Oceanic anoxic events (OAEs) and plankton evolution: a case study from mid-Cretaceous Radiolaria

The impact of OAEs on the marine biosphere is of interest to palaeobiology because OAEs represent major environmental perturbations of the ocean-climate system. As a siliceous group with a long evolutionary history, Radiolaria constitute an interesting proxy to gauge the biotic response of zooplankton. Previous studies suggest that Radiolaria experienced important faunal turnovers during the mid-Cretaceous OAEs. We have focused on the members of family Archaeodictyomitridae (Early Jurassic-Palaeocene) for which we have first analysed the phylogenetic relationships of its various Cretaceous morphospecies. Our analysis was based on literature review, collection of new material with a high resolution sampling and phenetic analyses performed with the help of PAST software. We find that some previously thought extinctions of Archaeodictyomitrid species during OAE1b (late Aptian - early Albian) are in fact pseudoextinctions. Indeed, our material from Albania suggests that a major diversification took place at the base of this OAE. A high-resolution study across the Bonarelli level (OAE2) confirms the step-by-step pattern of numerous real extinctions (end of lineages), some of which started in the late Cenomanian, long before the C/T boundary. This might suggest that extinctions were not driven by abrupt environmental changes, but by the ca. 2 Ma environmental deteriorations which began with the mid-Cenomanian event

An Akouemma hemisphaeria Organic Macrofossils Colony Hosting Biodiversity Assemblage on the Seafloor of Okondja Basin (Gabon) dated at 2.2 Ga

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