Diversity dynamics of planktic foraminifera across the Cretaceous–Palaeogene and Eocene–Oligocene transitions

Jamson, K., Fraass, A.J., Moon, B.C. 2020 Diversity dynamics of planktic foraminifera across the Cretaceous–Palaeogene and Eocene–Oligocene transitions. Progressive Palaeontology (Leeds)

Abstract

Planktic foraminifera are cosmopolitan organisms with an exceptional, well-studied fossil record and their diversity fluctuates temporally and spatially. Microfossil diversity has been documented, but how this diversity arises and the effect of major events on speciation and extinction rates is uncertain. PyRate, a program operating within Python, calculates speciation and extinction rates from global occurrence data within a Bayesian framework, to accurately determine taxon longevity. This method is used here to estimate diversification dynamics across two extinction events: The Cretaceous-Paleogene boundary and the Eocene-Oligocene transition.

Results from these analyses demonstrate a steep rise in extinction rate at 66Ma coupled with very low speciation rates. This coincides temporally with the end-Cretaceous impact that devastated almost all planktic foraminifera populations. A decline in net diversification rates and mean species longevity reflect this extinction event, indicating a perturbation in diversity for 4-5Ma. Following the impact, disaster fauna with low diversity and short species turnover, recolonised vacant niches and are likely the cause of a highly significant change in speciation rate at 64Ma. Results for the Eocene-Oligocene transition show two periods of significant extinction: at the Middle Eocene Climatic Optimum and at the Oligocene-Miocene boundary. However, speciation rates show little change, contrasting a gradual biotic turnover shown to occur across the Eocene-Oligocene from the literature. This analysis indicates that different preservation models within PyRate need to be examined to reduce uncertainty. Additional work with palaeoclimatic modelling will ensure increased understanding of what external factors drive diversity change across extinction events.