Affirming life aquatic for the Ediacara biota in China and Australia

The Ediacara biota has been long championed as a snapshot of the marine ecosystem on the eve of the Cambrian explosion, providing important insights into the early evolution of animals. Fossiliferous beds in the eponymous Ediacara Member of South Australia have been recently reinterpreted as paleosols and Ediacara fossils as lichens or microbial colonies that lived on terrestrial soils. This reinterpretation, here dubbed the terrestrial Ediacara hypothesis, would fundamentally change our views of biological evolution just prior to the Cambrian explosion. We take a comparative paleobiology approach to test this hypothesis. The Ediacara Member shares a number of forms with assemblages in Ediacaran marine black shales in South China, shales that show no evidence of pedogenesis. Thus, the shared Ediacara fossils, and by extension other co-occurring fossils, are unlikely to have been terrestrial organisms. A terrestrial interpretation is also inconsistent with functional morphological evidence; some of the shared forms are not morphologically adapted to address the most critical challenges for terrestrial life (e.g., mechanical support and desiccation). Thus, the terrestrial Ediacara hypothesis can be falsified on comparative paleobiological and functional morphological grounds, and we urge paleopedologists to critically reevaluate evidence for pedogenesis in the Ediacara Member and other Ediacaran successions.