Taxonomic and ecologic transitions in Triassic marine bivalve communities

The Permian-Triassic mass extinction was a pivotal event in shaping marine benthic ecosystems, leading to the rise of mollusks such as bivalves and gastropods as representatives of the Modern Evolutionary Fauna. However, the detailed changes in the ecological structure of marine benthic communities throughout the Triassic remain underexplored, particularly the interrelationship between taxonomic and ecological diversities. Here, we present a study on the Triassic bivalve communities from the typical shallow marine facies in South China to document regional evolutionary patterns and explore how these patterns connect to the global trends. Broad congruence in the timing of taxonomic and ecological changes was observed through the Triassic in South China. However, both the South China materials and global data revealed a decoupling of taxonomic and ecological diversities. Substantial variability in taxonomic richness was observed alongside stable ecological diversity. Taxonomic recovery occurred early in the Early Triassic, whereas ecological diversity fully recovered only in the Middle Triassic. The Carnian stage represents a significant transition in ecosystem structure, characterized by a shift towards infaunal dominance and the expansion of habitat depth.