New Washakiin primates (Omomyidae) from the Eocene of Wyoming and Colorado, and comments on the evolution of the Washakiini

Abstract

Two new species of washakiin omomyids occur in deposits of early Bridgerian age. Shoshonius bowni , sp. nov., from the Aycross Formation, Absaroka Range, Wyoming, differs from S. cooperi in having enlarged conules on the upper molars and a second metaconule, features convergent with Washakius insignis. Washakius izetti , sp. nov., from the Green River Formation, Piceance Creek Basin, Colorado, is the most primitive known species of Washakius , showing incipient development of features present in the later W. insignis and W. woodringi. Washakius , cf. W. izetti occurs in the early Bridgerian of the Huerfano Basin. W. izetti is closely related to Utahia kayi , a. washakiin possibly related to Stockia. Hemiacodon , sometimes included in the Washakiini, is probably more closely related to the Omomyini. Stockia is distinct from Omomys and is questionably included in the Washakiini, of which Loveina is the stem taxon. More advanced washakiins form two groups between which there was significant parallel evolution in dental morphology. One group includes Washakius, Dyseolemur, Utahia , and possibly Stockia , and is characterized by development of an open talonid notch before the consistent appearance of metastylids. The other group consists of Shoshonius , where the establishment of metastylids preceded the full opening of the talonid basins.