Brontotheriidae (Greek: βροντη, brontē + θήριον, thêrion; "thunder beast") is an extinct family of large mammals resembling rhinoceros, which once lived in North America and Asia.
The brontotheres were named in part due to accounts of discovery of their remains by the Lakota Sioux in what is now the Dakotas and Montana of the United States; they had believed they were creatures who ran on top of the clouds, delivering rain and thunder on the plains.
Characteristics shared by all brontotheriid species include an abbreviated face, an elongated postorbital cranium, and the outer shearing blades on the molars bearing a "W" or wedge shape. Despite being members of Perissodactyla, all species had four toes on the front feet; the rear feet bore three.
The familiar species (Embolotherium, Megacerops, etc.) were of large size, easily standing over eight feet at the shoulder with estimated weight of nearly four tons. The head bore horns on the snout made entirely of bone; unlike rhinos, these horns were side-by-side instead of one behind the other, and in some brontothere species the horns were fused into a bizarre "slingshot" or "battering ram" appearance. It has been surmised that the horns were used in combat between bulls during mating season.
Brontotheres are claimed by evolutionists to have first evolved from Eotitanops during the late Paleocene 56 million years ago, and reached their peak in the late Eocene, 33.9 million years ago.
- Osborn, Henry Fairfield. The Titanotheres of Ancient Wyoming, Dakota, and Nebraska; Washington, D.C. United States Department of the Interior (1929)