TITANOTHERES.—
This group of odd-toed mammals appeared first in the [Eocene], at which time they were about the size of a sheep. By Middle [Oligocene] time they had increased to gigantic proportions but still had a small and primitive brain. Brontotherium ([Pl. 48]) was slightly rhinoceros-like in appearance and is believed to be the largest land animal that ever inhabited the North American continent. This animal was about 8 feet tall at the shoulders; a large bony growth protruded from the skull and this was extended into a flattened horn, which was divided at the top.
Plate 48
[TERTIARY] MAMMALS
UINTATHERIUM × ¹/₄₅ BRONTOTHERIUM × ¹/₃₅
Although the titanotheres underwent rapid development during the early [Tertiary], these huge beasts became extinct during the middle of the [Oligocene] epoch. Titanothere remains have been reported from the Trans-Pecos region of Texas.
CHALICOTHERES.—
The chalicotheres were in some ways like the titanotheres, but they also exhibited many peculiarities of their own. The head and neck of Moropus, a typical chalicothere, were much like that of a horse, but the front legs were longer than the hind legs, and the feet resembled those of a rhinoceros except that they bore long claws instead of hoofs. The chalicotheres lived in North America from [Miocene] until [Pleistocene] time but were probably never very numerous, and their remains have not yet been discovered in Texas.
RHINOCEROSES.—
The rhinoceroses are also odd-toed animals, and there are many interesting and well-known fossils in this group. The woolly rhinoceros ([Pl. 49]) was a [Pleistocene] two-horned form that ranged from southern France to northeastern Siberia. The woolly rhinoceros is well known from complete carcasses recovered from the frozen tundra of Siberia and from remains that were found preserved in an oil seep in Poland. These unusual specimens plus cave paintings made by early man have given a complete and accurate record of this creature. Although the woolly rhinoceros has not been reported from Texas, other [fossil] rhinoceroses have been found in the High Plains and Gulf Coastal Plain of Texas. These fossils have been found in rocks ranging from Middle [Oligocene] to late [Pliocene] in age.