AUSTRALIAN REGION
THE AUSTRALIAN REGION.
The Australian is the great insular region of the earth. As a whole it is one of the best marked, and has even been considered to be equal in zoological value to all the rest of the globe; but its separate portions are very heterogeneous, and their limits sometimes ill-defined. Its central and most important masses consist of Australia and New Guinea, in which the main features of the region are fully developed. To the north-west it extends to Celebes, in which a large proportion of the Australian characters have disappeared, while Oriental types are mingled with them to such an extent that it is rather difficult to determine where to locate it. To the south-east it includes New Zealand, which is in some respects so peculiar, that it has even been proposed to constitute it a distinct region. On the east it embraces the whole of Oceania to the Marquesas and Sandwich Islands, whose very scanty and often peculiar fauna, must be affiliated to the general Australian type.
Australia is the largest tract of land in the region, being several times more extensive than all the other islands combined, and it is here that the greatest variety of peculiar types have been developed. This island-continent, being situated in the track of the southern desert zone, and having no central mountains to condense the vapours from the surrounding ocean, has a large portion of its interior so parched up and barren as to be almost destitute of animal life. The most extensive tract of fertile and well-watered country is on the east and south-east,where a fine range of mountains reaches, in the Colony of Victoria, the limits of perpetual snow. The west coast also possesses mountains of moderate height, but the climate is very dry and hot. The northern portion is entirely tropical, yet it nowhere presents the luxuriance of vegetation characteristic of the great island of New Guinea immediately to the north of it. Taken as a whole, Australia is characterized by an arid climate and a deficiency of water; conditions which have probably long prevailed, and under which its very peculiar fauna and flora have been developed. This fact will account for some of the marked differences between it and the adjacent sub-regions of New Guinea and the Moluccas, where the climate is moist, and the vegetation luxuriant; and these divergent features must never be lost sight of, in comparing the different portions of the Australian region. In Tasmania alone, which is however, essentially a detached portion of Australia, a more uniform and moister climate prevails; but it is too small a tract of land, and has been too recently severed from its parent mass to have developed a special fauna.
The Austro-Malay sub-region (of which New Guinea is the central and typical mass) is strikingly contrasted with Australia, being subjected to purely equatorial conditions,—a high, but uniform temperature, excessive moisture, and a luxuriant forest vegetation, exactly similar in general features to that which clothes the Indo-Malay Islands, and the other portions of the great equatorial forest zone. Such a climate and vegetation, being the necessary result of its geographical position, must have existed from remote geological epochs with but little change, and must therefore have profoundly affected all the forms of life which have been developed under their influence. Around New Guinea as a centre are grouped a number of important islands, more or less closely agreeing with it in physical features, climate, vegetation, and forms of life. In most immediate connection we place the Aru Islands, Mysol and Waigiou, with Jobie and the other Islands in Geelvinck Bay, all of which are connected with it by shallow seas; they possess one of its most characteristic groups, the Birds of Paradise, and have no doubt only recently (ina geological sense) been separated from it. In the next rank come the large islands of the Moluccas on the west, and the range terminating in the Solomon Islands on the east, both of which groups possess a clearly Papuan fauna, although deficient in many of the most remarkable Papuan types.
All these islands agree closely with New Guinea itself in being very mountainous, and covered with a luxuriant forest vegetation; but to the south-west we find a set of islands extending from Timor to Lombock, which agree more nearly with Australia, both in climate and vegetation; being arid and abounding in eucalypti, acacias, and thickets of thorny shrubs. These, like the Moluccas, are surrounded by deep sea, and it is doubtful whether they have either of them been actually connected with New Guinea or Australia in recent geological times; but the general features of their zoology oblige us to unite all these islands with New Guinea as forming the Austro-Malay sub-division of the Australian region. Still further west however, we have the large island of Celebes, whose position is very difficult to determine. It is mountainous, but has also extensive plains and low lands. Its climate is somewhat arid in the south, where the woods are often scattered and thorny, while in the north it is moister, and the forests are luxuriant. It is surrounded by deep seas, but also by coralline and volcanic islets, indicating former elevations and subsidences. Its fauna presents the most puzzling relations, showing affinities to Java, to the Philippines, to the Moluccas, to New Guinea, to continental India, and even to Africa; so that it is almost impossible to decide whether to place it in the Oriental or the Australian region. On the whole the preponderance of its relations appears to be with the latter, though it is undoubtedly very anomalous, and may, with almost as much propriety, be classed with the former. This will be better understood when we come to discuss its zoological peculiarities.
The next sub-region consists of the extensive series of islands scattered over the Pacific, the principal groups being the Sandwich Islands, the Marquesas and Society Islands, the Navigators', Friendly, and Fiji Islands. New Caledonia and the NewHebrides have rather an uncertain position, and it is difficult to decide whether to class them with the Austro-Malay Islands, the Pacific Islands, or Australia. The islands of the west Pacific, north of the equator, also probably come into this region, although the Ladrone Islands may belong to the Philippines; but as the fauna of all these small islets is very scanty, and very little known, they are not at present of much importance.
There remains the islands of New Zealand, with the surrounding small islands, as far as the Auckland, Chatham, and Norfolk Islands. These are situated in the south temperate forest-zone. They are mountainous, and have a moist, equable, and temperate climate. They are true oceanic islands, and the total absence of mammalia intimates that they have not been connected with Australia or any other continent in recent geological times. The general character of their zoology, no less than their botany, affiliates them however, to Australia as portions of the same zoological region.
