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, includingAlbumares,Anfesta,Coronacollina,Hallidaya,Rugoconites,SkinneraandTribrachidiumand evaluate the possibility that their shared symmetry unites them phylogenetically. We find that, with the exception ofCoronacollina, 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.