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1.
Silicified plant tissues (phytoliths) preserved in Late Cretaceous coprolites from India show that at least five taxa from extant grass (Poaceae) subclades were present on the Indian subcontinent during the latest Cretaceous. This taxonomic diversity suggests that crown-group Poaceae had diversified and spread in Gondwana before India became geographically isolated. Other phytoliths extracted from the coprolites (from dicotyledons, conifers, and palms) suggest that the suspected dung producers (titanosaur sauropods) fed indiscriminately on a wide range of plants. These data also make plausible the hypothesis that gondwanatherian mammals with hypsodont cheek teeth were grazers. 相似文献
2.
Shoreline erosion along man-made lakes in North Dakota and South Dakota has led to the discovery of stratified preceramic cultural remains in an area where previously few such materials have been found. One important exposure, the Walth Bay site, contains a 7000-year sequence of alluvial and eolian deposition capping an abandoned Missouri River terrace. Three distinct soil profiles are associated with successive Late Paleo-Indian, Plains Archaic, and Plains Village Tradition occupations. 相似文献
3.
Late Jurassic and Early Cretaceous birds from northeastern China, including many complete skeletons of Confuciusornis, provide evidence for a fundamental dichotomy in the class Aves that may antedate the temporal occurrence of the Late Jurassic Archaeopteryx. The abundance of Confuciusornis may provide evidence of avian social behavior. Jurassic skeletal remains of an ornithurine bird lend further support to the idea of an early separation of the line that gave rise to modern birds. Chaoyangia, an ornithurine bird from the Early Cretaceous of China, has premaxillary teeth. 相似文献
4.
广东地质发展简史及植物区系溯源 总被引：2，自引：0，他引：2
广东植物区系的发展由来已久，现代的广东植物是晚白垩世或早第三世的孑遗物，地层中存在磊量的古植物化石。如本内苏铁，银杏，苏铁等极为丰富，种子特别是大羽羊齿尤为突出，而且在白垩纪晚期至第三纪的广东地层中，存在着丰富的现代植物的化石或化石孢粉组合，如朴树，桦木、鹅耳枥及松、冷杉、雪松等，还有其它阔叶树和针叶树，所有这些都与广东复杂的地质发展史密切相关，它预示着广东植物区系可能起源于亚带山地，而且广东无颖 相似文献
5.
PC Sereno DB Dutheil M Iarochene HCE Larsson GH Lyon PM Magwene CA Sidor DJ Varricchio JA Wilson 《Science (New York, N.Y.)》1996,272(5264):986-991
Late Cretaceous (Cenomanian) fossils discovered in the Kem Kem region of Morocco include large predatory dinosaurs that inhabited Africa as it drifted into geographic isolation. One, represented by a skull approximately 1.6 meters in length, is an advanced allosauroid referable to the African genus Carcharodontosaurus. Another, represented by a partial skeleton with slender proportions, is a new basal coelurosaur closely resembling the Egyptian genus Bahariasaurus. Comparisons with Cretaceous theropods from other continents reveal a previously unrecognized global radiation of carcharodontosaurid predators. Substantial geographic differentiation of dinosaurian faunas in response to continental drift appears to have arisen abruptly at the beginning of the Late Cretaceous. 相似文献
6.
Cores recovered from horizon A are Late Cretaceous (Maestrichtian) in age and consist o alternating layers of calcareous turbidites and "red clay." The presence of red clay suggests that the water depth in this area during Cretaceous time was at least as great as at present-more than 5100 meters. A middle Cretaceous (Cenomanian) core consisting of interbedded sand and gravel and light-to-dark-gray lutite was taken in the same area from a layer stratigraphically below the horizon; the presence of hydrogen sulfide and iron sulfide may indicate anaerobic conditions that may be attributable to local ponding of sediment in Cenomanian time. 相似文献
7.
Exceptionally well preserved larval bivalve shells have been isolated from Late Cretaceous (Maestrichtian) sediments. Specimens were readily identified to familial level on the basis of gross morphology and hinge structures. Reconstruction of fossil larval ontogeny, linked with the distribution of adult stages, will provide an important interpretative tool in molluskan phylogenetic and paleoecologic studies. 相似文献
8.
Storey M Mahoney JJ Saunders AD Duncan RA Kelley SP Coffin MF 《Science (New York, N.Y.)》1995,267(5199):852-855
Widespread basalts and rhyolites were erupted in Madagascar during the Late Cretaceous. These are considered to be related to the Marion hot spot and the breakup of Madagascar and Greater India. Seventeen argon-40/argon-39 age determinations reveal that volcanic rocks and dikes from the 1500-kilometer-long rifted eastern margin of Madagascar were emplaced rapidly (mean age = 87.6 +/- 0.6 million years ago) and that the entire duration of Cretaceous volcanism on the island was no more than 6 million years. The evidence suggests that the thick lava pile at Volcan de l'Androy in the south of the island marks the focal point of the Marion hot spot at approximately 88 million years ago and that this mantle plume was instrumental in causing continental breakup. 相似文献
9.