General Zoological Characteristics of the Australian Region.—For the purpose of giving an idea of the very peculiar and striking features which characterise the Australian region, it will be as well at first to confine ourselves to the great central land masses of Australia and New Guinea, where those features are manifested in their greatest force and purity, leaving the various peculiarities and anomalies of the outlying islands to be dealt with subsequently.
Mammalia.—The Australian region is broadly distinguished from all the rest of the globe by the entire absence of all the orders of non-aquatic mammalia that abound in the Old World, except two—the winged bats (Chiroptera), and the equally cosmopolite rodents (Rodentia). Of these latter however, only one family is represented—the Muridæ—(comprising the rats and mice), and the Australian representatives of these are all of small or moderate size—a suggestive fact in appreciating the true character of the Australian fauna. In place of the Quadrumana, Carnivora, and Ungulates, which abound in endless variety in all the other regions under equally favourable conditions, Australia possesses two new orders (or perhapssub-classes)—Marsupialia and Monotremata, found nowhere else on the globe except a single family of the former in America. The Marsupials are wonderfully developed in Australia, where they exist in the most diversified forms, adapted to different modes of life. Some are carnivorous, some herbivorous; some arboreal, others terrestrial. There are insect-eaters, root-gnawers, fruit-eaters, honey-eaters, leaf or grass-feeders. Some resemble wolves, others marmots, weasels, squirrels, flying squirrels, dormice or jerboas. They are classed in six distinct families, comprising about thirty genera, and subserve most of the purposes in the economy of nature, fulfilled in other parts of the world by very different groups; yet they all possess common peculiarities of structure and habits which show that they are members of one stock, and have no real affinity with the Old-World forms which they often outwardly resemble.
The other order, Monotremata, is only represented by two rare and very remarkable forms,OrnithorhynchusandEchidna, probably the descendants of some of those earlier developments of mammalian life which in every other part of the globe have long been extinct.
The bats of Australia all belong to Old-World genera and possess no features of special interest, a result of the wandering habits of these aerial mammals. The Rodents are more interesting. They are all more or less modified forms of mice or rats. Some belong to the widely distributed genusMus, others to four allied genera, which may be all modifications of some common Old-World form. They spread all over Australia, and allied species occur in Celebesand the Papuan Islands, so that although not yet known fromthe Moluccas, there can be little doubt that some of them exist there.
Birds.—The typical Australian region, as above defined, is almost as well characterized by its birds, as by its mammalia; but in this case the deficiencies are less conspicuous, while the peculiar and characteristic families are numerous and important. The most marked deficiency as regards wide-spread families, is the total absence of Fringillidæ (true finches), Picidæ (woodpeckers), Vulturidæ (vultures), and Phasianidæ (pheasants).and among prevalent Oriental groups, Pycnonotidæ (bulbuls), Phyllornithidæ (green bulbuls), and Megalæmidæ (barbets) are families whose absence is significant. Nine families are peculiar to the region, or only just pass its limits in the case of single species. These are Paridiseidæ (paradise-birds), Meliphagidæ (honey-suckers), Menuridæ (lyre-birds), Atrichidæ (scrub-birds), Cacatuidæ (cockatoos), Platycercidæ (broad-tailed and grass-paroquets), Trichoglossidæ (brush-tongued paroquets), Megapodiidæ (mound-makers), and Casuariidæ (cassowaries). There are also eight very characteristic families, of which four,—Pachycephalidæ (thick-headed shrikes), Campephagidæ (caterpillar shrikes), Dicæidæ (flower-peckers), and Artamidæ (swallow-shrikes)—are feebly represented elsewhere, while the other four—Ploceidæ (weaver-finches), Alcædinidæ (kingfishers), Podargidæ (frog-mouths), and Columbidæ (pigeons)—although widely distributed, are here unusually abundant and varied, and (except in the case of the Ploceidæ) better represented in the Australian than in any other region. Of all these the Meliphagidæ (honeysuckers) are the most peculiarly and characteristically Australian. This family abounds in genera and species; it extends into every part of the region from Celebes and Lombock on the west, to the Sandwich Islands, Marquesas, and New Zealand on the east, while not a single species overpasses its limits, with the exception of one (Ptilotis limbata) which abounds in all the islands of the Timorese group, and has crossed the narrow strait from Lombock to Baly; but this can hardly be considered to impugn the otherwise striking fact of wide diffusion combined with strict limitation, which characterizes it. This family is the more important, because, like the Trichoglossidæ or brush-tongued paroquets, it seems to have been developed in co-ordination with that wealth of nectariferous flowering shrubs and trees which is one of the marked features of Australian vegetation. It probably originated in the extensive land-area of Australia itself, and thence spread into all the tributary islands, where it has become variously modified, yet always in such close adaptation to the other great features of the Australian fauna, that it seems unable to maintain itself when subject to the competition of the morevaried forms of life in the Oriental region; to which, possessing great powers of flight, some species must occasionally have emigrated. Its presence or absence serves therefore to define and limit the Australian region with a precision hardly to be equalled in the case of any other region or any other family of birds.
