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1.	Davies, Thomas G., et al. (författare) Open data and digital morphology. 2017 Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 284:1852, s. 1-10 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.
2.	Bengtson, Stefan, 1947-, et al. (författare) A merciful death for the “earliest bilaterian,” Vernanimalcula. 2012 Ingår i: Evolution and Development. - 1520-541X. ; 14:5, s. 421-427 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.
3.	Brate, Jon, et al. (författare) Unicellular Origin of the Animal MicroRNA Machinery 2018 Ingår i: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 28:20, s. 3288- Tidskriftsartikel (refereegranskat)abstract The emergence of multicellular animals was associated with an increase in phenotypic complexity and with the acquisition of spatial cell differentiation and embryonic development. Paradoxically, this phenotypic transition was not paralleled by major changes in the underlying developmental toolkit and regulatory networks. In fact, most of these systems are ancient, established already in the unicellular ancestors of animals [1-5]. In contrast, the Microprocessor protein machinery, which is essential for microRNA (miRNA) biogenesis in animals, as well as the miRNA genes themselves produced by this Microprocessor, have not been identified outside of the animal kingdom [6]. Hence, the Microprocessor, with the key proteins Pasha and Drosha, is regarded as an animal innovation [7-9]. Here, we challenge this evolutionary scenario by investigating unicellular sister lineages of animals through genomic and transcriptomic analyses. We identify in Ichthyosporea both Drosha and Pasha (DGCR8 in vertebrates), indicating that the Microprocessor complex evolved long before the last common ancestor of animals, consistent with a pre-metazoan origin of most of the animal developmental gene elements. Through small RNA sequencing, we also discovered expressed bona fide miRNA genes in several species of the ichthyosporeans harboring the Microprocessor. A deep, pre-metazoan origin of the Microprocessor and miRNAs comply with a view that the origin of multicellular animals was not directly linked to the innovation of these key regulatory components.
4.	Butler, Aodhán D., 1986-, et al. (författare) The role of microbes in decay and preservation: a Cambrian Explosion of animals and Lagerstätten. Annan publikation (övrigt vetenskapligt/konstnärligt)abstract The abrupt appearance of animals in the early Cambrian has been interpreted either as an explosive biological diversification or, alternatively, as an artefact resulting from a sudden increase in the probability of animal remains becoming fossilised. We attempt to reconcile these competing interpretations in exceptionally-preserved biota, which provide a vital part of our knowledge of the disparity and diversity of the Cambrian fauna. We assess the factors influencing the potential for exceptional fossil preservation using the brine shrimp Artemia salina as our experimental model. Following gut wall rupture, but prior to cuticle failure, internal, gut-derived microbes spread into the body cavity and formed pseudomorphs of tissues. Gut-derived microbes were shown to be the main factor mediating both decay and biofilm replacement and tissue stabilisation. This pattern of preservation is consistent with results from other experimental studies and with the nature of Burgess Shale type fossil remains. Thus, the evolution of a through-gut may have not only underpinned the ecological revolution that bilaterian diversification represents, but also catalysed the exceptional preservation of early bilaterian fossils.
5.	Cunningham, J.A., et al. (författare) Distinguishing geology from biology in the Ediacaran Doushantuo biota relaxes constraints on the timing of the origin of bilaterians. 2012 Ingår i: Proceedings of the Royal Society. B. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 279:1737, s. 2369-2376 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.
6.	Cunningham, J. A., et al. (författare) Experimental taphonomy of giant sulphur bacteria: implications for the interpretation of the embryo-like Ediacaran Doushantuo fossils. 2012 Ingår i: Proceedings of the Royal Society of London. B. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 279:1734, s. 1857-1864 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.
