A new species of <i>Pinnarctidion</i> 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 <i>Pinnarctidion</i>, 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. <i>Pinnarctidion iverseni</i> 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 <i>P. iverseni</i> as most closely related to <i>P. bishopi</i> 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.