Brontotheriidae

Brontotheriidae or brontotheres, also called the invalid name Titanotheriidae, is a family of extinct mammals belonging to the order Perissodactyla, the order that includes horses, rhinoceroses, and tapirs. Despite their superficial similarity to rhinos, the family's exact relationships to other perissodactyls are unknown, and are not classified any more specifically than as perissodactyls. They lived around 56–34 million years ago, until the very close of the Eocene.