The Trichoglossidæ, as already intimated, are another of these peculiarly organized Australian families,—parrots with an extensile brush-tipped tongue, adapted to extract the nectar and pollen from flowers. These are also rigidly confined to this region, but they do not range so completely over the whole of it, being absent from New Zealand (where however they are represented by a closely allied formNestor), and from the Sandwich Islands. The Paradiseidæ (birds of paradise and allies) are another remarkable family, confined to the Papuan group of Islands, and the tropical parts of Australia. The Megapodiidæ (or mound-builders) are another most remarkable and anomalous group of birds, no doubt specially adapted to Australian conditions of existence. Their peculiarity consists in their laying enormous eggs (at considerable intervals of time) and burying them either in the loose hot sand of the beach above high-water mark, or in enormous mounds of leaves, sticks, earth, and refuse of all kinds, gathered together by the birds, whose feet and claws are enlarged and strengthened for the work. The warmth of this slightly fermenting mass hatches the eggs; when the young birds work their way out, and thenceforth take care of themselves, as they are able to run quickly, and even to fly short distances, as soon as they are hatched. This may perhaps be an adaptation to the peculiar condition of so large a portion of Australia, in respect to prolonged droughts and scanty water-supply, entailing a periodical scarcity of all kinds of food. In such a country the confinement of the parents to one spot during the long period of incubation would often lead to starvation, and the consequent death of the offspring. But the same birds with free power to roam about, might readily maintain themselves. This peculiar constitution and habit, which enabled the Megapodii to maintain an existence under the unfavourable conditions of theiroriginal habitat gives them a great advantage in the luxuriant islands of the Moluccas, to which they have spread. There they abound to a remarkable extent, and their eggs furnish a luxurious repast to the natives. They have also reached many of the smallest islets, and have spread beyond the limits of the region to the Philippines, and North-Western Borneo, as well as to the remote Nicobar Islands.
The Platycercidæ, or broad-tailed paroquets, are another wide-spread Australian group, of weak structure but gorgeously coloured, ranging from the Moluccas to New Zealand and the Society Islands, and very characteristic of the region, to which they are strictly confined. The Cockatoos have not quite so wide a range, being confined to the Austro-Malayan and Australian sub-regions, while one species extends into the Philippine Islands. The other two peculiar families are more restricted in their range, and will be noticed under the sub-regions to which they respectively belong.
Of the characteristic families, the Pachycephalidæ, or thick-headed shrikes, are especially Australian, ranging over all the region, except New Zealand; while only a single species has spread into the Oriental, and one of doubtful affinity to the Ethiopian region. The Artamidæ, or swallow-shrikes, are also almost wholly confined to the region, one species only extending to India. They range to the Fiji Islands on the east, but only to Tasmania on the south. These two families must be considered as really peculiar to Australia. The Podargidæ, or frog-mouths—large, thick-billed goat-suckers—are strange birds very characteristic of the Australian region, although they have representatives in the Oriental and Neotropical regions. Campephagidæ (caterpillar-shrikes) also abound, but they are fairly represented both in India and Africa. The Ploceidæ, or weaver-birds, are the finches of Australia, and present a variety of interesting and beautiful forms.
We now come to the kingfishers, a cosmopolitan family of birds, yet so largely developed in the Australian region as to deserve special notice. Two-thirds of all the genera are found here, and no less than 10 out of the 19 genera in the family arepeculiar to the Australian region. Another of the universally distributed families which have their metropolis here, is that of the Columbidæ or pigeons. Three-fourths of the genera have representatives in the Australian region, while two-fifths of the whole are confined to it; and it possesses as many species of pigeons as any other two regions combined. It also possesses the most remarkable forms, as exemplified in the great crowned pigeons (Goura) and the hook-billedDidunculus, while the green fruit-pigeons (Ptilopus) are sometimes adorned with colours vying with those of the gayest parrots or chatterers. This enormous development of a family of birds so defenceless as the pigeons, whose rude nests expose their eggs and helpless young to continual danger, may perhaps be correlated, as I have suggested elsewhere (Ibis, 1865, p. 366), with the entire absence of monkeys, cats, lemurs, weasels, civets and other arboreal mammals, which prey on eggs and young birds. The very prevalent green colour of the upper part of their plumage, may be due to the need of concealment from their only enemies,—birds of prey; and this is rendered more probable by the fact that it is among the pigeons of the small islands of the Pacific (where hawks and their allies are exceedingly scarce) that we alone meet with species whose entire plumage is a rich and conspicuous yellow. Where the need of concealment is least, the brilliancy of colour has attained its maximum. We may therefore look upon the genusPtilopus, with its fifty species whose typical coloration is green, with patches of bright blue, red, or yellow on the head and breast, as a special development suited to the tropical portion of the Australian region, to which it is almost wholly confined.
It will be seen from the sketch just given, that the ornithological features of the Australian region are almost as remarkable as those presented by its Mammalian fauna; and from the fuller development attained by the aërial class of birds, much more varied and interesting. None of the other regions of the earth can offer us so many families with special points of interest in structure, or habits, or general relations. The paradise-birds, the honeysuckers, the brush-tongued paroquets, the mound-builders, and the cassowaries—all strictly peculiarto the region—with such remarkable developments as we have indicated in the kingfishers and pigeons, place the Australian region in the first rank for the variety, singularity, and interest of its birds, and only second to South America as regards numbers and beauty.
