OREODON (i.e. " hillock-tooth ")  , the name of an Oligocene genus of North American primitive ruminants related to the camels, and typifying the family Oreodontidae . Typical oreodonts were long-tailed, four-toed, partially plantigrade ruminants with sharp-crowned crescentic molars, of which the upper ones carry four cusps, and the first lower premolar canine-like both in shape and function . In the type genus there are forty-four teeth, forming an uninterrupted series . The vertebral artery pierces the neck-vertebrae in the normal manner . The name Oreodon is preoccupied by Orodus, the designation of a genus of Palaeozoic fishes, and is likewise antedated by Merycoidodon, which is now used by some writers . See TYLOPODA .