Psittacosaurus
Coronosauria
Protoceratops
Ceratopsidae
Ceratopia (ser-a-TOP-ee-ah) or Ceratopsia is a group of herbivorous and possibly omnivorous beaked dinosaurs that evolved during the Cretaceous in what is now Asia, and then spread to North America where they grew in size and developed elaborate horns and neck frills. The horns may have been used for display, defense, and combat with other members of the same species. The frills were probably too fragile for defense, and may have been used for display or thermoregulation
Early members such as Psittacosaurus were bipedal and had very small frills. This group later gave rise to a subgroup, the Coronosauria ("crowned lizards"), which were quadrupedal, much larger, and frequently horned. The coronosaurians include earlier ceratopsids like Protoceratops, and the Ceratopsidae like Centrosaurus and Triceratops.
The paleontologist Othniel Charles Marsh originally named the group "Ceratopsia" in 1890, which has an incorrect Greek ending. While "Ceratopia" is linguistically correct, and thus preferred by many taxonomists; "Ceratopsia" has chronological precedence and is more widely used, probably because of the association with Triceratops. Since no official authority like the ICZN regulates higher level zoological taxa, there is no official answer.
In either case, the name means "horned face", from the Greek keras ("horned") and ops ("face").
