Iguanodontia

Iguanodontia is a clade of dinosaurs within the larger ornithopod group that includes Iguanodon and all more derived relatives that share a more recent common ancestry with Iguanodon than with Hypsilophodon. In widely used cladistic definitions, it is the smallest clade containing Iguanodon bernissartensis and Hadrosaurus foulkii and excluding Hypsilophodon foxii.

They existed from the Early Cretaceous to the Late Cretaceous, about 130 to 66 million years ago. Fossils have been found on multiple continents, including Europe, North America, and Asia, indicating a wide distribution.

Morphologically, iguanodontians were herbivorous dinosaurs characterized by beaked mouths; early forms had elongated bodies with grasping hands, while the later hadrosauroids had dental batteries and specialized teeth for processing tough vegetation. They were capable of facultative quadrupedal locomotion, meaning they could move on all fours or two legs as needed.

Taxonomically, Iguanodontia includes the early iguanodontids (such as Iguanodon and its close relatives) and the later hadrosaurs (duck-billed dinosaurs) and their kin, representing a major evolutionary transition within Ornithopoda. The hadrosaurs in particular became some of the most common and successful herbivores in Late Cretaceous ecosystems.

Notable members include Iguanodon, Mantellisaurus, and Camptosaurus among the earlier iguanodontians, and Hadrosauridae such as Edmontosaurus and Parasaurolophus among the later forms.