ARE CHANGING ENVIRONMENTS REFLECTED IN THE MORPHOLOGICAL DISPARITY OF FOSSIL AND RECENT SCALLOPS FROM THE TROPICAL AMERICAS?

The closure of the Central American Seaway (~3.5 Ma) resulted in the restructuring of marine ecosystems throughout the Caribbean and tropical Western Atlantic. Post-closure shifts toward oligotrophic conditions led to the development of extensive coral reefs and associated benthic habitats as well as elevated turnover rates in a diversity of clades, including corals, bryozoans, and mollusks. Here we assess the effects these environmental changes had on morphological disparity in fossil and Recent scallops. Broad-scale differences in shell shape among scallop species reflect differences in life habits (e.g., free-living vs. gliding vs. bysally-attached) which are associated with different environments and/or substrata. Using 3D shape data gathered from museum specimens, we examine changes in morphological disparity, and by extension life habit diversity, over time. One of the strengths of this approach is that life habit variation can be considered as a continuous character without having to impose a discrete classification, a process that can be challenging when considering lineages such as Argopecten in which individual species can exhibit a combination of life habits. Counter to our expectation that increased environmental variability and habitat diversity led to increased morphological disparity, our preliminary results show little difference in the morphological disparity of tropical scallops before and after the closure of the Central American Seaway. These analyses can be extended further to consider changes in morphological disparity within subclades and functional groups as well as rates of life habit evolution in a phylogenetic context.