Three-dimensional reconstruction of ediacaran ceramiales (Rhodophyta) from the phosphorite doushantuo formation, South China.

The Ediacaran Doushantuo Formation (551-635 Ma) is known to include excellently preserved microfossils that reveal information about early eukaryotic evolution. Here, we report the presence of Vetusceramium sinense gen. et sp. nov., a new multicellular red algal fossil from the Weng'an Phosphorite Member of the Doushantuo Formation, South China. Reconstruction of the fossils using synchrotron X-ray tomography shows that these specimens bear a multilayered uniaxial thallus comprising a large central axial cell, pericentral corticated cell filaments, and possible pit connections, which bear similarity to the branches of modern Ceramiales belonging to Rhodophyta. However, the absence of reproductive features, such as gametangia, prevents crown group classification, suggesting a stem group affinity within the Ceramiales. This evidence suggests the possibility of pushing back the occurrence of Ceramiales-like multicellularity to the late Ediacaran Period, demonstrating sophisticated developmental strategies in early photoautotrophs. This report highlights the importance of phosphatization in uncovering subcellular details and offers key insights into the evolution of red algae before the Cambrian radiation.