Gradual dinosaur extinction and simultaneous ungulate radiation in the hell creek formation 总被引：1，自引：0，他引：1
Dinosaur extinction in Montana, Alberta, and Wyoming was a gradual process that began 7 million years before the end of the Cretaceous and accelerated rapidly in the final 0.3 million years of the Cretaceous, during the interval of apparent competition from rapidly evolving immigrating ungulates. This interval involves rapid reduction in both diversity and population density of dinosaurs. The last dinosaurs known are from a channel that contains teeth of Mantuan mammals, seven species of dinosaurs, and Paleocene pollen. The top of this channel is 1.3 meters above the likely position of the iridium anomaly, the Cretaceous/Tertiary boundary. 相似文献
10.
A Late Cretaceous (probably Maestrichtian) silicoflagellate assemblage has been recovered for the first time from the middle section of a core taken from the Alpha Cordillera in the central Arctic Ocean. The finding of Globigerina pachyderma in the top and very rarely in the bottom part of the core suggests a faulting or slumping process in the area. 相似文献
11.
The fossil record of early feathers has relied on carbonized compressions that lack fine structural detail. Specimens in amber are preserved in greater detail, but they are rare. Late Cretaceous coal-rich strata from western Canada provide the richest and most diverse Mesozoic feather assemblage yet reported from amber. The fossils include primitive structures closely matching the protofeathers of nonavian dinosaurs, offering new insights into their structure and function. Additional derived morphologies confirm that plumage specialized for flight and underwater diving had evolved in Late Cretaceous birds. Because amber preserves feather structure and pigmentation in unmatched detail, these fossils provide novel insights regarding feather evolution. 相似文献
12.
Müller RD Sdrolias M Gaina C Steinberger B Heine C 《Science (New York, N.Y.)》2008,319(5868):1357-1362
Earth's long-term sea-level history is characterized by widespread continental flooding in the Cretaceous period (approximately 145 to 65 million years ago), followed by gradual regression of inland seas. However, published estimates of the Late Cretaceous sea-level high differ by half an order of magnitude, from approximately 40 to approximately 250 meters above the present level. The low estimate is based on the stratigraphy of the New Jersey margin. By assimilating marine geophysical data into reconstructions of ancient ocean basins, we model a Late Cretaceous sea level that is 170 (85 to 270) meters higher than it is today. We use a mantle convection model to suggest that New Jersey subsided by 105 to 180 meters in the past 70 million years because of North America's westward passage over the subducted Farallon plate. This mechanism reconciles New Jersey margin-based sea-level estimates with ocean basin reconstructions. 相似文献
13.
Predatory dinosaur remains from madagascar: implications for the cretaceous biogeography of gondwana 总被引：1，自引：0，他引：1
SD Sampson LM Witmer CA Forster DW Krause PM O'Connor P Dodson F Ravoavy 《Science (New York, N.Y.)》1998,280(5366):1048-1051
Recent discoveries of fossil vertebrates from the Late Cretaceous of Madagascar include several specimens of a large theropod dinosaur. One specimen includes a nearly complete and exquisitely preserved skull with thickened pneumatic nasals, a median frontal horn, and a dorsal projection on the parietals. The new materials are assigned to the enigmatic theropod group Abelisauridae on the basis of a number of unique features. Fossil remains attributable to abelisaurids are restricted to three Gondwanan landmasses: South America, Madagascar, and the Indian subcontinent. This distribution is consistent with a revised paleogeographic reconstruction that posits prolonged links between these landmasses (via Antarctica), perhaps until late in the Late Cretaceous. 相似文献
14.
Axelrod DI 《Science (New York, N.Y.)》1959,130(3369):203-207
1) During the opening phase of the Early Cretaceous (Neocomian), angiosperms commenced to invade lowland basins of deposition at generally lower latitudes. They reached high northern and middle southern latitudes at the close of the epoch (Albian) and only replaced the relict Jurassic-type vegetation at high latitudes during the early part of Late Cretaceous time. 2) This poleward migration of angiosperms is consistent with the theory that the phylum had its center of origin and dispersal at tropical latitudes, which ranged between 45 degrees N and 45 degrees S in pre-Cretaceous time. 3) Recognition of the time-space factor involved in the Early Cretaceous poleward migration of angiosperms removes most of the conflicts in the testimony on age supplied by fossil plants and by marine invertebrates-conflicts which have persisted for nearly a century (17). 相似文献
15.
