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The sharing of ecospace with organisms of the same or different species is one of the most fundamental properties of life. The excavation and conservation of nearly 40 bedding plans covered with in situ Ediacaran fossils at Nilpena Ediacara National Park in South Australia, allows for the application of spatial ecological techniques typically used on modern ecosystems to test hypotheses about spatial properties of Earth’s oldest animal communities. Using a combination of photogrammetry and spatial point pattern analysis, the spatial relationships of the sessile taxa Aspidella, Obamus, and Tribrachidium in the context of body size and abundance is presented here. Two Aspidella dominated beds, a Tribrachidium dominated bed and one Obamus populated bed from two of the four fossiliferous facies at Nilpena were examined for this study. Results reveal that Aspidella and Obamus are distributed into segregated clusters, while Tribrachidium are more spatially homogenous. The Aspidella clusters are heavily influenced by the taxon’s dominance on the beds and by environmental factors (surrounding taxa, taphonomy, etc.). Additionally, sized-based analysis reveals the potential for intraspecific competition amongst the Aspidella, while also fortifying a continuous reproduction hypothesis. Obamus show “hyper aggregation,” which is potentially a result of dispersal limitation. Finally, Tribrachidium spatial results support a seasonal reproductive method and passive suspension feeding strategy.

Tribrachidium is a monospecific genus of the Ediacara biota that is found globally. In the Flinders Ranges of South Australia, the spatial distribution of Tribrachidium across the seafloor is best described as patchy. Although Tribrachidium is the dominant fossil on two of the twenty-six beds currently excavated and is present in large numbers on another, the genus most commonly occurs as no more than a handful of specimens on a bed. Tribrachidium size frequency distributions of each of the three beds with more than 5 specimens are all statistically distinguishable from one another. Additionally, the size range on any given bed is smaller than the overall size range observed for the genus. These patterns suggest that these organisms lived in populations composed of cohorts. The beds with numerous Tribrachidium come from different facies and are characterized by the presence of dissimilar mixes of taxa and textured organic surfaces, indicating that Tribrachidium was a generalist, able to adapt to a variety environments. Uniquely, the base or internal structure of Tribrachidium is also found preserved in both positive and negative relief as a sequence of concentric ridges on beds where Tribrachidium is the dominant genus. The most parsimonious explanation for the presence of these concentric ridge fossils is that they are the fossilized form of a Tribrachidium preserved when the organism was buried upside-down, flipped over, or partially decayed prior to burial.

There are multiple tri-radially symmetric taxa among the Ediacara Biota, but the tri-radial body plan is unique to this time; taxa with threefold symmetry go extinct by the beginning of the Cambria...

Computational fluid dynamics demonstrates that the Precambrian organism Tribrachidium was likely a passive suspension feeder., The first diverse and morphologically complex macroscopic communities appear in the late Ediacaran period, 575 to 541 million years ago (Ma). The enigmatic organisms that make up these communities are thought to have formed simple ecosystems characterized by a narrow range of feeding modes, with most restricted to the passive absorption of organic particles (osmotrophy). We test between competing feeding models for the iconic Ediacaran organism Tribrachidium heraldicum using computational fluid dynamics. We show that the external morphology of Tribrachidium passively directs water flow toward the apex of the organism and generates low-velocity eddies above apical “pits.” These patterns of fluid flow are inconsistent with osmotrophy and instead support the interpretation of Tribrachidium as a passive suspension feeder. This finding provides the oldest empirical evidence for suspension feeding at 555 to 550 Ma, ~10 million years before the Cambrian explosion, and demonstrates that Ediacaran organisms formed more complex ecosystems in the latest Precambrian, involving a larger number of ecological guilds, than currently appreciated.

