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Wang X, Liu AG, Chen Z, Wu C, Liu Y, Wan B, Pang K, Zhou C, Yuan X, Xiao S. A late-Ediacaran crown-group sponge animal. Nature 2024; 630:905-911. [PMID: 38839967 DOI: 10.1038/s41586-024-07520-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2023] [Accepted: 05/03/2024] [Indexed: 06/07/2024]
Abstract
Sponges are the most basal metazoan phylum1 and may have played important roles in modulating the redox architecture of Neoproterozoic oceans2. Although molecular clocks predict that sponges diverged in the Neoproterozoic era3,4, their fossils have not been unequivocally demonstrated before the Cambrian period5-8, possibly because Precambrian sponges were aspiculate and non-biomineralized9. Here we describe a late-Ediacaran fossil, Helicolocellus cantori gen. et sp. nov., from the Dengying Formation (around 551-539 million years ago) of South China. This fossil is reconstructed as a large, stemmed benthic organism with a goblet-shaped body more than 0.4 m in height, with a body wall consisting of at least three orders of nested grids defined by quadrate fields, resembling a Cantor dust fractal pattern. The resulting lattice is interpreted as an organic skeleton comprising orthogonally arranged cruciform elements, architecturally similar to some hexactinellid sponges, although the latter are built with biomineralized spicules. A Bayesian phylogenetic analysis resolves H. cantori as a crown-group sponge related to the Hexactinellida. H. cantori confirms that sponges diverged and existed in the Precambrian as non-biomineralizing animals with an organic skeleton. Considering that siliceous biomineralization may have evolved independently among sponge classes10-13, we question the validity of biomineralized spicules as a necessary criterion for the identification of Precambrian sponge fossils.
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Affiliation(s)
- Xiaopeng Wang
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China
- University of Chinese Academy of Sciences, Beijing, China
- Department of Earth Sciences, University of Cambridge, Cambridge, UK
| | - Alexander G Liu
- Department of Earth Sciences, University of Cambridge, Cambridge, UK
| | - Zhe Chen
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Chengxi Wu
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Yarong Liu
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Bin Wan
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China.
- University of Chinese Academy of Sciences, Beijing, China.
| | - Ke Pang
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Chuanming Zhou
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China
- University of Chinese Academy of Sciences, Nanjing, Nanjing, China
| | - Xunlai Yuan
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China.
- University of Chinese Academy of Sciences, Beijing, China.
| | - Shuhai Xiao
- Department of Geosciences and Global Change Centre, Virginia Tech, Blacksburg, VA, USA.
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Strother PK, Brasier MD, Wacey D, Timpe L, Saunders M, Wellman CH. A possible billion-year-old holozoan with differentiated multicellularity. Curr Biol 2021; 31:2658-2665.e2. [PMID: 33852871 DOI: 10.1016/j.cub.2021.03.051] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Revised: 12/07/2020] [Accepted: 03/15/2021] [Indexed: 02/05/2023]
Abstract
Sediments of the Torridonian sequence of the Northwest Scottish Highlands contain a wide array of microfossils, documenting life in a non-marine setting a billion years ago (1 Ga).1-4 Phosphate nodules from the Diabaig Formation at Loch Torridon preserve microorganisms with cellular-level fidelity,5,6 allowing for partial reconstruction of the developmental stages of a new organism, Bicellum brasieri gen. et sp. nov. The mature form of Bicellum consists of a solid, spherical ball of tightly packed cells (a stereoblast) of isodiametric cells enclosed in a monolayer of elongated, sausage-shaped cells. However, two populations of naked stereoblasts show mixed cell shapes, which we infer to indicate incipient development of elongated cells that were migrating to the periphery of the cell mass. These simple morphogenetic movements could be explained by differential cell-cell adhesion.7,8 In fact, the basic morphology of Bicellum is topologically similar to that of experimentally produced cell masses that were shown to spontaneously segregate into two distinct domains based on differential cadherin-based cell adhesion.9 The lack of rigid cell walls in the stereoblast renders an algal affinity for Bicellum unlikely: its overall morphology is more consistent with a holozoan origin. Unicellular holozoans are known today to form multicellular stages within complex life cycles,10-13 so the occurrence of such simple levels of transient multicellularity seen here is consistent with a holozoan affinity. Regardless of precise phylogenetic placement, these fossils demonstrate simple cell differentiation and morphogenic processes that are similar to those seen in some metazoans today.
