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Gross M.,Universalmuseum Joanneum | Ramos M.I.F.,Coordenacao de Ciencias da Terra e Ecologia | Piller W.E.,University of Graz
Journal of Systematic Palaeontology | Year: 2015

A huge wetland (the ‘Pebas system’) covered western Amazonia during the Miocene, hosting a highly diverse and endemic aquatic fauna. One of the most contentious issues concerns the existence, potential pathways and effects of marine incursions on this ecosystem. Palaeontological evidences (body fossils) are rare. The finding of a new, presumably marine ostracod species (Pellucistoma curupira sp. nov.) in the upper middle Miocene Solimões Formation initiated a taxonomic, ecological and biogeographical review of the genus Pellucistoma. We demonstrate that this marine (sublittoral, euhaline), subtropical–tropical taxon is biogeographically confined to the Americas. The biogeographical distribution of Pellucistoma largely depends on geographical, thermal and osmotic barriers (e.g. land bridges, deep and/or cold waters, sea currents, salinity). We assume an Oligocene/early Miocene, Caribbean origin for Pellucistoma and outline the dispersal of hitherto known species up to the Holocene. Pellucistoma curupira sp. nov. is dwarfed in comparison to all other species of this genus and extremely thin-shelled. This is probably related to poorly oxygenated waters and, in particular, to strongly reduced salinity. The associated ostracod fauna (dominated by the eurypotent Cyprideis and a few, also stunted ostracods of possibly marine ancestry) supports this claim. Geochemical analyses (δ18O, δ13C) on co-occurring ostracod valves (Cyprideis spp.) yielded very light values, indicative of a freshwater setting. These observations point to a successful adaptation of P. curupira sp. nov. to freshwater conditions and therefore do not signify the presence of marine water. Pellucistoma curupira sp. nov. shows closest affinities to Caribbean species. We hypothesize that Pellucistoma reached northern South America (Llanos Basin) during marine incursions in the early Miocene. While larger animals of marine origin (e.g. fishes, dolphins, manatees) migrated actively into the Pebas wetland via fluvial connections, small biota (e.g. P. curupira sp. nov.) were phoretically freighted and developed freshwater tolerance over long timescales. http://zoobank.org/urn:lsid:zoobank.org:pub:886C6476-393D-4323-8C0E-06BB8BD02FD9 © The Trustees of the Natural History Museum, London 2015. All rights reserved. Source

Vasconcelos H.L.,Federal University of Uberlandia | Vilhena J.M.S.,National Institute of Amazonian Research | Facure K.G.,Federal University of Uberlandia | Albernaz A.L.K.M.,Coordenacao de Ciencias da Terra e Ecologia
Journal of Biogeography | Year: 2010

Aim To determine the effect and relative importance of geographic and local environmental factors on species richness and turnover of ant assemblages in floodplain forests across the Amazon basin. Location Twenty-six mature forest sites scattered along the entire extension of the Amazon River in Brazil. The study area encompassed nearly 18° of longitude and 3.5° of latitude. Methods Systematic collections of ants were performed at each site during the low-water season (i.e. when forests are not inundated) using three complementary sampling methods. We used variance partitioning techniques to assess the relative effects of the spatial (latitude and longitude) and environmental (rainfall, length of the dry season and flood height) variables on ant species richness and composition. Results There was a twofold variation in the number of species per site, which was largely explained by inter-site variations in rainfall seasonality and flooding intensity. In general, there were more species at sites located in the western part of the basin, where the dry season is less severe, or near the river estuary, where precipitation is also high and flooding is less intense. Ant community composition was also affected by environmental heterogeneity. For instance, some species only occurred at those sites less affected by the river's seasonal flooding, whereas others were mostly associated with the drier or wetter regions of the basin. In addition, the turnover of species increased significantly as geographic distances increased. Nevertheless, the rate of change was small given that many species had a broad distribution across the study area. Main conclusions Ant distribution patterns along the floodplain forests of the Amazon appear to be controlled to a relatively large extent by the current gradient in flooding intensity and - most importantly - in precipitation. Altered rainfall regimes resulting from global warming and land-use change thus have the potential to influence these patterns. © 2009 Blackwell Publishing Ltd. Source

Gross M.,Universalmuseum Joanneum | Piller W.E.,University of Graz | Ramos M.I.,Coordenacao de Ciencias da Terra e Ecologia | Douglas da Silva Paz Jackson J.,Federal University of Mato Grosso
Journal of South American Earth Sciences | Year: 2011

