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Marc Laflamme - One of the best experts on this subject based on the ideXlab platform.
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paleoenvironmental analysis of ernietta bearing Ediacaran deposits in southern namibia
Palaeogeography Palaeoclimatology Palaeoecology, 2020Co-Authors: Katie Maloney, Thomas H. Boag, Simon A.f. Darroch, Rachel A. Racicot, Alison T Cribb, Charlotte G Kenchington, Bryce Koester, Brandt M Gibson, Amanda Facciol, Marc LaflammeAbstract:Abstract Ediacaran fossils from the Nama Group (Kuibis Subgroup) of southern Namibia have a long history of scientific scrutiny, however many of the fossil localities still require investigation from a sedimentary facies and sequence stratigraphic standpoint. Detailed sedimentary analyses utilizing chemostratigraphy and facies-based approaches resulted in five proposed facies and two paleoenvironmental settings that allow for interpretation of the fossiliferous sections as a nearshore to a protected shallow marine paleoenvironment. The classic Ediacaran taxon Ernietta was restricted to the Kliphoek Member of the Nama Group, which limits the stratigraphic range of these organisms to the younger depositional sequence of the Kuibis Subgroup. The paleoenvironment has been interpreted as a mixed carbonate-siliciclastic, protected shallow marine environment at Farm Hansburg, suggesting that these organisms thrived in environments with medium to high flow velocities and periodic clastic sediment supply. Studies that utilize detailed paleoenvironmental reconstructions may aid in constraining phylogenetic affinities of the Ediacara biota by placing reasonable bounds on the local habitat.
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increase in metazoan ecosystem engineering prior to the Ediacaran cambrian boundary in the nama group namibia
Royal Society Open Science, 2019Co-Authors: Thomas H. Boag, Rachel A. Racicot, Alison T Cribb, Charlotte G Kenchington, Bryce Koester, Brandt M Gibson, Helke Mocke, Marc LaflammeAbstract:The disappearance of the soft-bodied Ediacara biota at the Ediacaran–Cambrian boundary potentially represents the earliest mass extinction of complex life, although the precise driver(s) of this ex...
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Ediacaran extinction and cambrian explosion
Trends in Ecology and Evolution, 2018Co-Authors: Simon A.f. Darroch, Emily F Smith, Marc Laflamme, Douglas H. ErwinAbstract:The Ediacaran-Cambrian (E-C) transition marks the most important geobiological revolution of the past billion years, including the Earth's first crisis of macroscopic eukaryotic life, and its most spectacular evolutionary diversification. Here, we describe competing models for late Ediacaran extinction, summarize evidence for these models, and outline key questions which will drive research on this interval. We argue that the paleontological data suggest two pulses of extinction - one at the White Sea-Nama transition, which ushers in a recognizably metazoan fauna (the 'Wormworld'), and a second pulse at the E-C boundary itself. We argue that this latest Ediacaran fauna has more in common with the Cambrian than the earlier Ediacaran, and thus may represent the earliest phase of the Cambrian Explosion.
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lithostratigraphy and sedimentary environment of the precambrian kushk series of central iran
Canadian Journal of Earth Sciences, 2018Co-Authors: Seyed Hamid Vaziri, Marc LaflammeAbstract:The Kushk Series is a distinctive late Ediacaran succession occurring in the Bafq and Behabad regions of central Iran that has yielded an extensive community of diverse Ediacara biota, including se...