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Affiliation(s)
- Paul K Strother
- Department of Earth & Environmental Sciences, Weston Observatory of Boston College, 381 Concord Road, Weston, MA 02493, USA.
| | - Martin D Brasier
- Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK
| | - David Wacey
- Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia
| | - Leslie Timpe
- Department of Biology, San Francisco State University, San Francisco, CA 94132, USA
| | - Martin Saunders
- Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia
| | - Charles H Wellman
- Department of Animal & Plant Sciences, University of Sheffield, Alfred Denny Building, Western Bank, Sheffield S10 2TN, UK
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Cui H, Xiao S, Cai Y, Peek S, Plummer RE, Kaufman AJ. Sedimentology and chemostratigraphy of the terminal Ediacaran Dengying Formation at the Gaojiashan section, South China. GEOLOGICAL MAGAZINE 2019; n/a:10.1017/S0016756819000293. [PMID: 31631899 PMCID: PMC6800678 DOI: 10.1017/s0016756819000293] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The late Ediacaran Dengying Formation (ca. 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 a relatively continuous chemostratigraphic profile for the terminal Ediacaran stage. In this study, a detailed sedimentological and chemostratigraphic (δ13Ccarb, δ18Ocarb, δ13Corg, δ34Spyrite, and 87Sr/86Sr) investigation was conducted on the Dengying Formation at the Gaojiashan section, Ningqiang County of the 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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Affiliation(s)
- Huan Cui
- Research Group of Analytical, Environmental and Geo- Chemistry (AMGC), Division of Earth System Science, Vrije Universiteit Brussel (VUB), Brussels 1050, Belgium
- ET-HOME (Evolution and Tracers of the Habitability of Mars and Earth) Astrobiology Research Consortium, Belgium
- NASA Astrobiology Institute, Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
- Department of Geology, University of Maryland, College Park, MD 20742, USA
- Author for correspondence: (H. Cui) or (H. Cui), Present address: Research Group of AMGC, Free University of Brussels (VUB), Brussels 1050, Belgium
| | - Shuhai Xiao
- Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA
| | - Yaoping Cai
- State Key Laboratory of Continental Dynamics, Shaanxi Key Laboratory of Early Life and Environment, Department of Geology, Northwest University, Xi’an 710069, China
| | - Sara Peek
- Department of Geology, University of Maryland, College Park, MD 20742, USA
- United States Geological Survey, Menlo Park, CA 94025, USA
| | - Rebecca E. Plummer
- Department of Geology, University of Maryland, College Park, MD 20742, USA
- Hydrology and Remote Sensing Laboratory, Beltsville Agricultural Research Center, US Department of Agriculture, Beltsville, MD 20705 USA
| | - Alan J. Kaufman
- Department of Geology, University of Maryland, College Park, MD 20742, USA
- Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742, USA
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4
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Chen Z, Chen X, Zhou C, Yuan X, Xiao S. Late Ediacaran trackways produced by bilaterian animals with paired appendages. SCIENCE ADVANCES 2018; 4:eaao6691. [PMID: 29881773 PMCID: PMC5990303 DOI: 10.1126/sciadv.aao6691] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 04/25/2018] [Indexed: 05/15/2023]
Abstract
Ediacaran trace fossils provide key paleontological evidence for the evolution of early animals and their behaviors. Thus far, however, this fossil record has been limited to simple surface trails and relatively shallow burrows. We report possible trackways, preserved in association with burrows, from the terminal Ediacaran Shibantan Member (ca. 551 to ca. 541 million years ago) in the Yangtze Gorges area of South China. These trace fossils represent the earliest known trackways. They consist of two rows of imprints arranged in poorly organized series or repeated groups. These trackways may have been produced by bilaterian animals with paired appendages, although the phylum-level phylogenetic affinity of the trace makers remains unknown. It is possible that the trackways and associated burrows were produced by the same trace maker, indicating a complex behavior involving both walking and burrowing. Together, these trackways and burrows mark the arrival of a new era characterized by an increasing geobiological footprint of bilaterian animals.
