The genus _†Amynodon_ is also represented in the upper Bridger beds, but by a species different from that of the Uinta stage. This more ancient species was a smaller animal than its upper Eocene successor and had less enlarged canine tusks, but it already possessed the typical rhinoceros molar teeth, the only Bridger mammal of which this is true. Beyond this species the line, as at present understood, cannot be traced, though probably some species of _†Hyrachyus_, or an allied genus, will prove to be the ancestor sought; but the connecting link has not yet been brought to light. The history of the rhinoceroses and rhinoceros-like animals, of which a very much simplified sketch has just been given, is a highly complex one, much more so than that of the horses, †titanotheres, or tapirs, and is less fully recorded, the earlier chapters of the story being still missing. However, in the progress of discovery these chapters will almost certainly be recovered, and it is already possible to draw close inferences as to what they will reveal. The complexity of the history is chiefly due to the fact that, as compared with the other perissodactyl groups, the rhinoceros stem ramified more widely and gave rise to more divergent and diversified forms. At one extreme, we find huge, massive, slow-moving types; and, at the other, light, slender, cursorial creatures, almost horse-like in appearance, with intermediate forms of moderate size. Some were long and others short legged, mostly adapted to terrestrial life, but some with aquatic habits. The three very different sorts of modification which the anterior teeth (incisors and canines) underwent in the three principal series may be taken as an illustration of this divergent development, and to these may be added a fourth, the complete suppression of all the incisors and canines above and below, as is exemplified by the modern African species.