نتایج جستجو برای: oligocene
تعداد نتایج: 2183 فیلتر نتایج به سال:
The Paleogene evolution of the NW margin African Plate (Western External Rif Zone) was studied by means multidisciplinary analyses twenty-one stratigraphic logs, including tectofacies recognition, petro-mineralogical results, and thicknesses analysis. Four intervals were recognized separated three unconformities coarsely aligned with Cretaceous–Paleogene, Eocene–Oligocene Oligocene–Miocene boun...
The present paper reviews the geological development of the Faroes part of the NE Atlantic Margin in the Cenozoic Era. The Faroes area is located west of the post-Caledonian rift basin system formed in the Devonian after the collapse of the Caledonian mountains. Tectonic movements and plate reorganizations during several phases have strongly influenced sedimentation and erosion along the Caledo...
The order Proboscidea includes extant elephants and their extinct relatives and is closely related to the aquatic sirenians (manatees and dugongs) and terrestrial hyracoids (hyraxes). Some analyses of embryological, morphological, and paleontological data suggest that proboscideans and sirenians shared an aquatic or semiaquatic common ancestor, but independent tests of this hypothesis have prov...
Growth of the first permanent Antarctic ice sheets at the Eocene-Oligocene Transition (EOT), ∼33.7 million years ago, indicates a major climate shift within long-term Cenozoic cooling. The driving mechanisms that set the stage for this glaciation event are not well constrained, however, owing to large uncertainties in temperature reconstructions during the Eocene, especially at lower latitudes....
Reaumuria is an arid adapted genus with a distribution center in Central Asia; its evolution and dispersal is investigated in this paper. Eighteen species of Reaumuria and nine species of two other genera in the Tamaricaceae, Tamarix and Myricaria, were sampled, and four markers ITS, rps16, psbB-psbH, and trnL-trnF were sequenced. The reconstructed phylogenetic tree is fundamentally consistent ...
OBJECTIVE Primates were common in North America through most of the Eocene, but vanished in the Chadronian, about 35 million years ago. In the Arikareean, about 6 million years later, the enigmatic primate Ekgmowechashala appeared in the Great Plains and Oregon. This taxon shows little resemblance to other North American primates and its phylogenetic position has long been debated. New material...
Although geomorphic observations suggest that the Sierra Nevada has tilted so that the crest has risen 1–2 km since late Miocene time, deuterium and oxygen-18 isotope concentrations in Cenozoic geologic materials decrease eastward across California and Nevada similarly to those in modern, orographically induced precipitation, as if little change in Sierra Nevadan elevations has occurred since E...
To examine Holarctic snake dispersal, we inferred a phylogenetic tree from four mtDNA genes and one scnDNA gene for most species of the Old World (OW) and New World (NW) colubrid group known as ratsnakes. Ancestral area distributions are estimated for various clades using divergence-vicariance analysis and maximum likelihood on trees produced using Bayesian inference. Dates of divergence for th...
Cenozoic sediments of the Taatsiin Gol and TaatsiinTsagaan Nuur area are rich in fossils that provide unique evidence of mammal evolution in Mongolia. The strata are intercalated with basalt flows. 40Ar/39Ar data of the basalts frame the time of sediment deposition and mammal evolution and enable a composite age chronology for the studied area. We investigated 20 geological sections and 6 fossi...
The subgenus Geckoella, the only ground-dwelling radiation within Cyrtodactylus, closely overlaps in distribution with brookii group Hemidactylus in peninsular India and Sri Lanka. Both groups have Oligocene origins, the latter with over thrice as many described species. The striking difference in species richness led us to believe that Geckoella diversity is underestimated, and we sampled for ...
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