Paleoenvironmental control of species distributions and intraspecific variability in Neogene Corbulidae (Bivalvia: Myacea) of the Dominican Republic

Abstract

The widespread occurrence and local abundance of corbulid bivalves in Neogene deposits of the northern Dominican Republic provide an opportunity to evaluate physical controls on species distributions and intraspecific variability in this group. First and last appearances of species probably do not record speciation and extinction, but instead represent migrations into and out of the study area, and reflect corbulids' preference for marginal-marine and shallow-marine conditions. Corbula cercadica and C. viminea show patterns of intraspecific morphologic variability over time and space. Corbula cercadica shows continuous morphologic variability along a paleoenvironmental gradient of salinity, depth, and bioclastic fabric, whereas variation in C. viminea is morphologically clinal from west to east in roughly contemporaneous sediments, with variability related to sediment type and bioclastic fabric. Ecophenotypic variation or genetic differences, rather than taphonomic processes, seem to control geographic variability within C. cercadica and C. viminea. Although it is not possible to determine whether intraspecific morphologic variability was under genetic control, its stronger relationship with paleoenvironmental conditions relative to stratigraphic position suggests lack of anagenetic morphological evolution.