An ornithopod is the infraorder of bird-hipped dinosaur, 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. Their major evolutionary advantage was the progressive development of a chewing apparatus that became the most sophisticated ever developed by a reptile. They had beaks, multiple teeth rows, cheek pouches and true chewing. Efficient chewing means faster digestion, as the material is broken into smaller pieces.
|Ornithopod dinosaurs. Far left: Camptosaurus|
left: Iguanodon, centre: Shantungosaurus
centre foreground: Dryosaurus, right: Corythosaurus, far right: Tenontosaurus.
They reached their apex in the duck-bills, before they were wiped out by the Cretaceous–Tertiary extinction event with all other non-avian dinosaurs. Members are known from all seven continents, although the Antarctic remains are unnamed, and they are generally rare in the Southern Hemisphere. They are the sister group to the horned dinosaurs (Ceratopsia) and the hard-headed dinosaurs (Pachycephalosauria).