extinct genus of mammals (mammal) found as fossils (fossil) in deposits dated to the Paleocene Epoch (65.5–55.8 million years ago) of North America. Ptilodus was a multituberculate, a group of rodentlike (rodent) mammals that were once the dominant herbivores and granivores in terrestrial ecosystems. The teeth of Ptilodus included long rodentlike incisors, bladelike shearing teeth with striations, and molars with parallel rows of cusps. The palate had large spaces, and powerful chewing muscles were attached to the lower jaw.