TRILOBITES AS A HARD SUBSTRATE FOR EPISKELETOZOANS FROM THE UPPER ORDOVICIAN OF THE CINCINNATI, OHIO AREA

Epibiosis on living, motile hard substrates has evolved multiple times as a strategy for sessile marine invertebrates. Numerous examples can be found of extant bryozoans, barnacles, and serpulids living on various hosts such as whales, sea snakes, decapod crustaceans, horseshoe crabs, and isopods. In contrast, examples from the fossil record of arthropods are rare. This is most likely due to larval preference and/or the loss of the epicuticle during fossilization. The epicuticle is the non-calcified, outer-most layer of the arthropod carapace. To test this idea, 15,400 articulated, Flexicalymene trilobites were examined for epibionts from the Maysvillan and Richmondian Stages of the Cincinnatian Series of the Upper Ordovician rocks exposed in southwestern Ohio, southeastern Indiana, and northern Kentucky. Carcasses and molts were treated separately. Only 16 specimens (0.1 %) contained episkeletozoans. Nine specimens were colonized by trepostome bryozoans, 4 with cornulitids, and 2 with inarticulate brachiopods, and 1 with articulate brachiopods. As expected, fouled carcasses were significantly larger than non-fouled carcasses. The dorsal area covered by episkeletozoans increased significantly with host size. This low incidence of fouling is put into context through comparison with those on extant hosts.