KANGAROO, an Australian pouched mammal (marsupial) with the hind limbs enlarged for hopping and a long thick tail. The enlarged median lower incisors point forward and are used in snipping grass and other vegetation, which is cut up by the sharp cross-crests of the molar teeth. The kangaroo (a native Australian word) was described in 1773 by Captain Cook, who saw some in what is now north Queensland.
The kangaroos belong to the order Marsupialia, one of whose characters is the possession of a pouch in which the young remain for a considerable time after birth. They belong in the suborder Diprotodontia or that group of marsupials having the two median lower incisor teeth enlarged and inclined forward. The nearest living relatives of the kangaroos are the phalangers, which inhabit the same region. The kangaroos differ, however, from the phalan gers, which are slow-moving, arboreal forms, in that they are adapted to rapid progression on the ground by hopping on the enlarged hind limbs.
The largest living kangaroos have a head the size of that of a sheep and stand about 8f t. high. The largest extinct form had a head as large as that of a Shetland pony and stood I oft. or more. Hypsiprymnodon, the tiny musk kangaroo, has a head smaller than that of a rabbit. The foot is greatly elongated and very narrow. The first toe or hallux is wanting (except in Hypsiprym nodon) ; the second and third toes are exceedingly slender and joined throughout their length by skin. These syndactylous digits have no function in locomotion but are of use in scratching and cleaning the fur. The straight, long fourth digit forms the princi pal part of the foot and is provided with a heavy claw. The fifth digit also takes part in locomotion ; its metatarsal is closely appressed to that of the fourth digit but the toe diverges.
The tail is long, tapering and very heavy. It is used for bal ancing during rapid progression and when the animal moves slowly with its forefeet on the ground, the tail and forefoot together act as supports while the hind feet are moved forward.
In standing and sitting with body erect and forefeet off the ground, the tail acts as a prop.
Except in Hypsiprymnodon the stomach is usually sacculated. The mouth opening is small and partly hidden by the lips. The dark brown eyes are of moderate size. The rounded ears are rather large and capable of being turned back and forth. The fur is soft and somewhat woolly in most large forms. In some rat kangaroos the pelage consists of stiff hairs and soft under fur.
In all kangaroos the pouch is well developed, opens forward and contains the four teats. As a rule there is but one young born at a time. In the colder parts of Australia the young are usually born at the beginning of the cold season. For an account of the birth of the young kangaroo, see MARSUPIALIA.
Among living mammals no other group affords a more striking example of the principle of adaptive radiation that do the Macro podidae or kangaroo family. The living kangaroos form an almost unbroken series illustrating the structural stages in the evolution of its members from the small forest-living type to the giant of the plains, to the hare-like forms of thickets and the secondarily arboreal forms of the tropical forests.
On the damp floor of the tropical rain forest of north Queens land lives the musk kangaroo (Hypsiprymnodon moschatus). This form, the most primitive and generalized member of the Macro podidae, has a number of characters in common with the pha langers and stands near to the primitive diprotodonts from which both were derived. It also resembles the phalangers in its general arboreal heritage. From its peculiar characters Hypsiprymnodon is considered a distinct subfamily in which is included the some what larger Pleistocene Propleopus.
The bulky, heavy-jawed, short-headed and rather short-footed kangaroos of the Australian Pleistocene have been grouped to gether in the genus Sthenurus. All the short-footed kangaroos of the present time are forest-living animals; it is therefore assumed that the species of Sthenurus also lived largely in forests.