| 1. |
- Agić, Heda, 1989-, et al.
(författare)
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Organically-preserved multicellular eukaryote from the early Ediacaran Nyborg Formation, Arctic Norway
- 2019
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Eukaryotic multicellularity originated in the Mesoproterozoic Era and evolved multiple times since, yet early multicellular fossils are scarce until the terminal Neoproterozoic and often restricted to cases of exceptional preservation. Here we describe unusual organically-preserved fossils from mudrocks, that provide support for the presence of organisms with differentiated cells (potentially an epithelial layer) in the late Neoproterozoic. Cyathinema digermulense gen. et sp. nov. from the Nyborg Formation, Vestertana Group, Digermulen Peninsula in Arctic Norway, is a new carbonaceous organ-taxon which consists of stacked tubes with cup-shaped ends. It represents parts of a larger organism (multicellular eukaryote or a colony), likely with greater preservation potential than its other elements. Arrangement of open-ended tubes invites comparison with cells of an epithelial layer present in a variety of eukaryotic clades. This tissue may have benefitted the organism in: avoiding overgrowth, limiting fouling, reproduction, or water filtration. C. digermulense shares characteristics with extant and fossil groups including red algae and their fossils, demosponge larvae and putative sponge fossils, colonial protists, and nematophytes. Regardless of its precise affinity, C. digermulense was a complex and likely benthic marine eukaryote exhibiting cellular differentiation, and a rare occurrence of early multicellularity outside of Konservat-Lagerstatten.
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| 2. |
- Hoshino, Yosuke, et al.
(författare)
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Cryogenian evolution of stigmasteroid biosynthesis
- 2017
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Ingår i: Science Advances. - : AMER ASSOC ADVANCEMENT SCIENCE. - 2375-2548. ; 3:9
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Tidskriftsartikel (refereegranskat)abstract
- Sedimentary hydrocarbon remnants of eukaryotic C-26-C-30 sterols can be used to reconstruct early algal evolution. Enhanced C-29 sterol abundances provide algal cellmembranes a density advantage in large temperature fluctuations. Here, we combined a literature review with new analyses to generate a comprehensive inventory of unambiguously syngenetic steranes in Neoproterozoic rocks. Our results show that the capacity for C-29 24ethyl- sterol biosynthesis emerged in the Cryogenian, that is, between 720 and 635 million years ago during the Neoproterozoic Snowball Earth glaciations, which were an evolutionary stimulant, not a bottleneck. This biochemical innovation heralded the rise of green algae to global dominance of marine ecosystems and highlights the environmental drivers for the evolution of sterol biosynthesis. The Cryogenian emergence of C-29 sterol biosynthesis places benchmark for verifying older sterane signatures and sets a new framework for our understanding of early algal evolution.
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| 3. |
- Loron, Corentin, et al.
(författare)
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Tonian (Neoproterozoic) eukaryotic and prokaryotic organic-walled microfossils from the upper Visingsö Group, Sweden
- 2018
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Ingår i: Palynology. - : TAYLOR & FRANCIS INC. - 0191-6122 .- 1558-9188. ; 42:2, s. 220-254
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Forskningsöversikt (refereegranskat)abstract
- The diversification of protists and multicellular microorganisms is recorded in numerous worldwide Tonian age successions, including the Visingso Group in Sweden. The Visingso Group contains a taxonomically rich assemblage of cyanobacteria, stromatolites, algal phytoplankton and vase-shaped microfossils. A new record of organic-walled microfossils from the Visingso 1 drillcore reveals the high taxonomic diversity. Several species are reported for the first time from the Visingso Group, and one new species Leiosphaeridia gorda n. sp. is described. They are in gross phycoma-like cysts of the prasinophycean algae Pterospermopsimorpha, Pterospermella, Simia, Macroptycha and Dictyotidium. Morphologically similar to zygotic cysts of chlorophycean algae are Leiosphaeridia gorda n. sp., Cerebrosphaera, Culcitulisphaera and Lanulatisphaera. Schizofusa may represent the earliest yellow-green algae of the Eustigmatiphyte among Stramenopiles. The recorded biodiversity documents the global trend in the evolution of eukaryotic protists during the Tonian Period and the increased radiation of numerous, presumably photoautotrophic biotas, representing various algal lineages.
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| 4. |
- Miao, Lanyun, et al.
(författare)
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A diverse organic-walled microfossil assemblage from the Mesoproterozoic Xiamaling Formation, North China
- 2021
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Ingår i: Precambrian Research. - : Elsevier. - 0301-9268 .- 1872-7433. ; 360
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Tidskriftsartikel (refereegranskat)abstract
- The mid-Proterozoic (ca. 1.85–0.85 Ga) might have been environmentally “boring”, but was a crucial interval of time for the early establishment of eukaryotic life on Earth. The Mesoproterozoic shale-dominated Xiamaling Formation (ca. 1.4–1.35 Ga) in North China preserved abundant organic-walled microfossils, some of which were of eukaryotic affinity but their taxonomic diversity and evolutionary implications remain unclear. In this paper, we present a palynological study of the lower Xiamaling Formation in the northern Tianjin Municipality. Similar to other Mesoproterozoic microbiotas, this assemblage consists of well-preserved and diverse spheroidal to ellipsoidal vesicles, filamentous microfossils and cellular aggregates. In total, 36 species belonging to 28 genera are identified, including 1 new species Quadrimurus clavatus gen. et sp. nov., and 5 unnamed forms. Majority of these taxa are recognised for the first time from this formation, indicating a richer assemblage than previously known. Although most taxa are of unknown biological affinities, this microbiota is thought to be composed of prokaryotic and eukaryotic microorganisms, in which 12 taxa are inferred to be eukaryotic. These microfossils indicate a moderate diversity of eukaryotic life documented in the Xiamaling Formation, which is consistent with other microbiotas in the mid-Proterozoic. The presence of Jixiania lineata Yan, 1986 (=Lineaforma elongata Vorob’eva and Sergeev, 2015) in North China extends its geographic distribution and further enhances its potential as index fossil for the early Mesoproterozoic strata. The Xiamaling assemblage provides one of the broader pictures of the Mesoproterozoic biosphere, in which eukaryotes were predominantly protistan-grade microorganisms.
