Chasmosaurinae Lambe, 1915

Phylogenetic definition. All ceratopsids more closely related to Triceratops than to Pachyrhinosaurus (Sereno, 1998; Sereno favoured the name Ceratopsinae for this clade, but we follow the majority of other authors and all recent works in preferring the name Chasmosaurinae).

Amended diagnosis. Modified from Lehman (1989): large ceratopsian dinosaurs with long, low facial region (preorbital length/height ratio = 1.4 to 3.0); inter-premaxillary fossae present; premaxilla and predentary with horizontal or poorly developed lateral cutting flange; nasal horn core, if present, small and formed in part by a separate ossification (epinasal); postfrontal foramen present; frontoparietal fontanelle walled mostly by the postorbital bones; frontal bones reduced; prefrontal bones small; cranial frill long (0.94 to 1.70 basal length of skull, except in Triceratops); triangular squamosal bones (length/height ratio = 2.0 to 3.5); prominent longitudinal channel in ventral surface of sacrum; triangular acromial process of the scapula arises about half way along the scapula blade; deep triceps fossa on the caudolateral deltopectoral crest of the humerus; foramen on the caudomedial humerus located dorsal to the apex of the deltopectoral crest; strongly curved ischium.