Psittacosauridae

Members of the Psittacosauridae, including Psittacosaurus, were mostly bipedal and lived during the Early Cretaceous; they had a beak, a small frill, and no horns. Members of the Protoceratopsidae, including Protoceratops and Leptoceratops, were mostly quadrupedal and slightly larger and lived from the Early to Late

…trends through time: the primitive psittacosaurids, such as Psittacosaurus; the protoceratopsids, including Protoceratops of Asia and Leptoceratops of North America; and the ceratopsids, encompassing all the advanced and better-known kinds such as the chasmosaurines Triceratops and Torosaurus as well as the centrosaurines such as Centrosaurus (or