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  • 1
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    The evolution of thecideide microstructures and textures: traced from Triassic to Holocene (2021)
    Details
    Publikationsdatum: 2021-07-21
    Beschreibung: Thecideide brachiopods are an anomalous group of invertebrates. In this study, we discuss the evolution of thecideide brachiopods from the Triassic to the Holocene and base our results and conclusions on microstructure and texture measurements gained from electron backscatter diffraction (EBSD). In fossil and Recent thecideide shells, we observe the following mineral units: (1) nanometric to small granules; (2) acicles; (3) fibres; (4) polygonal crystals; and (5) large roundish crystals. We trace for thecideide shells the change of mineral unit characteristics such as morphology, size, orientation, arrangement and distribution pattern. Triassic thecideide shells contain extensive sections formed of fibres interspersed with large, roundish crystals. Upper Cretaceous to Pleistocene thecideide hard tissues consist of a matrix of minute to small grains reinforced by acicles and small polygonal crystals. Recent thecideide species form their shell of mineral units that show a wide range of shapes, sizes and arrangements. We find from Late Triassic to Recent a gradual decrease in mineral unit size, regularity of mineral unit morphology and orientation and the degree of calcite co‐orientation. While crystallite co‐orientation is the highest for fibrous microstructures, it is strikingly low for taxa that form their shell out of nanogranular to acicular mineral units. Our results indicate that Upper Jurassic species represent transitional forms between ancient taxa with fibrous shells and Recent forms that construct their shells of acicles and granules. We attribute the observed changes in microstructure and texture to be an adaptation to a different habitat and lifestyle associated with cementation to hard substrates.
    Beschreibung: H2020 Marie Skłodowska‐Curie Actions http://dx.doi.org/10.13039/100010665
    Beschreibung: WOA Institution: LUDWIG‐MAXIMILIANS‐UNIVERSITAET MUNCHEN
    Schlagwort(e): 560 ; Brachiopoda ; calcite crystals ; calcite fibre ; EBSD ; shell microstructure evolution ; thecideides
    Materialart: article
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    CITATION GEO-LEO
  • 2
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    Out of the tropics, but how? Fossils, bridge species, and thermal ranges in the dynamics of the marine latitudinal diversity gradient (2013)
    National Academy of Sciences
    Details
    Publikationsdatum: 2013-06-12
    Print ISSN: 0027-8424
    Digitale ISSN: 1091-6490
    Thema: Biologie , Medizin , Allgemeine Naturwissenschaft
    Publiziert von National Academy of Sciences
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  • 3
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    A decline in molluscan carbonate production driven by the loss of vegetated habitats encoded in the Holocene sedimentary record of the Gulf of Trieste (2018)
    Wiley
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    Publikationsdatum: 2018
    Beschreibung: Abstract Carbonate sediments in non‐vegetated habitats on the north‐east Adriatic shelf are dominated by shells of molluscs. However, the rate of carbonate molluscan production prior to the 20th century eutrophication and overfishing on this and other shelves remains unknown because: (i) monitoring of ecosystems prior to the 20th century was scarce; and (ii) ecosystem history inferred from cores is masked by condensation and mixing. Here, based on geochronological dating of four bivalve species, carbonate production during the Holocene is assessed in the Gulf of Trieste, where algal and seagrass habitats underwent a major decline during the 20th century. Assemblages of sand‐dwelling Gouldia minima and opportunistic Corbula gibba are time‐averaged to 〉1000 years and Corbula gibba shells are older by 〉2000 years than shells of co‐occurring Gouldia minima. This age difference is driven by temporally disjunct production of two species coupled with decimetre‐scale mixing. Stratigraphic unmixing shows that Corbula gibba declined in abundance during the highstand phase and increased again during the 20th century. In contrast, one of the major contributors to carbonate sands – Gouldia minima – increased in abundance during the highstand phase, but declined to almost zero abundance over the past two centuries. Gouldia minima and herbivorous gastropods associated with macroalgae or seagrasses are abundant in the top‐core increments but are rarely alive. Although Gouldia minima is not limited to vegetated habitats, it is abundant in such habitats elsewhere in the Mediterranean Sea. This live–dead mismatch reflects the difference between highstand baseline communities (with soft‐bottom vegetated zones and hard‐bottom Arca beds) and present‐day oligophotic communities with organic‐loving species. Therefore, the decline in light penetration and the loss of vegetated habitats with high molluscan production traces back to the 19th century. More than 50% of the shells on the sea floor in the Gulf of Trieste reflect inactive production that was sourced by heterozoan carbonate factory in algal or seagrass habitats.
