Search

An iconic member of the Ediacara Biota, Dickinsonia Sprigg is one of few such taxa with multiple species. Here we use Gaussian finite mixture models to assess the validity of species distinctions for this genus. Our results indicate that the five described species of Dickinsonia from the Ediacara Member, South Australia are better classified as two based on multiple approaches. Two different methods for dimension reduction both provide strong support for two groups, with overlapping but distinct mixture models. The variable selection method produces the most biologically realistic clusters, indicating that the two species can be primarily differentiated based on the greater relative size of the anterior most unit of Dickinsonia costata Sprigg compared with Dickinsonia tenuis Glaessner & Wade. Despite differences in aspect ratio and number of modules, both species regulated growth to maintain overall shape. The greater likelihood of preservation of a midline and an irregular outer margin in D. tenuis highlights differential structural integrity and flexibility. Co-occurrence in the Ediacara Member indicates that both species occupied the same environments and temporal distribution. Smaller maximum and average size for D. costata, combined with higher abundance, may suggest a comparatively shorter lifespan and increased rates of reproduction. [ABSTRACT FROM AUTHOR]

The oldest evidence of motile complex benthic multicellular organisms is found in Ediacaran aged rocks. At Nilpena Ediacara National Park (NENP), South Australia, one of the most iconic of such organisms, Dickinsonia, are found in abundance, with over 500 individuals preserved across the site's 33 in situ, fossiliferous beds. These beds vary in mat type and maturity, community diversity and population size. Here, we investigate six beds using spatial point pattern analysis (SPPA) to compare Dickinsonia spatial distributions between populations. Five populations were best-fit to a completely spatially random pattern, with a single outlier (TC-MM3) exhibiting signs of environmental heterogeneity. When distributions were examined in relation to other taxa, no indication of spatial competition was detected. Univariate and bivariate spatial distributions imply that Dickinsonia was generally not impacted by competition with other taxa, meter-scale environmental heterogeneity, or other external factors. These patterns hold when analyses were split between populations of large and small individuals, and these two size cohorts had no measurable effect on each other's spatial distributions. Additionally, we find no indication of intraspecific competition for Dickinsonia or any change in the preferred resources or habitats with growth. These results suggest that the anactualistic environmental conditions produced by ubiquitous organic mats present across Ediacaran seafloors at NENP provided such abundant nutrients that Dickinsonia did not have to compete for resources at the meter scale. These results further inform community-scale dynamics of Earth's earliest complex ecosystem. • Dickinsonia • Abundant resources in the Ediacaran promoted random and independent distributions. • Ongoing research at Nilpena Ediacara National Park, South Australia. • Applied spatial point pattern analysis. • Motile organisms' interactions with Ediacaran ecosystems. [ABSTRACT FROM AUTHOR]

Analysis of modern animals and Ediacaran trace fossils predicts that the oldest bilaterians were simple and small. Such organisms would be difficult to recognize in the fossil record, but should have been part of the Ediacara Biota, the earliest preserved macroscopic, complex animal communities. Here, we describe Ikaria wariootia gen. et sp. nov. from the Ediacara Member, South Australia, a small, simple organism with anterior/posterior differentiation. We find that the size and morphology of Ikaria match predictions for the progenitor of the trace fossil Helminthoidichnites—indicative of mobility and sediment displacement. In the Ediacara Member, Helminthoidichnites occurs stratigraphically below classic Ediacara body fossils. Together, these suggest that Ikaria represents one of the oldest total group bilaterians identified from South Australia, with little deviation from the characters predicted for their last common ancestor. Further, these trace fossils persist into the Phanerozoic, providing a critical link between Ediacaran and Cambrian animals. [ABSTRACT FROM AUTHOR]

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 life. Preservation of abundant specimens from the Ediacara Member (Rawnsley Quartzite), South Australia, in a variety of taphonomic states allows the unparalleled opportunity to compare the biomechanical responses of Dickinsonia tissue 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, and capable of elastic and plastic deformation. 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 complete tearing suggests that Dickinsonia was composed of relatively thick tissues, signifying higher oxygen requirements than previously hypothesized. The ability to be transported and still be preserved as 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. [ABSTRACT FROM AUTHOR]

