The world's oldest cerapodan ornithischian dinosaur from the Middle Jurassic of Morocco.

The cerapodan dinosaurs were an ornithischian clade that achieved a global distribution in the Cretaceous Period. The ichnological record suggests that these dinosaurs had evolved by the Middle Jurassic, but only a single cerapodan body fossil, an isolated femur from the Callovian of the UK, is known from this interval. In order to elucidate the early stages of cerapodan evolution and help to resolve the many phylogenetic inconsistencies in the clade, new specimens, particularly from historically undersampled localities, are needed. Herein, we report the proximal femur of a cerapodan dinosaur from the Bathonian El Mers III Formation of the Middle Atlas Mountains, Morocco. The specimen, although fragmentary, bears characteristics, including a femoral head offset on a distinct neck and a constriction between the head and greater trochanter, that unite it with Cerapoda to the exclusion of other neornithischians. This specimen represents the world's oldest cerapodan. The El Mers III Formation has also yielded the world's oldest ankylosaur (and the first discovered in Africa), as well as one of the oldest stegosaurs. Further sampling of these rocks will therefore be crucial for understanding the radiation of ornithischian dinosaurs.