Two cosmopolitanism events driven by different extreme paleoclimate regimes

Cosmopolitanism represents the formation of globally homogenous biotas, usually of low-diversity, and normally form under unusual environmental conditions. But the factors driving such important biogeographic states remain unclear. The Carboniferous to Triassic encompasses the Late Paleozoic Ice Age (LPIA) and a hothouse beginning in the latest Permian and persisting through the Early Triassic. These dramatic environmental changes caused complex paleobiogeographic changes and were also associated with such severe biological events as the mid-Carboniferous biotic crisis, and the end-Permian and end-Triassic mass extinctions. This interval is a unique natural window for studying biogeographic patterns under different climate backgrounds and with greatly changed taxonomic composition. In this study, we apply multiple biogeographic indices to examine two episodes of cosmopolitanism based on global marine invertebrate fossil records during the Carboniferous to Triassic. The LPIA cosmopolitanism event was characterized by high faunal similarity at middle latitudes generated by di-versity loss and complex glacial/interglacial climatic changes. By contrast, the EPME cosmopolitanism event was characterized by high faunal similarity globally resulting from a faunal changeover, when communities char-acterized by high richness were replaced by widespread and monotonous communities with high evenness and extremely low richness. The two cosmopolitanism events differed in durations, taxon preference and geographic influence, but in both cases their driving mechanisms were linked to extreme icehouse and hothouse climates. These two episodes illustrate the complexity of deep time marine ecosystem response to climatic changes and the multiple drivers of cosmopolitanism in the marine biosphere.

Automated summary

This study reveals that the two episodes of cosmopolitanism during the Carboniferous to Triassic had different characteristics and driving mechanisms, but both were linked to icehouse and hothouse climates. These findings highlight the complex response of deep time marine ecosystems to climate changes and the multiple drivers of cosmopolitanism in the marine biosphere.