The Kealey Springs West (KSW) local fauna from the Cypress Hills Formation (Eocene to Miocene), Saskatchewan, is probably latest Chadronian in age, and is the northernmost assemblage representing a time near the Eocene–Oligocene boundary in North America. Presence of Pseudocylindrodon neglectus is strong evidence that the assemblage is Chadronian. Herpetotherium valens, Protosciurus, Namatomys cf. N. lloydi, and Centimanomys also suggest a Chadronian age. The assemblage contains Adjidaumo maximus and Palaeolagus cf. P. hemirhizis, species that have been cited as characteristic of the early part of the Orellan Land Mammal Age (early Oligocene), and the typically Orellan Heliscomys hatcheri and Eumys elegans. Several other tara in the KSW assemblage are known from both the Chadronian (late Eocene) and Orellan.