[Show abstract][Hide abstract] ABSTRACT: Ocean drilling provides a global record of deposits throughout the oceans. An international collaborative ocean research program was established in 1966, and the International Ocean Discovery Program (IODP) is the most recent manifestation of this. During each expedition a large amount of data are generated and collected by the shipboard science team. It could be suggested that due to the different staff and objectives during each expedition there would be significant variations in the consistency of data recorded in the shipboard visual core descriptions (VCDs). Use of shipboard VCD data in a global study of volcanism through time required the ground truthing of VCD data, to assess the consistency of ash layer reporting and to identify the amount of under/over recording of volcanic ash layers in cores. Approximately 1400 ash layers in DSDP, ODP, IODP and JAMSTEC cores were examined and it was found that on average 70-75% of recorded volcanic ash layers were present as described, an average of 17-20% were over recorded and 10-15% were under recorded. A number of factors could contribute to this variability, such as VCD format, lack of time for shipboard sampling of every ash layer, significant ash layer colour changes since time of coring, or differences in VCD recording and volcanic ash layer identification and description schemes between expeditions. These findings are important and will allow greater confidence in further studies based on data compiled from shipboard VCDs.
[Show abstract][Hide abstract] ABSTRACT: Volume estimates of the 1815 Tambora eruption were re-analysed using new ash thickness data and new methods, giving a range of possible volumes for the different eruption phases. Volume calculations include ash fall extrapolation and caldera size approximations, as well as volume estimates from mass eruption rates and eruption duration, to find the most likely range of volumes consistent with the different methods and possible eruption dynamics. The results give a total volume of about 41 ± 4 km3 DRE, made of 23 ± 3 km3 DRE ash fall and 18 ± 6 km3 DRE pyroclastic flows. The ash fall volume can be further divided into 11 ± 2 km3 DRE Plinian ash fall and 12 ± 4 km3 DRE co-ignimbrite, making the Plinian ash fall larger than previously assumed, and more intense due to a higher mass eruption rate of 2 x 109 kg/s.
Journal of Volcanology and Geothermal Research 10/2014;
[Show abstract][Hide abstract] ABSTRACT: Volcanic deformation during an unrest episode can provide valuable insights into potential magmatic plumbing system dynamics. Paramount to this is a model linking the recorded ground movement to the causative source at depth. Most models employ analytical techniques due to their simplicity, but these are limited in their approach due to a number of necessary assumptions, and restricted to crude subsurface representations. We address this problem by providing guidelines and example model files to benchmark against a simple, analytical model with a numerical Finite Element approach using COMSOL Multiphysics. The boundary conditions should also be applicable to other Finite Element modeling packages. Then, due to the flexibility of the Finite Element method, this allows a progression of adding increasing complexities to reproduce the likely intricacies of the subsurface. We thus provide further guidelines and accompanying model files to incorporate subsurface heterogeneity, benchmarked viscoelastic rheology and temperature-dependent mechanics. In doing so, we highlight that setting up more integrated geodetic models is not particularly difficult and can alter inferred source characteristics and dynamics. The models are applied to Uturuncu volcano in southern Bolivia to demonstrate the approach.
Journal of Volcanology and Geothermal Research 06/2014;
[Show abstract][Hide abstract] ABSTRACT: Computer-aided visualization and analysis of fossils has revolutionized the study of extinct organisms. Novel techniques allow fossils to be characterized in three dimensions and in unprecedented detail. This has enabled paleontologists to gain important insights into their anatomy, development, and preservation. New protocols allow more objective reconstructions of fossil organisms, including soft tissues, from incomplete remains. The resulting digital reconstructions can be used in functional analyses, rigorously testing long-standing hypotheses regarding the paleobiology of extinct organisms. These approaches are transforming our understanding of long-studied fossil groups, and of the narratives of organismal and ecological evolution that have been built upon them.
[Show abstract][Hide abstract] ABSTRACT: Since the discovery of the basal sauropodomorph dinosaur Thecodontosaurus in the 1830s, the associated fauna from the Triassic fissures at Durdham Down (Bristol, UK) has not been investigated, largely because the quarries are built over. Other fissure sites around the Bristol Channel show that dinosaurs represented a minor part of the fauna of the Late Triassic archipelago. Here we present data on microvertebrates from the original Durdham Down fissure rocks, which considerably expand the taxonomic diversity of the island fauna, revealing that it was dominated by the sphenodontian Diphydontosaurus, and that archosauromorphs, including sphenosuchian crocodylomorphs, coelophysoid theropods, and the basal sauropodomorph Thecodontosaurus, were diverse. Importantly, a few fish teeth provide new information about the debated age of the fissure deposit, which is identified as lower Rhaetian. Thecodontosaurus had been assigned an age range over 20–25 Myr of the Late Triassic, so this narrower age determination (209.5–204 Myr) is important for studies of early dinosaurian evolution.
