The Cretaceous-Tertiary biotic transition Macleod, N; Rawson, P. F; Forey, P. L ...
Journal of the Geological Society,
03/1997, Letnik:
154, Številka:
2
Journal Article
Recenzirano
Mass extinctions are recognized through the study of fossil groups across event horizons, and from analyses of long-term trends in taxonomic richness and diversity. Both approaches have inherent ...flaws, and data that once seemed reliable can be readily superseded by the discovery of new fossils and/or the application of new analytical techniques. Herein the current state of the Cretaceous-Tertiary (K-T) biostratigraphical record is reviewed for most major fossil clades, including: calcareous nannoplankton, dinoflagellates, diatoms, radiolaria, foraminifera, ostracodes, scleractinian corals, bryozoans, brachio-pods, molluscs, echinoderms, fish, amphibians, reptiles and terrestrial plants (macrofossils and palynomorphs). These reviews take account of possible biasing factors in the fossil record in order to extract the most comprehensive picture of the K-T biotic crisis available. Results suggest that many faunal and floral groups (ostracodes, bryozoa, ammonite cephalopods, bivalves, archosaurs) were in decline throughout the latest Maastrichtian while others (diatoms, radiolaria, benthic foraminifera, brachiopods, gastropods, fish, amphibians, lepidosaurs, terrestrial plants) passed through the K-T event horizon with only minor taxonomic richness and/or diversity changes. A few microfossil groups (calcareous nannoplankton, dinoflagellates, planktonic foraminifera) did experience a turnover of varying magnitudes in the latest Maastrichtian-earliest Danian. However, many of these turnovers, along with changes in ecological dominance patterns among benthic foraminifera, began in the latest Maastrichtian. Improved taxonomic estimates of the overall pattern and magnitude of the K-T extinction event must await the development of more reliable systematic and phylogenetic data for all Upper Cretaceous clades.
We present new data on
87Sr/
86Sr, δ
13C and δ
18O, and elemental compositions of belemnites from 85 m of Valanginian, Hauterivian and Barremian strata at Speeton, Yorkshire, eastern England. The
...87Sr/
86Sr data provide a global standard for
87Sr/
86Sr isotopic dating, and correlation to the biostratigraphic schemes of NW Europe. Values of
87Sr/
86Sr increase from 0.707380±0.000003, at the base of the Hauterivian, to 0.707493±0.000004 in the earliest Late Barremian
Paracrioceras elegans ammonite Zone before decreasing thereafter towards an Aptian minimum. The downturn in the
elegans Zone coincided with the onset of volcanism on the present Ontong Java Plateau. A linear interpretation of the
87Sr/
86Sr profile shows that the relative durations of ammonite zones differ by a factor ≤18. The basal Hauterivian unconformably overlies Valanginian strata; the discontinuity in
87Sr/
86Sr across this surface represents a gap in sedimentation of 2.0 myr. In our belemnites (mostly of the genera
Hibolites,
Acroteuthis, and
Aulacoteuthis) the absence of a correlation between δ
18O and δ
13C suggests that strong non-equilibrium fractionation has not affected the isotopic composition of the calcite. Our δ
18O values therefore approximate to a valid record of marine palaeo-temperatures. Specimens of the genus
Hibolites have δ
18O values that are 0.4‰ more positive than those of co-occurring specimens of the genus
Acroteuthis. This offset may be explained as resulting from small (0.4‰) departures from equilibrium during precipitation of calcite, different depth habitats, or changing temperature in the Speeton sea in the time that elapsed between deposition of our individual belemnites. The averaged belemnite record of δ
18O through the section shows that seawater warmed from around 11°C at the base of the Hauterivian to a maximum around 15°C in the middle of the Hauterivian
regale Zone, and returned to a cooler temperature of around 11°C by the middle of the overlying
inversum Zone, a temperature that persisted to the basal Barremian. Through the Barremian, temperature increased to a peak of 20°C in the early Late Barremian
elegans Zone then, in the same zone, precipitately and temporarily decreased to around 14°C at about the time of onset of volcanism on the Ontong Java Plateau, before they returned to around 16°C in the uppermost part of the section. In specimens of
Aulacoteuthis and
Acroteuthis, a good correlation between δ
18O and the content of Na, Sr, and Mg suggests that incorporation of these trace elements in these genera is largely controlled by temperature. The dependency of concentration on temperature ranges from 7 to 20% per degree Celsius, if equilibrium fractionation of oxygen isotopic composition is assumed, so the Mg, Na and Sr content of these genera may be used as palaeo-temperature proxies. The trace element content of
Hibolites shows no relation to stable oxygen isotopic composition and so does not record palaeo-temperature.
Machine learning (ML) is a growing field in medicine. This narrative review describes the current body of literature on ML for clinical decision support in infectious diseases (ID).
We aim to inform ...clinicians about the use of ML for diagnosis, classification, outcome prediction and antimicrobial management in ID.
References for this review were identified through searches of MEDLINE/PubMed, EMBASE, Google Scholar, biorXiv, ACM Digital Library, arXiV and IEEE Xplore Digital Library up to July 2019.