Reptiles.—In Reptiles the peculiarity of the main Australian region is less marked, although the fauna is sufficiently distinct. There is no family of snakes confined to the region, but many peculiar genera of the families Pythonidæ and Elapidæ. About two-thirds of the Australian snakes belong to the latter family, and are poisonous; so that although the Crotalidæ and Viperidæ are absent, there are perhaps a larger proportion of poisonous to harmless snakes than in any other part of the world. According to Mr. Gerard Krefft the proportion varies considerably in the different colonies. In Victoria, New South Wales, and Queensland the proportion is about two to one; in West Australia three to one; and in South Australia six to one. In Tasmania there are only 3 species and all are poisonous. The number of species, as in other parts of the world, seems to increase with temperature. The 3 in Tasmania have increased to 12 in Victoria, 15 in South Australia and the same in West Australia; 31 in New South Wales, and 42 in sub-tropical Queensland.
The lizards of Australia have lately been catalogued by Dr. Günther in the concluding part of the "Voyage of the Erebus and Terror," issued in 1875. They belong to 8 families, 3 of which are peculiar; 57 genera of which 36 are peculiar; and about 140 species, all but 2 or 3 of which are peculiar. The scinks and geckoes form the great bulk of the Australian lizards, with a few Agamidæ, Gymnopthalmidæ, and Varanidæ. The three peculiar families are the Pygopodidæ, Aprasiidæ and Lialidæ; comprising only 4 genera and 7 species. The above all belong to Australia proper. Those of the other sub-regions are few in number and will be noticed under their respective localities. They will perhaps bring up the number of genera to 70. West and South Australia seem to offer much peculiarity in their lizards; these districts possessing 12 peculiar genera,while a much smaller number are confined to the East and South-East, or to the North.
Among the fresh-water turtles of the family Chelydidæ there are three peculiar genera—Chelodina,Chelemys, andElseya, all from Australia.
Amphibia.—No tailed amphibians are known from the whole region, but no less than eleven of the families of tail-less Batrachians (toads and frogs) are known to inhabit some part or other of it. A peculiar family (Xenorhinidæ), consisting of a single species, is found in New Guinea; the true toads (Bufonidæ) are only represented by a single species of a peculiar genus in Australia, and by aBufoin Celebes. Nine of the families are represented in Australia itself, and the following genera are peculiar to it:—Pseudophryne(Phryniscidæ),Pachybatrachus, andChelydobatrachus(Engystomydæ);Helioporus(Alytidæ);PelodyrasandChirodyras(Pelodryadæ);Notaden(Bufonidæ).
Fresh-water Fish.—There is only one peculiar family of fresh-water fishes in this region—the Gadopsidæ—represented by a single genus and species. The other species of Australia belong to the families Trachinidæ, Atherinidæ, Mugillidæ, Siluridæ, Homalopteræ, Haplochitonidæ, Galaxidæ, Osteoglossidæ, Symbranchidæ, and Sirenoidei; most of the genera being peculiar. The large and widely-distributed families, Cyprinodontidæ and Cyprinidæ, are absent. The most remarkable fish is the recently discoveredCeratodus, allied to theLepidosirenof Tropical America, andProtopterusof Tropical Africa, the three species constituting the Sub-class Dipnoi, remains of which have been found fossil in the Triassic formation.
Summary of Australian Vertebrata.—In order to complete our general sketch of Australian zoology, and to afford materials for comparison with other regions, we will here summarize the distribution of Vertebrata in the entire Australian region, as given in detail in the tables at the end of this chapter. When an undoubted Oriental family or genus extends to Celebes only we do not count it as belonging to the Australian region, that island being so very anomalous and intermediate in character.
The Australian region, then, possesses examples of 18 families of Mammalia, 8 of which are peculiar; 71 of Birds, 16 being peculiar; 31 of Reptiles, 4 being peculiar; 11 of Amphibia, with 1 peculiar; and 11 of Fresh-water fish, with 1 peculiar. In all, 142 families of Vertebrates, 30 of which are almost or quite confined to it, or between one-fourth and one-fifth of the whole number.
The genera of Mammalia occurring within the limits of this region are 70, of which 45 are almost, or quite, confined to it.
Of Land-Birds there are 296 genera, 196 of which are equally limited. The proportion is in both cases very nearly five-eighths.
This shows a considerable deficiency both in families of Vertebrates and genera of Mammalia, as compared with the Oriental and Ethiopian regions; while in genera of Birds it is a little superior to the latter in total numbers, and considerably so in the proportion of peculiar types.
Supposed Land Connection between Australia and South America.
We may now consider how far the different classes and orders of vertebrates afford indications that during past ages there has been some closer connection between Australia and South America than that which now exists.
