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1. MORPHOLOGY AND PRESERVATION OF GAOJIASHANIA , AN ENIGMATIC TUBULAR FOSSIL FROM THE UPPER EDIACARAN DUNFEE MEMBER, DEEP SPRING FORMATION, NEVADA, USA

   https://doi.org/10.2110/palo.2024.007  

   Rivas, Ashley; Myrow, Paul M; Smith, Emily F; Nelson, Lyle L; Briggs, Derek EG; Tarhan, Lidya G (December 2024, Palaios)

   Abstract The upper Ediacaran stratigraphic record hosts fossil assemblages of Earth’s earliest communities of complex, macroscopic, multicellular life. Tubular fossils are a common and diverse, though frequently undercharacterized, component of many of these assemblages. Gaojiashania cyclus is an enigmatic tubular fossil and candidate index fossil found in upper Ediacaran strata globally and is best known from the Gaojiashan Lagerstätte of South China. Here we describe a recently discovered assemblage of Gaojiashania fossils from the Ediacaran Dunfee Member of the Deep Spring Formation of Nevada, USA. Both body and trace fossil affinities have been proposed for Gaojiashania; we present morphological and biostratinomic evidence for a body fossil affinity for the Dunfee specimens. Additionally, previous studies have highlighted that Ediacaran tubular fossils are characterized by a wide range of preservational modes, including association with pyrite, apatite, or clay minerals and preservation as carbonaceous compressions. Petrographic, SEM, and EDS data indicate that the Dunfee Gaojiashania specimens are preserved as ‘Ediacara-style’ external, internal and composite molds, in siltstone and sandstone with a clay mineral-rich matrix of both aluminosilicates and non-aluminous Mg- and Fe-rich silicate minerals that we interpret as authigenic clays. Authigenic clay-mediated fossilization of unmineralized tissues, including moldic preservation in heterolithic siliciclastic strata, as indicated by the Dunfee Gaojiashania, may be linked to the prevalence of both silica-rich and ferruginous seawater conditions prior to both the radiation of silica-biomineralizing organisms and the rise of ocean and atmospheric oxygen to modern levels. In this light, clay authigenesis may have played a critical role in facilitating multiple modes of Ediacaran and Cambrian exceptional fossilization, thus shaping the stratigraphic distribution of a range of Ediacara macrofossil taxa. 

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2. Deep‐water first occurrences of Ediacara biota prior to the Shuram carbon isotope excursion in the Wernecke Mountains, Yukon, Canada

   https://doi.org/10.1111/gbi.12597  

   Boag, Thomas_H; Busch, James_F; Gooley, Jared_T; Strauss, Justin_V; Sperling, Erik_A (May 2024, Geobiology)

   Abstract Ediacara‐type macrofossils appear as early as ~575 Ma in deep‐water facies of the Drook Formation of the Avalon Peninsula, Newfoundland, and the Nadaleen Formation of Yukon and Northwest Territories, Canada. Our ability to assess whether a deep‐water origination of the Ediacara biota is a genuine reflection of evolutionary succession, an artifact of an incomplete stratigraphic record, or a bathymetrically controlled biotope is limited by a lack of geochronological constraints and detailed shelf‐to‐slope transects of Ediacaran continental margins. The Ediacaran Rackla Group of the Wernecke Mountains, NW Canada, represents an ideal shelf‐to‐slope depositional system to understand the spatiotemporal and environmental context of Ediacara‐type organisms' stratigraphic occurrence. New sedimentological and paleontological data presented herein from the Wernecke Mountains establish a stratigraphic framework relating shelfal strata in the Goz/Corn Creek area to lower slope deposits in the Nadaleen River area. We report new discoveries of numerousAspidellahold‐fast discs, indicative of frondose Ediacara organisms, from deep‐water slope deposits of the Nadaleen Formation stratigraphically below the Shuram carbon isotope excursion (CIE) in the Nadaleen River area. Such fossils are notably absent in coeval shallow‐water strata in the Goz/Corn Creek region despite appropriate facies for potential preservation. The presence of pre‐Shuram CIE Ediacara‐type fossils occurring only in deep‐water facies within a basin that has equivalent well‐preserved shallow‐water facies provides the first stratigraphic paleobiological support for a deep‐water origination of the Ediacara biota. In contrast, new occurrences of Ediacara‐type fossils (including juvenile fronds,Beltanelliformis,Aspidella, annulated tubes, and multiple ichnotaxa) are found above the Shuram CIE in both deep‐ and shallow‐water deposits of the Blueflower Formation. Given existing age constraints on the Shuram CIE, it appears that Ediacaran organisms may have originated in the deeper ocean and lived there for up to ~15 million years before migrating into shelfal environments in the terminal Ediacaran. This indicates unique ecophysiological constraints likely shaped the initial habitat preference and later environmental expansion of the Ediacara biota. 

