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The analysis of 13 top push-core samples from the São Paulo Ridge, São Paulo Plateau, and Rio Grande Rise, collected during the Iatá-Piuna/Quelle cruise is the study of the deepest ostracods collected off Brazil, ranging between 1252.6 and 3606 m water depth. The 65 recorded species correspond predominantly to cytherurids, krithids, pontocypridids, and bythocytherids. Cytheropteron (nine spp.), Krithe (seven spp.), and Pseudocythere (five spp.) are the most diversified genera. Thirty-two of the species found have been formally described in previous studies, and many of the remaining ones are possibly new. Differences in the taxonomic composition with previous studies of ostracods from the Brazilian margin are attributed to the North Atlantic Deep Water (NADW) influence. Despite evidence of gas and oil seepages in the study area, no ostracod taxa putatively ascribed to chemosynthetic communities (e.g., Xylocythere) have been observed in the samples. Zoogeographic relations with Australasia and the long chronostratigraphic distribution of some taxa are briefly discussed. [ABSTRACT FROM AUTHOR]

Abyssocythere and Dutoitella are extant benthic bathyal ostracod genera that evolved during Coniacian to Santonian/Campanian time from shallow-water progenitors around southeastern Africa. Their Late Cretaceous development was primarily in the South Atlantic, but during the Palaeogene they spread to the Indian and Pacific oceans. The establishment of the psychrosphere (late Eocene-mid-Oligocene) flushed populations of each genus from their central Atlantic cradles into the Pacific, presumably through the Panama Seaway, so that contemporaneous centres of evolution developed disjunct clades: A. trinidadensis and D. praesuhmi. The psychrospheric oceanic event defined temporal thermophyllic and cryophyllic populations of the two genera. Three Neogene ocean events appear to have affected several regionally-confined species, inter alia one of which entailed a counterflow migration of A. atlantica from the eastern Pacific back into the central Atlantic during the mid-Miocene. Modern distributions of Abyssocythere and Dutoitella are disjunct: in the Atlantic both genera occur south of ~40o N (Dutoitella), and equatorial areas (Abyssocythere); in the Indian Ocean both are confined to the southern part; and in the Pacific, Abyssocythere is restricted to central and north-eastern areas, and Dutoitella to the west and northwest. Neither genus evolved species that were more than para-cosmopolitan: A. diagrenona (South Atlantic-Indian; Eocene-Oligocene), A. trinidadensis complex (central Atlantic-NW Pacific; Oligocene-Miocene), D. crassinodosa complex (South Atlantic-Indian; Eocene), and D. praesuhmi (north and central Atlantic-central Pacific; Oligocene-Miocene). [ABSTRACT FROM AUTHOR]

Ostracods are tiny bivalved crustaceans with a fossil record extending into rocks of the Lower Ordovician. They occupy almost all aquatic environments today, from the ocean abyssal planes to damp forest leaf litter. Their stratigraphical record suggests they had diversified into a wide range of marine and non-marine habitats already during the Palaeozoic. Through the Ordovician, ostracods are mostly known from marine shelf depositional settings. These are mostly podocope ostracods that appear to have had a benthic mode of life like their modern counterparts; myodocope ostracods, though known from the Ordovician, likely became pelagic only in the Silurian. As they are considered benthic, and possessed no pelagic larval stage, Ordovician podocope ostracods have been widely used as key biogeographical index species for much of the early Palaeozoic. A fundamental question in the oceanographic evolution of ostracods is: when did a psychrosphere evolve (a fauna inhabiting cool waters below the thermocline)? A psychrospheric ostracod fauna in the Ordovician would question some of their biogeographic utility, given that such taxa might have a much wider dispersal capability than more shallow shelf faunas. Here we describe a new ostracod fauna from a palaeotropical South China plate setting, preserved in Upper Ordovician mudstones and siltstones from northern Vietnam. The fauna contains taxa endemic to the South China palaeoplate, but also yields several taxa at the generic level that are known from European and North American Ordovician settings. We discuss whether these latter taxa might be indicative of a more widely dispersed deeper marine psychrospheric Ordovician ostracod fauna, and the implications this would have on traditional biogeographic models. We also discuss other possibilities for these apparently more cosmopolitan taxa, including homeomorphy, previously unknown palaeogeographical connections, and the possibility of pelagic podocope taxa.

Ostracods are tiny bivalved crustaceans with a fossil record extending into rocks of the Lower Ordovician. They occupy almost all aquatic environments today, from the ocean abyssal planes to damp forest leaf litter. Their stratigraphical record suggests they had diversified into a wide range of marine and non-marine habitats already during the Palaeozoic. Through the Ordovician, ostracods are mostly known from marine shelf depositional settings. These are mostly podocope ostracods that appear to have had a benthic mode of life like their modern counterparts; myodocope ostracods, though known from the Ordovician, likely became pelagic only in the Silurian. As they are considered benthic, and possessed no pelagic larval stage, Ordovician podocope ostracods have been widely used as key biogeographical index species for much of the early Palaeozoic. A fundamental question in the oceanographic evolution of ostracods is: when did a psychrosphere evolve (a fauna inhabiting cool waters below the thermocline)? A psychrospheric ostracod fauna in the Ordovician would question some of their biogeographic utility, given that such taxa might have a much wider dispersal capability than more shallow shelf faunas. Here we describe a new ostracod fauna from a palaeotropical South China plate setting, preserved in Upper Ordovician mudstones and siltstones from northern Vietnam. The fauna contains taxa endemic to the South China palaeoplate, but also yields several taxa at the generic level that are known from European and North American Ordovician settings. We discuss whether these latter taxa might be indicative of a more widely dispersed deeper marine psychrospheric Ordovician ostracod fauna, and the implications this would have on traditional biogeographic models. We also discuss other possibilities for these apparently more cosmopolitan taxa, including homeomorphy, previously unknown palaeogeographical connections, and the possibility of pelagic podocope taxa. [ABSTRACT FROM AUTHOR]

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Copyright of Revue de Micropaleontologie is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)