| 1. |
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| 2. |
- Arvestål, Emma, et al.
(författare)
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Organic-walled microfossils in the Ediacaran of Estonia: Biodiversity on the East European Platform
- 2020
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 341
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Tidskriftsartikel (refereegranskat)abstract
- Precambrian organic-walled microfossils are not only a source for studying evolution but also increasingly associated with stratigraphic correlation, based on key fossils and assemblage composition. For this reason, two drill cores from north-eastern Estonia have been studied for their content and stratigraphic distribution of organic-walled microfossils (OWM), analysing samples from the Precambrian Gdov, Kotlin, and Voronka formations. The recovered assemblages are generally well-preserved and diverse consisting of abundant sphaeromorphs, such as Leiosphaeridiaspp. and Pterospermopsimorpha spp., filamentous cyanobacteria, e.g. Cephalonyx geminatus and Palaeolyngbya catenata, and different types of cellular/colonial aggregates. In contrast, acanthomorphic acritarchs are rare with only a few unidentified examples present. The presence of taxa such as Pomoria rhomboidalisand Primoflagella speciosa in combination with the absence of large acanthomorphs suggests a late Ediacaran age of the studied samples. All in all, 38 species within 22 different genera are described herein, as are 9 taxa of unknown taxonomic affiliation. Another 11 taxa are briefly mentioned and depicted in order to provide for a better overview of the diversity of the assemblage. The stratigraphic distribution of the recognized taxa and assemblages can provide a powerful tool for correlation on the East European Platform as well as between Baltica and other palaeogeographic regions during the Ediacaran.
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| 3. |
- Botting, Joseph P., et al.
(författare)
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A Middle Ordovician Burgess Shale-type fauna from Castle Bank, Wales (UK)
- 2023
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Ingår i: Nature Ecology & Evolution. - : Springer Nature. - 2397-334X. ; 7:5, s. 666-674
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Tidskriftsartikel (refereegranskat)abstract
- Burgess Shale-type faunas are critical to our understanding of animal evolution during the Cambrian, giving an unrivalled view of the morphology of ancient organisms and the ecology of the earliest animal-dominated communities. Rare examples in Lower Ordovician strata such as the Fezouata Biota illustrate the subsequent evolution of ecosystems but only from before the main phase of the Great Ordovician Biodiversification Event. Later Ordovician Konservat-Lagerstätten are not directly comparable with the Burgess Shale-type faunas as they do not represent diverse, open-shelf communities, limiting our ability to track ecological development through the critical Ordovician biodiversification interval. Here we present the Castle Bank fauna: a highly diverse Middle Ordovician Burgess Shale-type fauna from Wales (UK) that is directly comparable with the Burgess Shale and Chengjiang biotas in palaeoenvironment and preservational style. The deposit includes animals with morphologies similar to the iconic Cambrian taxa Opabinia, Yohoia and Wiwaxia, combined with early examples of more derived groups such as barnacles. Many taxa such as kinorhynchs show the small sizes typical of modern faunas, illustrating post-Cambrian miniaturization. Castle Bank provides a new perspective on early animal evolution, revealing the next chapter in ecosystem development following the Chengjiang, Burgess Shale and Fezouata biotas.
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| 4. |
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| 5. |
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| 6. |
- Grey, Kathleen, et al.
(författare)
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Neoproterozoic subdivision in Australia
- 2005
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Ingår i: Central Australian Basins Symposium.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Neoproterozoic subdivision is well advanced in Australia using integrated results from lithostratigraphy, palynology, isotope chemostratigraphy and stromatolite biostratigraphy. Previously proposed Cryogenian correlations were tested by the drilling of GSWA Lancer-1 in the western Officer Basin and were found to be reliable. The consistency of the results allows the succession to be tied to limited geochronological ages from the Adelaide Rift Complex. Data are still sparse on the interval between the Sturtian and Marinoan glaciations, but good correlations exist in the Ediacaran.The base of the cap carbonate in Enorama Creek in the Adelaide Rift Complex has been ratified as the Global Stratotype Section and Point (GSSP) for the newly defined Ediacaran System and Period. The Flinders Ranges have a near-continuous section from the Marinoan glaciation to the Cambrian boundary, especially around the Brachina and Bunyeroo gorges. Lithostratigraphy, and local and regional correlations are well established, including links between the type sections, measured sections throughout the Adelaide Rift Complex and continuously cored drillhole sections on the Stuart Shelf, 80–100 km to the northeast, and to the Officer and Amadeus basins. An integrated approach, using lithostratigraphy; stratigraphic markers (glacial episodes, the time-synchronous Acraman impact ejecta layer, canyon cutting); carbon isotope chemostratigraphy; sequence stratigraphy; seismic interpretation; stromatolite biostratigraphy; and the first appearance of bilaterians and associated trace fossils, has proved successful.Acritarchs are acid-insoluble fossils of single-celled, phytoplanktonic green algae and are ideal for zonation. A rigorous sampling program began in 1991 to establish an acritarch biostratigraphy throughout Australian Neoproterozoic basins, based on palynological studies of continuously cored drillholes. Extensive field sampling of sections in the Flinders Ranges was unsuccessful, partly because the rift succession is too thermally mature for palynomorphs to be preserved, and partly because organic material has been leached from a deeply weathered profile. No identifiable acritarchs were recovered from this area, or from outcrops in other basins. However, Stuart Shelf drillholes contain well-preserved palynomorphs, although preservation is patchy in parts of the succession. Nevertheless, there are enough data for correlation with excellently preserved assemblages from the Officer and Amadeus basins. Georgina Basin preservation is too poor for useful analysis at present. Data from the Officer and Amadeus basins demonstrate the potential for biostratigraphic zonation in the lower and middle Ediacaran. Biostratigraphic correlation parallels correlations based on organic carbon isotope curves.Middle Ediacaran acritarch assemblages are extraordinarily diverse taxonomically, morphologically complex, and show typical patterns of secular diversity. These characteristics are ideal for the development of a zonal scheme, with levels of precision equivalent to the Phanerozoic record. The zones are independent of taphonomic and palaeoenvironmental influences, and they are demonstrably independent of lithology, lithostratigraphy, and sequence stratigraphy. Using composite sections, two palynofloras, the Ediacaran Leiosphere Palynoflora (ELP) and the Ediacaran Complex Acanthomorph Palynoflora (ECAP), have been recognised. The ECAP has been subdivided into four zones. The scheme is preliminary, but represents a significant advance in Neoproterozoic biostratigraphic studies, and should provide an important tool for future stratigraphic correlation. Additional studies are in progress to refine the correlations by examining undocumented parts of the succession, especially from Murnaroo-1 and Giles-1. The presence of certain acritarch species in probably coeval successions in Australia, Siberia, China, and northern Europe, suggests that the proposed zonation has good potential for global application, and that biostratigraphic principles and methodology can be applied to the Neoproterozoic.
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| 7. |
- Grey, Kathleen, et al.
(författare)
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Subdividing the Ediacaran of Australia using biostratigraphy
- 2005
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Ingår i: Central Australian Basins Symposium.
