SEASONAL VARIATION IN ECOLOGICAL AND TAPHONOMIC PROCESSES RECORDED IN SHELLY DEATH ASSEMBLAGES

Abstract

Modern valves of Lucina pensylvanica (Bivalvia: Lucinidae) were analyzed for 18O/16O ratios, drilling predation traces, biometric measurements, and taphonomic descriptors to explore seasonal variations in ecological and taphonomic processes within a death assemblage from Grand Bahama Island. The d18O values at the shell margin (5last growth episode) were used as a proxy for temperature at the time closest to the organism’s death. Temperature estimates suggest that most individuals died in warmer months, whereas mortality appeared to have been lower during cooler seasons ( ,24 6C). Only drilled valves yielded the coldest temperatures at the shell margin (,18.1–21.3 6C), whereas exclusively undrilled valves exhibited the hottest temperatures at the last growth episode (,25.5–26.5 6C). Drilled valves were significantly smaller and exhibited higher taphonomic alteration than undrilled valves, pointing to postmortem transport and sorting. While seasonal variations in predation and growth rates may have affected the observed patterns to some extent, the results, at least partly, reflect hydrodynamic variations throughout the year, which may have induced seasonal variation in postmortem sorting of drilled and undrilled valves. This study illustrates that, by combining geochemical proxies and quantitative paleoecological data, more informed ecologic and taphonomic interpretations can be achieved for subfossil and fossil assemblages.