The Origin of Continents and Oceans/Chapter 5

by Alfred Wegener

CHAPTER V

PALÆONTOLOGICAL AND BIOLOGICAL ARGUMENTS

The palæontological and biological proofs of a former connection of the continents under consideration are extremely numerous, so much so that it is impossible to give a statement on them in the compass of the present book. Meanwhile these matters have already often been dealt with in their relation to the geographical distribution of plants and animals, especially by the adherents of the land-bridge hypothesis, so that only a general reference to the literature will be given.^[1] Therefore we can confine ourselves to a general synopsis and the selection of a few especially important facts.

The question whether a connection has prevailed between two continents will frequently be answered in different ways by specialists in different directions, because each of them tends to generalize the results of his own particular field of research. It was therefore a happy thought of Arldt, when trying to obtain a synopsis on broader lines, to take a vote on each land-bridge and each period from the various specialists. It goes without saying that this procedure gives rise to many uncertainties. But any other way seems scarcely possible, because of the vast amount of the material facts. The results also appear to justify his method. For the purpose he made use of the papers or maps of Arldt, Burckhardt, Diener,

Australia–Africa
(Deccan, Madagascar). Africa–South
America. India–Madagascar. Europe–North
America. Tierra del Fuego–
West Antarctica. Australia–East
Antarctica. North America–
South America. Alaska–Siberia.   + − + − + − + − + − + − + − + − Lower Cambrian 2 2 1 2 5 2 2 5 5 Upper 3 1 3 1 3 6 3 3 6 6 Lower Silurian 5 4 1 5 6 1 4 4 4 3 1 6 Upper 5 4 1 5 6 1 4 4 1 7 1 6 Lower Devonian 5 4 1 5 6 4 4 3 3 2 4 Middle 5 1 5 1 5 1 7 1 1 4 1 4 4 4 1 7 Upper 2 2 2 3 1 1 1 2 3 Lower Carboniferous 5 5 4 6 1 3 4 1 7 7 Middle 5 5 5 7 1 3 4 7 2 5 Upper 6 6 6 8 5 5 8 2 6 Lower Permian 3 3 3 3 1 1 2 1 2 1 2 2 1 Middle 1 1 2 2 1 2 2 2 1 2 2 1 Upper 2 1 3 3 1 2 3 3 2 1 3 Lower Trias 4 1 4 1 5 4 1 1 3 4 3 3 5 Middle 4 4 4 5 3 3 2 3 4 Upper 5 2 5 1 6 4 3 1 4 5 8 8 Rhætic 2 2 2 3 1 1 2 2 Lias 2 3 5 5 4 4 4 6 4 2 Inferior Oolite 1 3 4 4 2 1 3 2 4 3 1 Great 3 3 3 2 2 1 2 3 1 2 Upper Jurassic 5 5 5 6 4 1 3 7 6 Wealden Lower Cretaceous 6 4 2 6 5 3 1 4 2 3 8 7 WealdenAlbian 1 1 1 1 1 1 1 1 2 Middle 5 1 4 6 1 5 1 4 1 4 3 4 2 5 Upper 7 2 5 8 7 1 1 6 1 6 4 6 4 6 Lower Eocene 6 3 3 1 5 5 2 6 3 3 2 5 7 1 Upper 6 1 5 1 5 6 2 2 4 1 5 8 7 1 Oligocene 4 4 2 2 4 2 1 4 4 6 7 Miocene 6 6 1 4 4 4 1 6 6 2 6 7 1 Pliocene 3 3 3 2 2 1 3 3 4 3 1 Quaternary 3 3 3 1 3 3 3 4 3  

Frech, Fritz, Handlirsch, Haug, Ihering, Karpinsky, Koken, Koszmat, Katzer, Lapparent, Matthew, Neumayr, Ortmann, Osborn, Schuchert, Uhlig and Willis. The table on p. 74 shows an extract from Arldt’s statistics, and the first four land-bridges are illustrated by curves in Fig. 15.

Fig. 15.—Votes on the question of the four post-Cambrian land-bridges.

The number of favourable votes is shown by the upper thick curve, the number of unfavourable votes by the lower thick curve. The difference is simply shaded if favourable; cross-hatched if unfavourable.