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Konferensbidrag (refereegranskat)abstract
- A new Global Stratotype and Section (GSSP) for the terminal Neoproterozoic, the Ediacaran Period and System, has been ratified by the International Union of Geological Sciences (IUGS), but problems of subdivision and correlation remain. Hydrocarbon and mineral exploration in the Officer, Amadeus, and Georgina basins, and the Adelaide Rift Complex has resulted in the development of palynological (mainly acritarch) correlations using range charts, based on >1000 samples from >30 drillholes sampled about every 10 m. As in the Cryogenian, biostratigraphic correlations, based on palynology and stromatolite biostratigraphy, are feasible, and results are consistent with correlations based on carbon isotope curves established using splits of palynology samples.So far, zonation is only possible for the lower and middle Ediacaran in Australia. Upper Ediacaran lithologies are generally unsuitable for palynomorph preservation and assemblages appear to be highly impoverished. However, a distinctive assemblage of large acanthomorph acritarchs, with highly complex morphologies and short stratigraphic ranges, characterises the middle Ediacaran. They are ideal candidates for biostratigraphy and this interval can be correlated with a high degree of confidence. Assemblages from Baltica and the East European Platform suggest that palynological zonation of the upper Ediacaran may be possible, despite species reduction and a return to simple morphologies. Moreover, the upper Ediacaran contains the Ediacara fauna, which may also be a suitable tool for correlation.Stromatolites indicate Australia-wide correlation at certain levels of the Ediacaran. Incipient columns of Elleria minuta, characteristic of the Amadeus Basin (Marinoan-equivalent) cap dolomite, were identified in a 50 cm-thick dolomite horizon above a diamictite, in Empress-1/1A in Western Australia. Tungussia julia is widespread and appears to be facies independent. It occurs in shallow-water carbonates of the Julie Formation (Amadeus Basin), Wonoka Formation (Adelaide Rift Complex), Elkera Formation (Georgina Basin), and Wilari Dolomite Member of the Tanana Formation (eastern Officer Basin), and is present in the periglacial Egan Formation in the Kimberley area. Relative stratigraphy indicates that the Egan Formation is considerably younger than the Elatina Formation (Marinoan glaciation). The Egan glaciation took place at about 560 Ma, only a short time before the appearance of the first bilaterian trace fossils.Palynomorph assemblages are sparse during and between the Sturtian and Marinoan glaciations (~700–600 Ma) and samples immediately above the Marinoan glaciation are barren. Post-glacial benthic mats and leiospheres quickly re-established and flourished, as sea level and temperatures rose, but there is no obvious post-glacial species diversification, and no evidence of invasion by extremophiles from hot-spring refugia as envisaged in Snowball Earth predictions. Only a handful of species survived, but pre-glacial species appear to be identical to post-glacial species. Specimen numbers increased rapidly as sea-level rose, but so far, no new taxa have been identified below the Acraman impact ejecta layer.Above the Acraman impact layer, during a second sea-level rise, there is a striking change in the palynoflora, when >50 species of large acanthomorph acritarchs, belonging to several new genera, first appear and diversify rapidly. They differ significantly from older taxa and in some aspects resemble dinocysts. At least four zones have been recognised, based mainly on assemblages from continuous core in the eastern Officer Basin (Munta-1, Observatory Hill-1, Lake Maurice West-1, and Birksgate-1), the Adelaide Rift Complex succession (SCYW-1a, WWD-1 and MJ-1) and the Amadeus Basin (Wallara-1 and Rodinga-4). More detailed studies are in progress on distributions in Lake Maurice West-1, Observatory Hill-1, Murnaroo-1, and Giles-1. These drillholes are of particular significance because the precise position of the ejecta layer is known in each.Although the acanthomorph assemblage was recognised previously in Murnaroo-1, systematic sampling was not carried out and the position of the ejecta layer was not known. More refined sampling and the discovery of the ejecta layer at 279.55 m has now confirmed observations from other drillholes that the earliest appearance of the acanthomorphs is above the ejecta layer and that diversification was rapid, with 10 species already present, less than 50 m above the ejecta layer. Studies continue in an attempt to locate the earliest appearance of acanthomorphs. Preliminary examination of samples from Giles-1, where the ejecta layer was found at 554.90 m, confirms the acritarch distribution pattern. Stable isotope studies are also providing significant data about the effect of the Acraman impact on the biosphere.Several key acanthomorph species are present elsewhere in the world, including Svalbard, Norway, Siberia, and China, raising the possibility of global correlation. In particular, the Australian assemblage has several taxa in common with a succession in an area in eastern Siberia that contains one of the giant Neoproterozoic gas fields. Further work is required to define the ranges of key species outside Australia, so the scheme can be extended globally.At present, contradictions arise when correlations are attempted with the Doushantuo Formation in China. In part, this reflects the lack of methodical stratigraphic sampling in the Chinese succession and the disparity in thickness between the Chinese succession (<200 m) and the Australian succession (>2000 m). There are also discrepancies in the acritarch biostratigraphy and carbon isotope curves that raise issues about whether the Nantuo Tillite should be correlated with the type ‘Marinoan’ glaciation, the Elatina Formation, and these discrepancies have implications about how many glacial episodes happened in the Neoproterozoic. Recent dating on probable equivalents of the Elatina Formation in King Island and Tasmania suggest an age of 580 Ma. This is similar to the age of the Gaskiers and Squantum Tillites in western Canada, but considerably younger than recently obtained ages of 635 Ma on successions in southern Africa and the Nantuo Tillite in China.Prospects for subdividing and correlating the Ediacaran using biostratigraphy are excellent, provided taxonomic ranges are properly documented. Biostratigraphic subdivisions can be integrated with other means of correlation to provide a rigorous means of global correlation.
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| 8. |
- Grey, Kathleen, et al.
(författare)
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Taphonomy of Ediacaran acritarchs from Australia: significance for taxonomy and biostratigraphy
- 2009
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Ingår i: Palaios. - : Society for Sedimentary Geology. - 0883-1351 .- 1938-5323. ; 24:3-4, s. 239-256
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Tidskriftsartikel (refereegranskat)abstract
- A diverse assemblage of Australian Ediacaran (late Neoproterozoic) acritarchs from the Centralian Superbasin and Adelaide Rift Complex demonstrates a range of taphonomic degradation. Recognition of taphonomic variants is critical for taxonomic studies and biostratigraphic interpretation. Taphonomic features observed include compression features, folding and tearing of vesicle walls, pitting, perforation, abrasion, exfoliation, shrinking, twisting, splitting, curling, shredding, pyritization, particle entrapment, and thermal maturation effects. The physical and chemical structure of the vesicle wall is instrumental in determining the degree of taphonomic damage. Consistent associations allow Identification of degradation series that incorporate previously described individual species and provide a framework for taxonomic revision. Taphonomic associations may also characterize taphofacies, providing an additional tool for basin analysis.
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| 9. |
- Hill, Andrew C., et al.
(författare)
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New records of Ediacaran Acraman ejecta in drillholes from the Stuart Shelf and Officer Basin, South Australia
- 2007
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Ingår i: Meteoritics and Planetary Science. - 1086-9379 .- 1945-5100. ; 42:11, s. 1883-1891
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Tidskriftsartikel (refereegranskat)abstract
- New occurrences of the Acraman impact ejecta layer were recently discovered in two South Australian drillholes, SCYW-79 1a (Stuart Shelf) and Munta 1 (Officer Basin) using lithostratigraphy, acritarch biostratigraphy, carbon isotope stratigraphy, and biomarker anomalies to predict the stratigraphic position. The ejecta layer is conspicuous because it consists of pink, sand-sized, angular fragments of volcanic rock distributed along the bedding plane surface of green marine siltstone. In SCYW-79 1a it forms a layer 5 mm thick; in Munta 1 the ejecta layer is thin and discontinuous because of its distance (similar to 550 km) from the impact structure. Palynological, biomarker, and carbon isotope anomalies can now be shown to coincide with the ejecta layer in SCYW-79 1a and Munta 1 suggesting the Acraman impact event may have had far reaching influences on the rapidly evolving Ediacaran biological and geochemical cycles.
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| 10. |
- Huld, Sigrid, et al.
