New information on the holotype of “ Chasmosaurus ” russelli (Ornithischia: Ceratopsidae) necessitates the establishment of a new genus to receive the species

A re-evaluation of the holotype of Chasmosaurus russelli from Dinosaur Provincial Park, Alberta, reveals it cannot be classified within the genus Chasmosaurus or any other known chasmosaurine taxon due to its unique premaxilla and frill epiossifications. Phylogenetic analysis suggests ambiguous relationships, with the specimen potentially representing a migrant from the southern Pentaceratops clade or an independent lineage exhibiting convergent evolution of Pentaceratops-like traits. Consequently, the authors establish a new genus, Cryptarcus, to accommodate this species, refuting recent hypotheses of an evolutionary trend from Cryptarcus russelli through Pentaceratops to Terminocavus.

Holmes, R. B., Mallon, J. C., Ryan, M. J., & Evans, D. C. (2026). New information on the holotype of “ Chasmosaurus ” russelli (Ornithischia: Ceratopsidae) necessitates the establishment of a new genus to receive the species. Canadian Journal of Earth Sciences, 63, 1–20. https://doi.org/10.1139/cjes-2025-0031