Variation in shell morphology in the fossil freshwater gastropod Tanousia subovata (SETTEPASSI 1965) from the Mercure Basin (Middle Pleistocene, southern Italy): Distinct taxa or ecophenotypic variation? (Gastropoda Prosobranchia: Hydrobiidae)

Abstract

The study of the shell plasticity of the extinct Hydrobiidae Tanousia subovata (settePassI 1965) resulted in a better understanding of the relationships between the shape of the organisms and the environment that influenced their life. Three populations, from distinct sections of the lacustrine Middle Pleistocene Mercure Basin (Basilicata-Calabria, southern Italy), have been investigated, using a landmark-based geometric morphometric analysis to quantify the morphological variability. Morphometric data and data coming from independent proxies (such as lithology and other fossils), already published on the studied basin, have been taken into account. Results have been interpreted to discriminate between internal and external factors influencing the shape of the shell. The geometric morphometric method proved useful to reveal some morphological variations between the three populations, which, following the comparisons with palaeoenvironmental data and with the literature appear to result from ecological or maybe chronological factors rather than indicating distinct species.