DIVERSITY TRENDS IN THE PLANKTONIC FORAMINIFERA

The Planktonic Foraminifera are an excellent microfossil group for evolutionary study, but previous studies have generally focused on specific episodes of their history, rather than taking a holistic approach. With the publication of several new references that present a unified taxonomy, a new analysis of foraminiferal diversity trends at the species and genus levels throughout their complete range is warranted. This study entailed the compilation of 600+ species and 118 genera ranges spanning the late Jurassic to Recent. The overall shape of this diversity curve appears less affected by traditional preservational biases as indicated by roughly equal species numbers during episodes of peak diversity in the Cretaceous, Eocene and Recent. Generic diversity increases via a logistic pattern while species diversity increase is exponential during the Cretaceous, a notable departure from this species-level pattern is due to the rapid diversification and extinction within the genus Hedbergella. Further, Ocean Anoxic Events appear to have a negligible effect on overall diversity during the Cretaceous. The extinction and origination rates also show that each extinction event and ensuing recovery have an entirely different character. For example, the end-Cretaceous event is characterized by an abrupt increase in extinction rates, while the end-Eocene event is typified by a decrease in origination rates. The Oligocene stands out as a particularly unique period in the foraminiferal record due to exceptionally low origination rates. The generic trends also stand in sharp contrast to the species trends during the Neogene, as the number of genera stay roughly the same while species diversity increases to nearly four times the Oligocene number.