98-6 Extinction Selectivity in Bivalves Across the Phanerozoic: Trait–Environment Interactions Under Changing Seawater Chemistry and Climate

Session: Linking Biodiversity Loss to Environmental Stressors Through Integrated Approaches

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Abstract:

Marine calcifiers face elevated risk under future climate change due to their sensitivity to ocean acidification, warming, and disrupted carbonate chemistry. Understanding how intrinsic traits mediate extinction vulnerability under these stressors requires insights from the fossil record. Here, we investigate how shell mineralogy and ecological life habits—two traits linked to physiological sensitivity and environmental exposure—influence extinction risk in bivalves across the post-Cambrian era. We focus on their interactions with three major environmental filters: long-term shifts in seawater Mg/Ca ratio, secular changes in sea surface temperature (SST), and mass extinction events.

We used a global dataset of bivalve genera spanning ~485 million years from the Paleobiology Database, with revised assignments of shell mineralogy (aragonitic vs. bimineralic) and life habit (infaunal vs. epifaunal), and linked these to environmental reconstructions. We classify intervals as aragonite- or calcite-sea regimes, and distinguish mass extinction events from background turnover. We used logistic regression, survivorship models, and diversification analyses to quantify trait-based selectivity across SST gradients and environmental regimes.

Our results show that in background intervals, warming is generally associated with reduced extinction odds for aragonitic taxa and a slight increase in risk for infaunal bivalves, a pattern that appears consistent across ocean chemistry states. During mass extinction events, however, these filters shift: in calcite-sea crises, warming tends to reduce extinction risk across traits (especially for infauna), but in aragonite-sea crises, warming strongly favors aragonitic taxa while disproportionately disadvantageous infaunal ones. Survivorship and diversification analyses suggest that extinction pulses produce a sharp increase in turnover that overrides background trait differences.

Our findings suggest that extinction risk emerges from context-dependent interactions between traits and environmental conditions. Background SST trends act gradually and predictably across chemistry regimes, while mass extinctions reconfigure extinction filters and sometimes invert long-term trajectories. Our study contributes to a broader understanding of trait-mediated extinction dynamics in the fossil record and may offer context for interpreting biotic responses to ongoing environmental change.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8738

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