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The terminal Ediacaran Shibantan biota (∼550–543 Ma) from the Dengying Formation in the Yangtze Gorges area of South China represents one of the rare examples of carbonate-hosted Ediacara-type macrofossil assemblages. In addition to the numerically dominant taxa—the non-biomineralizing tubular fossil Wutubus and discoidal fossils Aspidella and Hiemalora, the Shibantan biota also bears a moderate diversity of frondose fossils, including Pteridinium, Rangea, Arborea, and Charnia. In this paper, we report two species of the rangeomorph genus Charnia, including the type species Charnia masoniFord, 1958 emend. and Charnia gracilis new species, from the Shibantan biota. Most of the Shibantan Charnia specimens preserve only the petalodium, with a few bearing the holdfast and stem. Despite overall architectural similarities to other Charnia species, the Shibantan specimens of Charnia gracilis n. sp. are distinct in their relatively straight, slender, and more acutely angled first-order branches. They also show evidence that may support a two-stage growth model and a epibenthic sessile lifestyle. Charnia fossils described herein represent one of the youngest occurrences of this genus and extend its paleogeographic and stratigraphic distributions. Our discovery also highlights the notable diversity of the Shibantan biota, which contains examples of a wide range of Ediacaran morphogroups.

We report new high-resolution laser scanning of the type material for the earliest, complex Ediacaran genera Charnia, Bradgatia, Charniodiscus and Ivesheadia from Charnwood, UK, and compare these with Beothukis mistakensis gen. et sp. nov. and the recently described taxa Charnia wardi, Charnia antecedens and Fractofusus spp. from broadly coeval strata in Newfoundland. We use the laser and other techniques to map the similarities and differences in morphology between these Ediacaran rangeomorphs. Key features are suggested to include the number of growth axes, the number and placement of growth tips, the presence of radiating or subparallel axes for the first- and higher-order branches, the extent of displayed or undisplayed leaf-like \"rangeomorph\" architecture, and the extent of furling of the margins of these leaf-like elements. These features are then used to propose suggested homologies between these taxa, leading to a preliminary phylogenetic hypothesis for the evolution of the Avalonian Ediacara biota.

Ediacaran rangeomorphs were the first substantially macroscopic organisms to appear in the fossil record, but their underlying biology remains problematic. Although demonstrably heterotrophic, their current interpretation as osmotrophic consumers of dissolved organic carbon (DOC) is incompatible with the inertial (high Re) and advective (high Pe) fluid dynamics accompanying macroscopic length scales. The key to resolving rangeomorph feeding and physiology lies in their underlying construction. Taphonomic analysis of three-dimensionally preserved Charnia from the White Sea identifies the presence of large, originally water-filled compartments that served both as a hydrostatic exoskeleton and semi-isolated digestion chambers capable of processing recalcitrant substrates, most likely in conjunction with a resident microbiome. At the same time, the hydrodynamically exposed outer surface of macroscopic rangeomorphs would have dramatically enhanced both gas exchange and food delivery. A bag-like epithelium filled with transiently circulated seawater offers an exceptionally efficient means of constructing a simple, DOC-consuming, multicellular heterotroph. Such a body plan is broadly comparable to that of anthozoan cnidarians, minus such derived features as muscle, tentacles and a centralized mouth. Along with other early bag-like fossils, rangeomorphs can be reliably identified as total-group eumetazoans, potentially colonial stem-group cnidarians.

Ediacaran fronds at Spaniard's Bay on the Avalon Peninsula of Newfoundland exhibit exquisite, three-dimensional preservation with morphological features less than 0.05 mm in width visible on the best preserved specimens. Most of the nearly 100 specimens are juvenile rangeomorphs, an extinct Ediacaran clade that numerically dominated the early evolution of complex multicellular life. Spaniard's Bay rangeomorphs are characterized by cm-scale architectural elements exhibiting self-similar branching over several fractal scales that were used as modules in construction of larger structures. Four taxa of rangeomorph fronds are present – Avalofractus abaculus n. gen. et sp., Beothukis mistakensis Brasier and Antcliffe, Trepassia wardae (Narbonne and Gehling), and Charnia cf. C. masoni Ford. All of these taxa exhibit an alternate array of primary rangeomorph branches that pass off a central stalk or furrow that marks the midline of the petalodium. Avalofractus is remarkably self similar over at least four fractal scales, with each scale represented by double-sided rangeomorph elements that were constrained only at their attachment point with the higher-order branch and thus were free to rotate and pivot relative to other branches. Beothukis is similar in organization, but its primary branches show only one side of a typical rangeomorph element, probably due to longitudinal branch folding, and the position of the individual branches was moderately constrained. Trepassia shows only single-sided branches with both primary and secondary branches emanating from a central stalk or furrow; primary branches were capable of minor pivoting as reflected in bundles of secondary branches. Charnia shows only single-sided primary branches that branch from a zigzag central furrow and that were firmly constrained relative to each. This sequence provides a developmental linkage between Rangea-type and Charnia-type rangeomorphs. Avalonian assemblages show a wide array of rangeomorph constructions, but later Ediacaran assemblages contain a lower diversity of rangeomorphs represented mainly by well-constrained forms.