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relating Ediacaran fronds
Paleobiology, 2017Co-Authors: Alexander T Dececchi, Carolyn Greentree, Guy M Narbonne, Marc LaflammeAbstract:Ediacaran fronds are key components of terminal-Proterozoic ecosystems. They represent one of the most widespread and common body forms ranging across all major Ediacaran fossil localities and time slices postdating the Gaskiers glaciation, but uncertainty over their phylogenetic affinities has led to uncertainty over issues of homology and functional morphology between and within organisms displaying this ecomorphology. Here we present the first large-scale, multigroup cladistic analysis of Ediacaran organisms, sampling 20 ingroup taxa with previously asserted affinities to the Arboreomorpha, Erniettomorpha, and Rangeomorpha. Using a newly derived morphological character matrix that incorporates multiple axes of potential phylogenetically informative data, including architectural, developmental, and structural qualities, we seek to illuminate the evolutionary history of these organisms. We find strong support for existing classification schema and devise apomorphy-based definitions for each of the three frondose clades examined here. Through a rigorous cladistic framework it is possible to discern the pattern of evolution within and between these clades, including the identification of homoplasies and functional constraints. This work both validates earlier studies of Ediacaran groups and accentuates instances in which previous assumptions of their natural history are uninformative.
Shuhai Xiao - One of the best experts on this subject based on the ideXlab platform.
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sedimentology and chemostratigraphy of the terminal Ediacaran dengying formation at the gaojiashan section south china
Geological Magazine, 2019Co-Authors: Shuhai Xiao, Sara Peek, Rebecca E Plummer, Alan J KaufmanAbstract:The terminal Ediacaran Dengying Formation ( c . 551.1–538.8 Ma) in South China is one of two successions where Ediacara-type macrofossils are preserved in carbonate facies along with skeletal fossils and bilaterian animal traces. Given the remarkable thickness of carbonate-bearing strata deposited in less than 12.3 million years, the Dengying Formation holds the potential for construction of a relatively continuous chemostratigraphic profile for the terminal Ediacaran Period. In this study, a detailed sedimentological and chemostratigraphic (δ 13 C carb , δ 18 O carb , δ 13 C org , δ 34 S pyrite , and 87 Sr/ 86 Sr) investigation was conducted on the Dengying Formation at the Gaojiashan section, Ningqiang County of southern Shaanxi Province, South China. Sedimentological results reveal an overall shallow-marine depositional environment. Carbonate breccia, void-filling botryoidal precipitates and aragonite crystal fans are common in the Algal Dolomite Member of the Dengying Formation, suggesting that peritidal facies were repeatedly karstified. The timing of karstification was likely early, probably soon after the deposition of the dolomite sediments. The presence of authigenic aragonite cements suggests high alkalinity in the terminal Ediacaran ocean. Geochemical analysis of micro-drilled samples shows that distinct compositions are registered in different carbonate phases, which should be considered when constructing chemostratigraphic profiles representative of true temporal variations in seawater chemistry. Integrated chemostratigraphic data suggest enhanced burial of organic carbon and pyrite, and the occurrence of extensive marine anoxia (at least in the Gaojiashan Member). Rapid basinal subsidence and carbonate accumulation during a time of elevated seawater alkalinity and increased rates of pyrite burial may have facilitated the evolutionary innovation of early biomineralizing metazoans.
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diverse biomineralizing animals in the terminal Ediacaran period herald the cambrian explosion
Geology, 2019Co-Authors: Yaoping Cai, Shuhai Xiao, Hong HuaAbstract:The origin and radiation of biomineralizing metazoans represents an important evolutionary innovation in the history of life. The earliest known skeletal metazoans are dominated by four genera in the terminal Ediacaran Period (ca. 550-539 Ma), followed by the diversification of new and diverse shelly fossils in the early Cambrian Period (ca. 539-510 Ma). Thus, terminal Ediacaran skeletal fossils and early Cambrian shelly fossils are commonly regarded as two distinct assemblages, with little overlap in stratigraphic distribution and taxonomic composition, implying a possible extinction event and a subsequent radiation event at the Ediacaran-Cambrian boundary. However, it has been shown recently that some Ediacaran skeletal taxa may have extended into the early Cambrian, indicating evolutionary continuity between these two assemblages. Here we document an assemblage of diverse skeletal fossils from the terminal Ediacaran Dengying Formation in South China. This assemblage is dominated by terminal Ediacaran taxa such as Cloudina and Sinotubulites, but also contains rare elements that morphologically resemble early Cambrian shelly fossils. This finding suggests that terminal Ediacaran skeletal animals are more diverse than previously thought and further reinforces the evolutionary continuity of biomineralizing animals across the Ediacaran-Cambrian transition.
