A NEW CERATOPSID FROM THE JUDITH RIVER FORMATION, MONTANA, WITH IMPLICATIONS FOR THE ORIGIN OF CHASMOSAURINAE

A new chasmosaurine ceratopsid is described based on cranial material collected from a bonebed in the Judith River Formation (Campanian) near Havre, Montana. Originally, all ceratopsid material from the bonebed was referred to the basal centrosaurine Albertaceratops Ryan 2007, the holotype of which was collected from roughly equivalent-aged beds of the Oldman Formation of Alberta, Canada. Reevaluation of key cranial characters from the Montanan bonebed, including the number and shape of the preserved epiparietals, necessitate referral of at least some material from this site to a new chasmosaurine taxon. Although the bonebed does include centrosaurine cranial (and probably postcranial) elements that may eventually be referable to Albertaceratops, the site appears to be dominated by elements of chasmosaurine affinity. In addition to being the first unequivocal occurrence of a Campanian-aged chasmosaurine ceratopsid in Montana, the new chasmosaur is also the oldest known Chasmosaurine ceratopsid (approximately 77.5 Ma). Assessment of all known chasmosaurines gives support to the origin of this group in the Late Cretaceous northern paleobiogeographic zone.