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| 5. |
- Miao, Lanyun, et al.
(författare)
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New record of organic-walled, morphologically distinct microfossils from the late Paleoproterozoic Changcheng Group in the Yanshan Range, North China
- 2019
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Ingår i: Precambrian Research. - : ELSEVIER SCIENCE BV. - 0301-9268 .- 1872-7433. ; 321, s. 172-198
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Tidskriftsartikel (refereegranskat)abstract
- Eukaryotic life has likely existed since the late Paleoproterozoic, yet little is known about its early diversity and phylogenetic relationships. Organic-walled microfossils (OWMs) with conspicuous morphology provide a unique material to investigate the deep evolution of eukaryotic and prokaryotic microbial clades. Here we report a diverse assemblage of OWMs from the lower Changcheng Group (c. 1673-1638 Ma, Changzhougou and Chuanlinggou formations) in the Yanshan Range, North China, which consists of 15 species, including 2 that are newly described. The fossil assemblage is dominated by spheromorphs with less numerous process-bearing vesicles, as are colonial and filamentous forms. Among these, 6 morphologically complex taxa (Dictyosphaera, 2 species of Germinosphaera, Pterospermopsimorpha, Simia, and Valeria) are identified as unambiguous unicellular eukaryotes. Four species (Cucumiforma, Navifusa, Schizofusa and large Leiosphaeridia) with relatively simple morphology but having large size, thick wall, and some showing median-split excystment structures, are of probable eukaryotic affinity. However, various colonial microfossils could be either eukaryotes or prokaryotes. The new record of morphologically disparate OWMs represents one of the earliest occurrences of eukaryotes in both China and the world, and indicates that the eukaryotic life was already well established in the late Paleoproterozoic and was of moderate diversity, similar to that of the Mesoproterozoic.
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| 6. |
- Moczydlowska, Malgorzata, 1951-, et al.
(författare)
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A Tonian age for the Visingsö Group in Sweden constrained by detrital zircon dating and biochronology : implications for evolutionary events
- 2018
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Ingår i: Geological Magazine. - 0016-7568 .- 1469-5081. ; 155:5, s. 1175-1189
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Tidskriftsartikel (refereegranskat)abstract
- Detrital zircon U–Pb ages from samples of the Neoproterozoic Visingsö Group, Sweden, yield a maximum depositional age of ≤ 886±9 Ma (2σ). A minimum depositional age is established biochronologically using organic-walled and vase-shaped microfossils present in the upper formation of the Visingsö Group; the upper formation correlates with the Kwagunt Formation of the 780–740 Ma Chuar Group in Arizona, USA, and the lower Mount Harper Group, Yukon, Canada, that is older than 740 Ma. Mineralized scale microfossils of the type recorded from the upper Fifteenmile Group, Yukon, Canada, where they occur in a narrow stratigraphic range and are younger than 788 Ma, are recognized for the first time outside Laurentia. The mineralized scale microfossils in the upper formation of the Visingsö Group seem to have a wider stratigraphic range, and are older than c. 740 Ma. The inferred age range of mineralized scale microfossils is 788–740 Ma. This time interval coincides with the vase-shaped microfossil range because both microfossil groups co-occur. The combined isotopic and biochronologic ages constrain the Visingsö Group to between ≤ 886 and 740 Ma, thus Tonian in age. This is the first robust age determination for the Visingsö Group, which preserves a rich microfossil assemblage of worldwide distribution. The organic and mineralized microorganisms preserved in the Visingsö Group and coeval successions elsewhere document global evolutionary events of auto- and heterotrophic protist radiations that are crucial to the reconstruction of eukaryotic phylogeny based on the fossil record and are useful for the Neoproterozoic chronostratigraphic subdivision.
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| 7. |
- Moczydlowska, Malgorzata, 1951-
(författare)
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New records of late Ediacaran microbiota from Poland
- 2008
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Ingår i: Precambrian Research. - Amsterdam : Elsevier. - 0301-9268 .- 1872-7433. ; 167:1-2, s. 71-92
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Forskningsöversikt (refereegranskat)abstract
- New records of organic-walled microfossils, including cyanobacteria, phytoplankton (certain acritarchs) and some microbiota of unknown biological affinities, are reported from the late Ediacaran Włodawa Formation in the Łopiennik IG-1 borehole, Poland. The microfossil association consists mostly of known species, which originated prior to the Cryogenian Period, evidence that these microorganisms survived the Neoproterozoic glacial epochs. The longevity of most of the species is extended herein to ca. 545 Ma. One species is new but described as gen. et sp. indet., because only a single specimen is available. Although the microfossils represent both prokaryotic and eukaryotic groups of organisms, and benthic and planktic modes of life, all, with the exception of Valkyria, are photoautotrophic aerobes. Metabolic processes of nutrition, respiration and reproductive cycles, and ecologic habitats of these biota and the evolutionary lineages to which they belong are analyzed with respect to the basic requirements needed to survive prolonged periods of environmental perturbation.All recorded here cyanobacteria are benthic microbial mat-dwellers, requiring ample water and regular oxygen supply and sun light for their metabolism. Planktic species of Leiosphaeridia studied here are considered to be green algae (chlorophyceans), forming resting cysts and alternating sexual/vegetative generations in their life cycle. They also required habitats of well-oxygenated open water in the photic zone and periodic access to bottom sediment (to rest the cyst) in order to survive the glacial epochs, as they evidently did. It is argued that the natural habitats of all these biota must have been preserved and ecologically functional throughout the Cryogenian Period, and have been robust enough to sustain viable populations and genetic stocks of at least some evolutionary lineages known at the time. This is a primary constraint imposed by contemporaneous marine biosphere on the Earth System model, which can be accepted among hypothetical versions of the Snowball Earth hypotheses based on sedimentological, geochemical, physical and other geological records. The Slushball Earth model, or comparable, is thus favoured over strict Snowball Earth model because it reconciles the habitable conditions with other envisaged geo- and physical conditions during the period.
