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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'. [ABSTRACT FROM AUTHOR]

The lower Cambrian (Stage 3) Yu'anshan Formation in Yunnan Province, South China hosts the Chengjiang Lagerstätte , an exceptional window on the Cambrian Explosion. However, skeletal microfossils from this formation have long been neglected owing to the dominance of siliciclastics over carbonates. Here we characterize a new assemblage of small shelly fossils from the Maotianshan Shale Member of the Yu'anshan Formation. The assemblage consists of univalved mollusc, hyolith and brachiopod shells, trilobite and bradoriid carapaces, chancelloriid sclerites, sponge spicules, and echinoderm ossicles. Combining this information with taxonomic data previously tabulated for fossil assemblages from three other facies, we performed quantitative comparisons of the genus-level taxonomic diversity and modes of life and nutrition of four mutually equivalent, early Cambrian (Age 3) paleocommunities: (1) skeletal faunas of the inner shelf; (2) predominantly soft-bodied faunas of the intra-shelf basin; (3) archaeocyathan faunas of the carbonate shelf; and (4) sponge-dominated faunas of the slope to basin areas. The taxonomic and paleoecological distinctness of these four paleocommunities indicate possible low levels of competition within the communities and rapid expansion of habitat (ecospace) ranges, though with similarities in the taxonomic composition of poriferans and arthropods reflecting the rapid migration of these two groups into new habitats. The present, integrative study provides a more comprehensive portrait of metazoan diversification and paleocommunity evolution during the peak phase of the Cambrian Explosion than do investigations based on single communities. • New assemblage of skeletal fossils from the Cambrian Stage 3, South China. • The fauna is dominated by hyoliths, chancelloriids, bradoriids and molluscs. • The different paleocommunity compositions and structures are documented. • The paleocommunitites are highly facies-controlled. • The highest biodiversity of the Cambrian Explosion in South China [ABSTRACT FROM AUTHOR]