Subjects -> PALEONTOLOGY (Total: 43 journals)
Showing 1 - 21 of 21 Journals sorted alphabetically
Alcheringa: An Australasian Journal of Palaeontology     Hybrid Journal   (Followers: 6)
Ameghiniana     Open Access  
Annales de Paléontologie     Full-text available via subscription   (Followers: 4)
Annals of Carnegie Museum     Full-text available via subscription   (Followers: 1)
Boreas: An International Journal of Quaternary Research     Hybrid Journal   (Followers: 12)
Comptes Rendus Palevol     Open Access  
European Journal of Protistology     Hybrid Journal   (Followers: 5)
EvoDevo     Open Access   (Followers: 4)
Facies     Hybrid Journal   (Followers: 9)
Fossil Record     Open Access   (Followers: 5)
Geobios     Full-text available via subscription   (Followers: 4)
Historical Biology: An International Journal of Paleobiology     Hybrid Journal   (Followers: 8)
Ichnos: An International Journal for Plant and Animal Traces     Hybrid Journal  
International Journal of Speleology     Open Access   (Followers: 3)
Journal of Paleolimnology     Hybrid Journal   (Followers: 5)
Journal of Paleontology     Hybrid Journal   (Followers: 8)
Journal of Quaternary Science     Hybrid Journal   (Followers: 29)
Journal of Vertebrate Paleontology     Full-text available via subscription   (Followers: 8)
Marine Micropaleontology     Hybrid Journal   (Followers: 2)
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen     Full-text available via subscription   (Followers: 3)
Novitates Paleoentomologicae     Open Access   (Followers: 1)
Open Quaternary     Open Access  
Palaeogeography, Palaeoclimatology, Palaeoecology     Hybrid Journal   (Followers: 11)
Palaeontographica A     Full-text available via subscription   (Followers: 7)
Palaeontology     Hybrid Journal   (Followers: 17)
Palaeoworld     Hybrid Journal   (Followers: 3)
Paläontologische Zeitschrift     Hybrid Journal   (Followers: 4)
Paleobiology     Full-text available via subscription   (Followers: 5)
PaleoBios     Open Access   (Followers: 1)
Paleoceanography and Paleoclimatology     Full-text available via subscription   (Followers: 4)
Paleontological Journal     Full-text available via subscription   (Followers: 4)
Palynology     Hybrid Journal   (Followers: 1)
Papers in Palaeontology     Hybrid Journal  
Quaternaire     Open Access   (Followers: 3)
Quaternary Research     Full-text available via subscription   (Followers: 19)
Quaternary Science Reviews     Hybrid Journal   (Followers: 24)
Review of Palaeobotany and Palynology     Hybrid Journal   (Followers: 1)
Revue de Micropaleontologie     Full-text available via subscription  
Rivista Italiana di Paleontologia e Stratigrafia (Research In Paleontology and Stratigraphy)     Open Access   (Followers: 1)
Spanish Journal of Palaeontology     Open Access  
Swiss Journal of Palaeontology     Hybrid Journal   (Followers: 4)
Vertebrate Anatomy Morphology Palaeontology     Open Access   (Followers: 1)
Zitteliana     Open Access  
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Paläontologische Zeitschrift
Journal Prestige (SJR): 0.658
Citation Impact (citeScore): 1
Number of Followers: 4  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1867-6812 - ISSN (Online) 0031-0220
Published by Springer-Verlag Homepage  [2469 journals]
  • First data on in situ pollen of Permotheca sardykensis Zalessky 1929 from
           the middle Permian of the Russian Platform

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      Abstract: Pollen grains were extracted from sporangia of the pollen organ Permotheca sardykensis for the first time. The material originates from the middle Permian deposits of the Kostovaty locality (Udmurt Republic, Russia). The pollen grains were studied with light, scanning, and transmission electron microscopy. The pollen grains are rounded to oval, protobisaccate, with a leptoma. The sacci are very small and difficult to see under transmitted light, but, in a scanning electron microscope, differ from the corpus region in their sculpture (they can be distinguished by their psilate surface versus verrucate corpus sculpture). The leptoma was distinguished in the transmission electron microscope only by a considerable thinning of the pollen wall. The pollen wall consists of two layers which may be interpreted as a thick ectexine without a clear subdivision into sublayers and a thin endexine. Outside the pollen grains, remnants of a thin probable tapetal layer are present. The observed results could arise from pollen wall deterioration during diagenesis or incomplete pollen wall development. The pollen grains from the sporangia of P. sardykensis strongly differ from in situ pollen types which were described from other Permotheca species earlier or were associated with Peltaspermales. This may indicate a heterogeneity of the genus Permotheca.
      PubDate: 2022-01-07
       
