Molluscan fauna

66 p. : ill., maps ; 27 cm.Includes bibliographical references (p. 62-66)."Fossiliferous sediments of Permian age occupy an area in the Paraná Basin of Brazil, Uruguay, Paraguay, and Argentina equivalent to about one and one-half times the size of the Gulf of Mexico. The Estrada Nova Formation, ranging from 100 to 1000 meters thick near the middle of the Permian section, contains a widely distributed and diverse fauna of bivalve molluscs made known by J. Camargo Mendes and others. Many of these are silicified and very well preserved. The fauna is remarkable in being wholly confined, so far as is known, to the Paraná Basin. A critical review of the bivalves undertaken in the present paper shows that their family affinities are with marine Gondwana forms found in underlying strata (Tubarão Group) and in other Gondwana continents. The remarkable endemicity of the Estrada Nova fauna and carbon isotope paleosalinities suggest intrabasinal evolutionary radiation under conditions of brackish water and extreme isolation. The history of this relict sea compares favorably with the well-documented, extraordinary history of the Pontian Sea of southeastern Europe of late Cenozoic times and is reminiscent of 'sympatric' evolution of the fishes of east African lakes. The taxonomy of 24 generic and 57 specific names employed for the Permian bivalves is revised and their biologic and ecologic significance is analyzed"--P. 5

Controls on the evolution of Ediacaran metazoan ecosystems: A redox perspective

A growing number of detailed geochemical studies of Ediacaran (635–541 Ma) marine successions have provided snapshots into the redox environments that played host to the earliest known metazoans. Whilst previous compilations have focused on the global evolution of Ediacaran water column redox chemistry, the inherent heterogeneity evident in palaeogeographically distinct environments demands a more dissected approach to better understand the nature, interactions and evolution of extrinsic controls on the development of early macrobenthic ecosystems. Here, we review available data of local-scale redox conditions within a palaeogeographic and sequence stratigraphic framework, to explore the mechanisms controlling water column redox conditions and their potential impact on the record of metazoans. The openly connected Laurentian margin, North America (632–540 Ma) and Nama basin, Namibia (550–538 Ma), and the variably restricted Yangtze Block, South China (635–520 Ma), show continued redox instability after the first fossil evidence for metazoans. This may support opportunistic benthic colonisation during periods of transient oxygenation amidst episodic upwelling of anoxic waters beneath a very shallow, fluctuating chemocline. The first skeletal metazoans appeared under conditions of continued redox stratification, such as those which characterise the Dengying Formation of the Yangtze Block and the Kuibis Subgroup of the Nama basin. Current data, however, suggests that successful metazoan reef-building demanded more persistent oxia. We propose that cratonic positioning and migration throughout the Ediacaran Period, in combination with gradually increasing dissolved oxygen loading, may have provided a first-order control on redox evolution through regulating circulation mechanisms in the Mirovian Ocean. Some unrestricted lower slope environments from mid-high latitudes benefited from sustained oxygenation via downwelling, whilst transit of isolated cratons towards more equatorial positions stifled pervasive ventilation either through ineffective surface ocean mixing, Ekman-induced upwelling, elevated surface ocean productivity or a combination of these processes

Supplemental dataset 1 for: Ediacaran palaeobiology and biostratigraphy of the Nama Group, Namibia, with emphasis on the erniettomorphs, tubular and trace fossils, and a new sponge, Arimasia germsi gen. et sp. nov.

<p class="MsoNormal">Ediacaran fossils, obtained in stratigraphic context in 1993, 1995 and 1996, with the assistance of A. Seilacher, IGCP project 320 scientists and the Geological Survey of Namibia, are described for the first time. Most are from the Kliphoek and Buchholzbrunn members of the Dabis Formation and the Huns and Spitskop members of the Urusis Formation, Witputs subbasin, but a significant number, including <em>Pteridinium</em>, are from the Kliphoek Member, Zaris Formation and the Neiderhagen Member, Nudaus Formation north of the Osis arch, which separates the two subbasins. We extend the stratigraphic ranges and geographic distributions of several important taxa, including <em>Archaeichnium</em>, <em>Ernietta</em>, <em>Pteridinium</em> and <em>Swartpuntia</em>, provide reassessments of the paleobiology of these and other organisms, and describe a new sponge—possibly an unmineralized archaeocyath—<em>Arimasia germsi</em> gen. et sp. nov. We also describe and illustrate various ichnofossils, including the oldest known traces from the Nama Group, narrow down the first appearance of <em>Treptichnus</em> in the Nama succession, and reinforce the idea that there was a prolific infauna of micrometazoans during the latest Ediacaran by naming and describing previously reported microburrows found on the surfaces of gutter casts as <em>Ariichnus vagus</em> igen. et isp. nov.</p><p>Funding provided by: National Science Foundation<br>Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000001<br>Award Number: EAR-9627924</p&gt

Molecular palaeontology

Volume: 29Start Page: 1End Page: 2

Preserved ligaments in Australian Permian bivalves

Volume: 11Start Page: 94End Page: 10