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Meister C.,Museum dHistoire naturelle de Geneva | Dommergues J.-L.,University of Burgundy | Rocha R.B.,New University of Lisbon
Bulletin of Geosciences | Year: 2012

The lowermost Portuguese Pliensbachian is characterized by the association of Apoderoceras dunrobinense Spath, Tragophylloceras numismale (Quenstedt) and Vicininodiceras aff. mouterdei Donovan. This ammonite fauna indicates the lower part of the Jamesoni Chronozone (lower to middle Taylori Subchronozone). Thanks to the numerous specimens collected, the ontogeny and variability of A. dunrobinense Spath, could also be investigated. The paleogeographical distribution of these ammonites underlines the close connections between the Lusitanian Basin and the Euroboreal seas during the Early Pliensbachian.


Dommergues J.-L.,University of Burgundy | Meister C.,Museum dHistoire Naturelle de Geneva
Acta Palaeontologica Polonica | Year: 2013

This paper discusses the phyletic interpretation of the genus Phricodoceras and its taxonomic classification at the subfamily, family, and superfamily levels from an historical and critical perspective. First a review of the latest find ings on this taxon is presented and the grounds for the attribution of Phricodoceras to the Schlotheimiidae (Psiloceratoidea) are summarized and illustrated. This review is a synthesis grounded on evolutionary (e.g., heterochronies, innovations), eco-ethological (e.g., assumed shell hydrodynamic capacities) and spatio-temporal pat terns (e.g., bio-chronostratigraphy, palaeobiogeography). Then, the main stages of understanding the taxonomy of Phricodoceras since the early nineteenth century are reviewed. Two main taxonomic concepts alternate over time. The first is based on the "overall resemblance" of Phricodoceras to some coeval Eoderoceratoidea leading to the genus be ing included in its own family or subfamily (e.g., Phricodoceratinae) among the Eoderoceratoidea. The second hypoth esis, recently confirmed by the discovery of an intermediate form (i.e., Angulaticeras spinosus), clearly includes Phricodoceras within the Schlotheimiidae (Psiloceratoidea). Comparison of these two very different conceptions re veals how "overall resemblance" can be misleading and shows that the discovery of intermediate forms is often the key to phyletic reconstructions in ammonites. Copyright © 2013 J.-L. Dommergues and C. Meister. This is an open-access article distributed under the terms of the Cre ative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, pro vided the original author and source are credited.


Dommergues J.-L.,University of Burgundy | Meister C.,Museum dHistoire naturelle de Geneva | Rocha R.B.,New University of Lisbon
Swiss Journal of Geosciences | Year: 2011

A review of the Pliensbachian ammonite faunas of the Algarve Basin is given covering their taxonomy, stratigraphy and palaeobiogeography (palaeobiodiversity). This review is based on both an extensive revision of the previously collected and/or published material and on new finds precisely located within the ammonite succession. This new material allows us to clarify the variations within the most abundant species-a new species Reynesocoeloceras elmii nov. sp. is described-and to improve our understanding (palaeobiodiversity, palaeobiogeography and bio- or chrono-stratigraphy) of the two single known Pliensbachian fossiliferous assemblages in the Algarve Basin. The first of these assemblages is relatively diverse and is ascribed to the upper half of the Luridum Subchronozone. The second assemblage is less diversified and probably partly condensed. It is broadly attributed to the upper half of the Stokesi Subchronozone. Despite the newly collected ammonites and extensive prospecting, our knowledge of the Pliensbachian ammonite faunas of the Algarve remains fragmentary. Therefore, it is difficult to propose an incontrovertible extensive palaeobiogeographical interpretation for these faunas, but it seems that Tethyan (Mediterranean) affinities were of major importance whereas there were probably no NW European influences via the Lusitanian Basin. © 2011 Swiss Geological Society.


