993 resultados para Mollusks, Fossil.
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Mode of access: Internet.
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The paludal deposits presented here belong to a geomorphological unit identified between Palafrugell Corridor and the littoral plains of Ter River (Baix Ter), associated to a carbonate-rich spring system. The sections show a distintic clay level, mixed with black silts, very rich in snail remains. The malacological assemblage contained stillwaters species (Bithynia leachii, Galba truncatula, Pisidium milium, Radix peregra) along with damp species (Monacha cartusiana, Oxyloma elegans, Succinea putris, Succinella oblonga, Vallonia pulchella, Vertigo sp.). Some open-dry species are also present (Cernuella virgata, Eobania vermiculata, Pomatias elegans, Rumina decollata) revailing a mosaic-like landscape. Radiocarbon dates place this level ca. 7.000BPwithin the Holocene sequence of the Baix Ter basin. Colluvial deposits on top of these paludal levels have a typical open-dry malacological assemblage (Cernuella virgata, Cochlicella acuta, Eobania vermiculata, Pomatias elegans, Rumina decollata, Trochoidea elegans) the same assemblage that inhabits the Empordà littoral plains nowadays
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v.10:no.3 (1884)
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Extracted from the Philippine Journal of Science, v.18, no.1.
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Mode of access: Internet.
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"Lue à l'Académie des sciences de l'Institut, le 26 mars 1832."
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Terrain tertiaire. Vol. 1, 2.
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Bibliography: p. 89-91.
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Vita.
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Bibliography: p. 299-325.
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Fossils of the gastropods Diodora patagonica, Zidona dufresnei, Olivancillaria carcellesi, Lamniconus lemniscatus carcellesi and the bivalve Arcinella brasiliana are registered for the first time from the outcrops of Chui Creek, on the coastal plain of Rio Grande do Sul State, southernmost Brazil, together with other taxa previously known elsewhere. The specimens were collected in a shallow Pleistocene marine facies exposed at the base of the banks of the creek, in a fossil concentration possibly formed by storm events. The taxa described here live in shallow environments (with the exception of A. brasiliana and Z. dufresnei) with sandy bottoms (except for D. patagonica, T patagonica, B. odites, C. rhizophorae and A. brasiliana). The presence of L. lemniscatus carcellesi, found living today only in Uruguay and Argentina, indicates a wider distribution for this taxon during the late Pleistocene.
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We determined the rate of migration of coastal vegetation zones in response to salt-water encroachment through paleoecological analysis of mollusks in 36 sediment cores taken along transects perpendicular to the coast in a 5.5 km2 band of coastal wetlands in southeast Florida. Five vegetation zones, separated by distinct ecotones, included freshwater swamp forest, freshwater marsh, and dwarf, transitional and fringing mangrove forest. Vegetation composition, soil depth and organic matter content, porewater salinity and the contemporary mollusk community were determined at 226 sites to establish the salinity preferences of the mollusk fauna. Calibration models allowed accurate inference of salinity and vegetation type from fossil mollusk assemblages in chronologically calibrated sediments. Most sediments were shallow (20–130 cm) permitting coarse-scale temporal inferences for three zones: an upper peat layer (zone 1) representing the last 30–70 years, a mixed peat-marl layer (zone 2) representing the previous ca. 150–250 years and a basal section (zone 3) of ranging from 310 to 2990 YBP. Modern peat accretion rates averaged 3.1 mm yr)1 while subsurface marl accreted more slowly at 0.8 mm yr)1. Salinity and vegetation type for zone 1 show a steep gradient with freshwater communities being confined west of a north–south drainage canal constructed in 1960. Inferences for zone 2 (pre-drainage) suggest that freshwater marshes and associated forest units covered 90% of the area, with mangrove forests only present along the peripheral coastline. During the entire pre-drainage history, salinity in the entire area was maintained below a mean of 2 ppt and only small pockets of mangroves were present; currently, salinity averages 13.2 ppt and mangroves occupy 95% of the wetland. Over 3 km2 of freshwater wetland vegetation type have been lost from this basin due to salt-water encroachment, estimated from the mollusk-inferred migration rate of freshwater vegetation of 3.1 m yr)1 for the last 70 years (compared to 0.14 m yr)1 for the pre-drainage period). This rapid rate of encroachment is driven by sea-level rise and freshwater diversion. Plans for rehydrating these basins with freshwater will require high-magnitude re-diversion to counteract locally high rates of sea-level rise.
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Preface signed: A.R. [i.e. Alexander Ramsay]
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Divergence dating studies, which combine temporal data from the fossil record with branch length data from molecular phylogenetic trees, represent a rapidly expanding approach to understanding the history of life. National Evolutionary Synthesis Center hosted the first Fossil Calibrations Working Group (3–6 March, 2011, Durham, NC, USA), bringing together palaeontologists, molecular evolutionists and bioinformatics experts to present perspectives from disciplines that generate, model and use fossil calibration data. Presentations and discussions focused on channels for interdisciplinary collaboration, best practices for justifying, reporting and using fossil calibrations and roadblocks to synthesis of palaeontological and molecular data. Bioinformatics solutions were proposed, with the primary objective being a new database for vetted fossil calibrations with linkages to existing resources, targeted for a 2012 launch.