Impressions of soft-bodied Ediacaran megafossils are common in deep-water slope deposits of the June beds at Sekwi Brook in the Mackenzie Mountains of NW Canada. Two taphonomic assemblages can be recognized. Soles of turbidite beds contain numerous impressions of simple (Aspidella) and tentaculate (Hiemalora, Eoporpita) discs. A specimen of the frond Primocandelabrum is attached to an Aspidella-like holdfast, but most holdfast discs lack any impressions of the leafy fronds to which they were attached, reflecting Fermeuse-style preservation of the basal level of the community. Epifaunal fronds (Beothukis, Charnia, Charniodiscus) and benthic recliners (Fractofusus) were most commonly preserved intrastratally on horizontal parting surfaces within turbidite and contourite beds, reflecting a deep-water example of Nama-style preservation of higher levels in the community. A well-preserved specimen of Namalia significantly extends the known age and environmental range of erniettomorphs into deep-water aphotic settings. Infaunal bilaterian burrows are absent from the June beds despite favorable beds for their preservation. The June beds assemblage is broadly similar in age and environment to deep-water Avalonian assemblages in Newfoundland and England, and like them contains mainly rangeomorph and arboreomorph fossils and apparently lacks dickinsoniomorphs and other clades typical of younger and shallower Ediacaran assemblages. Fossil data presently available imply that the classically deep- and shallow-water taxa of the Ediacara biota had different evolutionary origins and histories, with sessile rangeomorphs and arboreomorphs appearing in deep-water settings approximately 580 million years ago and spreading into shallow-water settings by 555 Ma but dickinsoniomorphs and other iconic clades restricted to shallow-water settings from their first known appearance at 555 Ma until their disappearance prior to the end of the Ediacaran.

Charnia from the Ediacara biota is here examined in terms of its growth and development. The Ediacara biota comes from the critical period of evolution just before the Cambrian Explosion and is key to our understanding of the origin of animal life. We show that Charnia cannot be related to the modern cnidarian group the sea pens (Pennatulacea) with which it has for so long been compared, as generative zones cannot be homologized between these forms.

A new assemblage of frondose and filamentous Ediacaran macrofossils is reported from the upper Drook Formation of Pigeon Cove, Newfoundland. The frondose forms, all less than 3 cm in length, are considered to represent the juvenile growth stages of Ediacaran organisms including Charnia spp. and Trepassia spp. This is the first report of an assemblage wholly dominated by such small juvenile rangeomorph forms, and provides insights into the ontogeny and ecology of these earliest members of the Ediacara biota. The fronds occur alongside filamentous forms with similarities to microbial taxa, and both morphotypes are considered to postdate an assemblage of large ivesheadiomorphs on the same bedding plane. If so, the assemblage represents one of the oldest documented examples of secondary community succession. The new Pigeon Cove fossils also extend the stratigraphic ranges of several key frondose taxa (Charnia masoni, Charniodiscus spp.) back into some of the oldest known macrofossil-bearing strata. These revised ranges lend support to the suggestion that the previously observed low diversity within the Drook Formation may represent a combination of taphonomic and sampling artefacts. Furthermore, this assemblage implies that the diversification of architectural morphotypes within the Ediacara biota took place earlier than hitherto suspected. SUPPLEMENTARY MATERIAL: A document containing figures of additional juvenile rangeomorphs and filamentous specimens, a table of specimen dimensions, and a complete digitized map of the Pigeon Cove bedding plane, is available at www.geolsoc.org.uk/SUP18529.

