A new species of the primitive carpolestid primate Elphidotarsius Gidley is described from relatively complete upper and lower dentitions collected from the upper Paleocene Paskapoo Formation of central Alberta, Canada. Dentally, this new species shows a combination of primitive and advanced features in a more realistic approximation of the evolutionary transition between Elphidotarsius and Carpodaptes than had been available before. This new species occurs at the same horizons as does the plesiadapiform primate Plesiadapis rex (Gidley) and, hence, is middle Tiffanian in age; it occurs with Carpodaptes hazelae Simpson, at a horizon well within the Carpodaptes zone, and is the youngest discovered species of the genus. The late occurrence of a species of Elphidotarsius brings into question the biostratigraphic utility of the succession of carpolestid species for zonation of the nonmarine upper Paleocene of North America.

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