ornithopods

Ornithopods are a clade of herbivorous dinosaurs within the larger group Ornithischia. The name, meaning "bird feet," refers to their distinct feet and hip morphology. They first appeared in the Early Jurassic and became one of the most diverse and widespread dinosaur groups, persisting into the Late Cretaceous.

Anatomically, ornithopods typically possessed a keratinous beak and a series of small, leaf-shaped teeth arranged in dental batteries that allowed efficient processing of vegetation. They ranged from small, agile bipeds such as Hypsilophodon to larger, often facultatively quadrupedal forms like Iguanodon and the later hadrosaurs, or duck-billed dinosaurs. Hadrosaurs are especially notable for their extensive dental batteries and, in many species, crested skulls used for display and possibly sound production.

Locomotion varied with size. Smaller species were primarily bipedal, while larger taxa could walk on four legs when feeding or at rest. They were numerically and geographically widespread, with fossils found across North America, Europe, Asia, Africa, and Antarctica, indicating a dominant role in many Cretaceous ecosystems.

Ecology and behavior evidence includes trackways and nesting sites that suggest social behavior in several hadrosaur taxa, including possible herd movement and group nesting. Notable genera include Hypsilophodon, Iguanodon, Parasaurolophus, and Edmontosaurus.