In this, three curves are drawn for each land-bridge, namely, for the number of votes in favour, of those in opposition, and of the difference, the latter thus giving the strength of the majority; this is emphasized by shading on the area concerned. These four early land-bridges are those extending over present-day oceanic areas, and are of special interest to us. The result, as is seen, is very clear in its broadest outlines in spite of many differences of opinion. The connection between Australia and India (united with Madagascar and South Africa) disappeared soon after the beginning of the Jurassic period; the connection between South America and Africa disappeared in the Lower to Middle Cretaceous; and the connection between India and Madagascar disappeared at the transition from Cretaceous to Tertiary. At all three places a land connection had prevailed from the Cambrian period until these points of time. The connection between North America and Europe was vastly more irregular. But nevertheless here also, in spite of the frequent differences, there exists a far-reaching agreement of views. The connection was repeatedly disturbed in the more ancient periods, namely, in the Cambrian and in the Permian, as well as the Jurassic and Cretaceous, but obviously only by transgressions, which later permitted the restoration of the continuity. The final breaking off of relations, which corresponds to the present-day separation by a broad ocean, can only first have happened in the Quaternary.

Of entirely different value are the two separations that we shall next discuss, which are concerned with the connections of the Antarctic with Patagonia on one side, and with Australia on the other. The strong majority of negative votes in this case evidently originates from the slightness of our knowledge concerning Antarctica, which has induced many authors to disregard a connection of this continent with the others, since no reason existed for such an hypothesis. Because of this, only the positive proportion of the votes will be considered. These seem to show that in the Drake Straits an exchange of forms took place chiefly from the Cretaceous up to the Pliocene, as well as at various times previously, and between Australia and the east of Antarctica particularly from the Jurassic up to the Eocene.^[2] Moreover, it is to be noticed that the very numerous faunal affinities of Australia to South America, which obviously used Antarctica as a bridge, but which up to now have not been found there, are not considered by Arldt, and his table on the whole is naturally not drawn up in the form most suitable for our purpose.

Both the remaining separations in our table give bridges near areas in which the blocks are still to-day connected, namely, the Central American bridge and that across the Bering Straits. Bridges of this sort naturally play no rôle in the displacement theory, since the previous ideas of a temporary emergence and re-submergence by shallow seas are not changed. The two bridges are really only mentioned as examples to remove certain misunderstandings. The study of maps shows that the present connection of the blocks between South and Central America does not at all depend on accidental contact. These blocks have rather been attached to each other from the most ancient periods, even if they have been temporarily submerged, as indicated in our table. Apparently the connection was above water in the Silurian and Devonian, again in the Permian to Middle Trias, still again in the Cretaceous, and—this is uncontested—after the Miocene. The continuous connection of the blocks is in no way contradictory to the fact that South America detached itself from Africa before North America did from Europe, particularly if the great plastic deformations which Central America must have undergone are borne in mind. The movement of South America consisted to a great extent in a rotation. A similar state of affairs applies to the connection of the blocks at the Bering Straits. Diener’s objection, already mentioned, “Whosoever pushes North America on to Europe breaks its connection at the Bering Straits with the Asiatic continental block,”^[3] is only met with in a Mercator’s map, but not on a globe, for the movement of North America consists essentially of rotation. At this point the blocks were never torn away from each other, and the bridge lay above water in the Silurian and Devonian, again in the Middle Carboniferous to the Middle Permian, then in the Lias and Middle Jurassic (Dogger), and finally from the Cretaceous to the Quaternary, when it was probably partially obstructed by the ice.

Let us now proceed to a discussion of the Atlantic rift from the biological point of view. The Atlantic is generally considered to be young in comparison to the Pacific. Ubisch writes: “In the Pacific Ocean we find numerous ancient forms, as Nautilus, Trigonia, ear-seals. These forms are absent in the Atlantic Ocean.”^[4] W. Michaelsen drew my attention to the fact that the present distribution of earth-worms offers particularly unobjectionable evidence of the former Atlantic land connection, because usually the sea is an insurmountable obstacle to these animals.^[5] A singularly large number of threads of affinity are spun by them across the Atlantic Ocean in the various latitudes. In the South Atlantic these relations refer more to the older periods (Chilotacæ, Glossoscolecinæ-Microchatinæ, Ocnerodrilinæ, the earlier Microchætinæ, Trigastrinæ), whilst the North Atlantic is not only spanned by the probably older genus, Sparganophilus, but also by the undoubtedly recent genera of Lumbricidæ, which are distributed continuously from Japan to Portugal, and at the same time occur as indigenous species on the other side of the Atlantic on the east, but not on the west, of the United States.^[6]

The following table, taken from Arldt (v.s., p. 73, etc.), is very instructive on the question of the North Atlantic bridge, and indicates the percentage figures of identical reptiles and mammals on both sides:—

Reptiles.
Percentage. Mammals.
Percentage.  