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Ediacaran integrative stratigraphy and timescale of china
Science China-earth Sciences, 2019Co-Authors: Chuanming Zhou, Shuhai Xiao, Xunlai Yuan, Zhe Chen, Hong HuaAbstract:Ediacaran successions occur widely in various depositional facies in South China and yield a series of fossil Lagerstatten, providing a complete fossil record for the evolution of marine ecosystems after the terminal Cryogenian global glaciation. Carbonate-dominated Ediacaran successions in shallow water facies in South China record a nearly complete δ 13C profile that may reflect variations of marine carbon isotopic composition during the Ediacaran Period. The Ediacaran fossils and δ 13C profiles from South China permit stratigraphic correlation and subdivision of the Ediacaran strata. Based on biostratigraphic, chemostratigraphic, and geochronometric data from the Ediacaran successions in South China, we propose that the Ediacaran System in China can be subdivided into two series, with three stages in each series. The lower series is characterized by acanthomorphic acritarchs and the upper series by Ediacara-type macrofossils, and the two series are separated by the declining limb of a pronounced δ 13C negative excursion (EN3) in the upper Doushantuo Formation. The basal boundary of Stage 1 is the same as the basal boundary of Ediacaran System, which has been defined at the base of the cap carbonate unit. Stage 2 represents the first radiation of Ediacaran microscopic organisms, with δ 13C feature representing by positive values (EP1). The base of the Stage 2 is placed at the first appearance level of a spiny acritarch species. Stage 3 is characterized by the occurrence of more diverse acritarchs and δ 13C feature EP2, with its basal boundary defined by a δ 13C negative excursion (EN2) occurring in the middle Doushantuo Formation. The basal boundary of Stage 4 is the same as the upper series. Stage 5 is marked by the occurrence of macrfossils of Miaohe biota, and its lower boundary can be placed at the level where δ 13C values transition from positive to negative in MNE, or the first appearance level of macrofossils of the Miaohe biota. Stage 6 is characterized by the occurrences of Ediacara-type Shibantan biota and Gaojiashan biota, with its lower boundary defined by the first appearance level of Conotubus hemiannulatus . The formal establishment of the aforementioned series and stages requires further and more detailed integrative stratigraphic study on the Ediacaran successions in China. Some of the Ediacaran successions in South China have great potential to become global standards in Ediacaran subdivision.
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stable carbon isotopes of sedimentary kerogens and carbonaceous macrofossils from the Ediacaran miaohe member in south china implications for stratigraphic correlation and sources of sedimentary organic carbon
Precambrian Research, 2017Co-Authors: Shuhai Xiao, Natalia Bykova, Alex Kovalick, Benjamin C GillAbstract:Abstract Ediacaran stratigraphic correlation depends on the integration of paleontological and δ13Ccarb data. However, these data often come from different lithologies (e.g., shales vs. carbonates), making it difficult to directly link biostratigraphic and chemostratigraphic markers. Ediacaran successions in South China consist of mixed carbonates and shales, offering an opportunity for integrated biostratigraphic and chemostratigraphic investigations. Black shales of the Ediacaran Miaohe Member in the Yangtze Gorges area contain macroalgae and Ediacara-type macrofossils, both preserved as carbonaceous compressions. The Miaohe Member has been traditionally regarded as an equivalent to Member IV of the uppermost Doushantuo Formation that records part of the Shuram negative δ13Ccarb excursion in South China. Thus, the Miaohe Member may have the potential to clarify the stratigraphic relationship between Ediacara-type fossils and the Shuram excursion. Recently, however, the Miaohe Member has been partially correlated with the Shibantan Member of the Dengying Formation (the “A” correlation) or partially with Member IV (the “Z” correlation). These correlations have different implications for the relationship between the Miaohe Member and the Shuram excursion. Here we test these two correlations using δ13C data of sedimentary kerogen or total organic carbon (δ13CorgTOC), taking advantage of the distinct δ13CorgTOC values between the Shibantan Member and Member IV. Our data show that δ13CorgTOC of the Miaohe Member is more similar to that of Member IV than to Shibantan Member, providing tentative support for the “Z” correlation. In addition, we also analyzed δ13Corg of individual carbonaceous compression fossils (δ13Corgtaxon), which have lower carbon isotope values than TOC. The data suggest that oxygenic photosynthesizers (e.g., macroalgae, cyanobacteria, and eukaryotic phytoplankton) were not the only contributors to sedimentary TOC. Methylotrophs, photoautotrophs, and chemoautotrophs living in anoxic waters or at the oxycline may have fixed recycled CO2 derived from organic carbon remineralization, thus contributing a significant amount of 13C-depleted organic carbon to sedimentary kerogen in the Miaohe Member.
