The short-lived but successful tri-radial body plan: a view from the Ediacaran of Australia

There are multiple tri-radially symmetric taxa among the Ediacara Biota, but the tri-radial body plan is unique to this time; taxa with threefold symmetry go extinct by the beginning of the Cambrian. Many of these taxa are included in a morphogroup referred to as Trilobozoa or Triradialomorpha. Abundant specimens of these tri-radial taxa exist at the Nilpena National Heritage Ediacara fossil site and at other sites throughout Australia. Here, we review the occurrence and diversity of tri-radial genera from the Australian Ediacaran, including Albumares, Anfesta, Coronacollina, Hallidaya, Rugoconites, Skinnera and Tribrachidium and evaluate the possibility that their shared symmetry unites them phylogenetically. We find that, with the exception of Coronacollina, these taxa are morphologically similar enough to justify considering them a clade of related organisms. The diversity and abundances of these taxa in South Australia provide a unique venue for research investigating the relationships among these Ediacaran taxa.