7.	Cunningham, John A., et al. (författare) Testing models of dental development in the earliest bony vertebrates, Andreolepis and Lophosteus 2012 Ingår i: Biology Letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 8:5, s. 833-837 Tidskriftsartikel (refereegranskat)abstract Theories on the development and evolution of teeth have long been biased by the fallacy that chondrichthyans reflect the ancestral condition for jawed vertebrates. However, correctly resolving the nature of the primitive vertebrate dentition is challenged by a dearth of evidence on dental development in primitive osteichthyans. Jaw elements from the Silurian-Devonian stem-osteichthyans Lophosteus and Andreolepis have been described to bear a dentition arranged in longitudinal rows and vertical files, reminiscent of a pattern of successional development. We tested this inference, using synchrotron radiation X-ray tomographic microscopy (SRXTM) to reveal the pattern of skeletal development preserved in the sclerochronology of the mineralized tissues. The tooth-like tubercles represent focal elaborations of dentine within otherwise continuous sheets of the dermal skeleton, present in at least three stacked generations. Thus, the tubercles are not discrete modular teeth and their arrangement into rows and files is a feature of the dermal ornamentation that does not reflect a polarity of development or linear succession. These fossil remains have no bearing on the nature of the dentition in osteichthyans and, indeed, our results raise questions concerning the homologies of these bones and the phylogenetic classification of Andreolepis and Lophosteus.
8.	Cunningham, John A., et al. (författare) The origin of animals: Can molecular clocks and the fossil record be reconciled? 2016 Ingår i: Bioessays. - : Wiley. - 0265-9247 .- 1521-1878. ; 38, s. 1-12 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.
9.	Cunningham, John A., et al. (författare) The Weng’an Biota (Doushantuo Formation): an Ediacaran window on soft bodied and multicellular microorganisms. 2017 Ingår i: journal of the geological society. - London : Geological Society. - 2041-479X .- 0016-7649. ; 174:5, s. 793-802 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.
10.	Cunningham, John, et al. (författare) Critical appraisal of tubular putative eumetazoans from the Ediacaran Weng’an Doushantuo biota 2015 Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 282, s. 1-9 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.
11.	Cunningham, John, et al. (författare) Distinguishing biology from geology in soft-tissue preservation. 2014 Ingår i: Reading and Writing of the Fossil Record. - : The Paleontological Society. ; , s. 275-287 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.
12.	Dong, Xi-ping, et al. (författare) Developmental biology of the early Cambrian cnidarian Olivooides. 2016 Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 59:3, s. 387-407 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.
13.	Dong, Xi-ping, et al. (författare) Embryos, polyps and medusae of the early Cambrian scyphozoan Olivooides. 2013 Ingår i: Proceedings of the Royal Society Biological Sciences Series B. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 280:2130071, s. 1-8 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.
14.	Donoghue, Philip C.J., et al. (författare) Embryology in deep time. 2015 Ingår i: Evolutionary Developmental Biology of Invertebrates 1. - Wien : Springer Science+Business Media B.V.. - 9783709118610 ; , s. 45-63 Bokkapitel (refereegranskat)abstract For anyone who has cared for animal embryos, it beggars belief that these squishy cellular aggregates could be fossilised. Hence, with hindsight, it is possible to empathise with palaeontologists who found such fossils and, in their naming of Olivooides, Pseudooides, etc., drew attention to their likeness to animal eggs and embryos but without going so far as to propose such an interpretation. However, in 1994, Zhang Xi-guang and Brian Pratt described microscopic balls of calcium phosphate from Cambrian rocks of China, one or two of which preserved polygonal borders that resembled blastomeres on the surface of an early cleaving animal embryo. In retrospect, these fossils are far from remarkable, some of them may not be fossils at all, and it is not as if anyone ever conceived Cambrian animals as having lacked an embryology. But Zhang Xi-guang and Brian Pratt dared the scientific world, not least their fellow palaeontologists, to believe that the fragile embryonic stages of invertebrate animals could be fossilised, that there was a fossil record of animal embryology, that this record hailed from the interval of time in which animal body plans were first established, and that it had been awaiting discovery in the rocks, for want of looking. The proof of this concept came a few years later, when phosphatised Cambrian fossils from China and Siberia were shown to display indisputable features of animal embryonic morphologies. In the case of Olivooides, a series of developmental stages from cleavage to morphogenesis through hatching and juvenile growth could be tentatively identified; in Markuelia, the coiled-up body of an annulated worm-like animal could be clearly seen within its fertilisation envelope.