    Print ISSN: 0037-0746
    Digitale ISSN: 1365-3091
    Thema: Geologie und Paläontologie
    Publiziert von Wiley
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  • 4
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    Tracing the effects of eutrophication on molluscan communities in sediment cores: outbreaks of an opportunistic species coincide with reduced bioturbation and high frequency of hypoxia in the Adriatic Sea (2018)
    Paleontological Society
    Details
    Publikationsdatum: 2018
    Beschreibung: 〈span〉〈div〉Abstract〈/div〉Estimating the effects and timing of anthropogenic impacts on the composition of macrobenthic communities is challenging, because early twentieth-century surveys are sparse and the corresponding intervals in sedimentary sequences are mixed by bioturbation. Here, to assess the effects of eutrophication on macrobenthic communities in the northern Adriatic Sea, we account for mixing with dating of the bivalve 〈span〉Corbula gibba〈/span〉 at two stations with high accumulation (Po prodelta) and one station with moderate accumulation (Isonzo prodelta). We find that, first, pervasively bioturbated muds typical of highstand conditions deposited in the early twentieth century were replaced by muds with relicts of flood layers and high content of total organic carbon (TOC) deposited in the late twentieth century at the Po prodelta. The twentieth century shelly muds at the Isonzo prodelta are amalgamated but also show an upward increase in TOC. Second, dating of 〈span〉C. gibba〈/span〉 shells shows that the shift from the early to the late twentieth century is characterized by a decrease in stratigraphic disorder and by an increase in temporal resolution of assemblages from ~25–50 years to ~10–20 years in both regions. This shift reflects a decline in the depth of the fully mixed layer from more than 20 cm to a few centimeters. Third, the increase in abundance of the opportunistic species 〈span〉C. gibba〈/span〉 and the loss of formerly abundant, hypoxia-sensitive species coincided with the decline in bioturbation, higher preservation of organic matter, and higher frequency of seasonal hypoxia in both regions. This depositional and ecosystem regime shift occurred in ca. 〈span〉a.d.〈/span〉 1950. Therefore, the effects of enhanced food supply on macrobenthic communities were overwhelmed by oxygen depletion, even when hypoxic conditions were limited to few weeks per year in the northern Adriatic Sea. Preservation of trends in molluscan abundance and flood events in cores was enhanced by higher frequency of hypoxia that reduced bioturbation in the late twentieth century.〈/span〉
    Print ISSN: 0094-8373
    Digitale ISSN: 1938-5331
    Thema: Geologie und Paläontologie
    Publiziert von Paleontological Society
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  • 5
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    Accounting for the effects of biological variability and temporal autocorrelation in assessing the preservation of species abundance (2011)
    Paleontological Society
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    Publikationsdatum: 2011-03-01
    Beschreibung: Quantifying the effects of taphonomic processes on species abundances in time-averaged death assemblages (DAs) is pivotal for paleoecological inference. However, fidelity estimates based on conventional "live-dead" comparisons are fundamentally ambiguous: (1) data on living assemblages (LAs) are based on a very short period of sampling and thus do not account for biological variability in the LA, (2) LAs are sampled at the same time as the DA and thus do not necessarily reflect past LAs that contributed to the DA, (3) compositions of LAs and DAs can be autocorrelated owing to shared cohorts, and (4) fidelity estimates are cross-scale estimates because DAs are time-averaged and LAs are not. Some portion of raw (total) live-dead (LD) variation in species composition thus arises from incomplete sampling of LAs and from biological temporal variation among LAs (together = premortem component of LD variation), as contrasted with new variation created by interspecific variation in population turnover and preservation rates and by the time-averaging of skeletal input (together = postmortem component of LD variation). To tackle these problems, we introduce a modified test for homogeneity of multivariate dispersions (HMD) in order to (1) account for temporal autocorrelation in composition between LAs and DAs and (2) decompose total LD compositional variation into premortem and postmortem components, and we use simulations to evaluate the contribution of within-habitat time-averaging on the postmortem component. Applying this approach to 31 marine molluscan data sets, each consisting of spatial replicates of LAs and DAs in a single habitat, we find that total LD variation is driven largely by variation among LAs. However, genuinely postmortem processes have significant effects on composition in 25-65% of data sets (depending on the metric) when the effects of temporal autocorrelation are taken into account using HMD. Had we ignored the effects of autocorrelation, the effects of postmortem processes would have been negligible, inflating the similarity between LAs and DAs. Simulations show that within-habitat time-averaging does not increase total LD variation to a large degree--it increases total LD variation mainly via increasing species richness, and decreases total LD variation by reducing dispersion among DAs. The postmortem component of LD variation thus arises from differential turnover and preservation and multi-habitat time-averaging. Moreover, postmortem processes have less effect on the compositions of DAs in habitats characterized by high variability among LAs than they have on DAs in temporally stable habitats, a previously unrecognized first-order factor in estimating postmortem sources of compositional variation in DAs.
