FORCEFUL RESPONSES: CONSTRAINING THE BIOMECHANICAL PROPERTIES OF DICKINSONIA

Dickinsonia is one of the oldest macroscopic metazoans in the fossil record. Determining the biological characters of this extinct taxon is critical to our understanding of the early evolution of animal life. Preservation of abundant specimens from the Ediacara Member, South Australia, in a variety of taphonomic settings allows the opportunity to compare the biomechanical responses of Dickinsonia to various forces with those typical of modern organisms. Dickinsonia are found as lifted, transported, folded, rolled, ripped, and expanded or contracted individuals, while maintaining diagnostic morphology. This suite of characters indicates that Dickinsonia was composed of material that was flexible, difficult to rip, capable of elastic and plastic deformation and permits a direct calculation of extensibility. While none of these traits are diagnostic of a single biomaterial component, we find many similarities with modern biopolymers, particularly collagen, keratin and elastin. Maintenance of significant relief following tearing suggests that Dickinsonia was composed of relatively thick tissues, signifying higher-oxygen requirements than previously hypothesized. The ability to be transported significant distances and still preserve recognizable fossils is unique amongst the Ediacara Biota and demonstrates that Dickinsonia was a taphonomic elite. Combined with discovery in multiple environmental settings, this indicates that the absence of Dickinsonia represents the likely extinction of this organism prior to the Nama assemblage, possibly due to a decrease in the global availability of oxygen in the latest Ediacaran.