Kimberella from the Terminal Ediacaran Shibantan Limestone, South China: The Persistence of Bilaterians During the White Sea-Nama Transition

Kimberella is an important taxon of the Ediacara biota (~575–539 million years ago), because it is one of the few with a widely accepted affinity with the Metazoa and even the Bilateria. However, this genus has a very limited temporal and spatial distribution, with previously known occurrences mainly from siliciclastic rocks in the White Sea assemblage (~560–550 Ma) from Russia and South Australia. Here we report a complete Kimberella specimen and a possibly related resting trace from limestone of the terminal Ediacaran Shibantan Member (ca. 550–543 Ma), Dengying Formation, in the Yangtze Gorges area of South China. The new fossils represent the youngest known occurrence of Kimberella, and the first record of this genus from carbonate rocks, expanding its known spatial and environmental distributions. Integrated with previous records of Dickinsonia and complex trace fossils, the discovery of Kimberella in the Shibantan Member identifies this biota as a crucial transition between the White Sea and Nama assemblages. The co-occurrence of Ediacaran soft-bodied bilateralomorphs and complex trace fossils in the Shibantan biota offers an opportunity to test the biotic replacement hypothesis to account for the decline of the White Sea assemblage. Consequently, the Shibantan biota and its host stratigraphic units offer biostratigraphic and chemostratigraphic potential for the subdivision of the Ediacaran System.