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The mineralogy and alteration history of the Yamato-type (CY) carbonaceous chondrites
No full textThe CY chondrites are a group of thermally metamorphosed carbonaceous chondrites. Although they share similarities with the CM and CI chondrites, their primary properties argue for a distinct classification. Previous studies have highlighted their isotopically heavy bulk compositions (δ17O = 10 ‰, δ18O = 21 ‰, Δ17O = 0 ‰) and exceptionally high sulphide abundances (10–30 vol%). In this work we explore their petrography and alteration history. The CYs accreted low abundances of chondrules (15–20 area%) with average apparent diameters slightly larger (∼320–340 µm) than the CM chondrites. In contrast to the CMs, the CYs record an early episode of brecciation prior to the main window of aqueous alteration. Subsequent fluid activity produced a range of alteration extents with both CY2 and CY1 chondrites documented. Phyllosilicate minerals in the CYs were a mix of serpentine and saponite (including occurrences of Na-saponite) with minor quantities of chlorite (within chondrules). An initial generation of Fe-sulphides formed by sulfidation of metal, and by precipitation from S-rich fluids. Three generations of carbonates are recognized, an early generation that infilled voids left by brecciation and co-precipitated with sulphide, a later generation that co-precipitated with magnetite and a final Fe-Mg-bearing generation which formed large (>100 µm) clasts. Only the first-generation carbonates are found in the CY2s, while the CY1s preserve all three generations. Phosphates occur as Ca-apatite or rarely as Mg-bearing apatite and have hydroxylapatite compositions, indicating low halogen activities in the alteration fluids. Refractory oxides (ilmenite and Cr-spinel) occur as precipitates adhering to the margins of phyllosilicates. They formed late in the alteration sequence and attest to oxidizing conditions. During the late-stages of aqueous alteration Fe-sulphides were replaced by magnetite. Thermal metamorphism (Stage II-IV: ∼300–750 °C) overprinted aqueous alteration leading to dehydration and recrystallization of the phyllosilicate matrix and the decomposition of some carbonate phases. Most Fe-sulphide grains survived heating without decomposition as initial partial decomposition from pyrrhotite to troilite under closed system conditions led to elevated ƒS2 gas and resulted in a stabilizing effect. Retrograde reactions between trapped S2 gas and metal/magnetite formed a final generation of Fe-sulphides. The survival of Fe-sulphides and their stochiometric troilite compositions are evidence for near-closed system heating. Analysis of organic matter by Raman spectroscopy supports an interpretation of short-duration heating (on the scale of minutes to days), at peak temperatures between 750 and 900 °C. Thus, an impact event was the most likely cause of metamorphic heating.Copyright © 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). The linked file is the published version of the article.NHM Repositor
Hapalosiphonacean cyanobacteria (Nostocales) thrived amid emerging embryophytes in an early Devonian (407-million-year-old) landscape
Get PDFCyanobacteria have a long evolutionary history, well documented in marine rocks. They are also abundant and diverse in terrestrial environments; however, although phylogenies suggest that the group colonized land early in its history, paleontological documentation of this remains limited. The Rhynie chert (407 Ma), our best preserved record of early terrestrial ecosystems, provides an opportunity to illuminate aspects of cyanobacterial diversity and ecology as plants began to radiate across the land surface. We used light microscopy and super-resolution confocal laser scanning microscopy to study a new population of Rhynie cyanobacteria; we also reinvestigated previously described specimens that resemble the new fossils. Our study demonstrates that all are part of a single fossil species belonging to the Hapalosiphonaceae (Nostocales). Along with other Rhynie microfossils, these remains show that the accommodation of morphologically complex cyanobacteria to terrestrial ecosystems transformed by embryophytes was well underway more than 400 million years ago.Copyright © 2023 The Authors. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). The attached file is the published version of the article.NHM Repositor
Impact‐Induced Porosity and Microfracturing at the Chicxulub Impact Structure
No full textAbstract: Porosity and its distribution in impact craters has an important effect on the petrophysical properties of impactites: seismic wave speeds and reflectivity, rock permeability, strength, and density. These properties are important for the identification of potential craters and the understanding of the process and consequences of cratering. The Chicxulub impact structure, recently drilled by the joint International Ocean Discovery Program and International Continental scientific Drilling Program Expedition 364, provides a unique opportunity to compare direct observations of impactites with geophysical observations and models. Here, we combine small‐scale petrographic and petrophysical measurements with larger‐scale geophysical measurements and numerical simulations of the Chicxulub impact structure. Our aim is to assess the cause of unusually high porosities within the Chicxulub peak ring and the capability of numerical impact simulations to predict the gravity signature and the distribution and texture of porosity within craters. We show that high porosities within the Chicxulub peak ring are primarily caused by shock‐induced microfracturing. These fractures have preferred orientations, which can be predicted by considering the orientations of principal stresses during shock, and subsequent deformation during peak ring formation. Our results demonstrate that numerical impact simulations, implementing the Dynamic Collapse Model of peak ring formation, can accurately predict the distribution and orientation of impact‐induced microfractures in large craters, which plays an important role in the geophysical signature of impact structures.Copyright ©2019. