| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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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| 11. |
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| 12. |
- 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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| 13. |
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| 14. |
- 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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| 15. |
- 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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| 16. |
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| 17. |
- 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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| 18. |
- 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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| 19. |
- 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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| 20. |
- 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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| 21. |
- Willman, Sebastian, Docent
(författare)
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The Ediacaran Diversification of Organic-walled Microbiota : Ocean Life 600 Million Years Ago
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The only direct evidence of past life is provided by fossils. Fossils tell us about the evolution of life on Earth and they give us clues concerning ancient environments. The Ediacaran Period (roughly 635-542 million years ago) is characterised by the appearance and diversification of various microbiota and also the diversification of metazoans. Well-preserved organic-walled microfossils referred to as acritarchs occur abundantly in Ediacaran sedimentary successions in the Officer Basin in South Australia. Acritarch assemblages from the Giles 1 and Murnaroo 1 drillcores show a wide morphological disparity and are taxonomically diverse. Assemblages change over short stratigraphic intervals which enables the recognition of different biozones. The presence of taxa common between Australia, Siberia, Baltica and China provides a means for global correlation of the Ediacaran System. Examination of the wall ultrastructure of several acritarch specimens by use of transmission electron microscopy reveals a complexity in the cell wall that is not seen in prokaryotes but is indicative in some cases of particular clades of microalgae. Wall ultrastructures range from single-layered to three- and four-layered and from homogeneous to porous. The wall ultrastructure can be used to assess biological affinities and the affinities of the studied taxa in relation to green algae, dinoflagellates and metazoans are discussed. However, before taxonomic interpretations can be made with confidence, an understanding of taphonomic degradation of microorganisms is required. With focus on illustrated specimens, one part of this thesis explains what happens to an acritarch as it undergoes various types of degradation and why an understanding of these processes is important for taxonomic identification. A meteorite impact in South Australia spread an ejecta layer over a 550 km radius area. This ejecta layer is recognised in subsurface drillcores and provides an independent stratigraphic marker horizon that supports an acritarch-based correlation.
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