  • Colonial Heterocorallia (Cnidaria, Anthozoa) and their epibionts from the
           lower Carboniferous of Montagne Noire and Pyrenees, southern France

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      Abstract: Colonial heterocorals are uncommon faunal component of the Serpukhovian limestones of the Montagne Noire and Pyrenees in southern France. Four species are introduced into the newly established genus Semenomalophyllia. They all share the typical septal arrangement of heterocorals, at least in early stage of development. The fused axial ends of septa commonly withdraw during the ontogeny of larger sized species such as Semenomalophyllia herbigi and S. perretae. In S. weyeri, the septa are withdrawn from the axis and arranged in two series (‘minor’ and ‘major’) that show a striking morphological convergence with rugose corals. The corallites of the smallest species S. webbi are very similar to the solitary heterocorallian Heterophyllia ornata and possibly evolved from it. S. weyeri and S. perretae are commonly colonised by alcyonacean octocorals as indicated by the occurrence of sclerites covering the corallites. These are described as Lafustalcyon vachardi gen. et sp. nov., a new taxon yet only known in the Serpukhovian strata, and only affecting heterocoral colonies. In addition to the alcyonacean octocorals, a diverse assemblage of epibionts colonised the heterocorals: calcifying microbes, bryozoans, foraminifers, microconchids, crinoids, boring organisms, and microproblematica. Syn-vivo relationships can be demonstrated only between Semenomalophyllia and Lafustalcyon as the first commonly bio-immured the second. Other encrusting organisms could have colonised either living, erected colonies or broken or tilted dead colonies.
      PubDate: 2022-01-04
       
  • Special issue: Going Deep—Tracking life processes through time and
           space

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      PubDate: 2021-12-23
       
  • A relict oasis of living deep-sea mussels Bathymodiolus and
           microbial-mediated seep carbonates at newly-discovered active cold seeps
           in the Gulf of Cádiz, NE Atlantic Ocean

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      Abstract: Extensive beds of the deep-sea mussel Bathymodiolus mauritanicus (currently also known as Gigantidas mauritanicus) linked to active cold seeps related to fissure-like activity on Al Gacel mud volcano, Gulf of Cádiz, were filmed and sampled for the first time during the oceanographic expedition SUBVENT-2 aboard R/V Sarmiento de Gamboa. Al Gacel mud volcano is one of up to 80 fluid venting submarine structures (mud volcanoes and mud volcano/diapir complexes) identified in the Gulf of Cádiz as result of explosive venting of hydrocarbon-enriched fluids sourced from deep seated reservoirs. This mud volcano is a cone-shaped edifice, 107 m high, 944 m in diameter constituted by mud breccias and, partially covered by pavements of seep carbonates. Extensive beds of this deep-sea mussel were detected at the northern flank at 810–815 m water depth associated with bacterial mats around intermittent buoyant vertical bubble methane plumes. High methane concentrations were measured in the water column above living mussel beds. Other chemosymbiotic species (Siboglinum sp., Solemya elarraichensis, Isorropodon sp., Thyasira vulcolutre and Lucinoma asapheus) were also found in different parts of Al Gacel mud volcano. Al Gacel mud volcano may currently represent one of the most active mud volcanoes in the Gulf of Cádiz, delivering significant amounts of thermogenic hydrocarbon fluids which contribute to foster the extensive chemosynthesis-based communities detected. This finding is of paramount importance for linking extremophile bivalve populations along the North Atlantic, including cold seeps of the Gulf of México, hydrothermal vents of the Mid-Atlantic Ridge and now, detailed documented at the Gulf of Cádiz.
      PubDate: 2021-12-23
       
  • A new look at Eccaparadoxides (Cambrian, Trilobita) and its
           biostratigraphic significance

