ONTOGENETIC VARIATION IN δ13C AND δ15N IN MODERN BIVALVES AND GASTROPODS

The carbon and nitrogen isotopic compositions of an organism’s tissues are representative of its diet. Hence, stable isotopic analysis has become a powerful tool to determine the diets of organisms with poorly understood ecologies. Although this approach has been extended to the fossil record only in a few cases, there is a prospect for a better understanding of the diets of fossil organisms and the trophic relation between them. The organic matter preserved from the extracellular matrix of fossil mollusks can be used for stable isotopic analysis. Here we explore ontogenetic variation in the carbon and nitrogen isotopic composition of shell organic matter for several bivalve and gastropod taxa. Because organisms are known to change their feeding behavior over ontogeny, we will use sclerochronological techniques to assess the ontogenetic variation in the isotopic composition of shell organic matter. Along with the ontogenetic variation we also aim to explore the taxonomic variation between species. The techniques developed for these recent materials will be applied to the reconstruction of ancient trophic strategies and ultimately food web reconstruction using specimens from the Late Cretaceous (Campanian/Maastrichtian) Lopez de Bertodano Formation exposed on the Antarctic Peninsula. Specimens were obtained from the Zinsmeister Collection housed at the Paleontological Research Institution in Ithaca, NY. The collection comprises of a broad group of near-shore organisms including bivalves, gastropods, ammonites, corals and calcareous worms, all co-occurring at one of several individual collection localities.