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| 8. |
- Moczydlowska, Malgorzata, 1951-
(författare)
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The Ediacaran microbiota and the survival of Snowball Earth conditions
- 2008
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Ingår i: Precambrian Research. - Amsterdam : Elsevier. - 0301-9268 .- 1872-7433. ; 167:1-2, s. 1-15
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Forskningsöversikt (refereegranskat)abstract
- Recently recovered assemblage of late Ediacaran cyanobacteria, phytoplankton and some microfossils of uncertain origin from the subsurface Włodawa Formation on the Lublin Slope in Poland, allowed to extend their stratigraphic ranges and provided a new evidence that more species survived the Cryogenian Period. Numerous other species of unicellular eukaryotes (informally called acritarchs) and prokaryotes (also coenobial and colonial) have been documented in recent years to lived-over to the Ediacaran, enlarging the global list of biota surviving the Neoproterozoic icehouse intervals. This compelling record revives the issue how marine biota could coup with the catastrophic consequences imposed by the global glaciations and/or to what extent the environmental and climatic change reduced the life habitats. For this purpose, the metabolic processes, modes of life and ecologic habitats of the biota are inferred and analyzed. The reviewed biota are autotrophic and aerobic: benthic cyanobacteria, which were solitary and largely colonial, living in functionally complex communities of mat-builders, and planktic and/or facultative benthic eukaryotes, which reproduced also sexually and some had advanced life cycle with alternating vegetative and reproductive generations. The environmental requirements of these microorganisms are well-oxygenated open marine waters in the photic zone, and permanent seafloor substrate for benthic and periodic access to bottom sediment for some planktic species with sexual reproduction to rest the cyst. Such natural habitats must have been preserved throughout the Cryogenian Period, and in a substantial extent (environmental “critical mass”) to sustain viable populations in the lineages that are represented by surviving species. Modern analogues of extraordinary adaptations of diverse biota to extreme conditions have their limitations when applied to the Cryogenian Period. Modern extreme environments (like those in Antarctica) with highly specialized organisms are maintained over relatively short time intervals (thousands of years) and may occasionally/periodically be in contact with the outside world to replenish their genetic stock. This is in a sharp contrast to the millions of years of environmental and genetic isolation invoked for the Cryogenian. The global fossil record, enlarged by recent new findings, is briefly reviewed to understand the impact of the Cryogenian glaciations on biodiversity and the rate of survival of microbiota. The Snowball Earth Hypothesis and its modified versions are discussed in pursuit of an environmentally plausible Earth System model consistent with the survival of biota. The radical version of the Snowball Earth Hypothesis is ruled out. An Earth System model with open marine water, ice-free shelf (at least seasonally) and access to the sea floor is obligatory for the Cryogenian in order to satisfy the living requirements of the biota that survived the period. The palaeobiological findings are entirely consistent with sedimentaological findings that require open marine water and well-functioning hydrologic cycle. The Slushball Earth model accommodates more adequately these requirements.
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| 9. |
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| 10. |
- Moczydlowska-Vidal, Malgorzata, 1951-, et al.
(författare)
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Ediacaran algal cysts from the Doushantuo Formation, South China
- 2022
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Ingår i: Geological Magazine. - : Cambridge University Press. - 0016-7568 .- 1469-5081. ; 159:7, s. 1050-1070
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Tidskriftsartikel (refereegranskat)abstract
- Early-middle Ediacaran organic-walled microfossils from the Doushantuo Formation studied in several sections in the Yangtze Gorges area, South China, show ornamented cyst-like vesicles of very high diversity. These microfossils are diagenetically permineralized and observed in petrographic thin-sections of chert nodules. Exquisitely preserved specimens belonging to seven species of Appendisphaera, Mengeosphaera, Tanarium, Urasphaera and Tianzhushania contain either single or multiple spheroidal internal bodies inside the vesicles. These structures indicate reproductive stages, endocyst and dividing cells, respectively, and are preserved at early to late ontogenetic stages in the same taxa. This new evidence supports the algal affiliations for the studied taxa and refutes previous suggestions of Tianzhushania being animal embryo or holozoan. The first record of a late developmental stage of a completely preserved specimen of T. spinosa observed in thin-section demonstrates the interior of vesicles with clusters of identical cells but without any cavity that is diagnostic for recognizing algal cysts vs animal diapause cysts. Various lines of evidence to infer biological affinities of these microfossils - morphology, reproductive characters, spatial arrangement of cells, and biochemical properties of the vesicle wall - are collectively characteristic of algal clades. Recognizing the biological affinities of these microfossils is key to understanding whether animals capable of producing such morphologically complex diapause cysts had an early Ediacaran fossil record (633-610 Ma), or the microfossils were non-animal holozoans or algae as argued herein for Tianzhushania spinosa and other studied microfossils.
