| 1. |
- Davies, Thomas G., et al.
(författare)
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Open data and digital morphology.
- 2017
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 284:1852, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Over the past two decades, the development of methods for visualizing and analysing specimens digitally, in three and even four dimensions, has transformed the study of living and fossil organisms. However, the initial promise that the widespread application of such methods would facilitate access to the underlying digital data has not been fully achieved. The underlying datasets for many published studies are not readily or freely available, introducing a barrier to verification and reproducibility, and the reuse of data. There is no current agreement or policy on the amount and type of data that should be made available alongside studies that use, and in some cases are wholly reliant on, digital morphology. Here, we propose a set of recommendations for minimum standards and additional best practice for three-dimensional digital data publication, and review the issues around data storage, management and accessibility.
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| 2. |
- Cunningham, J. A., et al.
(författare)
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Experimental taphonomy of giant sulphur bacteria: implications for the interpretation of the embryo-like Ediacaran Doushantuo fossils.
- 2012
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Ingår i: Proceedings of the Royal Society of London. B. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 279:1734, s. 1857-1864
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Tidskriftsartikel (refereegranskat)abstract
- The Ediacaran Doushantuo biota has yielded fossils interpreted as eukaryotic organisms, either animal embryos or eukaryotes basal or distantly related to Metazoa. However, the fossils have been interpreted alternatively as giant sulphur bacteria similar to the extant Thiomargarita. To test this hypothesis, living and decayed Thiomargarita were compared with Doushantuo fossils and experimental taphonomic pathways were compared with modern embryos. In the fossils, as in eukaryotic cells, subcellular structures are distributed throughout cell volume; in Thiomargarita, a central vacuole encompasses approximately 98 per cent cell volume. Key features of the fossils, including putative lipid vesicles and nuclei, complex envelope ornament, and ornate outer vesicles are incompatible with living and decay morphologies observed in Thiomargarita. Microbial taphonomy of Thiomargarita also differed from that of embryos. Embryo tissues can be consumed and replaced by bacteria, forming a replica composed of a threedimensional biofilm, a stable fabric for potential fossilization. Vacuolated Thiomargarita cells collapse easily and do not provide an internal substrate for bacteria. The findings do not support the hypothesis that giant sulphur bacteria are an appropriate interpretative model for the embryo-like Doushantuo fossils. However, sulphur bacteria may have mediated fossil mineralization and may provide a potential bacterial analogue for other macroscopic Precambrian remains.
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| 3. |
- Cunningham, J.A., et al.
(författare)
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Distinguishing geology from biology in the Ediacaran Doushantuo biota relaxes constraints on the timing of the origin of bilaterians.
- 2012
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Ingår i: Proceedings of the Royal Society. B. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 279:1737, s. 2369-2376
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Tidskriftsartikel (refereegranskat)abstract
- The Ediacaran Doushantuo biota has yielded fossils that include the oldest widely accepted record of the animal evolutionary lineage, as well as specimens with alleged bilaterian affinity. However, these systematic interpretations are contingent on the presence of key biological structures that have been reinterpreted by some workers as artefacts of diagenetic mineralization. On the basis of chemistry and crystallographic fabric, we characterize and discriminate phases of mineralization that reflect: (i) replication of original biological structure, and (ii) void-filling diagenetic mineralization. The results indicate that all fossils from the Doushantuo assemblage preserve a complex me´lange of mineral phases, even where subcellular anatomy appears to be preserved. The findings allow these phases to be distinguished in more controversial fossils, facilitating a critical re-evaluation of the Doushantuo fossil assemblage and its implications as an archive of Ediacaran animal diversity. We find that putative subcellular structures exhibit fabrics consistent with preservation of original morphology. Cells in later developmental stages are not in original configuration and are therefore uninformative concerning gastrulation. Key structures used to identify Doushantuo bilaterians can be dismissed as late diagenetic artefacts. Therefore, when diagenetic mineralization is considered, there is no convincing evidence for bilaterians in the Doushantuo assemblage.
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| 4. |
- Bengtson, Stefan, 1947-, et al.
(författare)
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A merciful death for the “earliest bilaterian,” Vernanimalcula.