Carboniferous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

64 —

Permian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12 —

Trias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

32 —

Jurassic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

48 —

Lower Cretaceous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17 —

Upper Cretaceous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

24 —

Eocene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

32 35

Oligocene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

29 31

Miocene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

27 24

Pliocene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

? 19

Quaternary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

? 30  

The run of these figures agrees very well with those given by the voting shown in Fig. 15, according to which the majority of specialists assumed land connections in the Carboniferous, in the Trias, then only in the Lower and not the Upper Jurassic, but again from the Upper Cretaceous to the lower Tertiary. The agreement in the Carboniferous is extremely well emphasized, possibly because the fauna is more completely known.^[7] The fauna of the European and the North American Carboniferous has been subjected to just as much detailed examination as the flora by Dawson, Bertrand, Walcott, Ami, Salter, Klebelsberg, and others. The last-mentioned has, in particular, referred to the faunal similarity of the intercalated marine beds in the coal-bearing strata from Donetz, through Upper Silesia, Ruhr district, Belgium, England, on to the west of North America, which is very remarkable owing to their short range of time. In these the similarity is not confined to such elements as have a world-wide distribution.^[8] We cannot go into any further details. The absence of identical species of reptiles in the Pliocene and Quaternary is a natural effect of the cold, which destroyed the old reptilian fauna. The mammals present a similar history to the reptiles from the time of their entrance into the earth’s history. The agreement was especially great in the Eocene. Thus Ubisch says: “In the Eocene we also find in Europe practically all the same sub-orders of mammals as in America. The case of other classes is similar.”^[9] The decrease in the affinities shown in our table for the Pliocene may very easily be traced to the effect of land-ice. Let us turn to the little map (Fig. 16) which Arldt has given for, the distribution of those organisms which appeared to him to be most decisive to the question of the North Atlantic bridge. The recent genera of earth-worms of the Lumbricidæ are, as already mentioned, distributed from Japan to Spain, but on the other side of the ocean only in the east of the United States. The pearl-mussel occurs on the line of fracture of the continents in Ireland and Newfoundland, and adjacent areas on both sides.

Fig. 16.—Distribution of North Atlantic organisms, after Arldt. Dotted line: garden snails. Dashes:—Lumbricus—earth-worms. Dots and dashes: perches. Shaded N.E.—S.W.: pearl-mussel. Shaded N.W.—S.E.: mud-minnows (Umbra).

The distribution of garden snails from South Germany across the British Isles, Iceland and Greenland to the American side, where they are only found in Labrador, Newfoundland and the Eastern States is still more striking. This also applies to the family of the perches (Percidæ), and other fresh-water fishes. Possibly the common heather (Calluna vulgaris), which outside Europe is only to be found in Newfoundland and the neighbouring districts, might be mentioned, and also, conversely, that many American plants are quite confined in Europe to the west of Ireland. Even if the Gulf Stream can possibly be drawn in as the explanation of the latter, this cannot be done in the case of the heather. Many things testify that the land connection from Newfoundland to Ireland remained in existence up to the beginning of the Quaternary. A second bridge, further to the north, which could hardly have been broken before the middle of the Quaternary,^[10] seems also to have been in existence.

The observations of Warming and Nathorst on the flora of Greenland are also instructive in this connection. They show that on the south-east coast of Greenland, and thus exactly on the stretch of coast which, according to the displacement theory, still lay during Quaternary times just in front of Scandinavia and North Scotland, the European elements predominate, whilst on the whole of the remaining coast of Greenland, including North-east Greenland, the American influence prevails. According to Semper, the Tertiary flora of Grinnell Land was more closely related (up to 63 per cent.) with that of Spitsbergen than to that of Greenland (30 per cent.), whilst to-day it is naturally the converse (64 and 96 per cent. respectively).^[11] Our reconstruction for the Eocene gives the solution of this puzzle, since the distance given from Grinnell Land to Spitsbergen is smaller than that between the former and the fossil localities in Greenland.

