EXCEPTIONAL PRESERVATION OF BIOEROSION IN LATE DEVONIAN BRACHIOPODS FROM NEW YORK AND PENNSYLVANIA

Bioerosion is commonly preserved in the fossil record as excavated cavities in the host’s shell or skeleton. Brachiopods from the Late Devonian of New York and Pennsylvania are commonly bored, but the borings often occur as natural casts. Upon burial, the borings were filled with siliciclastic sediment, which subsequently became lithified. When the shell material is removed by dissolution, the borings appear as three-dimensional casts on the surfaces of the brachiopod molds. Fine morphologic details can be seen on many specimens. Borings have also been observed on bivalves, although they have not been analyzed in detail. Conversely, encrusters are preserved as molds. Approximately 13% of the examined brachiopods were bored and 6% were encrusted. Four ichnotaxa of borers were identified, probably representing the activities of worms, sponges, and bryozoans. Three taxa of encrusters were identified, including microconchids, bryozoan mats, and hederellids. No predatory drillholes have been identified, although the fine detail evinced on non-predatory borings indicates that drillholes could be recognized in fossils preserved as molds in lithified Paleozoic rocks. The distribution and co-occurrence patterns of the borers and encrusters were examined to infer relationships among these organisms and between them and their hosts.