(författare)
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Experimental mineralisation in carbonate, phosphate, and silicate of the filamentous hydrogenotrophic methanogen Methanobacterium oryzae
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Methanogens are thought to be some of the most ancient organisms to have lived on Earth. Fossils of ancient mineralised filamentous forms have been described before from hydrothermal vents to sediments. The peculiarity of Archaea lies in their cell walls, where they lack the peptidoglycan layer found in Bacteria and instead have a proteinaceous S-layer that has been shown to promote mineralisation through the presence of charged polymers on the cell surface. Some methanogens, like the filamentous Methanobacterium oryzae do not have an S-layer but a cell wall made of pseudomurein, similar in structure to bacterial murein. In this work, experimental mineralisation with carbonate, phosphate, and silica on a strain of M. oryzae were analysed. Differences in the degree of morphological preservation in the various fossilisation agents were observed over a period of 3 months and chemical analyses using EDX and XRD were carried out on precipitates. Results indicate that the various minerals precipitate differently in association with the methanogens and only silica replicates the morphology with a relatively high degree of fidelity. This shows the presence of possible taphonomic biases in the rock record depending on mineralisation, size differences, and cell wall structure. Therefore, this work has important outcomes for the recognition of filamentous fossils in the rock record and on the different mineralisation mechanisms on early Earth.
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| 11. |
- Huld, Sigrid
(författare)
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Untangling ambiguities in the microbial fossil record : experimental abiotic and biological approaches
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Life on early earth has long been the topic of discussion for many researchers: how did it come to be? Which cells came first? Where can we find them? The most ancient rocks on our planet may hold some of the answers to these questions, but many may only be answered in laboratories. Chemical and morphological traces can be found from Archaean deposits, tantalisingly similar to modern day prokaryotes. Often, they are interpreted as the fossilised remains of bacteria or archaea. However, the caveat remains the abiotic mechanisms with which many similar traces and markers can be formed. The purpose of this thesis was to look into the similarities and differences in abiotic and biological formation of filamentous structures in rocks and observe whether there are chemical or morphological factors that allow for distinguishing between the two. Various laboratory methods were used: chemical gardens to form filamentous abiotic structures and experimental mineralisation of a filamentous methanogen in carbonate, phosphate, and silicate in order to compare and contrast the various mineralisation mechanisms in the fidelity of preservation of the microbes. In the former experiment, analysis with electron paramagnetic resonance (EPR) spectroscopy was carried out to identify potential chemical biomarkers. A combination of scanning and transmission electron microscopy, energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and Raman spectroscopy were also used to analyse the minerals and precipitates formed in both sets of experiments. The results of this research indicate that morphology of filamentous structures and the chemical signatures in biominerals may not be reliable as biogenic indicators. Furthermore, the work on experimental mineralisation reveals the possible biases in the rock record of microbial preservation which is highly dependent on the structure of the cell wall, chemistry of the environment, and the mineral formed. Finally, this work has important outcomes for the search for biomarkers on earth and on other planets and for the recognition of pseudofossils versus microbial fossils in the rock record.
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| 12. |
- 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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| 13. |
- Moczydlowska, Malgorzata, et al.
(författare)
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Ultrastructure of cell walls in ancient microfossils as a proxy to their biological affinities
- 2009
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 173:1-4, s. 27-38
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Forskningsöversikt (refereegranskat)abstract
- Bacteria and protoctists dominated the biosphere in the Archean and Proterozoic, their affinities being deduced by studies of their comparative morphology, palaeoecology, biogeochemistry, and wall ultrastructure. However, exact phylogenetic relationships are uncertain for most such microfossils. Because of the limitations imposed by the simple morphology and small dimensions of such microorganisms and their little known biochemistry, new techniques in microscopy, tomography and spectroscopy are applied to examine individual microfossils at the highest attainable spatial resolution. TEM/SEM studies of the wall ultrastructure of sphaero- and acanthomorphic acritarchs have revealed complex, single to multilayered walls, having a unique texture in sub-layers and an occasionally preserved trilaminar sheath structure (TLS) of the external layer. A variety of optical characteristics, the electron density and texture of fabrics of discrete layers, and the properties of biopolymers may indicate the polyphyletic affiliations of such microfossils and/or the preservation of various stages (vegetative, resting) in their life cycle. Primarily, wall ultrastructure allows discrimination between fossilized prokaryotic and eukaryotic cells. Composite wall ultrastructure provides evidence that some Proterozoic and Cambrian leiosphaerids are of algal affinities (but not, per se, that they are referable to "Leiosphaeridia"). Certain Cambrian specimens represent chlorophyceaens, having the multilayered composite wall with TLS structure known from vegetative and resting cells in modern genera of the Chlorococcales and Volvocales. The wall ultrastructure of the studied Cambrian and Proterozoic acanthomorphs resembles the resting cysts of green microalgae, but there is no evidence to suggest a close relationship of these taxa, to dinoflagellates. It is apparent that although there is no single and direct method to recognize the precise phylogenetic relations of such microfossils, ultrastructural studies of their preserved cell walls and encompassing sheaths, combined with biochemical analyses and other advanced methods, may further elucidate their affinities to the modern biota.
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| 14. |
- Moczydlowska-Vidal, Malgorzata, et al.
(författare)
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Life cycle of Early Ordovician acritarch species
- 2003
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Konferensbidrag (populärvet., debatt m.m.)abstract
- Acritarchs are marine planktonic autotrophic protistans of heterogeneous origins. Their diversification into many morphotypes occurred throughout Neoproterozic and Early Palaeozoic; some morphotypes represent green algal classes but most are of unknown biological affinities. Palaeobiology and relationships to extant microbiota of some acritarchs, with emphasis on their life cycle, reproduction and environmental adaptations, may be inferred from phonetic morphological features and cell wall ultrastucture. Microfossils from the Cambrian-Ordovician of China are studied to reveal the wall ultrastructure of vegetative cells and dormant/reproductive cysts, the structural complexity of early eukaryotic cytoskeleton, and to recognize by morphological and ultrastructural means the relationships between various phenotypes. Acritarchs are considered to be preservable cysts of unicellular algae. The new discovery of the entire organism consisting of vegetative envelope and internal cyst shows that some taxa indeed represent the dormant/reproductive cysts whereas other may represent vegetative cells in their complex life cycle. Formation of the cyst, the excystment structure (pylome) and change of the generations (sexual and asexual) in the life cycle of unicellular microbiota may shed light on the development of the early adaptations to survive ecological crises events and as a competitive advantage in increasingly complex marine ecosystems.
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| 15. |
- 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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| 16. |
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| 17. |
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| 18. |
- Peel, John Stuart, et al.
(författare)
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Cavity-dwelling microorganisms from the Ediacaran and Cambrian of North Greenland (Laurentia)
- 2022
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Ingår i: Journal of Paleontology. - : Cambridge University Press. - 0022-3360 .- 1937-2337. ; 96:2, s. 243-255
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Tidskriftsartikel (refereegranskat)abstract
- Records of diagenetically mineralized, filamentous, cavity-dwelling microorganisms extend back to strata from the early Paleoproterozoic (2400 Ma). In North Greenland (Laurentia), they are first known from the Ediacaran (Neoproterozoic; ca. 600 Ma) Portfjeld Formation of southern Peary Land, in association with a biota similar to that of the Doushantuo Formation of China. The Portfjeld Formation cavity dwellers are compared with more widespread occurrences in Cambrian (Series 2, Stage 4, Miaolingian Series) strata from the same region in which assemblages in postmortal shelter structures within articulated acrotretoid brachiopods and other invertebrates are common. All specimens were recovered by digestion of carbonate samples in weak acids. The described fossils are preserved as mineral encrusted threads but this diagenetic phosphatization unfortunately obscures their biological identity.
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| 19. |
- Peel, John Stuart, et al.
