Gastropod Fauna of the Zuodeng Permian-Triassic Boundary Section in the Nanpanjiang Basin and Its Geometric-Based Morphological Disparity Analysis

Gastropods, as one of the most common invertebrates in shallow marine environments, were heavily impacted by the Permian-Triassic mass extinction (PTME), with severe loss of diversity and remarkable dwarfism of body size. Here, we report a new gastropod fauna from the Permian-Triassic carbonates of Zuodeng, Guangxi Province, South China. Five species belonging to five genera and two indeterminate taxa are identified. The Zuodeng fauna is dominated by Paleozoic holdover taxa, including Holopea teres, Protostylus sp., and Wannerispira shangganensis although most of them are found in the basal Triassic microbialites. Three gastropod communities have been recognized by cluster analysis. Further morphological analyses show that the changing pattern of disparity, with diversity decreasing from community II to III, fits the interior-reduction model. In addition, the morphospace of community in microbialites is higher than those in non-microbialite bearing beds at Zuodeng, shedding new light on the ecological role of microbialites during the Permian-Triassic environmental stress.