Fossil decapod crustaceans from the late Oligocene to early Miocene Pysht Formation and late Eocene Quimper Sandstone, Olympic Peninsula, Washington

Fossil decapod crustaceans of the Twin River Group, including the Hoko River, Makah, and Pysht formations, of the Olympic Peninsula, Washington, have received little systematic attention since Rathbun's work in 1926. The current study provides emended descriptions of several taxa that were previously described by Rathbun as occurring in rocks that are now referrable to the Pysht Formation. Two new species are described from the Pysht Formation, Trichopeltarion berglundorum and Asthenognathus cornishorum. This marks the first notice of both Trichopeltarion and Asthenognathus on the west coast of North America. Macrocheira longirostra, new species from the late Eocene Quimper Sandstone, Olympic Peninsula, Washington, marks the earliest known occurrence of the genus Macrocheira, previously known from the Oligocene of Washington and the Miocene, Pliocene, and Recent of Japan. Decapod occurrences corroborate previously reported depths for the Pysht Formation, deposited in bathyal conditions that shallowed to inner sublittoral depths, and the Quimper Sandstone, deposited in littoral to sublittoral depths. Decapods of the Pysht and Makah formations and the Quimper Sandstone are remarkably similar to Cenozoic decapods described from Japan. This evidence provides a biogeographic link between the east and west North Pacific decapod faunas that appears to have existed as early as the late Eocene. This link persists in the Recent because five genera from the Twin River Group and Quimper Sandstone are represented among extant decapods of the North Pacific Ocean.