USING TAPHONOMY TO UNDERSTAND THE SIGNIFICANCE OF MACROSCOPIC ALGAE IN FOSSIL COMMUNITIES OF THE EDIACARA MEMBER, SOUTH AUSTRALIA

The fossil record of macroscopic algae extends from the Tonian on, but due to the fragile soft bodied nature of algae, their fossils are relatively rare. Fossils of Ediacaran algae occur as carbonaceous compressions in lagerstätten such as the Miaohe Member and Lantian Formation in China, but the Ediacara Member of the Rawnsley Quartzite at Nilpena Ediacara National Park (NENP), South Australia, is one of only a few sites globally that preserves Ediacaran algae as casts and molds. At NENP, fossils of likely green algae are abundant, preserved as bundles of filaments on almost all twenty excavated bedding planes from the shallow water Oscillation Rippled Sandstone facies. While most beds preserve only a handful of these filamentous algae fossils, two beds preserve communities dominated by them with up to 126 specimens on a single bed, thus providing an opportunity to study these fossils through a taphonomic and ecological lens.

An examination of over 250 specimens of macroscopic algae fossils belonging to multiple genera reveals that most individuals are incomplete, preserved only as a thallus that is sometimes differentiated into stipe and fan structures. While a few specimens are preserved whole and attached to a holdfast, individual holdfast structures can also be preserved without an attached thallus. On beds where algae are dominant, many individual filaments are also preserved, implying that these algae disarticulated easily upon death and burial. This, along with the relatively faint preservation of algae compared to the preservation of most metazoan taxa at NENP indicates that these algae were more abundant in Ediacaran communities than is generally recognized. This taphonomic model is used to assess the role of these macroscopic algae in Ediacaran communities by documenting the distribution of the four algal species across different bedding planes, evaluating and comparing the density of algae in individual fossil communities, and testing for any association between algae and metazoan taxa or size classes of taxa. This taphonomic and ecological assessment thus expands our view of the importance and abundance of Ediacaran algae, placing them in the foreground of Ediacaran communities.