15.	Donoghue, Philip C. J., et al. (författare) Synchrotron X-ray tomographic microscopy of fossil embryos 2006 Ingår i: Nature. - 0028-0836. ; 442:7103, s. 601-718 Tidskriftsartikel (refereegranskat)abstract Fossilized embryos from the late Neoproterozoic and earliest Phanerozoic have caused much excitement because they preserve the earliest stages of embryology of animals that represent the initial diversification of metazoans1, 2, 3, 4. However, the potential of this material has not been fully realized because of reliance on traditional, non-destructive methods that allow analysis of exposed surfaces only1, 2,3, 4, and destructive methods that preserve only a single two-dimensional view of the interior of the specimen5, 6. Here, we have applied synchrotron-radiation X-ray tomographic microscopy (SRXTM)7, obtaining complete three-dimensional recordings at submicrometre resolution. The embryos are preserved by early diagenetic impregnation and encrustation with calcium phosphate, and differences in X-ray attenuation provide information about the distribution of these two diagenetic phases. Three-dimensional visualization of blastomere arrangement and diagenetic cement in cleavage embryos resolves outstanding questions about their nature, including the identity of the columnar blastomeres. The anterior and posterior anatomy of embryos of the bilaterian worm-like Markuelia confirms its position as a scalidophoran, providing new insights into body-plan assembly among constituent phyla. The structure of the developing germ band in another bilaterian, Pseudooides, indicates a unique mode of germ-band development. SRXTM provides a method of non-invasive analysis that rivals the resolution achieved even by destructive methods, probing the very limits of fossilization and providing insight into embryology during the emergence of metazoan phyla.
16.	Gai, Zhikun, et al. (författare) The Evolution of the Spiracular Region From Jawless Fishes to Tetrapods 2022 Ingår i: Frontiers in Ecology and Evolution. - : Frontiers Media S.A.. - 2296-701X. ; 10 Tidskriftsartikel (refereegranskat)abstract The spiracular region, comprising the hyomandibular pouch together with the mandibular and hyoid arches, has a complex evolutionary history. In living vertebrates, the embryonic hyomandibular pouch may disappear in the adult, develop into a small opening between the palatoquadrate and hyomandibula containing a single gill-like pseudobranch, or create a middle ear cavity, but it never develops into a fully formed gill with two hemibranchs. The belief that a complete spiracular gill must be the ancestral condition led some 20th century researchers to search for such a gill between the mandibular and hyoid arches in early jawed vertebrates. This hypothesized ancestral state was named the aphetohyoidean condition, but so far it has not been verified in any fossil; supposed examples, such as in the acanthodian Acanthodes and symmoriid chondrichthyans, have been reinterpreted and discounted. Here we present the first confirmed example of a complete spiracular gill in any vertebrate, in the galeaspid (jawless stem gnathostome) Shuyu. Comparisons with two other groups of jawless stem gnathostomes, osteostracans and heterostracans, indicate that they also probably possessed full-sized spiracular gills and that this condition may thus be primitive for the gnathostome stem group. This contrasts with the living jawless cyclostomes, in which the mandibular and hyoid arches are strongly modified and the hyomandibular pouch is lost in the adult. While no truly aphetohyoidean spiracular gill has been found in any jawed vertebrate, the recently reported presence in acanthodians of two pseudobranchs suggests a two-step evolutionary process whereby initial miniaturization of the spiracular gill was followed, independently in chondrichthyans and osteichthyans, by the loss of the anterior pseudobranch. On the basis of these findings we present an overview of spiracular evolution among vertebrates.