(författare)
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THE BUEN FORMATION (CAMBRIAN SERIES 2) BIOTA OF NORTH GREENLAND
- 2018
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Ingår i: Papers in Palaeontology. - : WILEY. - 2056-2799 .- 2056-2802. ; 4:3, s. 381-432
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Tidskriftsartikel (refereegranskat)abstract
- The diverse metazoan fauna from the upper member of the Buen Formation of North Greenland is described as a complement to published descriptions of the exceptionally preserved fauna of the Sirius Passet Lagerstatte which occurs in the lowest beds of the formation. Considered together with organic-walled microfossils, which are absent from the Sirius Passet Lagerstatte on account of regional metamorphism, the fauna from the upper member provides an extended picture of the Buen Formation biota (Cambrian, Series 2, Stages 3-4; Montezuman-Dyeran of Laurentian usage). Although dominated numerically by specimens of the olenelline trilobites Limniphacos and Mesolenellus, the oldest assemblages (Montezuma-Dyeran boundary) from the upper member of the Buen Formation are characterized by a high diversity of hyoliths which often occur as partial associations of conch, operculum and helens in the dark mudstones; hyoliths are rare in the Sirius Passet Lagerstatte. Sponges are rare in the upper Buen Formation but diverse at Sirius Passet. Unlike the Sirius Passet Lagerstatte, fossil remains of non-mineralized metazoans with limbs and other details of internal anatomy do not occur in the upper Buen Formation, although organic tubes assigned to a new selkirkiid stem group priapulid (Sullulika) are common. New taxa: Alutella siku sp. nov., Sullulika broenlundi gen. et sp. nov., Nevadotheca boerglumensis sp. nov., Kalaallitia myliuserichseni gen. et sp. nov., Nasaaraqia hyptiotheciformis gen. et sp. nov., Trapezovitus malinkyi sp. nov., Decoritheca? hageni sp. nov.
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| 20. |
- Peel, John Stuart, et al.
(författare)
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The oldest hyolithids (Cambrian Series 2, Montezuman Stage) from the Iapetan margin of Laurentia
- 2020
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Ingår i: Journal of Paleontology. - : CAMBRIDGE UNIV PRESS. - 0022-3360 .- 1937-2337. ; 94:4, s. 616-623
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Tidskriftsartikel (refereegranskat)abstract
- The recent description of the nevadioid trilobiteBuenellus chilhoweensisWebster and Hageman,2018established the presence of early Cambrian Montezuman Stage (Cambrian Series 2, Stage 3) faunas in the Murray Shale of Chilhowee Mountain, Tennessee. The description recognized the oldest known age-diagnostic Cambrian trilobite from the Laurentian margin of the former Iapetus Ocean sinceBuenellusBlaker, 1988 is known otherwise only from the Sirius Passet Lagerstatte on the Innuitian margin of North Greenland. The bivalved arthropodsIsoxys chilhoweanusWalcott,1890andIndota tennesseensis(Resser,1938a) have also been described from the Murray Shale, but hyolithids appear to be the dominant body fossils in terms of diversity and abundance. Although poorly preserved, the hyolithids occurring together withBuenellus chilhoweensisare described to improve understanding of the Murray Shale biota. The hyolith assemblages of the Murray Shale and Sirius Passet Lagerstatte are not closely similar, although the poor preservation of both hinders comparison.
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| 21. |
- Peel, John Stuart, et al.
(författare)
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Unusual preservation of an Ordovician (Floian) arthropod from Peary Land, North Greenland (Laurentia)
- 2020
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Ingår i: Palaeontologische Zeitschrift. - : Springer Science and Business Media LLC. - 0031-0220 .- 1867-6812. ; 94:1, s. 41-51
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Tidskriftsartikel (refereegranskat)abstract
- Preservation of a fragment of an arthropod from starved trough sediments of the Bøggild Fjord Formation (Ordovician, Floian) of Johannes V. Jensen Land in north Peary Land, North Greenland, recalls that of the lower Cambrian Sirius Passet Lagerstätte of extreme north-west Peary Land and may suggest a second locality for exceptional preservation in North Greenland. A prominent petaloid pattern on the tergopleurae reflects impression onto the internal mould of terrace lines from the cuticle exterior. The arthropod is associated with poorly preserved sponges and a depauperate assemblage of organic-walled microfossils. It is tentatively compared to Mollisonia, originally described from the Burgess Shale Lagerstätte (middle Cambrian, Miaolingian Series) of Canada.
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| 22. |
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| 23. |
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| 24. |
- Slater, Ben, 1987-, et al.
(författare)
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Early Cambrian small carbonaceous fossils (SCFs) from an impact crater in western Finland
- 2019
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Ingår i: Lethaia. - : Scandinavian University Press / Universitetsforlaget AS. - 0024-1164 .- 1502-3931. ; 52:4, s. 570-582
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Tidskriftsartikel (refereegranskat)abstract
- We describe an assemblage of small carbonaceous fossils (SCFs) and acritarchs from cored siltstones of the Lappajärvi impact structure, west‐central Finland. Previous studies had detected a depauperate acritarch biota ascribed to a deep Proterozoic origin—this age, however, was based on recovery of long‐ranging poorly age‐diagnostic sphaeromorphs. To resolve the age and provenance of these crater sediments, we applied low‐manipulation processing techniques optimized for retrieval of larger organic‐walled microfossils. Our study revealed a previously undetected assemblage containing numerous metazoan SCFs consisting of flattened ‘protoconodonts’ (grasping spines assignable to total group Chaetognatha) and a distinctive fossilised chaeta, possibly representing the oldest known annelid remains. Phylogenetically problematic fossils include various acritarchs (large Leiosphaeridia sp., Tasmanites tenellus, smaller sphaeromorphs, Synsphaeridium, Archaeodiscina and Granomarginata) and filamentous forms (Palaeolyngbya‐ and Rugosoopsis‐like filaments, Siphonophycus), likely representing prokaryotic or protistan grades of organisation. As well as adding new diversity to an emerging SCFs record, these data substantially refine the age of these sediments by more than half a billion years, to an early Cambrian Terreneuvian age. More specifically, the assemblage is equivalent to that of the Lontova Formation from the Baltic States and northwest Russia, but is previously unreported from Finland. Identification of Lontova‐type SCFs/organic‐walled microfossils at Lappajärvi further constrains the poorly resolved extent of maximum flooding during the early Cambrian in Baltica. Renewed attention should be directed to strata that have thus far produced only biostratigraphically long‐ranging or ambiguous palynological assemblages—‘SCF‐style’ processing can reveal hitherto undetected, age‐informative microfossils that are otherwise selectively removed in conventional palynological studies.
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| 25. |
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| 26. |
- Slater, Ben, 1987-, et al.
(författare)
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Widespread preservation of small carbonaceous fossils (SCFs) in the early Cambrian of North Greenland
- 2018
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Ingår i: Geology. - 0091-7613 .- 1943-2682. ; 46:2, s. 107-110
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Tidskriftsartikel (refereegranskat)abstract
- The early Cambrian (ca. 518 Ma) Sirius Passet Lagerstätte of North Greenland is one of the most celebrated sites bearing fossils of soft-bodied organisms, and provides key insights into the Cambrian explosion of animal life. Unlike the younger Burgess Shale (508 Ma), the Sirius Passet biota does not preserve original carbonaceous material because of its history of metamorphic heating. Nearby sediments from within the same formation, however, have escaped the worst effects of thermal alteration. We report an entirely new diversity of metazoan remains preserved in a Burgess Shale–type fashion from sediments throughout the Buen Formation, in the form of small carbonaceous fossils (SCFs). The assemblages include the oldest known pterobranch hemichordates, diverse cuticular spines of scalidophoran worms, demineralized trilobite cuticle, bivalved arthropods (Spinospitella-like and Isoxys-like forms), protoconodonts, and a variety of less phylogenetically constrained metazoan and protistan forms. Together these SCFs capture exceptional microanatomical details of early Cambrian metazoans and offer new insights into taphonomic pathways at Sirius Passet and the nature of Burgess Shale–type preservation.
