by Charles Hedley (1912)
[[p. 80]] 1. INTRODUCTION.
Testimony in support of alteration in temperature and contour of Tertiary Antarctica is almost wholly based on a comparison of the living fauna and flora of surrounding countries. While biologists in general, led by Wallace, Sclater, and Hutton, opposed the idea of an extended and habitable Antarctica, geographers hesitated to adopt a hypothesis the arguments for which lay in a foreign field. But of late years most of those engaged in its discussion have been supporters of extension, so that the theory has advanced from the position of a disparaged heresy to that of an established view.
Accustomed to rely on biological evidence, in the form of palæontology, for important and far-reaching generalisations, geology may now accept from biology this theory of former Antarctic extension. Thereby is acquired a correlation of climate, of time, and of continental change, while incidentally a new light is thrown on the question of the permanence of ocean basins.
It seemed nothing unusual to find a similar fauna and flora, even to the extent of a large proportion of identical species, on the subantarctic islands all round the world. But collectors working in south temperate and even in south tropical zones were surprised to find related species and genera in opposite hemispheres. This correspondence is more pronounced in primitive groups and grows clearer southwards.
First, it was realised when the famous botanist Sir J. D. Hooker pointed to the distribution of the southern pines as indicating a common origin (Hooker, 'London Journal of Botany,' iv. 1845, p. 137).The relations of a southern fauna linking Australasia to South America were sketched firm and clear by a master hand in Professor Huxley's essay on the classification and distribution of the gallinaceous birds (Huxley, Proc. Zool. Soc. 1868, p. 294).
According to Ortmann, first Rütimeyer definitely proposed radiation from Antarctica as the solution of the problem (Rütimeyer, 'Ueber die Herkunft unserer Thierwelt,' 1867, p. 15).
Our knowledge of this subject was much advanced by Dr. H. O. Forbes (Forbes, Roy. Geogr. Soc. Suppl. Papers, iii. 1893). Starting from the fossil avifauna of the Chatham Islands, he reviewed the community of southern faunas and interpreted it by [[p. 81]] antarctic distribution. As the means of dispersal he mapped a vast continent stretching continuously from Madagascar to South America and Fiji during the "northern glacial epoch."
It was suggested by the present writer that a far smaller area of continental land, of an earlier date and of unstable form, was indicated by its surviving refugees (Hedley, Proc. Roy. Soc. N. S. Wales, xxix. 1896, p. 278); and that the last Antarctic phase as reflected by these might be expressed in arms reaching on one side to Tasmania, on the other to Cape Horn, while previous phases may have been represented by other rays extending to New Zealand, Madagascar, Ceylon, and perhaps South Africa.
A study of terrestrial and fluviatile molluscs induced Ancey to subscribe to these suggestions (C. F. Ancey, Journ. de Conch. xlix. 1901, p. 12).
Dr. Ortmann, while investigating the South American Tertiary Invertebrates, accepted my amendments to Forbes's proposition. To a clear exposition of the subject he added a map and bibliography ('Report Princeton University-Expedition to Patagonia,' iv. pt. 2, 1902, pp. 310-324).
The distribution of southern earthworms was discussed by Prof. W. B. Benham (Proc. Austr. Assoc. Adv. Sci. 1902, pp. 319-343). In his opinion the Acanthodrilids, a primitive group, originated in New Zealand and spread by way of Antarctica to South America. He emphasised the fact that the union they indicated between Antarctica and New Zealand was not synchronous with the Australian connection.
Examining the mammalian fauna A. Gaudry considered that unless Tertiary Patagonia was united to Antarctica its palæontological history would be incomprehensible (Compt. Rend. vol. cxli. 1905, p. 806).
From a study of the freshwater crustacea of Tasmania, Mr. Geoffrey Smith concludes that certain elements of this fauna "reached their present range by means of an Antarctic connection between the southernmost projections of Australia, South America, and New Zealand" (Trans. Linn. Soc. Lond. Ser. 2. Zool. ix. 1909, p. 67). His analysis revealed the presence in Tasmania of another element which he derived from the northern hemisphere and which he supposed to have travelled down the Andean chain and crossed to Australasia by the Antarctic route.
