An equally brief notice must suffice of the kangaroo tribe or Macropodidae, since these receive a special notice elsewhere. The dentition is i. 3⁄1 c. (0 or 1) / 0 p. 3⁄3 m. 3⁄3; the incisors being sharp and cutting, and those of the lower jaw frequently having a scissor-like action against one another. The broad molars are either bluntly tuberculated or transversely ridged; the outer side of the hind part of the lower jaw has a deep pocket; and the hind-limbs are generally very long, with the structure of the foot similar to that of the bandicoots. The family is connected with the Phalangeridae by means of the musk-kangaroo (Hypsiprymnodon moschatus); forming the sub-family Hypsiprymnodontinae. Then come the rat-kangaroos, or kangaroo-rats, constituting the sub-family Potoroinae; while the tree-kangaroos (Dendrolagus), rock-wallabies (Petrogale), and wallabies and kangaroos (Macropus) form the Macropodinae (see [Kangaroo]).

Extinct Marsupials

Reference has been made to the Australasian Pleistocene genera Phascolonus, Diprotodon, Nototherium and Thylacoleo, whose affinities are with the wombats and phalangers. The same deposits have also yielded remains of extinct types of kangaroo, some of gigantic size, constituting the genera Sthenurus, Procoptodon and Palorchestes. Numerous types more or less nearly allied to the phalangers, such as Burramys and Triclis have also been described, as well as a flying form, Polaeopetaurus. It is also interesting to note that fossil remains indicate the former occurrence of thylacines and Tasmanian devils on the Australian mainland. Of more interest is the imperfectly known Wynyardia, from older Tertiary beds in Tasmania, which apparently presents points of affinity both to phalangers and dasyures. From the Oligocene deposits of France and southern England have been obtained numerous remains of opossums referable to the American family Didelphyidae. These ancient opossums have been separated generically from Didelphys (in its widest sense) on account of certain differences in the relative sizes of the lower premolars, but as nearly the whole of the species have been formed on lower jaws, of which some hundreds have been found, it is impossible to judge how far these differences are correlated with other dental or osteological characters. In the opinion of Dr H. Filhol, the fossils themselves represent two genera, Peratherium, containing the greater part of the species, about twenty in number, and Amphiperatherium, with three species only. All are comparatively small animals, few of them exceeding the size of a rat.

Besides these interesting European fossils, a certain number of didelphian bones have been found in the caves of Brazil, but these are either closely allied to or identical with the species now living in the same region.

From Owen.
Fig. 13.—Lower Jaw of Triconodon mordax (nat. size).

The occurrence in the Santa Cruz beds of Patagonia of fossil marsupials allied to the living Caenolestes has been mentioned above. The alleged occurrence in the same beds of marsupials allied to the thylacine is based on remains now more generally regarded as referable to the creodont carnivores (see [Creodonta]).

Mesozoic Mammals.—Under the heading of [Multituberculata] will be found a brief account of certain extinct mammals from the Mesozoic formations of Europe and North America which have been regarded as more or less nearly related to the monotremes. The same deposits have yielded remains of small mammals whose dentition approximates more nearly to that of either polyprotodont marsupials or insectivores; and these may be conveniently noticed here without prejudice to their true affinities. Before proceeding further it may be mentioned that the remains of many of these mammals are very scarce, even in formations apparently in every way suitable to the preservation of such fossils, and it hence seems probable that these creatures are stragglers from a country where primitive small mammals were abundant. Not improbably this country was either “Gondwana-land,” connecting Mesozoic India with Africa, or perhaps Africa itself. At any rate, there seems little doubt that it was the region where creodonts and other primitive mammals were first differentiated from their reptilian ancestors.

From Owen.
Fig. 14.—Lower Jaw and Teeth of Phascolotherium bucklandi (nat. size in outline).
From Owen.
Fig. 15.—Spalacotherium tricuspidens (twice nat. size), Purbeck beds.

Of the Old World forms, the family Triconodontidae is typified by the genus Triconodon, from the English Purbeck, in which the cheek-teeth carry three cutting cusps arranged longitudinally. There seems to have been a replacement of some of these teeth; and it has been suggested that this was of the marsupial type. To the same family are referred Phascolotherium (fig. 14), of the Lower Jurassic Stonesfield slate of England, and Spalacotherium (fig. 15), of the Dorsetshire Purbeck; the latter having the three cusps of the cheek-teeth rotated so as to assume a tritubercular type. Other genera are Menacodon and Priacodon, the former American, and the latter common to Europe and North America. By one authority Amphilestes (fig. 16), of the Stonesfield Slate, is included in the same group, while by a second it is regarded as representing a family by itself. Amphitherium, of the Stonesfield Slate, typifies the family Amphitheriidae, which includes the American Dryolestes, and in which some would class the European Purbeck genus Amblotherium, although Professor H. F. Osborn has made the last the type of a distinct family. Yet another family, according to the palaeontologist last named, is typified by the genus Stylacodon, of the English Purbeck. To mention the other forms which have received names will be unnecessary on this occasion.