Discovered at the White River formation 

The Merycoidodon fossil belongs to an extinct genus of herbivorous mammals from the Oreodont family, which thrived in North America during the Eocene to Miocene epochs (about 35 to 5 million years ago). Merycoidodon was a sheep-sized ungulate with a stocky body, short limbs, and a large skull featuring well-developed molars for grinding plant material. Fossils of Merycoidodon are commonly found in the White River Formation of the western United States, particularly in South Dakota, Nebraska, and Wyoming. These fossils provide insight into the evolution of early hoofed mammals and their adaptation to ancient grassland and woodland ecosystems. Due to their abundance and well-preserved skeletal structures, Merycoidodon fossils are widely studied in paleontology.

Merycoidodon and other oreodonts do not have any direct living descendants, as they belong to an extinct group of Artiodactyls (even-toed ungulates) that diverged from modern lineages. However, their closest living relatives are thought to be camels (Camelidae), pigs (Suidae), and peccaries (Tayassuidae) within the order Artiodactyla.

Molecular and anatomical studies suggest that oreodonts were more closely related to camels and llamas rather than pigs, despite some superficial similarities to the latter. While oreodonts themselves went extinct during the Miocene, their distant relatives continue to thrive in various ecosystems worldwide.