ABSTRACT

The Cypress Hills Formation of southwestern Saskatchewan preserves fossil mammals of Uintan (middle Eocene) to Hemingfordian (early Miocene) age. Deposition was nearly continuous during this interval, and the widely held belief that a limited period of Uintan sedimentation on the Swift Current Plateau was followed by Chadronian sedimentation throughout the area, the two separated by a period of non-deposition, is incorrect. Eocene assemblages from the Cypress Hills Formation have aided in identifying the profound middle Eocene faunal turnover as taxonomic displacement, and in documenting the greatly increased faunal provinciality of the Duchesnean. Late Eocene and Oligocene assemblages, many of them newly discovered, provide a rare opportunity to trace the evolution and eventual replacement of the White River Chronofauna in the northern Great Plains. The classic concept of the “Cypress Hills Oligocene” is based on Chadronian to Hemingfordian specimens collected from a large geographical area, and must be abandoned in favor of a model involving many successive local faunas. The local fauna most similar to the “Cypress Hills Oligocene” of the literature is the middle Chadronian (late Eocene) Calf Creek Local Fauna.