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Abstract Silicified microfossils are reported from nine stratigraphic sections of the Ediacaran Doushantuo Formation deposited in shelf margin, slope, and basin environments in Hunan Province of South China. These microfossils include sphaeromorphic and acanthomorphic acritarchs (15 genera and 29 species, including three new acanthomorph species,Bullatosphaera?colliformisn. sp.,Eotylotopalla inflatan. sp., andVerrucosphaera?undulatan. sp.), multicellular algae, tubular microfossils, and other problematic forms, representing major fossil groups similar to those from the Doushantuo Formation in more proximal facies (e.g., inner shelf and shelf lagoon). A database of the abundance and occurrences of Doushantuo acanthomorphs is assembled and analyzed using quantitative and data-visualization methods (e.g., rarefaction analysis, non-parametric multidimensional scaling, and network analysis). The results show that, at the genus and species levels, taxonomic richness of Doushantuo acanthomorphs exhibits considerable variation among facies, but this variation is largely due to sampling and taphonomic biases. The results also show that numerous acanthomorph taxa have broad facies distribution, affirming their biostratigraphic value. The analysis confirms that acanthomorphs in the Weng'an biota of shelf margin facies are composed of a mixture of Member II and Member III assemblages of shelf-lagoon facies in the Yangtze Gorges area. The study shows the biostratigraphic potential of acanthomorphs in the establishment of regional biozones using the first appearance datum of widely distributed taxa, highlighting the importance of continuing exploration of under-sampled Doushantuo sections in slope and basinal facies. UUID:http://zoobank.org/6fc92858-4054-4117-8043-1f06cfe77155 

ABSTRACT An increase in atmospheric pO2 has been proposed as a trigger for the Cambrian Explosion at ∼539–514 Ma but the mechanistic linkage remains unclear. To gain insights into marine habitability for the Cambrian Explosion, we analysed excess Ba contents (Baexcess) and isotope compositions (δ138Baexcess) of ∼521-Myr-old metalliferous black shales in South China. The δ138Baexcess values vary within a large range and show a negative logarithmic correlation with Baexcess, suggesting a major (>99%) drawdown of oceanic Ba inventory via barite precipitation. Spatial variations in Baexcess and δ138Baexcess indicate that Ba removal was driven by sulfate availability that was ultimately derived from the upwelling of deep seawaters. Global oceanic oxygenation across the Ediacaran–Cambrian transition may have increased the sulfate reservoir via oxidation of sulfide and concurrently decreased the Ba reservoir by barite precipitation. The removal of both H2S and Ba that are deleterious to animals could have improved marine habitability for early animals. 

Abstract Earth’s magnetic field was in a highly unusual state when macroscopic animals of the Ediacara Fauna diversified and thrived. Any connection between these events is tantalizing but unclear. Here, we present single crystal paleointensity data from 2054 and 591 Ma pyroxenites and gabbros that define a dramatic intensity decline, from a strong Proterozoic field like that of today, to an Ediacaran value 30 times weaker. The latter is the weakest time-averaged value known to date and together with other robust paleointensity estimates indicate that Ediacaran ultra-low field strengths lasted for at least 26 million years. This interval of ultra-weak magnetic fields overlaps temporally with atmospheric and oceanic oxygenation inferred from numerous geochemical proxies. This concurrence raises the question of whether enhanced H ion loss in a reduced magnetic field contributed to the oxygenation, ultimately allowing diversification of macroscopic and mobile animals of the Ediacara Fauna. 

Abstract This work presents a detailed taxonomic study on organic-walled microfossils from the Ediacaran Sete Lagoas Formation (Bambuí Group) at the Barreiro section in the Januária area of the São Francisco basin, Brazil. Seven species are described, includingSiphonophycus robustum(Schopf, 1968),Ghoshia januarensisnew species,Leiosphaeridia crassa(Naumova, 1949),Leiosphaeridia jacutica(Timofeev, 1966),Leiosphaeridia minutissima(Naumova, 1949),Leiosphaeridia tenuissimaEisenack, 1958, and Germinosphaera bispinosaMikhailova, 1986. These taxa are recovered for the first time in the Sete Lagoas Formation. They occur abundantly in the lower portion of the studied section, but onlyGhoshia januarensisis present in the upper part of the studied section, probably due to environmental or taphonomic changes.Leiosphaeridiaspecies, particularlyLeiosphaeridia minutissima, dominate the organic-walled microfossil assemblage. Although most taxa described here have long stratigraphic ranges, they are consistent with a terminal Ediacaran age as inferred from detrital zircon data and tubular fossils (e.g.,CloudinaandCorumbella) from the Sete Lagoas Formation. UUID:http://zoobank.org/7f92b900-0176-4da6-93a3-fd51edb22cbf 

