Relating Ediacaran Fronds

Abstract

Ediacaran fronds are key components of terminal-Proterozoic ecosystems. They represent one of the most widespread and common body forms ranging across all major Ediacaran fossil localities and time slices postdating the Gaskiers glaciation, but uncertainty over their phylogenetic affinities has led to uncertainty over issues of homology and functional morphology between, and within, organisms displaying this ecomorphology. Here we present the first large scale, multi-group cladistic analysis of Ediacaran organisms, sampling 20 ingroup taxa with previously asserted affinities to the Arboreomorpha, Erniettomorpha and Rangeomorpha. Using a newly derived morphological character matrix that incorporates multiple axes of potential phylogenetically informative data, including architectural, developmental, and structural qualities, we seek to illuminate the evolutionary history of these organisms. We find strong support for existing classification schema and devise apomorphy-based definitions for each of the three frondose clades examined here. Through a rigorous cladistics framework it is possible to discern the pattern of evolution within, and between, these clades, including the identification of homoplasies and functional constraints. This work both validates earlier studies of Ediacaran groups and accentuates instances where previous assumptions of their natural history are uninformative.

Cambrian petalonamid Stromatoveris phylogenetically links Ediacaran biota to later animals

“…These genera were selected because they represent intersecting sets of taxa previously suggested to fall within a single Ediacaran clade (Pflug ; Seilacher ; Jenkins & Nedin ; Dececchi et al . ), cover a broad range of previously suggested Ediacaran groups and recovered clades (e.g. all named clades identified in the phylogenetic analysis of Dececchi et al .…”

“…Age ranges for clades based, first, on only fossil genera included in this phylogenetic study and, additionally, on incorporated clade membership information from a previous phylogenetic analysis of Ediacaran species (Dececchi et al . ). The maximum range estimate, based on published radiometric dates and all available phylogenetic information, is shown in bold .…”

“…The Ediacaran ingroup genera were Rangea (the type genus for the rangeomorphs; Dececchi et al . ; Sharp et al . ), Pteridinium , Ernietta , Swartpuntia , Arborea (using the specimen classifications of the South Australian Museum which incorporate some specimens previously classified as Charniodiscus ; Laflamme et al .…”

“…all named clades identified in the phylogenetic analysis of Dececchi et al . (): Rangeomorpha, Arboreomorpha and Erniettomorpha) and are represented by accessioned fossil specimens with excellent preservation (including three‐dimensional anatomy), facilitating morphological character analysis alongside Stromatoveris .…”

“…) within Petalonamae and Metazoa) and a previous, complementary phylogenetic analysis of Ediacaran species (Dececchi et al . ) (which places the oldest known rangeomorph genera Charnia and Trepassia (Narbonne & Gehling ) in a sub‐clade, ‘Rangeomorpha’ with Rangea ).…”