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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; PipridaB, or manakins; Cotingidse, or chatterers; Formicariidae, or ant-thrushes; Dendrocolaptidae, or tree-creepers ; Pteroptochidae; Khamphastidae, or toucans; Bucconidae, or puff-birds; Galbuliche, or jacamas; Todidae, or todies; Momotidae, or motmots; Steatornithidae. the guacharo, or oil-bird; Cracidae, or curassows; Tinamidae, or tinamous; Opisthocomidae, the hoazin; Thinocoridae; CariamidaB; Aramidas; 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; Tanagridse, or tanagers; Icteridas, 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 aa 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 (Cebidse) 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 Carnivore, 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 Caviidee, 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 (Bradypodidee), 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 no 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 classi 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 Picarise, we have first, the toucans (Ehamphastidae); an extraordinary and beautiful family, whose enormous gailycoloured bills and long feathered tongues, separate them widely from all other birds. The Galbulidse or jacamars, the motmots (Momotidse), and the curious little todies (Todidaj) 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 ot 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 Conuridai, 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 Tinamidee 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 altogether peculiar families, and several others which only range into the Nearctic region, as well as a very large number of peculiar or characteristic genera. As the orders of reptiles differ considerably in their distributional features, they must be considered separately.
The snakes (Ophidia) differ from all other reptiles, and from most other orders of vertebrates, in the wide average distribution of the families; so that such an isolated region as the Neotropical possesses no peculiar family, nor even one confined to the American continent The families of most restricted range are— the Scytalidae, only found elsewhere in the Philippine islands; the Amblycephalidae, common to the Oriental and Neotropical regions; and the Tortricidse, most abundant in the Oriental region, but found also in the Austro-Malay islands and Tropical South America. Sixteen of the families of snakes occur in the region, the Colubridse, Amblycephalida;, and Pythonidae, being those which are best represented by peculiar forms. There are 25 peculiar or characteristic genera, the most important being Dromiciis (Colubridae); Boa, Epicrates, and Unyalia (Pythonidae); Elaps (Elapidae); and Craspedocephalus (Crotalidte).
The lizards (Lacertilia) are generally more restricted in their range; hence we find that out of 15 families which inhabit the region, 5 are altogether peculiar, and 4 more extend only to N. America. The peculiar families are Heloderniidae, Anadiadae, Chirocolidae, Iphisiadse, and Cercosauridae ; but it must be noted that these all possess but a single genus each, and only two of them (Chirocolidae and Cercosauridae) have more than a single species. The families which range over both South and North America are Chirotidae, Chalcidae, Teidae, and Iguanidae; the first and second are of small extent, but the other two are very large groups, the Teidae possessing 12 genera and near 80 species; the Iguanidae 40 genera and near 150 species; the greater part of which are Neotropical. There are more than 50 peculiar or highly characteristic genera of lizards, about 40 of which belong to the Teidte and Iguanidae, which thus especially characterize the region. The most important and characteristic genera are the following: Ameiva (Teidae); Gymnopthalmus (Gynmopthalmidae);