The facts regarding the South Atlantic bridge are made still clearer and simpler in Fig. 15. As Stromer, among others, emphasizes, the distribution of the Glossopteris flora, the reptilian family of the Mesosauridæ,^[12] and many other elements, forces us to the assumption of a former large continental area uniting the southern continents. Thus Jaworski,^[13] by an examination of all possible objections (which naturally are not absent here) arrived at the result: “All that is known geologically of West Africa and of South America is in complete agreement with the assumption, to which we have arrived from the study of zoögeographical and phytogeographical facts of the present and of the past, that in the earliest periods of the earth a land connection was in existence between Africa and South America in the place of the present South Atlantic Ocean.” Engler was drawn to the conclusion from phytogeographical data that “on consideration of all these relations, the occurrences adduced of common plant-types in America and Africa would best find their explanation, if we were able to show that between Northern Brazil, south-east of the estuaries of the River Amazon, and the Bay of Biafra in West Africa, there had existed great islands or a land-mass connecting the continents; and a further connection might be postulated between Natal and Madagascar, the continuation of which in a north-easterly direction towards India, which was separated from the Sino-Australian continent, has already been long asserted. Besides, the numerous affinities of the Cape flora to that of Australia make a connection with Australia by means of the Antarctic continent desirable.”^[14] The latest connections seem to have prevailed between Northern Brazil and the Guinea Coast: “West Africa has in common with tropical South and Central America the sea-cow Manatus, which lives in streams and shallow warm sea-water, but is unable to swim across the Atlantic Ocean. It is concluded from this that in the immediate past a shallow water connection has existed between West Africa and South America, probably along the northern border of the South Atlantic” (Stromer).

Naturally all these arguments are those which are also used by the advocates of the hypothesis of submerged connecting continents. But the displacement theory offers a simpler solution from the purely biological standpoint as well, because it adduces, in explanation of the distribution of plants and animals, not only a land connection, but also variations in distance of the continents concerned. The island of Juan Fernandez is, perhaps, of especial interest in this connection. According to Skottsberg, it does not show any affinities botanically with the closely adjacent coast of Chile, but only with Tierra del Fuego (by winds and sea-currents, I suppose!), Antarctica, New Zealand, and the Pacific islands. This fits in excellently with our idea that South America, drifting westwards, has, in recent times, approached it to such an extent, that the difference of floras becomes very startling. The theory of the submerged bridges could not begin to account for this phenomenon.

Likewise, the Hawaian islands have a flora which is most closely related, not to North America, which lies nearest to them, and whence winds and sea-currents arrive, but with the Old World.^[15] This appears intelligible if it is borne in mind that in the Miocene, when the North Pole lay in the Bering Straits, Hawai had a geographical latitude of 40 to 50 degrees, and thus lay in the great westerly wind-drift which came from Japan and China. Moreover, the American coast at that time was much farther removed from Hawai than it is now.

The biological relations between the Deccan and Madagascar, explained by a sunken “Lemuria,” are so well known that we shall here be content with a reference to Fig. 15, and to the work of Arldt. In this case also, the superiority of the displacement theory is again shown, since the two parts possess in their present positions a considerable difference of latitude, and have a similar climate and shelter similar forms of life only because the equator lies between them. In view of this great distance, the period of the Glossopteris flora presents us with a climatic puzzle, which, however, is solved by the displacement theory. Moreover, the whole of the Glossopteris deposits in the southern continents may be considered, not only, as already mentioned, as proof of a land connection at that period, but also as a proof of the superiority of the displacement theory as compared with that of submerged continents, for it is impossible to assume from their present position that they could all have had the same climate at every period of the earth’s history. This will, however, be still further considered in the next chapter.

We will only now discuss here the Australian animal kingdom, which appears to me to be of quite considerable importance to the question of displacement. Wallace^[16] long ago detected a clear division into three different ancient stocks, and this result has not essentially been altered by the more recent investigations, such as those of Hedley. The oldest element, which occurs mainly in the south-west of Australia, shows affinities especially with India and Ceylon, as well as with Madagascar and South Africa. Here the warmth-loving animals also are represented in the relationship, as well as earth-worms, which shun the frozen soil.^[17] This affinity originates from the time when Australia was still connected to India. According to Fig. 15, this connection had already been broken in the Lower Jurassic.

