- Name: Uintatherium (Greek for "Uinta beast"); pronounced WIN-tah-THEE-ree-um
- Habitat: Plains of North America
- Historical Period: Middle Eocene (45-40 million years ago)
- Size and Weight: About 13 feet long and 1-2 tons
- Diet: Plants
- Distinguishing Characteristics: Large size; small brain; three pairs of knobby horns on the skull
One of the first prehistoric megafauna mammals ever to be discovered, in late-nineteenth-century Wyoming, Uintatherium figured in the "Bone Wars" waged between the famous American paleontologists Edward Drinker Cope and Othniel C. Marsh. This bizarre, plant-eating beast was worth a good fight: Uintatherium was distinguished by the three, count 'em, three pairs of knobby horns on its head (which may only have grown on males, as a way to increase their attractiveness to females during mating season), making it look a bit like a mutated rhinoceros. (So enamored were Cope and Marsh of Uintatherium that they managed to name it half a dozen times, the now-discarded genera including Dinoceras, Ditetradon, Elachoceras, Octotomus, Tinoceras and Uintamastix.)
As with other early mammals of the Eocene epoch, about 40 million years ago, Uintatherium didn't exactly excel in the intelligence department, with an unusually small brain compared to the rest of its bulky body--no doubt an artifact of its plant-eating diet and its relative lack of natural enemies, as full-grown Uintatherium adults would have been virtually immune to predation. How it survived for so long is a bit of a mystery, one compounded by the fact that this mysterious beast (and its fellow "uintatheres") vanished completely off the face of the earth by the later Eocene epoch, leaving very few fossil remains in its wake. One theory is that Uintatherium was gradually displaced by better-adapted megafauna mammals, such as the "thunder beast" Brontotherium.