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SECTION VI.—PAST HISTORY OF THE MAMMAL
FAUNA OF THE AUSTRAL SUB-REGION
The past history of the Australian mammals is still very obscure; the only remains of extinct species yet discovered have been found in certain bone-caves and in surface-deposits generally attributed to the Pleistocene Epoch.
Putting aside the Dingo, all the Pleistocene mammals of Australia belong to the Monotremes or to the Marsupials, and, with two exceptions, can be accommodated in still existing families. These exceptions are Nototherium and Diprotodon, the latter of which was a very large animal, equalling a Rhinoceros in bulk, but both of them were probably allied to the existing Kangaroos.
Recently a deposit containing bones of these and other large Marsupials has been found in a dry salt lagoon, called Lake Mulligan, in South Australia, and when these remains have been worked out, a great deal more information as regards this pliocene or pleistocene fauna may be expected. As in South America, these extinct animals appear in many cases to have attained a size far surpassing that of their degenerate descendants.
None of the remains hitherto found in Australia throw much light on the origin of its remarkable fauna. But quite recently evidence of an extensive mammalian fauna has been discovered in certain beds, of probably Upper Eocene age, in Santa Cruz, Patagonia. In addition to a number of other forms, this series contains the remains of many Marsupials, and though the most prominent of them belong to the Didelphyidae—the Marsupial family now confined to America, and apparently distributed over the whole northern hemisphere during Tertiary times, but not found in Australia—a certain number of them show an Australian stamp. Some of them have even been relegated by Ameghino (1), to whose researches our knowledge of the Santa Cruzian fauna is mainly due, to the existing Australian family Dasyuridæ.
If, on further investigation, these references shall be found to be correct, the inference would seem to be that in very remote times—probably in the early Tertiary or the late Secondary Period—there has been some sort of landconnection between South America and Australia. In such case there would be no necessity to suppose that Australia was ever directly connected with the rest of the Old World at all, none of the peculiar forms of Australian Marsupials having yet been detected in any other part of the globe.
Besides the common possession of Marsupials, many other resemblances between the faunas of Australia and South America have been pointed out to occur among the Birds and Amphibians, and especially among the Fishes. Two families of freshwater fishes (Galaxiidæ and Haplochitonidæ) are found exclusively in these two Regions, and are not known to occur elsewhere.
Apart from speculation, however, there is no question that Australia has been isolated from all the other continents since the end of the Secondary, or at least since the beginning of the Tertiary Period of geological time.
SECTION VII.—THE PAPUAN SUB-REGION
In contrast to Australia, the great island of New Guinea, or Papua, is traversed throughout by mountains of high altitude. The rivers rising in these ranges, aided by the suns of the tropics, produce a luxuriant vegetation, and such a country as we should suppose would be especially favourable to mammal-life. Yet mammals are by no means abundant in New Guinea and in the adjacent islands which constitute the Papuan Sub-region. As is the case in Australia, the greater number of the indigenous animals of New Guinea and the neighbouring islands consist of Monotremes, Marsupials, and Rodents, together with a certain number of the cosmopolitan order of Bats (8, 10, 11).
Of the Monotremes, two species have been met with in New Guinea, both of them belonging to the family of Echidnas above referred to. Of these one species, only at present known from the south of New Guinea, is but a slightly modified form of the small Australian Echidna. But in the mountains, in various parts of New Guinea, has been lately discovered a larger representative of the same family (Proechidna), which, moreover, differs from the typical form in having only three toes on its fore limbs, and in other particulars (Fig. 6, p. 38).
The Papuan Marsupials, as yet discovered, are about thirty-three in number, and embrace representatives of the Dasyures, Bandicoots, Phalangers, and Kangaroos, which are also characteristic families of the Australian mammalfauna.
There are only two genera of Marsupials peculiar to the Papuan Sub-region. One of these is Distochurus, a small mouse-like animal belonging to the family of Phalangers, and remarkable for its long tail, which bears at its tip a double row of hairs on either side, and thus resembles a feather. The other genus is Dorcopsis, containing three species of animals somewhat nearly allied to the true
Kangaroos. A third genus (Dendrolagus), containing Kangaroos specially modified for arboreal life, was formerly supposed to be peculiar to New Guinea. But a species of the same form, as already mentioned, has been ascertained of late years to exist in Northern Queensland also, thus giving further proof of the close alliance of the Papuan and Austral mammal-faunas.
Nearly all the Marsupials found in the Papuan Subregion are confined to the island of New Guinea; a few, however-for example, the Phalangers—also inhabit the other islands of this Sub-region. The Grey Cuscus (Phalanger orientalis) extends from Amboyna in the Moluccas and from Timor all across New Guinea, and as far east as New Britain and the island of San Christoval in the Solomons. As regards the remaining orders of mammals, a few scattered representatives of the higher forms (Ungulates, Insectivores, and Carnivores) are found in the islands of the Papuan Sub-region. Some of these have, undoubtedly, been introduced by the Malays from the neighbouring islands of the Oriental Region; but others have been described by naturalists as peculiar species. In the latter case, even if we assume that the specific distinctions have been satisfactorily established, it is not probable that such species have been brought into the Papuan Region by the hand of man. It is more likely that they have migrated into it at an earlier period, since a considerable lapse of time is necessary before the effects of isolation can produce new races of sufficient distinctness from the original form to be entitled to specific separation. As regards the Papuan Ungulates, several kinds of Swine (Sus) are stated to be met with in the Papuan Region. How far these differ from one another, and whether they are really distinct from the allied wild pigs of the Oriental Region, seems a little uncertain. It is probable, however, that many of these so-called “species” of wild pig may be descendants of the domestic animal, which has run wild, as is well known, in many of the Pacific Islands. The other representatives of the Order Ungulata found in the Papuan Sub-region are three species of Deer belonging to what is