A diverse new omomyid primate fauna from the early Eocene of southern Wyoming with implications for interpreting...

A richly fossiliferous sandstone outcrop in the Wasatch Formation, Great Divide Basin, southern Wyoming, has yielded exceptionally well-preserved fossils of three omomyid primates. Here we report new occurrences of two rarely documented omomyids, Arapahovius gazini and Anemorhysis savagei, describe a new species of Tetonius, and perform a phylogenetic analysis of Tetonius and its allies; the two previously described omomyids are new additions to the fossil record of the Great Divide Basin and represent only the second and third occurrences of these species, respectively. Tetonius, Arapahovius, and Anemorhysis are not known to co-occur elsewhere, particularly in the well-documented Bighorn Basin of northwestern Wyoming, where the Tetonius + Pseudotetonius clade is locally extirpated prior to the first appearances of Arapahovius and Anemorhysis. Morphological support for the new species of Tetonius is corroborated by biostratigraphic data suggesting it is younger than Pseudotetonius ambiguus from the Bighorn Basin. However, the new species of Tetonius retains key dental symplesiomorphies that signal a relatively early divergence from the Tetonius + Pseudotetonius clade as it is recorded in the Bighorn Basin. Results from our maximum parsimony analysis indicate that Tetonius varleyorum sp. nov. from the Great Divide Basin is more closely related to P. ambiguus than either of the species of Tetonius known from the Bighorn Basin, underscoring the paraphyletic status of Tetonius with respect to Pseudotetonius proposed by earlier workers. The evolutionary history of the Tetonius + Pseudotetonius clade was more complex than previously recognized, and this added complexity can only be recognized through broader geographic sampling.