我国某些常见化石硅藻的环境分析

本文详细研究了中国海表层沉积物中的常见化石硅藻,结果表明,这些种的分布范围及数量变化随环境的不同而变化。因此,根据柱状样品中这些种类数量的变化,能够推断古气候变化,恢复古地理环境,再现海平面波动历程,进而划分、对比第四系地层。     

Early Permian facies and paleogeography of the Southeastern Russian craton

Summary During the Early Permian deep-water basins existed in the southeastern part of the Russian craton. North and west of the Cis-Ural foredeep and the Precaspian depression (micro-ocean) carbonate platforms were formed on a shallow-marine shelf during the Asselian, Sakmarian and Early Artinskian. Reefs developed on the margin of these platforms along the slopes of the Cis-Ural foredeep and the Precaspian depression. The reefs shifted platform ward in the eastern areas, due to the tectonic subsidence of the platform margin and at the same time, prograded basinward in the south. Movements of continental blocks from the south during the Late Artinskian and Kungurian caused the separation of the Early Permian basin of the Russian craton from the Palaeo-Tethys, followed by evaporite sedimentation in the restricted basins. The existence of source rocks (bituminous deep-water sediments), thick reservoir rocks (limestones and dolostones), evaporitic seals and structural as well as stratigraphic traps are responsible for large productive gas and oil fields (e.g., Orenburg field), some of which are distinctly associated with reef carbonates.     

Origines du peuplement mammalien en Afrique du Nord durant le miocène terminal

The late Miocene North African mammalianassemblage is considered here from three viewpoints: survivals, extinctions, and immigrations. The Eurasiatic affinities of the large mammals slightly prevail over the Ethiopian affinities. Amongst the North African large mammals, 4 to 8 taxa are Eurasiatic immigrants, while 4 to 6 are of Subsaharian origin. Contrarily, the micromammalian fauna is highly endemic, with only one species, a murid (Paraethomys miocaenicus), considered here as being related to an Asiatic form (Karnimata darwini). Our study of Eurasian and African Miocene faunas reveals that during the late Astaracian-early Turolian interval, the Saharo-Arabic belt permitted very little latitudinal faunal exchanges. However, during the middle and late Turolian such faunal exchanges became frequent. The micromammal record unequivocally indicates that a brief period of faunal exchange occurred between Africa and western Europe at the end of the Miocene, corresponding with the Messinian Salinity Crisis. The increased intercontinental faunal exchange between Africa and Eurasia during the late Miocene coincides with, and counterbalances the extinction of more than 10 taxa at the Mio/Pliocene boundary.     

Le prétendu rhinocéros de Nouvelle Calédonie est un marsupial (Zygomaturus diahotensis nov. sp.): Solution d'une énigmeet conséquences paléogéographiques

The first mammalian remain ever found in NewCaledonia is an upper tooth found by golddiggers in the Plio-Pleistocene terrace from the Diahot river. This tooth, given to the Muséum national d'Histoire naturelle (Paris) in 1876, was determined as a rhinoceros tooth and then completely forgotten. Its detailed study shows that it belongs to Zygomaturus, a large marsupial diprotodontid genus whose story is rather complicated. The Diahot tooth represents a new species of Zygomaturus, Z. diahotensis nov. sp., close to Z. trilobus from the Australian Pleistocene. That kinship suggests a Plio-Pleistocene land connection between Australia and New Caledonia, whereas till now New Caledonia was supposed to be separated from Australia since the end of the Cretaceous, because of the total absence of indigenous mammals, fossil or recent, in New Caledonia. The latest geological studies in the East Pacific do not contradict our hypothesis.     

Paléobiogéographie de quelques Stephanocerataceae (Ammonitina) du Jurassique moyen et supérieur; une confrontation avec la théorie mobiliste

From Bajocian to lower Kimmeridgian, the subfamilyStephanocerataceae represents a large stock of the ammonite fauna. Though it is tributary of author's stratigraphical correlations and systematical interpretations, its geographical distribution with a drifting continents concept gives many teaching about the study of this superfamily, the continental drift and its consequences. Showing a world wide repartition at its apparition this stock then presents branches; the one (Stephanoceratidae) is not envisaged here; the second (Sphaeroceratidae and Cardioceratidae families) characterises rather the «boreal province; the third (Macrocephalitidae family) is chiefly specific of the «tethysian province. A «north-east pacific province with boreal affinities and a «south-east province with tethysian affinities are delimited. It is probably from its fauna that the tethysian macrocephalitid stock appears; first represented by ammonites specifically north american in middle and upper Bathonian stage, they extend during upper Bathonian and lower Callovian and reach South America and the Tethys. The presence of a narrow sea, on Patagonia, West Antarctica, East Africa, Madagascar and India, joining the Tethys and the south edge of Gondwania, is proved at various times, at Bajocian and Callovian stages.     

A protocol to compare nestedness among submatrices

Searching for nestedness has become a popular exercise in community ecology. Significance of a nestedness index is usually evaluated using z values, and finding that a matrix is nested is typically a common result. However, nestedness is not likely to be spread uniformly within a matrix of species presence/absence per site. Selected parts of the matrix may show a degree of nestedness significantly higher (or lower) than expected from the overall pattern. Here we describe a procedure to assess if a particular submatrix (i.e., a peculiar combination of rows and columns extracted from the complete matrix) is more or less nested than expected for an assortment of sites and species taken at random from the same overall matrix. The idea is to obtain several submatrices of different sizes from the same overall matrix and to calculate their z values. A regression is then performed between z values of submatrices and their sizes. A nestedness index independent of matrix size is suggested as the deviation of the z value of a particular submatrix from that expected according to the regression line. We applied our protocol to 55 matrices with different nestedness indices under various null-models and, for purpose of demonstration, we discussed in detail a single case study regarding various animal groups of the Aegean Islands (Greece). The obtained results strongly encourage further research to focus not only on the question whether a matrix is nested or not, but also on where and why nestedness is confined.     

