REVUE DE MICROPALEONTOLOGIE最新文献

Well-preserved Early Triassic radiolarians were recovered from lower Smithian (lower Olenekian) beds in NE Vietnam. The radiolarian assemblage consists only of Paleozoic relict species of Latentifistularia and some entactinarians. Three latentifistularian species, Ruzhencevispongus vietnamensis nov. sp., Tetragregnon chilangensis nov. sp., and Tetragregnon langsonensis nov. sp., belonging to the families Ruzhencevispongidae Kozur and Tetratormentidae Nestell and Nestell are erected herein. The entactinarian family Triassothamnidae nov. fam. and one new genus and two new species of Langsonsphaera pseudocubica nov. gen. nov. sp. and Stigmosphaerostylus amabilis nov. sp. are also described. In this region, the Paleozoic-type radiolarian groups Latentifistularia and Entactinaria survived across the Permian–Triassic boundary and were present during the Induan–early Olenekian interval. Thus, in the eastern Tethyan seaway near the equator, the true extinction of some Paleozoic radiolarian groups took place at the middle of the Early Triassic, immediately after the Smithian, rather than during the Permian–Triassic crisis.

Peneroplis turonicus Said and Kenawy is a poorly known benthic foraminifer that was originally described based on isolated specimens from the Upper Cretaceous of Egypt. Specimens from the Cenomanian Sarvak Formation of Iran indicate the presence of a finely agglutinated test wall displaying a pseudo-keriothecal texture, therefore, excluding this taxon from the porcelaneous Miliolida, namely family Peneroplidae. Based on the test morphology, wall structure and foraminal features, the species is herein tentatively assigned to Neodubrovnikella Schlagintweit and Rashidi (order Loftusiida), with the new combination Neodubrovnikella turonica (Said and Kenawy). A critical literature review leads to the conclusion that N. turonica represents a southern Neotethys Cenomanian marker taxon reported so far from Italy, Slovenia, Croatia, Kosovo, Greece, Lebanon, Syria, Morocco, Egypt, Turkey, Iraq, and Iran. Therefore, Neodubrovnikella does not represent a Maastrichtian genus as previously assumed but is as old as Cenomanian, disappeared from the fossil record in the proximity of the Cenomanian-Turonian boundary and reappeared after a considerable gap and ghost range.

The presence and diversity of polycystine radiolarians in the North-Eastern Mediterranean Sea is explored for the first time through the analysis of sinking particles obtained from sediment traps moored in three open marine sites. In total, thirty species are identified for which we provide appropriate references and illustrations to clarify the species concept followed in this study; 13 of the identified species are Spumellarians, 16 are Nassellarians and one is an Entactinarian. The highest diversity is recorded in the Ionian site, in which 23 species were observed during November 2014, with approximately as many Nassellarian species as Spumellarians; a large number of species are in common with the fauna reported from the Adriatic Sea, off Dubrovnik, but interestingly, 16 others are not. The lowest levels of radiolarian diversity, with 3 to 4 species at best, were observed in the north Aegean and Cretan Sea sites. Our observations improve also the paleobiogeographic knowledge of two polycystine species, one of which (Gonosphaera primordialis Jørgensen) was known previously from the high latitudes of both the northern and southern hemisphere and the other (Qiuripylolena chikuchik Zhang and Suzuki) from the Pacific ocean.

The Araripe, Jatobá and Tucano Norte basins, northeast Brazil, have an extensive fossil record. Among the groups found, are the ostracods, which have great relevance for this region due to their significant occurrence and wide diversity during the Upper Jurassic–Lower Cretaceous. These basins contain the rift process record of the Gondwana breakup for the posterior installation of the South Atlantic Ocean, data reinforced by the correlated ostracod non-marine fauna with some African basins. This paper presents a detailed taxonomic and biostratigraphic study of the ostracod species recovered from outcrops from these three basins. A total of 29 species were identified, distributed in eight genera: Theriosynoecum pricei, Theriosynoecum sp. cf. T. sp. 6, Cypridea acicularis, Cypridea ambigua, Cypridea indiennensis densipunctata, Cypridea sellata, Cypridea semilunaris, Cypridea vianai, Cypridea paraibensis, Cypridea (Morinina?) bibullata bibullata, Cypridea (Morinina?) bibullata tribullata, Cypridea sp. cf. C. (Morinina?) langei, Cypridea sp. cf. Cypridea miritiensis, Cypridea sp. 1, Paracypridea brasiliensis, Paracypridea quadrirugosa quadrirugosa, Paracypridea ex. gr. elegans, Salvadoriella redunca posterior, Reconcavona? jatobaensis, Reconcavona striata, Reconcavona striatula, Reconcavona swaini, Reconcavona aff. R.? polita, Reconcavona sp. cf. R. triebeli, Reconcavona sp.1, Reconcavona sp.2, Rhinocypris sp.1, Darwinula? sp. cf. D. oblonga, Alicenula sp. cf. Alicenula leguminella. From the identification of these species, it was possible to infer a stratigraphic range from Tithonian to Barremian, which corresponds to the local RT-001 to RT-007 biozones.

The morphological evolution was investigated in the tropical Neogene planktonic foraminiferal lineage Globorotalia menardii, G. limbata and G. multicamerata during the past 8 million years at ODP Hole 806C (Ontong-Java Plateau, western equatorial Pacific). This research is an extension of several similar studies since 2007 from the Caribbean Sea, the tropical Atlantic and the Eastern Equatorial Pacific. The goal is to find empirical and quantitative confirmation for morphological speciation – splitting or phyletic gradualism or accelerated evolution – in planktonic foraminifera with the above lineage as model objects. The present study from ODP Hole 806C serves as a test to discriminate between these evolutionary scenarios.

In the western equatorial Pacific warm and stable environments prevailed back to Pliocene times, and potential influences of Northern Hemisphere Glaciation are thought to bear less severely on shell size evolution than in the Atlantic Ocean. A slow and gradual pattern of shell size increase is therefore expected in the western tropical Pacific, in contrast to the intermittent rapid menardiform shell size increase during periods of intensified formation of warm water eddies in the southern to tropical Atlantic.

For this study a total of 11,101 specimens from 37 stratigraphic levels extending over the past 8 million years were morphometrically investigated thanks to the AMOR robot for imaging and microfossil orientation. Of those, 6080 specimens comprise the G. menardii–limbata-multicamerata plexus. Special attention was given to trends of spiral height (δX) versus axial length (δY) in keel view, for which bivariate contour- and volume-density diagrams were constructed to visualize speciation and evolutionary trends.

The investigation at Hole 806C showed, that G. menardii evolved in a more gradual manner than in the Atlantic. Contour plots of δX versus δY reveal modest bimodality between 3.18 Ma – 2.55 Ma with a dominant branch consisting of smaller G. menardii (δX<∼300 μm) persisting until the Late Quaternary, and a less dominant branch of larger G. menardii (δX>∼300 μm) until 2.63 Ma. There is evidence for cladogenesis – splitting with subsequent morphological divergence in the Late Pliocene G. menardii-limbata-multicamerata lineage, and which may be linked to changes in the thermocline. Due to the general scarcity of G. multicamerata at Site 806, the divergence was less clearly expressed than originally expected. Up-section, bimodality vanished but G. menardii populations shifted towards extra large shells between 2.19-1.95 Ma.

The morphological evolution of Pacific menardiform globorotalids contrasts the one observed in the Atlantic. This inter-oceanic asymmetry may indicate possible long-distance dispersal of G. menardii, at least during intermittent phases.