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towards an Ediacaran time scale problems protocols and prospects
Episodes, 2016Co-Authors: Shuhai Xiao, Chuanming Zhou, Marc Laflamme, Guy M Narbonne, D V Grazhdankin, Malgorzata Moczydlowskavidal, Huan CuiAbstract:The Ediacaran Period follows the Cryogenian Period in the wake of a snowball Earth glaciation and precedes the Cambrian Period with its rising tide of animal radiation. It is also the longest among all stratigraphically defined geological periods, lasting 94 million years (635-541 Ma). Hence, a good Ediacaran time scale is essential, not only to elucidate geological time, but also to provide a temporal context for extreme climatic events and transformative evolutionary transitions. Ediacaran fossils are known from many sections and boreholes around the world, permitting ready age recognition and stratigraphic correlation of Ediacaran strata. However, the Ediacaran fossil record is colored by taphonomic biases that variously affect the preservation of the soft-bodied organisms that dominated Ediacaran marine ecosystems, and the Phanerozoic approach of defining stratigraphic boundaries using the first appearance datum (FAD) of widely distributed, rapidly evolving, easily recognizable, and readily preservable species would have limited success in the Ediacaran System. The subdivision of the Ediacaran System must therefore be founded on a holistic approach integrating biostratigraphic, chemostratigraphic, and geochronometric data for correlation. Series-level subdivision of the Ediacaran System is a challenging task, and alternative models subdividing the Ediacaran System into two or three series can be recognized. Resolving these alternatives critically depends on obtaining further data to constrain the age, duration, and global extent of the Shuram negative δ 13 C excursion, to calibrate and correlate Ediacaran acanthomorph biozones, and to determine the temporal relationship among the Shuram excursion, the Gaskiers glaciation, and Ediacaran acanthomorph biozones. Stage-level subdivisions at the bottom and top of the Ediacaran System, however, are realistic goals in the near future, and we propose that the subdivision of the Ediacaran System should initially aim at the second Ediacaran stage (SES) and the terminal Ediacaran stage (TES) where stratigraphic information is relatively rich and consensus for stratigraphic correlation is emerging. Potential stratigraphic markers for the definition of the SES include the post-glacial radiation of eukaryotes as represented by the first appearance of acanthomorph acritarchs, the termination of the cap carbonate series, or the end of the negative δ 13 C excursion (EN1 = Ediacaran negative excursion 1) associated with the cap carbonate. Terminal Ediacaran strata are well dated and host several taxa of skeletal and tubular fossils that postdate the Shuram negative δ 13 C excursion (or its probable equivalent, EN3 = Ediacaran negative excursion 3) where their stratigraphic relationship can be determined; these biostratigraphic markers may be used to define the TES in a Phanerozoic fashion. Additional Ediacaran stages between the SES and TES can be envisioned. Through collaborative efforts in the Ediacaran community, we hope that the first Precambrian stage will be established in the near future to facilitate a better understanding of the geological aftermath of snowball Earth, the redox history of global oceans, the early evolution of multicellular life, and the evolutionary fuse of the Cambrian explosion.
James G. Gehling - One of the best experts on this subject based on the ideXlab platform.
