Search results for "Class"

Hydrothermalism in the Tyrrhenian Sea: Inorganic and microbial sulfur cycling as revealed by geochemical and multiple sulfur isotope data

2011

15 pages; International audience; The Palinuro volcanic complex and the Panarea hydrothermal field, both located in the Tyrrhenian Sea (Italy), are associated with island arc magmatism and characterized by polymetallic sulfide mineralization. Dissolved sulfide concentrations, pH, and Eh measured in porewaters at both sites reveal a variable hydrothermal influence on porewater chemistry. Multiple sulfur isotopic measurements for disseminated sulfides (CRS: chromium reducible sulfur) extracted from sediments at Palinuro yielded a broad range in δ34S range between −29.8 and +10.2‰ and Δ33S values between+0.015 and+0.134‰. In contrast, sediments at Panarea exhibit a much smaller range in δ34SCR…

Morphology and preliminary biomechanical interpretation of mandibular sutures in Metoposaurus krasiejowensis (Temnospondyli, Stereospondyli) from the…

2019

Altres ajuts: CERCA Programme/Generalitat de Catalunya The morphology of the mandibular sutures in the Late Triassic temnospondyl Metoposaurus krasiejowensis has been examined in order to determine their role in mandible biomechanics. Until now, no histological studies of mandibular sutures in extinct vertebrates were performed, in contrast to cranial sutures. As a consequence, mandibular suture interpretations herein are based mainly on comparisons with previous studies of cranial sutures and with 3D cranial finite element analysis of this species. A total of 32 standard thin sections were studied under standard petrographic microscope observations in order to differentiate the morphology …

A little walk between Early Jurassic sponges and corals: a confusing morphological convergence.

2019

24 pages; International audience; Hispaniastraea Turnšek et Geyer, 1975 is a unique coral genus from the Early Jurassic Epoch (Liassic). Corals of this genus are characterised by a highly dominant major septum and a set of eleven minor septa that are very short or even abortive. Initially discovered in Spain, new samples of this genus were depicted from Morocco by Beauvais in 1980; however, this genus was interpreted as a synonym of Pseudoseptifer Fischer, 1970, a chaetetid sponge (i.e., a sponge with siliceous spicules embedded in a calcareous skeleton). The skeleton of Pseudoseptifer is composed of adjacent tubules that increase by fissiparity by means of a pseudoseptum. Based on the stud…

Preliminary report on new echinoderm Lagerstatten from the Upper Ordovician of the eastern Anti-Atlas, Morocco.

2006

8 pages (p.23-30); International audience; Four distinct echinoderm Lagerstatten have recently been discovered in the Upper Ordovician of the eastern Anti-Atlas, Morocco. They have yielded hundreds of exquisitely preserved specimens. Their taphonomy and associated lithology both suggest rapid, in situ burial. Here we discuss the diverse range of assemblages represented and their significance to the diversity of echinoderms in the Lower Palaeozoic. The oldest assemblage (Izegguirene Formation, lowermost Caradoc) is dominated by eocrinoids, large ophiuroids, and mitrate stylophorans associated with rare crinoids. It shows strong similarities with slightly older faunas described from the under…

Jaws and teeth of the earliest bony fishes

2007

Extant jawed vertebrates, or gnathostomes, fall into two major monophyletic groups, namely chondrichthyans (cartilaginous fishes) and osteichthyans (bony fishes and tetrapods). Fossil representatives of the osteichthyan crown group are known from the latest Silurian period, 418 million years (Myr) ago, to the present. By contrast, stem chondrichthyans and stem osteichthyans are still largely unknown. Two extinct Palaeozoic groups, the acanthodians and placoderms, may fall into these stem groups or the common stem group of gnathostomes, but their relationships and monophyletic status are both debated. Here we report unambiguous evidence for osteichthyan characters in jaw bones referred to th…

Meet Adonis, Europe’s oldest dendrochronologically dated tree

2017

Water mass exchange and variations in seawater temperature in the NW Tethys during the Early Jurassic: evidence from neodymium and oxygen isotopes of…

2009

10 pages; International audience; Oxygen and neodymium isotope analyses performed on biostratigraphically well-dated fish remains recovered from the Hettangian to Toarcian of the Paris Basin were used to reconstruct variations of Early Jurassic seawater temperature and to track oceanographic changes in the NW Tethys. Our results indicate a strong correlation between δ18O trends recorded by fish remains and belemnites, confirming the paleoenvironmental origin of oxygen isotope variations. Interestingly, temperatures recorded by pelagic fishes and nektobenthic belemnites and bottom dwelling fishes are comparable during the Late Pliensbachian sea-level lowstand but gradually differ during the …

The Mid-Cenomanian Event in southeastern France: evidence from palaeontological and clay mineralogical data.

2013

16 pages; International audience; Reconstruction of main palaeoenvironmental conditions across the Mid-Cenomanian Event (MCE I) in the hemipelagic Tethyan section of Blieux (Southeast France, Vocontian Basin) is proposed. Quantitative analyses of calcareous nannofossil, ammonoid and clay mineral assemblages have been made and compared with respect to sea level changes and the carbon cycle perturbations. The nannofossil primary productivity, as recorded by nannofossil fluxes and relative abundances of meso-eutrophic taxa, is low just below and during the MCE Ia, then slightly increases in the interval including the MCE Ib. The clay assemblages mainly consist of illite/smectite mixed-layers w…

Facies variations in response to Holocene sea-level and climate change on Bora Bora, French Polynesia: Unravelling the role of synsedimentary siderit…

2017

International audience; Five mixed carbonate-siliciclastic sedimentary facies were identified in the barrier-reef lagoon of Bora Bora using microfacies and statistical analyses of 70 sediment samples taken at high resolution from two vibrocores. Fades and fades successions were interpreted with respect to Holocene sea-level and climate changes. The windward lagoon core is characterized by sideritic marly wackestones and foraminifera-sideritic wackestones, deposited around 7700 years BP (years before present) during the early-mid Holocene transgression. At that time, extensive weathering and erosion of iron-bearing minerals from the volcanic island, due to a wetter climate, were expressed in…

Radial Symmetry, the Anterior/Posterior Axis, and Echinoderm Hox Genes

2008

20 pages; International audience; The strangeness of echinoderm pentaradiality results from superposition of radial symmetry onto ancestral deuterostome bilaterality. The Extraxial- Axial Theory shows that echinoderms also have an anterior/posterior (A/P) axis developed independently and ontogenetically before radiality. The A/P axis is first established via coelomic stacking in the extraxial region, with ensuing development of the pentamerous hydrocoel in the axial region. This is strongly correlated with a variety of gene expression patterns. The echinoid Hox cluster is disordered into two different sets of genes. During embryogenesis, members of the posterior class demonstrate temporal, …