A Chengjiang-type fossil assemblage from the Hongjingshao Formation (Cambrian Stage 3) at Chenggong, Kunming, Yunnan

A new Chengjiang-type fossil assemblage is reported herein from the lower part of the Hongjingshao Formation at Xiazhuang village of Chenggong, Kunming, Yunnan. The fossil assemblage, named as Xiazhuang fossil assemblage, yields predominantly soft-bodied fossils, including arthropods, brachiopods, priapulids, lobopods and some problematic taxa, with arthropods being the most dominant group. Preservation and composition of the fossil assemblage are very similar to the typical Chengjiang biota, which is preserved in the middle Yu'anshan Formation in the large area of eastern Yunnan. The associated trilobites demonstrate that the soft-bodied fossil assemblage belongs to the late Qiongzhusian in age (Stage 3, Cambrian), suggesting that the Hongjingshao Formation is probably a diachronous lithostratigraphic unit ranging from the upper Qiongzhusian to the lower Canglangpuan stages in eastern Yunnan. The fossil assemblage from the Xiazhuang area fills up the missing link between the typical older Chengjiang biota and the younger Malong and Guanshan biotas, making eastern Yunnan a unique area in the world to reveal the early evolutionary history of animals and palaeocommunity dynamics during the "Cambrian explosion".