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3. The Ediacaran frondose fossil Arborea from the Shibantan limestone of South China

   https://doi.org/10.1017/jpa.2020.43  

   Wang, Xiaopeng; Pang, Ke; Chen, Zhe; Wan, Bin; Xiao, Shuhai; Zhou, Chuanming; Yuan, Xunlai (November 2020, Journal of Paleontology)

   Abstract Bituminous limestone of the Ediacaran Shibantan Member of the Dengying Formation (551–539 Ma) in the Yangtze Gorges area contains a rare carbonate-hosted Ediacara-type macrofossil assemblage. This assemblage is dominated by the tubular fossil Wutubus Chen et al., 2014 and discoidal fossils, e.g., Hiemalora Fedonkin, 1982 and Aspidella Billings, 1872, but frondose organisms such as Charnia Ford, 1958, Rangea Gürich, 1929, and Arborea Glaessner and Wade, 1966 are also present. Herein, we report four species of Arborea from the Shibantan assemblage, including the type species Arborea arborea (Glaessner in Glaessner and Daily, 1959) Glaessner and Wade, 1966, Arborea denticulata new species, and two unnamed species, Arborea sp. A and Arborea sp. B. Arborea arborea is the most abundant frond in the Shibantan assemblage. Arborea denticulata n. sp. resembles Arborea arborea in general morphology but differs in its fewer primary branches and lower length/width ratio of primary branches. Arborea sp. A and Arborea sp. B are fronds with a Hiemalora -type basal attachment. Sealing by microbial mats and authigenic cementation may have played an important role in the preservation of Arborea in the Shibantan assemblage. The Shibantan material of Arborea extends the stratigraphic, ecological, and taphonomic ranges of this genus. UUID: http://zoobank.org/554f21da-5f09-4891-9deb-cbc00c41e5f1 

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4. The rangeomorph fossil Charnia from the Ediacaran Shibantan biota in the Yangtze Gorges area, South China

   https://doi.org/10.1017/jpa.2022.97  

   Wu, Chengxi; Pang, Ke; Chen, Zhe; Wang, Xiaopeng; Zhou, Chuanming; Wan, Bin; Yuan, Xunlai; Xiao, Shuhai (December 2022, Journal of Paleontology)

   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 

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5. The trace fossil record of the Nama Group, Namibia: Exploring the terminal Ediacaran roots of the Cambrian explosion

   https://doi.org/https://doi.org/10.1016/j.earscirev.2020.103435  

   Darroch, S.A. (January 2020, Earthscience reviews)

   null (Ed.)

   The Ediacaran–Cambrian transition marks one of the most important geobiological revolutions in Earth History, including multiple waves of evolutionary radiation and successive episodes of apparent mass extinction. Among the proposed drivers of these events (in particular the extinction of the latest Neoproterozoic ‘Ediacara biota’) is the emergence of complex metazoans and their associated behaviors. Many metazoans are thought to have crucial geobiological impacts on both resource availability and the character of the physical environment – ‘ecosystem engineering’ – biological processes best preserved in the geological record as trace fossils. Here, we review this model using the trace fossil record of the Ediacaran to Cambrian Nama Group of southern Namibia, combining previous published accounts with the results of our own field investigations. We produce a revised ichnostratigraphy for the Nama Group that catalogues new forms, eliminates others, and brings the trace fossil record of the Nama into much closer alignment with what is known from other Ediacaran sections worldwide. We provide evidence for a link between sequence stratigraphy, oxygen, and the emergence of more complex bilaterian behaviors. Lastly, we show that observed patterns of extinction and survival over pulses of Ediacaran extinction are hard to ally with any one specific source of ecological stress associated with bioturbation, and thus a biologically-driven extinction of the Ediacara biota, if it occurred, was more likely to have been driven by some combination of these factors, rather than any single one. 

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