Proposed system for categorizing bioclaustrations on Ordovician bryozoans

Bryozoans are among the most abundant fossils in the Ordovician, especially in the Cincinnatian Series of northern Kentucky, which makes understanding their interactions with other fauna critical for interpretation of Ordovician ecosystems. Bioclaustrations are formed when a soft-bodied organism settles on a living skeletal organism and the skeleton grows around it, creating a cavity or embedment structure. Skeletal bryozoans wall off such soft-bodied organisms syn vivo, creating reaction rims around them. These reaction rims of skeletal calcite, combined with the fact that bioclaustrations do not cut across zooecial walls, distinguish them from borings. Bioclaustrations occur on bryozoans throughout the Phanerozoic and are especially common in the Cincinnatian. Their abundance and distribution have not been widely studied. We collected bryozoans with bioclaustrations from six lithological units in the Cincinnatian Group in the Cincinnati region. They range in paleoenvironments from lagoonal to subtidal. We found that the same bryozoan may exhibit different bioclaustration types, suggesting that the bioclaustration structure is moderated by the soft-bodied infesting organism to some degree, not just the bryozoan itself. We also did not find significant variation in bioclaustration type or spatial distribution between bryozoan species, suggesting that other factors moderated these traits. We here propose a system for categorizing bioclaustrations in Ordovician bryozoans based on their morphology.