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A newly discovered maxillary dentition from the Early Eocene rocks of the Bighorn Basin, Wyoming, is unlike that of any mammal previously known from this intensively collected region. It represents a new genus and species, here named Alocodon atopum. The new form bears superficial resemblance to various mammals, but specific features suggest a real relationship only to palaeanodonts, particularly Tubulodon taylori, aformof uncertain family ties, and the epoicotheriid Pentapassalus pearcei. The most significant features of the molars are their cylindrical shape, their odd cusp arrangement, and their reduced enamel. Because of its similarity to Tubulodon, Alocodon is tentatively allocated here to the Epoicotheriidae (Pholidota, Palaeanodonta). If correctly assigned, it represents the oldest known member of this poorly represented family and the first from the Bighorn Basin.