WHO ARE YOU?: INESTIGATING THE PHYLOGENETIC RELATIONSHIPS AMONG BILATERAL EDIACARAN TAXA

The late Ediacaran biota is suspected to contain the roots of many different metazoan lineages based on either molecular dating techniques or the large disparity in early Cambrian forms. While much work has been done trying to link individual taxa to extant clade, with mixed success, little has been done to examine and test the myriad of proposed group affinities and interrelationships seen in the literature using a rigorous phylogenetic framework. Here using a large dataset of species representing broadly bilaterally symmetrical Ediacaran organisms we seek to uncover the evolutionary history of the “bilateromorphs” including establishing well supported, apomorphy based clades as well as testing previous suggested groupings such as the Vendobionta, Bilateromorpha, Proarticulata or Dipleurozoa. As current definitions rely on potential non-homologous features such as anterior to posterior differentiation or the presence of a “headshield- like anterior region” and are the basis for many macroevolutionary models, determining the validity of these groupings is critical. Amongst our findings is a strongly supported subdivision between the Dickinsonia species complex and other bilaterally symmetrical taxa such as Spriggina, Parvancorina or Kimberella which has implications on previous suggestions of the former clade’s affinities. Finally, we use this tree as the basis to map several major traits of evolutionary, such as mobility and growth pattern, to examine previous assertions about the distribution and significance of these features in establishing taxa used here as stem members of extant phyla.