EXTINCT RHINOCEROTIDAE.--The existing Rhinoceroses are thus confined to Africa, to certain parts of the continent of Asia, and to some of the large islands lying to the south of that continent. But formerly the genus, and allied genera, had a wider range. As far back as the Miocene we meet with remains of Rhinoceroses closely allied to existing forms. The more ancient forms have, as is natural, more ancient characters. Thus in _Rh. schleiermacheri_ of the Miocene, canines appear to have been present. The Miocene _Aceratherium_, primitive in the absence of horns as its {259} name denotes,[170] had also canines and, in one species, six incisors in the lower jaw. This _Aceratherium_ had, moreover, four toes in the fore-feet. In the Miocene and later the Rhinoceros existed in Europe and America. There was even a purely northern form, the _Rh. tichorhinus_, which possessed a woolly covering and had the same range as the Mammoth. This Rhinoceros was two-horned. The post-Pliocene and European _Elasmotherium_ was a colossal rhinocerotine creature. This great beast had two horns and a body 15 feet long. Its limbs are not known, and as the teeth are different from those of Rhinoceroses in general, it may not have belonged to this group at all, though Osborn is inclined to derive it from _Aceratherium_, admitting at the same time that the evidence is "decidedly slender." The teeth in fact are like those of a Horse in being hypselodont and prismatic in form. As to the two horns, they were apparently not exactly like those of typical Rhinoceroses; there was an enormous horn posteriorly, supported on a huge boss of bone, and in front of this a roughened spot suggests a smaller or at least a much more slender horn. It is important to notice that fossil Rhinoceroses belonging to the restricted genus _Rhinoceros_ were in Europe invariably two-horned; it is only in India, where they still exist, that one-horned forms are met with in a fossil state. [Illustration] FIG. 134.--Skeleton of _Hyracodon nebrascensis_. x 1/12 (After Scott.)