Uintatherium is an extinct genus of mammals. Fossil remains were discovered near Fort Bridger, Wyoming. This was a large browsing animal, about the size of a rhinoceros. What was most unusual about Uintatherium was its skull which was large and strongly built. Uintatherium had a flat, concave skull - a feature not found in any other mammal, save, perhaps in some brontotheres. Its cranial cavity was exceptionally small due the walls of the cranium being tremendously thick. The weight of the skull was mitigated by numerous sinuses permeating the walls of the cranium, like those in an elephant's skull. The large upper canines were apparently formidable defensive weapons, which resembled the canines of the saber-toothed cats and were larger in males than in females.
The skulls of the males bore six prominent knob-like ossicones which grew from the frontal region of the skull. The function of these structures is unknown. They may have been of use for defense or sexual display. Uintatherium lived during the early to middle portions of the Eocene period (45-40 million years ago). It was an herbivore, eating leaves, grasses and shrubs. Uinthaterium lived near water and used its sabre-like canines to pluc the aquatic and marsh plants which comprised its diet. It became extinct by climatic changes and competition with brontotheres, and true and hyrachodont rhinocerii without leaving any descendants.
A cast of a Uintatherium skeleton is on display at the Utah Field House of Natural History State Park.