Living in the shadow of brachiopods: bivalves from upper Visean (Mississippian) mud mounds of Derbyshire, UK

Few studies have been conducted on Carboniferous marine bivalves in the British Isles and Ireland since pioneering studies performed during the 19th century. Herein, we examine from a systematic, taphonomic and palaeoecological point of view, the bivalve fauna occurring as a minor component of brachiopod-dominated fossil assemblages in upper Visean (upper Brigantian) mud mounds in the southern Peak District, Derbyshire (UK). Our results show moderate bivalve diversity, with the fauna being composed of eight genera, representing eight families in four orders (Nuculida, Arcida, Ostreida, Pectinida) and one superorder (Anomalodesmata). Sulcatopinna flabelliformis (Martin, 1809), Aviculopecten planoradiatus M’Coy, 1851, and Cosmomya variabilis (M’Coy, 1851) are herein re-described. Taphonomic bias related to the early dissolution of the aragonitic shell of seminfaunal and infaunal taxa cannot account alone for the scarcity of bimineralic epifaunal pectinids. Indeed, the scarcity of bivalves is also likely due to the presence of the diverse brachiopod community, acting as competitive dominant and ecosystem engineer, well-adapted to the low-turbidity and mesotrophic environment of the mud mound.