PROVIDING PALEOECOLOGICAL CONTEXT FOR MORPHOLOGICAL CHANGE: NEOGENE DOMINICAN REPUBLIC MOLLUSCAN ASSEMBLAGES

Although the Neogene marine sections of the Domincan Republic are considered by many paleontologists to represent continuous sedimentation through a gradually deepening depositional environment, in reality most fossils found along the famous Rio Gurabo section are found in event beds, tubular tempestites or possible slump features representing short-lived sedimentologic events. Using this depositional context, these assemblages allow us to examine the roles and feedbacks of environmental fluctuation, paleocommunity compositional changes, and morphological evolution within species.

An extensive collection of Dominican Republic marine invertebrate fossils (>250,000) which were collected in 2000 as bulk fossil samples is now available at the California Academy of Sciences. The bulk sampling and careful processing of this material has allowed for quantitative paleocommunity analysis of these assemblages, including individuals in the smaller size classes. Employing a variety of analytical techniques on a variety of different molluscan taxa, we compared samples within close stratigraphic proximity to one another. We examined bivalve paleocommunity composition using abundances, diversity indices, and presence/absence data and found that among different groups, there were stark differences in dominance and number of species present. In addition, species abudances and morphometric patterns found within specific molluscan taxa such as naticids, arcids, pectinids and venerids either exhibited significant differences between closely spaced samples or showed no overall trend through the section. These data along with predation intensity analyses on different prey items suggest a complex pattern of stasis and change; some taxa exhibit major changes while other taxa—even sometimes closely related taxa—can exhibit little to no morphological and/or paleoecological change through the same interval.