Among Mammalia we have the remarkable fact of a group of marsupials inhabiting South America, and extending even into the temperate regions of North America, while they are found in no other part of the globe beyond the limits of the Australian region; and this has often been held to be evidence of a former connection between the two countries. A preliminary objection to this view is, that the opossums seem to be rather a tropical group, only one species reaching as far as 42° south latitude on the west coast of South America; but whatever evidence we have which seems to require a former union of these countries shows that it took place, if at all, towards their cold southern limits, the tropical faunas on the whole showing no similarity. This is not a very strong objection, since climates may have changed in the south to as great an extent as weknow they have in the north. Perhaps a more important consideration is, thatDidelphysis a family type unknown in Australia; and this implies that the point of common origin is very remote in geological time. But the most conclusive fact is that in the Eocene and Miocene periods this very family, Didelphyidæ, existed in Europe, while it only appeared in America in the Post-pliocene or perhaps the Pliocene period; so that it is really an Old-World group, which, though long since extinct in its birthplace, has survived in America, to which country it is a comparatively recent emigrant. Primeval forms of marsupials we know abounded in Europe during much of the Secondary epoch, and no doubt supplied Australia with the ancestors of the present fauna. It is clear, therefore, that in this case there is not a particle of evidence for any former union between Australia and South America; while it is almost demonstrated that both derived their marsupials from a common source in the northern hemisphere.
Birds offer us more numerous but less clearly defined cases of this kind. Among Passeres, the wonderful lyre bird (Menura) is believed by some ornithologists to be decidedly allied to the South American Pteroptochidæ, while others maintain that it is altogether peculiar, and has no such affinity. The Australian Pachycephalidæ have also been supposed to find their nearest allies in the American Vireonidæ, but this is, perhaps, equally problematical. That the mound-makers (Megapodiidæ) of the Australian region are more nearly allied to the South American curassows (Cracidæ) than to any other family, is perhaps better established; but if proved, it is probably due, as in the case of the marsupials, to the survival of an ancient and once wide-spread type, and thus lends no support to the theory of a land connection between the two regions. A recent author, Professor Garrod, classesPhapsand other Australian genera of pigeons along withZenaidaand allied South American forms; but here again the affinity, if it exists, is so remote that the explanation already given will suffice to account for it. There remain only the penguins of the genusEudyptes; and these have almost certainly passed from one region to the other, butno actual land connection is required for birds which can cross considerable arms of the sea.
Reptiles again seem to offer no more support to the view than do mammalia or birds. Among snakes there are no families in common that have not a very wide distribution. Among lizards the Gymnopthalmidæ are the only family that favour the notion, since they are found in Australia and South America, but not in the Oriental region. Yet they occur in both the Palæarctic and Ethiopian regions, and their distribution is altogether too erratic to be of any value in a case of this kind; and the same remarks apply to the tortoises of the family Chelydidæ.
The Amphibia, however, furnish us with some more decided facts. We have first the family of tree-frogs, Pelodryade, confined to the two regions;Litoria, a genus of the family Hylidæ peculiar to Australia, but with one species in Paraguay; and in the family Discoglossidæ, the Australian genusChirolepteshas its nearest ally in the Chilian genusCalyptocephalus.
Fresh-water fishes give yet clearer evidence. Three groups are exclusively found in these two regions;Aphritis, a fresh-water genus of Trachinidæ, has one species in Tasmania and two others in Patagonia; the Haplochitonidæ inhabit only Terra del Fuego, the Falkland Islands and South Australia; while the genusGalaxias(forming the family Galaxidæ) is confined to South Temperate America, Australia, and New Zealand. We have also the genusOsteoglossumconfined to the tropical rivers of Eastern South America, the Indo-Malay Islands and Australia.
It is important here to notice that the heat-loving Reptilia afford hardly any indications of close affinity between the two regions, while the cold-enduring amphibia and fresh-water fish, offer them in abundance. Taking this fact in connection with the absence of all indications of close affinity among the mammalia and terrestrial birds, the conclusion seems inevitable that there has been no land-connection between the two regions within the period of existing species, genera, or families. Yet some interchange of amphibia and fresh-waterfishes, as of plants and insects, has undoubtedly occurred, but this has been effected by other means. If we look at a globe we see at once how this interchange may have taken place. Immediately south of Cape Horn we have the South Shetland Islands and Graham's land, which is not improbably continuous, or nearly so, with South Victoria land immediately to the south of New Zealand. The intervening space is partly occupied by the Auckland, Campbell, and Macquaries' Islands, which, there is reason to believe are the relics of a great southern extension of New Zealand. At all events they form points which would aid the transmission of many organisms; and the farthest of the Macquaries' group, Emerald Island, is only 600 miles from the outlying islets of Victoria land. The ova of fish will survive a considerable time in the air, and the successful transmission of salmon ova to New Zealand packed in ice, shows how far they might travel on icebergs. Now there is evidently some means by which ova or young fishes are carried moderate distances, from the fact that remote alpine lakes and distinct river systems often have the same species. Glaciers and icebergs generally have pools of fresh water on their surfaces; and whatever cause transmits fish to an isolated pond might occasionally stock these pools, and by this means introduce the fishes of one southern island into another. Batrachians, which are equally patient of cold, might be transported by similar means; while, as Mr. Darwin has so well shown, (Origin of Species, 6th Ed. p. 345) there are various known modes by which plants might be transmitted, and we need not therefore be surprised that botanists find a much greater similarity between the production of the several Southern lands and islands, than do zoologists. It is important to notice that, however this intercommunication was effected, it has continued down to the epoch of existing species; for Dr. Günther finds the same species of fresh-water fish (Galaxias attenuatus) inhabiting Tasmania, New Zealand, the Falkland Islands, and Temperate South America; while another species is common to New Zealand and the Auckland Islands. We cannot believe that a land connection has existed between all these remote lands within the period of existence of this one species of fish,not only on account of what we know of the permanence of continents and deep oceans, but because such a connection must have led to much more numerous and important cases of similarity of natural productions than we actually find. And if within the life ofspeciessuch interchange may have taken place across seas of greater or less extent, still more easy is it to understand, how, within the life ofgeneraandfamilies, a number of such interchanges may have occurred; yet always limited to those groups whose conditions of life render transmission possible. Had an actual land connection existed within the temperate zone, or during a period of warmth in the Antarctic regions, there would have been no such strict limitations to the inter-migration of animals. It may be held to support the view that floating ice has hadsomeshare in the transmission of fish and amphibia, when we find that in the case of the narrow tropical sea dividing Borneo from Celebes and the Moluccas, no proportionate amount of transmission has taken place, but numerous species, genera, and whole families, terminate abruptly at what we have other reasons for believing to be the furthest limits of an ancient continent. We can hardly suppose, however, that this mode of transmission would have sufficed for such groups as tree-frogs, which are inhabitants of the more temperate or even warm portions of the two southern lands. Some of these cases may perhaps be explained by the supposition of a considerable extent of land in the South-Temperate and Antarctic regions now submerged, and by a warm or temperate climate analogous to that which prevailed in the Arctic regions during some part of the Miocene epoch; while others may be due to cases of survival in the two areas of once wide-spread groups, a view supported in the case of the Amphibia by the erratic manner in which many of the groups are spread over the globe.
