An analysis of the impact of Eocene climate and environmental changes on Pan-American marine mollusc assemblages

The phylum Mollusca experienced significant radiation and a broad redistribution of families during the Eocene epoch. However, these processes were interrupted by abrupt climatic and environmental events, including early Eocene hyperthermal events, a cooling trend followed by rapid warming in the middle Eocene, and a subsequent cooling phase in the late Eocene. Recent research has sought to correlate molluscan faunal associations to elucidate regional palaeoenvironmental changes and shifts in species distribution. In this study, we correlate four Pan-American marine provinces: Northeastern Pacific Ocean Province (NEPP), Southeastern Pacific Ocean Province (SEPP), Caribbean Province (CP), and Gulf Province (GP). The NEPP and GP exhibited closer interprovincial relationships, facilitated by the Tethys current during the Ypresian and Lutetian stages, with the Central American Seaway playing a crucial role in enabling faunal exchange among these provinces. Our results also indicate maximum marine biodiversity of molluscs coincided with hyperthermal events. In the NEPP, peak biodiversity occurred during the Ypresian (early Eocene Climatic Optimum), while in the GP it was observed during the Bartonian (middle Eocene Climatic Optimum). The Priabonian in the NEPP marked a phase of faunal redistribution, possibly driven by changes in surface current dynamics in the northwestern Pacific. By contrast, cooling intervals in the GP were associated with marked reductions in taxonomic richness. In the SEPP, affinities with Northern Hemisphere provinces during the Bartonian and Priabonian are likely attributable to the northward drift of the South American plate and the persistence of Tethyan faunal elements.