Time filter

Source Type

Whitehouse M.J.,Swedish Museum of Natural History
Geostandards and Geoanalytical Research | Year: 2013

High spatial resolution multiple sulfur isotope studies undertaken by multi-collector secondary ion mass spectrometry (SIMS) commonly use well-characterised sulfide reference materials that do not (or are assumed not to) exhibit mass-independent fractionation in 33S and 36S, taking advantage of the three-isotope plot to evaluate the extent of such fractionation in unknown targets. As a result, few studies to date have used a mass independently fractionated reference sulfide to demonstrate accuracy of measurement and/or data reduction procedures. This article evaluates two mass independently fractionated sulfides, a pyrite from the 3.7 Ga Isua greenstone belt and a pyrrhotite from a 2.7 Ga gold deposit in Minas Gerais, Brazil, which may be used to provide additional confidence in the obtained multiple sulfur isotope data. Additionally, the article presents a method for measuring quadruple sulfur isotopes by SIMS at a comparable spatial and volume resolution to that typically employed for triple sulfur isotopes. This method has been applied to the Isua pyrite as well as to a sample of 2.5 Ga pyrite from the Campbellrand, Transvaal, South Africa, previously investigated using SIMS for triple sulfur isotopes, illustrating its potential for quadruple sulfur investigations. © 2012 The Author. Geostandards and Geoanalytical Research © 2012 International Association of Geoanalysts. Source

McLoughlin S.,Swedish Museum of Natural History
Australian Journal of Botany | Year: 2011

Single, midrib-positioned galls and midrib-flanking oviposition scars are described from four species of Permian glossopterid foliage from Australia and South Africa. Several of these traces have been mistaken previously for glossopterid reproductive organs or fructification detachment scars. A single Early Triassic corystosperm leaf from Australia is reported bearing multiple disc-like galls on both the midrib and pinnules. A Middle Triassic taeniopterid gymnosperm leaf from Australia is described hosting oviposition scars between consecutive secondary veins flanking the midrib. These fossils attest to a much richer record of plantarthropod interactions in the late Palaeozoic and early Mesozoic of high-latitude Gondwana than previously reported, and indicate that herbivory and reproductive strategies involving galling and foliar ovipositioning were re-established relatively soon after the end-Permian mass extinction event that saw major turnovers in both the flora and insect fauna. © 2011 CSIRO. Source

Pott C.,Swedish Museum of Natural History
International Journal of Plant Sciences | Year: 2014

Premise of research. The concept of Wielandiella angustifolia, a shrub-sized bennettite from the Rhaetian of southern Sweden and East Greenland, became the standard interpretation of the habit and plant architecture of the Williamsoniaceae during the last 100 years. This concept, however, was never critically reinvestigated to evaluate the validity of the restoration. In addition, the new International Code of Nomenclature for algae, fungi, and plants (Melbourne Code) allows erecting fossil taxa for whole-plant concepts, wherefore Wielandiella angustifolia is an ideal candidate. Methodology. The excellently preserved plant fossils were reinvestigated using modern methods, such as cuticular analysis and light, fluorescence, and scanning electron microscopy. Pivotal results. The reinvestigation led to the rejection of the bisexual nature of the plant and provides deeper insights into the plant's nature, biology, and ecology. The rejection of the bisexual nature necessitated emendation of the diagnosis of Wielandiella. Conclusions. The revised diagnosis circumscribes a whole-plant concept that includes branched axes bearing leaves, immature seed cones, and monosporangiate, flowerlike reproductive structures. Good candidates for the hitherto-unidentified microsporangiate structure and the mature seed cone are Bennettistemon and Vardekloeftia, respectively. Discussion of the results concluded that Wielandiella definitely forms a separate genus within the Williamsoniaceae that is distinct from Williamsoniella and Williamsonia. © 2014 by The University of Chicago. All rights reserved. Source

Ericson P.G.P.,Swedish Museum of Natural History
Journal of Biogeography | Year: 2012

Aim To reconstruct the biogeographical history of a large clade of mainly terrestrially adapted birds (coraciiform and piciform birds, owls, diurnal raptors, New World vultures, trogons, mousebirds, cuckoo-rollers, seriemas, parrots and passerines) to test the hypothesis of its Gondwanan origin. Location Global. Methods The phylogenetic tree used in the analysis was a family-level tree estimated from previously published nuclear DNA sequence data. Each family for which a thorough and taxonomically well-sampled phylogenetic analysis exists was subject to an initial dispersal-vicariance analysis in order to reconstruct ancestral areas for its two most basal lineages. Both basal lineages were then used to represent the family in the subsequent reconstruction of ancestral distributions for the entire radiation. Results The analysis showed that three reciprocally monophyletic groups of terrestrial birds have diversified in the Gondwanan land areas of Australia, South America and Africa, respectively. Although each of these three groups may also have originally included other groups, the only survivors today from the Australian radiation are the passerines and parrots, while the falcons and seriemas have survived from the South American radiation. The group of survivors from the African radiation is considerably more taxonomically diverse and includes all coraciiform and piciform birds, owls, diurnal raptors (except falcons), New World vultures, trogons, mousebirds and cuckoo-rollers. Main conclusions The outlined evolutionary scenario with three geographically isolated clades of terrestrial birds is consistent with the available estimates of Late Cretaceous to early Palaeogene dates for these radiations. The diversifications and ecological adaptations within each of the three groups most likely took place in isolation on the different continents. Many cases of convergently evolved adaptations may be revealed through the increased understanding of the phylogenetic relationships of terrestrial birds. © 2011 Blackwell Publishing Ltd. Source

Ronquist F.,Swedish Museum of Natural History | Deans A.R.,North Carolina State University
Annual Review of Entomology | Year: 2010

Bayesian inference and Markov chain Monte Carlo techniques have enjoyed enormous popularity since they were introduced into phylogenetics about a decade ago. We provide an overview of the field, with emphasis on recent developments of importance to empirical systematists. In particular, we describe a number of recent advances in the stochastic modeling of evolution that address major deficiencies in current models in a computationally efficient way. These include models of process heterogeneity across sites and lineages, as well as alignment-free models and model averaging approaches. Many of these methods should find their way into standard analyses in the near future. We also summarize the influence of Bayesian methods on insect systematics, with particular focus on current practices and how they could be improved using existing and emerging techniques. © 2010 by Annual Reviews All rights reserved. Source

Discover hidden collaborations