67 research outputs found
The Origin and Initial Rise of Pelagic Cephalopods in the Ordovician
BACKGROUND: During the Ordovician the global diversity increased dramatically at family, genus and species levels. Partially the diversification is explained by an increased nutrient, and phytoplankton availability in the open water. Cephalopods are among the top predators of today's open oceans. Their Ordovician occurrences, diversity evolution and abundance pattern potentially provides information on the evolution of the pelagic food chain. METHODOLOGY/PRINCIPAL FINDINGS: We reconstructed the cephalopod departure from originally exclusively neritic habitats into the pelagic zone by the compilation of occurrence data in offshore paleoenvironments from the Paleobiology Database, and from own data, by evidence of the functional morphology, and the taphonomy of selected cephalopod faunas. The occurrence data show, that cephalopod associations in offshore depositional settings and black shales are characterized by a specific composition, often dominated by orthocerids and lituitids. The siphuncle and conch form of these cephalopods indicate a dominant lifestyle as pelagic, vertical migrants. The frequency distribution of conch sizes and the pattern of epibionts indicate an autochthonous origin of the majority of orthocerid and lituitid shells. The consistent concentration of these cephalopods in deep subtidal sediments, starting from the middle Tremadocian indicates the occupation of the pelagic zone early in the Early Ordovician and a subsequent diversification which peaked during the Darriwilian. CONCLUSIONS/SIGNIFICANCE: The exploitation of the pelagic realm started synchronously in several independent invertebrate clades during the latest Cambrian to Middle Ordovician. The initial rise and diversification of pelagic cephalopods during the Early and Middle Ordovician indicates the establishment of a pelagic food chain sustainable enough for the development of a diverse fauna of large predators. The earliest pelagic cephalopods were slowly swimming vertical migrants. The appearance and early diversification of pelagic cephalopods is interpreted as a consequence of the increased food availability in the open water since the latest Cambrian
Cephalopods from reef limestone of the Vasalemma Formation, northern Estonia (latest Sandbian, Upper Ordovician) and the establishment of a local warm-water fauna
Siphonal and cameral deposits inAllumettoceras and the position of the tripteroceratidae (nautiloidea)
The cephalopods of the Kullsberg Limestone Formation, Upper Ordovician, central Sweden and the effects of reef diversification on cephalopod diversity
Upper Ordovician (Harjuan) oncoceratid nautiloids from the Boda Limestone, Siljan District, Sweden
Molekulare Virologie am Beispiel des Hepatitis-B-Virus
Die nachfolgend beschriebenen Forschungsprojekte der Nachwuchsgruppe I am Robert Koch-Institut (RKI) befassen sich am Beispiel des Hepatitis-B-Virus (HBV) mit der Charakterisierung intrazellulärer Signalkaskaden und der Analyse ihrer Bedeutung für den viralen Lebenszyklus (Replikaktionsprozess) sowie für die Entstehung von HBV assoziierten Tumoren. Darüber hinaus werden auf der Basis eines neuen, aus dem HBV-Oberflächenprotein isolierten zellpermeablen Peptides neue Strategien zum Protein- und Gentransfer entwickelt
Devonohelicoceras hidaense, a new torticonic oncocerid (Cephalopoda) from the Lower Devonian of Central Japan.
LXVIII.— Upper Llandovery Brachiopoda from Coneygore Coppice and Old Storridge Common, near Alfrick, Worcestershire
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