| 1. |
- Arvestål, Emma, et al.
(författare)
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A new species of Cyrtograptus (Graptoloidea) from the Llandovery of Västergötland (Sweden)
- 2011
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Ingår i: The 2nd Wiman Meeting. - Uppsala. ; , s. 2-2
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Konferensbidrag (refereegranskat)abstract
- A new species of the genus Cyrtograptus from the late Llandovery of southern Sweden (Västergötland) is presented. The new species has been found near the top of Kinnekulle (Högkullen) in the Retiolites Shales, which are part of the lapworthi zone (late Telychian). Although it resembles the coeval C. lapworthi in appearance, a detailed comparison of the type material of C. lapworthi revealed distinct differences: the new species is more openly coiled in the proximal part, has a larger Two Thecae Repeat Distance (2TRD), and, most significantly, bears a second order cladium. Second order cladia are unknown from C. lapworthi. The new species is also compared with other species of Cyrtograptus that are characterized by second order cladia, such as the cotemporaneous C. laqueus and the slightly younger C. insectus (insectus zone; latest Telychian). However, C. laqueus differs from the new species in having a lower number of thecae separating the cladia, and also by the appearance of its proximal part, which forms a loop by crossing its own main stipe. C. insectus differs by having wider spaced cladia and a stronger coiled proximal part. Furthermore, the need of a redefinition of C. lapworthi is highlighted, due to the large morphological variations within this species.
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| 2. |
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| 3. |
- Arvestål, Emma, et al.
(författare)
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Cyrtograptids from the Telychian (upper Llandovery) of Kinnekulle Mountain, southern Sweden
- 2013
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 135:1, s. 45-56
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Tidskriftsartikel (refereegranskat)abstract
- The late Llandovery graptolite fauna of the Retiolites Shales on Kinnekulle Mountain in the province of Västergötland has long been known but never illustrated or studied in detail. New collections of graptolites from an interval at the very top of the exposed succession confirm previous reports of cyrtograptids, which make the shales on Kinnekulle the youngest preserved Palaeozoic rocks in the area. The co-occurrence of Oktavites spiralis and Cyrtograptus lapworthi constrains the strata to the lower lapworthi Biozone of the upper Telychian. The associated graptolite fauna comprises numerous monograptids and Retiolites angustidens as well as Cyrtograptus kinnekullensis n. sp., characterised by its open coiling and the presence of a second-order cladium on the second thecal cladium. This early occurrence of a cyrtograptid species with a second-order cladium on Baltica matches evolutionary patterns observed in Laurentia, suggesting that the ability to grow cladia of both first and higher order evolved approximately, synchronously and at the very beginning of cyrtograptid evolution.
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| 4. |
- Arvestål, Emma
(författare)
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Organic microfossils from the Ediacaran of Estonia—behind the scenes
- 2017
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Ingår i: <em>Abstract Volume, International Symposium on the Ediacaran-Cambrian transition, St. John’s</em>. ; , s. 9-9
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Konferensbidrag (refereegranskat)abstract
- When seeing a play, one easily gets caught by everything therein; the music, the dancing, and of course, the story. Still, most of the work took place before it even had its premiere. When the evolutionary curtain was lifted for most of the animals back in the beginning of the Cambrian, it had been preceded by many hundreds of millions of years of preparation. Still, as for any play, it was in the very last few moments that everything was coming together, that the scene became set. Hence, if we truly want to understand the events that was about to happen, we should peek behind the curtain before act one, into the Ediacaran Period and on its very busy little stage workers: the acritarchs. In order to better understand the dynamics of acritarch evolution at the Ediacaran-Cambrian transition two drill cores of allegedly Ediacaran age were studied. The drill cores had been taken in northern Estonia, and a total of 48 samples were prepared with the purpose of identifying the acritarchs and other organic microfossils using light microscopy. However, despite a relatively high taxonomic diversity, the recovered associations were strikingly different from other well-described Ediacaran acritarch faunas, most prominently by the absence of the large acanthomorphic acritarchs known from Australia, China and Siberia. Equally absent were the much smaller acanthomorphic acritarchs, characteristic of Cambrian sediments. Instead, a number of smooth-walled leiospheres was found to dominate the associations together with a variety of different types of filaments as well as unusually shaped fragments from yet unidentified organisms. It seems that the acritarchs were more than just stage workers: they had their own play going on, and this play appears to have been full of surprises.
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| 5. |
- 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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| 6. |
- Chi Fru, Ernest, et al.
(författare)
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Arsenic stress after the Proterozoic glaciations
- 2015
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Protection against arsenic damage in organisms positioned deep in the tree of life points to early evolutionary sensitization. Here, marine sedimentary records reveal a Proterozoic arsenic concentration patterned to glacial-interglacial ages. The low glacial and high interglacial sedimentary arsenic concentrations, suggest deteriorating habitable marine conditions may have coincided with atmospheric oxygen decline after ~2.1 billion years ago. A similar intensification of near continental margin sedimentary arsenic levels after the Cryogenian glaciations is also associated with amplified continental weathering. However, interpreted atmospheric oxygen increase at this time, suggests that the marine biosphere had widely adapted to the reorganization of global marine elemental cycles by glaciations. Such a glacially induced biogeochemical bridge would have produced physiologically robust communities that enabled increased oxygenation of the ocean-atmosphere system and the radiation of the complex Ediacaran-Cambrian life.
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| 7. |
- Chi Fru, Ernest, et al.
(författare)
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Proterozoic arsenic dynamics controlled by glaciations
- 2015
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Ingår i: Abstracts of the 25<sup>th</sup>Goldschmidt Conference, Prague. ; , s. 537-537
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Konferensbidrag (refereegranskat)abstract
- Increased chemical weathering of trace elements from land to ocean after the Great Oxidation Event is often correlated to biological stimulation near the ocean margins. However, life had to develop strategies to combat the sudden bioavailability of a range of toxic/redox-sensitive elements that became widely accessible because of the GOE. Here, sedimentary As marine records reveal a cyclic Proterozoic arsenic concentration pattern influenced by glacial-interglacial cycles. Postglacial sedimentary arsenic concentrations suggest deterioration of habitable marine conditions may have coincided with atmospheric oxygen decline after ~2.1 billion years ago (Ga). This changed after ~0.58 Ga when marine biota developed widespread stress responses against postglacial reorganization of global marine elemental cycles, producing physiologically robust communities that enabled increased oxygenation of the atmosphere-ocean system and radiation of complex life.
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