Article: The taxonomy, shell structure, and palaeoecology of the trimerellid brachiopod Gasconsia Northrop
Nils-Martin Hanken and David A. T. Harper
The large trimerellid brachiopod Gasconsia Northrop is reassessed on the basis of the type species and abundant, well-preserved material from the upper part of the Bonsnes Formation (Rawtheyan: Ashgill Series) in the Ringerike district of the Oslo Region. Hitherto the genus was known only from indifferently preserved moulds from the upper Silurian of Quebec. The Norwegian specimens are assigned to a new species, G. worsleyi, and include valve interiors which permit a detailed analysis of the articulation and musculature. The shell has been replaced by sparry calcite which also characterizes the shells of the associated gastropods and cephalopods. This confirms the assumption that trimerellid brachiopods originally possessed an aragonitic shell. The unusual fauna containing Gasconsia in Norway is of low diversity and comprises articulate brachiopods, bryozoans, trilobites, ostracods, gastropods, corals, and calcareous algae. It is suggested that Gasconsia may have adopted a quasi-infaunal mode of life.