Hypsilophodontidae Family of bipedal (ornithopod), ornithischian dinosaurs, ranging from the Upper Triassic to the Upper Cretaceous. Hypsilophodon itself, from the Wealden of the Lower Cretaceous, is the most primitive of the ornithopod dinosaurs known to date, despite its relatively late appearance in the Mesozoic fossil record.

Hypsilophodontidae (order Ornithischia, suborder Ornithopoda) A family of bipedal dinosaurs that ranged from the Upper Triassic to the Upper Cretaceous. Hypsilophodon itself, from the Wealden of the Lower Cretaceous, is the most primitive of the ornithopod dinosaurs known to date, despite its relatively late appearance in the Mesozoic fossil record.