The second faunal element in Australia is very well known, for to it belong the singular mammals—the Marsupialia and Monotremata—which are so sharply differentiated from the fauna of the Sunda Islands (the Wallace-Limit of the mammals). This element of the fauna shows kindred relationships to that of South America. For example, marsupials now live not only in Australia, the Moluccas and various Pacific islands, but also in South America (a single species of opossum is found even in North America); there are also known fossil from North America and Europe, but not from Asia. Even the parasites of the Australian and South American marsupials are the same. E. Bresslau^[18] emphasizes the fact that three-quarters of the approximately 175 species of the Geoplanidæ among the flat-worms are found in these two areas. “The geographical distribution of the Trematodæ and Cestodæ, which naturally corresponds to that of their hosts, has up to now been but rarely the subject of research work. The Cestodian genus Linstowia, which is found exclusively in the South American Didelphyidæ (opossums) and in Australian marsupials (Perameles) and Monotremata (Echidna), shows that here also facts have yet to be discovered of great zoögeographical interest.” Wallace says of this affinity with South America (loc. cit. vol. i, p. 400): “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.”

The same peculiarity is shown by the whole of the remaining fauna, so that Wallace believed that the land connection of Australia-South America, if it existed at all, lay nearer the colder boundaries of these continents. The earth-worms also have not made use of this bridge. Since Antarctica is immediately indicated as the connecting link, and it lies on the shortest route, it is not to be wondered that the South Pacific bridge, proposed in its place by a few authors, which seems the nearest way on a Mercator’s map only, is rejected by nearly all.^[19] This second element of the Australian fauna thus dates from the period when Australia was still attached by Antarctica to South America, that is, between the lower Jurassic (the breaking away of India) and the Eocene (the separation of Australia from Antarctica). As the present position of Australia no longer affords isolation to these forms, they gradually encroach further and further into the Sunda Archipelago, so that Wallace had to lay his limits for the mammals between the Islands of Bali and Lombok and through the Straits of Macassar.

The third fauna of Australia is the most recent; emigrating from the Sunda Islands, it has made its home in New Guinea and has already conquered North-eastern Australia. The dingo (wild-dog), rodents, bats, and others were post-Pleistocene immigrants to Australia. The recent genus Pheretima of the earth-worms, which has displaced most of the older genera by its greater vitality on the Sunda Islands, and on the coastal areas of South-east Asia from the Malay Peninsula to China and Japan, has also completely conquered New Guinea, and has already obtained a firm foothold in the northern point of Australia. All this indicates a rapid exchange of fauna and flora which began in recent geological time.

This threefold division of the Australian fauna is in most beautiful agreement with the displacement theory. It is only necessary to glance at the three reconstructed maps (Fig. 1) in order immediately to read from them the explanation. Even these purely biological facts show the distinct advantages which the displacement theory possesses over that of the submerged bridges. The distance from the nearest points of South America and Australia, namely, Tierra del Fuego and Tasmania, amounts to-day to 80°, measured along a great circle, that is, quite as much as that between Germany and Japan. Central Argentina lies just as far from Central Australia as from Alaska, or as South Africa from the North Pole. Does one really believe that a mere land connection is sufficient to secure the exchange of forms? And how strange it is that Australia had no interchange of forms with the immediately adjoining Sunda Islands to which it is like a foreign body from another world! No one can deny that our assumption, which reduces the distance of Australia from South America to a fraction, and on the other hand separates it from the Sunda Islands by a broad ocean basin, provides a key for the explanation of the Australian animal kingdom.