    Print ISSN: 0094-8373
    Digitale ISSN: 0094-8373
    Thema: Geologie und Paläontologie
    Publiziert von Paleontological Society
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  • 6
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    TRACING ORIGIN AND COLLAPSE OF HOLOCENE BENTHIC BASELINE COMMUNITIES IN THE NORTHERN ADRIATIC SEA (2019)
    Society for Sedimentary Geology (SEPM)
    In: PALAIOS
    Details
    Publikationsdatum: 2019
    Beschreibung: 〈span〉〈div〉ABSTRACT〈/div〉The shallow northern Adriatic Sea has a long history of anthropogenic impacts that reaches back many centuries. While the effects of eutrophication, overfishing, pollution, and trawling over recent decades have been extensively studied, the major ecological turnovers during the Holocene as a whole remain poorly explored. In this study, we reconstruct ecological baselines defining benthic ecosystem composition prior to major anthropogenic changes at four stations characterized by low sedimentation and millennial-scale time averaging of molluscan assemblages. We discriminate between natural and anthropogenic drivers based on (1) stratigraphic changes in the composition of molluscan communities observed in sediment cores and (2) changes in concentrations of heavy metals, pollutants, and organic enrichment. The four 1.5-m long sediment cores reach back to the Pleistocene–Holocene boundary, allowing for a stratigraphic distinction of the major sea-level phases of the Holocene. During the transgressive phase and maximum flooding, sea-level and establishment of the modern circulation pattern determined the development of benthic communities in shallow-water, vegetated habitats with epifaunal biostromes and, in deeper waters, with bryozoan meadows. After sea-level stabilization, the composition of these baseline communities remained relatively uniform and started to change markedly only with the intensification of human impacts in the late highstand, leading to a dominance of infauna and a decline of epifauna at all sites. This profound ecological change reduced species richness, increased the abundance of infaunal suspension feeders, and led to a decline of grazers and deposit feeders. We suggest that modern soft-bottom benthic communities in the northern Adriatic Sea today do not show the high geographic heterogeneity in composition characteristic of benthos prior to anthropogenic influences.〈/span〉
    Print ISSN: 0883-1351
    Digitale ISSN: 0883-1351
    Thema: Geologie und Paläontologie
    Publiziert von Society for Sedimentary Geology (SEPM)
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  • 7
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    Millennial‐Scale Age Offsets Within Fossil Assemblages: Result of Bioturbation Below the Taphonomic Active Zone and Out‐of‐Phase Production (2019)
    Wiley
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    Publikationsdatum: 2019
    Beschreibung: Abstract Oceanographic and evolutionary inferences based on fossil assemblages can be obscured by age offsets among co‐occurring shells (i.e., time averaging). To identify the contributions of sedimentation, mixing, durability, and production to within‐ and between‐species age offsets, we analyze downcore changes in the age‐frequency distributions of two bivalves on the California shelf. Within‐species age offsets are ~50–2,000 years for Parvilucina and ~2,000–4,000 years for Nuculana and between‐species offsets are 1,000–4,000 years within the 10‐ to 25‐cm‐thick stratigraphic units. Shells within the top 20–24 cm of the seabed are age‐homogeneous, defining the thickness of the surface completely‐mixed layer (SML), and have strongly right‐skewed age‐frequency distributions, indicating fast shell disintegration. The SML thus coincides with the taphonomic active zone and extends below the redoxcline at ~10 cm. Shells 〉2,000–3,000 years old occurring within the SML have been exhumed from subsurface shell‐rich units rich where disintegration is negligible (sequestration zone, SZ). Burrowers (callianassid shrimps) penetrate 40–50 cm below the seafloor into this SZ. The millennial offsets within each increment result from the advection of old shells from the SZ, combined with an out‐of‐phase change in species production. Age unmixing reveals that Parvilucina was abundant during the transgressive phase, rare during the highstand phase, and increased steeply in the twentieth century in response to wastewater. Nuculana was abundant during the highstand phase and has declined over the past two centuries. This sequestration‐exhumation dynamic accentuates age offsets by allowing both the persistence of shells below the SML and their later admixing with younger shells within the SML.
