Trace fossils from the Meishucun section of South China: revisiting ichnotaxonomy, behavioural diversification and ecosystem engineering from a key Ediacaran–Cambrian succession

The Ediacaran–Cambrian transition was a time of profound geobiological revolution and sedimentary change in Earth's history, including arguably the most dramatic evolutionary radiation and a remarkable biotic replacement. The complex feedback between diversification of metazoans and their ecological interactions, especially after the extinction of the latest Ediacaran biota, is still debated. Here, we systematically studied the trace fossil content of the Ediacaran–Cambrian succession from the Meishucun section of South China. A total of 20 ichnogenera comprising 31 ichnospecies have been identified in the succession. The occurrence of Treptichnus pedum in the Lower Phosphate of the Zhongyicun Member reinforces the importance of this ichnotaxon as an indicator of the Ediacaran–Cambrian boundary. Our critical review of the trace fossil record of this key succession shows that increases in ichnodiversity, ichnodisparity, degree of bioturbation, and bioturbation depth were accompanied by increases in modes of life and ecosystem engineering throughout the early Cambrian. The dramatic and stepped increased in ichnodiversity and ichnodisparity in the Ediacaran–Cambrian transition, from simple trace fossil morphologies in the Ediacaran to complex branching in the Fortunian, and finally horizontal looping trails and suspension feeding burrows in Cambrian Stage 2, paralleled the shift from the Cambrian information revolution to the agronomic revolution. The dramatic hike in bioturbation intensity and depth that occurred during Cambrian Stage 2 may have resulted in an increase in bioirrigation levels and was conducive to a further deepening of the redox discontinuity surface.