The ceratopsian subfamily Chasmosaurinae: sexual dimorphism and systematics

Advanced ceratopsians (family Ceratopsidae) are divisible into two groups, based primarily on the relative proportions and fenestration of their neck frills. Lambe's subfamily Eoceratopsinae is abandoned because of the placement of Eoceratops in synonymy with Chasmosaurus, and the inclusion of Triceratops within the "long-frilled' ceratopsids. Lambe's subfamilies Chasmosaurinae and Centrosaurinae should be revived, however, for the "long-frilled' and "short-frilled' ceratopsids, respectively. Species-level taxonomy of ceratopsids is complicated by pronounced individual and ontogenetic variability, and sexual dimorphism, in most species. A population sample of Chasmosaurus from Texas suggests that orientation of the supraorbital horncores is a useful criterion for separating sexual morphs. Based on this criterion, all chasmosaurine genera contain a species or group of species exhibiting the supposed "female' morph, and one exhibiting the supposed "male' morph. -from Author