xe : HORNLESS EXTINCT FORMS 259 
name denotes,! had also canines and, in one species, six incisors 
in the lower jaw. This Aceratheriwm 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 Aceratheriwm, 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. 7 
The Rhinoceroses of America were mostly hornless.  Dicera- 
thertwm is an exception ; but in many cases it had two parallel not 
successive horns, and these were, to judge from the sheht promi- 
nences, but feeble in development, and perhaps hardly exactly 
comparable with the formidable weapons of the Old-World forms. 
Aceratherium tridactylum, with indications of paired horns, may 
be ancestral to Dicerathertum. The American forms have weak and 
slender nasals in correspondence with the absence of horns; the 
sagittal crest 1s retained in contradistinction to the great flattened 
surface of the skull in the horned Rhinoceroses. _Aceratheriwm of 
both divisions of the globe probably represents the ancestral group 
of the horned and the hornless forms. This being the case it is 
highly interesting to note a distinct convergence in the quite 
' Quite recently, however, a species, A. incisivwm, preserved at Darmstadt, 
has been found by Professor Osborn to possess a slight rugosity upon the frontal 
bones, which probably indicates the presence of a rudimentary horn, and the same 
author is apparently inclined to place in Aceratheriwm the horned Teleoceras 
(see p. 261). 
