The Pantolestidae are an extinct family of mammals known principally from the early Paleocene to late Oligocene (from approximately 64 to 30 million years ago) of North America and Europe. Although never particularly abundant, pantolestids are relatively well represented in the Eocene and Oligocene, with several taxa known from exceptionally well-preserved skulls and postcranial material. The early evolutionary history of the group, however, similar to that of many contemporaneous mammals, remains comparatively poorly known. The current study reports on several previously undescribed pantolestids from the early late Paleocene (late middle Tiffanian, Ti4) Roche Percée local fauna, Ravenscrag Formation, of southeastern Saskatchewan, Canada. Aatotomus placochton n. gen. n. sp. resembles the enigmatic pantolestid Paleotomus in having sectorial premolars with well-developed crests and tall, sharp molar trigonids, but differs principally in possessing narrow molar talonids. Besseocetor krausei n. sp. shares numerous similarities with B. thomsoni and B. septentrionalis but differs in being considerably smaller and less robust. Palaeosinopa reclusum n. sp., the oldest species of Palaeosinopa yet discovered, reveals a unique combination of primitive and derived pantolestid features, and supports previous suggestions of a close evolutionary relationship between Palaeosinopa and Bessoecetor. The new taxa document an unusually high diversity of pantolestids in the Tiffanian of western Canada and provide important new knowledge to the evolutionary history of this group during the Paleocene.

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