Evidence of traits and faunal turnover in planktonic foraminifera during extreme climate: A biological Traits Analysis approach

The Palaeocene-Eocene Thermal Maximum (PETM) is a paleoclimatic event associated with massive radiation and the extinction of planktonic foraminifera. It is still unclear which planktonic foraminiferal attribute was responsible for its enormous turnover during the PETM event. It has been hypothesized that biotic interaction with the environment is driven by biological traits rather than faunal composition. This idea stimulated this research where a combination of faunal composition and biological traits of planktonic foraminifera from Ocean Drilling Program (ODP) Site 1265 (Walvis Ridge, SE Atlantic Ocean) were used to understand the planktonic foraminiferal attribute responsible for biotic turnover during the PETM. Our results show that the studied section cut across three planktonic foraminiferal (PF) zones namely Morozovella valescoensis, Pseudohastigerina wilcoxensis, and Morozovella marginodentata dated 54.5 – 55.5 Ma. The faunal occurrence showed high variability in abundance and diversity with the last appearance (local extinction) of nineteen (19) species and the first appearance of eight (8) species including Globoturborotalita bassriverensis. Statistical analyses showed that the faunal compositions of the recovered planktonic foraminifera differed across the three sections of the PETM. Multivariate analyses of the faunal and trait compositions suggest evidence of disturbance in planktonic foraminiferal ecology during the PETM. The key foraminiferal traits that increased in abundance during the extreme climate event were triangular/trapezoid chamber arrangement, muricate wall texture, presence of accessories like lip in the aperture, umbilical and extraumblical apertures, perforations in the test wall, grazing and surface-dwelling habits. These traits are believed to characterize resilient types that enabled taxa to survive the PETM.