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| 11. |
- Moczydlowska-Vidal, Malgorzata, 1951-, et al.
(författare)
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Ediacaran metazoan fossils with siliceous skeletons from the Digermulen Peninsula of Arctic Norway
- 2021
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Ingår i: Journal of Paleontology. - : Cambridge University Press. - 0022-3360 .- 1937-2337. ; 95:3, s. 440-475
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a new assemblage of Ediacaran metazoan fossils is reported from the basal Stahpogieddi Formation on the Digermulen Peninsula of Arctic Norway, including Anulitubus n. gen. Moczydlowska in Moczydlowska et al., Anulitubus formosus n. gen. n. sp. Moczydlowska in Moczydlowska et al., Coniculus n. gen. Moczydlowska in Moczydlowska et al., Coniculus elegantis n. gen. n. sp. Moczydlowska in Moczydlowska et al., Fistula n. gen. Moczydlowska in Moczydlowska et al., and Fistula crenulata n. gen. n. sp. Moczydlowska in Moczydlowska et al. The specimens are three-dimensionally preserved and include tubular and conical skeletons that are morphologically distinguished by their body-wall constructions, radial symmetry, polarity, segmentation, and annulation. The skeletons are interpreted to be biomineralized by primary silica based on computed micro-tomographic, petrographic, geochemical, and spectroscopic evidence of originally rigid body wall with layers of constant thicknesses, composed of opal, microcrystalline quartz, and an admixture of carbonaceous material, which differ from the host sediment mineralogy and do not show replacement or encrustation. The fossil-bearing interval immediately overlies strata of Gaskiers age and can be bracketed within 580-541 Ma, but it is estimated to be ca. 575 Ma on the basis of averaged sedimentation rates and biostratigraphic correlations with Ediacaran biota found in up-section deposits of ca. 558-555 Ma. Future new findings of such fossils in different preservation modes and further multi-collector inductively coupled plasma mass spectrometry, which shows the silicon fractionation and traces its biogenic origin versus inorganic mineralization, may corroborate the interpretation of biogenic silicification of these earliest skeletal fossils.
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| 12. |
- Moczydlowska-Vidal, Malgorzata, 1951-, et al.
(författare)
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Ediacaran radiation of organic-walled microbiota recorded in the Ura Formation, Patom Uplift, East Siberia
- 2012
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Ingår i: Precambrian Research. - Elsevier : Elsevier BV. - 0301-9268 .- 1872-7433. ; 198, s. 1-24
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Tidskriftsartikel (refereegranskat)abstract
- A new assemblage of morphologically complex, ornamented and large organic-walled microfossils (acritarchs) from the Ura Formation in the Patom Uplift, East Siberia, is identified and taxonomically described as a continuation of the previous studies (0245 and 0305). Nine new species and three new genera are recognised; 10 other species are known from occurrences in the Ediacaran strata of Australia, China, the Siberian Platform (SP), and the East European Platform (EEP). The new species are morphologically advanced phenotypes, showing innovative elements of vesicle ornamentation and variable symmetry, and internal bodies within zygotic cyst-like vesicles that are indicative of the sexual reproduction stage of the microorganism. The morphological features and the preliminarily recognised cell wall ultrastructure are characteristic of phytoplankton; thus the described microfossils are identified as green microalgae. The relative age of the Ura assemblage, by comparison to microfossil records elsewhere and estimated in the regional geologic context of the Dalniaya Taiga (containing the Ura Formation) and the Zhuya (overlying) groups, is suggested to be early Ediacaran. Radiation of the Ura-type microorganisms pre-dates the records of Ediacaran microbiota from Australia (the Pertatataka association/Ediacaran Complex Acanthomorphic Palynoflora), the Siberian Platform (Khamaka-type assemblages), and the EEP (Vychegda association) but is preceded by the appearance of certain species recorded in China at the base of the Doushantuo Formation. The stratigraphic ranges of genera co-occurring in these palaeocontinents (Appendisphaera, Cavaspina, Ceratosphaeridium, Gyalosphaeridium,Labruscasphaeridium, Multifronsphaeridium, Tanarium, and Variomargosphaeridium) are extended by their lower record in the Patom Uplift and may span a major portion of the Ediacaran Period. The refined stratigraphic distribution of microfossils may provide a means for zoning the entire Ediacaran System in addition to the upper zones established in Australia.
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| 13. |
- Moczydlowska-Vidal, Malgorzata, 1951-
(författare)
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Life cycle of early Cambrian microalgae from the Skiagia-plexus acritarchs
- 2010
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Ingår i: Journal of Paleontology. - 0022-3360 .- 1937-2337. ; 84:2, s. 216-230
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Tidskriftsartikel (refereegranskat)abstract
- Light microscopy studies on new materials and museum collections of early Cambrian organic-walled microfossils, informally called acritarchs, provide the observations on phenetic features that permit a comparison to certain Modern microalgae and the recognition of various developmental stages in their life cycle. The microfossils derive from various depositional settings in Estonia, Australia, Greenland, Sweden and Poland. The exceptionally preserved microfossils reveal the internal body within the vesicle, - the endocyst -, and the process of releasing the endocyst from the cyst. Vegetative cells, cysts and endocysts are distinguished, and the hypothetical reconstruction of a complex life cycle with the alternation of sexual and asexual generations is proposed. Acritarchs from the Skiagia-plexus are cysts, and likely zygotes in the sexual generation, which periodically rested as “benthic plankton”. Some microfossils of the Leiosphaeridia-plexus are inferred to be vegetative cells, were planktonic and probably haplobiontic. These form-taxa may belong to a single biological species, or a few closely related species, and represent the developmental stages and alternating generations in a complex life cycle that are expressed by polymorphic, sphaero- and acanthomorphic acritarchs. The morphological resemblance and diagnostic cell walls ultrastructure with the trilaminar sheath structure known from earlier studies suggest that the early Cambrian microfossils are the ancestral representatives and/or early lineages to Modern Class Chlorophyceae, and the orders Volvocales and Chlorococcales.