- 2012
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Ingår i: Evolution and Development. - 1520-541X. ; 14:5, s. 421-427
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Tidskriftsartikel (refereegranskat)abstract
- Fossils described as Vernanimalcula guizhouena, from the nearly 600 million-year-old Doushantuo Formation in South China, have been interpreted as the remains of bilaterian animals. As such they would represent the oldest putative record of bilaterian animals in Earth history, and they have been invoked in debate over this formative episode of early animal evolution. However, this interpretation is fallacious. We review the evidential basis of the biological interpretation of Vernanimalcula, concluding that the structures key to animal identity are effects of mineralization that do not represent biological tissues, and, furthermore, that it is not possible to derive its anatomical reconstruction on the basis of the available evidence. There is no evidential basis for interpreting Vernanimalcula as an animal, let alone a bilaterian. The conclusions of evolutionary studies that have relied upon the bilaterian interpretation of Vernanimalcula must be called into question.
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| 5. |
- Cunningham, John A., et al.
(författare)
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The origin of animals: Can molecular clocks and the fossil record be reconciled?
- 2016
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Ingår i: Bioessays. - : Wiley. - 0265-9247 .- 1521-1878. ; 38, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- The evolutionary emergence of animals is one of the most significant episodes in the history of life, but its timing remains poorly constrained. Molecular clocks estimate that animals originated and began diversifying over 100 million years before the first definitive metazoan fossil evidence in the Cambrian. However, closer inspection reveals that clock estimates and the fossil record are less divergent than is often claimed. Modern clock analyses do not predict the presence of the crown-representatives of most animal phyla in the Neoproterozoic. Furthermore, despite challenges provided by incomplete preservation, a paucity of phylogenetically informative characters, and uncertain expectations of the anatomy of early animals, a number of Neoproterozoic fossils can reasonably be interpreted as metazoans. A considerable discrepancy remains, but much of this can be explained by the limited preservation potential of early metazoans and the difficulties associated with their identificationin the fossil record. Critical assessment of both recordsmay permitbetter resolutionof the tempo and mode of early animal evolution.
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| 6. |
- Cunningham, John A., et al.
(författare)
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The Weng’an Biota (Doushantuo Formation): an Ediacaran window on soft bodied and multicellular microorganisms.
- 2017
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Ingår i: journal of the geological society. - London : Geological Society. - 2041-479X .- 0016-7649. ; 174:5, s. 793-802
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Tidskriftsartikel (refereegranskat)abstract
- The Weng’an Biota is a fossil Konservat-Lagerstätte in South China that is approximately 570-600 million years old and provides an unparalleled snapshot of marine life during the interval in which molecular clocks estimate that animal clades were diversifying. It yields specimens that are three-dimensionally preserved in calcium phosphate with cellular and sometimes subcellular fidelity. The biota includes candidates for the oldest animals in the fossil record, including embryonic, larval and adult forms. We argue that, while the Weng’an Biota includes forms that could be animals, none can currently be assigned to this group with confidence. Nonetheless, the biota offers a rare and valuable window on the evolution of multicellular and soft-bodied organisms in the prelude to the Cambrian radiation.
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| 7. |
- Cunningham, John, et al.
(författare)
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Critical appraisal of tubular putative eumetazoans from the Ediacaran Weng’an Doushantuo biota
- 2015
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 282, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- Molecular clock analyses estimate that crown-group animals began diversifying hundreds of millions of years before the start of the Cambrian period. However, the fossil record has not yielded unequivocal evidence for animals during this interval. Some of the most promising candidates for Precambrian animals occur in theWeng’an biota of South China, including a suite of tubular fossils assigned to Sinocyclocyclicus, Ramitubus, Crassitubus and Quadratitubus, that have been interpreted as soft-bodied eumetazoans comparable to tabulate corals. Here, we present new insights into the anatomy, original composition and phylogenetic affinities of these taxa based on data from synchrotron radiation X-ray tomographic microscopy, ptychographic nanotomography, scanning electron microscopy and electron probe microanalysis. The patterns of deformation observed suggest that the cross walls of Sinocyclocyclicus and Quadratitubus were more rigid than those of Ramitubus and Crassitubus. Ramitubus and Crassitubus specimens preserve enigmatic cellular clusters at terminal positions in the tubes. Specimens of Sinocyclocyclicus and Ramitubus have biological features that might be cellular tissue or subcellular structures filling the spaces between the crosswalls. These observations are incompatible with a cnidarian interpretation, in which the spaces between cross walls are abandoned parts of the former living positions of the polyp. The affinity of the Weng’an tubular fossils may lie within the algae.
