Page:EB1911 - Volume 28.djvu/1039

Rh coursers (Glareolidae), and bustards (Otididae), of which there are numerous genera confined to the area. The two families last named, together with that of the Panuridae (represented by the bearded tit), being solely Old World, are of themselves sufficient to distinguish the Palaearctic from the Nearctic fauna.

Of reptiles there is not much to be said, the Palaearctic subregion, in its restricted sense, being characterized by the poverty of its fauna, several of the widely spread families of the Old World, such as the Varanidae and Agamidae, stopping short of its southern limits. Among batrachians, the tailed salamanders are common in this and the Mediterranean region (as in the northern hemisphere generally), the genera Salamandra and Chioglossa, as well as the frogs and toads of the genera Alytes and Pelobates, being unknown in the Nearctic subregion, while newts (Molge) abound in the Palaearctic and are rare in the Nearctic subregion. The olm (Proteus) is a native of the Mediterranean rather than the proper Palaearctic area.

As regards fishes, the subregion differs from the Nearctic province by the absence of bony-pike (Lepidosteidae), bow-fins (Amiidae), and the family Catostomatidae, as typified by the "suckers," "red horses" and "stone-rollers" of the genus Catostomus, and the presence of loaches (Cobitidae) and barbels (Barbus).

As compared with the Palaearctic (and Mediterranean) province of the Holarctic region the Nearctic subregion (together with the Sonoran transitional zone) is characterized by the extreme poverty of its fauna of hollow-horned ruminants. Of so region, is generically (and subgenerically) identical with its European relative, while the musk-ox can scarcely be regarded as a distinctive Nearctic type, seeing that it is only since the Pleistocene epoch that it has ceased to be a denizen of northern Europe and Asia. The only other living members of the group are the bighorn sheep (Ovis canadensis), which has representatives in Kamchatka and north-eastern Siberia, and the white, or Rocky Mountain goat (Oreamnus, or Haploceros), which is a peculiar type. All must be regarded as originally immigrants from Europe; and it is noteworthy that in the Nearctic Pleistocene are several extinct types of musk-oxen, together with certain other genera which may possibly serve to connect the white goat and the musk-ox with the serow and the takin of the Old World. The deer (Cervidae), apart from the three Old World types alluded to under the heading of the Holarctic region, are altogether peculiar types referable to the genus Mazama (subgenus Dorcelaphus, Cariacus or Odocoileus), but they may be akin to the Asiatic Elaphurus, and the group is certainly of Old World origin. The same may be said of the bears (Ursidae), in which the black bear (Ursus americanus) is a peculiar species, although probably allied to the Himalayan U. torqualus. In the brown bear group (U. arctus) it is noteworthy that while the Alaskan forms are very close to those inhabiting Kamchatka and Amurland, the Rocky Mountain grizzly, which has penetrated farther into the continent, is more distinct. The grey-fox (subgenus Urocyon) is a characteristic Nearctic type. Among other groups of mammals, the following generic groups distinguish the Nearctic from the Palaearctic subregion, although some of them enter the Sonoran area. In the Insectivora we have Blarina, Scalops and Scapanus; in the Carnivora Procyon among the raccoons, Mephitis among the skunks, and Taxidea among the badgers. Cynomys ("prairie-dog ") is a characteristic rodent; and in the same order a very important feature is the replacement of all the true rats and mice (Murinae) of the Old World by the deer-mice and their allies belonging to the subfamily Cricetinae, which is but poorly represented in the Old World. Peromyscus is a very characteristic Nearctic genus, although it has an analogue in the Old World in the form of the single representative of the Persian Calomyscus. The wood-rats of the genus Neotoma and the musquash (Fiber) are characteristic Nearctic types of the vole-group. More important is the family Haplodontidae, represented only by the sewellels (Haplodon, or Aplodon), all the members of which are exclusively North American, although some are Sonoran. The pocket-gophers (Geomyidae) and kangaroo-rats (Heteromyidae) are also solely American, though more developed in the Sonoran than in the Nearctic area; Geomys and Thomomys in the former and Perognathus in the latter family are, however, found in the Nearctic area. Lastly, among the rodents, we have the Canadian porcupine (Erithizon), typifying the New World family Erithizontidae. Among bats it must suffice to state that the genus Lasiurus (Atalapha) is solely North American.