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      Abstract: Eccaparadoxides is a geographically widely distributed trilobite genus that occurs in the middle part of the Cambrian System. However, the systematically important morphologic characteristics that can be used to differentiate taxa are often problematical in their application. A review of the large number (over 30) of significant species or forms assigned to Eccaparadoxides clearly indicates that only the pygidia offer fairly reliable morphologic criteria that can be used taxonomically and phylogenetically. The pygidia allow for recognition of four different morphological groups (pusillus, lamellatus, pradoanus and asturianus) of which the asturianus group can only be questionably assigned to the genus. Species known only from cranidia cannot be assigned to Eccaparadoxides with certainty. This study refines the biostratigraphy for the interval from the upper Wuliuan to the middle Drumian and shows that this interval brackets the range of most Eccaparadoxides species. The genera or subgenera Baltoparadoxides, Rejkocephalus and Macrocerca are evaluated. Eccaparadoxides zelus, E. epimetheus and Eccaparadoxides' hestia are newly proposed species.
      PubDate: 2021-12-10
       
  • Molecular fossils within bitumens and kerogens from the ~ 1 Ga
           Lakhanda Lagerstätte (Siberia, Russia) and their significance for
           understanding early eukaryote evolution

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      Abstract: The emergence and diversification of eukaryotes during the Proterozoic is one of the most fundamental evolutionary developments in Earth’s history. The ca. 1-billion-year-old Lakhanda Lagerstätte (Siberia, Russia) contains a wealth of eukaryotic body fossils and offers an important glimpse into their ecosystem. Seeking to complement the paleontological record of this remarkable lagerstätte, we here explored information encoded within sedimentary organic matter (total organic carbon = 0.01–1.27 wt.%). Major emphasis was placed on sedimentary hydrocarbons preserved within bitumens and kerogens, including molecular fossils (or organic biomarkers) that are specific to bacteria and eukaryotes (i.e. hopanes and regular steranes, respectively). Programmed pyrolysis and molecular organic geochemistry suggest that the organic matter in the analyzed samples is about peak oil window maturity and thus sufficiently well preserved for detailed molecular fossil studies that include hopanes and steranes. Together with petrographic evidence as well as compositional similarities of the bitumens and corresponding kerogens, the consistency of different independent maturity parameters establishes that sedimentary hydrocarbons are indigenous and syngenetic to the host rock. The possible presence of trace amounts of hopanes and absence of steranes in samples that are sufficiently well preserved to retain both types of compounds evidences an environment dominated by anaerobic bacteria with no or very little inputs by eukaryotes. In concert with the paleontological record of the Lakhanda Lagerstätte, our study adds to the view that eukaryotes were present but not significant in Mesoproterozoic ecosystems.
      PubDate: 2021-12-08
       
  • Microbial processes during deposition and diagenesis of Banded Iron
           Formations

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      Abstract: Banded Iron Formations (BIFs) are marine chemical sediments consisting of alternating iron (Fe)-rich and silica (Si)-rich bands which were deposited throughout much of the Precambrian era. BIFs represent important proxies for the geochemical composition of Precambrian seawater and provide evidence for early microbial life. Iron present in BIFs was likely precipitated in the form of Fe3+ (Fe(III)) minerals, such as ferrihydrite (Fe(OH)3), either through the metabolic activity of anoxygenic photoautotrophic Fe2+ (Fe(II))-oxidizing bacteria (photoferrotrophs), by microaerophilic bacteria, or by the oxidation of dissolved Fe(II) by O2 produced by early cyanobacteria. However, in addition to oxidized Fe-bearing minerals such as hematite (FeIII2O3), (partially) reduced minerals such as magnetite (FeIIFeIII2O4) and siderite (FeIICO3) are found in BIFs as well. The presence of reduced Fe in BIFs has been suggested to reflect the reduction of primary Fe(III) minerals by dissimilatory Fe(III)-reducing bacteria, or by metamorphic (high pressure and temperature) reactions occurring in presence of buried organic matter. Here, we present the current understanding of the role of Fe-metabolizing bacteria in the deposition of BIFs, as well as competing hypotheses that favor an abiotic model for BIF deposition. We also discuss the potential abiotic and microbial reduction of Fe(III) in BIFs after deposition. Further, we review the availability of essential nutrients (e.g. P and Ni) and their implications on early Earth biogeochemistry. Overall, the combined results of various ancient seawater analogue experiments aimed at assessing microbial iron cycling pathways, coupled with the analysis of the BIF rock record, point towards a strong biotic influence during BIF genesis.
      PubDate: 2021-12-08
       
  • New Ediacaran fossils from the Ukraine, some with a putative tunicate
           relationship