    Print ISSN: 0883-8305
    Digitale ISSN: 2572-4525
    Thema: Geologie und Paläontologie
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 8
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    Persistently rare species experience stronger negative frequency dependence than common species: A statistical attractor that is hard to avoid (2019)
    Wiley
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    Publikationsdatum: 2019
    Beschreibung: Abstract Aim Why are so many species rare, yet persistent? Possibly, rare species experience strong negative frequency dependence (NFD, i.e. strong intraspecific competition relative to interspecific competition), which both makes them rare and buffers them against extinction. A second, not mutually exclusive, possibility is that rare species that experience weak NFD go extinct quickly due to demographic and environmental stochasticity. Both possibilities predict that persistent rare species will experience stronger NFD than common ones. A previous study confirmed this prediction in a range of mostly terrestrial communities. Here, we test that prediction in lake zooplankton and explore its theoretical basis. Location Fifty‐three temperate lakes. Time period 1970–2011. Major taxa studied Cladocerans, copepods. Methods We used long‐term time series data to estimate the covariance between strength of NFD and mean frequency (relative abundance) for crustacean zooplankton. We used a randomization test to ask whether the covariance between NFD and mean frequency is stronger than expected, given sampling error. We also calculated the covariance between NFD and mean frequency in simulated communities from three different ecological models. Results Rare species experience significantly stronger NFD than common species in over half of the communities. The distribution of associations between NFD and rarity is skewed towards weak associations, which always occur in communities with high evenness. All three theoretical models reproduce these empirical results, even though they are based on different mechanisms (demographic or environmental stochasticity, and mathematical constraints on possible NFD–frequency relationships). Main conclusions Rare species typically experience stronger NFD than common ones because there are many different ecological scenarios in which they will do so, and only a few scenarios in which they won't. Like several other macroecological patterns, the tendency for rare species to experience stronger NFD than common ones is a “statistical attractor” that is hard to avoid.
    Print ISSN: 1466-822X
    Digitale ISSN: 1466-8238
    Thema: Biologie , Geographie
    Publiziert von Wiley
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  • 9
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    Phanerozoic trends in the global diversity of marine invertebrates (2008)
    American Association for the Advancement of Science (AAAS)
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    Publikationsdatum: 2008-07-05
    Beschreibung: It has previously been thought that there was a steep Cretaceous and Cenozoic radiation of marine invertebrates. This pattern can be replicated with a new data set of fossil occurrences representing 3.5 million specimens, but only when older analytical protocols are used. Moreover, analyses that employ sampling standardization and more robust counting methods show a modest rise in diversity with no clear trend after the mid-Cretaceous. Globally, locally, and at both high and low latitudes, diversity was less than twice as high in the Neogene as in the mid-Paleozoic. The ratio of global to local richness has changed little, and a latitudinal diversity gradient was present in the early Paleozoic.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Alroy, John -- Aberhan, Martin -- Bottjer, David J -- Foote, Michael -- Fursich, Franz T -- Harries, Peter J -- Hendy, Austin J W -- Holland, Steven M -- Ivany, Linda C -- Kiessling, Wolfgang -- Kosnik, Matthew A -- Marshall, Charles R -- McGowan, Alistair J -- Miller, Arnold I -- Olszewski, Thomas D -- Patzkowsky, Mark E -- Peters, Shanan E -- Villier, Loic -- Wagner, Peter J -- Bonuso, Nicole -- Borkow, Philip S -- Brenneis, Benjamin -- Clapham, Matthew E -- Fall, Leigh M -- Ferguson, Chad A -- Hanson, Victoria L -- Krug, Andrew Z -- Layou, Karen M -- Leckey, Erin H -- Nurnberg, Sabine -- Powers, Catherine M -- Sessa, Jocelyn A -- Simpson, Carl -- Tomasovych, Adam -- Visaggi, Christy C -- New York, N.Y. -- Science. 2008 Jul 4;321(5885):97-100. doi: 10.1126/science.1156963.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉National Center for Ecological Analysis and Synthesis, University of California-Santa Barbara, 735 State Street, Santa Barbara, CA 93101, USA. alroy@nceas.ucsb.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18599780" target="_blank"〉PubMed〈/a〉
    Schlagwort(e): Animals ; *Biodiversity ; Biological Evolution ; Databases, Factual ; Environment ; *Fossils ; Geography ; Geologic Sediments ; *Invertebrates/classification ; *Paleontology/methods ; Population Dynamics ; Sampling Studies ; Seawater ; Time Factors
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 10
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    Molluscan benthic communities at Brijuni Islands (northern Adriatic Sea) shaped by Holocene sea-level rise and recent human eutrophication and pollution (2018)
    Sage
    Details
    Publikationsdatum: 2018
    Beschreibung: The Holocene, Volume 28, Issue 11, Page 1801-1817, November 2018. 〈br/〉
    Print ISSN: 0959-6836
    Digitale ISSN: 1477-0911
    Thema: Geographie , Geologie und Paläontologie
    Publiziert von Sage
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