Wilf P Labandeira CC Kress WJ Staines CL Windsor DM Allen AL Johnson KR 《Science (New York, N.Y.)》2000,289(5477):291-294
Stereotyped feeding damage attributable solely to rolled-leaf hispine beetles is documented on latest Cretaceous and early Eocene ginger leaves from North Dakota and Wyoming. Hispine beetles (6000 extant species) therefore evolved at least 20 million years earlier than suggested by insect body fossils, and their specialized associations with gingers and ginger relatives are ancient and phylogenetically conservative. The latest Cretaceous presence of these relatively derived members of the hyperdiverse leaf-beetle clade (Chrysomelidae, more than 38,000 species) implies that many of the adaptive radiations that account for the present diversity of leaf beetles occurred during the Late Cretaceous, contemporaneously with the ongoing rapid evolution of their angiosperm hosts. 相似文献
16.
Late triassic naticid drillholes: carnivorous gastropods gain a major adaptation but fail to radiate
Infaunal and reclining bivalves of the Late Triassic Cassian Formation of northern Italy contain drillholes that closely resemble those produced by modern naticid gastropods. The oldest drillholes previously reported are from the late Early Cretaceous; this suggests that the drilling adaptation was lost soon after its appearance in the Late Triassic and originated independently in another naticid clade 120 million years later. The perceived selective value of such an adaptation may thus not always be a good predictor of its long-term survival, which is ultimately governed by factors that affect the speciation and extinction rates of the clade that carries it. 相似文献
17.
Gases trapped in Miocene to Upper Cretaceous amber were released by gently crushing the amber under vacuum and were analyzed by quadrupole mass spectrometry. After discounting the possibility that the major gases N(2), O(2), and CO(2) underwent appreciable diffusion and diagenetic exchange with their surroundings or reaction with the amber, it has been concluded that in primary bubbles (gas released during initial breakage) these gases represent mainly original ancient air modified by the aerobic respiration of microorganisms. Values of N(2)/(CO(2) + O(2)) for each time period give consistent results despite varying O(2)/CO(2) ratios that presumably were due to varying degrees of respiration. This allows calculation of original oxygen concentrations, which, on the basis of these preliminary results, appear to have changed from greater than 30 percent O(2) during one part of the Late Cretaceous (between 75 and 95 million years ago) to 21 percent during the Eocene-Oligocene and for present-day samples, with possibly lower values during the Oligocene-Early Miocene. Variable O(2) levels over time in general confirm theoretical isotope-mass balance calculations and suggest that the atmosphere has evolved over Phanerozoic time. 相似文献
18.
Tarduno JA Duncan RA Scholl DW Cottrell RD Steinberger B Thordarson T Kerr BC Neal CR Frey FA Torii M Carvallo C 《Science (New York, N.Y.)》2003,301(5636):1064-1069
The Hawaiian-Emperor hotspot track has a prominent bend, which has served as the basis for the theory that the Hawaiian hotspot, fixed in the deep mantle, traced a change in plate motion. However, paleomagnetic and radiometric age data from samples recovered by ocean drilling define an age-progressive paleolatitude history, indicating that the Emperor Seamount trend was principally formed by the rapid motion (over 40 millimeters per year) of the Hawaiian hotspot plume during Late Cretaceous to early-Tertiary times (81 to 47 million years ago). Evidence for motion of the Hawaiian plume affects models of mantle convection and plate tectonics, changing our understanding of terrestrial dynamics. 相似文献
19.
You HL Lamanna MC Harris JD Chiappe LM O'connor J Ji SA Lü JC Yuan CX Li DQ Zhang X Lacovara KJ Dodson P Ji Q 《Science (New York, N.Y.)》2006,312(5780):1640-1643
Three-dimensional specimens of the volant fossil bird Gansus yumenensis from the Early Cretaceous Xiagou Formation of northwestern China demonstrate that this taxon possesses advanced anatomical features previously known only in Late Cretaceous and Cenozoic ornithuran birds. Phylogenetic analysis recovers Gansus within the Ornithurae, making it the oldest known member of the clade. The Xiagou Formation preserves the oldest known ornithuromorph-dominated avian assemblage. The anatomy of Gansus, like that of other non-neornithean (nonmodern) ornithuran birds, indicates specialization for an amphibious life-style, supporting the hypothesis that modern birds originated in aquatic or littoral niches. 相似文献
20.
Little Salt Spring in southwest Florida, consisting of a shallow, water-filled basin above a deep, vertical underwater cavern, was a freshwater cenote in the peninsula's drier past. It collected and preserved perishable organic artifacts and other evidence of Paleo-Indian and Archaic Indian origin ranging in age from 12,000 to 9000 and from 6800 to 5200 years ago. An Archaic Period cemetery containing an estimated 1000 burials occupies an adjoining muck-filled slough and presently drowned portions of the basin of the spring. Artifacts and the nature of interment suggest a cultural link between the Archaic people and the much later Glades Tradition of southern Florida. 相似文献