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| 14. |
- Moczydlowska-Vidal, Malgorzata, 1951-, et al.
(författare)
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Micro- and nano-scale ultrastructure of cell walls in Cryogenian microfossils : revealing their biological affinity
- 2010
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Ingår i: Lethaia. - : Scandinavian University Press / Universitetsforlaget AS. - 0024-1164 .- 1502-3931. ; 43:2, s. 129-136
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Tidskriftsartikel (refereegranskat)abstract
- Recently established protocols and methods in advanced microscopy and spectrometry applied to studies of ancient unicellular organic-walled microfossils of uncertain biological affinities (acritarchs) provide new evidence of the fine ultrastructure of cell walls and their biochemistry that support the interpretation of some such microfossils as photosynthesizing microalgae. The micro-scale and nanoscale ultrastructure of the cell walls of late Cryogenian sphaeromorphic acritarchs from the Chichkan Formation (Kazakhstan) revealed by the advanced techniques and studied originally by Kempe et al. (2005) is here further analyzed and compared to that of modern microalgal analogues. On the basis of such comparison, we interpret the preserved cell wall ultrastructure to reflect original layering and lamination within sublayers of the fossil wall, rather than being a result of taphonomic and diagenetic alteration. The outer thick layer represents the primary wall and the inner layer the secondary wall of the cell, whereas the laminated amorphous sub-layers, 10-20 nm in thickness and revealed by transmission electron and atomic force microscopy, are recognized as trilaminar sheath structure (TLS). Because two-layered cell walls, trilaminar sheaths, and the position of the TLS within the fossil cell wall are characteristic of the mature developmental state in cyst morphogenesis in modern microalgae, we infer that the Chichkan sphaeromorphs are likely resting cells (aplanospores) of chlorophyceaen green microalgae from the Order Volvocales.
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| 15. |
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| 16. |
- Moczydlowska-Vidal, Malgorzata, 1951-
(författare)
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Proterozoic acritarchs and divergences of green microalgae
- 2010
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Ingår i: CIMP 2010 Warsaw Abstracts. - : Institute of Geological Sciences, Polish Academy of Sciences (PAS). ; , s. 42-44
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Konferensbidrag (refereegranskat)abstract
- The morphology of microfossils with resistant cell walls, their ornamentation and functionally identifiable structures are the first source of information used to assess their biological affinities. Difficulties in relying on morphology alone due to the problem of convergent morphology may be resolved by the ultrastructure of the cell wall and its biochemistry. The cell walls of microfossils, which are acid-resistant and thus extractable by chemical processing from the host rocks, are composed of biopolymers that show the properties of the sporopollenin/algaenan classes of biomolecules synthesized by green algae, the green lineages of dinoflagellates, and the reproductive cells of higher plants (spores and pollen). These biota share primary biochemical pathways of organic synthesis of biopolymers for constructing cell walls, and show a common early lineage in their phylogeny. The geochronologic sequence of appearance of microfossils with diagnostic traits of phycoma-like cysts, zygotic cysts with ornamentation, pylomes, double-walled vesicles and endocysts, and spheroidal vegetative cells and /or aplanospores with trilaminar sheath structure (TLS), which are interpreted to be green microalgae, is aligned on the phylogenetic tree of the Viridiplantae. The radiometric datings of the first appearance datum of these taxa provide the minimum age of the origin of the classes to which they are assigned. According to the affinities of microfossils inferred herein, the sequence of evolutionary events is as it follows. The stem-group of the Viridiplantae extends in time prior to c. 1800 Ma, and the major branching nodes in a common lineage are at c. 1800 Ma for the Chlorophytes, c. 1650 Ma for the Prasinophyceae, and at c. 1450 Ma for the Chlorophyceae-Ulvophyceae lineage. The divergence of the Ulvophyceae might have occurred before c. 950 Ma. The origin of the Chlorophytes is constrained by the earliest record of the Leiosphaeridia-type microfossils from the Changzhougou Formation. The “leiosphaerid” morphology, which is recognized among the prasinophyceaen or chlorophyceaen microalgae, has deep roots in their common ancestral group and it is not only the result of a convergent morphology expressed later on. The prasinophyceaen lineage is recognized by Tasmanites rifejicus, and co-occurring species with phycoma-like, double-walled cysts: Simia, Pterospermopsimorpha, and Pterospermella, and striated Valeria. Valeria appears at c. 1650 Ma in the Mallapunyah Formation, and it marks the minimum age at which the Prasinophyceae lineage split from the basal Chlorophytes. Phycoma-like microfossils are subsequently recorded at c. 950 Ma (Octoedryxium), c. 580 Ma (Tasmanites, Simia, Octoedryxium, Pterospermopsimorpha), and since c. 540 Ma through the Cambrian (Tasmanites, Granomarginata, Pterospermella, Cymatiosphaera). The chlorophyceaen lineage is recognized by various species of Leiosphaeridia showing the TLS in their cell walls, which are likely the early members of the orders Volvocales and/or Chlorococcales. Leiosphaerids with such traits are present at c. 1450 Ma, 650 Ma and 520 Ma. The divergence of the Ulvophyceae prior to c. 950 Ma is suggested by the dasycladacean Archaeoclada and