THE PALEOGEOGRAPHICAL RELATIONS OF ANTARCTICA.1

By CHARLES HEDLEY, F.L.S.,

Assistant Curator of the Australian Museum, Sydney, New South Wales.

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 an 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 paleontology for important and far-reaching generalizations, 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 around 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 southward.

First, it was realized 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, vol. 4, 1845, p. 137.)

The relations of a southern fauna linking Australasia to South America were sketched firm and clear by a master hand in Prof. Huxley's essay on the classification and distribution of the gallinaceous birds. (Huxley, Proc. Zool. Soc. 1868, p. 294.)

1 Reprinted by permission from the Proceedings of the Linnean Society of London, session 124, 1911-12. Read June 6, 1912.

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 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, vol. 29, 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 mollusca induced Ancey to subscribe to these suggestions. (C. F. Ancey, Journ. de Conch., vol. 49, 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, vol. 4, 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 emphasized 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 paleontological history would be incomprehensible. (Compt. Rend., vol. 141, 1905, p. 806.)

From a study of the fresh-water 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., vol. 9, 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 traveled 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, vol. 2, 1909, p. 467.) A full bibliography is included in this article.

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

2. ARGUMENT.

The distribution records of recent and fossil species upon which the generalizations 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:

I.

That decadent groups were expelled from their original seats by more vigorous competitors; retreating from a northern center 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," vol. 1, 1876, p. 398; Pfeffer, Zool. Jahrb. Suppl. vol. 8, 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

1 While this article was in the press there reached me an important memoir by Dr. Pilsory on "The Non-Marine Mollusca of Patagonia." (Rep. Princeton Univ. Exped. Patagonia, I, 1912, pt. v, pp. 513633.) My friend considers Antarctica rather as a road for migration, especially an American exit, than as a center 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 southeastwardly 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.

southern forms in question became more alike and more numerous proceeding south. Thus radiation rather than convergence is indicated.

II.

That birds, winds, or circumpolar currents, by a process of picking up and setting down passengers from the continents or islands by the way, established a uniformity of fauna and flora. Thus, Dr. Michaelson writes (Journ. West. Aust. Nat. Hist. Soc., vol. 5, 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 Oligochata, 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, vol. 2, 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 feet to 1,000 feet 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 can not account for the transference of Oligochata from the various land surfaces of this subantarctic region." (Benham, "Subantarctic Islands of New Zealand," vol. 1, 1909, p. 254.)

III.

That a trans-Pacific continent conveyed to New Zealand, Australia, and South America a common stock otherwise recognized as the Antarctic element. (Hutton, Proc. Linn. Soc. N. S. Wales, vol. 21, 1896, p. 36; Baur, "American Naturalist," vol. 31, 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 Chile 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 midPacific 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 birds, platyrhine monkeys, hystricomorph rodents, edentates, or notoungulates. Dr. von Jhering explains (Trans. N. Z. Inst, vol. 24, 1891, p. 431, and N. Jahrb. f. Mineralogie, etc., Beil.-Bd., vol. 32, 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 Chile, Argentina, and southern Brazil. The northern area, called "Archiguyana," embraced northern Brazil, Venezuela, and Guiana.

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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 organized 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 traveled 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 southward, more groups successively appear, till ultimately Tasmania has, as Prof. 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