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Affiliation(s)
- Zhe Chen
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
- Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
- Corresponding author. (S.X.); (Z.C.)
| | - Xiang Chen
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Chuanming Zhou
- Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
- CAS Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
| | - Xunlai Yuan
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
- Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Shuhai Xiao
- Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
- Corresponding author. (S.X.); (Z.C.)
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5
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Bykova N, Gill BC, Grazhdankin D, Rogov V, Xiao S. A geochemical study of the Ediacaran discoidal fossil Aspidella preserved in limestones: Implications for its taphonomy and paleoecology. GEOBIOLOGY 2017; 15:572-587. [PMID: 28397387 DOI: 10.1111/gbi.12240] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Accepted: 03/22/2017] [Indexed: 06/07/2023]
Abstract
The Ediacara biota features the rise of macroscopic complex life immediately before the Cambrian explosion. One of the most abundant and widely distributed elements of the Ediacara biota is the discoidal fossil Aspidella, which is interpreted as a subsurface holdfast possibly anchoring a frondose epibenthic organism. It is a morphologically simple fossil preserved mainly in siliciclastic rocks, which are unsuitable for comprehensive stable isotope geochemical analyses to decipher its taphonomy and paleoecology. In this regard, three-dimensionally preserved Aspidella fossils from upper Ediacaran limestones of the Khatyspyt Formation in the Olenek Uplift of northern Siberia offer a rare opportunity to leverage geochemistry for insights into their taphonomy and paleoecology. To take advantage of this opportunity, we analyzed δ13 Ccarb , δ18 Ocarb , δ13 Corg , δ34 Spyr , and iron speciation of the Khatyspyt Aspidella fossils and surrounding sediment matrix in order to investigate whether they hosted microbial symbionts, how they were fossilized, and the redox conditions of their ecological environments. Aspidella holdfasts and surrounding sediment matrix show indistinguishable δ13 Corg values, suggesting they did not host and derive significant amount of nutrients from microbial symbionts such as methanogens, methylotrophs, or sulfide-oxidizing bacteria. δ13 Ccarb , δ18 Ocarb , and δ34 Spyr data, along with petrographic observations, suggest that microbial sulfate reduction facilitated the preservation of Aspidella by promoting early authigenic calcite cementation in the holdfasts before matrix cementation and sediment compaction. Iron speciation data are equivocal, largely because of the low total iron concentrations. However, consideration of published sulfur isotope and biomarker data suggests that Aspidella likely lived in non-euxinic waters. It is possible that Aspidella was an opportunistic organism, colonizing the seafloor in large numbers when paleoenvironments were favorable. This study demonstrates that geochemical data of Ediacaran fossils preserved in limestones can offer important insights into the taphonomy and paleoecology of these enigmatic organisms living on the eve of the Cambrian explosion.
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Affiliation(s)
- N Bykova
- Department of Geosciences, Virginia Tech, Blacksburg, VA, USA
- Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch Russian Academy of Sciences, Novosibirsk, Russia
| | - B C Gill
- Department of Geosciences, Virginia Tech, Blacksburg, VA, USA
| | - D Grazhdankin
- Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch Russian Academy of Sciences, Novosibirsk, Russia
- Novosibirsk State University, Novosibirsk, Russia
| | - V Rogov
- Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch Russian Academy of Sciences, Novosibirsk, Russia
| | - S Xiao
- Department of Geosciences, Virginia Tech, Blacksburg, VA, USA
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6
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Chen Z, Zhou C, Xiao S, Wang W, Guan C, Hua H, Yuan X. New Ediacara fossils preserved in marine limestone and their ecological implications. Sci Rep 2014; 4:4180. [PMID: 24566959 PMCID: PMC3933909 DOI: 10.1038/srep04180] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2013] [Accepted: 02/07/2014] [Indexed: 11/23/2022] Open
Abstract
Ediacara fossils are central to our understanding of animal evolution on the eve of the Cambrian explosion, because some of them likely represent stem-group marine animals. However, some of the iconic Ediacara fossils have also been interpreted as terrestrial lichens or microbial colonies. Our ability to test these hypotheses is limited by a taphonomic bias that most Ediacara fossils are preserved in sandstones and siltstones. Here we report several iconic Ediacara fossils and an annulated tubular fossil (reconstructed as an erect epibenthic organism with uniserial arranged modular units), from marine limestone of the 551–541 Ma Dengying Formation in South China. These fossils significantly expand the ecological ranges of several key Ediacara taxa and support that they are marine organisms rather than terrestrial lichens or microbial colonies. Their close association with abundant bilaterian burrows also indicates that they could tolerate and may have survived moderate levels of bioturbation.
