A POSSIBLE FRONDOSE EDIACARAN FOSSIL FROM NEOPROTEROZOIC BITUMINOUS LIMESTONE OF THE DENGYING FORMATION: ITS BODY PLAN, LIFESTYLE, AND TAPHONOMY

The paleobiology, paleoecology, and taphonomy of Ediacaran fossils are poorly understood, despite their global distribution in terminal Neoproterozoic siliciclastic successions. We describe a new Ediacaran-like fossil preserved three-dimensionally in bituminous limestone of the Dengying Formation in South China.

BODY CONSTRUCTION: The fossil has a frondose form, defined by several orders of “monopodial” or “pseudomonopodial” branches on the top bedding surface. Some of the branches, however, penetrate the sediment laminae (ca. 1 mm in thickness) to form vertical membranes, and then extend horizontally to form floor membranes that link the vertical membranes. Thus, in cross sections perpendicular to the bedding surface, the fossil consists of a series of U-shaped units, each of which is defined by a floor membrane and two vertical membranes. There are, however, some higher-order branches that don’t reach the floor membrane and form free vertical membranes within the U-shaped units. This Ediacaran body plan can be considered an open quilting construction.

PALEOECOLOGY: The U-shaped units are filled with laminated sediments, suggesting that the Dengying Ediacaran organism may have lived procumbently within the sediments, with its vertical membrances growing upward to catch up with sedimentation. If true, this lifestyle would have important implications for the trophic strategy and tiering structure of this Dengying organism, and perhaps several other frondose Ediacaran taxa.

TAPHONOMY: Like many other Ediacaran fossils, the Dengying population is associated with abundant microbial structures such as elephant skin structures. However, the three-dimensional preservation of Ediacaran fossils in the Dengying Formation is also aided by two additional taphonomic processes: (1) the organic membranes of the Dengying fossil are coated by calcite spars on the inner surface of the U-shaped units; and (2) the Dengying fossil is typically covered by a thin (<0.5 mm) layer of silts. It is possible that a surge of silt sediments might have inundated and killed the Dengying Ediacaran population, and perhaps helped its preservation.