Cranial anatomy of the small ornithischian dinosaur Changchunsaurus parvus from the Quantou Formation (Cretaceous: Aptian–Cenomanian) of Jilin Province, northeastern China

The Quantou Formation of Jilin Province, People's Republic of China, has recently yielded an important new fauna of ‘middle’ Cretaceous vertebrates. This fauna includes the small-bodied cerapodan ornithischian dinosaur Changchunsaurus parvus, represented by excellent cranial and postcranial material. When initially described, Changchunsaurus was hypothesed to represent one of the most basal known ornithopods; however, similarities to ceratopsians were also noted, suggesting that Changchunsaurus may be crucial to elucidating the interrelationships of basal cerapodans, one of most problematic areas of ornithischian phylogeny. Here we present a detailed description of the craniodental anatomy of Changchunsaurus, rediagnose the taxon based upon three autapomorphies, and provide comparisons to other basal cerapodans, as a foundation for future studies of basal cerapodan relationships. Changchunsaurus shows strong similarities to the Chinese Early Cretaceous cerapodan Jeholosaurus, and it is likely that they are sister taxa.