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discovery of the oldest bilaterian from the Ediacaran of south australia
Proceedings of the National Academy of Sciences of the United States of America, 2020Co-Authors: Scott D Evans, James G. Gehling, Ian V Hughes, Mary L DroserAbstract: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.
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the rise of animals in a changing environment global ecological innovation in the late Ediacaran
Annual Review of Earth and Planetary Sciences, 2017Co-Authors: Mary L Droser, Lidya G Tarhan, James G. GehlingAbstract:The evolutionary trajectory of early complex life on Earth is interpreted largely from the fossils of the Precambrian soft-bodied Ediacara Biota, which appeared and evolved during a time of dynamic biogeochemical and environmental fluctuation in the global ocean. The Ediacara Biota is historically divided into three successive Assemblages—the Avalon, the White Sea, and the Nama—which are marked by the appearance of novel biological traits and ecological strategies. In particular, the younger White Sea and Nama Assemblages record a “second wave” of ecological innovations, which included not only the development of uniquely Ediacaran body plans and ecologies, such as matground adaptations, but also the dual emergence of bilaterian-grade animals and Phanerozoic-style ecological innovations, including spatial heterogeneity, complex reproductive strategies, ecospace utilization, motility, and substrate competition. The late Ediacaran was an evolutionarily dynamic time characterized by strong environmental cont...
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microbial mat sandwiches and other anactualistic sedimentary features of the ediacara member rawnsley quartzite south australia implications for interpretation of the Ediacaran sedimentary record
PALAIOS, 2017Co-Authors: Lidya G Tarhan, James G. Gehling, Mary L Droser, Matthew P DzaugisAbstract:Abstract: The Ediacara Member of the Rawnsley Quartzite of South Australia hosts some of the most ecologically and taxonomically diverse fossil assemblages of the eponymous Ediacara Biota—Earth's earliest fossil record of communities comprised of macroscopic, complex, multicellular organisms. At the National Heritage Site, Nilpena, fifteen years of systematic excavation and reassembly of bedding planes has resulted in reconstruction of over 400 square meters of Ediacaran seafloor, permitting detailed and sequential sedimentary, paleoecological and taphonomic assessment of Ediacara fossilized communities and the shallow marine settings in which these ecosystems lived. Sedimentological investigation reveals that the Ediacara Member consists of successions of sandstone event beds and a paucity of other lithologies. Moreover, these Ediacara sandstones are characterized by a suite of sedimentary features and style of stratigraphic packaging uncharacteristic of Phanerozoic sandstone successions considered to ha...
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How diverse were early animal communities? An example from Ediacara Conservation Park, Flinders Ranges, South Australia
Alcheringa, 2016Co-Authors: Felicity J. Coutts, James G. Gehling, Diego C. García-bellidoAbstract: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...
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taphonomy and morphology of the ediacara form genus aspidella
Precambrian Research, 2015Co-Authors: Lidya G Tarhan, James G. Gehling, Mary L Droser, Matthew P DzaugisAbstract:Abstract Aspidella, the disk-like Ediacaran form genus, is a common and globally distributed member of the Ediacara Biota. In South Australia, it occurs prolifically (n > 1000) in locally dense assemblages on the bases of sandstone beds in the eponymous Ediacara Member of the Rawnsley Quartzite. Association with stalks, fronds and textured organic surfaces (TOS) has led to the interpretation of Aspidella as the holdfast of a frondose, Charniodiscus-like organism which lived with its holdfast secured within or under a sandy microbial mat and its stalk and frond protruding above the substrate and into the water column. As the dominant component of four fossiliferous beds and a minor component of most others, Aspidella exemplifies the bed-scale faunal heterogeneity characteristic of Ediacara fossil assemblages. Aspidella itself, moreover, is characterized by strong morphological variability, including variation in the presence or absence of particular distinct morphological features, variable preservation as internal and external molds, variable relief and a broad size range. However, the distribution of morphological characters is unrelated to either Aspidella specimen size or bed assemblage composition. Herein we demonstrate that this morphological diversity is an expression of neither ontogenetic nor species-level anatomical differences, but rather is the product of differential taphonomy related to variation in local substrate-related sedimentological and biogenic factors, particularly the presence or absence of TOS composed of the eukaryotic tubular organism Funisia.
