Pennsylvanian Heteroconchia (Mollusca, Bivalvia) from the Piauí Formation, Parnaíba Basin, Brazil

Abstract

Dolostones of the upper Piaui Formation, Parnaiba Basin, Northern Brazil, record a rich and diversified invertebrate fauna of the Middle Pennsylvanian (Morrowan to Desmoinesian) age. Among bivalves, Heteroconchia is the most diversified (seventeen species) followed by Pteriomorphia (eleven species) and Palaeotaxodonta (three species). Heteroconch bivalves are found in parautochthonous to autochthonous fossil concentrations, some in storm (obrution) beds (Mucambo dolostones), showing disharmonious time-averaging. Among the species described [Pleurophorella? sp.; Schizodus alpinus (Hall, 1858); S. acuminatus Hoare, Sturgeon & Kindt, 1978; S. ulrichi, Worthen, 1890; S. cf. wyomingensis Newell & Boyd, 1975; Astartella subquadrata Lee & Girty, 1909; Astartella cf. concentrica (Conrad, 1842); Wilkingia terminalis (Hall, 1852); Sanguinolites sp. 1; Sanguinolites sp. 2; Exochorhynchus sp.; cf. Anomalodesmata indet. 1 and Anomalodesmata indet. 2], three are new (Pleurophorella parnaibaensis n. sp.; Chaenomya caatingaensis n. sp.; Exochorhynchus buriti n. sp.). In addition, the genus Carnauba (Megadesmidae) is proposed and represented by a single species, C. oiticica n. gen. and n. sp. The internal diagnostic features of some species, especially those belonging to Schizodus, are reported here for the first time. Finally, the bivalves studied show affinities to species of the Amazon basin (Itaituba Formation), and the Carboniferous of North America reinforcing a Middle Pennsylvanian age for the fauna.