Morphological variability of Polyconites hadriani (Hippuritida, Bivalvia) in the Aptian carbonate platforms of the western Maestrat Basin, eastern Iberia

Abstract

This investigation is aimed to study the morphological variability of the polyconitid rudist, Polyconites hadriani, from the Aptian carbonate platforms of the western Maestrat Basin, in Iberia. The individuals of the platform top to upper slope carbonates differ from those of the slope deposits in the size and external shape of the shell. Therefore, the populations of these two distinct platform habitats were compared by morphometric measures (dorso-ventral commissural diameter and antero-posterior commissural diameter). The results of the morphometric analysis showed that shell size and shell form were correlated with depth. (1) Larger shells occur in the slope deposits while smaller shells in the shallower platform top to upper slope settings; (2) commissural outline is compressed dorso-ventrally in the individuals from the platform top to upper slope environments and in half the individuals from the slopes, whereas the commissural outline is compressed antero-posteriorly in the other half of the slope group. It is suggested that phenotypic plasticity allowed P. hadriani to adapt shell growth to the different ecological conditions prevailing in the two habitats.