the same sort of habitat as do the kangaroos.
They hop about on the open plains and take refuge among bushes.
Thus the family Macropodidae may be divided into four sub families, the first and most generalized being the Hypsiprymno dontinae, including the genera Hypsiprymnodon and Propleopus; the second, the Potoroinae, including Potorous, Bettongia, Calo prymnus and Aepyprymnus; the third, by far the largest, the Macropodinae, including Dorcopsis, Dendrolagus, Thylogale, Petrogale, Peradorcas, Protemnodon, Macropus and Onychogale; the fourth, Sthenurinae, comprising Sthenurus and Palorchestes.
All the evidence indicates that the ancestors of the kangaroos were forest animals with an arboreal heritage. The members of the family now show various stages of specialization for terres trial bipedal locomotion and for a vegetable diet. There is also a definite correlation between the foot and tooth structure of the animals and the type of habitat they occupy. The first two sub families feed principally on berries, roots, and fallen fruits in the forest or thickets and all have low-cusped molar teeth. The mem bers of the third sub-family either browse on leaves of vines and saplings in the forest, in which case they have crested, short crowned molars, or graze in the open grass-lands, in which case they have crested, long-crowned molar teeth ; the crested molars being better adapted to grinding than the low-cusped type. The more specialized members of the Potorinae inhabit thickets in more open country and correlated with this is an elongation of the hind feet ; thus these forms are exceedingly swift.
As recently revised the family of kangaroos comprises 21 genera, in which are included 158 species and subspecies; of these, five genera and 29 species are known only as Pleistocene fossils.
BumoGRApiay.—Writings of Oldfield Thomas, especially the Cata logue Marsupialia and Monotremata in the British Museum (1888); R. Owen, Fossil Mammals of Australia (1877) ; H. C. Raven, American Museum Novitiates (1928). (H. C. R.)