From an examination of the facts presented by the various classes of vertebrates, we are, then, led to the conclusion, that there is no evidence of a former land-connection between the Australian and Neotropical regions; but that the various scattered resemblances in their natural productionsthat undoubtedly occur, are probably due to three distinct causes.
First, we have the American Didelphyidæ, among Mammals, and the Cracidæ, among birds, allied respectively to the Marsupials and the Megapodiidæ of Australia. This is probably more a coincidence than an affinity, due to the preservation of ancient wide-spread types in two remote areas, each cut off from the great northern continental masses, in which higher forms were evolved leading to the extinction of the lower types. In each of these southern isolated lands the original type would undergo a special development; in the one case suited to an arboreal existence, in the other to a life among arid plains.
The second case is that of the tree-frogs, and the genusOsteoglossumamong fishes; and is most likely due to the extension and approximation of the two southern continents, and the existence of some intermediate lands, during a warm period when facilities would be afforded for the transmission of a few organisms by the causes which have led to the exceptional diffusion of fresh-water productions in all parts of the world. As howeverOsteoglossumoccurs also in the Sunda Islands, this may be a case of survival of a once wide-spread group.
The third case is that of the same genera and even species of fish, and perhaps of frogs, in the two countries; which may be due to transmission from island to island by the aid of floating ice, with or without the assistance of more intervening lands than now exist.
Having arrived at these conclusions from a consideration of the vertebrata, we shall be in a position to examine how far the same causes will explain, or agree with, the distribution of the invertebrate groups, or elucidate any special difficulties we may meet with in the relations of the sub-regions.
Insects.
The insects of the Australian region are as varied, and in some respects as peculiar as its higher forms of life. As we have already indicated in our sketch of the Oriental region, a vast number of forms inhabit the Austro-Malay sub-regionwhich are absent from Australia proper. Such of these as are common to the Malay archipelago as a whole, have been already noted; we shall here confine ourselves more especially to the groups peculiar to the region, which are almost all either Australian or Austro-Malayan, the Pacific Islands and New Zealand being very poor in insect life.
Lepidoptera.—Australia itself is poor in butterflies, except in its northern and more tropical parts, where greenOrnithopteræand several other Malayan forms occur. In South Australia there are less than thirty-five species, whereas in Queensland there are probably over a hundred. The peculiar Australian forms are few. In the family Satyridæ,XenicaandHeteronympha, withHypocistaextending to New Guinea; among the Lycænidæ,OgyrisandUticaare confined to Australia proper, andHypochrysopsto the region; and in Papilionidæ, the remarkableEurycusis confined to Australia, but is allied toEuryades, a genus found in Temperate South America (La Plata), and to theParnassiusof the North-Temperate zone.
The Austro-Malay sub-region has more peculiar forms.Hamadryas, a genus of Danaidæ, approximates to some South American forms;HyadesandHyantisare remarkable groups of Morphidæ;MynesandProthoëare fine Nymphalidæ, the former extending to Queensland;Dicallaneura, a genus of Erycinidæ, andElodina, of Pieridæ, are also peculiar forms. The fineÆgeusgroup ofPapilio, andPriamusgroup ofOrnithoptera, also belong exclusively to this region.
Xoisis confined to the Fiji Islands,Bletogonato Celebes, andAcropthalmiato New Zealand, all genera of Satyridæ. Seventeen genera in all are confined to the Australian region.
Among the Sphingina,Pollanisus, a genus of Zygænidæ, is Australian; also four genera of Castniidæ—Synemon,Euschemon,Damias, andCocytia, the latter being confined to the Papuan islands. The occurrence of this otherwise purely South American family in the Australian region, as well as the affinity ofEurycusandEuryadesnoticed above, is interesting; but as we have seen that the genera and families of insects are more permanent than those of the higher animals, and as the groups in question areconfined to the warmer parts of both countries, they may be best explained as cases of survival of a once wide-spread type, and may probably date back to the period when the ancestors of the Marsupials and Megapodii were cut off from the rest of the world.
