Iguanodon, genus of large, herbivorous dinosaurs (see Dinosaur), of the suborder Ornithopoda, that lived worldwide during the Early Cretaceous period. Iguanodon weighed as much as 4.5 metric tons, attained a length of 7.5 m (25 ft), and stood up to 4.5 m (15 ft) tall on stout hind legs. The three toes of the feet and four of the five digits of the shorter forelimbs were equipped with flat, hooflike claws; the hand's first digit, a bony, spike-shaped thumb situated at a right angle to the other fingers, may have been used for defense. Iguanodon's long, flat head ended in a horny beak, and its jaws contained teeth that somewhat resemble those of the iguana lizard—hence, the name. These animals may have browsed in packs and probably assumed a four-legged stance while eating.