Plesiadapis anceps was named by Simpson (1936). Its type specimen is Amer. Mus. No. 33822, a partial skull (left lower jaw with incisor and M1-3, right [lower] P4 and M1, right [upper] P3-M1, left [upper] M1-2, and other fragments, all of one individual), and it is a 3D body fossil. Its type locality is Scarritt Quarry, which is in a Tiffanian terrestrial horizon in the Melville Formation of Montana.