Environmental determinants and ecologic selectivity of benthic faunas from nearshore to bathyal zones in the end-Permian mass extinction: Brachiopod evidence from South China

Abstract

In South China the Changhsingian brachiopods are extraordinarily abundant and diverse, comprising 447 species in 143 genera. They were widespread in nearshore, shallow sea, reef, carbonate platform, shelf basin, and bathyal zones. Brachiopod attachment modes were also highly diversified and include burrowing, body cementation, pedicle attaching on substratum, body spines anchoring on substratum, pedicle attaching on objects, and clasping spines anchoring on other objects. They suffered the species and genus extinction rates of 91.5% and 86%, respectively in the first episode of the end-Permian mass extinction and further species and genus extinction rates of 84.2% and 80.0%, respectively in the second crisis. For the Permian−Triassic (P–Tr) brachiopods, there were (1) selective extinction of the normal shallow marine dwellers relative to these inhabiting deep sea or marginal seas, and (2) among the normal shallow marine habitats, selective extinction of reef-dwellers relative to non-reef forms. Ecologically, the body-cementation forms suffered much higher extinction rates than other lifestyle elements. In contrast, both the burrowing and clasping spine-anchoring forms had much lower extinction rates than other lifestyle elements. Although the reef and bathyal dwellers partly survived the first extinction event, they migrated to other habitats to survive the crisis. The estimation of extinction rates based on the single-episode mass extinction pattern cannot reveal precisely the extinction severity of brachiopod faunas over the P–Tr transition. Brachiopod diversity changes support the two-stage mass extinction pattern near the P−Tr boundary.