1. The separate land-bridges are considered by T. Arldt, among others, in his Handbuch d. Paläogeographie, 1, Paläaktologie, Leipzig, 1917, where a copious literature of the subject is also given.
2. According to O. Wilckens, the parallel but in many respects separated bridge (New Guinea), New Zealand, West Antarctica, South America was still in existence in the Cretaceous, for the marine beds of the Upper Senonian on the east coast of New Zealand have faunal relationships with those of the west coast of South America.
3. C. Diener, “Die Groszformen der Erdoberfläche,” Mitt. d. k.k. geol. Ges. Wien, 58, pp. 329–349, 1915. The same author, “Die marinen Reiche der Triasperiode,” Denkschr. d. Akad. d. Wiss., Wien, math.-naturw. Kl., 1915.
4. L. v. Ubisch, “Wegeners Kontinentalverschiebungstheorie und die Tiergeographie,” Verh. d. Physik.-Med. Gesz. Würzburg, 1921. (Author’s copy, 13 pages).
5. Herr Michaelsen was good enough to bring up to date the little maps of his work, Die geographische Verbreitung der Oligochaeten, pp. 1–186, Berlin, 1903, and to supplement this by valuable verbal communications.
6. By a similar train of thought, Irmscher came to the conclusion in his inaugural lecture given in Hamburg on October 11th, 1919, on “Die Entstehung der Kontinente in ihren Beziehungen zur Pflanzenverbreitung,” that the latter can likewise be brought into harmony with the displacement theory. The possibilities of the wide-spread distribution of plant-seeds, for example, by storms, provides a far-reaching mingling of floras.
7. The less completely the fauna be known, the less must also be the percentage number of identical species.
8. R. v. Klebelsberg, “Die Marine Fauna der Ostrauer Schichten,” Jahrb. d. k.k. Geol. Reichsanstalt, 62, pp. 461–556, 1912, as well as communication by letter.
9. L. v. Ubisch, “Wegeners Kontinentalverschiebungstheorie und die Tiergeographie,” Verh. d. Physik.-Med. Ges. z. Würzburg, 1921.
10. R. F. Scharff, “On the Evidences of a former Land-bridge between Northern Europe and North America,” Proc. Roy. Irish Acad., 28, Sect. B., pp. 1–28, 1909.
11. M. Semper, “Das paläothermale Problem, speziell die klimatischen Verhältnisse des Eozäns in Europa und im Polargebiete,” Zeischr. Deutsch. Geol. Ges., 48, pp. 261, etc., 1896.
12. C. Diener’s objection that the Permo-Triassic vertebrate faunas of South Africa and South America are different is regarded as weak by Stromer, since that in South America is insufficiently known.
13. E. Jaworski, “Das Alter des südatlantischen Beckens,” Geol. Rundsch., pp. 60–74. 1921.
14. From the article “Geographie der Pflanzen” in the Handwörterbuch der Naturwissenschaften.
15. A. Grisebach, Die Vegetation der Erde nach ihrer klimatischen Anordnung. Ein Abrisz der vergleichenden Geographie der Pflanzen. Leipzig, 1872. Bd. 2, pp. 528 and 632.—O. Drude, Handbuch der Pflanzengeographie. Stuttgart, p. 487, 1890.
16. A. R. Wallace, The Geographical Distribution of Animals, Vol 2. London, 1876.
17. According to Michaelsen’s information, the Octochætinæ connect New Zealand directly to Madagascar and India, together with northern Further India, by an interesting skipping-over of the large Australian block lying between. But the most striking relations are shown by the numerous genera of Megascolecinæ, which connect Australia, and either the North Island of New Zealand, or the whole area of New Zealand, with Ceylon, and, in particular, Southern India, and sometimes also the north of India and of Further India (and, strange to say, occasionally the west coast of North America). The fact that the earthworms show no relationship between Australia and Africa confirms our assumption that these continents did not directly adjoin one another, but were connected only through India and Antarctica respectively.
18. E. Bresslau, Artikel Plathelminthes in Handwörterbuch der Naturwissenschaften, 7, p. 993.—Zschokke, Zentralbl. Bakt. Paras., 1, p. 36, 1904.
19. Burckhardt is almost alone in advocating the existence of such a South Pacific bridge from the Devonian to the Eocene, but he does so not on biological grounds, which, as Simroth (“Über das Problem früheren Landzusammenhangs auf der südlichen Erdhälfte,” Geogr. Zeitschr., 7, pp. 665–676, 1901), among others, has shown, cannot be adduced, but only on a geological basis. On the west coast of South America, between southern latitudes 32° and 39°, coarse porphyritic conglomerates are found which were described by previous authors as volcanic, but are considered by Burckhardt to be consolidated beach-pebbles. Since they are replaced further east by sand, Burckhardt concluded that they must represent a coast-line—in the estuarine area of a great river—from which the distribution of land and water must have been exactly the reverse of that of to-day. Simroth (vide supra), Andrée (“Das Problem der Permanenz der Ozeane und Kontinente,” Petermann’s Mitt., 63, p. 348, 1917), Diener, and Sörgel have rejected this continent of Burckhardt, and Arldt himself, one of the few adherents, had to allow that it was based on very slight evidence (“Die Frage der Permanenz der Kontinente und Ozeane,” Geogr. Anzeiger, 19, pp. 2–12, 1918). Quite another explanation must therefore be sought for Burckhardt’s observations.