Variaclada in the Lakhanda Group, and the siphonocladacean Proterocladus from the c. 700-750 Ma Svanbergfjellet Formation. The presented minimum ages of the origin of the Viridiplantae and the divergence of the major microalgal clades differ from the molecular clocks estimates. They also suggest that previously inferred time of the origin of Chlorophytes at c. 1 Ga or 1.5 Ga is too young. The molecular clocks estimates of these events are in conflict with microfossil records, and the interpretation of some of them as being photosynthesizing biota, and seem to be delayed in time. Following the Great Oxygenation Event at c. 2.2 Ga, the oxygen pressure in the ocean-atmosphere system has been apparently increasing although with significant fluctuations through time. This was due to the variation in carbon cycles and carbonate formation, assembly and breaking off the supercontinents and weathering rate change, and hydrological cycle and stratification of the oceans. The Palaeo-Mesoproterozoic oceans were stratified with deep layers anoxic and only the surface layer oxygenated by photosynthesis within the photic zone. The late Neoproterozoic oxygenation event resulted in full oxygenation of the oceans and deep currents circulation. The increasing pressure of oxygen in marine environments is argued to have played a decisive role in the evolution of metazoans in the Ediacaran and Cambrian, yet the cause-effect relationships may be in reverse as it comes to photosynthetic organisms diversification and growing abundance observed through the Proterozoic. The recorded diversification of green microalgae (acritarchs) must have enhanced the rates of primary productivity in the surface ocean layers and organic carbon burial in shelf sediments. Photosynthesis most profoundly increased the oxygen pressure in the global ocean. Precise correlation in time of the geochemical signatures and radiations of photosynthetic biota may reveal critical relationships between biotic and environmental evolution.
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| 17. |
- Moczydlowska-Vidal, Malgorzata, 1951-
(författare)
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Proterozoic microfossils revealing the time of algal divergences
- 2010
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Ingår i: Geophysical Research Abstracts, Vol. 12, 7th EGU General Assembly 2010. - : Copernicus Publications. ; , s. 702-702
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Konferensbidrag (refereegranskat)abstract
- Morphological and reproductive features and cell wall ultrastructure and biochemistry of Proterozoic acritarchs are used to determine their affinity to modern algae. The first appearance datum of these microbiota is traced to infer a minimum age of the divergence of the algal classes to which they may belong. The chronological appearance of microfossils that represent phycoma-like and zygotic cysts and vegetative cells and/or aplanospores, respectively interpreted as prasinophyceaen and chlorophyceaen microalgae, is related to the Viridiplantae phylogeny. These divergence times differ from molecular clock estimates, and the palaeontological evidence suggests that they are older. The best examples of unicellular, organic-walled microfossils (acritarchs) from the Mesoproterozoic to Early Ordovician are reviewed to demonstrate features, which are indicative of their affinity to photosynthetic microalgae. The first indication that a microfossil may be algal is a decay- and acid-resistant cell wall, which reflects its biochemistry and ultrastructure, and probably indicates the ability to protect a resting/reproductive cyst. The biopolymers synthesized in the cell walls of algae and in land plants (“plant cells”), such as sporopollenin/algaenan, are diagnostic for photosynthetic taxa and were inherited from early unicellular ancestors. These preservable cell walls are resistant to acetolysis, hydrolysis and acids, and show diagnostic ultrastructures such as the trilaminar sheath structure (TLS). “Plant cell” walls differ in terms of chemical compounds, which give high preservation potential, from fungal and animal cell walls. Fungal and animal cells are fossilized only by syngenetic permineralization, whereas “plant cells” are fossilized as body fossils more ubiquitously and without mineralization. Microalgae radiated quickly in the Cambrian and Ordovician; however, several morphotypes with features related to the reproductive cycle occur in the Proterozoic, although they are not always recognized as such. The assignment of Proterozoic unicellular microfossils with resistant cell walls to specific eukaryotic groups is tentative. However, we argue that the new interpretations of their functional morphology, combined with cell wall ultrastructure and biochemistry, allow their assignment to microalgal classes. Microfossils with advanced ornamentation and ontogenetically formed excystment structures or endocysts, which prove that they are cysts in a complex life cycle with sexual reproduction, are related to the basal lineage of the Chlorophytes and the class Chlorophyceae. A cell wall ultrastructure with a TLS supports the affinity of some spheroidal taxa to the Chlorophytes. The phylogeny of the Chlorophytes shows a sequence of branching nodes from a stem-group of the Viridiplantae that leads to the classes Prasinophyceae and Chlorophyceae, and then the Ulvophyceae. Based on a modern interpretation of the record, the timing of these nodes is deduced to be prior to c. 1650 Ma for the Prasinophyceae, c. 1450 Ma for the Chlorophyceae, and c. 950 Ma for the Ulvophyceae. The origin of the Chlorophytes, and in general the Viridiplantae, predates 1.8 Ga. These ages, based on microfossils, are earlier than the estimates based on molecular clocks.
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| 18. |
- Moczydlowska-Vidal, Malgorzata, 1951-, et al.
