Merycoidodontoidea

Extinct superfamily of mammals

Merycoidodontoidea, previously known as "oreodonts" or "ruminating hogs," are an extinct superfamily of prehistoric cud chewing artiodactyls with short faces and fang like canine teeth. As their name implies, some of the better known forms were generally hog like, and the group has traditionally been placed within the Suina (pigs, peccaries and their ancestors), though some recent work suggests they may have been more closely related to camels. "Oreodont" means "mountain teeth," referring to the appearance of the molars. Most oreodonts were sheep sized, though some genera grew to the size of cattle. They were heavy bodied, with short four toed hooves and comparatively long tails. The animals would have looked rather pig or sheep like, but features of their teeth indicate they were more closely related to camelids. They were most likely woodland and grassland browsers, and were widespread in North America during the Oligocene and Miocene. Later forms diversified to suit a range of different habitats. For example, Promerycochoerus had adaptations suggesting a semiamphibious lifestyle, similar to that of modern hippos. and many of these genera may prove to be synonymous. The last researchers to fully review oreodont taxonomy, C. Bertrand Schultz and Charles H. Falkenbach, have been criticized for erecting excessive numbers of genera, based in part on apparent anatomical differences between different specimens that were actually taphonomic deformations due to postburial forces.

This diverse group of stocky prehistoric mammals grazed amid the grasslands, prairies, or savannas of North and Central America throughout much of the Cenozoic era. First appearing 48 million years ago (Mya) during the warm Eocene epoch of the Paleogene period, the oreodonts dominated the American landscape 34 to 23 Mya during the dry Oligocene epoch, but they mysteriously disappeared 4 Mya during the colder Pliocene epoch of the late Neogene period. Today, fossil jaws and teeth of the Oreodonta are commonly found amid the 'Oreodon beds' (White River Fauna) of the White River badlands in South Dakota, Nebraska, Colorado and Wyoming. Many oreodont bones have also been reported at the John Day Fossil Beds National Monument in Oregon. Some oreodonts have been found at Agate Fossil Beds National Monument. In Oligocene/Miocene Florida, oreodonts are surprisingly rare. Instead of the swarms found elsewhere, only six genera of oreodonts are known to have ranged there, and only one, Mesoreodon, is known from a single, good skeleton.

The majority of oreodonts are presumed to have lived in herds, as suggested by the thousands of individuals in the various mass mortalities seen in the White River Badlands, Nebraska Oreodont beds, or Chula Vista, California.