For many decades paleontologists thought that Hypsilophodon's long fingers and toes enabled it to live in trees, but this inference was based on an incorrect reconstruction of its hind foot, which suggested it could grasp and perch. The dinosaur is now recognized to have been a ground dweller with a conventional ornithopod foot. Hypsilophodon is typical of a lineage of ornithopods (ornithopod) known as Hypsilophodontidae. Two other major groups of ornithopods—the hadrosaurs, or duck-billed dinosaurs, and the iguanodontids (Iguanodon)—are closely related. Hypsilophodontids survived into the Late Cretaceous, when they lived alongside the iguanodontids and hadrosaurs that probably arose from early members of the lineage.