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| 27. |
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| 28. |
- Wallet, Elise, 1995-, et al.
(författare)
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Morphometric analysis of Skiagia-plexus acritarchs from the early Cambrian of North Greenland : toward a meaningful evaluation of phenotypic plasticity.
- 2022
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Ingår i: Paleobiology. - : Cambridge University Press. - 0094-8373 .- 1938-5331. ; 48:4, s. 576-600
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Tidskriftsartikel (refereegranskat)abstract
- The Cambrian evolutionary radiations are marked by spectacular biotic turnovers and the establishment of increasingly tiered food chains. At the base of these food chains are primary producers, which in the Cambrian fossil record are chiefly represented among organic-walled microfossils. The majority of these microfossil remains have traditionally been attributed to an informal category of incertae sedis called “acritarchs,” based entirely on form taxonomy. Acritarch form taxa have been intensely used for biostratigraphy and in large-scale studies of phytoplankton diversity. However, both prospects have been challenged by cases of taxonomic inconsistencies and oversplitting arising from the large phenotypic plasticity seen among these microfossils. The acritarch form genus Skiagia stands as an ideal case study to explore these taxonomic challenges, because it encompasses a number of form species widely used in lower Cambrian biostratigraphy. Moreover, subtle morphological differences among Skiagia species were suggested to underlie key evolutionary innovations toward complex reproductive strategies. Here we apply a multivariate morphometric approach to investigate the morphological variation of Skiagia-plexus acritarchs using an assemblage sourced from the Buen Formation (Cambrian Series 2, Stages 3–4) of North Greenland. Our analysis showed that the species-level classification of Skiagia discretizes a continuous spectrum of morphologies. While these findings bring important taxonomic and biostratigraphic hurdles to light, the unequal frequency distribution of life cycle stages among Skiagia species suggests that certain elements of phytoplankton paleobiology are nonetheless captured by Skiagia form taxonomy. These results demonstrate the value of using morphometric tools to explore acritarch phenotypic plasticity and its potential ontogenetic and paleoecological drivers in Cambrian ecosystems.
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| 29. |
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| 30. |
- Wallet, Elise, 1995-, et al.
(författare)
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Organic-walled microfossils from the lower Cambrian of North Greenland : a reappraisal of diversity
- 2023
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Ingår i: Palynology. - : Taylor & Francis. - 0191-6122 .- 1558-9188. ; 47:4
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Tidskriftsartikel (refereegranskat)abstract
- The early Cambrian Buen Formation (North Greenland) hosts an exceptionally rich fossil biota that has contributed significantly to our knowledge of early metazoans, yet the fossil remains of primary producers from this deposit have received less attention. Here we examine the palynological component of the Buen Formation, with a focus on acritarchs and filamentous microfossils. Our analysis revealed the presence of 49 form taxa, 15 of which are described for the first time in the Buen Formation. These include large elements of presumably benthic origin, together with cyst-like acritarchs. Comasphaeridium longispinosum Vidal 1993 is renamed Comasphaeridium? brillesensis nom. nov., and Comasphaeridium densispinosum Vidal 1993 is reassigned to a new genus, Pearisphaeridium, becoming Pearisphaeridium densispinosum comb. nov. The diagnoses of Pearisphaeridium densispinosum (Vidal 1993) comb. nov. and Skiagia pura Moczydlowska 1988 are emended. Further, careful analysis of disparity in the recovered assemblage has revealed the presence of numerous transitional morphologies among the recorded acritarch form taxa. Though some of these transitional forms likely represent biologically meaningful entities (e.g. life cycle stages, ecophenotypes), others appear to have been artificially generated by taphonomic processes. Accounting for taphonomic factors and other sources of morphological variation has curtailed diversity down to 30 acritarch morphotypes, ten of which represent distinct abundance peaks broadly corresponding to acritarch genera. This analysis illustrates how population-based studies of early Cambrian acritarchs can help to discern the different factors that impinge on acritarch morphology, detect instances of taxonomic inflation, and refine our measures of diversity at the base of early Palaeozoic food webs.
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| 31. |
- Wallet, Elise, 1995-, et al.
(författare)
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Small carbonaceous fossils (SCFs) from North Greenland : new light on metazoan diversity in early Cambrian shelf environments
- 2021
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Ingår i: Papers in Palaeontology. - : Wiley. - 2056-2799 .- 2056-2802. ; 7:3, s. 1403-1433
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Tidskriftsartikel (refereegranskat)abstract
- The Sirius Passet Lagerstätte of North Greenland is one of the oldest records of soft-bodied metazoan-dominated ecosystems from the early Cambrian. The Lagerstätte site itself is restricted to just a single c.a. 1-km-long outcrop located offshore from the shelf margin, in an area affected by metamorphic alteration during the Ellesmerian Orogeny (Devonian–Early Carboniferous). The recent recovery of small carbonaceous fossils (SCFs) to the south, in areas that escaped the effects of this deformation, has substantially expanded the known coverage of organic preservation into shallower water depositional settings in this region. Here, we describe additional SCF assemblages from the siliciclastic shelf succession of the Buen Formation (Cambrian Series 2, stages 3–4; c.a. 515 Ma), expanding the previously documented SCF biota. Newly recovered material indicates a rich diversity of non-mineralizing metazoans, chiefly represented by arthropod remains. These include the filtering and grinding elements of a sophisticated crustacean feeding apparatus (the oldest crustacean remains reported to date), alongside an assortment of bradoriid sclerites, including almost complete, 3D valves, which tie together a number of SCFs previously found in isolation. Other metazoan remains include various trilobite cuticles, diverse scalidophoran sclerites, and a range of metazoan fragments of uncertain affinity. This shallower water assemblage differs substantially from the Sirius Passet biota, which is dominated by problematic euarthropod stem-group members and sponges. Although some of these discrepancies are attributable to taphonomic or temporal factors, these lateral variations in taxonomic composition also point to significant palaeoenvironmental and/or palaeoecological controls on early Cambrian metazoan communities.
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| 32. |
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| 33. |
- Wallet, Elise, 1995-
(författare)
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Unlocking the hidden diversity of organic-walled microfossils from the early Cambrian of North Greenland
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The early Cambrian Buen Formation of North Greenland is celebrated for hosting one of the oldest Cambrian Burgess Shale-type deposits known to date – the Sirius Passet Lagerstätte. Further south in a shallower shelf facies belt, the Buen Formation yielded organic-walled microfossils (OWMs) that were originally described with a focus on acritarchs. Later sampling revealed a diversity of small carbonaceous fossils (SCFs) of metazoan origin. This PhD thesis investigates the diversity of OWMs from the Buen Formation using a novel combination of approaches. First, new samples are processed using a gentle acid maceration protocol designed for the recovery of large, delicate elements. Second, a population-based analysis of disparity is conducted to evaluate acritarch diversity, and illuminate the poorly known palaeobiology of these microfossils. New sampling revealed a remarkable diversity of metazoan fragments, including the oldest-known crustacean feeding apparatus, almost complete bradoriid valves preserved in three dimensions, new types of scalidophoran teeth and scalids, and a wide range of cuticular elements of uncertain affinity. Further, an abundance of large and/or asymmetrical acritarchs and filamentous microfossils was recovered, contributing to a rare but expanding record of benthic Proterozoic-like forms among Cambrian OWMs. The recovered diversity of acritarchs and filamentous microfossils totals 50 form taxa, of which 19 are described for the first time in the region. Quantitative and semi-quantitative analyses of acritarch disparity suggest a substantial proportion of these form taxa represent taphomorphs and/or arbitrary portions of abundance peaks. Placing form species in the context of their wider morphological variations allows the recorded diversity to be pared down to 30 morphotypes. On this basis, the presumed life history of Skiagia-plexus acritarchs is updated following quantitative analysis of openings, inner bodies, and clustering patterns in the recovered population. Three additional morphotypes are interpreted as bloom-forming and/or colonial species. Collectively, the results of this PhD project demonstrate that a fundamentally different picture of Cambrian diversity emerges when the full spectrum of OWM size ranges and disparity is considered. Applying these methods to the wider Cambrian record clearly shows potential to refine our understanding of macroevolution and palaeoecology as modern ecosystems were being established.
