Redescription of UALVP 40, an unusual specimen of Chasmosaurus Lambe, 1914 (Ceratopsidae: Chasmosaurinae) bearing long postorbital horns, and its implications for ontogeny and alpha taxonomy of the genus

A newly redescribed Chasmosaurus skull (UALVP 40) from Dinosaur Provincial Park, Canada, reveals significant asymmetries and developmental features suggesting it is a subadult. The right postorbital horncore inclines at a steeper angle (60°) than the left, while unfused cranial sutures and a short predentary support its immature status. Analysis of UALVP 40 alongside other Canadian Chasmosaurus specimens with long postorbital horns (>150 mm) indicates an isometric relationship between interorbital width and horn length, implying these may represent an ontogenetic series of a single species. The study also introduces a novel diagnostic trait for the genus: a straight squamosal dorsal border adjacent to the supratemporal fenestra, sloping posteroventrally before ascending to form the parietal fenestra's lateral border.

Konishi, T. (2015). Redescription of UALVP 40, an unusual specimen of Chasmosaurus Lambe, 1914 (Ceratopsidae: Chasmosaurinae) bearing long postorbital horns, and its implications for ontogeny and alpha taxonomy of the genus. Canadian Journal of Earth Sciences, 52(8), 608–619. https://doi.org/10.1139/cjes-2014-0167