Iguanodontidae is a family of large, herbivorous ornithopods that flourished during the Early Cretaceous, roughly 140 to 100 million years ago, primarily across Europe and Asia. The family's most recognizable feature is a prominent conical spike on each thumb, likely used for defense, for sparring between individuals, or for processing tough vegetation, paired with a long, flexible fifth finger thought to have aided in gathering food. Diagnostic skeletal traits also include a jaw joint set below the tooth row, which allowed a grinding, side-to-side chewing motion unusual for reptiles of the time, along with leaf-shaped cheek teeth suited to breaking down fibrous plant material.
The type genus Iguanodon, described from England in the early 19th century, was one of the first dinosaurs ever scientifically named and played a foundational role in establishing dinosaurs as a distinct group of animals. Iguanodontids could move on two legs or drop to all fours depending on speed and activity, and their success is reflected in an extensive fossil record across Belgium, England, Germany, and parts of Asia. The family is frequently treated as a model for understanding the broader radiation of large ornithopods that continued into the mid-Cretaceous hadrosaur lineages.