MORPHOLOGICAL EVOLUTION FOLLOWING THE CLOSURE OF THE CENTRAL AMERICAN SEAWAY

The closure of the Central American Seaway had profound effects on marine and terrestrial biodiversity. Consequently this spatiotemporal window on Earth’s history has become a model for investigating species response to long-term environmental change. In the Caribbean and western Atlantic, post-closure development of oligotrophic conditions led to marine environments that contrast markedly with those in the eastern Pacific. The effects these environmental changes had on species divergence and biotic turnover on either side of the Central American Isthmus are well-documented through analyses of modern and fossil data. Here we investigate their influence on functional morphology, focusing on a clade of bivalve mollusks in which broad-scale differences in shell shape reflect life habit variation and possibly also habitat preference. We generated a 3D morphological dataset for extinct and extant scallop species that spans the Miocene to Recent. Our data include 95% of extant species found in the tropical to temperate waters of the Panamic, Californian, Caribbean, and Transatlantic provinces. Digitization of fossil shells is ongoing; more than 45 extinct taxa were included in these analyses. We hypothesized that post-closure expansion of coral reefs in the Caribbean and western Atlantic led to increased morphological disparity over time as well as shifts in morphospace occupation. Analyses restricted to present-day faunas on either side of the Central American Isthmus revealed no difference in disparity, though significant differences in mean shell shape. Integration of fossil data found little change in disparity over time in the eastern Pacific relative to pre-closure faunas. In contrast, disparity increased significantly among species in the Caribbean and western Atlantic post-closure consistent with our hypothesis. Mean shell shape also differed significantly among these three spatiotemporal grouping of species. We plan to extend these analyses in the future to consider shape-biased patterns of extinction and origination through the Neogene.