Mobility represents a key innovation in the evolution of complex animal life. The ability to move allows for the exploration of new food sources, escapes from unfavorable environmental conditions, enhanced ability to exchange genetic material, and is one of the major reasons for the diversity and success of animal life today. The oldest widely accepted trace fossils of animal mobility are found in Ediacaran‐aged rocks (635–539 Ma). The earliest definitive evidence for movement associated with exploitation of resources for feeding occurs in the White Sea assemblage of the Ediacara Biota—macroscopic, soft‐bodied fossils of Ediacaran age. Here, we evaluate potential support for mobility in dickinsoniomorphs, presenting new data regarding abundant Dickinsonia and associated trace fossils from the Ediacara Member, South Australia. Results quantitatively demonstrate that Dickinsonia was capable of mobility on relatively short, ecological timescales. This organism was bilaterally symmetrical, likely moved via muscular peristalsis, and left trace fossils due to active removal of the organic mat related to feeding. Analogous structures associated with Yorgia indicate that it was also mobile and fed in a similar manner. Morphological evidence suggests that two other modular taxa, Andiva and Spriggina, were able to move but did not feed in a manner that impacted the organic mat. Together, these data suggest that mobility was present in multiple disparate bilaterally symmetrical Ediacaran taxa. [ABSTRACT FROM AUTHOR]

Dickinsonia , an iconic member of the Ediacara biota, is abundant in the Ediacaran deposits found at the Nilpena field site, South Australia. Despite exquisite fossil preservation at this site, many specimens of Dickinsonia appear to be incomplete, with an apparently “missing piece” on the periphery. Orientation measurements from specimens on three fossil beds suggest that these so-called “missing pieces” are aligned irrespective of the axial orientation of Dickinsonia . The nonrandom orientation of incomplete specimens matches that of other aligned structures found on two of these beds. The preferred directionality of this feature suggests the molding of incomplete specimens under the influence of current activity prior to or during burial. We propose that this feature originates where part of a Dickinsonia was lifted off of the substrate during a storm event and that sand was deposited beneath this lifted portion. This model suggests that Dickinsonia was easily separated from the sea floor and was not attached to the substrate on which it lived. This is consistent with the data from Dickinsonia footprints suggesting that Dickinsonia was mobile. [ABSTRACT FROM AUTHOR]

• Primary producers are commonly not included in studies of the Ediacara Biota. • Here we describe new taxa that are most likely benthic macroalgae from the Ediacaran of South Australia. • Specimens consist of bundled filaments. • These taxa are similar to those described from China. The Ediacara biota records the rise of morphologically complex macroscopic eukaryotes, including animals and other heterotrophs. Eltonian ecology demands that Ediacaran ecosystems must have been supported by primary producers (e.g., cyanobacteria, phytoplanktonic eukaryotes, benthic macroalgae). But the fossil record of Ediacaran primary producers has not been fully documented, particularly with respect to benthic macroalgae, hampering a complete understanding of Ediacaran ecosystems. Here we provide systematic description of probable benthic macroalgal fossils from the Ediacara Member of the Rawnsley Quartzite at the National Heritage site Nilpena in South Australia. These fossils include Flabellophyton stupendum sp. nov., F. typicum , Liulingitaenia irregularis sp. nov., and Longifuniculum cf. dissolutum. Previously informally referred to as Bundles of Filaments (BOF), they are characterized by bundled filaments that can be twisted, loosened, or otherwise deformed. Although many are fragmented, some specimens of Flabellophyton stupendum sp. nov., F. typicum , and possibly Longifuniculum cf. dissolutum bear structures that resemble variants of Pseudorhizostomites and "mop", but interpreted here as holdfasts, suggesting that in life these were epibenthic organisms attached to the substrate. Atypical populations of relatively small Ediacara-type fossils are found on a bedding surface dominated by benthic macroalgae, suggesting that, together with microbial mats, these primary producers were beneficial for juvenile settlement of Ediacara-type organisms, potentially contributing both oxygen and nutrients. Although debates about animal affinity dominate Ediacaran paleontology, this study highlights the importance of benthic macroalgae in Ediacaran ecosystems. [ABSTRACT FROM AUTHOR]