Protoceratops, one of the earliest ceratopsians, lacked proper horns, but displayed the frill and large beak of their later relatives. Later ceratopsians displayed a vast array of horn and frill structures: some ceratopsians having one large horn going straight up on the front of their head, such as Centrosaurus. Others, such as Styracosaurus, had frills adorned with long spikes. Others, such as Chasmosaurus and the well-known Triceratops, had a single horn on their snout and two larger horns up by their eyes. Other well-known ceratopsians include Pachyrhinosaurus, a ceratopsian with a large nasal boss instead of a proper horn, and Einiosaurus, a ceratopsian with a forward-curving horn on its snout.