Protoceratopsid

Classification

The family Protoceratopsidae was introduced by Walter W. Granger and William King Gregory in May 1923 as a monotypic family for Protoceratops andrewsi. Granger and Gregory recognized Protoceratops's close relationship to other ceratopsians, but considered it primitive enough to warrant its own family, and perhaps suborder. Protoceratopsidae was later expanded to include all ceratopsians that were too advanced to be psittacosaurids, but too primitive to be ceratopsids. In 1998, Paul Sereno defined Protoceratopsidae as the stem-based clade including "all coronosaurs closer to Protoceratops than to Triceratops". Sereno's definition ensures that Protoceratopsidae is monophyletic, but probably excludes some dinosaurs that have been traditionally thought of as protoceratopsids (for example, Leptoceratops and Montanoceratops). The latter genera are now often classified in a mostly North American family Leptoceratopsidae.