ENCRUSTERS AND BORERS THROUGH AN EXTINCTION EVENT: A DESCRIPTION OF SKELETOBIONT ASSEMBLAGES THROUGH THE FRASNIAN-FAMENNIAN BOUNDARY OF THE APPALACHIAN FORELAND BASIN

Communities in which groups of organisms depend on other organisms for substrate space are common throughout the fossil record and can be highly diverse in modern ecosystems. An understanding of the long-term dynamics of these commensal systems is important for managing conservation efforts because many of these relationships are experiencing or are at risk of experiencing anthropogenic perturbation. Fossil assemblages of aquatic skeletobiont communities—organisms that encrust on or bore into the skeletons of other organisms—offer a unique view into these types of ecological guilds over deep time in that they occurred throughout the Phanerozoic and have a high preservation potential. Mass extinctions provide the best cases for observing effects of ecological and environmental perturbation because they represent the largest known shifts in diversity in the fossil record. The Frasnian-Fammenian extinction event is of particular utility because it represents a time of drastic restructuring of ecosystems even when compared to other mass extinction events. Skeletobiont assemblages within the Appalachian foreland basin before and after the Frasnian-Fammenian extinction are described and documented. These rocks contain a variety of brachiopod fossils which were hosts for microconchids, bryozoans, and hederellids as well as the traces of shell-boring porifera, phoronids, and polycheates. A preliminary assessment indicates that the assemblages are dominated by the ichnogenus Talpina (borings of phoronid worms) and microconchids, indicating that these small vermiform skeletobionts had a more effective dispersal strategy than the other taxa in the assemblage. Greater ability to disperse may be advantageous during recovery following a mass extinction. If so, these groups may be expected to be dominant taxa in their communities both before and after the extinction event.