Identifying and evaluating the role of paleogeography of marine mammal dispersal across ocean regions using beta diversity metrics
We tested the roles of several intraoceanic connections, including the Strait of Gibraltar, Central American Seaway, Bering Strait, and Arctic Ocean in the dispersal of marine mammals from their points of origin to their existing distribution. A comprehensive dataset of occurrences, derived from the Paleobiology Database (paleobiodb.org), was compiled for all seven groups of marine mammals (Cetacea, Sirenia, Pinnipedimorpha, Desmostylia, Thalassocnus, Ursus maritimus, and marine Mustelidae). The Cenozoic oceans were divided into thirteen distinct regions and each occurrence was assigned to a region based on its paleogeographic location. Overlap among regions was measured using the Sørensen-Dice Coefficient for all possible combinations of ocean regions in each time frame.
Results confirm the hypothesis that the Strait of Gibraltar served as the avenue through which cetaceans and sirenians left their sites of origin in the Tethys Sea. Results also support the hypothesis that the Bering Strait is a key route through which several groups of marine mammals disperse across the Pacific Ocean. Conversely, the Central American Seaway is found to play only a minimal role in dispersal across the Atlantic and Pacific. We demonstrate that the high overlap values between the Atlantic and Pacific of the present day are achieved in the Quaternary, well after the closure of the Central American Seaway. We suggest the Arctic Ocean as an alternate route and demonstrate the viability of this hypothesis.