Chasmosaurus Lambe, 1914a

Maidment, Susannah C. R. & Barrett, Paul M., 2011, A new specimen of Chasmosaurus belli (Ornithischia: Ceratopsidae), a revision of the genus, and the utility of postcrania in the taxonomy and systematics of ceratopsid dinosaurs, Zootaxa 2963, pp. 1-47 : 4

Chasmosaurus Lambe, 1914a

Type species. Chasmosaurus belli Lambe, 1902 .

Amended diagnosis. Chasmosaurus is diagnosed based on the following combination of characters: (1) Premaxillary flange along entire anterior margin of external naris; (2) supraorbital horns, when present, curve posteriorly along their length; (3) frill broadens posteriorly to form triangular shield with maximum width more than twice the skull width at orbits; (4) medial margin of squamosal, where it articulates with the lateral bar of the parietal, straight; (5) parietal fenestrae large, occupying most of the parietal, and being rounded or anteroposteriorly longer than transversely wide; (6) epiparietals triangular in shape and project posteriorly or dorsally but do not curve anteriorly. Characters 1–3 after Forster et al. (1993). All of these features are seen in other chasmosaurines and do not, therefore, represent autapomorphies, but this combination of features appears to be unique to Chasmosaurus . See discussion for more details.