Coutts, F.J., Gehling, J.G. & Garcia-Bellido, D.C., August 2016. How diverse were early animal communities? An example from Ediacara Conservation Park, Flinders Ranges, South Australia. Alcheringa 40, xxx–xxx. ISSN 0311-5518Fossils of the Ediacara biota record the earliest evidence of animal communities and, as such, provide an invaluable glimpse into the abiotic and biotic processes that helped shape the evolution of complex life on Earth. A diverse community of Ediacaran macro-organisms is preserved with high resolution in a fossil bed recently excavated from north Ediacara Conservation Park (NECP) in the Flinders Ranges, South Australia. Many of the commonly described Ediacaran taxa from the Flinders Ranges are represented on the bed surface and include: Parvancorina, Rugoconites, Spriggina, Dickinsonia, Tribrachidium, Kimberella, Charniodiscus and Yorgia, including two new taxa. Numerous additional fossil-bed fragments from the same locality were analysed that preserve a similar suite of taxa and shar...

Tribrachidium is a monospecific genus of the Ediacara biota found globally. In the Ediacara Member of the Rawnsley Quartzite, Flinders Ranges of South Australia, the spatial distribution of Tribrachidium across the seafloor is best described as patchy. Although Tribrachidium is the dominant fossil on two of the twenty-six beds currently excavated and is present in large numbers on another, the genus most commonly occurs as no more than a handful of specimens on a bed. Tribrachidium size frequency distributions of each of the three beds with more than 5 specimens are all statistically distinguishable from one another. Additionally, the size range on any given bed is smaller than the overall size range observed for the genus. These patterns suggest that these organisms lived in populations composed of single generations. The beds with numerous Tribrachidium come from different facies and are characterized by the presence of dissimilar mixes of taxa and textured organic surfaces, indicating that Tribrachidium was a generalist, able to adapt to a variety environments. Uniquely, the base or internal structure of Tribrachidium is also found preserved in both positive and negative relief as a sequence of concentric ridges on beds where Tribrachidium is the dominant genus. The most parsimonious explanation for the presence of these concentric ridge fossils is that they are the fossilized form of a Tribrachidium preserved when the organism was buried upside-down, flipped over, or dead and partially decayed prior to burial.

We describe traces of macroorganisms in association with the body imprints of trace-producers from Ediacaran (Vendian) deposits of the southeastern White Sea region. They are interpreted as traces of locomotion and are not directly related to a food gathering. The complex remains belong to three species: Kimberella quadrata, Dickinsonia cf. menneri, and Tribrachidium heraldicum. They were found in three different burials. The traces have the form of narrow ridges or wide bands (grooves and linear depressions on natural imprints). In elongated Kimberella and Dickinsonia, the traces are stretched parallel to the longitudinal axis of the body and extend from its posterior end. In the case of the isometric Tribrachidium, the trace is directed away from the margin of the shield. A short length of the traces indicates that they were left by the organisms that were covered with the sediment just before their death. The traces overlaid the microbial mat with no clear signs of deformation under or around the traces. A trace substance, apparently, differed from the material of the bearing layers (i.e., a fine-grained sandstone or siltstone) and was not preserved on the imprints. This suggests that the traces were made with organic material, probably mucus, which was secreted by animals in a stressful situation. The mucus traced the movements of the organism before death. The discovered traces of locomotion are direct evidence of the ability of some Ediacaran macroorganisms to move independently.

Ediacara fossil surfaces from the Flinders Ranges (South Australia) commonly record excellent preservation quality and can provide a palaeoecological window into some of the oldest communities on Earth (ca. 555 Ma). An excavated semi-contiguous sandstone bed of 6.5 m2 from a fossil locality at Crisp Gorge in the central Flinders Ranges records an abundance of taxa and structures characteristic of White Sea assemblage communities. Stratigraphic analysis places the fossil surface within the Oscillation Rippled Sandstone Facies of the Ediacara Member at Crisp Gorge. The community appears to be predominantly juvenile forms, with Dickinsonia costata, Parvancorina minchami and Tribrachidium heraldicum present only within interpreted juvenile size ranges. The textured organic surface contains structures including low relief ridges and round bosses, but overall records a smooth bed surface and is interpreted as representing a surface with only an immature microbial mat developed before burial. No effaced or decayed organisms were identified. Community analysis describes an intermediate Shannon diversity (1.27) and an uneven community dominated by the population of D. costata, which comprises more than 50% of the individuals. The examined parameters, when combined with the presence of small, juvenile taxa and an immature organic mat, suggests that the community inhabiting this surface prior to its catastrophic burial may have been comparable to a modern early-stage, primary successional community. The Crisp Gorge bed emphasizes that Ediacara fossil surfaces from South Australia span a range of developmental stages and offer a window into Ediacaran sea-floor communities at various stages of maturity. Refereed/Peer-reviewed