Abstract The Viridiplantae comprise two main clades, the Chlorophyta (including a diverse array of marine and freshwater green algae) and the Streptophyta (consisting of the freshwater charophytes and the land plants). Lineages sister to core Chlorophyta, informally refer to as prasinophytes, form a grade of mainly planktonic green algae. Recently, one of these lineages, Prasinodermophyta, which is previously grouped with prasinophytes, has been identified as the sister lineage to both Chlorophyta and Streptophyta. Resolving the deep relationships among green plants is crucial for understanding the historical impact of green algal diversity on marine ecology and geochemistry, but has been proven difficult given the ancient timing of the diversification events. Through extensive taxon and gene sampling, we conduct large-scale phylogenomic analyses to resolve deep relationships and reveal the Prasinodermophyta as the lineage sister to Chlorophyta, raising questions about the necessity of classifying the Prasinodermophyta as a distinct phylum. We unveil that incomplete lineage sorting is the main cause of discordance regarding the placement of Prasinodermophyta. Molecular dating analyses suggest that crown-group green plants and crown-group Prasinodermophyta date back to the Paleoproterozoic-Mesoproterozoic. Our study establishes a plausible link between oxygen levels in the Paleoproterozoic-Mesoproterozoic and the origin of Viridiplantae. 

Abstract Macrofossils with unambiguous biogenic origin and predating the one-billion-year-old multicellular fossilsBangiomorphaandProterocladusinterpreted as crown-group eukaryotes are quite rare.Horodyskiais one of these few macrofossils, and it extends from the early Mesoproterozoic Era to the terminal Ediacaran Period. The biological interpretation of this enigmatic fossil, however, has been a matter of controversy since its discovery in 1982, largely because there was no evidence for the preservation of organic walls. Here we report new carbonaceous compressions ofHorodyskiafrom the Tonian successions (~950–720 Ma) in North China. The macrofossils herein with bona fide organic walls reinforce the biogenicity ofHorodyskia. Aided by the new material, we reconstructHorodyskiaas a colonial organism composed of a chain of organic-walled vesicles that likely represent multinucleated (coenocytic) cells of early eukaryotes. Two species ofHorodyskiaare differentiated on the basis of vesicle sizes, and their co-existence in the Tonian assemblage provides a link between the Mesoproterozoic (H.moniliformis) and the Ediacaran (H.minor) species. Our study thus provides evidence that eukaryotes have acquired macroscopic size through the combination of coenocytism and colonial multicellularity at least ~1.48 Ga, and highlights an exceptionally long range and morphological stasis of this Proterozoic macrofossils. 

Abstract 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 fossilWutubusand discoidal fossilsAspidellaandHiemalora, the Shibantan biota also bears a moderate diversity of frondose fossils, includingPteridinium,Rangea,Arborea, andCharnia. In this paper, we report two species of the rangeomorph genusCharnia, including the type speciesCharnia masoniFord, 1958 emend. andCharnia gracilisnew species, from the Shibantan biota. Most of the ShibantanCharniaspecimens preserve only the petalodium, with a few bearing the holdfast and stem. Despite overall architectural similarities to otherCharniaspecies, the Shibantan specimens ofCharnia gracilisn. 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.Charniafossils 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. UUID:http://zoobank.org/837216cd-4a4a-4e13-89e2-ee354ba48a4c 

Archaeocyaths are biocalcified sponges largely restricted to the early Cambrian Period. Their perforated cup-shaped body facilitated filter feeding. Many of them were clonal modular animals that formed the earliest metazoan skeletal reefs. In Siberia, archaeocyaths extend from late Age 2 to Age 4 of the early Cambrian, representing an ∼15 m.y. range (ca. 525−510 Ma). Elsewhere, archaeocyaths emerged later than in Siberia and, in places, survived to the middle-late Cambrian. The existing fossil record thus indicates an out-of-Siberia scenario and delayed biomineralization in archaeocyaths relative to many other animals, which acquired biomineralization in the Fortunian Age of the early Cambrian. Here we report two microscopic archaeocyath species—Primocyathus uniseriatus Wang and Xiao, gen. et sp. nov. and Sinocyathus biseriatus Wang and Xiao, gen. et sp. nov.—from the Fortunian Kuanchuanpu Formation (ca. 533 Ma) in South China. Preserved as phosphatized internal molds, they are interpreted to have had a biomineralized, two-walled, perforated, cup-shaped skeleton. They were likely filter feeders, but their solitary habit and millimetric body size indicate that they were unlikely reef framework builders. They substantially extend the stratigraphic range of archaeocyaths, challenge the out-of-Siberia hypothesis, support archaeocyath biomineralization in the beginning of the Cambrian explosion, and imply a Precambrian divergence of sponge classes.