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| 34. |
- Willman, Sebastian
(författare)
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A PRECAMBRIAN EXPLOSION?
- 2005
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The well-known Cambrian explosion was an evolutionary event that lacks counterparts in Earth history. The appearance of shelly organisms easily preserved as fossils illustrates an exceptional record of diversifying organisms. It is established that this was a true biological diversification but was it the first one? The Cambrian was preceded by the Neoproterozoic, a period that was characterised by severe environmental turbulence during its terminal interval (Ediacaran). At least two global glaciations between ca. 700-580 Ma might have acted as evolutionary bottlenecks that led to a rapid diversification of several lineages of single-celled and, eventually, multicellular organisms. The appearance of more than 50 ornamented acritarchs (Grey et al., 2003) in the Ediacaran of present day southern Australia suggests a possible Precambrian evolutionary explosion. Acritarchs, being primary producers, may have had a profound effect on the evolution of metazoans resulting, among other factors, in the Cambrian explosion. The apparent diversification event requires studies of more material but will hopefully result in either recognition of a Precambrian explosion hypothesis or simply a normal, gradual development of phytoplankton.The diversification of acritarchs provides an excellent potential for these organisms to be used in biostratigraphy. The Ediacaran System’s lower boundary is defined at the base of glacial deposits from the last major glaciation, the Marinoan glaciation, and the upper boundary at the base of the Cambrian System. The Ediacaran System is not very well known and in terms of fossil studies it is just in its infancy. Palynomorph assemblages containing mainly eukaryotic acritarchs and prokaryotic bacteria were recovered from numerous drillholes located in southern Australia. Preliminary studies of a large number of acritarch samples from more than 30 drillcores (Grey, 2005) have resulted in a subdivision of the middle Ediacaran into biozones based on the first appearance of index species and characteristic assemblages. Additional studies of drillcores from the Officer Basin in Australia will aid in the correlation between different basins in Australia and hopefully also in global correlation. The studies of the Murnaroo 1 succession indicate a consistency with the previously examined boreholes and allow more accurate recognition of the acritarch biozones.Grey, K., Walter, M.R. & Calver C.R., 2003. Neoproterozoic biotic diversification: Snowball Earth or aftermath of the Acraman impact? Geology, v. 31.Grey, K., 2005, in press. Ediacaran Palynology of Australia. Australasian Association of Palaeontologists, Memoirs, v. 31.
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| 35. |
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| 36. |
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| 37. |
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| 38. |
- Willman, Sebastian, et al.
(författare)
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Acritarchs in the Ediacaran of Australia — Local or global significance? : Evidence from the Lake Maurice West 1 drillcore
- 2011
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Ingår i: Review of Palaeobotany and Palynology. - : Elsevier BV. - 0034-6667 .- 1879-0615. ; 1-2:166, s. 12-28
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Tidskriftsartikel (refereegranskat)abstract
- The Lake Maurice West 1 drillhole is located in the Officer Basin in South Australia and penetrates a siliciclastic rock succession of Ediacaran age (ca 635–542 Ma). Within this succession well-preserved organic-walled microfossils called acritarchs have been recovered from the Dey Dey Mudstone and Karlaya Limestone, which constitutes a major part of the Ungoolya Group. The assemblage consists of biostratigraphically useful acanthomorphic acritarchs in addition to a diverse assemblage of unornamented leiospheres, filamentous microbiota and some undetermined taxa. Here we describe eight acanthomorphic taxa belonging to three distinctive Ediacaran genera (Cavaspina, Ceratosphaeridium and Tanarium), of which one is described as a new species (Cavaspina amplitudinis sp. nov.). Similar acanthomorphic assemblages are known from Ediacaran strata worldwide and biostratigraphic subdivision of the system based on the occurrence of cosmopolitan taxa is possible in Australia, China, Siberia and Baltica (East European Platform), and perhaps in other areas. The Lake Maurice West 1 microfossil assemblage adds to the growing record of the Ediacaran acritarchs and supports a biostratigraphic scheme for the Ediacaran System at a global scale.
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| 39. |
- Willman, Sebastian, et al.
(författare)
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Acritarchs in the Ediacaran seas
- 2005
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Ingår i: The Palaeontological Association. ; , s. 64-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The terminal Neoproterozoic radiation of planktonic photosynthetic microbiota (acritarchs) is one of the most significant evolutionary events of the time, including diversification of prokaryotic cyanobacteria and eukaryotic green and brown algae, the appearance of thecoamoebaens and subsequently metazoans (the Ediacara fauna). The Ediacaran radiation of phytoplankton is recognizable by the first appearance of more than fifty new species of large ornamented acritarchs in a short interval of time at ca. 570 Ma. This radiation event occurred after the Snowball Earth conditions returned to a kind of "normal" environmental stasis, and it may be interpreted as a recovery diversification of phytoplankton after a major biotic extinction caused by the global glaciation.The appearance of numerous, morphologically innovative and large acritarch taxa may also be connected with the Acraman impact event in South Australia, suggested recently by Grey et al. (2003), as a biotic recovery after the catastrophic environmental disturbance caused by the giant bolide. The latter hypothesis has to be tested, however, because a few individual taxa of ornamented acritarchs may have actually appeared below the ejecta layer, which is difficult to recognize with certainty in some borehole successions.The Ediacaran acritarch records are from Australia (the Officer and Amadeus Basins), China and Siberia, showing a worldwide distribution in a relatively short interval of time (ca. 20 Ma; Grey, 2004, in press). The greatest taxonomic diversity is known from Australia (ibidem), and the present study is focused on the investigation of Ediacaran microbiota in greater detail and from different stratigraphic levels, their palaeobiology and affinities, mode of life and reproduction cycle. The new assemblage of organic-walled microfossils from the Murnaroo 1 borehole comprises filamentous cyanobacteria, and ornamented and spheroidal acritarchs.The Ediacaran successions in Australia have been well documented in terms of lithostratigraphy, depositional settings and structural geology. The sedimentation proceeded in two different depositional regimes, recognized today in a series of sub-basins. One of them is the Officer Basin, comprised of complex intracratonic, east-west trending troughs and sub-basins extending from Western Australia to South Australia. The studied Murnaroo 1 borehole is also located there. The sediments accumulated in tidal, sub- and intertidal shelf conditions, and the predominantly mudstone lithology from which the samples were collected, is ideal for palynological processing and preservation of microfossils. The lack of macrofossils in the successions rendered efforts and advances in acritarch biostratigraphy since the 1980's, which helped to reveal a complex history of the Officer Basin. The discovery of two distinct palynofloras, an older leiosphere-dominated flora (ELP) and a younger acanthomorph-dominated flora (ECAP), is suggested to be largely environmentally independent (Grey, 2004, in press) in terms of the observed lithology and sedimentological sequences. However, the possible coupling between the Marinoan glaciation, the Acraman impact and the radical change in the palynofloras was inferred (ibidem) and this will be examined with the new data available from the Murnaroo 1 borehole. Previously, the Murnaroo succession was only studied preliminarily.In my communication, I will discuss the stratigraphic sequence of appearances of various species and their relationship to the environmental conditions, the Acraman impact event and the changes associated with the global glaciations.GREY, K., WALTER, M.R. and CALVER, C.R. (2003) Neoproterozoic biotic diversification: "Snowball Earth" or aftermath of the Acraman impact? Geology 31, p. 459-462.GREY, K., (2004, in press) Ediacarian Palynology of Australia. Australasian Association of Palaeontologists, Memoirs.