A new interpretation of fossilized soils (palaeosols) suggests that at least some Ediacaran (625–542 million years ago) organisms lived on land; thus these Ediacaran fossils were not animals, but a fungus-dominated terrestrial biota that predated vascular plants by about 100 million years. Ediacaran fossils —542 to 635 million years old — occur worldwide in a variety of sedimentary deposits, generally interpreted as shallow to deep marine origin. They have been regarded as early animal ancestors of the Cambrian evolutionary explosion of marine invertebrate phyla, as giant marine protists and as lichenized fungi. Here, Gregory Retallack raises doubts over the assumption that Ediacaran organisms were marine: a new interpretation of fossilized soils ('palaeosols') from South Australia suggests that at least some lived on land. Retallack's suggestion that some Ediacaran fossils were large sessile organisms of cool, dry soils is compatible with observations that Ediacaran fossils are similar in appearance and preservation to lichens and other microbial colonies of biological soil crusts, rather than marine animals or protists. Ediacaran (635–542 million years ago) fossils have been regarded as early animal ancestors of the Cambrian evolutionary explosion of marine invertebrate phyla1, as giant marine protists2 and as lichenized fungi3. Recent documentation of palaeosols in the Ediacara Member of the Rawnsley Quartzite of South Australia4 confirms past interpretations of lagoonal–aeolian deposition based on synsedimentary ferruginization and loessic texture5,6. Further evidence for palaeosols comes from non-marine facies, dilation cracks, soil nodules, sand crystals, stable isotopic data and mass balance geochemistry4. Here I show that the uppermost surfaces of the palaeosols have a variety of fossils in growth position, including Charniodiscus, Dickinsonia, Hallidaya, Parvancorina, Phyllozoon, Praecambridium, Rugoconites, Tribrachidium and ‘old-elephant skin’ (ichnogenus Rivularites7). These fossils were preserved as ferruginous impressions, like plant fossils8, and biological soil crusts9,10 of Phanerozoic eon sandy palaeosols. Sand crystals after gypsum11 and nodules of carbonate12 are shallow within the palaeosols4, even after correcting for burial compaction13. Periglacial involutions and modest geochemical differentiation of the palaeosols are evidence of a dry, cold temperate Ediacaran palaeoclimate in South Australia4. This new interpretation of some Ediacaran fossils as large sessile organisms of cool, dry soils, is compatible with observations that Ediacaran fossils were similar in appearance and preservation to lichens and other microbial colonies of biological soil crusts3, rather than marine animals1, or protists2.

