In some cases (as in rat-kangaroos) this tooth retains its place and function until the animal has nearly, if not quite, 1 The presence or absence of the corpus callosum has been much disputed; the latest researches, however, indicate its absence.
They were then arboreal; but they speedily entered upon a rapid, although short-lived, course of evolution, during which leaping terrestrial forms like the kangaroos were developed.
- The third and last sub-order of marsupials is the Diprotodontia, which is exclusively Australasian and includes the wombats, koala, cuscuses, kangaroos and their relatives.
In the lower jaw there are also one or two small and early deciduous premolars; third premolars of both jaws formed on the same type as that of the rat-kangaroos, but relatively much larger; molars rudimentary, tubercular.
By means of the little musk-kangaroo, the cuscuses and phalangers, constituting the family Phalangeridae, are so closely connected with the kangaroos, or Macropodidae, that in the opinion of some naturalists they ought all to be included in a single family, with three sub-families.
Then come the rat-kangaroos, or kangaroo-rats, constituting the sub-family Potoroinae; while the tree-kangaroos (Dendrolagus), rock-wallabie's (Petrogale), and wallabies and kangaroos (Macropus) form the Macropodinae (see Kangaroo).
The opossums of America are marsupials, though not showing anomalies as great as kangaroos and bandicoots (in their feet), and Myrmecobius (in the number of teeth).
Australia is inhabited by at least if o different species of marsupials, which is about two-thirds of the known species; these have been arranged in five tribes, according to the food they eat, viz., the grass-eaters (kangaroos), the root-eaters (wombats), the insect-eaters (bandicoots), the flesh-eaters (native cats and rats), and the fruit-eaters (phalangers).
Of the larger kangaroos, which attain a weight of 200 lb and more, eight species are named, only one of which is found in Western Australia.
Fossil bones of extinct kangaroo species are met with; these kangaroos must have been of enormous size, twice or thrice that of any species now living.
There are some twenty smaller species in Australia and Tasmania, besides the rock wallabies and the hare kangaroos; these last are wonderfully swift, making clear jumps 8 or io ft.
The Arunta hold that the spirits of kangaroos are expelled by human blood from certain rocks.
Their hinder limbs are shorter than in the true kangaroos, and their fore limbs are longer and more robust, and have very strong curved and pointed claws.
Huxley in 1880 briefly suggested the arboreal origin, or primordial treehabitat of all the marsupials, a suggestion abundantly confirmed by the detailed studies of Dollo and of Bensley, according to which we may imagine the marsupials to have passed through (r) a former terrestrial phase, followed by (2) a primary arboreal phase - illustrated in the tree phalangers - followed by (3) a secondary terrestrial phase - illustrated in the kangaroos and wallabies - followed by (4) a secondary arboreal phase - illustrated in the tree kangaroos.
It may also be noticed that in mammals and birds which hop on two legs, such as jerboas, kangaroos, thrushes and finches, the proportionate length of the thigh-bone or femur to the tibia and foot (metatarsus and toes) is constant, being 2 to 5; in animals, on the other hand, such as hares, horses and frogs, which use all four feet, the corresponding lengths are 4 to 7.
There seems to be no doubt that fossilized remains of the dingo occur intermingled with those of the extinct Australian mammals, such as giant kangaroos, giant wombats and the still more gigantic Diprotodon.
Although intimately connected with the cuscuses and phalangers by means of the musk-kangaroo, the kangaroos and wallabies, together with the rat-kangaroos, are easily distinguishable from other diprotodont marsupials by their general conformation, and by peculiarities in the structure of their limbs, teeth and other organs.
The dentition of the kangaroos, functionally considered, thus consists of sharp-edged incisors, most developed near the median line of the mouth, for the purpose of cropping herbage, and ridged or tuberculated molars for crushing.
Kangaroos are vegetable-feeders, browsing on grass and various kinds of herbage, but the smaller species also eat FIG.
The larger wallabies, or brush-kangaroos, such as the red-necked wallaby (M.
In the tree-kangaroos, which include the Papuan Dendrolagus inustus, D.
These kangaroos are largely arboreal in their habits, but they descend to the ground to feed.
In the rat-kangaroos, or kangaroo-rats, as they are called in Australia, constituting the sub-family Potoroinae, the first upper incisor is narrow, curved, and much exceeds the others in length; the upper canines are persistent, flattened, blunt and slightly curved, and the first two premolars of both jaws have large, simple, compressed crowns, with a nearly straight or slightly concave free cutting-edge, and both outer and inner surfaces usually marked by a series of parallel, vertical grooves and ridges.