NEW OBSERVATIONS OF BRANCHING MACROFOSSILS FROM THE EDIACARAN DENGYING FORMATION IN THE YANGTZE GORGES AREA, SOUTH CHINA

Carbonate-hosted macroscopic Ediacaran fossils provide a unique taphonomic window on the paleobiology and paleoecology of soft-bodied Ediacaran organisms. The Shibantan Member (551–541 Ma) of the Dengying Formation in the Yangtze Gorges area of South China represents such a carbonate-hosted assemblage, and is known to contain several iconic Ediacara-type fossils (Hiemalora, Pteridinium, Rangea, and Charniodiscus), an annulated tubular fossil (Wutubus annularis), as well as a branching macrofossil (Yangtziramulus zhangi). Yangtziramulus zhangi was interpreted as a benthic organism consists of a central axis and biserially arranged tubes, each with two vertical side walls, a floor, a roof, and an open distal end. Here we report new Shibantan fossils similar to or conspecific with Yangtziramulus zhangi. These fossils share with Yangtziramulus zhangi a similar branching system, but some of them bear transverse bars between branches, whereas others show a transition from a dichotomously branching system to a reticulate network. While the branching system in Yangtziramulus zhangi was interpreted as a reflection of tri-layered walls of distally open tubes, the new material suggests that the organisms consist of solid branches (sometimes with connecting bars), rather than open tubes/quilts. The phylogenetic affinities of these fossils remain unconstrained, although they are similar in some respects to encrusting algae, fungi, lichens, and slime molds.