Summing up a biological examination of the southern islands of New Zealand, Prof. C. Chilton concludes: "The evidence pointing to former extensions of land from the Antarctic continent northward, and to the warm climate that was enjoyed by this continent in early Tertiary times, seems to offer a fairly satisfactory explanation of the facts before us" ('Subantarctic Islands of New Zealand,' ii. 1909, p. 467). A full bibliography is included in this article.
[[p. 82]] Finally, Osborn describes the hypothetical reconstruction of Antarctica as "one of the greatest triumphs of recent biological investigation" ('The Age of Mammals,' 1910, p. 75).1
The distribution records of recent and fossil species upon which the generalisations of the foregoing authors depend have never been denied. Indeed, they continue to increase with the progress of science.
To other, and usually earlier, authors these views presented two insuperable difficulties. One is the extreme change in climate which formerly permitted temperate and subtropical animals and plants to exist where cold is now so intense. The other is the demand for the existence of Tertiary land where an ocean now extends so broad and deep as that between Antarctica and Tasmania or New Zealand.
To evade these difficulties and yet explain existing distribution the following three alternatives have been advanced.
That decadent groups were expelled from their original seats by more vigorous competitors; retreating from a northern centre to the ends of the earth, such groups divided into fugitive parties which converged as southern lands approached the pole. Or discontinuous distribution in southern continents were simply considered remnants of a former universal distribution (Wallace, 'The Geographical Distribution of Animals,' i. 1876, p. 398; Pfeffer, Zool. Jahrb. Suppl. viii. 1905, pp. 407-442).
But whereas, under the circumstances postulated, the northern wanderers would be expected to diminish and to vary as they receded, the southern forms in question became more alike and more numerous proceeding south. Thus radiation rather than convergence is indicated.
That birds, winds, or circumpolar currents, by a process of picking up and setting down passengers from the continents or [[p. 83]] islands by the way, established a uniformity of fauna and flora. Thus Dr. Michaelson writes (Journ. West. Aust. Nat. Hist. Soc. v., July 1908, p. 13): "There is no need for the supposition of an ancient great Antarctic continent which connected Australia and South America as some scientific men still suppose. Certain littoral Oligochæta consisting of euryhaline forms, for which the salt sea is no barrier, can be transported by the west wind drift over the stations on the different islands lying between one continent and another."
The flora of the circumantarctic islands, as instanced by Kerguelen, was thought by W. Schimper to have been conveyed by sea birds and ocean drift (Schimper, Wissenschaft. Ergebn. Valdivia, ii. 1905, p. 75). Although this might apply to species which recur through several archipelagoes, such would not explain the presence of endemic plants and on Kerguelen the occurrence of an endemic snail, Amphidoxa hookeri.
Such transport accounts only for a wide range of individual species capable of air or water carriage. It has doubtless been a small but real factor in distribution. But it does not account for the existence of related and representative species, for the subtropical element, or for the species incapable of such conveyance. Prof. W. B. Benham raises the objection that a species might drift yet never land:--"When I stood at the top of the sheer cliffs, some 500 ft. to 1000 ft. in height, which form the whole of the west coast of Auckland Island, and saw the tremendous breakers which even in moderately calm weather dash with incredible force against the rocks, I was more than ever convinced that the 'west-wind drift' cannot account for the transference of Oligochæta from the various land surfaces of this subantarctic region" (Benham, 'Subantarctic Islands of New Zealand,' i. 1909, p. 254).
That a trans-Pacific continent conveyed to New Zealand, Australia, and South America a common stock otherwise recognised as the Antarctic element (Hutton, Proc. Linn. Soc. N. S. Wales, xxi. 1896, p. 36; Baur, 'American Naturalist,' xxxi. 1897, p. 661).
This alternative seems the weakest. Had a trans-Pacific bridge really disseminated the species under discussion, then they should be best developed in the central remaining portion (for instance, in Tahiti or Samoa) and least at the extremity (as in Chili or Tasmania). Actually the reverse is the case: South America is the most closely associated with Tasmania, then New Zealand is less so, and the Mid-Pacific islands not at all.