17.	Huldtgren, Therese, et al. (författare) Fossilized nuclei and germination structures identify Ediacaran ‘animal embryos’ as encysting protists. 2011 Ingår i: Science. - Washington, DC : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 334:6063, s. 1696-1699 Tidskriftsartikel (refereegranskat)abstract Globular fossils showing palintomic cell cleavage in the Ediacaran Doushantuo Formation, China, are widely regarded as embryos of early metazoans, although metazoan synapomorphies, tissue differentiation, and associated juveniles or adults are lacking. We demonstrate using synchrotron-based x-ray tomographic microscopy that the fossils have features incompatible with multicellular metazoan embryos. The developmental pattern is comparable with nonmetazoan holozoans, including germination stages that preclude postcleavage embryology characteristic of metazoans. We conclude that these fossils are neither animals nor embryos. They belong outside crown-group Metazoa, within total-group Holozoa (the sister clade to Fungi that includes Metazoa, Choanoflagellata, and Mesomycetozoea) or perhaps on even more distant branches in the eukaryote tree. They represent an evolutionary grade in which palintomic cleavage served the function of producing propagules for dispersion.
18.	Huldtgren, Therese, et al. (författare) Response to comment on “Fossilized nuclei and germination structures identify Ediacaran ‘animal embryos’ as encysting protists”. 2012 Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 335:6073, s. 1169d- Tidskriftsartikel (refereegranskat)abstract The objections of Xiao et al. to our reinterpretation are based on incorrect assumptions. The lack of nanocrystals lining the nuclear membrane is consistent with membrane fossilization, and nucleus volume through development is correlated to cytoplasm volume and fully consistent with sizes of eukaryote nuclei. Identical envelope structure unites the developmental stages of the fossils, and 2n cleavage and Y-shaped junctions are holozoan symplesiomorphies.
19.	Maas, Andreas, et al. (författare) The ‘Orsten’—More than a Cambrian Konservat-Lagerstätte 2006 Ingår i: Palaeoworld. - 1871-174X .- 1875-5887. ; 15, s. 266-282 Tidskriftsartikel (populärvet., debatt m.m.)abstract In several areas of southern Sweden, limestone nodules, locally called Orsten occur within bituminous alum shales. Theseshales and nodules were deposited under dysoxic conditions at the bottom of what was most likely a shallow sea during the lateMiddle to Upper Cambrian (ca. 500 million years ago). Subsequently, the name ‘Orsten’ has been referred to particular, mainlyarthropod, fossils from such nodules, and, in a wider sense, to the specific type of preservation of minute fossil through secondarilyphosphatization. This preservation is exceptional in yielding uncompacted and diagenetically undeformed three-dimensional fossils.‘Orsten’-type preservation resulted from incrustation of a thin external layer and also by impregnation by calcium phosphate and,therefore, mineralization of the surface of the former animals during early diagenesis. Primarily, this type of preservation seems tohave affected only cuticle-bearing metazoans such as cycloneuralian nemathelminths and arthropods. ‘Orsten’ preservation in thissense seems to be limited by size, in having yielded no partial or complete animals larger than 2 mm. On the other end of the scale,even larvae 100
20.	Murdock, Duncan J.E., et al. (författare) Evaluating scenarios for the evolutionary assembly of the brachiopod body plan. 2014 Ingår i: Evolution & Development. - : Wiley. - 1520-541X .- 1525-142X. ; 16:1, s. 13-24 Tidskriftsartikel (refereegranskat)abstract The fossil faunas of the Cambrian provide the only direct insight into the assembly of animal body plans. However, for many animal groups, their early fossil record is linked to disarticulated remains, interpretation of which is problematic since they possess few characters from which their affinity to phyla can be established and, indeed, few characters at all. One such group is the tommotiids, which has been interpreted, on the basis of skeletal anatomy, as a paraphyletic assemblage uniting brachiopods and phoronids, through the acquisition and subsequent modification, or loss, of an imbricated set of dorsal phosphatic sclerites. Here we present a reexamination of the fossil evidence uniting the tommotiids and brachiopods, supplemented with new anatomical data from synchrotron radiation X-ray tomographic microscopy of key tommotiid taxa. The characters used to support the complex hypothesis of character evolution in the brachiopod stem lineage relies on scleritome reconstructions and inferred mode of life which themselves rely on brachiopods being chosen as the interpretative model. We advocate a more conservative interpretation of the affinity of these fossils, based a priori on their intrinsic properties, rather than the modern analogue in whose light they have been interpreted.
