Page:Mammals of Australia (Gould), introduction.djvu/22

by the D. ursinus, are now extinct on the Australian continent; but one species of each still exists on the adjacent island of Tasmania; the rest were extinct Wombats, Phalangers, Potoroos, and Kangaroos-—some of the latter (Macropus Atlas, M. Titan) being of great stature. A single tooth, in the same collection of fossils, gave the first indication of the former existence of a type of the Marsupial group, which represented the Pachyderms of the larger continents, and which seems now to have disappeared from the face of the Australian earth,—of the great quadruped, so indicated under the name of Diprotodon in 1838; and successive subsequent acquisitions have established the true marsupial character and the near affinities of the genus to the Kangaroo (Macropus), but with an osculant relationship with the herbivorous Wombat. The entire skull of the Diprotodon, lately acquired by the British Museum, shows in situ the tooth on which the genus was founded. This skull measures 3 feet in length, and exemplifies by its size the huge dimensions of the primeval Kangaroo. Like the contemporary gigantic Sloth in South America, the Diprotodon of Australia, while retaining the dental formula of its living homologue, shows great and remarkable modifications of its limbs. The hind pair were much shortened and strengthened compared with those of the Kangaroo; the fore pair were lengthened, as well as strengthened. Yet, as in the case of the Megatherium, the ulna and radius were maintained free, and so articulated as to give the fore paw the rotatory actions. These, in Diprotodon, would be needed, as in the herbivorous Kangaroo, by the economy of the marsupial pouch. The dental formula of Diprotodon was the same as in Macropus major: the first of the grinding series was soon shed, but the other four two-ridged teeth were longer retained; and the front upper incisor was very large and scalpriform, as in the Wombat. The zygomatic arch sent down a process for augmenting the origin of the masseter muscle, as in the Kangaroo. The foregoing skull, with parts of the skeleton of the Diprotodon australis, were discovered in a lacustrine deposit, probably