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Bettongia and its allied genus Potorous embrace the Kangaroo-rats, as they are often termed. These are all small, never exceeding a rabbit in size; they possess welldeveloped canine teeth, and have the central toes of the fore feet elongated to accommodate their digging habits.
Having completed our survey of the Monotremes and Marsupials of the Australian Sub-region, we must now consider the Eutherian series, which, as has been already shown, plays a very subordinate part in this extraordinary fauna. Putting aside the marine mammals—the Seals, Cetaceans, and Sirenians—and confining our attention to the terrestrial groups, we find only three of the usually recognised orders, namely, the Rodents, Bats, and Carnivores, with any representatives in this strange country. And the Carnivores would be perhaps better considered as quite external to the fauna of Australia proper, since the solitary member of this group found within its limits is the semidomesticated Dingo, which, as already suggested, has not improbably been introduced by the primitive native inhabitants.
Monkeys, Insectivores, and the most useful Order of Ungulates, to which its grassy plains would appear to be, and, as we know by actual experience are, excellently adapted, are alike unknown, except as introductions, in Australia, and their functions in a state of nature seem to be performed by the various groups of Marsupials.
Of the other orders, the Rodents are represented by six genera, all belonging to the Mice (Muridm). Of these four are confined to Australia proper, while two others also occur in the Papuan Sub-region; the remaining one, the cosmopolitian Mus, or true Mouse, numbers no less than eighteen species in Australia. The habits of the Watervoles of Europe are assumed by the species of the genus Hydromys, which are modified for aquatic life, while the species of Hapalotis are found chiefly in the dry sandy scrubs.
The Bats, with one exception, all belong to genera of considerably wide distribution, and the number of species known to inhabit Australia is not very great. Thirty only are described in Dr. Dobson's catalogue of the Bats as Australian. Pteropus, the great genus of Fruit-eating Bats, is represented by a few species; so too are the widespread insectivorous genera Vesperugo and Miniopterus. One species of the former genus, the Southern Pipistrelle (V. abramus), is found almost throughout the Old World, from Sweden to North Australia.
Section V.—Analysis Of The Austral
The full list of the Mammalian Fauna of the Austral Sub-region contains the names of about 169 species, referable to fifty-nine genera. Of these genera twenty-nine, just half, are not found outside the Austral Sub-region, the greater number of them (twenty-five) being Marsupials; they include, however, three genera of Mice (Xeromys, Hapalotis, and Mastacomys) and one peculiar Bat (Rhinonycteris). Thirteen genera are confined to the Australian Region, that is, are found in the Papuan Subregion as well as in the Austral Sub-region; of these,
again, the majority are Marsupials, besides which there
are two genera of Rodents (Hydromys and Uromys), and one Bat (Nyctophilus). Seventeen genera which are found in Australia extend beyond the limits of the Region, to the Oriental, and in some cases range even into the Ethiopian and Palsearctic Regions. Of these the greater number (fourteen) are Bats; one is a Marsupial (Phalanger), of which two species occur in Celebes; another is the widely spread genus Mus, which is found throughout the Old World; and the last is a Carnivore (Canis), of which the Australian representative is the Dingo. Canis is spread over the whole of the rest of the world, both Old and New.
Turning now to the distribution of the genera within the continent of Australia itself, it will be found that out of forty-three genera (of Monotremes, Marsupials, and Rodents), twenty are fairly represented throughout the whole area, thirteen are confined to the east (several of these ranging north into New Guinea), seven are restricted to the western and central parts of the continent (these latter are chiefly desert forms such as Perogale, Chceropus, and Notoryctes), and the three remaining genera are found only in Tasmania. These are Thylacinus, Dasyurus, and Mastacomys.
If now we reconsider the list, counting only Monotremes, Marsupials, and Rodents, it will be found that out of 130 species, thirty-five range from west to east to greater or less extent; forty-nine are confined to the eastern part of Australia, in many cases extending to Tasmania; and thirty-six are peculiar to Western Australia( while ten species out of the whole Mammal-fauna are peculiar to Tasmania.
Section VI.—Past History Of The Mammal-
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 Didelphyidm—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 Dasyuridm.
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 (Galaxiidm and Haplochitonidm) 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.