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      Abstract: Sack-like body fossils Finkoella ukrainica gen. et sp. nov. and F. oblonga sp. nov., and reticulate fossil Pharyngomorpha reticulata gen. et sp. nov. are described from the upper Ediacaran shallow-marine deposits of Ukraine, which are no younger than 557 Ma. The first two resemble the flattened bodies of tunicates showing mainly the outline of tunica, while the third is considered as a fragment of the pharyngeal basket of a tunicate. F. ukrainica is represented by smaller individuals interpreted as juveniles, which may occur in clusters together with less numerous larger individuals. The larger forms are interpreted as adults, some of which show the preserved oral/atrial syphons and possible traces of internal organs bulging through the tunica. Moreover, Burykhia sp. from the uppermost Ediacaran of the same region is presented. This is the second and younger occurrence of the genus Burykhia, which is preserved as a possible fragment of the pharyngeal basket. All the fossils are preserved as the “death masks” between microbial mats, and their appearance depends partly on the relation to the parting surface on which they are observed. The presented new taxa along with the literature data reinforce the possibility that tunicates originated already in late Ediacaran.
      PubDate: 2021-12-08
       
  • Ultrastructure and in-situ chemical characterization of intracellular
           granules of embryo-like fossils from the early Ediacaran Weng’an biota

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      Abstract: Embryo-like fossils from the early Ediacaran Weng’an biota provide a window of exceptional fossil preservation onto the period of life history in which molecular clocks estimate the fundamental animal lineages to have diverged. However, their diversity and biological affinities have proven controversial, because they are morphologically simple and, consequently, their interpretation lacks phylogenetic constraint. The subcellular structures preserved in these embryo-like fossils might help to understand their cytology, biology, and diversity, but the potential of these structures has not been fully realized, because detailed microscale physical and chemical investigations are lacking. Here, to remedy this deficiency, we performed a comprehensive study to characterize their micro- and ultra-structures as well as in-situ chemical components. Our results reveal three types of subcellular structure that differ in size, shape, and mineral components: (1) relatively small and spheroidal granules in embryo-like fossils with equal cell division pattern; (2) relatively large, spheroidal, or polygonal granules in embryo-like fossils with unequal and asynchronous cell division pattern; and (3) irregular multi-layered rim-bounded granules in embryo-like fossils with unequal and asynchronous cell division pattern. We propose that the three types may be rationalized to a single taphonomic pathway of preferential mineralization of the cell cytoplasm, preserving an external mould of subcellular granules. We followed the previous interpretation that the spheroidal and polygonal granules should be fossilized lipid droplets or yolk platelets. The distinction between these subcellular structures are largely the result of postmortem degradation processes such as autolysis. The widely preserved lipid droplets or yolk platelets within these Ediacaran embryo-like fossils are compatible with the interpretion of large yolky embryos with maternal nourishment and direct development.
      PubDate: 2021-12-06
       
  • Eifelosaurus triadicus Jaekel, 1904, a “forgotten” reptile from the
           Upper Buntsandstein (Triassic: Anisian) of the Eifel region, Germany

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      Abstract: We provide a detailed description of the poorly known reptile Eifelosaurus triadicus Jaekel, 1904 from the Upper Buntsandstein (Triassic: early Anisian) of Oberbettingen in the southwestern Eifel region of Rhineland-Palatinate, Germany. The holotype and only known specimen is a partial postcranial skeleton exposed in ventral view. Since its original description Eifelosaurus triadicus has been almost completely ignored in the literature. Our phylogenetic analysis recovered this taxon within Rhynchosauria and Rhynchosauridae, as the sister taxon to the clade comprising Stenaulorhynchinae and hyperodapedontine-line rhynchosaurids. A unique combination of character states allows distinguishing Eifelosaurus triadicus from other rhynchosaur species with preserved matching postcranial bones. Thus, we tentatively consider this taxon valid until more information about the postcrania of other Early to Middle Triassic rhynchosaurs becomes available. Eifelosaurus triadicus represents a paleobiogeographically important record, showing that rhynchosaurs had already attained a broad paleolatitudinal distribution by the early Middle Triassic.
      PubDate: 2021-12-03
       
  • A remarkable new thorny lacewing from mid-Cretaceous amber from northern
           Myanmar (Neuroptera: Rhachiberothidae)

