Date: Eocene Epoch (56-34 million years ago)
Description: Brontotheres were mammals that belonged to the same order as modern rhinoceroses and horses. Originally quite small, Brontotheres quickly grew in size in the Eocene Epoch until they were over 8 feet in height. They had four toes on their hind feet and three on the front, unlike modern horses and rhinos which only have one toe on each foot. They had horn-like appendages on their faces much like the modern rhinoceros, but these “horns” were made of bone instead of ivory. Their teeth, like the ones shown here, had shearing cusps to grind down vegetation. They died out when the climate became drier and tough grasses replaced their usual food supply. Brontothere fossils like these teeth can be found in southern South Dakota.
Donor: Sioux City Academy of Science and Letters