Colony repair strategies in large trepostome bryozoans from the Upper Ordovician (Katian) of the Cincinnati region, USA

Calcitic skeletons of trepostome bryozoans from the Upper Ordovician (Katian) of the Cincinnati region (Kentucky and Indiana, USA) record diverse interactions with encrusting and boring organisms. Trepostomes from four units (Bellevue Member, Corryville Formation, Bull Fork Formation, Whitewater Formation) were sectioned and analyzed. Many trace fossils were found, with Trypanites borings and bioclaustrations the most common. The borings often contain calcite “ghosts” and were likely excavated mechanically by an organism like a sipunculan or phoronid. Some borings prompted growth reactions in their host bryozoan. Growth reactions sealed the cavity and regained feeding surfaces by: (1) zooids growing laterally over the cavity opening, sealing it with a “roof”; and (2) zooids budding into the cavity then angling upwards. Other bioclaustrated features include cornulitids and a possible sphenothallid.