PHENACODUS

extinct genus of primitive mammals known from fossils of the Early Eocene Epoch (57.8 to 52 million years ago). Though too late in time to have been the ancestral form from which the hoofed mammals evolved, Phenacodus represents a late-surviving form that retained many of the primitive traits that a common ancestor must have possessed. In structure and dentition, Phenacodus appears to be intermediate between the early carnivores and the early herbivores. Though the canine teeth are large and well developed, the cheek teeth were at least partly adapted to a plant diet.