Ceratopsians

Ceratopsians are classified by their bony frill that sits behind the  skull as well as the beak bone on the upper jaw called a rostral. There are three groups that branch off of Ceratopsians. These are called Psittacosauridae, Protoceratopsidae and Ceratopsidae. Psittacosauridae were bipedal with small frills and no horns. Protoceratopsidae walked on four legs with large frills and still no horns. Ceratopsidae walked on four legs and had large frills like Protoceratopsidae but had three horns, one above each eye and one on the nose. Ceratopsidae are broken down into two more categories, Chasmosaurinae and Centrosaurinae. Chasmosaurinae had large horns above the eyes and a small one on the nose whereas Centrosaurinae had small ones above the eyes and a large one on the nose.