Shell morphometric variation of Ameghinomya antiqua (Mollusca, Bivalvia) during the Late Quaternary reflects environmental changes in North Patagonia, Argentina

Mollusk shells have shown to be useful as biological proxies for palaeo environmental reconstructions. In this study we perform an integral assessment of geometric morphometrics of Ameghinomya antiqua shells from San Matías Gulf (SMG) (Patagonia, Argentina) with special attention on the protected natural area Caleta de Los Loros. In order to relate morphological variation with environmental changes, we analyzed size and shape variation from Holocene and modern shells (temporal variation) and from within the gulf (spatial variation) by carrying out landmark and semilandmark morphometrics studies. Results showed that Holocene shells were rounder and larger than modern ones, with posterior muscle scar, cardinal teeth and ligament more developed. These features in Holocene shells from Caleta de Los Loros could be a response to a higher degree of mechanical stability in a high-energy habitat. Besides, morphometric differences in modern shells in SMG could be linked to variations in wave action, tidal influences, sea surface temperature substrate and/or predation pressure, which modify the shape and size of this species. This study allows highlighting the phenotypic plasticity of A. antiqua as a possible response to different environmental conditions making this species a good proxy when evaluating environmental changes.