Coleoptera.—The same remark applies here as in the Lepidoptera, respecting the affinity of the Austro-Malay fauna to that of Indo-Malay Islands; but Australia proper is much richer in beetles than in butterflies, and exhibits much more speciality. Although the other two parts of the Australian region (Polynesia and New Zealand) are very poor in beetles, it will, nevertheless, on the whole compare favourably with any of the regions except the very richest.
Cicindelidæ are not very abundant.TheratesandTricondylaare the characteristic genera in Austro-Malaya, but are absent from Australia, where we haveTetrachaas the most characteristic genus, with one species ofMegacephalaand two ofDistypsidera, a genus which is found also in New Zealand and some of the Pacific Islands. The occurrence of the South American genus,Tetracha, may perhaps be due to a direct transfer by means of intervening lands during the warm southern period; but considering the permanence of coleopterous forms (as shown by the Miocene species belonging almost wholly to existing genera), it seems more probable that it is a case of the survival of a once wide-spread group.
Carabidæ are well represented, there being no less than 94 peculiar genera, of which 19 are confined to New Zealand. The Australian genera of most importance areCarenum(68 species),Promecoderus(27 species),Silphomorpha(32 species),Adelotopus(27 species),Scaraphites(25 species),Notonomus(18 species),Gnathoxys(12 species),Eutoma(9 species),Ænigma(15 species),Lacordairea(8 species),Pamborus(8 species),Catadromus(4 species),—the latter found in Australia and Celebes. Common to Australia and New Zealand areMecodema(14 species),Homalosoma(32 species),Dicrochile(12 species), andScopodes(5 species). The larger genera, confined to New Zealand only, areMetaglymma(8 species), andDemetrida(3 species). The curious genusPseudomorpha(10 species), is divided between California, Brazil,and Australia; and the Australian genera,Adelotopus,Silphomorpha, andSphallomorpha, form with it a distinct tribe of Coleoptera. These being all confined to the warmer regions, and having so scattered a distribution, are no doubt the relics of a widespread group. The Australian genus,Promecoderus, has, however, closely allied genera (Casceliusand its allies), in Chili and Patagonia; while two small genera confined to the Auckland Islands (HeterodactylusandPristancyclus) are allied to a group found only in Terra-del-Fuego and the Falkland Islands, (Migadops); and in these cases we may well believe that a direct transmission has taken place by some of the various means already indicated.
In Lucanidæ, Australia is only moderately rich, having 7 peculiar genera. The most important areCeratognathusandRhyssonotus, confined to Australia;Lissotesto Australia and New Zealand;Lamprimato Australia and Papua.MitophyllusandDendroblaxinhabit New Zealand only; whileSyndesusis found in Australia, New Caledonia, and tropical South America.
The beautiful Cetoniidæ are poorly represented, there being only 3 peculiar genera;—Schizorhina, mainly Australian, but extending to Papua and the Moluccas;Anacamptorhina, confined to New Guinea, andSternoplusto Celebes.Lomapterais very characteristic of the Austro-Malay Islands. This almost tropical family shows no approximations between the Australian and Neotropical faunas.
In Buprestidæ, the Australian region is the richest, possessing no less than 47 genera, of which 20 are peculiar to it. Of these, 15 are peculiar to Australia itself, the most important beingStigmodera(212 species),Ethon(13 species), andNascio(3 species);Cisseis(17 species), and the magnificentCalodema(3 species), are common to Australia and Austro-Malaya; whileSambus(10 species) andAnthaxomorpha(4 species), with some smaller groups, are peculiarly Austro-Malayan. In this family occur several points of contact with the Neotropical region.Stigmoderais said to have a species in Chili, while there are undoubtedly several allied genera in Chili and South Temperate America. The genusCurishas 5 Australian and 3 Chilian species, andAcherusiahas 2 species in Brazil, 1 in Australia. These resemblances may probably have arisen from intercommunication during the warm southern period, when floating timber would occasionally transmit a few larvæ of this family from island to island across the antarctic seas. When the cold period returned, they would spread northward, and become more or less modified under the new physical conditions and organic competition, to which they were subjected.
We now come to the very important group of Longicorns, in which the Australian region as a whole, is very rich, possessing 360 genera, of which 263 are peculiar to it. Of these about 50 are confined to the Austro-Malay Islands, 12 to New Zealand, and the remainder to Australia proper with Tasmania. Of the genera confined to, or highly characteristic of Australia, the following are the most important:—Cnemoplites, belonging to the Prionidæ;Phoracantha, to the Cerambycidæ;Zygocera,Hebecerus,Symphyletes, andRhytidophora, to the Lamiidæ. Confined to the Austro-Malay Islands areTethionea(Cerambycidæ):Tmesisternus,Arrhenotus,Micracantha, andSybra(Lamiidæ); but there are also such Malayan genera asBatocera,Gnoma,Praonetha, andSphenura, which are very abundant in the Austro-Malay sub-region. A species of each of the Australian genera,Zygocera,Syllitus, andPseudocephalus, is said to occur in Chili, and one of the tropical American genus,Hammatochærus, in tropical Australia; an amount of resemblance which, as in the case of the Buprestidæ, may be imputed to trans-oceanic migration during the Southern warm period. This concludes our illustrations of the distribution of some of the more important groups of Australian insects; and it will be admitted that we have not met with any such an amount of identity with the fauna of Temperate South America, as to require us to modify the conclusions we arrived at from a consideration of the vertebrate groups.
