Diverse biomineralizing animals in the terminal Ediacaran Period herald the Cambrian explosion

Abstract

The origin and radiation of biomineralizing metazoans represents an important evolutionary innovation in the history of life. The earliest known skeletal metazoans are dominated by four genera in the terminal Ediacaran Period (ca. 550-539 Ma), followed by the diversification of new and diverse shelly fossils in the early Cambrian Period (ca. 539-510 Ma). Thus, terminal Ediacaran skeletal fossils and early Cambrian shelly fossils are commonly regarded as two distinct assemblages, with little overlap in stratigraphic distribution and taxonomic composition, implying a possible extinction event and a subsequent radiation event at the Ediacaran-Cambrian boundary. However, it has been shown recently that some Ediacaran skeletal taxa may have extended into the early Cambrian, indicating evolutionary continuity between these two assemblages. Here we document an assemblage of diverse skeletal fossils from the terminal Ediacaran Dengying Formation in South China. This assemblage is dominated by terminal Ediacaran taxa such as Cloudina and Sinotubulites, but also contains rare elements that morphologically resemble early Cambrian shelly fossils. This finding suggests that terminal Ediacaran skeletal animals are more diverse than previously thought and further reinforces the evolutionary continuity of biomineralizing animals across the Ediacaran-Cambrian transition.