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. The linked article is the published version of the article.NHM Repositor
A microchondrule‐bearing micrometeorite and comparison with microchondrules in <scp>CM</scp> chondrites
No full textAbstract: We report the discovery of a partially altered microchondrule within a fine‐grained micrometeorite. This object is circular, <10 μm in diameter, and has a cryptocrystalline texture, internal zonation, and a thin S‐bearing rim. These features imply a period of post‐accretion parent body aqueous alteration, in which the former glassy igneous texture was subject to hydration and phyllosilicate formation as well as leaching of fluid‐mobile elements. We compare this microchondrule to three microchondrules found in two CM chondrites: Elephant Moraine (EET) 96029 and Murchison. In all instances, their formation appears closely linked to the late stages of chondrule formation, chondrule recycling, and fine‐grained rim accretion. Likewise, they share cryptocrystalline textures and evidence of mild aqueous alteration and thus similar histories. We also investigate the host micrometeorite's petrology, which includes an unusually Cr‐rich mineralogy, containing both Mn‐chromite spinel and low‐Fe‐Cr‐rich (LICE) anhydrous silicates. Because these two refractory phases cannot form together in a single geochemical reservoir under equilibrium condensation, this micrometeorite's accretionary history requires a complex timeline with formation via nonequilibrium batch crystallization or accumulation of materials from large radial distances. In contrast, the bulk composition of this micrometeorite and its internal textures are consistent with a hydrated carbonaceous chondrite source. This micrometeorite is interpreted as a fragment of fine‐grained rim material that once surrounded a larger parent chondrule and was derived from a primitive carbonaceous parent body; either a CM chondrite or Jupiter family comet.Copyright © The Meteoritical Society, 2019. The linked article is the published version of the article.NHM Repositor
Recovery and curation of the Winchcombe (<scp>CM2</scp>) meteorite
No full textAbstract: The Winchcombe meteorite fell on February 28, 2021 and was the first recovered meteorite fall in the UK for 30 years, and the first UK carbonaceous chondrite. The meteorite was widely observed by meteor camera networks, doorbell cameras, and eyewitnesses, and 213.5 g (around 35% of the final recovered mass) was collected quickly—within 12 h—of its fall. It, therefore, represents an opportunity to study very pristine extra‐terrestrial material and requires appropriate careful curation. The meteorite fell in a narrow (600 m across) strewn field ~8.5 km long and oriented approximately east–west, with the largest single fragment at the farthest (east) end in the town of Winchcombe, Gloucestershire. Of the total known mass of 602 g, around 525 g is curated at the Natural History Museum, London. A sample analysis plan was devised within a month of the fall to enable scientists in the UK and beyond to quickly access and analyze fresh material. The sample is stored long term in a nitrogen atmosphere glove box. Preliminary macroscopic and electron microscopic examinations show it to be a CM2 chondrite, and despite an early search, no fragile minerals, such as halite, sulfur, etc., were observed.Copyright © 2023 The Authors. Meteoritics & Planetary Science published by Wiley Periodicals LLC on behalf of The Meteoritical Society. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. The linked file is the published version of the article.NHM Repositor
A new subspecies of Boletoxenus mixtus Grimm, 2014 (Coleoptera: Tenebrionidae: Tenebrioninae)
Get PDFBoletoxenus mixtus dynastes ssp. nov., a new subspecies of mycetophagous Bolitophagini darkling beetles from mainland SE Asia, is described and illustrated.Copyright © 2023, The Author. The attached file is the published version of the article.NHM Repositor
Purchasing models for scholarly materials in the UK: a case‐study
No full textThe current purchasing models employed at the London School of Economics
(LSE) for the acquisition of e-resources are outlined. The authors present LSE’s
fund structure and how budgets are distributed between print and electronic
purchases. A discussion that ranges from format types to national deals and
consortia provides the context for LSE’s collection development and
preservation policies.The uncertain position of e-books is examined, as for the
first time issues normally limited to journals stray into the realm of monographs,
affecting purchasing decisions for this newcomer to the e-resources sphere.