Simon A.f. Darroch - One of the best experts on this subject based on the ideXlab platform.
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the trace fossil record of the nama group namibia exploring the terminal Ediacaran roots of the cambrian explosion
Earth-Science Reviews, 2021Co-Authors: Gerard J B Germs, Emily F Smith, Luis A. Buatois, Simon A.f. Darroch, Alison T Cribb, Charlotte G Kenchington, Helke MockeAbstract:Abstract 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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paleoenvironmental analysis of ernietta bearing Ediacaran deposits in southern namibia
Palaeogeography Palaeoclimatology Palaeoecology, 2020Co-Authors: Katie Maloney, Thomas H. Boag, Simon A.f. Darroch, Rachel A. Racicot, Alison T Cribb, Charlotte G Kenchington, Bryce Koester, Brandt M Gibson, Amanda Facciol, Marc LaflammeAbstract:Abstract Ediacaran fossils from the Nama Group (Kuibis Subgroup) of southern Namibia have a long history of scientific scrutiny, however many of the fossil localities still require investigation from a sedimentary facies and sequence stratigraphic standpoint. Detailed sedimentary analyses utilizing chemostratigraphy and facies-based approaches resulted in five proposed facies and two paleoenvironmental settings that allow for interpretation of the fossiliferous sections as a nearshore to a protected shallow marine paleoenvironment. The classic Ediacaran taxon Ernietta was restricted to the Kliphoek Member of the Nama Group, which limits the stratigraphic range of these organisms to the younger depositional sequence of the Kuibis Subgroup. The paleoenvironment has been interpreted as a mixed carbonate-siliciclastic, protected shallow marine environment at Farm Hansburg, suggesting that these organisms thrived in environments with medium to high flow velocities and periodic clastic sediment supply. Studies that utilize detailed paleoenvironmental reconstructions may aid in constraining phylogenetic affinities of the Ediacara biota by placing reasonable bounds on the local habitat.
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Ediacaran extinction and cambrian explosion
Trends in Ecology and Evolution, 2018Co-Authors: Simon A.f. Darroch, Emily F Smith, Marc Laflamme, Douglas H. ErwinAbstract:The Ediacaran-Cambrian (E-C) transition marks the most important geobiological revolution of the past billion years, including the Earth's first crisis of macroscopic eukaryotic life, and its most spectacular evolutionary diversification. Here, we describe competing models for late Ediacaran extinction, summarize evidence for these models, and outline key questions which will drive research on this interval. We argue that the paleontological data suggest two pulses of extinction - one at the White Sea-Nama transition, which ushers in a recognizably metazoan fauna (the 'Wormworld'), and a second pulse at the E-C boundary itself. We argue that this latest Ediacaran fauna has more in common with the Cambrian than the earlier Ediacaran, and thus may represent the earliest phase of the Cambrian Explosion.
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Ediacaran distributions in space and time: testing assemblage concepts of earliest macroscopic body fossils
Paleobiology, 2016Co-Authors: Thomas H. Boag, Simon A.f. Darroch, Marc LaflammeAbstract:The mid-late Ediacaran Period (~579–541 Ma) is characterized by globally distributed marine soft-bodied organisms of unclear phylogenetic affinities colloquially called the “Ediacara biota.” Despite an absence of systematic agreement, previous workers have tested for underlying factors that may control the occurrence of Ediacaran macrofossils in space and time. Three taxonomically distinct “assemblages,” termed the Avalon, White Sea, and Nama, were identified and informally incorporated into Ediacaran biostratigraphy. After ~15 years of new fossil discoveries and taxonomic revision, we retest the validity of these assemblages using a comprehensive database of Ediacaran macrofossil occurrences. Using multivariate analysis, we also test the degree to which taphonomy, time, and paleoenvironment explain the taxonomic composition of these assemblages. We find that: (1) the three assemblages remain distinct taxonomic groupings; (2) there is little support for a large-scale litho-taphonomic bias present in the Ediacaran; and (3) there is significant chronostratigraphic overlap between the taxonomically and geographically distinct Avalonian and White Sea assemblages ca. 560–557 Ma. Furthermore, both assemblages show narrow bathymetric ranges, reinforcing that they were paleoenvironmental–ecological biotopes and spatially restricted in marine settings. Meanwhile, the Nama assemblage appears to be a unique faunal stage, defined by a global loss of diversity, coincident with a noted expansion of bathymetrically unrestricted, long-ranging Ediacara taxa. These data reinforce that Ediacaran biodiversity and stratigraphic ranges of its representative taxa must first statistically account for varying likelihood of preservation at a local scale to ultimately aggregate the Ediacaran macrofossil record into a global biostratigraphic context.
