Tropical nature, and other essays

by Alfred Russel Wallace

Regions of the New World.—We will now pass across the Atlantic to the Western Hemisphere, and consider first the Nearctic region, or temperate North America, whose present and past zoological relations with the rest of the world are of exceeding interest.

If we omit such animals as the musk-sheep (Ovibos), which is purely Arctic, and the peccaries (Dicotyles), which are hardly less distinctly tropical, the land-mammalia of North America are not very numerous; and they can be for the most part divided into two groups, the one allied to the Palæarctic, and the other to the Neotropical fauna. The bears, the wolves, the cats, the bison, sheep and antelope, the hares, the marmots, and the pikas, resemble Palæarctic forms; while the racoons, skunks, opossum, and vesper-mice are now more peculiarly Neotropical. There are also many genera which are altogether peculiar and characteristic of the region, as the prong-horn antelope (Antilocapra), the jumping-mouse (Jaculus), five genera of pouched rats (Saccomyidæ), the prairie dogs (Cynomys), the tree porcupines (Erethizon), and some others.

Birds present the same mixture of the two types; but the wild turkeys (Meleagris), the passenger pigeon (Ectopistes), the crested quails (Lophortyx, &c.), the ruffed grouse (Cupidonia), and some other groups of less importance, are peculiar; while the family of the wood warblers (Mniotiltidæ) is so largely developed that it may claim to be more characteristic of North than of South America.

Reptiles and Amphibia present a number of peculiar types; while no less than five peculiar families of fresh-water fishes would alone serve to mark out this as distinct from every other part of the world.

Considering the evident affinity between the Nearctic and Palæarctic regions, there are here some curious deficiencies of groups which are common and widely spread in the latter. Thus hedgehogs, wild horses and asses, swine, true oxen, goats, dormice, and true mice are absent; while sheep and antelopes are only represented by solitary species in the Rocky Mountains. Among birds, too, we have such striking deficiencies as the extensive families of flycatchers, starlings, and pheasants.

Turning now to the Neotropical region, comprising all South America and the tropical parts of the northern continent, we find that the Old World types have still further diminished, while a number of new and altogether peculiar forms have taken their place. Insectivora have wholly disappeared with the exception of one anomalous form in the greater Antilles; bears are represented by one Chilian species; swine are replaced by peccaries; the great Bovine family are entirely unknown; the camel tribe are confined to the Southern Andes and the south-temperate plains; deer are not numerous; and all the varied Ungulata of the Old World are represented only by a few species of tapirs. These great gaps are, however, to some extent filled up by a variety of interesting and peculiar types. Two families of monkeys (Cebidæ and Hapalidæ) differ in many points of structure from all the Quadrumana of the eastern hemisphere. There is a peculiar family of bats—the vampyres; many peculiar weasels and Procyonidæ; a host of peculiar rodents, comprising five distinct families, among which are the largest living forms of the order; and a great number of Edentata, comprising the families of the sloths, armadillos, and ant-eaters; and lastly, a considerable number of the marsupial family of opossums. As compared with the Old World, we find here a great abundance and variety of the lower types, with a corresponding scarcity of such higher forms as characterise the tropics of Africa and Asia.

In birds we meet with corresponding phenomena. The most abundant and characteristic families of the Old World tropics are replaced here by a series of families of a lower grade of organisation, among which are such remarkable groups as the chatterers (Cotingidæ), the manakins (Pipridæ), the ant-thrushes (Formicariidæ), the toucans (Rhamphastidæ), the motmots (Momotidæ), and the humming-birds (Trochilidæ), the last perhaps the most remarkable and beautiful of all developments of the bird-type. Parrots are numerous, but these, too, are mostly of peculiar families; while pheasants and grouse are replaced by curassows and tinamous, and there are an unusual number of remarkable and isolated forms of waders.

Reptiles, amphibia, fresh-water fishes, insects, and land-shells, are all equally peculiar and abundant; so that South America presents, on the whole, an assemblage of curious and beautiful natural objects, unsurpassed—perhaps even unequalled—in any other part of the globe.

Past History of the American Continents.—We will now proceed to examine what is known of the past history of the two American continents, and endeavour to determine what have been their former relations to each other and to the Old World, and how their existing zoological and geographical features have been brought about. And first let us see what knowledge we possess of the past relations of North America with the Eastern continents.

If we go back to that recent period termed the Post-Pliocene—corresponding nearly to the Post-Glacial period and to that of prehistoric man in Europe—we find at once a nearer approximation than now exists between the Nearctic and Palæarctic faunas. North America then possessed several large cats, six distinct species of the horse family, a camel, two bisons, and four species of elephants and mastodons. A little earlier, in the Pliocene period (although fossil remains of this age are scanty), we have in addition the genus Rhinoceros, several distinct camels, some new forms of ruminants and an Old-World form of porcupine. Further back, in the Miocene period, we find a Lemuroid animal, numerous insectivora, a host of carnivora, chiefly feline and canine, a variety of equine and tapirine forms, rhinoceroses, camels, deer, and an extensive extinct family—the Oreodontidæ—allied to deer, camels, and swine. There are, however, no elephants. In the still earlier Eocene period most of the animals were peculiar, and unlike anything now living, but some were identical with European types of the same age, as Lophotherium and the family Anchitheridæ.