Fossils That Changed Dinosaur History: Iguanodon (1820)

Iguanodon was only the second dinosaur after Megalosaurus to be given a formal genus name; more important, its numerous fossils (first investigated by Gideon Mantell in 1820) precipitated a heated debate among naturalists about whether or not these ancient reptiles even existed. Georges Cuvier and William Buckland laughed away the bones as belonging to a fish or a rhinoceros, while Richard Owen (if you can overlook a few wacky details and his overbearing personality) pretty much hit the Cretaceous nail on the head.