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| 8. |
- Cunningham, John, et al.
(författare)
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Distinguishing biology from geology in soft-tissue preservation.
- 2014
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Ingår i: Reading and Writing of the Fossil Record. - : The Paleontological Society. ; , s. 275-287
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Bokkapitel (refereegranskat)abstract
- Knowledge of evolutionary history is based extensively on relatively rare fossils that preserve soft tissues. These fossils record a much greater proportion of anatomy than would be known solely from mineralized remains and provide key data for testing evolutionary hypotheses in deep time. Ironically, however, exceptionally preserved fossils are often among the most contentious because they are difficult to interpret. This is because their morphology has invariably been affected by the processes of decay and diagenesis, meaning that it is often difficult to distinguish preserved biology from artifacts introduced by these processes. Here we describe how a range of analytical techniques can be used to tease apart mineralization that preserves biological structures from unrelated geological mineralization phases. This approach involves using a series of X-ray, ion, electron and laser beam techniques to characterize the texture and chemistry of the different phases so that they can be differentiated in material that is difficult to interpret. This approach is demonstrated using a case study of its application to the study of fossils from the Ediacaran Doushantuo Biota.
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| 9. |
- Dong, Xi-ping, et al.
(författare)
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Developmental biology of the early Cambrian cnidarian Olivooides.
- 2016
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 59:3, s. 387-407
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Tidskriftsartikel (refereegranskat)abstract
- Fossilized embryos afford direct insight into the pattern of development in extinct organisms, providing unique tests of hypotheses of developmental evolution based in comparative embryology. However, these fossils can only be effective in this role if their embryology and phylogenetic affinities are well constrained. We elucidate and interpret the development of Olivooides from embryonic and adult stages and use these data to discriminate among competing interpretations of their anatomy and affinity. The embryology of Olivooides is principally characterized by the development of an ornamented periderm that initially forms externally and is subsequently formed internally, released at the aperture, facilitating the direct development of the embryo into an adult theca. Internal anatomy is known only from embryonic stages, revealing two internal tissue layers, the innermost of which is developed into three transversally arranged walls that partly divide the lumen into an abapertural region, interpreted as the gut of a polyp, and an adapertural region that includes structures that resemble the peridermal teeth of coronate scyphozoans. The anatomy and pattern of development exhibited by Olivooides appears common to the other known genus of olivooid, Quadrapyrgites, which differs in its tetraradial, as opposed to pentaradial symmetry. We reject previous interpretations of the olivooids as cycloneuralians, principally on the grounds that they lack a through gut and introvert, in embryo and adult. Instead we consider the affinities of the olivooids among medusozoan cnidarians; our phylogenetic analysis supports their classification as totalgroup Coronata, within crown-Scyphozoa. Olivooides and Quadrapyrgites evidence a broader range of life history strategies and bodyplan symmetry than is otherwise commonly represented in extant Scyphozoa specifically, and Cnidaria more generally.
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| 10. |
- Dong, Xi-ping, et al.
(författare)
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Embryos, polyps and medusae of the early Cambrian scyphozoan Olivooides.
- 2013
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Ingår i: Proceedings of the Royal Society Biological Sciences Series B. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 280:2130071, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The Early Cambrian organism Olivooides is known from both embryonic and post-embryonic stages and, consequently, it has the potential to yield vital insights into developmental evolution at the time that animal body plans were established. However, this potential can only be realized if the phylogenetic relationships of Olivooides can be constrained. The affinities of Olivooides have proved controversial because of the lack of knowledge of the internal anatomy and the limited range of developmental stages known. Here, we describe rare embryonic specimens in which internal anatomical features are preserved. We also present a fuller sequence of fossilized developmental stages of Olivooides, including associated specimens that we interpret as budding ephyrae ( juvenile medusae), all of which display a clear pentaradial symmetry. Within the framework of a cnidarian interpretation, the new data serve to pinpoint the phylogenetic position of Olivooides to the scyphozoan stem group. Hypotheses about scalidophoran or echinoderm affinities of Olivooides can be rejected.
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