Sur des spécimens historiques inédits d’arthropodes marins des Calcaires Lithographiques de Solnhofen et Nusplingen (Jurassique supérieur, Allemagne) conservés au Muséum national d’Histoire naturelle, Paris

International audiencePlusieurs spécimens fossiles d’arthropodes marins inédits, conservés au Muséum national d’Histoire naturelle à Paris (France) et provenant des Calcaires lithographiques de Solnhofen et de Nusplingen (Jurassique supérieur, Allemagne), sont décrits et illustrés. Nous décrivons notamment des spécimens d’Antrimpos undenarius Schweigert, 2001, d’Eryma modestiforme (Schlotheim, 1822) et de Mecochirus longimanatus (Schlotheim, 1820). Mecochirus foresti Secrétan, 1968 est considéré comme un synonyme plus récent de Mecochirus longimanatus. Une révision des spécimens décrits précédemment est également réalisée. Cet article fournit ainsi de nouvelles informations sur les espèces d’Antrimpos présentes dans les Plattenkalks de Solnhofen et donne un aperçu complet des arthropodes marins fossiles provenant de ces localités et disponibles au MNHN

Sulfur sedimentary processes and fossilization

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Étude expérimentale de spécimens pyriteux : altérations de schistes argileux fossilifères et traitements de bois lignitisés.

An experimental study of pyritic specimens of two different types (fossiliferous shales, and lignitized wood) was undertaken in order to better understand the processes responsible for degradations observed in historical collections, and to work out conservative treatments in order to avoid them. A behavioral study of fossiliferous shales was conducted by artificial ageing. We focused on material from the Autun Basin (Saône-et-Loire, France ; Permian) because, on one hand, damaged historical specimens, allowing a final state to be characterized, are available (collection Flouest, MNHN), and, on the other hand, it was possible to collect new material, comparable to an initial state, available for our experiments. These experiments allowed to observe 1/ in the matrix, an oxidation of reduced sulfur compounds into calcium sulfate, usually little harmful ; 2/ at the matrix/fossil interface, more damaging efflorescence of iron sulfates, due to the degradation of framboidal pyrite, pyrrhotite and sulfur. Regarding lignitized wood, various treatments aiming to improve conservation were tested. Experiments using drying showed that this technique generates cracks and/or efflorescence, and does not solve the chemical reactivity issue ; therefore additional washes were conducted. They allowed oxidizing the sulfides occurring in the wood and dissolving the sulfates ions formed, making the material less reactive and easier to dry. Water washing is slower but more respectful of the material than washing using hydrogen peroxide.Une étude expérimentale menée sur des spécimens pyriteux de deux types différents (schistes argileux fossilifères et bois lignitisé) a été entreprise afin de mieux comprendre les phénomènes à l’origine des dégradations constatées en collection et de mettre au point des traitements de conservation pour les éviter. Une étude de comportement de schistes argileux fossilifères a été menée par vieillissement artificiel. Nous avons choisi d’étudier du matériel provenant du Bassin d’Autun (Saône-et-Loire, France ; Permien) car, d’une part, nous disposons de matériel historique dégradé permettant de caractériser un état final (collection Flouest, MNHN), et d’autre part, il a été possible de collecter du nouveau matériel, assimilable à un état initial et utilisable pour nos expérimentations. Ces expérimentations ont permis d’observer 1/ dans l’encaissant, une oxydation des composés soufrés réduits, donnant lieu à du sulfate de calcium, généralement peu nuisible ; 2/ à l’interface encaissant/fossile, des efflorescences plus dommageables de sulfates de fer dues à la dégradation de pyrite framboïdale, soufre et pyrrhotite. Concernant le bois lignitisé, différents traitements visant à améliorer sa conservation ont été expérimentés. Les essais de séchage ont montré que l’eau est le responsable principal de l’oxydation de la pyrite. Le séchage génère des dégâts d’ordre mécanique et/ou un développement d’efflorescences sur nos échantillons, et ne résout pas le problème de réactivité chimique. Des lavages additionnels ont donc été menés. Ils ont permis d’oxyder les sulfures présents dans le bois et de dissoudre les ions sulfates formés, rendant le matériau moins réactif et plus aisé à sécher. Le lavage à l’eau s’avère plus lent mais plus respectueux du matériau que le lavage au peroxyde d’hydrogène

Une espèce nouvelle de langouste mécochiridée du Crétacé supérieur de France préservée avec ses œufs

La découverte de Mecochirus cenomanicus n. sp. (Decapoda, Glypheoidea, Mecochiridae) dans le stratotype du Cénomanien (Le Mans, France) étend la distribution biostratigraphique de Mecochirus Germar, 1827 du Crétacé inférieur au Crétacé supérieur. L’holotype conserve sous le pléon environ 80 gros œufs fixés aux pléopodes et représente ainsi la seconde mention d’un crustacé décapode fossilisé avec une ponte d’œufs. Le nombre et la taille des œufs suggèrent un développement ontogénétique similaire à celui des crustacés décapodes actuels au stade larvaire court.The discovery of Mecochirus cenomanicus n. sp. (Decapoda, Glypheoidea, Mecochiridae) from the Cenomanian stratotype (Le Mans, France) extends the biostratigraphic range of Mecochirus Germar, 1827 from the Early to the Late Cretaceous. The holotype preserves under the pleon about 80 large eggs carried by the pleopods, and thus represents the second record of a decapod crustacean fossilized with clusters of eggs. The size and number of eggs suggest an ontogenetic development like that of the extant decapod crustaceans with short larval stage.</p