Those who consider the demand for land between Tasmania and Antarctica as exorbitant are not consistent in asking so much larger a grant in the Pacific.
Another difficulty is why that South American contingent which flooded Tertiary Antarctica, and then Australia, failed to include such characteristic South American fauna as the humming- [[p. 84]] birds, platyrhine monkeys, hystricomorph rodents, edentates, or notoungulates. Dr. von Jhering explains (Trans. N. Z. Inst. xxiv. 1891, p. 431; and N. Jahrb. f. Mineralogie, &c. Beil.-Bd. xxxii. 1911, p. 176, pl. v.) that two former subcontinents, of late mesozoic or early tertiary age, are now fused in the present South America. Before the rise of the Andes these were separated from each other by a broad sea and maintained distinct fauna and flora. The southern tract, which he calls "Archiplata," comprised what is now Chili, Argentina, and Southern Brazil. The northern area, called "Archiguyana," embraced Northern Brazil, Venezuela, and Guiana.
It was from Archiplata that the last phase of Antarctica had its American derivatives, and that at a time when many forms now regarded as typically South American had not yet reached Archiplata. Not until after Antarctica was released from Archiplata did the latter join Archiguyana, and then the southern fauna suffered the usual fate from the incursion of the more highly organised northern types.
3. THE AUSTRAL FAUNA AND FLORA.
More space than is here available would be required to enumerate the Antarctic refugees in austral lands. A few of the more striking instances are now selected.
Recent marsupials are restricted to Australasia and to the Americas, the monotremes to the former. It seems to have been assumed generally that marsupials necessarily had a European origin and travelled across Siberia to North America. A shorter connection between Western Europe and South America by way of Archhelenis is at any rate worth debate. Had the entry to Australia been by the Malay Archipelago, as opponents of the Antarctic hypothesis advance, then stragglers by the way should have lingered in the East Indies. In Australasia marsupials and monotremes are least developed in the north; proceeding southwards more groups successively appear till ultimately Tasmania has, as Professor Spencer expressed it, "a condensation of most that is noteworthy in the Australian region" (Spencer, Proc. Austr. Assoc. Adv. Sci. 1892, p. 106). Indeed, the most convincing proof of the Antarctic theory is the fact that in Australasia the South American affinities regularly increase as Tasmania is approached and there attain their maximum. Those who deny marsupial migration across Antarctica are obliged to assume that the Thylacinidæ were independently evolved in each hemisphere. That Tasmania was the point of entry is supported by the discovery in Tasmania of the earliest fossil Australian marsupial. This, Wynyardia bassiana, is apparently one of the Phalangeridæ, but the unique example is too imperfect for positive identification (Spencer, Proc. Zool. Soc. 1900, p. 776). [[p. 85]] Local geologists class the stratum in which it occurred as Eocene, but English and American geologists are less disposed to grant these beds such antiquity.
If marsupials had not been available, the case could have been made as clear from herpetological evidence. And, indeed, were the vertebrata disregarded, the hypothesis could still be as well established from the invertebrata or the plants.
Among the reptiles, fifty genera of the Iguanidæ are known, all of which are confined to the New World, chiefly South America, except one genus in Fiji and two in Madagascar. Australian snakes are divisible into the venomous and the non-venomous groups. All the venomous are of the family Elapidæ, related to South American types; they focus in Tasmania, where non-venomous snakes are absent. The non-venomous snakes are of Asiatic or Papuan affinity, and focus in North Queensland. The majority of Australian frogs are also akin to South American forms.