21.	Murdock, Duncan J.E., et al. (författare) Ontogeny and microstructure of the enigmatic Cambrian tommotiid Sunnaginia Missarzhevsky 1969. 2012 Ingår i: Palaeontology. - : Wiley. - 0031-0239. ; 55:3, s. 661-676 Tidskriftsartikel (refereegranskat)abstract The tommotiids are a significant component of the earliest skeletal animal remains in the fossil record, occurring in large numbers in the Lower Cambrian. Sclerites of the tommotiid genus Sunnaginia have been implicated as integral to hypotheses regarding the evolution of the brachiopod body plan, with a morphology intermediate between the unspecialized sclerites of the tubular Eccentrotheca and the specialized sclerites of the tannuolinids. Abundant Sunnaginia ?imbricata sclerites, of a broad ontogenetic spectrum, were recovered from the Comley Limestone, Lower Cambrian (Stages 3–4), Shropshire, UK and compared to Sunnaginia imbricata from the Aldan River, Siberia (uppermost Tommotian). New microstructural data, collected using synchrotron radiation X-ray tomographic microscopy, reveal a unique microstructure for Sunnaginia ?imbricata sclerites among the tommotiids; interlamellar cavities spanned by a series of continuous pillars, giving a colonnaded appearance contrasting to that of S. imbricata. These data refute the inclusion of Eccentrotheca within the Sunnaginiidae and highlight the need for a revision of suprageneric classification of the tommotiids. Rather, structural similarities between Sunnaginia sclerites and those of the tannuolinids suggest a close affinity to this group. Recent phylogenetic hypotheses place the tannuolinids as stem-linguliform brachiopods, with Paterimitra plus the paterinid (and possibly rhynchonelliform) brachiopods as their sister group. Our new data therefore resolve Sunnaginia as close to the node defining crown-Brachiopoda. However, the characters supporting this phylogenetic scheme cannot be consistently applied to all taxa, nor do they define a series of nested clades. We therefore suggest that a more thorough phylogenetic analysis is required in the light of the data presented here and other recent descriptions.
22.	Raff, Elizabeth C., et al. (författare) Doushantuo fossils are not giant bacteria, but bacterial pseudomorphs of animal embryos 2008 Ingår i: The Palaeontological Association. Konferensbidrag (refereegranskat)abstract Embryos from the Ediacaran Doushantuo Formation are among the most astonishing examples of exceptional fossilization. However, the mechanism of fossilization ispoorly understood, leading directly to debate over the interpretation of the fossils, someauthors even questioning their interpretation as embryos. It has been hypothesized thatmicrobial processes are responsible for preservation and mineralization of organic tissues.However, the actions of microbes in preservation of embryos have not been demonstratedexperimentally. We show that bacterial biofilms assemble rapidly in marine embryos,forming detailed pseudomorphs of cellular organization and structure. We define threeessential steps in embryo preservation: 1) blockage of autolysis by reducing or anaerobic conditions; 2) rapid formation of microbial biofilms that consume the embryo butform a replica that retains cell organization and morphology; 3) bacterially-catalyzedmineralization. We identified major bacterial taxa in embryo decay biofilms using16S rDNA sequencing. Decay processes were similar in different taphonomic conditions,but bacterial populations depended on specific conditions. Experimental taphonomyresembles preservation states of fossils. Our data show how fossilization of soft tissues insediments is mediated by bacterial replacement and mineralization, providing a foundationfor experimentally creating biofilms from defined microbial species to model fossilization asa biological process.
