PLANKTONIC FORAMINIFERAL BIOGEOGRAPHIC EXTINCTION TRAJECTORIES FROM THE PLIOCENE TO MODERN

Each species of planktonic foraminifera has a unique biogeographic extinction pattern. Because these single celled organisms have an abundant fossil record, it is possible to compare early Pliocene to Holocene extinctions. Such records are crucial to understanding how species respond to global-scale climate events, like the Pliocene ice sheet expansion (~2.7 million years ago). Being able to identify biogeographic patterns before and after these climate events allows us to gain a clearer picture of the ever-changing process that is evolution. For this study, the biogeographic ranges of 44 planktonic foraminifera species that have extinction dates within the last 5.3 million years were extracted from the planktonic foraminifera database, Triton.

Species were assigned to their respective ecogroup, morphogroup, speciation age, and extinction age. After this, the data were binned into 53 discrete 100,000-year long time bins and we plotted each species’ total global occurrences during the falling limb of their biogeographic range prior to extinction, and documented the inflection points where the extinction slope experienced the most dramatic change in occurrences. We observed a positive correlation between the length of falling limb and when extinction occurred, implying species with a more recent extinction date required longer to go extinct once their biogeographic range began to decline. This result persisted when plotting extinction vs length of decline after the inflection point. When we compared the logarithmic rate of decline for each species, we saw considerable variation. Morphogroup 3 had the most uniform and consistent extinction rates among all morphogroups. Additionally, most short-falling limbs occurred before the Pliocene ice sheet expansion suggesting that extensive cooling may have had a positive impact on planktonic foraminiferal extinction resilience.