Imágenes de páginas
PDF
EPUB

Seals, Monachus, amongst the Pinnipeds, and of the Sirenian genus Manatus.

III. Regio Indopelagica, characterized by the presence of the Sirenian Halicore and by the absence of Pinnipeds.

IV. Regio Arctirenica, with Phoca like the Regio Arctatlantica, but having Otaria also; the home of the (now extinct) Sirenian Rhytina and of the endemic Cetacean Rhachianectes.

V. Regio Mesirenica, without true Seals (Phocinm), but having Otaria and Macrorhinus from the south; no Sirenian being known there.

VI. Regio Notopelagica, characterized by four endemic genera of Phocidm, and by the presence of many Otarim; without Sirenians, but with two endemic forms of Cetaceans (NeobaUena and Berardius).

In conclusion, attention may be called to some of the more remarkable points in the general distribution of the marine mammals and to their apparent significance.

In the first place it is evident that the Pacific has much more in common with the Notopelagian Region than the Atlantic. Otaria and Macrorhinus, quite unknown in the Atlantic, extend themselves to the northern extremity of the Pacific, the former pervading that ocean up to Behring's Strait, and the latter reaching to the Californian coast. It follows that in former ages there must have been some barrier in the Atlantic which did not exist in the Pacific to stop their progress northwards. The only barrier one can imagine that would have effected this must have been a land uniting South America and Africa, across which they could not travel. Adopting this hypothesis, we have at the same time an explanation of the presence of the Manatee on both the American

[graphic]
[graphic]

and African coasts. The Manatee could hardly live to cross the Atlantic. It is only found close to the coast, in estuaries and rivers, where it browses on sea-weeds and other vegetable food in shallow water. How did it travel from America to Africa (or vice versd), unless there were a continuous shore-line between them? The same may be said of the Monk-Seal (Monachv^i), of which one species lives in the Mediterranean and on the African coast and islands, and another in the West Indies. We can hardly believe that these creatures could easily traverse the whole Atlantic. The hypothesis of a former barrier of land between Africa and America, which we know is supported by other facts of distribution,1 would alone explain the difficulty.

On the other hand, in the Pacific we find no such break between the north and south. The aquatic mammals of Notopelagia have evidently had free access to the whole of the Pacific for a long period, and have well availed themselves of this facility.

Again, while the great Southern Ocean exhibits a considerable uniformity of marine mammalian life, we see the Northern waters divided into two distinctly recognizable Regions by the interposed masses of land. All these facts, with the one exception of the supposed Atlantic barrier, would tend in favour of the now generally accepted doctrine that the principal masses of land and water are not of modern origin, but have existed mainly in their present shapes throughout all ages.

1 Cf. Wallace, Geogr. Distrib., vol. i., p. 156.

CHAPTER IX

DISTRIBUTION OF MONKEYS AND LEMURS

Section I.—Introductory Remarks

Having now completed the discussion of the great Zoological Regions of terrestrial and marine mammals and their leading peculiarities, it is proposed to take the subject in another way, and considering the Orders, or great primary groups of mammals, one after the other, to sketch out the mode in which their leading forms are distributed over the surface of the world We shall then see whether the conclusions thus arrived at appear to lead to similar results to those attained by making geographical divisions our primary subject of study. In doing this it will be more convenient to take the most highly organized groups of mammals first, and to descend gradually to the lowest, reversing the arrangement used in the previous chapters of this work. The divisions and names now employed are taken from the last edition of the "List of Yertebrated Animals in the Zoological Society's Gardens," (1896), but do not differ materially from those used in Flower and Lydekker's "Mammals Living and Extinct," which we have hitherto mainly followed. These

« AnteriorContinuar »