(författare)
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The Ediacaran Aspidella-type impressions in the Jinxian successions of Liaoning Province, northeastern China
- 2016
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Ingår i: Lethaia. - John Wiley & Sons Ltd : Scandinavian University Press / Universitetsforlaget AS. - 0024-1164 .- 1502-3931. ; 49:4, s. 617-630
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Tidskriftsartikel (refereegranskat)abstract
- We identify the macroscopic impression fossils from the Xingmincun Formation of the Jinxian Group, Liaoning Province of northeastern China as members of the Aspidella plexus of the Ediacaran age. This is the first recognition of the taxon in the Liaoning Province, although such fossils have been previously recorded in the succession but were referred to as new species and relegated to an earlier Neoproterozoic age. A revision of the taxonomic interpretation and relative age estimation of the previous record is provided as well as an evaluation of abiotic vs biotic processes that could produce similar structures to studied impressions. We consider the mode of preservation of the fossils from a biochemical point of view and the properties of organic matter in the integument of soft-bodied metazoans. The selective preservation of the Ediacaran organisms, including metazoans, as impressions (moulds and casts) against the organically preserved contemporaneous cyanobacterial and algal microfossils and an exceptionally small number of terminal Ediacaran metazoan fossils (Sabellidites, Conotubus and Shaanxilites), demonstrates the non-resistant characteristics and the very different biochemical constitution of the Ediacaran metazoans compared with those that evolved in the Cambrian and after. The refractory biomacromolecules in cell walls of photosynthesizing microbiota (bacterans, cutans, algaenan and sporopollenin groups) and in the chitinous body walls of Sabellidites sharply contrast to the labile biopolymers in Ediacaran metazoans known only from impressions. The newly emerging biosynthesis of resistant biopolymers in metazoans (chitin and collagen groups) initiated by the annelids at the end of Ediacaran and fully evolved in Cambrian metazoans, considered with the ability to biomineralize, made their body preservation possible. The Chengjiang and Burgess Shale metazoans show evidence of this new biochemistry in body walls and cuticles, and not only because of the specific taphonomic window that enhanced their preservation.
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| 19. |
- Mus, Mónica Martí, et al.
(författare)
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Morphologically diverse vase-shaped microfossils from the Russoya Member, Elbobreen Formation, in Spitsbergen
- 2020
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 350
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Tidskriftsartikel (refereegranskat)abstract
- Vase-shaped microfossils (VSMs) constitute a distinct group of fossils characteristic of late Tonian marine rocks. They often occur in high densities and in relatively diverse assemblages that include several morphotypes. All VSMs may have shared a test wall of similar structure and composition, as inferred from common patterns of preservation. However, little is known about the detailed morphology and structure of this wall. Here we examine the diversity, preservation, and wall morphology of a diverse assemblage of VSMs from the Russoya Member of the Elbobreen Formation in northeastern Spitsbergen. SEM imaging of exceptionally preserved specimens with their wall replicated in iron oxide reveals that these VSMs shared a well-defined, smooth, micrometre-thick wall ornamented with complex structures including facets, closed "pores", and intricate relief patterns on the internal surface of the aperture. The observed similarities among different morphotypes suggest VSMs assemblages reflect the diversification of a single Glade, likely related to the Arcellinida (Amoebozoa), an extant order to which they have been phylogenetically linked.
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| 20. |
- Pease, Victoria, et al.
(författare)
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Baltica in the Cryogenian, 850-650 Ma
- 2008
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 160:1-2, s. 46-65
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Forskningsöversikt (refereegranskat)abstract
- This new tectonic synthesis provides a framework for understanding the dynamic evolution of Baltica and for constraining tectonic correlations within the context of the Neoproterozoic break-up of Rodinia–Pannotia. Cryogenian Baltica is described with respect to five geographic regions: the northwest, northeast, east, south, and southwest (modern coordinates). These geographic regions define three principal Cryogenian tectonic margins: a rifting northwestern margin, a passive northeastern margin, and a poorly understood southern margin. The northwest region is characterized by Neoproterozoic to lower Ordovician sedimentary successions deposited on Archean to late Mesoproterozoic crystalline complexes, reworked during Caledonian orogenesis. Lare Neoproterozoic to lower Ordovician sedimentary strata record the change from an alluvial setting to a marine environment, and eventually to a partially starved (?) turbidite basin. They document rifting from the Rodinian-Pannotian supercontinent, which was unsuccessful until ca. 620–550 Ma when voluminous dikes and mafic/ultramafic complexes were intruded. Baltica's northeastern and eastern regions document episodic intracratonic rifting throughout the Mesoproterozoic, followed by pericontinental passive margin deposition throughout the Cryogenian. In the northeast platformal and deeper-water basin deposits are preserved, whereas the eastern region was later affected by Paleozoic rifting and preserves only shelf deposits. The northeastern and eastern regions define Baltica's Cryogenian northeastern tectonic margin, which was an ocean-facing passive margin of the Rodinia–Pannotia supercontinent. It remained a passive margin until the onset of Timanian orogenesis at ca. 615 Ma, approximately synchronous with the time of Rodinia–Pannotia rifting. Baltica's southern and southwestern regions remain enigmatic and controversial. Precambrian basement is generally hidden beneath thick successions of Ediacaran and younger platform sediments. Similarities between these regions exist, however, and suggest that they may share a similar tectonic evolution in the Cryogenian and therefore define the southern tectonic margin of Baltica at this time. Paleo- to Mesoproterozic basement was affected by Neoproterozoic and younger tectonism, including Cryogenian (?) and Ediacaran rifting. This was followed by Ediacaran (ca. 550 Ma) passive margin sediment deposition at the time of Rodinia–Pannotia break-up, until Early Paleozoic accretion of allochthonous terranes record the transition from rifting to a compressional regime. Paleomagnetic and paleontological data are consistent with Baltica and Laurentia drifting together between ca. 750 and 550 Ma, when they had similar apparent polar wander paths. Microfossil assemblages along the eastern margin of Laurentia and the western margin of Baltica (modern coordinates), suggest proximity between these two margins at this time. At ca. 550 Ma, Laurentia and Baltica separated, consistent with paleomagnetic, paleontological, and geological data, and a late break-up for Rodinia–Pannotia.
