Iguanodon

A conical thumb spike, at first mistaken for a nose horn, is the signature feature of the herbivore Iguanodon bernissartensis, among the earliest dinosaurs ever discovered and named. Gideon Mantell recognized it in 1825 from Sussex, England, near the dawn of paleontology. Roughly 10 meters long and 3,400 kilograms, this ornithischian could move on either two legs or all fours and lived during the Early Cretaceous, roughly 145 to 100 million years ago. Its teeth, resembling those of a living iguana, gave the genus its name and helped establish that giant extinct reptiles had once roamed the land, a foundational idea in the young science.