« AnteriorContinuar »
period. At the beginning of Pliocene time, during the deposition of the Araucanian formation in Argentina and the "Equus-beds" in the United States, a wide bridge between North and South America, affording an easy road to migrating animals, must have existed, and this again seems to have become considerably narrowed to form the present Isthmus of Panama.
List Of The Principal Authorities Referred To
(1) Allen, J. A.—"The Geographical Distribution of North American Mammals." Bull. Amer. Mm. N.H., iv., p. 199, 1892.
(2) Allen, J. A.—"On a Small Collection of Mammals from the Galapagos Islands, collected by Dr. G. Baur." Bull. Amer. Mm. N.H., iv., p. 47, 1892.
(3) Alston, E. R.—"Biologia Centrali-Americana, Mammalia. London, 1879-82.
(4) Chapman, F. M.—"Notes on Birds and Mammals observed near Trinidad, Cuba, with remarks on the Origin of West Indian Bird-life." Bull. Amer. Mm. N.H., iv., p. 279, 1892.
(5) Cope, E. D. —" Description of two large extinct Rodents from Anguilla, West Indies, with remains of human art associated." Proc Amer. Philos. Soc. Philad., xi., 1871, p. 183.
(6) Leidy, J.—"Remarks on Mylodon." Proc. Acad. Nat. Sci. Philad., 1885, p. 49.
(7) Salvin, 0.—" On the Avifauna of the Galapagos Archipelago.' Trans. Zool. Soc., ix., p. 447 (1876).
(8) Sclater, P. L.—"Address to Section D. (Biology)." "Report of Forty-fifth Meeting of the British Association, at Bristol," p. 85 (1876).
(9) Thomas, 0—" On Some Mammals from Central Peru." P.Z.S., 1893, p. 333.
(10) Trotjessart, E. L.—" Note sur le rat musque' (Mm pilorides) des Antilles." Ann. Sci. Nat. Zool. (6), xix., No. 5 (1885).
(11) Wallace, A. R.—" The Geographical Distribution of Animals." 2 vols. London, 1876.
(12) Zittel, K. A. Von.—" The Geological Development, Descent, and Distribution of the Mammalia." S. B. k. bayer. Akad. Wiss., xxiii., p. 137, 1893. Translation in Oeol. Mag. (3), x., p. 401 (1893).
THE ETHIOPIAN REGION (plate IV., p. 122) Section I.—Boundaries Of The Ethiopian Region
The Ethiopian Region (see Map, Plate IV.) contains the whole of Africa south of the Sahara, together with Southern Arabia and the island of Madagascar. As in all other cases where there is a long land-frontier between two neighbouring Regions, so here it is impossible to lay down anything but an approximate line of demarcation between the Ethiopian and Palsearctic Regions.
The boundary usually adopted is the line of the Tropic of Cancer, which strikes Africa between Morocco and Senegambia, runs through the middle of the Sahara, crosses the Nile between the first and second cataracts, and passes through Arabia to the neighbourhood of Oman, on the Persian Gulf. Most of the country through which this line passes is desert, and its mammalian fauna is consequently meagre. Mr. 0. Thomas (6) has recently published an account of a collection of mammals received at the British Museum from Oman, which shows, as would naturally be expected, that "the geographical relationships of this district are about equal with Africa and India; three of the species being distinctly African in affinities, three Indian, and the remainder either peculiar or widely spread and of no special significance." On the whole. therefore, the line of the tropic of Cancer, adopted by Wallace, seems to be a fairly suitable boundary.
Besides the island of Madagascar and its appendages, which contain one of the richest and most interesting of all known Insular Faunas, and form a very important Sub-region, which will be considered in greater detail below, the Ethiopian Region possesses other islands. These, however, are mostly Oceanic, and not of any great importance.
The Azores, Madeira, Canaries, and Cape Verde groups, although geographically African, seem to have derived their animals chiefly from Europe. They therefore belong to the Palsearctic Region, and will be dealt with under that head.
The islands of St. Helena and Ascension, situated in the South Atlantic, are both of them of volcanic origin, and separated from the mainland of Africa by more than 800 miles of deep water. Neither of these islands possesses any Vertebrates. The only land-groups well represented in them are the Beetles and the Land-shells—a study of which shows that the affinities of these islands are to Southern Europe and Southern Africa, but that the Fauna is in all probability an exceedingly ancient one; since its peculiarities are very great, and opportunities of migration of new forms to these islands have been few and far between.
The other islands in the Atlantic connected with Africa are Fernando Po, Prince's Island, St. Thomas, and Anno Bon, all situated in the Gulf of Guinea at various distances from its head. Fernando Po, an island of some 40 miles in length, but separated from the mainland by a somewhat shallow sea about 20 miles across is said to be inhabited by a considerable number of Mammals which, however, in all probability, also occur on the adjacent mainland.
The other islands above mentioned, Prince's Island, St. Thomas, and Anno Bon, are all considerably more distant from the coast of Africa, and, so far as we know, do not possess any native Mammals. A certain number of Landbirds have been obtained from these islands, and a few of these are peculiar, but they are all closely allied to forms that occur in the neighbouring West African mainland.
The most important islands in the Indian Ocean are, apart from Madagascar, Socotra, the Seychelles, the Amirante Islands, the Comoros, and finally Reunion, Mauritius, and Rodriguez.
Socotra is situated about 150 miles due east of Cape Guardafui, the extreme eastern point of Africa. Its fauna and flora were carefully investigated some years ago by Professor Bay ley Balfour (1). He found that the only Mammals inhabiting the island are a Bat, which he was unable to obtain, and a Civet (Viverricula), met with also in South Asia, and probably introduced by human agency.
The Seychelles are distant about 700 miles from the northern point of Madagascar in a north-easterly direction, a more or less continuous chain of islands (Amirante, Providence, and Farquhar) forming a series of stepping-stones between them. But two narrow deep channels of over 1000 fathoms run between the Seychelles and Amirante on the one hand, and between Amirante and Providence on the other, thus cutting the Seychelles off from Madagascar by their deep water.
There do not appear to be any indigenous terrestrial Mammals in the Seychelles, except two Bats, which have been recorded as occurring there. The Land-birds are most of them peculiar, though belonging to genera found in Madagascar or Africa; the reptiles and amphibians are fairly numerous for islands such as these, and several of the species are not found elsewhere. It is difficult to say whether these islands have ever had a land-connection with Madagascar, but probably, if such were ever the case, it was at a remote time, geologically speaking.
The Comoros are a group of several islands lying about midway between the most northerly point of Madagascar and the mainland of Africa. They are separated from Africa by the Mozambique channel, more than 1000 fathoms in depth, while the depression between them and Madagascar is considerably less. Inhabiting these islands there are three Bats. Two of these are of the genus Pteropus, which is entirely absent from the mainland of Africa, but is found in Madagascar and many islands of the Indian Ocean. There is also a peculiar species of Lemur (Lemur mayottensis) and the Indian Civet ( Viverricula), which last is also found in Madagascar and Socotra, and has in all probability been introduced by human agency. A fair proportion of the Land-birds of the Comoros, though in some instances peculiar, belong to Madagascar forms, and everything goes to show tnat the relation of this group of islands is with Madagascar rather than with the mainland.
The islands of Reunion, Mauritius, and Rodriguez are distant from Madagascar in an easterly direction 450, 550, and 800 miles respectively. They are all of volcanic origin, and separated from Madagascar by water of more