PSEUDO-BORINGS AND PREDATOR TRACES - ARTIFACTS OF PRESSURE-DISSOLUTION IN FOSSILIFEROUS SHALES

Well-preserved brachiopods from two Paleozoic deposits (Ordovician Ric hmond Group, Indiana; Devonian Silica Formation, Ohio and Michigan) oc casionally contain skeletal fragments embedded in their exterior surfa ces. Cross-sections of the shells reveal that the fragments are the re mains of brachiopods that cleanly pierce one or both valves of the hos t specimen. A sharp contact between fragment and host, a coincident fi lm of insoluble residue, and, in some samples, a thin zone of recrysta llization, all suggest that the fragments were emplaced via pressure-d issolution during post-burial sediment compaction. Diagenetically empl aced fragments may disintegrate during weathering and leave grooves (p seudo-borings) that resemble the traces of shell-boring organisms. App arent teeth or rhyncholites found embedded in brachiopod shells may ar ise from pressure-dissolution between fortuitously associated particle s. If pressure-dissolution artifacts, like these, are not distinguishe d from true biological traces, an overestimation of boring and predati on intensities in paleoecological studies may result. Several simple c riteria for distinguishing artifacts from traces are proposed, includi ng regular plicate or linear shape of groove, random orientation and l ack of host response. This study documents that even in exceptionally well-preserved fossil deposits, pressure-dissolution can be an importa nt taphonomic process.