A SAMPLING STRATEGY FOR RECENT AND FOSSIL BRACHIOPODS: SELECTING THE OPTIMAL SHELL SEGMENT FOR GEOCHEMICAL ANALYSES

Recent and fossil brachiopod shells have a long record as biomineral archives for (palaeo)climatic and (palaeo)environmental reconstructions, as they lack or exhibit limited vital effects in their calcite shell and generally are quite resistant to diagenetic alteration. Despite this, only few studies address the issue of identifying the best or optimal part of the shell for geochemical analyses. We investigated the link between ontogeny and geochemical signatures recorded in different parts of the shell. To reach this aim, we analysed the elemental (Ca, Mg, Sr, Na) and stable isotope (δ18O, δ13C) compositions of five recent brachiopod species (Magellania venosa, Liothyrella uva, Aerothyris kerguelensis, Liothyrella neozelanica and Gyphus vitreus), spanning broad geographical and environmental ranges (Chile, Antarctica, Indian Ocean, New Zealand and Italy) and having different shell layer successions (two-layer and three-layer shells). We observed similar patterns in the ventral and dorsal valves of these two groups, but different ontogenetic trends by the two- and three-layer shells in their trace element and stable isotope records. Our investigation led us to conclude that the optimal region to sample for geochemical and isotope analyses is the middle part of the mid-section of the shell, avoiding the primary layer, posterior and anterior parts as well as the outermost part of the secondary layer in recent brachiopods. Also, the outermost and innermost rims of shells should be avoided due to diagenetic impacts on fossil brachiopods

Hierarchical architecture of the inner layers of selected extant rhynchonelliform brachiopods

International audienceIn spite of several attempts fora best knowledge of the phylum, brachiopods remain, compared with molluscs, among those least analysed in terms of biomineralization. The lack of economic impact for extant species is probably liable for that situation. Much attention has been on the microstructure of calcite biomaterials (rhynchonelliforms and craniiforms). Here, we emphasize the sub-micrometric structure of selected examples of rhynchonelliform shells using Atomic Force Microscopy (AFM) to complement Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analyses. The hierarchical organization of the shell layers (secondary and/or tertiary elements) is highlighted for species non-yet observed from this point of view, and is compared to a few already mentioned in the literature. Previous analysis revealed that granules are composed of a complex aggregation of sub-units in intimate relation with an intracrystalline matrix. Their shape, size and probably early orientation depend on the species as well as age and living environments of the specimens studied. The control of the inorganic part of the composite fibrous elements is constrained by the deposition of nearly arched shape or polygonal protein membranes at the inner boundary of the primary layer, prior to the deposition of the first granules, membranes becoming proteinaceous sheathes progressively enshrining fibres. The diverse orientations of the granules in fibrous neighbours thus further increase arguments in favour of the tendency to improve the shell strength. (C) 2016 Elsevier Inc. All rights reserved

The debated question of asymmetrical rhynchonellids (Brachiopoda, Rhynchonellida): examples from the Late Cretaceous of Western Europe

Many Cretaceous asymmetrical rhynchonellid brachiopods (Brachiopoda, Rhynchonellida) have long been considered as Rhynchonella difformis (Valenciennes in Lamarck, 181

La tomographie à rayons X : un outil prometteur pour l’investigation des coquilles de brachiopodes. Modélisation 3D et impact taxonomique

Des brachiopodes rhynchonelliformes du Barrémien et du Cénomanien, une espèce du Santonien et une de l’Holocène (Rhynchonellida et Terebratulida) ont été examinés en tomographie à rayons X en raison des possibilités offertes par cette technique dans l’investigation des caractéristiques internes des coquilles. Comparée à l’utilisation des sections sériées transversales, la tomographie à RX est un outil prometteur, qui permet une modélisation 3D du brachidium, important dans la classification des brachiopodes. Quatre types de brachidium fréquemment observés au Crétacé – crura (Rhynchonellida), boucle courte avec et sans anneau (Terebratulidina) et boucle longue (Terebratellidina) –, ainsi que les relations du lophophore avec son support chez une espèce actuelle, sont examinés. Les limites de la méthode sont discutées : nature du sédiment inclus entre les valves, diagenèse et nécessité d’observer plusieurs classes d’âge pour les Terebratellidina. Enfin, les points positifs sont soulignés : modélisation 3D du brachidium sans destruction de coquille, évaluation taxonomique et aide à la conservation des collections.Barremian and Cenomanian rhynchonelliform brachiopods, one Santonian and one Holocene species (Rhynchonellida and Terebratulida), have been observed using X-ray Computed Tomography in order to investigate the shell interior. Compared to transverse serial sections used formerly, X-ray CT is a promising tool. It permits 3D modelling of the brachidium, which is important for brachiopod classification. Four types of brachidium present during the Cretaceous have been observed (crura for the Rhynchonellida, short loop for Terebratulidina–Terebratulidae, ring-loop for Terebratulidina–Cancellothyrididae and long-loop for Terebratellidina), as well as relationships lophophore/brachidium in a Holocene species. Limitations are discussed, including the nature of the sediments enclosed between the valves, diagenesis, and the necessity to observe several age groups concerning the Terebratellidina. Finally, this non-destructive tool facilitates 3D reconstruction of inaccessible brachidia to improve brachiopod taxonomy and as an aid in curating collections.</p

