Paleocene to Miocene larger foraminiferal biodiversity as a response to climate changes in the Neotethys

Modern global warming is proven to affect shallow water calcifiers among which are symbiont-bearing larger foraminifera (LF). To better understand the possible effects on modern faunas, we can explore the response of LF to past global events, referring to the last greenhouse megacycle terminated near the end of the Paleogene. Here we present a biodiversity analysis based on a comprehensive and critical review of the scientific literature on LF and other accompanying shallow-water foraminifera of the Neotethys. It has been obtained by compiling a list of over 1,300 species belonging to 215 genera in the interval from the Danian to the Langhian, currently subdivided into 26 biozones (Shallow Benthic Zones SBZ).

The results show that LF, after their abrupt extinction at the end of Cretaceous, underwent a rapid radiation, with high origination rates at both genus and species level in the Danian, followed by a rather constant biodiversity throughout the rest of the Paleocene. The Paleocene-Eocene Thermal Maximum (PETM) recorded one of the most important LF turnover ever recorded, followed by a rapid radiation of K-strategists species, mainly grouped in the genera Alveolina,Nummulites, Discocyclina, Orbitoclypeus and Assilina.

Immediately after the Early Eocene Climatic Optimum (EECO), roughly corresponds to the SBZ10 and 11, we see a second minor turnover, with a rapid differentiation in SBZ12. 

Within the general cooling trend recorded during the Lutetian and Bartonian, the Middle Eocene Climatic Optimum (MECO) seems having no effects on the final decline of most Eocene LF whose generalized extinction coincides with the Eocene/Oligocene transition (EOT) with a cooling event.

The Oligocene is characterized by the radiation of lepidocyclinids and miogypsinids in the Neotethys, but at the end of SBZ23, right after the Late Oligocene Warming Event (LOWE), a new extinction of LF set their diversity to very low levels. Therefore, our data cannot resolve their response to the last global warming event of the studied interval: the Middle Miocene Climatic Optimum (MMCO).

Study funded by the Italian Ministry of University and Research (MUR), funds PRIN 2017: project “Biota resilience to global change: biomineralization of planktic and benthic calcifiers in the past, present and future” (prot. 2017RX9XXY).