Conditions that would need to be met before LSE could consider adopting an
e-only purchasing policy are discussed.Test 202
The dynamic adaptive landscape of cetacean body size
No full textAdaptive landscapes are central to evolutionary theory, forming a conceptual bridge between micro- and macroevolution.1,2,3,4 Evolution by natural selection across an adaptive landscape should drive lineages toward fitness peaks, shaping the distribution of phenotypic variation within and among clades over evolutionary timescales.5 The location and breadth of these peaks in phenotypic space can also evolve,4 but whether phylogenetic comparative methods can detect such patterns has largely remained unexplored.6 Here, we characterize the global and local adaptive landscape for total body length in cetaceans (whales, dolphins, and relatives), a trait that spans an order of magnitude, across their ∼53-million-year evolutionary history. Using phylogenetic comparative methods, we analyze shifts in long-term mean body length7 and directional changes in average trait values8 for 345 living and fossil cetacean taxa. Remarkably, we find that the global macroevolutionary adaptive landscape of cetacean body length is relatively flat, with very few peak shifts occurring after cetaceans entered the oceans. Local peaks are more numerous and manifest as trends along branches linked to specific adaptations. These results contrast with previous studies using only extant taxa,9 highlighting the vital role of fossil data for understanding macroevolution.10,11,12 Our results indicate that adaptive peaks are dynamic and are associated with subzones of local adaptations, creating moving targets for species adaptation. In addition, we identify limits in our ability to detect some evolutionary patterns and processes and suggest that multiple approaches are required to characterize complex hierarchical patterns of adaptation in deep time.Copyright © 2023 The Author(s). Published by Elsevier Inc. 1787 This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). The linked document is the published version of the article.NHM Repositor
Draft mitogenomes of the invasive ant Lepisiota frauenfeldi (Mayr 1855) (Hymenoptera: Formicidae)
Get PDFWe present the draft mitochondrial genomes (mitogenomes) of two Lepisiota frauenfeldi (Mayr 1855) workers from two separate invasive populations detected in Western Australia (Perth OK569858) and Queensland (Brisbane OK5569859), Australia. The draft mitogenomes ranged between 16,657 and 17,090 bp and contained 37 genes (13 protein-coding genes (PCGs), 22 transfer RNAs (tRNAs), and two ribosomal RNA (rRNA) genes). As with other arthropod mitogenomes, we observed high A + T content (A: 39.4-39.8%, T: 40.55-41.5%). We confirmed the species identity by molecular diagnostics based on the partial mtCOI gene that showed >99% similarity between the Australian populations and other L. frauenfeldi sequences reported to date, and in the process identified putative origins of the invasive populations as Pakistan and India for the WA and Qld incursions respectively that suggested separate introductions.Copyright © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.NHM Repositor
How to escape from insect egg parasitoids: a review of potential factors explaining parasitoid absence across the Insecta
Get PDFThe egg is the first life stage directly exposed to the environment in oviparous animals, including many vertebrates and most arthropods. Eggs are vulnerable and prone to mortality risks. In arthropods, one of the most common egg mortality factors is attack from parasitoids. Yet, parasitoids that attack the egg stage are absent in more than half of all insect (sub)orders. In this review, we explore possible causes explaining why eggs of some insect taxa are not parasitized. Many insect (sub)orders that are not attacked by egg parasitoids lack herbivorous species, with some notable exceptions. Factors we consider to have led to escape from egg parasitism are parental egg care, rapid egg development, small egg size, hiding eggs, by e.g. placing them into the soil, applying egg coatings or having thick chorions preventing egg penetration, eusociality, and egg cannibalism. A quantitative network analysis of host–parasitoid associations shows that the five most-speciose genera of egg parasitoids display patterns of specificity with respect to certain insect orders, especially Lepidoptera and Hemiptera, largely including herbivorous species that deposit their eggs on plants. Finally, we discuss the many counteradaptations that particularly herbivorous species have developed to lower the risk of attack by egg parasitoids.Copyright © 2020 The Author(s) Published by the Royal Society. All rights reserved. The linked file is the published version of the article.NHM Repositor