In Miocene times a vast wetland existed in Western Amazonia. Whereas the general development of this amazing ecosystem is well established, many questions remain open on sedimentary environments, stratigraphical correlations as well as its palaeogeographical configuration. Several outcrops located in a barely studied region around Eirunepé (SW Amazonas state, Brazil) were investigated to obtain basic sedimentological data. The observed deposits belong to the upper part of the Solimões Formation and are biostratigraphically dated to the Late Miocene. Vertically as well as laterally highly variable fine-grained clastic successions were recorded. Based on the lithofacies assemblages, these sediments represent fluvial deposits, possibly of an anastomosing river system. Sand bodies formed within active channels and dominant overbank fines are described (levees, crevasse splays/channels/deltas, abandoned channels, backswamps, floodplain paleosols). Lacustrine environments are restricted to local floodplain ponds/lakes. The mollusc and ostracod content as well as very light δ18O and δ13C values, measured on ostracod valves, refer to exclusively freshwater conditions. Based on palaeontological and geological results the existence of a long-lived lake (" Lake Pebas" ) or any influx of marine waters can be excluded for that region during the Late Miocene. © 2011 Elsevier Ltd. Source

Griffiths N.,Royal Holloway, University of London | Muller W.,Royal Holloway, University of London | Johnson K.G.,Natural History Museum in London | Aguilera O.A.,Coordenacao de Ciencias da Terra e Ecologia
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2013

Early Miocene corals (Siderastrea conferta and Montastraea limbata) from the Paraguaná Peninsula, Venezuela and a modern coral (S. radians) from Bermuda were examined in order to quantitatively assess the effect of skeletal preservation on element/Ca proxies used for palaeo-environmental reconstructions. The biostratigraphic age (Burdigalian) of the corals was confirmed via Sr isotope stratigraphy to 16.5 ± 0.4. Ma. Light and scanning electron microscopy revealed the presence of aragonite and calcite cements in both fossil and modern corals, but brucite cements were found only in the modern coral. Cement distribution is very heterogeneous, resulting in zones of excellent preservation juxtaposed with less well preserved regions in both modern and fossil coral. Oil-filled pore spaces were noted in the fossil specimens. Targeted LA-ICPMS depth profile analyses showed significant differences in Sr/Ca, Mg/Ca, B/Ca, Ba/Ca and U/Ca in aragonite and calcite cements compared to primary skeletal aragonite. Increased Sr/Ca and decreased Mg/Ca ratios were found in aragonite cements compared to skeletal aragonite, whereas in calcite cements these trends were reversed. B/Ca ratios were lower in both aragonite and calcite cements compared to primary aragonite. Estimates of the effect of 1% contamination by aragonite cements on coral Sr/Ca, Mg/Ca, B/Ca and U/Ca palaeo-sea-surface-temperature reconstructions for the fossil corals produced anomalies of - 1.2. °C, - 0.2. °C, + 0.3. °C and - 0.1. °C respectively. Similar percentage calcite cement contamination produced temperature anomalies of + 1.7. °C, + 2.7. °C, + 0.3. °C and - 0.1. °C. Because of both highly elevated and depleted Ba/Ca signatures in aragonite and calcite cements respectively, care has to be exercised when reconstructing past flood or upwelling events from fossil corals. When using targeted spatially-resolved analysis, well-preserved early Miocene corals may overall yield reliable 'deep-time' palaeo-proxy information in much the same way as commonly utilised Holo/Pleistocene corals. © 2012. Source

Da Costa K.G.,Federal University of Para | Bezerra T.R.,Federal University of Para | Monteiro M.C.,Polytechnic University of Catalonia | Vallinoto M.,Federal University of Para | And 3 more authors.
Journal of Coastal Research | Year: 2013

Garboza Da Costa, K.; Cunha Monteiro, M.; Rabelo Bezerra, T.; Vallinoto, M.; Francisco Berrêdo, J.; Cajueiro Carneiro Pereira, L., and Marinho Da Costa, R., 2013. Tidal-induced changes in the zooplankton community of an Amazon estuary. Because variations in the zooplankton community are common in macrotidal estuaries, the composition and density of these organisms in the estuary of the Paracauari River, an equatorial macrotidal system of the Amazon coastal zone, was studied during spring and neap tides to evaluate fluctuations related to variations in the physical and chemical characteristics of the water. Significant differences between tidal periods were recorded for salinity, pH, and dissolved oxygen. Phosphate concentrations were significantly higher in the spring tide. In all, 34 taxa were identified, with the Cirripedia dominating in both tides. Total density was highest in the spring tide (1871.6 ± 1248.4 individuals m-3), whereas chlorophyll a was lowest (10.46 ± 3.48 mg m-3). Diversity was also higher in the spring tide. Multivariate analyses indicated the formation of two distinct groups representing the spring and neap tides. The zooplankton comprised mainly estuarine and coastal species. Oithona oswaldocruzi, Paracalanus quasimodo, and Acartia tonsa were the most common, and their density was related directly to tidal oscillations. © 2013 Coastal Education & Research Foundation. Source

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