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| 21. |
- Shang, Xiaodong, et al.
(författare)
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Acritarchs from the Doushantuo Formation at Liujing section in Songlin area of Guizhou Province, South China : Implications for early-middle Ediacaran biostratigraphy
- 2019
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Ingår i: Precambrian Research. - : Elsevier. - 0301-9268 .- 1872-7433. ; 334
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Tidskriftsartikel (refereegranskat)abstract
- A taxonomically diverse and morphologically disparate microfossil assemblage is recovered from the upper Doushantuo Formation in the Liujing section of Songlin area, Guizhou Province, including acanthomorphic and sphaeromorphic acritarchs, multicellular algae, and filamentous cyanobacteria. Acritarch Mengeosphaera membranifera sp. nov. is newly erected and genus Cymatiosphaeroides and several species (C. forabilatus, C. kullingii, Bacatisphaera baokangensis) are emended in the systematics. The acanthomorphic species are dominated by Cymatiosphaeroides forabilatus and Mengeosphaera membranifera sp. nov. The Liujing assemblage shares many species with other Ediacaran coeval assemblages from South China, Australia, Siberia, the East European Platform, India, Mongolia and Svalbard, and indicates a significant taxonomic similarity to the global, agediagnostic assemblages. New occurrence of those known taxa in the Liujing succession documents the biodiversity of the Ediacaran acritarchs in South China. The Liujing assemblage extends the palaeogeographic distribution of the Ediacaran acritarchs and may be assigned to the Tanarium conoideum-Cavospina basiconica Assemblage Zone that was recognized in the Yangtze Gorges area of South China. Alternatively, it could be partially correlated with the barren interval between T. conoideum-C. basiconica Assemblage Zone and the overlying Tanarium pycnacanthum-Ceratosphaeridium glaberosum Assemblage Zone.
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| 22. |
- Shang, Xiaodong, et al.
(författare)
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Algal affinity and possible life cycle of the early Cambrian acritarch Yurtusia uniformis from South China
- 2020
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 63:6, s. 903-917
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Tidskriftsartikel (refereegranskat)abstract
- Abundant, well‐preserved specimens of spheroidal organic‐walled microfossil Yurtusia uniformis are reported from the basal Cambrian Yanjiahe Formation in the Changyang area of Hubei Province, South China. Thin and hollow processes extend between the double walls of the vesicle. The single to multiple internal bodies within the vesicle cavity are observed in the genus for the first time, representing reproductive structures (dividing daughter cells). A small circular perforation may occur on the vesicle wall to release the internal bodies. Morphological analyses of specimens preserved at various life stages reveal that processes gradually became longer as the vesicle grew in size. The internal bodies (daughter cells) underwent several successive divisions within the vesicle, which was accompanied by the simultaneous growth of both vesicle and processes. The regular growth of cells, formation and release of daughter cells, and the remarkable morphological similarity between extant algae and the studied microfossils suggest that Yurtusia uniformis is probably a green microalga that may be closely related to the Trebouxiophyceae or even Chlorellales (Chlorophyta). The growth and reproductive mode of individuals indicates that Y. uniformis is an actively growing vegetative cell of microalgae, rather than a metabolically inert cyst or resting spore. A life cycle involving vegetative growth and asexual reproduction is proposed for Y. uniformis on the basis of the life histories of modern chlorophytes. The multiple internal cells may represent autospores produced by a mature autosporangium during asexual reproduction, which subsequently developed into separate young vegetative cells after their release from the opened autosporangium.
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| 23. |
- Shang, Xiaodong, et al.
(författare)
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Organic composition and diagenetic mineralization of microfossils in the Ediacaran Doushantuo chert nodule by Raman and petrographic analyses
- 2018
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 314, s. 145-159
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Tidskriftsartikel (refereegranskat)abstract
- We studied microfossils and their embedding matrix minerals from chert nodules in the Ediacaran Doushantuo Formation of the Yangtze Gorges area in South China using Raman spectroscopy as well as transmitted- and polarized light microscopy. The microfossils are composed of organic carbonaceous material with weak structural organization/ordering, which indicates a low degree of thermal maturation and alteration. Raman spectral disparity of carbonaceous material among different portions (vesicle/inclusion) of microfossils reveals some differences in organic composition and structure of their precursor biological matters. The mineral phases of silica matrix that entombs the microfossils are recognized as opal-CT, cryptocrystalline quartz, and their transitional phases. Overall, Raman spectral analyses and petrographic observations document a complete and continuous sequence of silica phase transformation from opal-CT to quartz. When reconstructing the diagenetic history of sediments and mineralization process of microfossils in a localized microenvironment, the silica in pore waters precipitated preferentially at the periphery of microorganisms in the form of opal, gradually decreasing in abundance as it transformed into more stable cryptocrystalline quartz. The recrystallization took place in cryptocrystalline quartz to form grains. Authigenic fluorapatite readily precipitated in the vicinity of some microfossils and within their degraded organic fragments. While apatite was crystallizing around organisms and their biostructures, silica precipitated in the surrounding voids, inhibiting the space of potential apatite crystallization. The silicification and phosphatization of microfossils occurred in the microbial sulfate reduction (MSR) zone of the sediment column, and both were driven by the localized pH change resulting from MSR and pyrite precipitation in the microenvironment, thus facilitating the exceptional fossil preservation in the Doushantuo chert nodules.
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