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Three-dimensionally preserved stem-group hexactinellid sponge fossils from lower Cambrian (Stage 2) phosphorites of China
No full textThree-dimensionally, in situ preserved sponge fossils were collected from the phosphorites at the basal Niutitang Formation (Cambrian Stage 2) in Hunan Province, China. These fossils are preserved as nodular bodies in authigenic carbonaceous cherty Ca-phosphorites. Spicules are either completely embedded in cryptocrystalline phosphate or immediately overgrown by early isopachous phosphate cements, leaving the remaining interspace filled by other deposits. Two specimens are described in detail as examples. One is composed of hexactins of at least three size-hierarchies, the small spicules in which may be interpreted as microscleres. The other, investigated using grinding tomography, shows a skeletal frame composed of pentactins, hexactins, and diactins. These spicules exhibit a weak pattern of perpendicular orientation in 3D space and a possible differentiation of hypodermalia and parenchymalia. These skeletal architectures belong to new taxonomic groups and seem to represent very basic forms of hexactinellids. Disarticulated spicules scattered in other parts of the investigated phosphorites indicate a still unexplored diversity of the fossil community, and some show combined features, which were regarded characteristic and mutually exclusive in living hexactinellids and demosponges. This work suggests that the lower Cambrian phosphorite Lagerstätten have a great potential to preserve details of the early evolutionary history of sponges
‘Stromatolites’ built by sponges and microbes – a new type of Phanerozoic bioconstruction
No full textTwo stromatolites' from Carboniferous and Triassic carbonates previously regarded as microbial bioconstructions are analysed and reinterpreted as sponge-microbial build-ups. The automicritic aggregations in these build-ups are similar to the previously reported fossils of keratose demosponges in showing moulded anastomosing filamentous structures. All the studied columnar or domal constructions were formed in turbulent water with high sedimentation rate. The Carboniferous build-ups were constructed in the shallow subtidal zone of an open shelf or a ramp. The laminations within the stromatolite-like columns are composed of alternating dark micritic laminae of sponge fossils and pale laminae of neomorphic microspars. The accretion of these columns is probably related to the repeated cycles of sponge growth, rapid lithification after burial, re-exposure and erosion, and settlement of new generations. The Triassic rocks are presumed to have been precipitated in a slightly evaporitic environment based on lithological features. They show a transition from planar laminae, which were formed under the influence of microbial mats, to stromatolitic columnar or domal build-ups, which are dominated by stacked micritic clumps of probable sponge fossils. The sponge-microbe alternation may have been controlled by variation of salinity. Comparable with a recent study, this work shows that sponge-related bioconstructions can be morphologically similar to microbialites in the level of mega- and mesostructures.China Scholarship Council (CSC
First report of fossil “keratose” demosponges in Phanerozoic carbonates: preservation and 3-D reconstruction
No full textFossil record of Phanerozoic non-spicular sponges, beside of being important with respect to the lineage evolution per se, could provide valuable references for the investigation of Precambrian ancestral animal fossils. However, although modern phylogenomic studies resolve non-spicular demosponges as the sister group of the remaining spiculate demosponges, the fossil record of the former is extremely sparse or unexplored compared to that of the latter; the Middle Cambrian Vauxiidae Walcott 1920, is the only confirmed fossil taxon of non-spicular demosponges. Here, we describe carbonate materials from Devonian (Upper Givetian to Lower Frasnian) bioherms of northern France and Triassic (Anisian) microbialites of Poland that most likely represent fossil remnants of keratose demosponges. These putative fossils of keratose demosponges are preserved as automicritic clumps. They are morphologically distinguishable from microbial fabrics but similar to other spiculate sponge fossils, except that the skeletal elements consist of fibrous networks instead of assembled spicules. Consistent with the immunological behavior of sponges, these fibrous skeletons often form a rim at the edge of the automicritic aggregate, separating the inner part of the aggregate from foreign objects. To confirm the architecture of these fibrous networks, two fossil specimens and a modern thorectid sponge for comparison were processed for three-dimensional (3-D) reconstruction using serial grinding tomography. The resulting fossil reconstructions are three-dimensionally anastomosing, like modern keratose demosponges, but their irregular and nonhierarchical meshes indicate a likely verongid affinity, although a precise taxonomic conclusion cannot be made based on the skeletal architecture alone. This study is a preliminary effort, but an important start to identify fossil non-spicular demosponges in carbonates and to re-evaluate their fossilization potential
The Jinxian Biota revisited: taphonomy and body plan of the Neoproterozoic discoid fossils from the southern Liaodong Peninsula, North China