A family of large snails, conspicuous for the size and beauty of the shell and distinct in structural features, called by Dr. Pilsbry the Macroogona, has the following distribution:--In South America, chiefly tropical, Macrocyclis 1 species, Strophochilus 51 species, and Gonyostomus 5 species; in Madagascar, Ampelita 54 species and Helicophanta 16 species; in the Seychelles, Stylodonta 2 species; in Ceylon, Acavus 7 species; in the Moluccas, Pyrochilus 4 species; in Tasmania, Anoglypta 1 species and Caryodes 1 species; in Eastern Australia, Pedinogyra 1 species and Panda 4 species. The Chilian Macrocyclis and the Queensland Pedinogyra by shell characters pair together, while Helicophanta is a match for Panda. The absence of this family from New Zealand, its preponderance of species in Madagascar, of genera in Tasmania with Australia, and its development in the tropics are remarkable characters of this old austral group.
The snail family Bulimulidæ is characteristic of South America, beyond which two genera stray into the West Indies and North America, and two others, Bothriembryon and Placostylus, occur in Australasia. The first ranges from Tasmania to West Australia, and forms an exception to Antarctic rule by having its distribution centre in the latter. Indeed, Bothriembryon and the fluviatile crustacean Chæraps raise a suspicion that West Australia had direct relations with Antarctica, prior to and independent of the Tasmanian Isthmus. Placostylus extends from New Zealand to Fiji and New Guinea, "giving testimony," as Pilsbry remarks, "to the former existence of an Antarctic land connecting the austral continents of the two hemispheres" (Man. Conch., Index, vols. x.-xiv. 1902, p. ix).
The Buprestidæ, a family of large and handsome beetles, exhibit a striking affinity between Australia and South America. So [[p. 86]] much so that, opposed as Wallace was to the Antarctic connection, he here conceded that some exchange between the two areas was required. He thought that it took the form of larvæ in floating timber drifting round the antarctic seas in a warm period.
Among early Tertiary vegetation brought from Seymour Island in the Antarctic by Dr. Nordenskjöld's expedition, Dusén has recognised a species of Fagus and an Araucaria like A. brasiliensis (Schwedische Sudpolar. Exp., Bd. iii. Lief 3, 1908). In the light of this discovery the range of the living species of these genera acquires an importance for the student of the Antarctic hypothesis. The distribution of the beech trees is a particularly interesting one, for on the principle of Antarctic extension it is simple and intelligible, but without it is complicated and inexplicable.
This genus Fagus, sensu latu, has two representatives in Europe, one in North America, and several in China and Japan. But in South America there are eleven, in New Zealand seven, and in Tasmania with Australia three. The northern forms are deciduous, but with one or two exceptions the southern are evergreen. The genus being a natural one is certainly not of polyphyletic origin, and the question before us is, from what centre of migration has it spread? Did the southern species radiate from the south or converge from the north? It is a strong argument for a southern origin that the bulk of the species are southern. Again, the evergreen state is primitive, the deciduous derived, and this indicates that the northerners are offshoots from an evergreen stock. Thirdly, the southern species more closely resemble each other than any northern does any southern form. Even, as Mr. Rodway (Proc. Austr. Assoc. Adv. Sci. 1912) points out, the same parasite afflicts Tasmanian and South American trees. This agrees better with radiation from the south than with convergence from the north.
Another aspect of Antarctic distribution is presented by the genus Araucaria. None of the fifteen existing species reach the northern hemisphere, so the complication of a boreal factor is absent. It is chiefly subtropical and characterises a zone external to that of Fagus. In South America there are three species, in New Caledonia eight, in Norfolk Island one, in New Guinea one, and in Australia two. The latter pair are unlike each other, but one, A. bidwilli, from Queensland, stands very close to the Chilian A. imbricata. This indicates that the genus had already differentiated almost to its present extreme before the migration route between Australia and South America had closed. The large and heavy seeds of these trees possess no floating power and are unfitted for dispersal by birds. As Dr. Guppy remarks of the Fijian Kauri pine, "they may well be cited in support of any continental hypothesis" (Guppy, 'Naturalist in the Pacific,' ii. 1906, p. 301).
The preponderance of Araucaria in the Pacific is enforced by a [[p. 87]] related genus Agathis. If statistics carry a meaning, Fagus would seem to have come to Australasia from America, while Araucaria made the reverse journey.