Les Brachiopodes de la craie blanche de Meudon (Campanien supérieur) de la collection dˈOrbigny (MNHN, Paris)

Les Brachiopodes de la craie de Meudon (Campanien supérieur), répertoriés dans le catalogue de la collection dˈOrbigny, sont présentés dans le cadre de la classification révisée du phylum, non sans problème, compte tenu du petit nombre dˈindividus retrouvés dans la collection et/ou de lˈhétérogénéité des lots recensés sous un même numéro et un même nom. La faune de Brachiopodes dans la zone à Belemnitella mucronata est bien représentée par rapport à lˈensemble des Invertébrés reconnus dans cette zone. Deux représentants de Craniiformea et une dizaine dˈespèces de Rhynchonelliformea, répartis en deux ordres, dont plusieurs superfamilles, sont décrits de façon critique, en fonction des observations faites et des travaux publiés depuis ceux de dˈOrbigny.Brachiopods from the White Chalk of Meudon (Upper Campanian), listed in the catalogue of dˈOrbigny collection, are presented following the revised classification. This is not without difficulty, due to the few specimens found and/or to the heterogeneity of sets listed under the same number and labelled with the same name. The Brachiopod fauna in the Belemnitella mucronata Zone is well represented, considering the Invertebrate fauna as a whole. Two representatives of Craniiformea and about ten species of Rhynchonelliformea, from several superfamilies shared by two orders, are critically described, considering the recent observations and the last works after dˈOrbigny.</p

Diagenetic alterations reshape the hierarchical organization of Cretaceous Brachiopod shells- from nanoscale to higher scales

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Sellithyridinae Terebratulidae du Crétacé d'Europe occidentale : dynamique des populations, systématique et évolution / par Danièle Gaspard,...

Collection : Cahiers de paléontologieContient une table des matièresAvec mode text

Biochemical characteristics of the soluble organic matrix from the shell of three recent terebratulid brachiopod species.

7 pagesInternational audienceTo build their shells, brachiopods secrete a mixture of proteins and polysaccharides, collectively called the organic matrix. This matrix mediates the calcification process by allowing crystal nucleation followed by elongation and finally by stopping the crystal growth. Ultimately, the matrix controls the different microstructures formed. Brachiopod shells are composites with both organic and inorganic constituents intimately associated. This work represents an attempt to characterize the matrices using two combined approaches: (1) scanning electron microscopy for localization within the shell, (2) analysing extracted matrices at the molecular level to determine their biochemical properties. Representatives of the three terebratulid brachiopod genera: Gryphus , Liothyrella and Neothyris , were observed according to a standard procedure highlighting the microstructural details. Additionally, the acetic acid-soluble shell matrices were extracted and analyzed by sodium dodecyl polyacrylamide gel electrophoresis. Gels were subsequently stained with silver, Alcian blue and carbocyanine. In addition, the shell matrices were tested for their ability to bind calcium. Finally, functional in vitro assays were performed to check for the first time the effect of some of the shell matrices on calcium carbonate precipitation. Results show that the three matrices are extremely minor components ( < 0.05 wt %) of the shell and that the three genera exhibit some similarities in the electrophoretic patterns of their soluble matrices. Furthermore, the tested matrices drastically modify the morphology of calcite crystals in vitro. Putative similarities between brachiopod and molluscan shell matrices are discussed, as well as the early diagenesis effect that may affect brachiopod matrices

Staining SDS-PAGE gels of skeletal matrices after western blot: a way to improve their sharpness.

7 pagesInternational audienceDenaturing 1D electrophoresis on acrylamide gels - also referred as SDS-PAGE - is a classical technique for fractionating and visualizing the macromolecular constituents of matrices associated to calcified tissues. This technique has been widely used in association with the subsequent silver nitrate staining. But because matrices associated to calcified tissues are very often glycosylated and constituted of numerous polydisperse macromolecules, the obtained pattern is frequently 'smeary' and discrete bands, when present on the gel, are often blurred, thickened or totally masked by the polydisperse macromolecules. In this paper, we present a simple protocol that can circumvent this drawback and 'clean' the gels. In short, after the classical migration step of the matrix macromolecules, the gel is transferred (electro-blotting) on a PVDF membrane, similarly to a Western blot, but for a shorter time (partial transfer, i.e., one hour or less). The gel is subsequently stained with silver nitrate. The likely effect of the transfer is to partly remove polydisperse macromolecules and to 'sharpen' the discrete bands. We think that this extra-step may improve in several cases the gel pictures of skeletal matrix components. We illustrate this phenomenon with two examples taken from brachiopod and mollusc shell matrices