Early–Middle Ordovician chitinozoans from the Dawan Formation, Yichang area, Central China

Abstract. The late Early to early Middle Ordovician is a key interval for chitinozoan macroevolution, during which chitinozoans diversified significantly, reaching their first enormous radiation later in the Darriwilian. The South China palaeoplate is one of the classical regions for Ordovician palaeontological research; however, published chitinozoan data for this interval remain insufficient. This study presents new data from the Gudongkou section, western Yichang, western Hubei Province, in the central part of the South China palaeoplate. A total of 13 genera and 31 species are recognised, including three new species: Conochitina clavatus sp. nov., Conochitina tenellensis sp. nov., and Lagenochitina yangtzensis sp. nov. Systematical remarks on some taxa are provided, including Conochitina decipiens, C. ordinaria, and the group of Sagenachitina oblonga, S. striata, S. dapingensis, and Cyathochitina? dispar. Network analysis is applied based on the data from the Dawan Formation and its contemporaneous units on the Yangtze Platform to test whether chitinozoan assemblages vary among different lithological units that represent different palaeoenvironments. The result shows that chitinozoan assemblages may have palaeogeographical significance. The chitinozoan assemblage from the Dawan Formation at the Gudongkou section seems to be a more independent community compared with those from the Meitan and Zitai formations. However, shared taxa, including the zonal species Bursachitina maotaiensis and Sagenachitina dapingensis, and some other widely distributed, characteristic taxa, such as C. decipiens and C. poumoti, are well-preserved in almost all sections. The biostratigraphical significance of the Dawan chitinozoans, discussed herein, indicates an age ranging from the latest Floian to the earliest Darriwilian, consistent with prior understanding of this formation.