Recovery and Radiation of Crinoids Following the Permian–triassic Mass Extinction: A Case Study from the Anisian Qingyan Biota

The Middle Triassic was a crucial stage for the reconstruction of marine ecosystems following the Permian-Triassic mass extinction event. As an important component of benthic communities, the recovery and radiation of crinoids provide key evidence for understanding the recovery pathways and ecological reconstruction mechanisms of invertebrate communities. Based on newly collected crinoid stem fossils from the Qingyan Biota (Anisian) in Guizhou, this study conducted a systematic taxonomic revision and paleoecological reconstruction. A total of 7 genera and 8 species were identified: Holocrinus qingyanensis, H. hagdorni, Eckicrinus cf. radiatus, Encrinus cf. liliiformis, Tyrolecrinus cf. wugangi, Bangtoupocrinus kokeni, Silesiacrinus parvus, and Qingyanocrinus kueichounensis. All these groups belong to the Mesozoic-type crinoids that first appeared after the mass extinction, with no Paleozoic remnants observed. Stem morphology and functional inference reveal three distinct substrate-attachment strategies: (1) discoidal attachment to firm substrates; (2) root-like cirral anchoring adapted to unconsolidated, soft sediments; and (3) mobile cirral attachment enabling limited repositioning. The significant ecological functional differentiation indicates that crinoids in the early Middle Triassic had achieved morphological and ecological co-innovation, breaking the dependence on hard substrates and significantly expanding their habitat space and ecological niche width, thus laying a biological foundation for the further radiation and evolution of crinoids in the Late Triassic.