THREE-DIMENSIONAL FRONDS FROM THE EDIACARAN OF SOUTH AUSTRALIA

Exquisitely preserved three-dimensional examples of the classic Ediacaran (late Neoproterozoic; 575-543 Ma) frond Charniodiscus are herein reported from the Ediacara Member, Rawnsley Quartzite of South Australia, and allow for a detailed reinterpretation of its functional morphology, taxonomy, and evolutionary relationships. New specimens of Charniodiscus cast within sandy event beds (Nama-style preservation) showcase detailed branching morphology which highlights possible internal features never-before seen, and which are strikingly different from other Ediacaran fronds which display similar modes of preservation. Combined with dozens of well-preserved two-dimensional impressions from the Flinders Ranges of South Australia, morphological variations within the traditional Charniodiscus morphotype are interpreted as representing various stages of external moulding and rare examples of composite moulding of internal features consisting of structural supports or anchoring sites for feeding structures. Each primary branch consists of several, tear-drop-shaped secondary branches lying perpendicular to the primary branching and which are thought to correspond with similar structures occasionally accentuating well-preserved albeit flattened specimens of Charniodiscus. These secondary branches appear to be contained within pea-pod-like sheets which results in typically poor preservation of secondary structures in many specimens of Charniodiscus. In light of this new evidence, previous synonymies within this frond group appear to no longer be justified, and suggests that the taxonomy of the group be revised.