The remarkable and well known genus Fuchsia includes sixty-nine species. Four of these are natives of New Zealand, the rest inhabit South America, Mexico, and the West Indies. These figures are almost exactly reversed for the shrubby evergreen Veronicas, plants conspicuous in any New Zealand landscape, totally absent from Australia or Tasmania, and represented by a few stragglers in South America and Fuegia.
If it be resolved that the community of austral life is explicable only by former radiation along land-routes from the south polar regions, we reach a position to probe deeper into the intricacies of the problem.
In the scheme propounded by Dr. H. O. Forbes, the austral forms inhabited one vast continent, nearly a third of the southern hemisphere, at the same (?Pleistocene) time. But an analysis of the fauna in question shows that some groups avoid Tasmania and others avoid New Zealand. Clearly the Antarctica that supplied Australia with an abundant fauna of marsupials, monotremes, snakes, frogs, and so on, was not in touch with New Zealand, where these animals are conspicuously absent. Benham has emphasised the fact that the Acanthrodrilids, Antarctic earthworms, failed to reach Tasmania. When they, the fuschias and other associates, spread backwards and forwards from New Zealand to South America, it is equally clear that the road to Tasmania was barred to them. Iredale remarks (Proc. Malac. Soc. ix. 1910, p. 160) that the Antarctic element in the New Zealand Polyplacophora, a marine molluscan group, is distinct from that which reached Tasmania from the south. The differences are both positive and negative, and are not due merely to the more southern latitude of New Zealand preserving a larger proportion of cold types. When circumstances allowed Iguanidæ to wander from South America in two genera to Madagascar and in another to Fiji, the Australian road was apparently closed to them.
It becomes increasingly apparent that the Antarctic source of austral life was not simple but compound. This complexity has probably been the chief hindrance to its recognition. The problem before us is:--Was the complexity that of time or space, or both?
Shall we suppose, for instance, that at the close of a glacial period an Antarctic continent bare of life received a fauna and flora from one neighbour, then developed and transmitted it to another? That a subsequent glaciation swept all life away from the polar area? That a warm interglacial period succeeded when another transfer, but between different neighbours, took place? [[p. 88]] So that the fauna of New Zealand might represent the life of one interglacial antarctic phase and that of Australia another.
Or shall we consider that Tertiary Antarctica was an archipelago, the islands of which carried such different fauna and flora that emigrants from one quarter differed from those of another. It is not yet known whether the area between King Edward VII. Land and Graham Land is a lobe of the continent or an archipelago, or an independent island (Darwin, Proc. Roy. Soc. A. vol. lxxxiv, 1910, p. 420; and Mawson, Geogr. Journ. xxxvii. 1911, map, p. 613). In the latter case it is possible that King Edward VII. Land may have joined New Zealand, while Tasmania was separately linked to South Victoria Land. Under these circumstances New Zealand and Tasmania may have simultaneously imported an Antarctic and yet a different fauna and flora.
Or both conditions of interglacial succession and insularity may have combined in the past to produce present effects.
Prof. H. Pilsbry has shown (Proc. Acad. Nat. Sci. Philad. 1900, p. 568) that the land molluscan faunas of the Marquesas, Hawaii, and Society Islands are closely related, and that though of primitive type they are harmonic such as befits continental land, not a drift selection such as oceanic islands have. He proposes them as witness to the existence of a Palæozoic or early Mesozoic land mass. The tree-lobelias also testify to the antiquity and association of these distant Pacific archipelagoes (Guppy, 'A Naturalist in the Pacific,' ii. 1906, p. 250). Their relations are with the alpine floras of South America and Equatorial Africa. A third of the mountain flora of Hawaii is derived from high southern latitudes. It is now suggested that these primitive continental plants and animals reflect a meridional Pacific land-ray, the first visible vestige of Antarctic extension, as Tasmania was the last. To carry a cold flora across the Equator the land must have been lofty and continuous. In such a range some might see the rib of a former tetrahedral world.
As the Eocene was both a warm period and a time when land was largely developed in the Patagonian area, it is likely that the Archiplatan fauna then or earlier entered Antarctica. If the Tasmanian fossil Wynyardia is rightly dated Eocene, then during that age some at least of the American migrants reached Australia.