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| 40. |
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| 41. |
- Willman, Sebastian
(författare)
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Can acritarchs be used for Ediacaran suddivision?
- 2008
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Ingår i: Geology and hydrocarbon potential of the Neoproterozoic-Cambrian Basins in India, Pakistan and the Middle East. ; , s. 19-21
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Konferensbidrag (refereegranskat)abstract
- can acritarchs be used for ediacaran subdivison? Willman, Sebastian Uppsala University, Department of Earth Sciences, Palaeobiology, Villavägen 16, SE-752 36 Uppsala, Sweden. Email: Sebastian.Willman@geo.uu.se The fossil record of the three billion years before the Cambrian is patchy, but shows that early organisms had adapted to a variety of environments and that many major evolutionary innovations such as multicellularity, sexual reproduction and tissue formation occurred early in life history. The fossil record of the earliest prokaryotes is debated (e.g., Schopf, 1993; Brasier et al., 2002) but that of eukaryotic protists is better understood, although by no means well established. Protists and problematic biotas of limited diversity, including e.g., Grypania, are present between 2.5 and 1.5 Ga. Younger rock successions between 1.5 Ga and 750 Ma in age include more morphologically complex fossils such as Chuaria and Tawuia as well as the possible red algae Bangiomorpha (Knoll et al., 2006 gives an up to date summary of Proterozoic eukaryotes). However, it is not until the Ediacaran that organisms of undoubtedly metazoan affinities first appear (e.g., Narbonne, 2005). The Ediacaran biota remains largely problematic and even though the fossils are spread globally their distribution is uneven. Conversely, organic-walled microfossils referred to as acritarchs are commonly recorded throughout Meso- and Neoproterozoic rock successions worldwide. The Neoproterozoic was a time of major environmental change. At least two, possibly three, and even four global glaciations have been suggested to cover the entire Earth with thick ice during the Cryogenian Period (e.g., Hoffman et al., 1998). Following the last glaciation, the Marinoan glaciation, greenhouse conditions prevailed during the Ediacaran and caused major shifts in ocean geochemistry, oceanic stratification and oxygenation, and evolution of the marine biosphere (Kirschvink, 1992; Canfield, 1998; Shields et al., 1998; Grey, 2005; Fike et al., 2006; Canfield et al., 2007). It was during the Ediacaran that the first major diversification of organic-walled acritarchs occurred. This diversification is preserved in rock successions worldwide, including Siberia, China, Baltica, India and, especially, in the Centralian Superbasin in Australia. Grey et al. (2003) noted that the first appearance of acanthomorphic (ornamented) acritarchs in samples from drillcores in the Officer and Amadeus Basins and the Adelaide Rift Complex, occurred stratigraphically above a bolide ejecta layer, the result of a large impact some 580 Ma years ago (the Acraman impact; Walter et al., 2000). A problem in Neoproterozoic subdivision has been the lack of biostratigraphic control (Knoll & Walter, 1992), and although Neoproterozoic biostratigraphy is increasingly well-understood it is still a highly debated theme. As a result, anything and everything that can aid in the correlation of Ediacaran successions is especially sought after. The tools for correlation of the Neoproterozoic currently at hand include chemostratigraphy, sedimentology, event stratigraphy (impacts, glacial episodes, volcanic eruptions and the alike), magnetostratigraphy, and the subject of this presentation: Ediacaran biostratigraphy. The Officer Basin in South Australia is an intracratonic basin that extends some 1400 km in an east-west trend across Western and South Australia. Stratigraphic correlation of the Officer Basin has been based mainly on seismic, magnetic, and gravity studies but was recently reviewed by Grey (2005). The succession studied here (and in Grey, 2005) is the largely siliciclastic lower Ungoolya Group which, in ascending stratigraphic order, consists of the Dey Dey Mudstone, the Karlaya Limestone, and the Tanana Formation. The Dey Dey Mudstone is divided into two units separated by a bed of dolomitic intraclasts; the lower unit is mainly red-brown and occasionally green-grey silty mudstone that was deposited in a fluvial environment and the upper unit is a laminated dolomitic or calcareous siltstone and mudstone deposited in slightly deeper, prodelta and shelf environments (Zang, 1995; Morton, 1997). The Karlaya Limestone consists mainly of thin-bedded micritic limestone with dark grey silty mudstone layers and some limestone intraclasts, deposited on a subtidal shelf, probably below fair-weather wave base (Zang, 1995). The Tanana Formation overlies the Karlaya Limestone and consists of micritic limestone with silty mudstone interbeds deposited in a prodelta and distal delta front to shelf settings (Morton, 1997). Microfossils were collected from unevenly sampled intervals in the Giles 1, Murnaroo 1, Lake Maurice West 1, WWD 1, Observatory Hill 1, and Munta 1 drillcores. Samples were selected from lithologies that are suitable for palynological preservation (i.e., unoxidized mudstones, shales, and carbonaceous rocks) and collected from both sides of the Acraman impact ejecta layer. The microfossils are permanently fixed in strew mounts and were observed under transmitted light, and documented using a digital camera. The results of micropalaeontological studies provide further evidence for the acritarch diversification that was so typical for parts of the Ediacaran. Many of the acritarch taxa are stratigraphically constrained and the patterns observed in various drillholes match the patterns first reported by Grey (2005). The new palynological record further supports and enhances the subdivision and stratigraphic correlation of the Ediacaran System in Australia and potentially on a more interregional scale. Acritarchs are well-preserved and diverse, change over short stratigraphic intervals, and allow the recognition of the previously established zones by use of certain acanthomorphic species. The presence of common species and taxonomic similarities between entire assemblages from Australia, Siberia, Baltica, South China and India provide a means for global correlation of the Ediacaran System using palynology. Portions of the Ediacaran System can be confidently proved to be coeval by the occurrence of discrete species distributed across various palaeocontinents and ranging stratigraphically no longer than a few million years. This suggests that they can be used for biostratigraphic analysis and correlation because other fossils are too scarce, too geographically restricted, or too difficult to interpret. Keywords: Ediacaran, Neoproterozoic, Officer Basin, Australia, acritarchs, biostratigraphy References Brasier, M.D., Green, O.R., Jephcoat, A.P., Kleppe, A.K., Van Kranendonk, M.J., Lindsay, J.F., Steele, A., Grassineau, N.V., 2005. Questioning the evidence for Earth's oldest fossils. Nature 416, 76-81. Canfield, D.E., 1998. A new model for Proterozoic ocean chemistry. Nature 396, 450-453. Canfield, D.E., Poulton, S.W., Narbonne, G.M., 2007. Late-Neoproterozoic deep-ocean oxygenation and the rise of animal life. Science 315, 92-95. Fike, D.A., Grotzinger, J.P., Pratt, L.M., Summons, R.E., 2006. Oxidation of the Ediacaran Ocean. Nature 444, 744-747. Grey, K., 2005. Ediacaran Palynology of Australia. Australasian Association of Palaeontologists Memoir 31, 1-439. Grey, K., Walter, M.R., Calver C.R., 2003. Neoproterozoic biotic diversification: Snowball Earth or aftermath of the Acraman impact? Geology 31, 459-462. Hoffman, P.F., Kaufman, A.J., Halverson, G.P., Schrag, D.P., 1998. A Neoproterozoic Snowball Earth. Science 281, 1342-1346. Kirschvink, J.L., 1992. Late Proterozoic low-latitude global-glaciation: the Snowball Earth. In: Achopf, J.W., Klein, C. (Eds.), The Proterozoic biosphere. Cambridge University Press, 51-52. Knoll, A.H., Javaux, E.J., Hewitt, D., Cohen, P., 2006. Eukaryotic organisms in Proterozoic oceans. Philosophical Transactions of the Royal Society B 361, 1023-1038. Morton, J.G.G., 1997. Chapter 6: Lithostratigraphy and environments of deposition. In: Morton, J.G.G., Drexel, J.F. (Eds.), Petroleum Geology of South Australia, Vol. 3: Officer Basin. South Australia, Department of Mines and Energy Resources Report Book 19, 47-86. Narbonne, G.M., 2005. The Ediacara biota: Neoproterozoic origin of animals and their ecosystems. Annual Review of Earth and Planetary Sciences 33, 421-442. Schopf, J.W., 1993. Microfossils of the Early Archean Apex chert: new evidence of the antiquity of life. Science 260, 640-646. Shields, G.A., Stille, P., Brasier, M.D., Atudorei, V., 1998. Ocean stratification and oxygenation of the Late Precambrian environment: a post-glacial geochemical record from a Neoproterozoic section in W. Mongolia. Terra Nova 9, 218-222. Walter, M.R., Veevers, J.J., Calver, C.R., Gorjan, P., Hill, A.C., 2000. Dating the 840–544 Ma Neoproterozoic interval by isotopes of strontium, carbon, and sulfur in seawater, and some interpretative models. Precambrian Research 100, 371-433. Willman, S., Moczydłowska, M., Grey, K., 2006. Neoproterozoic (Ediacaran) diversification of acritarchs – A new record from the Murnaroo 1 drillcore, eastern Officer Basin, Australia. Review of Palaeobotany and Palynology 139, 17-39. Zang, W-L., 1995b. Neoproterozoic depositional sequences and tectonics, eastern Officer Basin, South Australia. South Australia. Department of Mines and Energy. Report Book, 1-21.