Land-Shells.—The distribution of many of the larger genera of land-shells is very erratic, while others are exceedingly restricted, so that it requires an experienced conchologist to investigate the affinities of the several groups, and thus workout the important facts of distribution. All that can be done here is to note the characteristic and peculiar genera, and any others presenting features of special interest.
In the great family of the snails (Helicidæ), the only genera strictly confined to the region are,Partula, now containing above 100 species, and ranging over the Pacific from the Solomon Isles on the west, to the Sandwich Islands and Tahiti on the east; andAchatinella, now containing nearly 300 species, and wholly confined to the Sandwich Islands.Pfeifferiais confined to the Philippine Islands and Moluccas;Cochlostylato the Indo-Malay Islands and Australia;Bulimusoccurs in most of the insular groups, including New Zealand, but is absent from Australia.
Among the Aciculidæ, the widely-scatteredTruncatellais the only genus represented. Among Diplommatinidæ,Diplommatinais the characteristic genus, ranging over the whole region, and found elsewhere as far as India, with one species in Trinidad. The extensive family Cyclostomidæ, is not well represented. Seven genera reach the Austro-Malay Islands, one of which,Registoma, is confined to the Philippines, Moluccas, New Caledonia, and the Marshall Islands.Omphalotropisis the most characteristic genus, ranging over the whole region;Calliais confined to the Philippines, Ceram, and Australia;Realiato New Zealand and the Marquesas. The genusHelicinaalone represents the Helicinidæ, and is found in the whole region except New Zealand. The number of species known from Australia is perhaps about 300; while the Polynesian sub-region, according to Mr. Harper Pease, contains over 600; the Austro-Malay Islands will furnish probably 200; and New Zealand about 100; making a total of about 1,200 species for the whole region.
Australian Sub-regions.
Few of the great zoological regions comprise four divisions so strongly contrasted as these, or which present so many interesting problems. We have first the Austro-Malay Islands, an equatorial forest-region teeming with varied and beautiful forms of life; next we have Australia itself, an island-continent with its satelliteTasmania, both tropical and temperate, but for the most part arid, yet abounding in peculiar forms in all the classes of animals; then come the Polynesian Islands, another luxuriant region of tropical vegetation, yet excessively poor in most of the higher groups of animals as well as in some of the lower; and lastly, we have New Zealand, a pair of temperate forest-clad islands far in the southern ocean, with a very limited yet strange and almost wholly peculiar fauna. We have now to consider the general features and internal relations of the faunas of each of these sub-regions, together with any external relations which have not been discussed while treating the region as a whole.
I. Austro-Malayan Sub-region.
The central mass on which almost every part of this sub-region is clearly dependent, is the great island of New Guinea, inhabited by the Papuan race of mankind; and this, with the surrounding islands, which are separated from it by shallow seas and possess its most marked zoological features, are termed Papua. A little further away lie the important groups of the Moluccas on one side and the Eastern Papuan Islands on the other, which possess a fauna mainly derivative from New Guinea, yet wanting many of its distinctive types; and, in the case of the Moluccas possessing many groups which are not Australian, but derived from the adjacent Oriental region. To the south of these we have the Timor group, whose fauna is clearly derivative, from Australia, from Java, and from the Moluccas. Lastly comes Celebes, whose fauna is most complex and puzzling, and, so far as we can judge, not fundamentally derivative from any of the surrounding islands.
Papua, or the New Guinea Group.—New Guinea is very deficient in Mammalia as compared with Australia, though this apparent poverty may, in part, depend on our very scanty knowledge. As yet only four of the Australian families of Marsupials are known to inhabit it, with nine genera, several of which are peculiar. It also possesses a peculiar form of wild pig; but as yet no other non-marsupial terrestrial mammal has been discovered, except a rat, described by Dr. Gray asUromysaruensis, but about the locality of which there seems some doubt.[13]Omitting bats, of which our knowledge is very imperfect, the Papuan Mammals are as follows:—
We have here no sign of any approach to the Mammalian fauna of the Oriental region, for thoughSushas appeared, the Muridæ (rats and mice) seem to be wanting.
In Birds the case is very different, since we at once meet with important groups, either wholly, or almost peculiar to the Papuan fauna. According to a careful estimate, embodying the recent discoveries of Meyer and D'Albertis, there are 350 species of Papuan land-birds comprised in 136 genera. About 300 of the species are absolutely peculiar to the district, while 39 of the genera are exclusively Papuan or just extend into the Moluccas, or into North Australia where it closely approaches New Guinea. In analysing the genera we may set aside 31 as having a wide range, and being of no significance in distribution; such are most of the birds of prey, with the generaHirundo,Caprimulgus,Zosterops; and others widely spread in both the Oriental and Australian regions, asDicæum,Munia,Eudynamis, &c. Of the remainder, as above stated, about 39 are peculiar to the Papuan fauna, 50 are characteristic Australian genera; 9 are more especially Malayan, and as much Australian as Oriental; while 7 only, appear to be typically Oriental with a discontinuous distribution, none of them occurring in the Moluccas.