Australia in like manner yields evidence of an analogous correspondence between its last extinct and its present aboriginal mammalian fauna, which is the more interesting on account of the very peculiar organization of most of the native quadrupeds of that division of the globe. That the Marsupialia form one great natural group, is now gene rally admitted by zoologists ; the represen tatives in that group of many of the orders of the more extensive placental sub-class of the Mammalia of the larger continents have also been recognized in the existing genera and species : the dasyures, for ex ample, play the parts of the Carnivora, the bandicoots (Perameles) of the Insectivora, the phalangers of the Quadrumana, the wombat of the Rodentia, and the kangaroos, in a remoter degree, that of the Ruminantia. The first collection of mammalian fossils from the ossiferous caves of Australia § brought to light the former existence on that continent of larger species of the same peculiar marsupial genera : some, as the Thylacine, and the dasyurine sub-genus represented 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, poto roos, and kangaroos—some of the latter (Macropus Atlas, H. 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 Diprotodon in 1838, successive subsequent acquisitions have established the true marsupial character and the near affini ties of the genus to the kangaroo (Macropus), but with an osculant relationship with the herbivorous wombat. The Skull, gigantic Pachydermoid Kangaroo (Diprotodon Pleistocene Australia.
entire skull of the Diprotodon Australis (fig. 139) has lately been acquired by the British Museum, showing in situ the tooth (i) on which the genus was founded. This skull measures 3 feet in length ; that of a man is inserted in the cut to exemplify 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 strength ened ; 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 i c p and, as in if acropus major, the first of the grinding series (p) was soon shed; but the other four two-ridged teeth were longer retained, and the front upper incisor (i, i) 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 pleistocene, intersected by creeks, in the plains of Darling Downs, Australia.
The same formation has yielded evidence of a somewhat smaller extinct herbivorous genus (Noto therium), combining, with essential affi nities to Macropus, some of the characters of the Koala The writer has recently communicated de scriptions and figures of the entire skull of the Nototherium Mitchelli to the Geo logical Society of London.t The genus Phascolomys was at the same period represented by a wombat (P. gigas) of the magnitude of a tapir, one of the grinding teeth of which is represented, of the natural size, in fig. 140.
The pleistocene marsupial Carnivora presented the usual relations of size and power to the Herbivora, whose undue in crease they had to check. Fig. 141 represents an almost entire skull, with part of the lower jaw of an animal (Th,ylatoleo) Skull of a large extinct Marsupial Carnivore (Thylacoleo earnifex), Pleistocene, Australia.
rivalling the lion in size, the marsupiality of which is demon strated by the position of the lacrymal foramen (1) in front of the orbit ; by the palatal vacuity (o), by the loose tympanic bone, the development of the tympanic bulla in the alisphenoid, by the very small relative size of the brain, and other characters detailed in the " Philosophical Transactions "* for 1859. The carnassial tooth (p) is 2 inches 3 lines in longitudinal extent, or nearly double the size of that in the lion. The upper tuber cular tooth (m, 1) resembles in its smallness and position that in the placental Felines. But in the lower jaw the carnassial (p) is succeeded by two very small tubercular teeth (m, z and 2.), as in Plagiaulax (fig. 93, p. 320) ; and there is a socket close to the symphysis of the lower jaw of Thyla,coleo which indicates that the canine may have terminated the dental series there, and have afforded an additional feature of resemblance to the Plagiaulax.
The foregoing are some of the more interesting illustrations of the law, that "with extinct as with existing Mammalia, par ticular forms were assigned to particular provinces, and that the same forms were restricted to the same provinces at a former geological period as they are at the present day."* That period, however, was the more recent tertiary one.
In carrying back the retrospective comparison of existing and extinct Mammals with those of the eocene and oolitic strata, in relation to their local distribution, we obtain indica tions of extensive changes in the relative position of sea and land during these epochs, in the degree of incongruity between the generic forms of the Mammalia which then existed in Europe and any that actually exist on the great natural conti nent of which Europe now forms part. It would seem, indeed, that the further we penetrate into time for the recovery of extinct Manunalia, the further we must go into space to find their existing analogues. To match the eocene Paheotheres and Lophiodons, we must bring Tapirs from Sumatra or South America, and we have to travel to the antipodes for Myrmeco bians, the nearest living analogues to the Amphitheres of our oolitic strata.