Late Maastrichtian-Danian Mytilids and Pinnids (Mollusca: Bivalvia) from Northern Patagonia, Argentina

The Upper Cretaceous - lower Paleogene rocks from northern Patagonia yield a rich fauna of marine mollusks that may be useful in elucidating paleobiogeographic and paleoenvironmental changes taking place across the K/P boundary in the region. Most of the mollusk faunas remain poorly understood, as the preservation is generally deficient. This paper describes three new species of mytilids (Septifer mayai n. sp., Mytilaster ? edseli n. sp. and Gregariella amara n. sp.), and records four species of pinnids, one of which is new (Plesiopinna pampeana n. sp.). All the material comes from the Maastrichtian Jaguel Formation, and the Maastrichtian/Danian Roca Formation, exposed in the provinces of Rio Negro, Mendoza and La Pampa (Argentina). A survey of the stratigraphic distribution of the material described shows that the only Maastrichtian species that survived into the Danian was Gregariella amara.