Popova O.,Russian Academy of Sciences | Borovicka J.,Czech Republic Astronomical Institute | Hartmann W.K.,Planetary Science Institute | Spurny P.,Czech Republic Astronomical Institute | And 3 more authors.
Meteoritics and Planetary Science | Year: 2011

We have assembled data on 13 cases of meteorite falls with accurate tracking data on atmospheric passage. In all cases, we estimate the bulk strength of the object corresponding to its earliest observed or inferred fragmentation in the high atmosphere, and can compare these values with measured strengths of meteorites in the taxonomic class for that fall. In all 13 cases, the strength corresponding to earliest observed or inferred fragmentation is much less than the compressive or tensile strength reported for that class of stony meteorites. Bulk strengths upon atmospheric entry of these bodies are shown to be very low, 0.1 to approximately 1MPa on first breakup, and maximal strength on breakup as 1-10MPa corresponding to weak and "crumbly" objects, whereas measured average tensile strength of the similar meteorite classes is about 30MPa. We find a more random relation between bulk sample strength and sample mass than is suggested by a commonly used empirical power law. We estimate bulk strengths on entry being characteristically of the order of 10-1-10-2 times the tensile strengths of recovered samples. We conclude that pre-entry, meter-scale interplanetary meteoroids are typically highly fractured or in some cases rubbly in texture, presumably as a result of their parent bodies' collisional history, and can break up under stresses of a few megapascals. The weakness of some carbonaceous objects may result from very porous primordial accretional structures, more than fractures. These conclusions have implications for future asteroid missions, sample extraction, and asteroid hazard mitigation. © The Meteoritical Society, 2011.


Hardy C.,CNRS Biogeosciences Laboratory | Fara E.,CNRS Biogeosciences Laboratory | Laffont R.,CNRS Biogeosciences Laboratory | Dommergues J.-L.,CNRS Biogeosciences Laboratory | And 2 more authors.
PLoS ONE | Year: 2012

Conservation biologists and palaeontologists are increasingly investigating the phylogenetic distribution of extinctions and its evolutionary consequences. However, the dearth of palaeontological studies on that subject and the lack of methodological consensus hamper our understanding of that major evolutionary phenomenon. Here we address this issue by (i) reviewing the approaches used to quantify the phylogenetic selectivity of extinctions and extinction risks; (ii) investigating with a high-resolution dataset whether extinctions and survivals were phylogenetically clustered among early Pliensbachian (Early Jurassic) ammonites; (iii) exploring the phylogenetic and temporal maintenance of this signal. We found that ammonite extinctions were significantly clumped phylogenetically, a pattern that prevailed throughout the 6.6 Myr-long early Pliensbachian interval. Such a phylogenetic conservatism did not alter - or may even have promoted - the evolutionary success of this major cephalopod clade. However, the comparison of phylogenetic autocorrelation among studies remains problematic because the notion of phylogenetic conservatism is scale-dependent and the intensity of the signal is sensitive to temporal resolution. We recommend a combined use of Moran's I, Pearson's φ and Fritz and Purvis' D statistics because they highlight different facets of the phylogenetic pattern of extinctions and/or survivals. © 2012 Hardy et al.


Bachmann O.,University of Washington | Deering C.D.,University of Washington | Deering C.D.,University of Wisconsin - Oshkosh | Ruprecht J.S.,Lamont Doherty Earth Observatory | And 3 more authors.
Contributions to Mineralogy and Petrology | Year: 2012

Multiple eruptions of silicic magma (dacite and rhyolites) occurred over the last ~3 My in the Kos-Nisyros volcanic center (eastern Aegean sea). During this period, magmas have changed from hornblende-biotite-rich units with low eruption temperatures (≤750-800°C; Kefalos and Kos dacites and rhyolites) to hotter, pyroxene-bearing units (>800-850°C; Nisyros rhyodacites) and are transitioning back to cooler magmas (Yali rhyolites). New whole-rock compositions, mineral chemistry, and zircon Hf isotopes show that these three types of silicic magmas followed the same differentiation trend: they all evolved by crystal fractionation and minor crustal assimilation (AFC) from parents with intermediate compositions characterized by high Sr/Y and low Nb content, following a wet, high oxygen fugacity liquid line of descent typical of subduction zones. As the transition between the Kos-Kefalos and Nisyros-type magmas occurred immediately and abruptly after the major caldera collapse in the area (the 161 ka Kos Plateau Tuff; KPT), we suggest that the efficient emptying of the magma chamber during the KPT drew out most of the eruptible, volatile-charged magma and partly solidified the unerupted mush zone in the upper crust due to rapid unloading, decompression, and coincident crystallization. Subsequently, the system reestablished a shallow silicic production zone from more mafic parents, recharged from the mid to lower crust. The first silicic eruptions evolving from these parents after the caldera collapse (Nisyros units) were hotter (up to >100°C) than the caldera-forming event and erupted from reservoirs characterized by different mineral proportions (more plagioclase and less amphibole). We interpret such a change as a reflection of slightly drier conditions in the magmatic column after the caldera collapse due to the decompression event. With time, the upper crustal intermediate mush progressively transitioned into the cold-wet state that prevailed during the Kefalos-Kos stage. The recent eruptions of the high-SiO 2 rhyolite on Yali Island, which are low temperature and hydrous phases (sanidine, quartz, biotite), suggest that another large, potentially explosive magma chamber is presently building under the Kos-Nisyros volcanic center. © 2011 Springer-Verlag.