We found 60 unique ML-clinical decision support systems (ML-CDSS) aiming to assist ID clinicians. Overall, 37 (62%) focused on bacterial infections, 10 (17%) on viral infections, nine (15%) on tuberculosis and four (7%) on any kind of infection. Among them, 20 (33%) addressed the diagnosis of infection, 18 (30%) the prediction, early detection or stratification of sepsis, 13 (22%) the prediction of treatment response, four (7%) the prediction of antibiotic resistance, three (5%) the choice of antibiotic regimen and two (3%) the choice of a combination antiretroviral therapy. The ML-CDSS were developed for intensive care units (n = 24, 40%), ID consultation (n = 15, 25%), medical or surgical wards (n = 13, 20%), emergency department (n = 4, 7%), primary care (n = 3, 5%) and antimicrobial stewardship (n = 1, 2%). Fifty-three ML-CDSS (88%) were developed using data from high-income countries and seven (12%) with data from low- and middle-income countries (LMIC). The evaluation of ML-CDSS was limited to measures of performance (e.g. sensitivity, specificity) for 57 ML-CDSS (95%) and included data in clinical practice for three (5%).
Considering comprehensive patient data from socioeconomically diverse healthcare settings, including primary care and LMICs, may improve the ability of ML-CDSS to suggest decisions adapted to various clinical contexts. Currents gaps identified in the evaluation of ML-CDSS must also be addressed in order to know the potential impact of such tools for clinicians and patients.
Detailed stratigraphic logging and systematic studies on late Valanginian–early Barremian ammonites from the Agrio Formation of the Neuquén Basin of west-central Argentina, have provided a detailed ...local ammonite zonation. Here we combine the ammonite data with an initial study of calcareous nannofossils and palynomorphs from two sections to produce a provisional integrated biostratigraphy for the Agrio Formation. While the palynomorphs are essentially of local value only, especially the continental forms, the nannofossils and the ammonites allow some correlations to be made with the European Mediterranean `standard' sequences.
The Neuquén Basin is a stratigraphically- and economically-important Early Cretaceous depocentre located in west-central Argentina. The Early Valanginian to Early Barremian succession (upper Vaca ...Muerta, Mulichinco and Agrio Formations) contains a rich fossil record, with abundant bivalves and ammonoids. Palaeosalinities are determined systematically throughout the succession, based on an oxygen isotope analysis of unaltered oyster shells from two localities in Neuquén province. A total of 188 oyster samples from 52 stratigraphic levels were processed. A total of 52 mean values of
δ
18O isotope are used to calculate palaeosalinities, assuming an estimated water temperature of 25 °C. The observed range of palaeosalinities, between the maximum and the minimum, is 19, which is in conflict with published accounts of this being a fully marine succession. The isotopic data are combined with independent faunal evidence to evaluate palaeosalinity variation both laterally and temporally. Significant fluctuations in water salinity are indicated, with a clear tendency to increase from brachyhaline to euhaline and near hyperhaline conditions through time. The fluctuations were probably due to dilution from normal marine water, caused primarily by variations in rainfall and continental runoff. In addition, the presence of a volcanic island arc along the western margin of the basin may have at least partially isolated the basin from the marine waters of the Pacific Ocean. Also, a gulf-shaped basin may have inhibited hydrodynamic exchange with the ocean while enhancing retention of continental waters.
Concern about the effects of global change on our planet's future has driven much research into the last few thousand years of earth history. In contrast, this volume takes a much longer viewpoint to ...provide a historical perspective to recent and future global change. Over 40 international specialists investigate the reaction of life to global environmental changes, from Cretaceous times to the turn of the century. During this time earth's climate has changed from a very warm, 'greenhouse' phase with no significant ice sheets to today's 'ice-house' world. A wide spectrum of animal, plant and protistan life is discussed, encompassing terrestrial, shallow-marine and deep-marine realms. Each chapter considers a particular taxonomic group, looking first at the general picture and then focusing on more specialized aspects such as extinctions, diversity and biogeography. This volume will form an invaluable reference for researchers and graduate students in paleontology, geology, biology, oceanography and climatology.
Knowledge of key drivers and therapeutic targets in mucosal melanoma is limited due to the paucity of comprehensive mutation data on this rare tumor type. To better understand the genomic landscape ...of mucosal melanoma, here we describe whole genome sequencing analysis of 67 tumors and validation of driver gene mutations by exome sequencing of 45 tumors. Tumors have a low point mutation burden and high numbers of structural variants, including recurrent structural rearrangements targeting TERT, CDK4 and MDM2. Significantly mutated genes are NRAS, BRAF, NF1, KIT, SF3B1, TP53, SPRED1, ATRX, HLA-A and CHD8. SF3B1 mutations occur more commonly in female genital and anorectal melanomas and CTNNB1 mutations implicate a role for WNT signaling defects in the genesis of some mucosal melanomas. TERT aberrations and ATRX mutations are associated with alterations in telomere length. Mutation profiles of the majority of mucosal melanomas suggest potential susceptibility to CDK4/6 and/or MEK inhibitors.
The ability to monitor intracellular events in real time is paramount to advancing fundamental biological and clinical science. We present the first demonstration of a direct interface of vertically ...aligned single-walled carbon nanotubes (VASWCNTs) with eukaryotic cells, RAW 264.7 mouse macrophage cell line. The cells were cultured on indium tin oxide with VASWCNTs. VASWCNTs entered the cells naturally without application of any external force and were shown to sense the intracellular presence of a redox active moiety, methylene blue. The technology developed provides an alluring platform to enable electrochemical study of an intracellular environment.
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