Sequence stratigraphy of Eocene incised valley clastics and associated sediments,Island of Rab,northern Adriatic Sea,Croatia

Clastic sediments of Middle–Late Eocene age were studied on the Island of Rab (northern Adriatic Sea, Croatia) in order to reconstruct their depositional history, depositional environments, and geometry of sandstone bodies. Detailed outcrop logging and mapping revealed the response of depositional systems to frequent relative sea-level changes, which initiated significant basinward and landward shifts of facies, respectively. Tidal sandstones are commonly underlain by shoreface sandstones, and overlain by offshore sandy marls, whereas the latter are again overlain by shoreface sandstones. Major relative sea-level falls initiated basinward shift of depositional systems and the incision of incised valleys or estuaries, and consequently truncated the underlying shelf sediments. In some cases, the accelerated sea-level fall caused rapid shoreface progradation which is interpreted as a forced regression. Relative sea-level rise caused flooding of the incised relief, and deposition of tidal sandstone bodies which overlie type-I sequence boundaries. The coarse lag sediment of these sequence boundaries locally disappears laterally, and the boundary is granulometrically less prominent. All of the major bounding surfaces have been recognized in the sections studied, although the maximum flooding surface is recognized as a thin “zone” instead of a single surface. Altogether, 28 complete sequences, and 15 parasequences are recognized in the informal unit of the Lopar sandstones, documenting the depositional response to high-frequency relative sea-level oscillations. They have so far not been recognized in the Eocene of the eastern Adriatic region.     

On some Pleistocene bird fossils from the south Aegean islandof Karpathos (Greece)

This paper deals with some Pleistocene fossil birds from the south Aegean island of Karpathos. The species which could be identified are surveyed, and the paleogeography of the area is discussed.     

Cenozoic biogeography and evolution in direct-developing frogs of Central America (Leptodactylidae: Eleutherodactylus) as inferred from a phylogenetic analysis of nuclear and mitochondrial genes

We report the first phylogenetic analysis of DNA sequence data for the Central American component of the genus Eleutherodactylus (Anura: Leptodactylidae: Eleutherodactylinae), one of the most ubiquitous, diverse, and abundant components of the Neotropical amphibian fauna. We obtained DNA sequence data from 55 specimens representing 45 species. Sampling was focused on Central America, but also included Bolivia, Brazil, Jamaica, and the USA. We sequenced 1460 contiguous base pairs (bp) of the mitochondrial genome containing ND2 and five neighboring tRNA genes, plus 1300 bp of the c-myc nuclear gene. The resulting phylogenetic inferences were broadly concordant between data sets and among analytical methods. The subgenus Craugastor is monophyletic and its initial radiation was potentially rapid and adaptive. Within Craugastor, the earliest splits separate three northern Central American species groups, milesi, augusti, and alfredi, from a clade comprising the rest of Craugastor. Within the latter clade, the rhodopis group as formerly recognized comprises three deeply divergent clades that do not form a monophyletic group; we therefore restrict the content of the rhodopis group to one of two northern clades, and use new names for the other northern (mexicanus group) and one southern clade (bransfordii group). The new rhodopis and bransfordii groups together form the sister taxon to a clade comprising the biporcatus, fitzingeri, mexicanus, and rugulosus groups. We used a Bayesian MCMC approach together with geological and biogeographic assumptions to estimate divergence times from the combined DNA sequence data. Our results corroborated three independent dispersal events for the origins of Central American Eleutherodactylus: (1) an ancestor of Craugastor entered northern Central America from South American in the early Paleocene, (2) an ancestor of the subgenus Syrrhophus entered northern Central America from the Caribbean at the end of the Eocene, and (3) a wave of independent dispersal events from South America coincided with formation of the Isthmus of Panama during the Pliocene. We elevate the subgenus Craugastor to the genus rank.     

Tropical freshwater teleosts from Miocene beds of eastern Patagonia, southern Argentina

Loricariid and pimelodid-like siluriforms—along with undetermined percomorph—are described for the first time from Patagonia. Vertebrate fossils, including fish, mammals and birds, were found in beds attributed to the top of the Puerto Madryn Formation. These levels supposedly corresponded to the “Rionegrense marino” of former authors. Mammals occurring in the site suggest a Huayquerian age for the fossiliferous beds. The base of the Huayquerian was dated at about 9 Ma and the top is younger than 6.5 Ma. Radioisotopic dating in the marine shell beds of the Puerto Madryn Formation ranges from 11 to 9 Ma. Consequently, the section described here appears to be younger than the typical Puerto Madryn Formation from which it is separated by an unconformity. The section is correlated with the type Río Negro Formation from northern Patagonia, which also includes Huayquerian fossils. Freshwater fishes were previously unknown in beds younger than the middle Miocene in southern South America. This is also the southernmost record of loricariid fishes. The association of aquatic continental and terrestrial vertebrates indicates for the first time in Península Valdés beds of freshwater origin. The evidence apported by fossils is also in agreement with global climate trends. The local extinction of loricariids in Patagonia possibly occurred much later than the time of deposition.