Elisabetta Erba

Along with diatoms, cyanobacteria, and dinoflagellates, coccolithophores are key marine functional groups responsible for primary productivity, energy transfer, export of biogenic particles, and exchanges with the atmosphere. Coccolithophores are the most abundant calcifying organisms in the oceans, and their fossils are key for tracking global climate-ocean changes. The evolutionary history of calcareous nannoplankton, reconstructed from nannofossil records, shows increased diversity through the Mesozoic.
The rise of coccolithogenesis is a profound ecological innovation in the ocean ecosystem. Early Triassic nannofossils from South China help understand the circumstances prompting (or allowing) phytoplankton to mineralize calcite, marking the birth of the modern ocean. Coccolithophore origination shortly after the Permian mass extinction reset marine ecosystems, forcing biota to adapt to extreme climatic and chemical conditions and novel niches. The onset of coccolithogenesis began a long and successful evolutionary history of coccolithophores that influenced oceanic ecosystem dynamics, biochemical processes, and sedimentation. The geological history of coccolithophores indicates Mesozoic evolution characterized by increasing diversity, punctuated by speciations, "mass" extinctions, and turnovers that led to 25 coccolith/nannolith families and 5 groups Incertae sedis, peaking before the end-Cretaceous mass extinction.
Times of accelerated rates or drops in nannofossil diversification correlate with global changes in the geosphere, hydrosphere, and atmosphere, linking evolutionary patterns to environmental perturbations. Significant events in Mesozoic nannoplankton origination and evolution align with changes in CO2 concentrations, nutrient availability, ocean chemistry, and climate. Global environmental changes are interconnected with Earth's processes, and biosphere evolution should be linked to the Earth's interior. However, it is challenging (and contentious) single out causes triggering coccolithophore evolution and calcification; a combination of environmental changes likely drives evolutionary innovations and stability.
Mesozoic coccolithophore biodiversity and calcification patterns can assess their resilience: calcareous nannoplankton as a whole showed high resistance to global disturbances maintaining diversity and recovering post-disturbances, while individual taxa varied in resilience. Calcification patterns reveal moderate to lowered resilience, with different taxa showing varying sensitivity and resistance.
The response of coccolithophores in timing, magnitude, and recovery dynamics aids understanding the potential impacts of current and future global changes on marine ecosystems' adaptability and thresholds leading to ecological crises. Improved chronology of paleobiological and geological events is crucial for understanding evolutionary processes.