Proceedings of the Geologists Association 01/2014;
[Show abstract][Hide abstract] ABSTRACT: The origin and function of a biomineralised skeleton in many of the non-motile groups of plankton remains an open question. Morphological diversity within these groups has often been explained by its relevance to hydrodynamic behaviour, principally buoyancy and settling. Consequently, ecological and evolutionary patterns of morphology have been associated with changes in surface water properties, but these hypotheses have rarely been critically assessed. Computational Fluid Dynamic simulations present a way to quantify the relative effect of size (maximum diameter), shape of the test and density (ratio between calcite and cavity volumes) of the specimen on settling velocity, as all variables can be manipulated independently. Here we interrogate the morphological diversity in planktic foraminifera as model organisms to explore the range of evolutionary options open to plankton to modulate settling velocity under varying environmental conditions. The evolutionary changes in morphology required to accommodate physical changes in the upper water column due to environmental changes, such as increased temperature, are small compared to the ecophenotypic variability of the population. In the modern ocean, the pattern of species distribution with depth is not likely to be determined by hydrodynamics as it is inconsistent with predictions based on settling velocity. These results suggest that intrinsic constraints on size, shape and calcification, such as heritage, exposure of the symbionts to light or oxygen diffusion into the cell, are likely to be more important than hydrodynamic function in determining the depth distribution and test morphology of planktic foraminifera.
[Show abstract][Hide abstract] ABSTRACT: Our knowledge of how Earth's natural satellite formed is increasingly
being challenged by observations and computer simulations. Two
scientists outline our current understanding from the point of view of
the satellite's geochemistry and its early dynamical history.
[Show abstract][Hide abstract] ABSTRACT: Maniraptoriformes, the speciose group of derived theropod dinosaurs that ultimately gave rise to modern birds, display a diverse and remarkable suite of skeletal adaptations. Apart from the evolution of flight, a large-scale change in dietary behavior appears to have been one of the main triggers for specializations in the bauplan of these derived theropods. Among the different skeletal specializations, partial or even complete edentulism and the development of keratinous beaks form a recurring and persistent trend in from the evolution of derived nonavian dinosaurs. Therizinosauria is an enigmatic maniraptoriform clade, whose members display these and other osteological characters thought to be correlated with the shift from carnivory to herbivory. This makes therizinosaurians prime candidates to assess the functional significance of these morphological characters. Based on a highly detailed biomechanical model of Erlikosaurus andrewsi, a therizinosaurid from the Upper Cretaceous of Mongolia, different morphological configurations incorporating soft-tissue structures, such as a keratinous rhamphotheca, are evaluated for their biomechanical performance. Our results indicate that the development of beaks and the presence of a keratinous rhamphotheca would have helped to dissipate stress and strain, making the rostral part of the skull less susceptible to bending and displacement, and this benefit may extend to other vertebrate clades that possess rhamphothecae. Keratinous beaks, paralleled by edentulism, thus represent an evolutionary innovation developed early in derived theropods to enhance cranial stability, distinct to postulated mass-saving benefits associated with the origin of flight.
Proceedings of the National Academy of Sciences 12/2013;
[Show abstract][Hide abstract] ABSTRACT: Conodonts are an extinct group of jawless vertebrates whose tooth-like elements are the earliest instance of a mineralized skeleton in the vertebrate lineage, inspiring the 'inside-out' hypothesis that teeth evolved independently of the vertebrate dermal skeleton and before the origin of jaws. However, these propositions have been based on evidence from derived euconodonts. Here we test hypotheses of a paraconodont ancestry of euconodonts using synchrotron radiation X-ray tomographic microscopy to characterize and compare the microstructure of morphologically similar euconodont and paraconodont elements. Paraconodonts exhibit a range of grades of structural differentiation, including tissues and a pattern of growth common to euconodont basal bodies. The different grades of structural differentiation exhibited by paraconodonts demonstrate the stepwise acquisition of euconodont characters, resolving debate over the relationship between these two groups. By implication, the putative homology of euconodont crown tissue and vertebrate enamel must be rejected as these tissues have evolved independently and convergently. Thus, the precise ontogenetic, structural and topological similarities between conodont elements and vertebrate odontodes appear to be a remarkable instance of convergence. The last common ancestor of conodonts and jawed vertebrates probably lacked mineralized skeletal tissues. The hypothesis that teeth evolved before jaws and the inside-out hypothesis of dental evolution must be rejected; teeth seem to have evolved through the extension of odontogenic competence from the external dermis to internal epithelium soon after the origin of jaws.
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