Keratose sponge fabrics from the lowermost Triassic microbialites in South China: Geobiologic features and Phanerozoic evolution

Abstract

The Permian-Triassic mass extinction (PTME) strongly devastated marine ecosystems, and, consequently, sponges, especially the reef-building clades, suffered dramatic losses in biodiversity. The Early Triassic therefore was believed to be an evolutionary gap for sponges. Microbialites spread over shallow marine carbonate settings across the entire low-latitude Tethys region following the PTME and occupied the ecospace that the pre-extinction metazoan reefs left. Here, we report putative keratose sponge consortia from the microbialites near the Permian-Triassic boundary in the Xiushui, Laolongdong, and Dongwan sections, South China. The putative keratose sponges exhibit vermiform, filamentous textures forming maze-like networks. Within the keratose sponge-microbial fabrics, the calcified sponge skeleton might firm the overall framework of microbialite, promoting construction of the sponge-microbial build-ups. The coeval occurrence of putative keratose sponges in both eastern Palaeotethys and central Neotethys regions indicates that sponges may have widely spread and played important roles in constructing metazoan-microbial reefs in earliest Triassic. Besides, several characteristics are conducive to keratose sponge surviving the stressful environments after the PTME. Global dataset shows that keratose sponges mostly confined to tropic and temperate zones. Keratose sponges overall flourished in coincidence with occurrence abundance peaks of microbial reefs during the Phanerozoic history, and they seem to be particularly abundant and widespread in the Cambrian-Ordovician, Late Devonian and the aftermath of the end-Permian mass extinction.