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number of groups to which verdant forests are essential, can be traced to the unsuitable conditions rather than to the existence of the mountain barrier. All Tropical South America, therefore, is here considered to form but one sub-region. The portion of North America that lies within the tropics, closely resembles the last sub-region in general zoological features. It possesses hardly any positive distinctions; but there are several of a negative character, many important groups being wholly confined to South America. On the other hand many genera range into Mexico and Guatemala from the north, which never reach South America; so that it is convenient to separate this district as a sub-region, which forms, to some extent, a transition to the Nearctic region. General Zoological Features of the Neotropical Region.—Richness combined with isolation is the predominant feature of Neotropical zoology, and no other region can approach it in the number of its peculiar family and generic types. It has eight families of Mammalia absolutely confined to it, besides several others which are rare elsewhere. These consist of two families of monkeys, Cebidae and Hapalidae, both abounding in genera and species; the Phyllostomidae, or blood-sucking bats; Chinchillidae and Caviidae among rodents; besides the greater part of the Octodontidae, Echimyidae and Cercolabidae. Among edentata, it has Bradypodidae, or sloths, Dasypodidae, or armadillos, and Myrmecophagidae, or anteaters, constituting nearly the entire order; while Procyonidae, belonging to the carnivora, and Didelphyidae, a family of marsupials, only extend into the Nearctic region. It has also many peculiar groups of carnivora and of Muridae, making a total of full a hundred genera confined to the region. Hardly less remarkable is the absence of many widespread groups. With the exception of one genus in the West Indian islands and a Sorex, which reaches Guatemala and Costa Itica, the Insectivora are wholly wanting; as is also the extensive and wide-spread family of the Viverridae. It has no oxen or sheep, and indeed no form of ruminant except deer and llamas; neither do its vast forests and grassy plains support a single form of non-ruminant ungulate, except the tapir and the peccary.
Birds.-In birds, the Neotropical region is even richer and more isolated. It possesses no less than 23 families wholly confined within its limits, with 7 others which only extend into the Nearctic region. The names of the peculiar families are: Caerebidae, or sugar-birds; Phytotomidae, or plant-cutters; Pipridae, or manakins; Cotingidae, or chatterers; Formicariidae, or ant-thrushes; Dendrocolaptidae, or tree-creepers; Pteroptochidae; Rhamphastidae, or toucans; Bucconidae, or puff-birds; Galbulidae, or jacamas; Todidae, or todies; Momotidae, or motmots; Steatornithidae. the guacharo, or oil-bird; Cracidae, or curassows; Tinamidae, or tinamous; Opisthocomidae, the hoazin; Thinocoridae; Cariamidae : Aramidae; Psophiidae, or trumpeters; Eurypygidae, or sun-bitterns; and Palamedeidae, or horned-screamers. The seven which it possesses in common with North America are: Vireonidae, or greenlets; Mniotiltidae, or wood-warblers; Tanagridae, or tanagers; Icteridae, or hang-nests; Tyrannidae, or tyrant-shrikes; Trochilidae, or humming-birds; and Conuridae, or macaws. Most of these families abound in genera and species, and many are of immense extent; such as Trochilidae, with 115 genera, and nearly 400 species; Tyrannidae, with more than 60 genera and nearly 300 species; Tanagridae, with 43 genera and 300 species; Dendrocolaptidae with 43 genera and more than 200 species; and many other very large groups. There are nearly 600 genera peculiar to the Neotropical region; but in using this number as a basis of comparison with other regions we must remember, that owing to several ornithologists having made the birds of South America a special study, they have perhaps been more minutely subdivided than in the case of other entire tropical regions. Distinctive Characters of Neotropical Mammalia.—It is important also to consider the kind and amount of difference between the various animal forms of this region and of the Old World. To begin with the Quadrumana, all the larger American monkeys (Cebidae) differ from every Old World group in the possession of an additional molar tooth in each jaw; and it is in this group alone that the tail is developed into a prehensile organ of wonderful power, adapting the animals to a purely arboreal life. Four of the genera, comprising more than half the species, have the prehensile tail, the remainder having this organ either short, or lax as in the Old World monkeys. Other differences from Old World apes, are the possession of a broad nasal septum, and a less opposable thumb; and the absence of cheekpouches, ischial callosities, and a bony ear-tube. The Hapalidae, or marmozets, agree with the Cebidae in all these characters, but have others in addition which still more widely separate them from the Simiidae; such as an additional premolar tooth, acute claws, and thumb not at all opposable; so that the whole group of American monkeys are radically different from the remainder of the order. The Procyonidae are a distinct family of Carnivora, which make up for the scarcity of Mustelidae in South America. The Suidae are represented by the very distinct genus Dicotyles (Peccary) forming a separate sub-family, and differing from all other genera in their dentition, the absence of tail and of one of the toes of the hind feet, the possession of a dorsal gland, and only two mammae. The rodents are represented by the Chinchillidae and Caviidae, the latter comprising the largest animals in the