EDIACARAN FROND ADAPTATIONS TO FLOW REGIME

The Ediacaran Biota is an enigmatic group of fossils from the latest Precambrian and consists of the oldest known architecturally complex multicellular fossils. Frond shaped-forms, such as Charniodiscus, are widespread with the greatest geographic and ecological range of all the Ediacaran organisms. They range in size from a few centimeters to over a meter in length (Narbonne, 2004, Peterson et al, 2005). These organisms exhibit a leaf shape with a stem and branches, and are attached to the substrate by a holdfast. The branches exhibit evidence of secondary and possible tertiary branches (LaFlamme, 2004). Specimens are strikingly similar in appearance to modern sea pens, but there is no evidence of polyps, which would suggest a direct relationship and feeding habit. The morphology of Charniodiscus has lead to proposed affiliations ranging from ctenophores, to fungal fruiting bodies, to Cnidaria, and even to a possible extinct kingdom Vendobionta (LaFlamme, 2004). However, these associations have been based on morphologic inference alone. Paleobiomechanics allows investigation of how these organisms may have interacted with flow. Whether Ediacaran fronds were filter feeding, chemo- or photosynthetic, or even fruiting bodies, elevation into the water column would put the organisms under significant influence of fluid flow. Through flow tank experiments, forces and stresses on frond morphology have been investigated in order to determine how fluid flows around these organisms. Models of Charniodiscus procerus and C. spinosus from Mistaken Point in Newfoundland were used to quantify how flow interacts with form and orientation to influence stability in soft sediment. Regardless of taxonomic affinity or mode of life, biomechanical studies of the morphology of Charniodiscus can give a deeper understanding of life's earliest adaptations to variations in substrate and flow.