INTRA AND INTERSPECIFIC OXYGEN STABLE ISOTOPE VARIABILITY OF SYMPATRIC SMALL LAND SNAILS FROM NORTH AMERICA

The durable and plentiful aragonitic shells of land snails are a common and well-preserved component of many Quaternary deposits in North America and elsewhere. Snail shell oxygen isotope values (δ¹⁸O) have been therefore increasingly used as a paleoatmospheric indicator since 1979. However, it seems yet unclear the minimum number of specimens required to extract an average value that is sufficiently representative of the target locality or time-interval. It is also uncertain if combining the isotopic data from multiple species that overlap in space and time is an adequate approach in paleoclimatic investigations. The present study quantitatively evaluates if several relevant present-day small snail species, which are common in modern and fossil localities from North America, record reliable environmental information, and if they do so in an equivalent manner regardless their potential differences in ecology. Ten modern individuals of 11 different species belonging to the families Discidae, Euconulidae, Vertiginidae, Pristilomatidae, Succineidae and Valloniidae were collected from multiple localities in Minnesota, at the latitudes between 46°and 48°. Preliminary results suggest that a minimum of five shells should be analyzed per locality to provide a representative average value of the target habitat. Moreover, different sympatric species of microsnails with comparable ecology from North America appear to generally record similar environmental information in their shell oxygen isotope codes. This study suggests that multi-taxa snail datasets seem to be a feasible approach for paleoatmospheric reconstructions when the same taxon is not present across broad spatio-temporal gradients.