THE ROLE OF SURVIVOR INCUMBENCY IN THE EVOLUTIONARY RECOVERY OF CALCAREOUS NANNOPLANKTON FROM THE CRETACEOUS/PALEOGENE (K/PG) MASS EXTINCTION

The earliest Paleocene record of calcareous nannoplankton presents a unique opportunity to understand the evolutionary recovery of life from mass extinction. Nannoplankton were devastated at the Cretaceous/Paleogene mass extinction and their subsequent recovery can be studied in great detail because of their abundance in sediments and near global distribution. Here we determine when and where new species of nannoplankton originated and how they dispersed following the Cretaceous/Paleogene mass extinction. We first focused our efforts on North Pacific and South Atlantic sites with orbital age control to determine high-resolution patterns in origination. We then broadened our investigation with six additional locations from different basins and a variety of environments. We found that many key Paleogene lineages originated in the North Pacific before appearing in the South Atlantic. Assemblages composed primarily of new Paleogene taxa were first established in the North Pacific, but were not found at other sites for several hundred thousand years. Survivors rapidly expanded in Southern Hemisphere sites after the extinction, and diversity plateaued in the South Atlantic for most of the study interval. We hypothesize that the survivors formed a regional incumbent assemblage in the Southern Hemisphere that limited diversification and dispersal of new Paleogene taxa. Waning survivor dominance correlated to the recovery of the biologic pump and subsequent decrease in surface ocean nutrient concentration 300-400 Kyr after the boundary. After the biologic pump recovered, surface water nutrients lessened and the abundance of the eutrophic incumbents declined. The removal of incumbent taxa allowed for the global dispersal of a new Paleogene nannoplankton assemblage. These results indicate that competition from incumbent survivors was as an important control on the K/Pg recovery of nannoplankton.