Discussion of the systematic placement of the Ordovician brachiopod generaCoopereaandCraspedeliaby Cocks and Rong (1989)

Abstract

Cocks and Rong (1989) subdivided the species of the Ordovician brachiopod genusBimuriainto two groups, those with a simple, or not undercut, cardinal process and those with an undercut cardinal process. They placed the second group in a new genus,Cooperea, and groupedCoopereawithCraspedeliain the new subfamily Craspedeliinae of the family Sowerbyellidae. However, the cardinal process ofBimuriaranges from not undercut to undercut within at least two species.Coopereais therefore placed in synonymy withBimuria, andCraspedeliais returned to the Bimuriidae.Cocks and Rong (1989) inferred that, with rare exceptions, the cardinal process of the Plectambonitacea evolved from simple to trifid to undercut. The evidence fromBimuriaindicates, however, that the undercut process developed more than once and, inBimuria, directly from the simple type.As an adjunct to the above discussion three new species are described:Bimuria gilbertella, Craspedelia intonsa, andCraspedeliasp. 1.Craspedeliais a rarely reported genus documented here for the first time in western North America (northern California). Additional evidence is introduced that the ratio Lmusbv/Lebv decreased from middle to late Ordovician species ofBimuria.