Reference to the Tertiary mammal-faunas of North America must be of the briefest. It may be mentioned that even in the Pleistocene these display a much greater development of large forms than occurs at the present day; while a notable feature at this epoch is the mingling of Arctogaeic and Neogaeic types, as exemplified by the occurrence of elephants and mastodons alongside of ground-sloths (Megalonyx and Mylodon). In the Pliocene and Miocene, the fauna was more of an Old World type, including a great development of camels (Tylopoda), horses (Equidae), rhinoceroses (Rhinocerotidae), mastodons, &c., but also a number of peculiar types, such as the ruminating oreodonts (Oreodontidae, or Merycodidae), the perissodactyle Titanotheriidae, and the more generalized Uintatheriidae, which typify a subordinal ungulate group

by themselves. It has been suggested that some of the more widely spread of these groups, such as the camels and horses, may have originated in the New World, but there seems at least an equal probability that Central Asia—or a land-area common to Asia and America—may have been their birthplace.

The earliest Tertiary North American fauna is that of the lowest, or Puerco, Eocene, which includes a number of mammals of various types, some of the largest being of the approximate dimensions of a mastiff. Evidently the Puerco epoch was a period of great development and radiation on the part of mammals; its fauna including primitive creodont Carnivora, amblypodous and condylarthrous Ungulata, and a number of smaller types, some of which were probably related to the modern Rodentia, Insectivora and Primates. As only a foreshadowing of the Puerco mammals is found in the under upper Cretaceous Laramie beds, it has been suggested that the fauna was largely of northern origin.

By the middle of the Eocene period the more generalized types of the Puerco fauna had almost disappeared, although a few creodonts survived till the Oligocene. It is surmised that the low brain-capacity of the members of this fauna rendered them unfit to cope with the irruption of more highly organized mammals which suddenly appeared on the scene in the Lower Eocene; this new fauna, it is conjectured, may have developed from a side-line of the original Puerco stock which had remained in the old northern home at the time of the earlier radiation.

"Assuming that the Puerco mammals," observes Mr Madison Grant, "were driven out of more northerly or boreal lands, where they had originally developed, by a declining temperature, it is conceivable that some animals remained behind and adjusted themselves to the changed conditions, until a still further increase of cold freed them also to follow the path of their predecessors, southward.

"Some of these Lower Eocene types of this second radiation, which are found in the Wasatch beds of Wyoming, have sent down lines of descendants, which have ultimately culminated in existing animals. At this time first appear the horses, tapirs, rhinoceroses, camels and dogs (or rather the ancestral stocks thereof). Some of these animals, such as the horses and rhinoceroses, are found contemporaneously in Europe, others, like the (ancestral) camels, are peculiar to America [some of the later types have recently been discovered in Asia].

"Being more highly organized and better adapted to their environment, these new types entirely supplanted the older fauna, and by the Oligocene this transformation was complete, and the older fauna had disappeared. This Wasatch fauna culminated, and then faded gradually away on this [American] continent, until in the Middle Pleistocene it was largely supplanted by arrivals from Asia."

The relationship of the fauna to that of South America, and the interchanges which took place between the two during the Pleistocene and Pliocene epochs, have been already sufficiently discussed when treating of Neogaea.

Of the birds of the Nearctic subregion and the adjacent Sonoran zone, there are a very large number of peculiar genera in the passerine order, a large proportion of which are referable to the finch-group (Fringillidae), and the American warblers (Mniotiltidae), the latter being solely a New World family; there are also a few stragglers from the Neogaeic family of tanagers (Tanagridae). Among game-birds the turkeys (Meleagris), the ruffed grouse (Bonasa), the prairie-grouse (Tympanuchus, or Cupidonia), the sage-cock (Centrocercus), the prairie-chicken (Pedioecetes), and several genera of the American partridges (Odontophorinae), such as Lophortyx and Ortyx ("bob-white"), may be cited as characteristic Nearctic groups, although some extend farther south. Turning to reptiles, the presence of rattlesnakes (Crotalus) is a feature broadly distinguishing the Nearctic subregion (together with America generally) from the Palaearctic; in the more southern territories we also enter the domain of iguanas; while among chelonians we have the family of snappers (Chelydridae), the "stink-pot terrapins" (Cinosternidae), and in the Testudinidae the box-tortoises (Cistudo), and the terrapins of the genera Chrysemys and Malacoclemmys are solely American, although some of them range far to the south, while during the Pliocene the snappers were represented in Europe. There are several more or less peculiar types of North American amphibians, but since these are for the most part Sonoran in range, they may be best noticed in a later paragraph.

From that of the Palaearctic (+Mediterranean) subregion the fish-fauna of the Nearctic subregion (together with that of at least much of the Sonoran area) is broadly distinguished by the presence of bony-pike (Lepidosteidae), bow-fins (Amiidae), and the members of the family Catostomatidae, for which there appears to be no collective English name, as well as by the absence of the loach family (Cobitidae), and barbels (Barbus) among the Cyprinidae.

The last of the zoological provinces into which the land-surface of the globe is divided on the evidence of the distribution of mammals and birds is the Sonoran, which, although often regarded as an