Iguanodon was a dinosaur that had a horny, toothless beak and tightly-packed cheek teeth. On each hand, Iguanodon had four fingers plus a conical thumb spike on each hand (that was perpendicular to the other fingers). The thumb spikes may have been used for defense or in obtaining food; it ranged from 2 to 6 inches long. Iguanodon had a flat, stiff tail and three-toed hind feet with hoof-like claws. Its legs were much larger than its arms.
Iguanodon averaged about 30 feet long (9.3 m), 16 feet tall (5 m), 9 ft (2.7 m) tall at the hips, and may have weighed 4 to 5 tons.Iguanodon lived in the early Cretaceous period, about 135-125 million years ago, toward the end of the Mesozoic. The supercontinent Pangaea was breaking up at this time, but Iguanodon managed to spread to all the continents except Antarctica. Among the contemporaries of Iguanodon were Baryonyx, Brachiosaurus, and Hypsilophodon.Iguanodon was probably a herding animal, as evidenced by bonebed discoveries in Belgium. In these bonebeds, dozens of Iguanodon fossils were found together, suggesting that they congregated during their lives.Iguanodon was an herbivore, a plant eater. It probably nipped cycads and other prehistoric plants with its tough, toothed beak. It had no teeth in the front of its mouth, but had strong teeth (about 2 inches long) in the side of its jaw (cheek teeth) which it used to grind up tough plant material. Iguanodon was an ornithopod, whose intelligence (as measured by its relative brain to body weight, or EQ) was midway among the dinosaurs.Iguanodon could run on two legs or walk on four; it was a relatively fast dinosaur. British paleontologist David Norman showed that some mature Iguanodons were quadrupedal. Iguanodon may have travelled as fast as 15-20 km/hr (according to D. Fastovsky and D. Weishampel in "The Evolution and Extinction of the Dinosaurs"). Dinosaur speeds are estimated using their morphology (characteristics like leg length and estimated body mass) and fossilized trackways.Iguanodon was named by Gideon A. Mantell in 1825; its teeth and a few bones were found in 1822 (perhaps by Gideon Mantell's wife, Mrs Mary Mantell) in Sussex, (southern) England. Mantell recognized the similarity between Iguanodon's tooth and that of the modern iguana, except the Iguanodon's was much larger. Iguanodon was the second dinosaur fossil named, and Mantell named it Iguanodon, meaning "iguana tooth." Hundreds of Iguanodon fossils have been found around the world, especially in Belgium, England, Germany, North Africa, and the USA. The type species, I. bernissartensis , was named by Boulenger and van Beneden in 1881.