No full textThe fossil record indicates that complex multicellular organisms started to become dominant in the second half of the Neoproterozoic. However, many macroscopic fossils of this period are not yet well understood. As one example, the Jinxian Biota includes some affinity-unresolved, millimeter-to centimeter-sized discoid fossils of probable pre-Ediacaran age from the shales of the Xingmincun Formation, in southern Liaodong Peninsula, China. This paper presents new observations of these fossils based on new material. Three types of preservation were identified and analyzed. The organisms were probably transported by turbidity currents, rapidly buried in fine-grained deposits and then compacted to yield thin films. Pyrite-and carbonate-related mineralization may have been involved in their early diagenesis, but local-controlled late diagenesis altered the fossil-related mineral composition to that observed today. The concentric annular relief on the fossil surfaces exhibits a "half convex, half concave'' pattern, which is interpreted to reflect the differentiated mechanical nature between adjacent annuli. New specimens have been found that support the existence of programmed fission and budding. In addition, another group of previously ignored discoid fossils are first described here. With the same preservation as the "normal'' discs, these fossils lack any concentric relief and always occur in clusters. The relationship between the two types of discs remains unclear. Even with all of the new information, it remains impossible to indubitably correlate the Jinxian Biota to any known taxonomic group. However, it is quite probable that these fossils represent a group of eukaryotic organisms
Chambered structures from the Ediacaran Dengying Formation, Yunnan, China: comparison with the Cryogenian analogues and their microbial interpretation
No full textAbstractEnigmatic chambered structures have been reported forming reef frames in Cryogenian interglacial carbonates, prior to the commonly acknowledged microbial-metazoan reefs at the terminal Ediacaran, and interpreted as fossils of possible sponge-grade organisms. A better constraint on the affinity of these structures is partly hindered by few analogues in other time periods. This study describes similar structures from peritidal dolostones of the Ediacaran Denying Formation from Yunnan, China. Samples were investigated using optical microscopy and three-dimensional (3-D) reconstruction based on grinding tomography. The Dengying chambered structures are comparable with Cryogenian structures in basic construction, but are not frame building, and show variations in overall shape and inhabiting facies. Two-dimensional (2-D) cross-sections show that thin, homogeneous micritic laminae are the basic building blocks of the chamber walls. Thick walls represent parallel accretion of these laminae, and thin walls developed from the angular growth of a single lamina or merging of multiple laminae. In 3-D space, the laminae primarily correspond to continuous surfaces which sometimes contain sub-circular holes, while a few represent filamentous elements connected to the surfaces. The morphological features and growth pattern of the Dengying chambered structures indicate that they are likely to be calcified microbial constructions rather than skeletal remains of basic metazoans. However, aside from the Cryogenian and Dengying examples, comparable chambered constructions with laminae-based architecture are yet unknown from other fossil or extant microbialites. Further work investigating related structures is needed to determine the microbial consortia and controlling environmental factors that produced these chambered structures.</jats:p
Revisiting the phosphorite deposit of Fontanarejo (central Spain): new window into the early Cambrian evolution of sponges and the microbial origin of phosphorites
Full text linkFossils within early Cambrian phosphorites worldwide are often well preserved due to early diagenetic permineralization. Here, we examine the fossil record contained within phosphorites of the Lower Cambrian Pusa Formation (late Fortunian to Cambrian Stage 2) in Fontanarejo, central Spain. The sedimentology and age of these phosphorites have been controversial and are here reviewed and discussed, providing also an updated geological map. The Pusa Formation is composed of fine clastic sediments that are partly turbiditic, with channels of quartz-rich conglomerates and abundant phosphorites in the upper part of the succession. The microfacies and mineralogy of these channel deposits are studied here for the first time in detail, showing that they are mainly composed of subspherical apatite clasts, with minor mudstone intraclasts, quartzite and mica grains. Numerous sponge spicules, as well as entirely preserved hexactinellid sponges and demosponges, were collected within these phosphorites and likely represent stem groups. In addition to sponges, other fossils, such as small shelly fossils (SSF) of the mollusc Anabarella sp., were found. The phosphorites exhibit multiple evidence of intense microbial activity, including diverse fabrics (phosphatic oncoidal-like microbialites, thrombolites, stromatolites and cements) and abundant fossils of filamentous microbes that strongly resemble extant sulphur-oxidizing bacteria. Our findings strongly suggest that microbial processes mediated the rapid formation of most of the Fontanarejo apatite, probably accounting for the exceptional preservation of fragile fossils such as sponge skeletons. The apparent presence of taxonomically diverse hexactinellid and demosponge communities at the lowermost Cambrian further corroborates a Precambrian origin of the phylum Porifera.Alexander von Humboldt FoundationGöttingen Academy of Sciences and HumanitiesUniversity of GöttingenNational Natural Science Foundation of ChinaDepto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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