OCR Text |
Show 256 MR. R. I. rOCOCK ON THE [Apr. 21, present time in this area, the former in Java and the Nicobars, the latter all over the Indo- and Austro-Malayan Islands and Australia. Selenocosmia, which must be regarded as a direct descendant of Phlogiellus, must itself be looked upon as the ancestor of the Malayan Coremiocnemis, the Assamese Lyrognathus, the Burmese, Indian, and Ceylonese Chilobrachys, and of the two Australian genera Selenotypus and Selenotholus, all of which, in the absence of evidence to the contrary, may be held to have originated within the areas of their present distribution. The affinities of the aberrant genus, Pcecilotherici, which is specialised both in structure and habits, are more doubtful; but there is no evidence against the hypothesis that it has been evolved in India itself. The presence of Pcecilotherici and Chilobrachys in Ceylon and India attests their occupation of the latter area before the severance of Ceylon; and the extension of Selenocosmia into Australia but not into New Zealand, similarly attests a southern migration into the former country before its separation from South-eastern Asia, but after the isolation of New Zealand. It seems probable, indeed, that this southern immigration into Australia synchronised with that of the ancestors of the Australian marsupial mammals, and in this connection it is significant to note that the latter are believed to have originated in South-eastern Asia1 and to have entered Australia in Eocene times. The great difference, however, in distribution between the Marsupials and Selenocosmiinfe may be explained by the survival of the latter, and the extinction of the former, in the area of their birth. The Thrigmopceina?, which are confined, so far as is known, to India, appear to have been developed from the Aviculariine stock at a late date, namely after the depression of the connecting land with Ceylon; and the Ornithoctoninse, which range from Siam and Burma to the Moluccas, seem similarly to have put in an appearance after the separation of Australia from the continent to the north of it. The Eumenophorinse must have entered or been developed in the Ethiopian Region at an early date, antecedent to the separation of South Arabia and Sokotra from what is now Somaliland, and before the formation of the Mozambique Channel divided Madagascar from East Africa. The Ilarpactirime, on the contrary, which range from Somaliland to Cape Colony but are unknown in Madagascar, seem to have originated independently within the Ethiopian Region subsequent to the Miocene period. The least specialised of the genera (Harpactirella and Pterinochilus) have not departed far from the type of structure found in the Aviculariinse. There remains the South-American fauna to be accounted for. Owing to the general similarity that obtains between the genera of this area and those of other parts of the world, the 1 Lydckker, ‘ Geogr. Hist. Mammals,' p. 55 (1896). |