Redescription of the skull and mandible of Parksosaurus from the Late Cretaceous, with comments on the family Hypsilophodontidae (Ornithischia)

Abstract

The head skeleton of Parksosaurus is more similar to that of Hypsilophodon from the Lower Cretaceous of England than to those of Dryosaurus and Dysalotosaurus, two closely re- lated genera of hypsilophodontids from the Upper Jurassic. The shallowness of the lower temporal bar is a primitive feature of the skull of Parksosaurus; specialized features include the form of the teeth, the small size of the antorbital fenestra, and the anteroposterior expansion of the posterodorsal end of the jugal. The presence of foramina for replacement teeth in several lower ornithopods represents a preadaptation for the formation of high alveolar walls necessary for the development of dental batteries in hadrosaurs and ceratopsians. The only other known hypsilophodont reported from the Late Cretaceous of the world is from British Columbia; it may represent a new species of Hypsilophodon