« AnteriorContinuar »
SECTION III.-SUBDIVISION OF THE NEOTROPICAL
The divisions of the Neotropical Region, as based on a consideration of the class of birds (8), are six in number, namely :
1. The Antillean Sub-region, containing the Greater and Lesser Antilles, exclusive of Tobago and Trinidad.
2. The Central-American Sub-region, containing all that part of the whole region that is north of Panama.
3. The Colombian Sub-region, containing Trinidad and the slopes of the Andes, through Venezuela, Colombia, Ecuador, and Peru, into Bolivia.
4. The Amazonian Sub-region, embracing the whole watershed of the Orinoco and Amazons up to the hills, and including the highlands of Guiana,
5. The South Brazilian Sub-region, containing the wood region of South-East Brazil, Paraguay, and the adjoining districts.
6. The Patagonian Sub-region, containing Patagonia, Southern Argentina, and Chili, and running up the west coast of the continent to Guyaquil.
This division, although perfectly good when the distribution of Birds is mainly relied upon, presents considerable difficulties in the case of Mammals, owing chiefly to our ignorance of the limits of the distribution of the greater number of the South American mammals, especially of the smaller forms. There is, however, no doubt that the Antilles or West Indies (excluding Trinidad and the other islands off the coast of Venezuela, which are connected with the mainland by quite shallow water) form a very well-marked Sub-region, in which the terrestrial mammals, though not very numerous, nearly all belong to peculiar genera.
The higher ranges of the Andes from Ecuador southwards, together with the pampas of Southern Argentina and Patagonia, form another well-marked Sub-region characterised by a number of peculiar genera and species. But the whole remainder of the Neotropical Region from Mexico to Southern Brazil contains, so far as we understand it at present, a more or less homogeneous mammalfauna, of which, however, the northern half possesses a considerable admixture of Nearctic forms, while the southern preserves a more purely indigenous facies. It will, therefore, be quite in accordance with the facts of nature, as well as convenient, to separate the northern portion of this extensive area as the Central American (or Transpanamanic) Sub-region. But as regards the southern portion, until our knowledge of the distribution of South American mammals has made greater progress, it seems best to unite the Colombian, Amazonian, and Brazilian Subregions of the Ornithologists into one combined Sub-region, which may be called the Guiano-Brazilian Sub-region.
We shall thus have, as regards Mammals, four Subregions of the Neotropical Region, as follows (see Map, Plate III., p. 82) =
1. The Antillean Sub-region, comprising the whole of the West India Islands except Curaçao, Trinidad, and Tobago.
2. The Central-American Sub-region, comprising the low-lying and southern parts of Mexico and Central America as far as the Isthmus of Panama.
3. The Guiano-Brazilian Sub-region, comprising the greater part of South America from the Isthmus of Panama to the southern limits of the great forest in about lat. 30° S., and from the forest of the eastern slopes of the Andes to the Atlantic, including Trinidad and the other islands off the coast of Venezuela. .
4. The Patagonian Sub-region, comprising the higher ranges and western slopes of the Andes from Guyaquil to Tierra del Fuego and the pampas of Argentina and Patagonia.
SECTION IV.—THE ANTILLEAN SUB-REGION
The Mammal-fauna of the Antillean Sub-region is exceedingly poor, so poor, indeed, that it seems almost doubtful whether the islands of which it is composed have ever been directly connected with the mainland of America as at present constituted. To begin with the Rodents, four genera of this order are represented within its limits, and three of these are restricted to the Sub-region. Megalomys (a large rat, over twelve inches in length without the tail) is allied to the Vesper-mice of the American continent, and has been obtained only in the islands of Martinique and St. Lucia, where it is now becoming very rare (10). A more important factor in the Antillean mammal-fauna is Capromys, a genus allied, according to Flower and Lydekker, to the Coypu rat of South America, but also showing some affinities to the Porcupines. There are five or six species of this genus usually recognised, of which two or three are restricted to Cuba, one is peculiar to Jamaica, and one to the Bahamas, while another species has been recently discovered in Swan Island, situated
in the middle of the Gulf of Mexico. An allied genus (Plagiodon) with one species, differing from Capromys only in a slight modification of the teeth, is found in Hayti. It is obviously derived from the same stock. A peculiar species of agouti (Dasyprocta cristata) is found in two of the Lesser Antilles-St. Vincent and St. Thomas; the other members of this genus belong to the mainland of Central and South America. The only other Order of terrestrial Mammals represented in this Sub-region is the Insectivora, and this is the more remarkable because, as already shown, one of the special characters of the Neotropical Region is the almost complete absence of this group within its limits. The West Indian representatives of this group are two in number, and belong to a peculiar genus (Solenodon), which is of rather doubtful affinities but of family rank. It is allied in some respects to the moles (Talpide), and in others to a peculiar Malagasian family, the Tenrecs (Centetidæ). The Solenodonts are small creatures with a somewhat shrew-like aspect, a long snout, and a long naked tail. There are two representative species of this genus confined to the islands of Hayti and Cuba respectively.
The Bats of the Antillean islands, as would naturally be expected, are somewhat more abundant than the terrestrial mammals. There have been recorded by naturalists about thirty species belonging to some twenty genera as found in the different islands, the greater number being from Cuba and Jamaica. On examining the list, it will be found that of these twenty genera three only seem to be confined to the West Indian Region, while thirteen are spread over the greater part of the Neotropical Region,one belongs to the Nearctic Region, and the others are of wider distribution.
The evidence of the Bats, therefore, points unmistakably to the inference that the West India Islands have been peopled with Mammalian life from South and not from North America. In this connection it may be noted that Mr. Frank Chapman in an instructive article (4) on the origin of the West Indian fauna, recently published, has stated, as regards the birds, that the total number as yet recorded as met with within the limits of this Sub-region amounts to 550. Of these 303 are endemic, while the remaining 247 may be allotted to the countries from which they have been apparently derived as follows:
Common to North and South America
in the Greater Antilles)
through Florida, and the larger proportion found in
160 This summary gives us a clue to the origin of the more recent additions to the West Indies fauna, which is obviously by migration from the north. If, however, the relationships of the 303 endemic species of Birds are examined, it will be at once evident that they are all more closely allied to South American than to North American forms, and, like the Bats, show that the islands have been stocked with life from the south. Moreover, Mr. Chapman, as well as Mr. Wallace, has pointed out that nearly all the more distinct and most characteristic West Indian Birds are found in the Greater Antilles (i.e. Cuba, Hayti, Porto Rico, and Jamaica), and that the Lesser Antilles form a distinct group, the line of separation between the two provinces coinciding nearly with the deep channel between