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- Willman, Sebastian, et al.
(författare)
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Ediacaran acritarch biota from the Giles 1 drillhole, Officer Basin, Australia, and its potential for biostratigraphic correlation
- 2008
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 162:3-4, s. 498-530
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Forskningsöversikt (refereegranskat)abstract
- The remarkable diversification of single-celled photosynthesising biota of algal and other as yet unknown affinities (acritarchs), followed by the diversification of metazoans, occurred during the Ediacaran Period, which is marked by extreme climatic and environmental changes. Here we describe a taxonomically diverse acritarch association from the Ediacaran part of the Giles 1 drillcore in the Officer Basin, South Australia, which documents further the Ediacaran phytoplankton radiation. The studied palynoflora comprises 21 known acritarch species belonging to 15 genera. One new monospecific genus is described (Calyxia xandaros sp. nov.) as well as one new species of Tanarium (Tanarium anozos sp. nov.). We also propose the genus Knollisphaeridium to replace the preoccupied genus Echinosphaeridium. Three stratigraphically successive assemblages that match previously observed patterns of acritarch replacement are distinguished. The present record is from slightly older strata than in previous records, thus extending the ranges of certain acanthomorphic species. The lower boundaries of three stratigraphically higher assemblage zones among the four formerly established zones, are identified by the occurrence of the index species Tanarium conoideum, Tanarium irregulare and Apodastoides verobturatus, respectively. The substantial morphological disparity of acritarchs in the Giles 1 succession suggests that they may represent a great diversity of microorganisms, not only as biological species but also representing perhaps vegetative and encysted stages in their life cycle. The reconstructed palaeogeographic distribution of several species between Australia, Siberia, Baltica (the East European Platform), and to South China, shows that acritarchs are suitable for both intra- and inter-regional correlation.
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- Willman, Sebastian, Docent, et al.
(författare)
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Ediacaran Doushantuo-type biota discovered in Laurentia
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- The Ediacaran period (635-541 Ma) was a time of major environmental change, accompanied by a transition from a microbial world to the animal world we know today. Multicellular, macroscopic organisms preserved as casts and molds in Ediacaran siliciclastic rocks are preserved worldwide and provide snapshots of early organismal, including animal, evolution. Remarkable evolutionary advances are also witnessed by diverse cellular and subcellular phosphatized microfossils described from the Doushantuo Formation in China, the only source showing a diversified assemblage of microfossils. Here, we greatly extend the known distribution of this Doushantuo-type biota in reporting an Ediacaran Lagerstätte from Laurentia (Portfjeld Formation, North Greenland), with phosphatized animal-like eggs, embryos, acritarchs, and cyanobacteria, the age of which is constrained by the Shuram-Wonoka anomaly (c. 570-560 Ma). The discovery of these Ediacaran phosphatized microfossils from outside East Asia extends the distribution of the remarkable biota to a second palaeocontinent in the other hemisphere of the Ediacaran world, considerably expanding our understanding of the temporal and environmental distribution of organisms immediately prior to the Cambrian explosion.
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| 46. |
- Willman, Sebastian, Docent, et al.
(författare)
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Late Ediacaran Microfossils from Finland
- 2021
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Ingår i: Geological Magazine. - : Cambridge University Press. - 0016-7568 .- 1469-5081. ; 158:12, s. 2231-2244
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Tidskriftsartikel (refereegranskat)abstract
- Here we present a detailed accounting of organic microfossils from late Ediacaran sediments of Finland, from the island of Hailuoto (northwest Finnish coast), and the Saarijärvi meteorite impact structure (~170 km northeast of Hailuoto, mainland Finland). Fossils were recovered from fine-grained thermally immature mudstones and siltstones and are preserved in exquisite detail. The majority of recovered forms are sourced from filamentous prokaryotic and protistan-grade organisms forming interwoven microbial mats. Flattened Nostoc-ball-like masses of bundled Siphonophycus filaments are abundant, alongside Rugosoopsis and Palaeolyngbya of probable cyanobacterial origin. Acritarchs include Chuaria, Leiosphaeridia, Symplassosphaeridium and Synsphaeridium. Significantly, rare spine-shaped sclerites of bilaterian origin were recovered, providing new evidence for a nascent bilaterian fauna in the terminal Ediacaran. These findings offer a direct body-fossil insight into Ediacaran mat-forming microbial communities, and demonstrate that alongside trace fossils, detection of a bilaterian fauna prior to the Cambrian might also be sought among the emerging record of small carbonaceous fossils (SCFs).
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| 49. |
- Willman, Sebastian, Docent
(författare)
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Morphology and wall ultrastructure of leiosphaeric and acanthomorphic acritarchs from the Ediacaran of Australia
- 2009
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Ingår i: Geobiology. - : Wiley. - 1472-4677 .- 1472-4669. ; 7:1, s. 8-20
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Tidskriftsartikel (refereegranskat)abstract
- Acritarchs are a group of organic-walled microfossils with unknown biological affinities. The wall ultrastructure of the unornamented, smooth Leiosphaeridia sp. and the acanthomorphic Gyalosphaeridium pulchrum from the Ediacaran Dey Dey Mudstone in the Officer Basin, South Australia, was studied by use of transmission and scanning electron microscopy, and transmitted light microscopy. The study of the ultrastructure reveals a complexity in the cell wall not seen in prokaryotes. Wall ultrastructures range from single-layered to three- or four-layered and from homogeneous to porous. Acritarchs with different wall ultrastructures may be different organisms, but may also reflect different stages in a life cycle. In this paper I review previous ultrastructure studies and discuss possible algal and metazoan affinities for the specimens studied herein.
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