Iguanodon (Mantell, 1825) is a genus of ornithopod dinosaur that lived from about 139 to 90 million years ago, from the early to late Cretaceous period.Iguanodon was the second dinosaur ever discovered and it was one of the first dinosaurs to be named, preceded only by Megalosaurus Iguanodon'sname means "iguana tooth" due to its iguana-like teeth. It was the largest of its kind.
When the first Iguanodon skeleton was discovered it was believed to walk much like an iguana, on all four legs. Its thumb spike was believed to be a horn on its head (only one thumb spike was found). At one point it was also thought to have lived in trees, but this has been long since proven completly wrong.
One of the more notable characteristics of the Iguanodon species is its "thumbs". Instead of a thumb it had a large spike that paleontologists believed Iguanodons used for defensive purposes, but could have also been used for getting food. The "pinky" finger of an Iguanodon is believed to have acted as its thumb.
Palentologists belive that Iguanadon may have traveled in herds. Paleontologists also think Iguanodon migrated with ankylosaurs, mostly nodosaurs.