Taxonomy and paleoecology of Devonian rostroconch mollusks from Ohio

Abstract

Rostroconchs are a common faunal component in the Devonian rocks of Ohio, particularly in the Columbus and Dundee Limestones. Hippocardia cunea (Conrad) is the most abundant species. Also present are H. monroica (Grabau), H. ohioense (Meek), H. curta n. sp., and Bransonia? sibleyense (La Rocque).Growth series of Hippocardia cunea show that the large hood and the rostrum begin to develop early in ontogeny. The rates of increase in the number of comarginal growth increments on the posterior or rostral face and radial ribs on the body of the shell are slow; most size increase of the shell occurred in the increasing widths of the ribs and the interspaces. The length/height ratio increases from young to juvenile specimens and then decreases in adult specimens. However, the length/width and height/width ratios show a general decrease from young to adult specimens. Considerable variation in shell lateral profile is present in H. cunea.Three specimens of Hippocardia cunea show borings entering the posterior rostral portion of the shell, presumably made by Trypanites, a polychaete worm. In one instance, a boring caused disfiguration of the shell material indicating that the host was alive at the time of the boring. The orientation and location of the borings and the presence of one specimen believed to be preserved in life position provides the base for interpreting H. cunea as an infaunal deposit feeder.