Autecology of Richmondian Brachiopods (Late Ordovician of Indiana and Ohio)

T-Studies of the autecology of Richmondian brachiopods indicate that correlations exist between life position, shell morphology, and substrate, and between shell morphology and the epizoic fauna. Three groups of articulate brachiopods may be recognized. (1) Species with concavo-convex shells usually lived on muddy bottoms resting on the convex valve, in some cases with only the upturned commissure projecting from the sediment. (2) Forms with plano-convex or biconvex shells having wide hingelines lived with the commissure inclined at a high angle to the bottom, usually attached by a stout pedicle to particles in a gravelly sediment. (3) Brachiopods of plano-convex to biconvex morphology, but with short hingelines and prominent pedicle beaks, rested on the posterior portion of the brachial valve with the pedicle valve uppermost. Positive height allometry caused gradual rotation of the commissure away from the sediment in some species. Among the inarticulates, Lingula lived infaunally in vertical burrows. The other species all lived with the pedicle valve close to the attachment surface. The size and shape of ornamentation of the brachiopod shell was a controlling factor in determining what epizoans would occupy the shells of a brachiopod species. In most cases, epizoans utilized the brachiopod only as a hard substrate, but some instances of apparent feeding commensalism are found. The relationship between epizoans and their Richmondian brachiopod hosts is thought to have been generally ectoparasitic.