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Affiliation(s)
- Zhe Chen
- LPS and LESP, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
| | - Chuanming Zhou
- LPS and LESP, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
| | - Shuhai Xiao
- Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
| | - Wei Wang
- LPS and LESP, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
| | - Chengguo Guan
- LPS and LESP, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
| | - Hong Hua
- State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University, Xi'an 710069, China
| | - Xunlai Yuan
- LPS and LESP, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
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7
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Rare earth elements and carbon isotope geochemistry of the Doushantuo Formation in South China: Implication for middle Ediacaran shallow marine redox conditions. ACTA ACUST UNITED AC 2012. [DOI: 10.1007/s11434-012-5082-6] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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8
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Miot J, Maclellan K, Benzerara K, Boisset N. Preservation of protein globules and peptidoglycan in the mineralized cell wall of nitrate-reducing, iron(II)-oxidizing bacteria: a cryo-electron microscopy study. GEOBIOLOGY 2011; 9:459-470. [PMID: 21955835 DOI: 10.1111/j.1472-4669.2011.00298.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Iron-oxidizing bacteria are important actors of the geochemical cycle of iron in modern environments and may have played a key role all over Earth's history. However, in order to better assess that role on the modern and the past Earth, there is a need for better understanding the mechanisms of bacterial iron oxidation and for defining potential biosignatures to be looked for in the geologic record. In this study, we investigated experimentally and at the nanometre scale the mineralization of iron-oxidizing bacteria with a combination of synchrotron-based scanning transmission X-ray microscopy (STXM), scanning transmission electron microscopy (STEM) and cryo-transmission electron microscopy (cryo-TEM). We show that the use of cryo-TEM instead of conventional microscopy provides detailed information of the successive iron biomineralization stages in anaerobic nitrate-reducing iron-oxidizing bacteria. These results suggest the existence of preferential Fe-binding and Fe-oxidizing sites on the outer face of the plasma membrane leading to the nucleation and growth of Fe minerals within the periplasm of these cells that eventually become completely encrusted. In contrast, the septa of dividing cells remain nonmineralized. In addition, the use of cryo-TEM offers a detailed view of the exceptional preservation of protein globules and the peptidoglycan within the Fe-mineralized cell walls of these bacteria. These organic molecules and ultrastructural details might be protected from further degradation by entrapment in the mineral matrix down to the nanometre scale. This is discussed in the light of previous studies on the properties of Fe-organic interactions and more generally on the fossilization of mineral-organic assemblies.
