Ornithopoda

Ornithopoda is a clade of herbivorous dinosaurs within the larger group Ornithischia. It includes a wide range of forms from small, agile bipeds to larger, possibly facultatively quadrupedal animals. The clade encompasses major lineages such as the iguanodontians and the hadrosaurs (duck-billed dinosaurs), which together were among the most successful and long-lived herbivores of the Mesozoic.

Anatomically, ornithopods are characterized by a beaked mouth and a dental system adapted for processing vegetation. Most have a rostral beak and cheeks with teeth arranged in dental batteries of tightly packed, replacement teeth suitable for grinding tough plant material. Forelimbs were often shorter than hind limbs in early members, with some later forms able to support weight on all fours.

Phylogeny and evolution: Ornithopoda first appears in the Early Jurassic and, through the late Jurassic and Cretaceous, undergoes several radiations. The iguanodontians gave rise to hadrosaurs, which became highly diverse and widespread. Hadrosaurs display sophisticated skull features and complex dental batteries that enable efficient processing of fibrous plants.

Distribution and ecology: Fossils are found worldwide, with particularly abundant record in North America, Europe, and Asia. Ornithopods occupied a variety of habitats, from coastal and riverine environments to forested areas. They ranged in size from small forms to large, duck-billed dinosaurs, and they played key roles as primary herbivores in many ecosystems.