Giese J.,University of Bern | Berger A.,Copenhagen University | Schreurs G.,University of Bern | Gnos E.,Museum dhistoire naturelle de Geneva
Precambrian Research | Year: 2011

In central southern Madagascar the crystalline basement is composed of mid-crustal rocks which have experienced polycyclic deformation and metamorphism coupled with repeated granitoid magmatism at the Neoproterozoic-Phanerozoic boundary. Based on the integration of in situ U-Th-Pb dating of monazite and structural relationships, two distinct phases of major ductile deformation, the Andreaba and Ihosy phases can be distinguished in central southern Madagascar. Both these deformation phases occur between ~550 and 520. Ma. Coeval with, and outlasting deformation, granitic plutons and dykes were emplaced. HT/HP granulite facies metamorphism (M1), including migmatisation and anatexis of the crust started at ~585. Ma and lasted until at least ~500. Ma. Monazite growth between 480 and 450. Ma postdates major ductile deformation and might be related to a second, HT/MP metamorphism (M2), indicating that the whole crustal section remained in a mid-crustal position. Metamorphic overprinting related to M2 is spatially limited and is heterogeneously distributed in central southern Madagascar. Newly developed M2 mineral assemblages are preferentially found in areas featuring Ihosy phase vertical foliation planes. Very often these structures show brittle/ductile or brittle overprint and might be considered as preferred pathways for fluid flow, thus localising metamorphic overprint. © 2011 Elsevier B.V.


Hollier A.,Museum dHistoire Naturelle de Geneva | Hollier J.,Museum dHistoire Naturelle de Geneva
Archives of Natural History | Year: 2013

The nineteenth-century Swiss entomologist Henri de Saussure is probably better known today as the father of linguist Ferdinand de Saussure than as a scientist in his own right. In this context, it is his personality rather than his work that has attracted attention, encouraged by the availability of letters and diaries in which he expresses himself openly on personal matters. This paper presents an overview of his life that includes analysis of his scientific contribution in order to give a more balanced assessment. Examination of his publications confirms his importance as a taxonomist, and shows interesting trends in his approach. He was also notable for his cultivation of a wide network of collaborators and for the way he used his status to enhance the collections of the Museum d'histoire naturelle de Geneve. © The Society for the History of Natural History.


Hollier J.,Museum dHistoire Naturelle de Geneva | Hollier A.,Museum dHistoire Naturelle de Geneva
Bulletin of the British Ornithologists' Club | Year: 2016

The cousins Louis-Albert Necker and Henri de Saussure exemplify the contribution to the study of birds made by non-specialists in the first half of the 19th century, during the period when ornithology was just emerging as a scientific discipline. Necker undertook local field observations and published some of the earliest detailed information on the birds of Switzerland, especially the Geneva region, and both men were important contributors to the Museum d'histoire naturelle de Geneve in ways characteristic of their time: via the donation of private collections or the procurement of exotic specimens through scientific expeditions.


So far, three species of the tribe Bacchini have been recorded from Madagascar. A review of the known species is given, including a redescription of Ptileuria (pBaccha) nigroscutata Enderlein, 1938. Five new species are described from the island: A. similis sp. n., A.fumosa sp. n., A. madecassa sp. n., A. obscura sp. n. and A. subflava sp. n. A brief historical account of the taxonomy of the Bacchini, in particular with regard to the status of Allobaccha is presented.

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