A new species of Pinnarctidion from the Pysht Formation of Washington State (U.S.A.) and a phylogenetic analysis of basal pan-pinnipeds (Eutheria, Carnivora)

A nearly complete skull and limited postcrania (SDSNH 146624), from the upper Oligocene of the Pysht Formation (Clallam County, Washington State, U.S.A.), represent a new species of Pinnarctidion, a pan-pinniped previously restricted to California and Oregon. Here, we describe SDSNH 146624 in detail and present results of a comprehensive phylogenetic analysis of early-diverging pan-pinnipeds. Pinnarctidion iverseni sp. nov., recognized on the basis of this specimen, is diagnosed by its posteriorly broad palate, anteriorly narrow rostrum, dorsoventrally deep zygomatic arches, and posterior accessory cusps on P3–4. Phylogenetic analysis recovered P. iverseni as most closely related to P. bishopi from the Jewett Sand of California’s Central Valley. The well-preserved and reasonably complete skull and upper dentition of SDSNH 146624 help clarify relationships among the proximal outgroups of crown clade pinnipeds.