Iguanodon was a large, herbivorous dinosaur that lived during the Late Jurassic to Early Cretaceous periods, around 140 to 125 million years ago. It was one of the first dinosaurs ever discovered and scientifically described. Measuring up to 10 meters (33 feet) in length and weighing up to 5 tons, Iguanodon was a bulky dinosaur with a beak-like mouth for cropping plants and teeth adapted for chewing vegetation. Its most distinctive feature was the large, spike-like thumb on each hand, which may have been used for defense or foraging. Iguanodon could walk on both two and four legs, making it versatile in its movement. Fossils of this iconic dinosaur have been found in Europe, North America, and Asia, highlighting its wide distribution.