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      Abstract: Thorny lacewings (Rhachiberothidae) are a small group of Neuroptera, and currently distributed only within sub-Saharan Africa. They are relatively abundant in the fossil record of various Cretaceous ambers across the Northern Hemisphere, but all the Cretaceous rhachiberothids belong to the extinct subfamily Paraberothinae. Here, a new thorny lacewing, Paradoxoberotha chimaera gen. et sp. nov., is described from the mid-Cretaceous Kachin amber of northern Myanmar. This new genus is characterized by absence of spine or spine-like setae on ventral edge of protibia, well-developed recurrent humeral vein in the forewing, and well-developed hypocauda and pseudohypocauda in female genital segments. The peculiar combination of the morphological characters found in Paradoxoberotha gen. nov. cannot allow the definitive subfamilial placement within the currently recognized two subfamilies of Rhachiberothidae. This new species enhances knowledge on the morphological and species diversity of the Rhachiberothidae in the Cretaceous.
      PubDate: 2021-12-02
       
  • Eckicrinidae: a new lineage of Triassic crinoids and the diversification
           of attachment strategies in the Early and Middle Triassic

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      Abstract: The re-discovery of a distal pluricolumnal of the Middle Triassic Eckicrinus radiatus requires separation of Eckicrinus from Holocrinidae and to establish the new family Eckicrinidae of undetermined systematic position. The pluricolumnal with enlarged radicular cirri with multiradiate articulations acted as a rhizoid holdfast. In the Early and Middle Triassic, three attachment modes occurred among benthic crinoids: (1) discoid or incrusting holdfasts (Encrinida, Millericrinida), (2) rhizoid holdfasts with radicular cirri (Eckicrinidae, Qingyanocrinidae), (3) motile cirri with synarthrial articulations (Holocrinida, Isocrinida). Encrinida and Holocrinida representing the two well known major clades of Middle Triassic crinoids are rooted in different Permian Ampelocrinida rather than in one Early Triassic common ancestor. Eckicrinidae may represent a third lineage. This evidence contributes to challenging the prevalent opinion that just one lineage of each of the five extant echinoderm groups passed the end-Permian extinction event.
      PubDate: 2021-12-01
       
  • Exceptionally preserved extracellular bone matrix proteins from the late
           Neogene proboscidean Anancus (Mammalia: Proboscidea)

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      Abstract: In an exceptional preservation state, bones conserve the entire pattern of extracellular bone matrix proteins over thousands or sometimes even millions of years. Here we present typical extracellular bone matrix proteins, which were extracted from a 3.0-million-year-old gomphothere proboscidean, and identified with special antibodies. For the first time, osteonectin, osteopontin and BMP-2 were confidently identified from the extinct Anancus arvernensis, based on late Pliocene material from Willershausen, Lower Saxony, Germany. Our study has value in demonstrating that the longevity of original extracellular bone matrix proteins is much greater than formerly expected, and that such materials may be stabilised for distinct geological periods of time, especially in Fossil Lagerstätten.
      PubDate: 2021-12-01
       
  • Sedimentary factories and ecosystem change across the Permian–Triassic
           

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      Abstract: The Permian–Triassic mass extinction included a potentially catastrophic decline of biodiversity, but ecosystem change across this event remains poorly characterized. Here we reconstruct sedimentary factories and ecosystem change across the Permian–Triassic Critical Interval (P–TrCI) in the Xiakou area (South China). Six microfacies (MF) were classified. The succession begins with a eukaryote-controlled carbonate factory (MF-1) that passes upward into an organomineralization-dominated carbonate factory (MF-2–3). Organic-rich marls atop these units reflect carbonate factory collapse (MF-4). Organomineralization-driven carbonate formation restarts prior to the Permian–Triassic boundary (MF-5) and subsequently develops into a mixed carbonate factory where organomineralization and biomineralization are almost equally important (MF-6). MF-1 reflects oxygenated shallow water environments. In contrast, MF-2–6 were all deposited in somewhat deeper environments, some of which episodically exhibited elevated salinities, oxygen depletion, and, possibly, euxinic conditions. Our results demonstrate that distinct changes in carbonate production styles, biodiversity, and environmental conditions are not synchronous at Xiakou. Furthermore, the Xiakou record is strikingly different to that of other localities, even from the same area (e.g., the Global Stratotype Section and Point section at Meishan). Together, these findings highlight the enormous complexity of the P–TrCI and calls simplified views of the Permian–Triassic mass extinction into question.
      PubDate: 2021-12-01
       
  • Taxon- and senescence-specific fluorescence of colored leaves from the
           Pliocene Willershausen Lagerstätte, Germany