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Affiliation(s)
- J Miot
- Institut de Minéralogie et de Physique des Milieux Condensés, UMR 7590, CNRS, Université Piere et Marie Curie et IPGP, Paris, France
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Evolutionary Trends in Remarkable Fossil Preservation Across the Ediacaran–Cambrian Transition and the Impact of Metazoan Mixing. TOPICS IN GEOBIOLOGY 2010. [DOI: 10.1007/978-90-481-8643-3_15] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
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10
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Spatio-temporal carbon isotope variation during the Ediacaran period in South China and its impact on bio-evolution. ACTA ACUST UNITED AC 2009. [DOI: 10.1007/s11430-009-0169-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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11
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Emergence of Animals from Heat Engines – Part 1. Before the Snowball Earths. ENTROPY 2009. [DOI: 10.3390/e11030463] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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12
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Abstract
The Ediacara biota include macroscopic, morphologically complex soft-bodied organisms that appear globally in the late Ediacaran Period (575-542 Ma). The physiology, feeding strategies, and functional morphology of the modular Ediacara organisms (rangeomorphs and erniettomorphs) remain debated but are critical for understanding their ecology and phylogeny. Their modular construction triggered numerous hypotheses concerning their likely feeding strategies, ranging from micro-to-macrophagus feeding to photoautotrophy to osmotrophy. Macrophagus feeding in rangeomorphs and erniettomorphs is inconsistent with their lack of oral openings, and photoautotrophy in rangeomorphs is contradicted by their habitats below the photic zone. Here, we combine theoretical models and empirical data to evaluate the feasibility of osmotrophy, which requires high surface area to volume (SA/V) ratios, as a primary feeding strategy of rangeomorphs and erniettomorphs. Although exclusively osmotrophic feeding in modern ecosystems is restricted to microscopic bacteria, this study suggests that (i) fractal branching of rangeomorph modules resulted in SA/V ratios comparable to those observed in modern osmotrophic bacteria, and (ii) rangeomorphs, and particularly erniettomorphs, could have achieved osmotrophic SA/V ratios similar to bacteria, provided their bodies included metabolically inert material. Thus, specific morphological adaptations observed in rangeomorphs and erniettomorphs may have represented strategies for overcoming physiological constraints that typically make osmotrophy prohibitive for macroscopic life forms. These results support the viability of osmotrophic feeding in rangeomorphs and erniettomorphs, help explain their taphonomic peculiarities, and point to the possible importance of earliest macroorganisms for cycling dissolved organic carbon that may have been present in abundance during Ediacaran times.
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Abstract
Fe speciation and S-isotope of pyrite data from the terminal Proterozoic Sheepbed Formation in Canada and Doushantuo Formation in China reveal that ocean deep waters were anoxic after the global glaciations (snowball Earth) ending 635 million years ago, but that marine sulfate concentrations and inferentially atmospheric oxygen levels were higher than before the glaciations. This supports a long-postulated link between oxygen levels and the emergence of eumetazoa. Subsequent ventilation of the deep ocean, inferred from shifts in Fe speciation in Newfoundland (previously published data) and western Canada (this report), paved the way for Ediacaran macrobiota to colonize the deep seafloors.
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14
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Pulsed oxidation and biological evolution in the Ediacaran Doushantuo Formation. Proc Natl Acad Sci U S A 2008; 105:3197-202. [PMID: 18299566 DOI: 10.1073/pnas.0708336105] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Recent geochemical data from Oman, Newfoundland, and the western United States suggest that long-term oxidation of Ediacaran oceans resulted in progressive depletion of a large dissolved organic carbon (DOC) reservoir and potentially triggered the radiation of acanthomorphic acritarchs, algae, macroscopic Ediacara organisms, and, subsequently, motile bilaterian animals. However, the hypothesized coupling between ocean oxidation and evolution is contingent on the reliability of continuous geochemical and paleontological data in individual sections and of intercontinental correlations. Here we report high-resolution geochemical data from the fossil-rich Doushantuo Formation (635-551 Ma) in South China that confirm trends from other broadly equivalent sections and highlight key features that have not been observed in most sections or have received little attention. First, samples from the lower Doushantuo Formation are characterized by remarkably stable delta(13)C(org) (carbon isotope composition of organic carbon) values but variable delta(34)S(CAS) (sulfur isotope composition of carbonate-associated sulfate) values, which are consistent with a large isotopically buffered DOC reservoir and relatively low sulfate concentrations. Second, there are three profound negative delta(13)C(carb) (carbon isotope composition of carbonate) excursions in the Ediacaran Period. The negative delta(13)C(carb) excursions in the middle and upper Doushantuo Formation record pulsed oxidation of the deep oceanic DOC reservoir. The oxidation events appear to be coupled with eukaryote diversity in the Doushantuo basin. Comparison with other early Ediacaran basins suggests spatial heterogeneity of eukaryote distribution and redox conditions. We hypothesize that the distribution of early Ediacaran eukaryotes likely tracked redox conditions and that only after approximately 551 Ma (when Ediacaran oceans were pervasively oxidized) did evolution of oxygen-requiring taxa reach global distribution.