Experimental degradation of helicoidal photonic nanostructures in scarab beetles (Coleoptera: Scarabaeidae): implications for the identification of circularly polarizing cuticle in the fossil record

Scarab beetles (Coleoptera: Scarabaeidae) can exhibit striking colours produced by pigments and/or nanostructures. The latter include helicoidal (Bouligand) structures that can generate circularly polarized light. These have a cryptic evolutionary history in part because fossil examples are unknown. This suggests either a real biological signal, i.e. that Bouligand structures did not evolve until recently, or a taphonomic signal, i.e. that conditions during the fossilization process were not conducive to their preservation. We address this issue by experimentally degrading circularly polarizing cuticle of modern scarab beetles to test the relative roles of decay, maturation and taxonomy in controlling preservation. The results reveal that Bouligand structures have the potential to survive fossilization, but preservation is controlled by taxonomy and the diagenetic history of specimens. Further, cuticle of specific genus (Chrysina) is particularly decay-prone in alkaline conditions; this may relate to the presence of certain compounds, e.g. uric acid, in the cuticle of these taxa

Sulfur sedimentary processes and fossilization

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Dégradation de schistes argileux fossilifères (Bassin d’Autun, France, Permien), partie III : pyrite framboïdale et soufre identifiés comme cause principale des efflorescences

International audienceFossil-bearing shale specimens that include sulfides are chemically reactive and sometimes also mechanically fragile. This decay is provoked by iron sulfate efflorescence resulting from the oxidation of sulfide compounds. The processes underlying these degradations are poorly known, thus impeding the elaboration of curative or preventive treatments. The present contribution aims to identify the origin of museum specimen alterations. It focuses on the Flouest collection housed at the Muséum national d'Histoire naturelle (MNHN, Paris, France) and originating from the Autun Basin (Saône-et-Loire, France; Permian). To evaluate the alteration of MNHN specimens, it appeared necessary to compare their composition with that of unaltered shale so as to identify chemical changes occurring during ageing. Therefore new material was collected in the Autun Basin, among others on the locality of Muse that corresponds to the same lithostratigraphic unit than that of the MNHN specimens. This work is divided in three parts. The two first, presented elsewhere, deal with the composition of the shale matrices and led to the conclusion that these matrices could not account for the large iron(II) sulfate efflorescence provoking damage on the MNHN specimens. The last part of this work, presented here, focus on artificial age-ing experiments performed on new shale material. Most of the alterations observed on artificially aged samples correspond to dispersed crystals of calcium sulfate (gypsum). Similar crystals may be found on MNHN specimens, but they are relatively few and sporadically distributed. They are thus considered as damage of secondary importance with respect to iron sulfate efflorescence. These latter could be reproduced on three samples only (upon the 142 aged samples). They were also found on a copro-lite and on a wood remain that had got severely damaged in ambient conditions within a few months after their excavation. On all these samples iron sulfate had grown on brownish layers consisting in crystals of framboidal pyrite (1 to 3 m) and eventually sulfur (20 to 50 m). These brownish layers are associated to thin maceral layers probably because of bacterial activity: during fossil diagenesis, bacteria need organic matter for their metabolism to produce hydrogen sulfide, a precursor of sedi-mentary pyrite formation. Most of the damaged specimens of the Flouest collection show as well a thin maceral layer nearby iron(II) sulfate efflorescence. On one of them, this layer is particularly thick. It corresponds to vitrinite and shows in some areas a brownish aspect. The topology of this surface (observed with scanning electron microscopy) shows numerous small holes (< 2 m) and large holes (10–20 m). This morphology is compatible with a former occurrence of isolated grains and aggregates of framboidal pyrite. These observations suggest that iron sulfate efflorescence was provoked by th

Experimental degradation of helicoidal photonic nanostructures in scarab beetles (Coleoptera: Scarabaeidae): implications for the identification of circularly polarizing cuticle in the fossil record [Data]

Light micrographs of decayed elytra of C. gloriosa and C. boucardi. Scale: 5 mm

Taphonomic experiments on caridean shrimp elucidate the timing and influence of organic matter on diagenetic pyritization and sulfurization

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Neutron imaging investigation of fossil woods: non-destructive characterization of microstructure and detection of in situ changes as occurring in museum cabinets

International audienceThis paper discusses the applicability of neutron imaging techniques for probing the internal microstructure of several fossil woods upon wetting and drying, two phenomena occurring in museum cabinets and endangering the fossil woods. Investigations were carried out using lignites (fossil woods) from two French localities (Rivecourt, Parisian Basin, Oise – Paleogene; Angeac, Aquitanian Basin, Char-ente – Cretaceous), which present different macroscopic behavior upon drying. Thanks to the high sensitivity of neutrons to hydrogen content, it was possible to track water diffusion through 3 mm thick samples and to follow in situ changes related to either supply or withdrawal of water without any special preparation and in a relevant time range (from 1 min to a few hours). Classical image analysis allows discriminating between the behavior of the two fossil woods with regard to their interaction with water. Further analysis based on a Fourier transform of projection images provides additional information regarding the existence of large pores in one of the samples. Differences in pore network and internal structures have important mechanical consequences as one of the samples retains its integrity upon drying, whereas the other one shatters into pieces. A better understanding of the underlying processes will clearly require multi-scale analyses, using additional techniques that could probe the materials at a lower scale. Such a combination of multi-scale analyses should provide valuable information for a better conservation of wood remnants, which is crucial for both pa-leobotanical research and museum exhibits