The siliciclastic succession of the late Neoproterozoic Vendian Group in the White Sea area demonstrates a wide range of lithofacies, some recurring in a vertical succession. Significantly, each lithofacies contains a distinct assemblage of Ediacaran fossils that represents in situ benthic paleocommunities smothered in life position. These lithofacies define (1) a monospecific Inaria assemblage, restricted to the lower-shoreface muds; (2) a Charnia assemblage, within the middle-shoreface graded siltstone-shale couplets; (3) a Dickinsonia-Kimberella assemblage, confined to the interstratified sandstone and shale of prodelta; and (4) a Onegia-Rangea assemblage, preserved within channelized sandstone beds of the distributary-mouth bar. In the White Sea area a strong correlation exists between taxonomic composition, biostratinomic features, and paleoecological context of the Ediacaran fossil assemblages. Facies-controlled distribution is also evident in other Ediacaran localities, demonstrating the recurrence of similar facies relationships on a global scale. This pattern is interpreted as representing Ediacaran biofacies with Avalon-type biotas distributed in deep marine habitats, Ediacara-type biotas inhabiting microbial biofilms in shallow marine prodeltaic settings, and infaunal Nama-type biotas found in distributary-mouth bar shoals. This in turn reveals a marked degree of environmental sensitivity and ecological specialization. Correspondence between depositional environment and taxonomic composition speaks against any obvious biogeographic provinciality of the Ediacaran biotas, and also casts doubt on claims of substantial evolutionary change.

The Mistaken Point and Trepassey formations (Conception and St. John's groups, respectively) comprise a terminal Neoproterozoic, deep-marine succession of fine-grained turbidites and volcanogenic deposits that are part of the Avalonian Terrane. Debris-flow beds, slumped units, the low dispersion of turbidity-current paleoflow directions, and the absence of wave-generated structures together indicate that the sediment was deposited on a deep-water, southeast-facing slope. Channels were not present in the study area. The upward increase in the abundance of slump structures suggests that these units represent toe-of-slope and mid-slope environments, respectively. These units prograded over basin-floor deposits of the Drook and Briscal formations, which have (axial) paleocurrent directions that are orthogonal to the inferred downslope flow that characterized the overlying deposits. Within the Mistaken Point and Trepassey formations, a diverse assemblage of soft-bodied, non-phototrophic Ediacaran organisms is preserved beneath volcanic ash layers on more than one hundred surfaces. Individual fossiliferous surfaces can be correlated up to several kilometres. The felling orientations of frondose fossils indicate that contour currents, as well as up- and downslope currents of tidal and (or) wind-forced origin, influenced the sea floor in the intervals between event beds when the organisms lived. The contour currents may have been responsible for sustaining the organisms in this deep-water setting. The current-produced inclination of the frondose organisms at the time of ash deposition allowed their preservation by preventing the accumulation of ash beneath them.

The siliciclastic succession of the late Neoproterozoic Vendian Group in the White Sea area demonstrates a wide range of lithofacies, some recurring in a vertical succession. Significantly, each lithofacies contains a distinct assemblage of Ediacaran fossils that represents in situ benthic paleocommunities smothered in life position. These lithofacies define (1) a monospecific Inaria assemblage, restricted to the lower-shoreface muds; (2) a Charnia assemblage, within the middle-shoreface graded siltstone-shale couplets; (3) a Dickinsonia-Kimberella assemblage, confined to the interstratified sandstone and shale of prodelta; and (4) a Onegia-Rangea assemblage, preserved within channelized sandstone beds of the distributary-mouth bar. In the White Sea area a strong correlation exists between taxonomic composition, biostratinomic features, and paleoecological context of the Ediacaran fossil assemblages. Facies-controlled distribution is also evident in other Ediacaran localities, demonstrating the recurrence of similar facies relationships on a global scale. This pattern is interpreted as representing Ediacaran biofacies with Avalon-type biotas distributed in deep marine habitats, Ediacara-type biotas inhabiting microbial biofilms in shallow marine prodeltaic settings, and infaunal Nama-type biotas found in distributary-mouth bar shoals. This in turn reveals a marked degree of environmental sensitivity and ecological specialization. Correspondence between depositional environment and taxonomic composition speaks against any obvious biogeographic provinciality of the Ediacaran biotas, and also casts doubt on claims of substantial evolutionary change.