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Shen B, Dong L, Xiao S, Kowalewski M. The Avalon Explosion: Evolution of Ediacara Morphospace. Science 2008; 319:81-4. [DOI: 10.1126/science.1150279] [Citation(s) in RCA: 129] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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16
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Conway Morris S. Darwin's dilemma: the realities of the Cambrian 'explosion'. Philos Trans R Soc Lond B Biol Sci 2006; 361:1069-83. [PMID: 16754615 PMCID: PMC1578734 DOI: 10.1098/rstb.2006.1846] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The Cambrian 'explosion' is widely regarded as one of the fulcrum points in the history of life, yet its origins and causes remain deeply controversial. New data from the fossil record, especially of Burgess Shale-type Lagerstätten, indicate, however, that the assembly of bodyplans is not only largely a Cambrian phenomenon, but can already be documented in fair detail. This speaks against a much more ancient origin of the metazoans, and current work is doing much to reconcile the apparent discrepancies between the fossil record, including the Ediacaran assemblages of latest Neoproterozoic age and molecular 'clocks'. Hypotheses to explain the Cambrian 'explosion' continue to be generated, but the recurrent confusion of cause and effect suggests that the wrong sort of question is being asked. Here I propose that despite its step-like function this evolutionary event is the inevitable consequence of Earth and biospheric change.
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Affiliation(s)
- Simon Conway Morris
- University of Cambridge, Department of Earth Sciences, Downing Street, Cambridge CB2 3EQ, UK.
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17
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Cavalier-Smith T. Cell evolution and Earth history: stasis and revolution. Philos Trans R Soc Lond B Biol Sci 2006; 361:969-1006. [PMID: 16754610 PMCID: PMC1578732 DOI: 10.1098/rstb.2006.1842] [Citation(s) in RCA: 147] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
This synthesis has three main parts. The first discusses the overall tree of life and nature of the last common ancestor (cenancestor). I emphasize key steps in cellular evolution important for ordering and timing the major evolutionary innovations in the history of the biosphere, explaining especially the origins of the eukaryote cell and of bacterial flagella and cell envelope novelties. Second, I map the tree onto the fossil record and discuss dates of key events and their biogeochemical impact. Finally, I present a broad synthesis, discussing evidence for a three-phase history of life. The first phase began perhaps ca 3.5 Gyr ago, when the origin of cells and anoxic photosynthesis generated the arguably most primitive prokaryote phylum, Chlorobacteria (= Chloroflexi), the first negibacteria with cells bounded by two acyl ester phospholipid membranes. After this 'chlorobacterial age' of benthic anaerobic evolution protected from UV radiation by mineral grains, two momentous quantum evolutionary episodes of cellular innovation and microbial radiation dramatically transformed the Earth's surface: the glycobacterial revolution initiated an oxygenic 'age of cyanobacteria' and, as the ozone layer grew, the rise of plankton; immensely later, probably as recently as ca 0.9 Gyr ago, the neomuran revolution ushered in the 'age of eukaryotes', Archaebacteria (arguably the youngest bacterial phylum), and morphological complexity. Diversification of glycobacteria ca 2.8 Gyr ago, predominantly inhabiting stratified benthic mats, I suggest caused serial depletion of 13C by ribulose 1,5-bis-phosphate caboxylase/oxygenase (Rubisco) to yield ultralight late Archaean organic carbon formerly attributed to methanogenesis plus methanotrophy. The late origin of archaebacterial methanogenesis ca 720 Myr ago perhaps triggered snowball Earth episodes by slight global warming increasing weathering and reducing CO2 levels, to yield runaway cooling; the origin of anaerobic methane oxidation ca 570 Myr ago reduced methane flux at source, stabilizing Phanerozoic climates. I argue that the major cellular innovations exhibit a pattern of quantum evolution followed by very rapid radiation and then substantial stasis, as described by Simpson. They yielded organisms that are a mosaic of extremely conservative and radically novel features, as characterized by De Beer's phrase 'mosaic evolution'. Evolution is not evenly paced and there are no real molecular clocks.
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