 In clade @-@ based phylogenetic taxonomy , Ceratopsia is often defined to include all <unk> more closely related to Triceratops than to <unk> . Under this definition , the most basal known ceratopsians are Yinlong , from the Late Jurassic Period , along with Chaoyangsaurus and the family Psittacosauridae , from the Early Cretaceous Period , all of which were discovered in northern China or Mongolia . The rostral bone and flared <unk> are already present in all of these forms , indicating that even earlier ceratopsians remain to be discovered . 
