Meeting Abstract
Early animal evolution is recorded in the soft body fossils of the Ediacara Biota but linking many of these taxa to specific clades has proved challenging, leaving large gaps in our understanding of the evolution of complex life. Many attempts to classify Ediacara taxa focused on shoehorning them into modern groupings have proved largely unsuccessful and contentious. Dickinsonia is an abundant member of the Ediacara Biota that has uncertain affinities, with interpretations ranging from annelids to lichen. Here we present analysis of over 900 specimens of Dickinsonia costata from the Flinders ranges and surrounding areas in South Australia to asses where it fits in the early evolution of complex, macroscopic life. Morphological observations demonstrate that D. costata was a bilaterally symmetric, modular organism without evidence for a mouth, anus or gut. Quantitative analysis suggests isometric growth with respect to length and width to maintain a high surface area to volume ratio. Growth was achieved via posterior addition and subsequent expansion of modules in a complex yet surprisingly well-regulated pattern to maintain an ovoid morphology. The suite of morphological characters identified, along with highly regulated, complex growth suggests that Dickinsonia contains some of the features common to bilaterians but not the suite of characters necessary for a bilaterian classification. We propose that this overlap in characters reflects the utilization of gene regulatory networks common to most metazoans and that Dickinsonia represents an extinct clade located between sponges and the last common ancestor of Protostomes and Deuterostomes, and likely belongs within the Eumetazoa.
