New data for Isoxys of the Balang Fauna (Cambrian Stage 4), South China

摘要

Isoxys Walcott, 1890 is a large bivalved arthropod taxon, commonly occurring in the Cambrian Series 2-3. Here, we report on a new group of Isoxys from the Balang Fauna (Cambrian Stage 4) of Guizhou, South China. It is composed of five species: Isoxys acutangulus (Walcott, 1908), I. auritus (Jiang, 1982), I. jianheensis sp. nov., I. globulus sp. nov., and Isoxys sp. Isoxys first appeared in the Chengjiang Biota (Cambrian Stage 3) located in the shallow-water Yangtze Platform in Yunnan, South China, and ranged to the Guanshan Biota (Cambrian Stage 4) above the Chengjiang Biota. The Balang Fauna of Guizhou Province is located in the transitional slope area of the deeper-water environments and is equivalent to the Guanshan Biota in age. The discovery of Isoxys in the Balang Fauna suggests that the genus, originally present in the shallow platform of Yunnan, migrated eastward to the deeper water shelf of Guizhou during the early Cambrian (Stage 4), becoming suited to a new ecological environment. The Isoxys assemblage of the Balang Fauna not only adds new taxa record for this genus but also provides new information for its palaeoecology, evolution, and geographic distribution.