Species resolution inTriceratops: cladistic and morphometric approaches

Sixteen species of Triceratops have been proposed since the genus was erected by O. C. Marsh in 1889. Five of these species are here considered technically invalid and a sixth is reassigned to Diceratops. Based on both cladistic analysis and morphometric shape analysis, all available skulls of the ten remaining “species” of Triceratops are placed in one of two species: T. horridus and T. prorsus, invalidating eight of the original ten species. These two species overlap in geographic and stratigraphic ranges. Because specimens of T. horridus greatly outnumber those of T. prorsus, these morphotypes may represent distinct taxa rather than a single sexually dimorphic species.