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Grice J.D.,Canadian Museum of Nature | Pring A.,South Australia Museum
American Mineralogist | Year: 2012

Crystal structures of the three polytypes of veatchite, Sr 2B 11O 16(OH) 5.H 2O, are determined by X-ray, single-crystal studies. The polytypes are: veatchite-1A, triclinic space group P1, with a = 6.6378(6), b = 6.7387(6), c = 20.982(2) A°, α = 87.860(1), β = 82.696(12), Δ = 60.476(1)°, V = 809.7(2) A°3; veatchite-1M, monoclinic space group P21, with a = 6.7127(4), b = 20.704(1), c = 6.6272(4) A°, β = 119.209(1)°, V = 805.4(2) A°3; and veatchite-2M,monoclinic space group Cc with a = 6.6070(3), b = 11.7125(5), c = 20.6848(9) A°, β = 91.998(1)°, V = 1599.7(2) A°3. The crystal structures have two layer types with similar fundamental building blocks: A layer FBB = 3Δ2o:<Δ2o>-<2Δo> and B layer FBB = 3Δ2o,1Δ:<Δ2o>-<2Δo>, Δ (Grice et al. 1999). Unique in this FBB is the lone polyhedron with triangular coordination, which consists of a neutrally charged [B(OH) 3] group. Layering has a directional component and depending on layer sequence the symmetry may be centrosymmetric or non-centrosymmetric. Related layered borate structures, biringuccite, nasinite, gowerite, and volkovskite, are compared. Observations indicate that veatchite-1A is the low-temperature and low-pressure polytype, veatchite-1M the high-temperature polytype, and veatchite-2M the moderate temperature and higher pressure polytype. © 1997 - 2012 Mineralogical Society of America. Source

Dennis D.S.,1105 Myrtle Wood Drive | Lavigne R.J.,South Australia Museum | Lavigne R.J.,University of Wyoming | Dennis J.G.,P.O. Box 861161
Journal of the Entomological Research Society | Year: 2012

There are many references on the Internet and in the published literature to robber flies preying upon spiders. However, an evaluation of available data summarized in the Asilidae Predator-Prey Database reveals that spiders make up only a small percentage of the robber fly diet (less than 1% of approximately 58,000 prey listed in the Database). The types of spider chosen as prey are discussed and examined in relation to robber fly classification. Robber fly methods of capturing spiders are examined and comments about spiders preying upon robber flies are provided. Source

Droser M.L.,University of California at Riverside | Gehling J.G.,South Australia Museum | Gehling J.G.,University of Adelaide
Proceedings of the National Academy of Sciences of the United States of America | Year: 2015

Patterns of origination and evolution of early complex life on this planet are largely interpreted from the fossils of the Precambrian soft-bodied Ediacara Biota. These fossils occur globally and represent a diverse suite of organisms living in marine environments. Although these exceptionally preserved fossil assemblages are typically difficult to reconcile with modern phyla, examination of the morphology, ecology, and taphonomy of these taxa provides keys to their relationships with modern taxa. Within the more than 30 million y range of the Ediacara Biota, fossils of these multicellular organisms demonstrate the advent of mobility, heterotrophy by multicellular animals, skeletonization, sexual reproduction, and the assembly of complex ecosystems, all of which are attributes of modern animals. This approach to these fossils, without the constraint of attempting phylogenetic reconstructions, provides a mechanism for comparing these taxa with both living and extinct animals. © 2015, National Academy of Sciences. All rights reserved. Source

Xiao S.,Virginia Polytechnic Institute and State University | Droser M.,University of California at Riverside | Gehling J.G.,South Australia Museum | Hughes I.V.,Riverside STEM Academy | And 3 more authors.
Geology | Year: 2013

The Ediacara biota has been long championed as a snapshot of the marine ecosystem on the eve of the Cambrian explosion, providing important insights into the early evolution of animals. Fossiliferous beds in the eponymous Ediacara Member of South Australia have been recently reinterpreted as paleosols and Ediacara fossils as lichens or microbial colonies that lived on terrestrial soils. This reinterpretation, here dubbed the terrestrial Ediacara hypothesis, would fundamentally change our views of biological evolution just prior to the Cambrian explosion. We take a comparative paleobiology approach to test this hypothesis. The Ediacara Member shares a number of forms with assemblages in Ediacaran marine black shales in South China, shales that show no evidence of pedogenesis. Thus, the shared Ediacara fossils, and by extension other co-occurring fossils, are unlikely to have been terrestrial organisms. A terrestrial interpretation is also inconsistent with functional morphological evidence; some of the shared forms are not morphologically adapted to address the most critical challenges for terrestrial life (e.g., mechanical support and desiccation). Thus, the terrestrial Ediacara hypothesis can be falsified on comparative paleobiological and functional morphological grounds, and we urge paleopedologists to critically reevaluate evidence for pedogenesis in the Ediacara Member and other Ediacaran successions. © 2013 Geological Society of America. Source

Droser M.L.,University of California at Riverside | Gehling J.G.,South Australia Museum | Gehling J.G.,University of Adelaide | Dzaugis M.E.,University of Rhode Island | And 3 more authors.
Journal of Paleontology | Year: 2014

Abstract Nilpenia rossi new genus new species, described here from the Ediacara Member (Rawnsley Quartzite, South Australia), provides evidence of a Precambrian macroscopic sessile sediment-dweller. Nilpenia, ranging up to 30 cm in diameter, consists of two zones, a complex central area surrounded by radiating, dichotomously branching structures that decrease in diameter from the center to the outer edges. Other elements of the Ediacara Biota are interpreted to have been mat-encrusters but Nilpenia uniquely grew within the upper millimeters of the actual sediment displacing sediment with growth. This sediment surface was rippled and cohesive and may well have included an endobenthic mat. The branching network on the upper surface of the organisms would have been in contact with the water. The phylogenetic relationships of the Ediacara biota are not well constrained and Nilpenia is no exception. However, the morphology and ecology of Nilpenia represent a novel growth strategy present in the Ediacaran and not common today. © 2014 The Paleontological Society. Source

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