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      Abstract: UV-light-induced fluorescence is widely used in the study of coal macerals and palynological samples, but to date has not been described in great detail for plant macrofossils. Here, we report the characteristics of bright UV-light-induced fluorescence of various fossil angiosperm leaf taxa from the Upper Pliocene of Willershausen, Lower Saxony, Germany. The fluorescence is exceptional, since different fluorescence colors ranging from green to yellow to red can be observed and fluorescence properties are found to be related to genera. Using confocal laser scanning microscopy, fluorescence was studied in detail and emission spectra were obtained that allowed to differentiate broad groups of fluorophores. Fluorescence emissions attributed to chlorophyll degradation products demonstrate that fluorescence can be used as an indicator for exceptional chemical preservation of leaf fossils. Comparison with present-day senescing plants suggests that the fluorescence differences in the fossil leaves are mainly caused by taxon-specific degeneration of organic compounds during senescence. The occurrence of various leaf taxa with different fluorescence properties, preserved under identical conditions of fossilization, indicate that diagenesis was not crucial for the differences in leaf fluorescence.
      PubDate: 2021-12-01
       
  • Current understanding on the Cambrian Explosion: questions and answers

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      Abstract: The Cambrian Explosion by nature is a three-phased explosion of animal body plans alongside episodic biomineralization, pulsed change of generic diversity, body size variation, and progressive increase of ecosystem complexity. The Cambrian was a time of crown groups nested by numbers of stem groups with a high-rank taxonomy of Linnaean system (classes and above). Some stem groups temporarily succeeded while others were ephemeral and underrepresented by few taxa. The high number of stem groups in the early history of animals is a major reason for morphological gaps across phyla that we see today. Most phylum-level clades achieved their maximal disparity (or morphological breadth) during the time interval close to their first appearance in the fossil record during the early Cambrian, whereas others, principally arthropods and chordates, exhibit a progressive exploration of morphospace in subsequent Phanerozoic. The overall envelope of metazoan morphospace occupation was already broad in the early Cambrian though it did not reach maximal disparity nor has diminished significantly as a consequence of extinction since the Cambrian. Intrinsic and extrinsic causes were extensively discussed but they are merely prerequisites for the Cambrian Explosion. Without the molecular evolution, there could be no Cambrian Explosion. However, the developmental system is alone insufficient to explain Cambrian Explosion. Time-equivalent environmental changes were often considered as extrinsic causes, but the time coincidence is also insufficient to establish causality. Like any other evolutionary event, it is the ecology that make the Cambrian Explosion possible though ecological processes failed to cause a burst of new body plans in the subsequent evolutionary radiations. The Cambrian Explosion is a polythetic event in natural history and manifested in many aspects. No simple, single cause can explain the entire phenomenon.
      PubDate: 2021-12-01
       
  • First Eugereonidae (Insecta: Palaeodictyoptera) from the Pennsylvanian
           (Late Carboniferous) of the Piesberg site near Osnabrück, Germany

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      Abstract: Sandiella herbigi sp. nov. is the first record of the family Eugereonidae Handlirsch, 1906 (Insecta: Palaeodictyoptera) in the Pennsylvanian (Late Carboniferous: Westphalian D) sequence of the Piesberg quarry near Osnabrück, Lower Saxony, Germany. It is represented by a single fragment of a mesothoracic wing with the typical coarse reticulation in this family. The species is mainly characterized by the following features: (i) the shape of the mesothoracic wing is extremely narrow, (ii) the posterior subcostal vein is ending before the wing apex, (iii) all the main veins show a typical bend close to the posterior margin. The new wing is the second most ancient record of the Eugereonidae.
      PubDate: 2021-12-01
       
  • Ooids forming in situ within microbial mats (Kiritimati atoll, central
           Pacific)