order. The Edentata are almost wholly confined to this region; and the three families of the sloths (Bradypodidae), armadillos (Dasypodidae), and ant-eaters (Myrmecophagidae), are widely separated in structure from any Old World animals. Lastly, we have the opossums (Didelphyidae), a family of marsupials, but having mo close affinity to any of the numerous Australian forms of that order. We have already arrived at the conclusion that the presence of marsupials in South America is not due to any direct transference from Australia, but that their introduction is comparatively recent, and that they came from the Old World by way of North America (vol. i., p. 155). But the numerous and deep-seated peculiarities of many other of its mammalia, would indicate a very remote origin; and a long-continued isolation of South America from the rest of the world is required, in order to account for the preservation and development of so many distinct groups of comparatively low-type quadrupeds. Distinctive Characters of Neotropical Birds.-The birds which are especially characteristic of this region, present similar distinctive features. In the enormous group of Passerine birds which, though comprising nearly three-fourths of the entire class, yet presents hardly any well-marked differences of structure by which it can be subdivided—the families confined to America are, for the most part, more closely related to each other than to the Old World groups. The ten families forming the group of “Formicaroid Passeres,” in our arrangement (vol. i., p. 94), are characterised by the absence of singing muscles in the larynx, and also by an unusual development of the first primary quill; and seven of this series of families (which are considered to be less perfectly developed than the great mass of Old World passeres) are exclusively American, the three belonging to the Eastern hemisphere being of small extent. Another group of ten families—our “Tanagroid Passeres,” are characterised by the abortion or very rudimentary condition of the first quill; and of these, five are exclusively American, and have numerous genera and species, while only two are non-American, and these are of small extent. On the other hand the “Turdoid Passeres,” consisting of 23 families and comprising all the true “singing-birds,” is poorly represented in America; no family being exclusively Neotropical, and only three being at all fully represented in South America, though they comprise the great mass of the Old World passeres. These peculiarities, which group together whole series of families of American birds, point to early separation and long isolation, no less surely than the more remarkable structural divergences presented by the Neotropical mammalia. In the Picariae, we have first, the toucans (Rhamphastidae); an extraordinary and beautiful family, whose enormous gailycoloured bills and long feathered tongues, separate them widely from all other birds. The Galbulidae or jacamars, the motmots (Momotidae), and the curious little todies (Todidae) of the Antilles, are also isolated groups. But most remarkable of all is the wonderful family of the humming-birds, which ranges over all America from Tierra del Fuego to Sitka, and from the level plains of the Amazon to above the snow-line on the Andes; which abounds both in genera, species, and individuals, and is yet strictly confined to this continent alone How vast must have been the time required to develop those beautiful and highly specialized forms out of some ancestral swift-like type; how complete and long continued the isolation of their birthplace to have allowed of their modification and adaptation to such divergent climates and conditions, yet never to have permitted them to establish themselves in the other continents. No naturalist can study in detail this single family of birds, without being profoundly impressed with the vast antiquity of the South American continent, its long isolation from the rest of the land surface of the globe, and the persistence through countless ages of all the conditions requisite for the development and increase of varied forms of animal life. Passing on to the parrot tribe, we find the peculiar family of the Conuridae, of which the macaws are the highest development, very largely represented. It is in the gallinaceous birds however that we again meet with wholly isolated groups. The Cracidae, including the curassows and guans, have no immediate relations with any of the Old World families. Professor Huxley considers them to approach nearest to (though still very remote from) the Australian megapodes; and here, as in the case of the marsupials, we probably have divergent modifications of an ancient type once widely distributed, not a direct communication between the southern continents. The Tinamidae or tinamous, point to a still more remote antiquity, since their nearest allies are believed to be the Struthiones or ostrich tribe, of which a few representatives are scattered widely over the globe. The hoazin of Guiana (Opisthocomus) is another isolated form, not only the type of a family, but perhaps of an extinct order of birds. Passing on to the waders, we have a number of peculiar family types, all indicative of antiquity and isolation. The Cariama of the plains of Brazil, a bird somewhat intermediate between a bustard and a hawk, is one of these; the elegant Psophia or trumpeter of the Amazonian forests; the beautiful little sun-bittern of the river banks (Eurypyga); and the horned screamers (Palamedea), all form distinct and isolated families of birds, to which the Old World offers nothing directly comparable. Reptiles—The Neotropical region is very rich in varied forms of reptile life, and the species are very abundant. It has six