Ornithopods

Ornithopods /ɔrˈnɪθɵpɒd/ or members of the clade Ornithopoda /ɔrnɨˈθɒpədə/ are a suborder of Ornithischian Dinosaurs that started out as small, bipedal running grazers, and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world, and dominated the North American landscape. Their major evolutionary advantage was the progressive development of a chewing apparatus that became the most sophisticated ever developed by a non-Avian Dinosaur, rivaling that of modern Mammals such as the Cattle. They reached their apex in the duck-billed Hadrosaurs, before they were wiped out by the Cretaceous–Paleogene Extinction Event along with all other non-Avian Dinosaurs. Members are known from all seven continents, though they are generally rare in the Southern Hemisphere.

They date back to the Middle Jurassic.