23.	Raff, Elizabeth C., et al. (författare) Embryo fossilization is a biological process mediated by microbial biofilms 2008 Ingår i: Proceedings of the National Academy of Sciences. ; 105:49, s. 19360-19365 Tidskriftsartikel (refereegranskat)abstract Fossilized embryos with extraordinary cellular preservation appear in the Late Neoproterozoic and Cambrian, coincident with the appearance of animal body fossils. It has been hypothesized that microbial processes are responsible for preservation and mineralization of organic tissues. However, the actions of microbes in preservation of embryos have not been demonstrated experimentally. Here, we show that bacterial biofilms assemble rapidly in dead marine embryos and form remarkable pseudomorphs in which the bacterial biofilm replaces and exquisitely models details of cellular organization and structure. The experimental model was the decay of cleavage stage embryos similar in size and morphology to fossil embryos. The data show that embryo preservation takes place in 3 distinct steps: (i) blockage of autolysis by reducing or anaerobic conditions, (ii) rapid formation of microbial biofilms that consume the embryo but form a replica that retains cell organization and morphology, and (iii) bacterially catalyzed mineralization. Major bacterial taxa in embryo decay biofilms were identified by using 16S rDNA sequencing. Decay processes were similar in different taphonomic conditions, but the composition of bacterial populations depended on specific conditions. Experimental taphonomy generates preservation states similar to those in fossil embryos. The data show how fossilization of soft tissues in sediments can be mediated by bacterial replacement and mineralization, providing a foundation for experimentally creating biofilms from defined microbial species to model fossilization as a biological process.
24.	Yin, Zongjun, et al. (författare) Nuclei and nucleoli in embryo-like fossils from the Ediacaran Weng’an Biota. 2017 Ingår i: Precambrian Research. - Amsterdam : Elsevier. - 0301-9268 .- 1872-7433. ; 301, s. 145-151 Tidskriftsartikel (refereegranskat)abstract The embryo-like microfossils from the Ediacaran Weng’an Biota (ca. 609 million years old) are among the oldest plausible claims of animals in the fossil record. Fossilization frequently extends beyond the cellular, to preserve subcellular structures including contentious Large Intracellular Structures (LISs) that have been alternately interpreted as eukaryote nuclei or organelles, degraded remains, or abiological structures. Here we present new data on the structure, morphology, and development of the LISs in these embryo-like fossils, based on Synchrotron Radiation X-ray Tomographic Microscopy (SRXTM) and quantitative computed tomographic analysis. All the lines of evidence, including consistency in the number, shape, position, and relative size (LIS-to-cytoplasm ratio) of the LISs, as well as their occurrence within preserved cytoplasm, support their interpretation as cell nuclei. Our results allow us to reject the view that nuclei cannot be preserved in early eukaryote fossils, offering new potential for interpreting the fossil record of early eukaryote evolution.
25.	Yin, Zongjun, et al. (författare) The early Ediacaran Caveasphaera foreshadows the evolutionary origin of animal-like embryology. 2019 Ingår i: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 29:25, s. 4307-4314 Tidskriftsartikel (refereegranskat)abstract The Ediacaran Weng’an Biota (Doushantuo Formation, 609 Ma old) is a rich microfossil assemblage that preserves biological structure to a subcellular level of fidelity and encompasses a range of developmental stages [1]. However, the animal embryo interpretation of the main components of the biota has been the subject of controversy [2, 3]. Here, we describe the development of Caveasphaera, which varies in morphology from lensoid to a hollow spheroidal cage [4] to a solid spheroid [5] but has largely evaded description and interpretation. Caveasphaera is demonstrably cellular and develops within an envelope by cell division and migration, first defining the spheroidal perimeter via anastomosing cell masses that thicken and ingress as strands of cells that detach and subsequently aggregate in a polar region. Concomitantly, the overall diameter increases as does the volume of the cell mass, but after an initial phase of reductive palinotomy, the volume of individual cells remains the same through development. The process of cell ingression, detachment, and polar aggregation is analogous to gastrulation; together with evidence of functional cell adhesion and development within an envelope, this is suggestive of a holozoan affinity. Parental investment in the embryonic development of Caveasphaera and co-occurring Tianzhushania and Spiralicellula, as well as delayed onset of later development, may reflect an adaptation to the heterogeneous nature of the early Ediacaran nearshore marine environments in which early animals evolved.

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