« AnteriorContinuar »
and the West Indies, the Falkland Islands and the Galapagos must likewise be included in the Neotropical Region.
The West Indies form an important sub-region, containing some forms of great interest, and will be treated of in detail below.
The Falkland Islands are situated in the south Atlantic, about 250 miles east of the nearest point of Patagonia. They are, however, known to be connected with the mainland by a shallow sea of less than 100 feet in depth, and therefore present all the characteristic features of a “continental”
of islands. The only indigenous mammals are a Wild Dog (Canis antarcticus) and a Vesper-mouse (Hesperomys), which seem to be distinct, though closely allied to the mainland forms. The birds also are mostly identical with those of the mainland, though there are some just recognisable representative forins.
The Galapagos, a group of five larger and ten smaller islands, are situated in the Pacific, exactly under the Equator, at a distance of from 500 to 600 miles west of Ecuador. They rise up from very deep water, and are entirely of volcanic origin. They are therefore typical “Oceanic” islands. With the exception of two Vespermice, slightly differing from those of the mainland, and a peculiar Bat (Atalapha brachyotis), there are no indigenous mammals (2) in the Galapagos. There are, however, a considerable number of birds in these islands, most of them not found elsewhere, and many of them restricted to individual islands in which they represent each other (7)
There can be no doubt that the Galapagos have never, at any period of their history, been joined to the mainland, and that, owing to the fact that they are situated in the region of equatorial calms, immigration from the mainland is very occasional. In this way has been gradually evolved the peculiar fauna, which, although highly specialised, shows abundant evidence of its having been derived from the nearest mainland.
SECTION II.- GENERAL VIEW OF THE MAMMAL-FAUNA
OF THE NEOTROPICAL REGION
The Neotropical Region is essentially one of luxuriant tropical vegetation, the great mass of the land from Central America to Uruguay being occupied by vast forests. South of the tropic of Capricorn the woods soon disappear, and the country, over a large part of its surface, becomes a flat treeless expanse covered with more or less abundant pasture known as the Pampas, while all along the western coast extends the giant range of the Andes, the eastern flanks of which are, as a rule, well watered and wooded, while the western slopes from the Gulf of Guyaquil to the island of Chiloe facing the Pacific are utterly dry and arid. There are, however, also in the higher parts of Venezuela, the Guianas, and Brazil, open grassy plains called “campos," which rise as islands from a surrounding sea of evergreen tropical forest.
The mammalian fauna of the Neotropical Region is naturally a rich one, but in the number of genera and species falls considerably short of that of the Ethiopian Region. This may perhaps be accounted for by the physical features of the country, which are certainly not so favourable for mammalian development as the more open and varied country of Africa.
This deficiency in mammalian life is, however, more than counterbalanced by the abundance of other groups of animals, more especially of birds and insects, to the development of which the luxuriant tropical vegetation seems to be especially conducive.
Again, the mammalian fauna of the Neotropical Region is quite as remarkable for what it does not possess (lipotypes) as for what it has. Everything points to the conclusion that during a long geological age, probably throughout the greater part of the Tertiary epoch, South America was entirely isolated from the rest of the world. Thus the present fauna has arisen from two quite different sources -first, from the original fauna of early Tertiary times; and, secondly, from immigrants from the north, some of these being of rather long standing, and others of later arrival.
Of the nine Orders of Terrestrial Mammals, representatives of eight occur in the Neotropical Region, the only Order entirely absent being the Monotremes, which are absolutely confined to Australia.
The Marsupials are represented in the Neotropical Region by a single family only,' out of seven into which this order is usually divided. This is the Didelphyidæ, or Opossums, of the twenty-four generally recognised species of which one (Didelphys marsupialis) ranges north with some modification into the Nearctic Region. The Quica Opossum (D. opossum) (Fig. 7, p. 56) is another well-known
1 Since this was written Mr. Thomas has described his wonderful new South-American genus Cænolestes, which seems to belong to the Australian Diprotodonts. See P. 2. S., 1895, p. 870.
species of the group, which is found all through the Region, from Southern Mexico to La Plata.
The third Order of mammals—the Edentata—is highly characteristic of the Neotropical Region. Of the five
generally recognised families two belong entirely to the Old World; the other three—the Sloths, the Ant-eaters, and the Armadilloes (which are more nearly allied to one another than to the two Old World families)—are, with the exception of one species of Armadillo (Totusia novemcincta), which extends into Texas, absolutely confined to the Neotropical Region, and are eminently characteristic of its mammal-fauna. The Sloths (Bradypodidæ) of the present epoch at least, are entirely arboreal
in their habits, and pass their lives suspended by their limbs on the underside of the branches of trees (Fig. 8). The Ant-eaters (Myrmecophagidæ) are also mainly inhabitants of forests, and one of the three existing forms (Cyclothurus) is exclusively arboreal. A second (Tamandua) may be said to be semi-arboreal, but the largest—the