ANALYSES OF TAPHONOMIC BIAS IN THE CANEPATCH FORMATION, UPPER PLEISTOCENE, HORRY COUNTY, SOUTH CAROLINA

Various factors, such as life mode, specimen size, and predatory drillholes, may impose taphonomic bias on fossil assemblages. The mollusc fauna of the Canepatch Formation (Upper Pleistocene) was analyzed for taphonomic bias by a graduate Paleoecology class at University of North Carolina Wilmington. Three bulk samples (Canepatch 1, 2, and 4) from Bed 8 of Dubar’s classic WA 56 locality at Windy Hill airstrip, Myrtle Beach, SC, were analyzed. Samples were wet sieved with 5 mm mesh; bivalves with beaks and gastropods with apices were retained for study and identified to genus level. The samples included 1559 bivalve specimens (26 genera) and 239 gastropods (12 genera).

Each specimen was assigned a taphonomic grade based on encrustation, non-predatory bioerosion, corrasion, and margin condition. Presence of predatory gastropod drillholes was tabulated and specimen size was measured. Life modes were determined from the NMITA and Paleobiology Databases. The following hypotheses were tested: 1) taxa with infaunal life modes will exhibit less taphonomic damage than epifaunal forms; 2) large specimens will exhibit greater damage than small specimens; 3) taphonomic bias will exist against shells with predatory drillholes.

Life mode showed no clear relation to taphonomic damage. No significant differences in taphonomic grade occurred between infaunal and epifaunal taxa for Canepatch 1, but infauna in Canepatch 2 had significantly less taphonomic damage than epifauna. In Canepatch 4, cemented bivalves showed the most damage, but unattached epifauna showed the lowest average taphonomic grade. The relationship of size to taphonomic grade was evaluated for Chione in Canepatch 1; results varied among taphonomic criteria. In Canepatch 4, bivalves and gastropods showed a positive relationship between specimen size and total taphonomic grade. Taphonomic grade was compared for drilled and undrilled specimens in Canepatch 1 and 2; if drillholes weaken shells, drilled shells should not survive to accumulate taphonomic damage and thus should have lower taphonomic grades. Chi squared tests produced no significant differences in taphonomic grade for drilled and undrilled shells indicating lack of bias. Drilled shells were not more prone to fragmentation, and fragments with drillholes were not broken through the hole.