Terminal Ediacaran Burgess Shale-Type Tongshan Biota

Early fossil Lagerstatten provide a unique window into understanding the early evolution of organisms. Widespread Burgess Shale-type preservation with high resolution in the Cambrian has largely improved our knowledge of early organisms, but tracking the origins of these organisms, particularly for metazoans, abruptly stops near the Ediacaran-Cambrian boundary. Ediacaran organisms become the most likely candidates for understanding the origins of Cambrian ones but are largely restricted to Ediacara-type preservation or moldic and cast-type preservation of lower resolution, making the comparison between Cambrian and Ediacaran organisms difficult because of the lack of directly comparable evidence. Here, we present the recently reported terminal Ediacaran Tongshan Biota from the uppermost carbonaceous mudstones and shales of the terminal Ediacaran Dengying Formation in Tongshan, Hubei, China. High-resolution zircon dating by CA-ID-TIMS and stratigraphical correlation constrain the Tongshan Biota to an age between about 551 Ma and 543.74±0.87 Ma, which is time equivalent to the Shibantan Biota and the early phase of the Nama Assemblage of the Ediacara Biota. The Tongshan Biota preserves a diversity of organisms, including algae (i.e., Baculiphyca, Chuaria, Doushantuophyton, possible Gesinella, Longifuniculum, Tawuia, Zhongbaodaophyton, and some new forms), the microbe Beltanielliformis, the putative metazoan Protoconites, the possible foraminifer Palaeopascichnus, the possible ctenophore Eoandromeda, and some new typical Ediacaran frondose organisms. The preservation of these organims with high quality indicates rapid, likely in situ burial in the marine photic zone below the storm wave base, representing an overlooked deep-water biodiversity coeval with the Nama Assemblage. The typical Ediacaran frondose metazoans are recorded for the first time with Burgess Shale-type preservation, not only expanding the Ediacara Biota with this preservation type but also reflecting the rarity of fine-grained deposits in the Ediacaran period. Henceforth, direct morpholoigcal comparison between Cambrian and Ediacaran organisms becomes available, paving the way to understanding the evolutionary transitions across the Ediacaran-Cambrian boundary.