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A mixed Ediacaran-metazoan assemblage from the Zaris Sub-basin, Namibia
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Simon A.f. Darroch, Thomas H. Boag, Douglas H. Erwin, Rachel A. Racicot, Sarah M. Tweedt, Sara J. Mason, Marc LaflammeAbstract:Abstract It has been proposed that the terminal Neoproterozoic Ediacara biota were driven to extinction by the evolution of metazoan groups capable of engineering their environments (the ‘biotic replacement’ model). However, evidence for an overlapping ecological association between metazoans and soft-bodied Ediacaran organisms is limited. Here, we describe new fossil localities from southern Namibia that preserve soft-bodied Ediacara biota, enigmatic tubular organisms thought to represent metazoans, and vertically-oriented metazoan trace fossils. Although the precise identity of the tracemakers remains elusive, the structures bear several striking similarities with the Cambrian-Recent ichnogenus Conichnus . These new data support inference of stratigraphic and ecological overlap between two very different eukaryotic clades, and indicate the existence of unusual ecosystems comprising both Ediacara biota and metazoans immediately prior to the Cambrian explosion.
Mary L Droser - One of the best experts on this subject based on the ideXlab platform.
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a tale of three taphonomic modes the Ediacaran fossil flabellophyton preserved in limestone black shale and sandstone
Gondwana Research, 2020Co-Authors: Bin Wan, Xunlai Yuan, Zhe Chen, Ke Pang, Qing Tang, Chengguo Guan, Xiaopeng Wang, Santosh Pandey, Mary L DroserAbstract:Abstract Ediacaran macrofossils are typically preserved in three taphonomic modes: casts/molds in siliciclastic rocks, casts/molds in carbonate rocks, and carbonaceous compressions in black shales. Only a few taxa are known to be preserved in more than one of these taphonomic modes. Flabellophyton is a genus that has been previously reported from lower Ediacaran black shale of the Lantian Formation (635–551 Ma) in South China and upper Ediacaran sandstone of the Ediacara Member (560–550 Ma) in South Australia. Here we report Flabellophyton from upper Ediacaran limestone of the Shibantan Member of the Dengying Formation (551–539 Ma) in South China, making Flabellophyton the only genus that occurs in all three taphonomic modes. We also provide a systematic description of Flabellophyton based on material from the Lantian and Dengying formations in South China, recognizing three morphospecies—F. lantianense, F. typicum sp. nov., and F. obesum sp. nov. Flabellophyton is reconstructed as an erect epibenthic marine organism attached to sandy, carbonate, and muddy substrates. Its phylogenetic affinity remains ambiguous though it was historically interpreted as an algal fossil. The wide environmental and stratigraphic distribution of Flabellophyton allow comparative taphonomic and paleoecological analysis. Taphonomic analysis of Flabellophyton indicates that multiple taphonomic pathways can facilitate the preservation of Ediacaran macrofossils. As a window into Ediacaran paleoecology, Flabellophyton and other Ediacaran fossils played a crucial role in the construction of epibenthic communities in Ediacaran oceans, and helps to understand the ecological migration and evolutionary expansion from deeper to shallower oceans during the Ediacaran Period.
