Intensive sampling of Neogene mollusk faunas in the Northern Dominican Republic, as part of an integrative international project, has provided a unique spatial and temporal framework for high-resolution macroevolutionary and paleoecological research. Independent analyses of multiple taxa show evidence of strong paleoenvironmental control of change in well-exposed, intensively sampled stratigraphic sections in the middle Miocene Baitoa Formation to the early Pliocene Mao Formation. In some taxa, however, there is clear evidence of macroevolutionary trends independent of obvious environmental change.

Large samples of well-preserved specimens of the neritid gastropods Smaragdia viridimaris and Neritina figulopicta from four stratigraphic sections preserve intricate color patterns that we classify into seven distinctive types. Color patterns, although rarely preserved in the fossil record, provide a chart of physiological activity that is under a combination of intrinsic and extrinsic control. Accordingly, changes in pattern frequencies in populations may reflect changes in gene frequency, changes in the environment, or both.

Our analyses show a clear environmental control on the overall distribution of both species. Based on independent estimates of paleodepths, samples containing Smaragdia and Neritina represent depths of >50m, and population sizes decline with increasing paleodepth. Living species of the genus Smaragdia occur obligately on sea grasses, especially in the genus Halophila, which is able to tolerate low light and turbid conditions and has been reported as deep as 85m in very clear water. Within each of the fossil species, change in color morph frequencies follows separate spatial and temporalpatterns. Within the space-time matrix, we document distributions that are geographically distinct and coherent within individual stratigraphic sections as well as distributions that appear to reflect a predominance of paleoenvironmental control and change up section. Differences between the two species support a conclusion that there is no single pattern of response intrinsic to Neritidae.

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