Mollusc extinction during the end-Triassic crisis

MICHAEL HAUTMANN; FERRARI MARIEL

Lausanne

Simposio; 20th Swiss Geoscience Meeting; 2022

The end-Triassic mass extinction is commonly ranked among the “big five”extinction events of the Phanerozoic and has attracted considerable scientificattention, but surprisingly, there is still a lack of comprehensive studies onthe taxonomic turnover of many major taxa (Hautmann 2021). This presentationprovides the first in-depth analysis of diversity changes of gastropods duringthe Triassic–Jurassic transition and a comparison with the diversitytrajectories of other molluscs. Gastropods suffered a loss of 56.8 % of generaand subgenera during the crisis, which was higher than the average of marinelife (46.8 %). The most strongly affected subclass was the Neritimorpha, whichlost 72.7 % of their Rhaetian genera; on the other extreme, the Heterobranchiaremained nearly unaffected (11 % loss). We analysed this extinction patternwith respect to larval development, palaeobiogeography, shell size, and anatomyand found that putative feeding of the pelagic larval stage, adaptation totropical-temperate water temperatures, and flexibility of the mantle attachmentwere among the factors that might explain extinction resilience ofheterobranchs during the end-Triassic crisis. Among molluscs, gastropods weremore strongly affected than bivalves (43.4 % extinction) but less thanammonoids, which were nearly annihilated. These differences in extinction magnituderoughly correlates with locomotion activity and thus metabolic rates. Wesuggest three potential kill mechanisms that could account for the observedextinction patterns: global warming, ocean acidification, and extinction ofmarine plankton. The end-Triassic extinction of gastropods fits to proposedextinction scenarios for this event, which invoke the magmatic activity of theCentral Atlantic Magmatic Province as the ultimate cause of death.