Middle-Late Ordovician brachiopods from Ningnan, southern Sichuan Province, Southwest China: Implications for macroevolution and palaeogeography

Middle to Late Ordovician brachiopods from the Huadan Formation (upper Darriwilian-Sandbian) of Ningnan County, southern Sichuan Province, are systematically documented here for the first time. The locality belongs to the western margin of the Upper Yangtze Platform, South China palaeoplate, and the brachiopod fauna includes one new genus and three new species as well as five other con-stituents: Hingganoleptaena sp., Acculina zhongliangziensis n. sp., Ningnanmena longisepta n. gen. n. sp., Kassinella (Trimurellina) minuta n. sp., Lepidorthis typicalis Wang, 1955, Protoskenidioides weixinensis Zhan and Jin, 2005, Porambonites transversus Xu, Rong and Liu, 1974, and Psilocamerella sp. Taxonomically it is a typical representative of a Middle to early Late Ordovician brachiopod fauna, and, together with some other evidence from other fossil groups like trilobites, conodonts, chitinozoans, a late Darriwilian-Sandbian age could be inferred for the horizon yielding this fauna. According to the richness of each constituent, this fauna is suggested to be called the Acculina-Ningnanmena fauna (ANF). Numerical palaeogeographical analysis shows that two broad palaeobiogeographic provinces could be recognized during this particular time interval, and, although the ANF is grouped into the South China cluster, it shares very little similarity with other representatives of that group except for two cosmopolitans. It further confirms that the Great Ordovician Bio-diversification Event (GOBE), in other words the Ordovician radiation, was actually manifested by the strong localization of major mar-ine organisms such as brachiopods, trilobites, graptolites, etc.(c) 2023 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights reserved.

Automated summary

This study systematically documents Middle to Late Ordovician brachiopods from Ningnan County, southern Sichuan Province, for the first time. It identifies new genus and species and suggests a late Darriwilian-Sandbian age based on other fossil groups. The brachiopod fauna is named the Acculina-Ningnanmena fauna and is found to have little similarity with other representatives of the South China cluster, confirming the Great Ordovician Biodiversification Event.