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discovery of the oldest bilaterian from the Ediacaran of south australia
Proceedings of the National Academy of Sciences of the United States of America, 2020Co-Authors: Scott D Evans, James G. Gehling, Ian V Hughes, Mary L DroserAbstract: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.
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the rise of animals in a changing environment global ecological innovation in the late Ediacaran
Annual Review of Earth and Planetary Sciences, 2017Co-Authors: Mary L Droser, Lidya G Tarhan, James G. GehlingAbstract:The evolutionary trajectory of early complex life on Earth is interpreted largely from the fossils of the Precambrian soft-bodied Ediacara Biota, which appeared and evolved during a time of dynamic biogeochemical and environmental fluctuation in the global ocean. The Ediacara Biota is historically divided into three successive Assemblages—the Avalon, the White Sea, and the Nama—which are marked by the appearance of novel biological traits and ecological strategies. In particular, the younger White Sea and Nama Assemblages record a “second wave” of ecological innovations, which included not only the development of uniquely Ediacaran body plans and ecologies, such as matground adaptations, but also the dual emergence of bilaterian-grade animals and Phanerozoic-style ecological innovations, including spatial heterogeneity, complex reproductive strategies, ecospace utilization, motility, and substrate competition. The late Ediacaran was an evolutionarily dynamic time characterized by strong environmental cont...
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microbial mat sandwiches and other anactualistic sedimentary features of the ediacara member rawnsley quartzite south australia implications for interpretation of the Ediacaran sedimentary record
PALAIOS, 2017Co-Authors: Lidya G Tarhan, James G. Gehling, Mary L Droser, Matthew P DzaugisAbstract:Abstract: The Ediacara Member of the Rawnsley Quartzite of South Australia hosts some of the most ecologically and taxonomically diverse fossil assemblages of the eponymous Ediacara Biota—Earth's earliest fossil record of communities comprised of macroscopic, complex, multicellular organisms. At the National Heritage Site, Nilpena, fifteen years of systematic excavation and reassembly of bedding planes has resulted in reconstruction of over 400 square meters of Ediacaran seafloor, permitting detailed and sequential sedimentary, paleoecological and taphonomic assessment of Ediacara fossilized communities and the shallow marine settings in which these ecosystems lived. Sedimentological investigation reveals that the Ediacara Member consists of successions of sandstone event beds and a paucity of other lithologies. Moreover, these Ediacara sandstones are characterized by a suite of sedimentary features and style of stratigraphic packaging uncharacteristic of Phanerozoic sandstone successions considered to ha...
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taphonomy and morphology of the ediacara form genus aspidella
Precambrian Research, 2015Co-Authors: Lidya G Tarhan, James G. Gehling, Mary L Droser, Matthew P DzaugisAbstract:Abstract Aspidella, the disk-like Ediacaran form genus, is a common and globally distributed member of the Ediacara Biota. In South Australia, it occurs prolifically (n > 1000) in locally dense assemblages on the bases of sandstone beds in the eponymous Ediacara Member of the Rawnsley Quartzite. Association with stalks, fronds and textured organic surfaces (TOS) has led to the interpretation of Aspidella as the holdfast of a frondose, Charniodiscus-like organism which lived with its holdfast secured within or under a sandy microbial mat and its stalk and frond protruding above the substrate and into the water column. As the dominant component of four fossiliferous beds and a minor component of most others, Aspidella exemplifies the bed-scale faunal heterogeneity characteristic of Ediacara fossil assemblages. Aspidella itself, moreover, is characterized by strong morphological variability, including variation in the presence or absence of particular distinct morphological features, variable preservation as internal and external molds, variable relief and a broad size range. However, the distribution of morphological characters is unrelated to either Aspidella specimen size or bed assemblage composition. Herein we demonstrate that this morphological diversity is an expression of neither ontogenetic nor species-level anatomical differences, but rather is the product of differential taphonomy related to variation in local substrate-related sedimentological and biogenic factors, particularly the presence or absence of TOS composed of the eukaryotic tubular organism Funisia.
