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The ostracode genus FossocytherideaSwain and Brown 1964 is emended herein. A summary of the diagnostic characters include: (1) a median sulcus, (2) a tripartite antimerodont hinge with distinct heart-shaped terminal elements, (3) distinct sexual dimorphism; (4) a narrow inner margin that has 20–28 straight radial pore canals, and (5) variability in the external carapace (pore shape, pore density, and patterns of reticulation) that bears close resemblance to Cyprideis. Two new species are described from southwest Utah (U.S.A): Fossocytheridea mosbyense sp. nov. and Fossocytheridea kirklandi sp. nov. and 21 taxa previously assigned to Fabanella, Sarlatina, Ovocytheridea, Dolocytheridea, Antibythocypris, and Cytheridea are assigned to the emended genus. Fossocytheridea resembles Cyprideis with respect to both shell morphology and ecology since it occurs in association with euryhaline biota in coal-bearing strata. Expansion of marginal marine environments during the highest sea level of the Mesozoic saw Fossocytheridea successfully migrate and dominate restricted coastal environments. Since this expansion, the prominent characters of Fossocytheridea have been preserved in descendent genera belonging to the tribe Cyprideidini Kollmann 1960 that are preserved to this day in Cyprideis.
Well preserved nannofossil assemblages in upper Albian and lower Cenomanian hemipelagic sections from Ocean Drilling Program (ODP) Leg 171B preserve a record of the early history and adaptive radiation of the genus Eiffellithus. Seven distinct taxa are recognized and differentiated, with one previously named taxon (E. monechiae) emended and four new species described: E. praestigium, E. vonsalisiae, E. equibiramus, and E. parvus. Sample census data indicate that most species evolved, rose to dominance, and then rapidly declined to extinction, to be replaced by other members of the genus. Newly evolved species tended to remain at low abundance levels until a significant disruption in the pelagic realm resulted in the precipitous decline of the dominant species. This decline provided open niche space in the pelagic realm into which the new species could rapidly rise to dominance. These major disruptions correspond to significant changes or shifts in the sedimentological and carbon isotopic records associated with the late Albian Oceanic Anoxic Event (OAE-1d), suggesting that major changes in the strength of deep mixing and the structure of the surface water mass drove the early adaptive radiation of Eiffellithus.
On the basis of thin-section studies of larger foraminifera in well cores and cuttings from the Amapá Formation of the Foz do Amazonas Basin nine informal biozones (LF1-LF9) have been recognized for the upper Paleocene to middle Miocene of this basin. Lepidocyclinids are the most abundant of the larger foraminifera in the formation, and the occurrence of Lepidocyclina rdouvillei in the late middle Eocene (LF4 biozone, equivalent to planktonic foraminiferal biozones P13-P14) corroborates the hypothesis of an American origin for this genus and its rapid colonization of the northeastern margin of South America in the middle Eocene. By at least middle Eocene times, strong American affinities of the larger foraminifera of the equatorial Atlantic margins of both South America and Africa had become established by eastward migration. The presence of larger foraminifera throughout the entire carbonate section in the basin suggests that there were no significant changes in the equatorial climate of this region during the Tertiary. Extinctions of some larger foraminifera in the basin were related to environmental and ecological changes associated with sea level fluctuations.
Distortion of diatom assemblages by differential dissolution has long hindered their utilization for paleoceanographic research. We propose a quantitative index defined as the ratio of number of complete valves/number of complete copulae (V/C ratio) to evaluate dissolution levels of Neodenticula seminae. We observe that an almost equal number of valves and copulae of this species occur in nearly undissolved assemblages from the water column. In spite of this, copulae are dominant in surface sediments, indicating differential dissolution between these frustule components. To confirm this, we carried out an experiment and found the copulae to be more dissolution tolerant than the valves. Based on these results, valve number in any assemblage prior to the start of dissolution is predicted with an expression using; 1) the number of both components after dissolution and their ratio; 2) the ratio of both components before dissolution starts (1.0) and 3) the ratio of dissolution tolerance between both components (shown experimentally). In short, we can obtain the quantified N. seminae dissolution level by a comparison of dissolution tolerance between both frustule components in experiment, and by counting both components in a sample. Neodenticua seminae is among the most important primary producers in the mid to high latitude North Pacific during the Quaternary. Thus, we strongly stress that the application of this index will allow us not only to revise opaline dissolution history, but to take the more quantitative step in reconstructing paleoproductivity and/or mass balance of opal during the Quaternary.
A new Orbitoidal foraminiferal genus Lakadongia (type species Lakadongia indica, n. gen., n. sp.) is described from the Thanetian Lakadong Limestone of Meghalaya, NE India, following a critical review of the previous works on the Paleocene (Thanetian) Orbitoidal foraminifera such as Lepidorbitoides tibetica Douvillé, Lepidocyclina (Polylepidina) punjabensis Davies, Orbitosiphon praepunjabensis Adams and Setia primitiva Ferràndez-Cañadell. Lakadongia, gen. nov. is characterized by the presence of low trochospiral, quadriserial nepionts and the duplication of equatorial chamber layers in the equatorial layer. Lakadongia indica, n. gen., n. sp. is associated with Orbitosiphon tibetica (Douvillé), and both species are assigned to one new family, the Orbitosiphonidae.