In Wonderful Life, Stephen Jay Gould (1989) argued that the morphological range of arthropods recovered from the Middle Cambrian Burgess Shale fauna in British Columbia demonstrated that morphologic diversity increased more rapidly than taxonomic diversity. As was so often the case with Steve, he was directly challenging what he viewed as the unjustified assumptions of traditional evolutionary theory. Gould’s claim initially generated considerable controversy (Briggs et al. 1992), but Wonderful Life triggered the development of rigorous empirical approaches to quantifying what subsequently became known as morphological disparity. The past 18 years of disparity studies have confirmed that Gould was substantially correct: most clades, particularly from the Paleozoic, display patterns of maximal early disparity relative to taxonomic diversity (Foote 1997; Erwin 2007). Until recently, no one had examined disparity before the onset of the Cambrian diversification some 530Ma. In particular, no one had tried to quantify the morphological disparity of the enigmatic organisms of the Ediacaran Fauna (575–542Ma). However, thanks to a recent paper by Shen et al. (2008) we now know that this earliest assemblage of animals followed the same pattern of an early increase in morphologic disparity uncoupled from taxonomic diversity. Several years ago Waggoner (2003) recognized three discrete Ediacaran assemblages, being, in temporal sequence: a low-diversity Avalonian assemblage, a geographically widespread and high-diversity White Sea assemblage, and a lower diversity Nama assemblage. These three assemblages were originally thought to represent early, middle and late evolutionary phases of the Ediacaran interval. However, it now appears that although the three assemblages do indeed differ in mean age, the earliest, Avalonian elements may have persisted through much of the interval. Shen and his colleagues examined both the taxonomic diversity and morphologic disparity of these three assemblages. They assessed 50 different morphologic characters from some 270 species occurrences at about 30 different localities around the world. They used rarefaction analysis to standardize for differences in sampling, and constructed a morphospace with nonparametric multidimensional scaling. Despite considerable turnover in the genera present between the three assemblages, each assemblage occupied substantially the same region of morphospace. In other words, as with Cambrian arthropods and many other groups, the earliest, Avalonian Ediacaran assemblage established a morphospace that persisted for over 30 million years despite a more than 4-fold increase in taxonomic diversity. The disparity analysis of Shen and colleagues carefully avoids the controversial issue of the phylogenetic affinities of the Ediacaran organisms. Are they a single clade? Do they represent early elements of otherwise familiar groups such as arthropods (Parvancorina, Yorgia), annelids (Dickinsonia), mollusks (Kimberella), echinoderms (Tribrachidium), and cnidarians (the various frond-like forms)? Or are they multicellular forms unrelated to metazoa? Are they, perhaps, even related to lichens or to protozoa? All of these suggestions (and more!) have been made in the past two decades. The variety of perspectives reflects both the wide range of morphologies, including bilateral forms reminiscent of true Bilateria, and the lack of appendages, eyes, mouthparts, and many other useful phylogenetic characters. Perhaps the most intriguing new perspective on the Ediacara fauna comes not from the fossils themselves but from new studies of the development of living cnidarians. The recently sequenced Nematostella genome (Putnam et al. 2007) has confirmed earlier work suggesting that the cnidarian genome is more complex than expected, with gene numbers, structure and organization quite similar to vertebrates but unlike the protostome bilaterians (flies and nematodes). Whether cnidarians were primitively radially or bilaterally symmetrical has been the subject of debate for decades, but evidence that Hox, Dpp, Wnt, and Hh are involved in patterning the primary oral–aboral and secondary axes adds weight to the hypothesis of bilateral symmetry (Ryan and Baxevanis 2007; Matus et al. 2008). Indeed, cnidarians possess a host of genes whose bilaterial toolkit function is axial patterning or mesoderm formation (Harding et al. 2005). EVOLUTION & DEVELOPMENT 10:3, 263 –264 (2008)

The classification advanced herein provides a framework to which any organism can be readily placed and offers comprehensive coverage of the entire biological spectrum. The viruses are incorporated as a kingdom of organisms and a rationale advanced for a 6-kingdom system. Many seldom-classified fossil organisms are included, with a significant number of them classified at an advanced level. Individual phyla are recognized for the fossil genera Tribrachidium, Amiskwia, Dinomischus, Anomalocaris, Tullimonstrum, Hallucigenia, Opabinia and Pikaia. Other seldom-recognized phyla include viruses, conularids, loriciferans, tentaculites, hyoliths, scleritophores, myzostomans, acorn worms, conodonts, monoblastozoans and volborthellids. The notion that failures (geologically) cannot be phyla is rejected. A system of kingdom-related and rank-related suffixes is incorporated with the flexible opportunity, if deemed necessary, to advance or reduce taxa by re-suffixing. Other features of the complete classification of Anderson (Classification of Organisms: Living and Fossil, Golden Crowns Press, Lancaster, OH, 1992) include the elimination of duplicate taxa, incorporation of geologic ranges and number of species for many groups, and extensive usage of common names, which are completely indexed.