SPACE UTILIZATION BY FAUNAL ELEMENTS ON A BIVALVE SHELL PAVEMENT, UPPER ORDOVICIAN MIAMITOWN SHALE, SHARONVILLE, OHIO

An approximately 7,700 cm² slab of a bivalve shell pavement from the Upper Ordovician Miamitown Shale was collected in Sharonville, Ohio to examine spatial distribution of taxa. This deposit was preserved by obrution and includes species of bivalves, gastropods, cephalopods, brachiopods, Cornulites, edrioasteroids, and bryozoans. The surface is smooth, having only a few centimeters of relief. Local topographic highs occur where dead bivalve shells are found. To examine how the taxa were distributed on the substrate, spatial analyses were run on each of the species. A pavement of dead bivalve shells forms hard substrate of the slab, and the valves were determined to have a uniform distribution on the surface. Some weak clustering of edrioasteroids was observed where they were attached to the bivalves on the surface. Small edrioasteroids preferentially attached to the edges of bivalves whereas large edrioasteroids were centrally positioned. Edrioasteroids also showed weak orientation, with almost all individuals oriented between 150 and 360 degrees. The brachiopod Zygospira was found apparently attached to bivalve shells, and determined to have a non-uniform, strongly clustered distribution. Although some Cornulites specimens attach directly to bivalve shells, the vast majority attach epibiotically upon Zygospira where they feed parasitically on the brachiopod feeding currents. Because these tubeworms are attached to brachiopods, their clustering pattern is similar to that of the brachiopod. Species of bryozoans found in the community were located both on the exterior and cryptically on the interior of the bivalve shells. There were more bryozoans encrusting valve exteriors than valve interiors. The bryozoans also exhibited non-uniform, strongly clustered distribution. Spatial patterns of edrioasteroids, brachiopods, and bryozoans are generally coincident suggesting local areas of preferred conditions for attachment. Despite strong clustering of certain taxa, causes for the clustering are not entirely clear. It does not appear that clustering and slab thickness are related. Instead, clustering may be a function of ancient marine sediment cover precluding encrustation before the obrution event occurred.