The Uinta †titanotheres were much more numerous and varied than those of the White River; in the upper part of these beds are found two genera (_†Diplacodon_ and _†Protitanotherium_) which already had quite prominent bony protuberances on the nose; their canines were large enough to be of value as weapons and the incisors were well developed and functional. Evidently, there was a change here in the manner of feeding, the front teeth were used for cropping and browsing, a function which in the White River members of the family must have been largely taken over by the lips and tongue, while the growth of the horn-like protuberances on the skull rendered the canines superfluous as weapons. This latter change is one which recurs frequently in different phyla of the hoofed animals, in which the earlier and more primitive members had canine tusks, and the later, more advanced representatives developed horns, the tusks diminishing as the horns increased. While this rule is a general one, it is not entirely without exceptions. In the lower Uinta and in the Bridger the †titanotheres were extremely abundant and numerically they are the commonest of all fossils in those beds; no less than five series or phyla may be distinguished, three of them being added in the upper Bridger. The differences between the phyla, however, principally concern the forms of the teeth and the shape of the skull; in some the head was short and broad, in others long and narrow, and in others again of medium proportions; some had broad and extremely low-crowned grinding teeth, which in others were higher and more erect. But these are matters of minor detail, useful as they are in pointing the way to a proper arrangement of the various species; in essentials, the forms all agreed and constituted several series of closely allied genera. Comparing these Bridger animals with the great †titanotheres of the lower White River, the first and most obvious difference that strikes the observer is the very much smaller size of the more ancient types. With some variation in this respect, hardly any of the Bridger species exceeded a modern tapir in stature and very much resembled one in proportions. The canine teeth were tusks as large as those of a bear and must have been very effective weapons; the molar-pattern was identical with that found in the great Oligocene beasts, but the premolars were simpler and relatively smaller. [Illustration: FIG. 163.—†Titanothere (_†Mesatirhinus superior_) with long, narrow head; Bridger stage. Restored from a skeleton in the American Museum.] [Illustration: FIG. 164.—Second upper molar, right side of a Bridger †titanothere (_†Palæosyops_).]