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      Abstract: Ooids (subspherical particles with a laminated cortex growing around a nucleus) are ubiquitous in the geological record since the Archean and have been widely studied for more than two centuries. However, various questions about them remain open, particularly about the role of microbial communities and organic matter in their formation and development. Although ooids typically occur rolling around in agitated waters, here, we describe for the first time aragonite ooids forming statically within microbial mats from hypersaline ponds of Kiritimati (Kiribati, central Pacific). Subspherical particles had been previously observed in these mats and classified as spherulites, but these particles grow around autochthonous micritic nuclei, and many of them have laminated cortices, with alternating radial fibrous laminae and micritic laminae. Thus, they are compatible with the definition of the term ‘ooid’ and are in fact very similar to many modern and fossil examples. Kiritimati ooids are more abundant and developed in some ponds and in some particular layers of the microbial mats, which leads to the discussion and interpretation of their formation processes as product of mat evolution, through a combination of organic and environmental factors. Radial fibrous laminae are formed during periods of increased supersaturation, either by metabolic or environmental processes. Micritic laminae are formed in closer association with the mat exopolymer (EPS) matrix, probably during periods of lower supersaturation and/or stronger EPS degradation. Therefore, this study represents a step forward in the understanding of ooid development as influenced by microbial communities, providing a useful analogue for explaining similar fossil ooids.
      PubDate: 2021-11-26
       
  • Burrows without a trace—How meioturbation affects rock fabrics and
           leaves a record of meiobenthos activity in shales and mudstones

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      Abstract: Understanding fine-grained sediment accumulation is critical for developing robust geologic models and inferring environmental conditions. Here we report on processes that produce compositional layering at the mm and sub-mm scale, with gradational rather than sharp layer boundaries. Sometimes described as fuzzy laminae, this feature occurs in modern muds that accumulate under oxygen-stressed conditions, caused by meiofauna (tiny organisms; benthic foraminifera, polychaetes, nematodes, etc.) that disrupts the original fabric. In the rock record, fuzzy laminae are common in shales that accumulated under presumed oxygen-stressed conditions. Like their presumed modern analogs, ancient examples contain remains of benthic foraminifera and other small benthic organisms that were the likely agents of fabric disruption. As preserved lamination is considered indicative of bottom water anoxia in ancient shales, we need to better understand the cause of fuzzy lamination, because such insights have the potential to allow much refined assessments of the depositional history of laminated organic-rich shales. In experiments, nematode activity blurred the originally sharp contacts between successive sediment layers with contrasting composition. Although nematode activity produces tiny temporary traces aside of blurring of primary fabric, the former have minimal preservation potential due to compaction of the water-rich substrate. Experimental fabrics compare well to those observed in a wide range of ancient black shales, suggesting common meiofaunal activity in the latter. Our findings imply that the details of lamination (fuzzy vs. sharp) in ancient shales are not necessarily controlled by bottom water oxygenation, but instead result from the interplay between sedimentation rates and bottom current activity.
      PubDate: 2021-11-23
       
  • Massive cryptic microbe-sponge deposits in a Devonian fore-reef slope
           (Elbingerode Reef Complex, Harz Mts., Germany)

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      Abstract: A massive occurrence of microbial carbonates, including abundant sponge remains, within the Devonian Elbingerode Reef Complex was likely deposited in a former cavity of the fore-reef slope during the early Frasnian. It is suggested that the formation of microbial carbonate was to a large part favored by the activity of heterotrophic, i.e., sulfate-reducing bacteria, in analogy to Quaternary coral reef microbialites. The Elbingerode Reef Complex is an example of an oceanic or Darwinian barrier reef system. In modern barrier reef settings, microbialite formation is commonly further facilitated by weathering products from the central volcanic islands. The Devonian microbialites of the Elbingerode Reef Complex occur in the form of reticulate and laminated frameworks. Reticulate framework is rich in hexactinellid glass sponges, the tissue decay of which led to the formation of abundant micrite as well as peloidal and stromatactis textures. Supposed calcimicrobes such as Angusticellularia (formerly Angulocellularia) and Frutexites, also known from cryptic habitats, were part of the microbial association. The microbial degradation of sponge tissue likely also contributed to the laminated framework accretion as evidenced by the occurrence of remains of so-called “keratose” demosponges. Further typical textures in the microbialite of the Elbingerode Reef Complex include zebra limestone, i.e., the more or less regular intercalation of microbial carbonate and cement. Elevated concentrations of magnesium in the microbialite as compared to the surrounding metazoan (stromatoporoid-coral) reef limestone suggests that the microbialite of the Elbingerode Reef Complex was initially rich in high-magnesium calcite, which would be yet another parallel to modern, cryptic coral reef microbial carbonates. Deposition and accretion of the microbialite largely occurred in oxygenated seawater with suboxic episodes as indicated by the trace element (REE + Y) data.
      PubDate: 2021-09-22
      DOI: 10.1007/s12542-021-00581-8
       
 
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