Thyasira alaskana, n. sp. is a large late Miocene-Pliocene species characteristic of both fossil and living Thyasiridae dominating the Atlantic and Arctic Faunal Realms, being closely related to the living species group of T. sarsi (Philippi) and the Late Cretaceous T. advena-T. becca species group of Western Interior North America. It occupies an evolutionary position midway between Cretaceous and Recent species and denotes a continuation of the trends toward more efficient burrowing forms described in the Cretaceous members of the lineage. Abundant single and articulated specimens in nearshore conglomeratic sandstone of shallow water, high energy origin are randomly oriented and suggest rapid burial of a transported assemblage, possibly during a storm episode.

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