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Show 3fl0 ISLAND LIFE. [PAllT 11. tropical .families, but Eeveral African genera ar~ represent_ed by peculiar species, and there are also some spec~es bel?ngi?g to two American genera of the Iguanidro, a fam1ly whiCh 1s exclusively American; while a genus of geckoes, inhabiting America and Australia, also occurs in Madagascar. Relation of J.lladagascar to Ajrica .. -These facts taken all together are certainly very extraordinary, since they show in a considerable number of cases as much affinity with America as with Africa.; while the most striking and characteristic groups of animals now inhabiting Africa are entirely wanting in Madagascar. Let us first deal with_ this fact, of the absence of so many of the most dominant African groups. The explanation of this deficiency is by no means difficult, for the rich deposits of fossil mamm::tls of Miocene age in France, Germany, Greece, and North-west India, have demonstrated the fact that all tho grea,t African mammals then inhabited Europe a.nd temperate Asia. We also know that a little earlier (in Eocene times) tropical Africa was cut off from Europe and Asia by a sea stretching from the Atlantic to the Bay of Bengal, at which time Africa must have formed a detached island-continent such as .Australia is now, and probably, like it, very poor in tl1e higher forms of life. Cou piing these two facts, the inference seems clear, that all the higher types of mamma1ia were developed in the great Euro-Asiatic continent (which then included Northern Africa), and that they only migrated into tropical Africa when the two continents became united by the upheaval of the sea-bottom, probably in the latter portion of the Miocene or early in the Pliocene period.1 1 This view wns, I believe, first advanced by Professor Huxley in his 'Anniversary Address to the Geological Society,'' in 1870. He says:-" In fact the Miocene mammalian fauna of Europe and the Himalayan regions contain, associated together, the types which are at present separately ocated in the South African and Indian provinces of Arctogrea. Now there IS every reason to believe, on other grounds, that both Hindostnn south of the Ganges, ann Africa south of the Sahara, were separated by a wide sea from Em· ope and North Asia during· the Middle and Upper Eocene epochs. Hence it becomes highly probable that the well-known similarities, and no less remarkable differences, between the present faun[C of India and South Africa have arisen in some such fashion as the following : CHAP. XIX.] '!'liE MADAGASCAR GROUP. 301 It is clear, therefore, that if Madagascar had once formed part of Africa, but had been separated from it before Africa was unite(l to Europe and Asia, it would not contain any of those kimls of animals which then 1lrst entered the country. But, besides the African mammals, we know that some birds now confined to Africa then inhabited Europe, and we may therefore fairly assume that all the more important groups of birds, reptiles, and insects, now abundant in Africa but absent from Madagascar, formed no part of the original African fauna, but entered tho country only after it was joined to Europe and Asia. Ea?'l?J lfisto7·y of Africa and ]Jtlaclagascrw.-We have seen that Madagascar contains an abundance of mammals, and that most of them are of types either pecnliar to, or existing also in, Africa; it follows that that continent must have had an earlier union with Europe, Asia, or America, or it could never have obtaiuecl any mammals at all. Now these ancient African mammals arc Lemur::;, Insectivora, and small Carnivora, chiefly Viverridro; and all these groups are known to have inhabited Europe iu Eocene and 1\.fiocene times; and tha.t the union was ·with Europe rather than with America is clearly provo'd by the fact that even the Insectivorous Centetidro, now confined to Mada< Yascar and the West Indies, inhabited France in tho Lower t> 1\lliocene period, while the Vi vcrridro, or civets, which form so Some time during the Miocene epoch, tl1e bottom of the nummulitic sea was upheaved and converted into dry land in the direction of a line extending from Abyssinia to the mouth of the Ganges. By tbi~ means ihe Dekkan on the one hand and South Africa on the other, became connected with the Miocene dry land and with one another. 'l'he Miocene mammall:l spread gradually over this intermediate dry land ; and if the condition of its eastern and western ends offered as wide contrasts as the va1leys of the Ganges and Arabia do now, many forms which made their way into Africa must have been different from those wl1ich reached the Dekkan, ,.,.bile others might pass into both these sub-provinces." 'l'his question is fully discussed in my Geographical Dist·ribution of Animals (Vol. I., p. 285), where I expressed views somewhat different from those of Professor Huxley and made some slight errors which are corrected in the present work. As I did not then refer to Professor Huxley's prior statement of the theory of Miocene immigration into Afric.a (which I had read but the reference to which I could not recall) I am happy to give hit> views here. |
