The most distinctive feature is their large skull, among the largest of all land animals. The largest known skull (specimen BYU 12183) is estimated to have been in length when complete, and could reach almost a third of the length of the entire animal. It bore a single horn on the snout, above the nostrils, and a pair of horns approximately 1 m (3 ft) long, with one above each eye. Most other ceratopsids had large holes (fenestrae) in their frills, while those of "Triceratops" were noticeably solid.