264 TITANOTHERES CHAP. X 
Hyracodonts, and it is suggested that when swimming it was 
raised above the surface as with the Hippopotamus. “This 
feature,” observes Professor Osborn, “with the long curved tusks, 
undoubtedly used in uprooting, suggests the resemblance between 
the habits of these animals and those of the hippopotami.” There 
were no horns in the Amynodonts. The face is shorter than 1 
the Hyracodonts, and the mastoid is covered as in recent Rhino- 
ceroses. The canines are very strongly developed into tusks, but 
the incisors show signs of disappearance. We know of the genera 
Amynodon, Metamynodon, and Cadurcotherium. All except the 
last, which is European, are American in range. 
Fam. 4. Titanotheriidae—— These Oligocene Ungulates, often 
attaining to large dimensions, are nearly peculiar, so far as is at 
present known, to the North American Continent, and are at least 
most abundant in it.’ Many generic names, such as 7%tanotherium, 
Lrontotherium, Brontops, Titanops, and Menodus, have been given 
to them; but a recent study of the entire material accessible for 
description or already described has led Professor Osborn to the 
opinion that there was but a single genus, to which the name 
Titanothervum must be applied. Of this genus there are some 
thirty well-characterised species, of which the gradual evolution 
can be traced from the lowest strata of the White River beds 
where their remains occur. An entire skeleton of 7. robustum 
enables us to understand the osteology of these forms and _ to 
compare them with other Perissodactyles. This animal was more 
than 13 feet long, standing some 7 feet 7 inches in height. It 
seems to have presented during life the aspect of a Rhinoceros with 
perhaps a touch of Elephant. The skull is not unlike that of a 
Rhinoceros in general dimensions and shape; but there are a pair 
of apparent horn cores anteriorly, which are smaller in the more 
ancient forms and acquire a large size, a forward direction with a 
divergence of the two in the later forms. A glance at the 
accompanying figures of skulls (Fig. 137) of early and later 
Titanotheres will exhibit the changes in this particular which the 
skulls underwent in the lapse of time occupied by the deposition 
of these Oligocene beds. The nasals are short in the later, longer 
in the more early species, such as 7. heloceras and T. coloradense. 
The zygomatic arch projects much, and is “shelf-lke” in the 
later forms, the skull thus getting:an immense breadth, which, 
] > 
temains of the genus have been met with in the Balkans. 
