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stupid compared with the shrewdness of their modern supplanters (Fig. 26).

Incursion of the modernized mammals. The archaic mammals barely survived the Eocene, only one group, the hyænodonts, being found in Oligocene rocks. Early in the Eocene, however, are seen the vanguard of an army of invaders, none of which seem directly related to the native mammals. Their

simultaneous appearance in North America and Europe points to a contiguous center of evolution somewhere to the north, either a circumpolar land or the northern part of what is now Asia. Here they underwent their primal evolution and here they were endowed with the highest potentialities along the three directions wherein the archaic mammals failed. Climatic oscillation in the north in the early Tertiary drove these modernized mammals south along the three continental radii, not all at once, but in a series of drives, until the competi

tion became too severe for the native inhabitants to endure. Assimilation of the native stocks by such an invading army is impossible among animals, however it may be with mankind. The archaic mammals, therefore, had but little choice. Some lingered on, enduring the competition until it became greater than they could bear, others may have migrated still farther south to find asylum, which served to postpone their inevitable fate. Yet others, a very few, may have evolved into higher types, such as the family Miacidæ of the archaic carnivores, although whether they deserve the stigma of genetic relationship with the other archaics in view of this potentiality is somewhat doubtful.

Rise of grazing mammals. The modernized invaders are now established in their kingdom; they are the early oddtoed ungulates-horses, rhinoceroses, tapirs; the even-toed ungulates, such as camels, deer, and swine; the rodents; the carnivores, insectivores, and primates; and in the Old World the proboscideans or elephants and mastodons. Continental elevation in Europe and more especially in Asia during the Miocene brought in its train a marked increase in aridity which in turn had a more or less profound effect upon the flora of the temperate zones, for it meant a diminution of shrubby and herbaceous plants and a wide expansion of the harsher grasses, which now become the dominant note in the world's flora.

This could not but affect the mammals most profoundly, especially the hoofed forms. Floral differentiation during the Oligocene had already made its impress upon certain groups, such as the horses, so that they in turn were differentiating along several lines, some with short-crowned teeth suited to tender herbage, others with grinders whose length and complexity forecast the grazing teeth of their successors and whose dietary choice led in the direction of the coming grasses. Then came the floral change of the Miocene and with it a rapid

PLATE IV.-Restorations of archaic mammals. A, cursorial type, Phenacodus primavus; B, swamp-dwelling amblypod, Coryphodon; C, four-horned amblypod, Dinoceras, the culmination of its race. After Lull.

expansion of grazing forms-horses, camels, deer-and the restriction and often the extinction of browsing types. It is true that browsing forms are still extant, but not in their old profusion nor in their old homes, while the grazing forms are numerous and characteristic of the widespread steppes the world over.

Origin of man. We have observed the influence of geologic change in the evolution of the brute, and we have now to inquire whether mankind in his long upward course has been amenable to those same laws or whether he has been a thing apart from other forms of life, whose development has been controlled by other influences. As the primates, the group to which mankind belongs, are to be classed with the modernized mammals, their course of evolution up to the point of their differentiation as primates must have been one with all the rest and hence the result of the same chain of causes. And their differentiation from the other mammals when they came to the parting of the ways seems to have been due to the departure of the latter from their primal mode of life and structure rather than to any special evolution of the primates themselves, for in many ways they are among the most primitive of the modernized hosts, and their tree habitations may well have been a very ancient habitat of the whole mammalian race.R

They throve in their northern home just as did their other compatriots, and like them drove southward along the several continental radii, the rear guard drawing in toward the equator with the northern limits of the tropical forests within which they dwelt and upon which, with rare exceptions, they are dependent to this day for food and safety. They reached North America, as the map (Fig. 27) indicates, early in Eocene time (Wasatch) and became so abundant as to form a

8 Matthew, W. D., "The Arboreal Ancestry of the Mammalia." Amer. Nat., vol. 38, 1904, pp. 811-818.