Whereas New Zealand in its relation with South America, via Antarctica, appears both as a giver and a receiver, Australia, on the contrary, seems to have made no return to South America, but to have received all and given nothing.2 No Eucalypts, for instance, crossed from Tasmania to Patagonia. One explanation [[p. 89]] may be that Australia was then too poor to afford emigrants. Another and more probable explanation is that Antarctica having received a fauna and flora from Archiplata was severed from it before joining Australia. Thus a stream of migration would be forced forward and checked backwards.
The austral fauna and flora appears extending in successive zones from the far south to the tropics. In New Zealand the warmth-loving plants and animals, such as the Kauri pine (a relation of Araucaria) and Placostylus snail, have been thrust to a northern refuge, while diminished temperature has probably exterminated others. The Araucaria and iguanas, the freshwater fish Osteoglossum, are examples of tropical austral forms of which a long list could be compiled.
It is unlikely that the Antarctica that bore this tropical and subtropical assembly reached much more broadly to the tropics than does the present continent. Had it done so, more traces would have been left of such extension in the South Sea Islands on the one side or in South Africa on the other.
But if the subtropical flora and fauna had in the Tertiary extended unbroken across the pole from Fuegia to Tasmania, what then became of the ancestors of the present subantarctic and south alpine life? Why were not these frigid forms driven from off the face of the earth when the heart of the Antarctic itself enjoyed a genial climate?
The discovery by Sir E. Shackleton of a plateau 10,000 feet high near the south pole, suggests a solution of the difficulty. If such a plateau existed when the climate was at its warmest, then the tropical migrants could have found a congenial climate on the coast, while the ancestors of the Kosciusko and Kerguelen plants and animals took refuge on the plateau heights. The inference is that such a plateau did then exist.
If the land-connection between the Antarctic and Tasmania had broken down during the warmest period of the interglacial phase, it would have isolated the flora and fauna at a time when the cold elements were gathered together on the central plateau heights, while the temperate and subtropical elements possessed the Antarctic periphery. In that case the cold forms would have had no opportunity to escape to the alpine stations of New Zealand or Australia, or to occupy the subantarctic islands.
The conclusion is therefore drawn that the land link was maintained during the period of refrigeration, and that from the Antarctic focus first the subtropical, then the temperate, lastly the alpine forms were expelled, each to gain a fresh footing in lower latitudes.
Possibly associated with the formation of great ice masses, a paroxysm of diastrophic energy ensued. This, which perhaps has not yet subsided, effected the destruction of the antarctic bridge, and to it may be due the recent disarticulation of the Dominion [[p. 90]] of New Zealand and the severance of Tasmania from its parent continent.
In the long perspective of past time Antarctica appears to fade and form like a summer cloud, now extending a limb, now shedding it, now resolving into a continent, now dissolving into an archipelago. At present it lies dead and cold under its white winding-sheet of snow. By the light of the magician's lamp we watch the summer of the cycles dawn. The glow of life returns, the ice mask melts, green spreads a mantle. At last a vision comes of rippling brooks, of singing birds, of blossoming flowers and of forest glades in the heart of Antarctica.
1. While this article was in the press,
there reached me an important memoir by Dr. Pilsbry on "The Non-Marine
Molluscs of Patagonia" (Rep. Princeton Univ. Exped. Patagonia, iii. 1912,
pt. v. pp. 513-633). My friend considers Antarctica rather as a road for
migration, especially an American exit, than as a centre of evolution.
He takes exception to my derivation of Australian Acavidæ from Antarctica,
and suggests that the group arose in Gondwana Land. On reconsideration
I would still maintain that the south-eastwardly increasing distribution
of Australian Acavidæ indicates their immediate Antarctic origin.
But previous to an Antarctic sojourn the group may have been Gondwana
bred. This memoir heightens the resemblance between east and west. Gundlachia,
Diplodon, and Radiodiscus are common, Petterdiana
scarcely differs from Littoridina, and Potamolithis
appears to have Tasmanian relatives. [[on p. 82]]