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Sediments from the Upper Cretaceous (Cenomanian-Turonian) Tropic Shale were deposited along the western margin of the Western Interior Seaway, in present-day southern Utah. Marine vertebrates from this formation include plesiosaurs, mosasaurs, bony fish, sharks, and turtles. They are concentrated in the lower portion of the Tropic Shale, mostly between Bentonites B and D. Study of the taphonomic condition of these vertebrates has contributed to an understanding of how they were preserved as well as a detailed paleoenvironment for the Tropic Shale. Physical factors played the dominant role in their preservation, with robust and durable skeletal elements, such as teeth and vertebrae, being most common within the shale. Isolated bones and teeth are also relatively common within the formation, while complete and nearly complete skeletons are more rare. Biological factors played a less dominant role, with no evidence of epifaunal or infaunal activity preserved with any of the skeletal remains. In addition, scavenging marks (both bite and gnaw marks) are relatively uncommon, typically only being found on more complete specimens. A signature of post-burial alteration can be recognized as low levels of abrasion, weathering, and compression and high levels of fracturing of vertebrate skeletal material. Slightly higher levels of abrasion and weathering occur to the west, closer to the ancient shoreline, suggesting some pre-burial alteration. The preservation of marine vertebrates in the Tropic Shale suggests a low energy marine environment with some weak bottom currents and low levels of benthic oxygen. The substrate ranged from soft and soupy to firm, with moderate sedimentation rates resulting in relatively rapid burial. 相似文献
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《Limnologica》2020
The removal of native forest affects stream characteristics, processes, and organisms at the local scale. We compared the structure of fish assemblages between microbasins impacted by deforestation and those in pristine condition in the Amazonian Machado River basin, Brazil. Fish were collected with seine and dip nets along an 80-m stretch of 28 streams. At each site, we recorded physical, chemical, and land-water ecotone variables. We collected 6,586 specimens of 109 species, being 39 and 18 of them exclusively of forested and deforested streams, respectively. Non-significant differences were found for abundance and species richness between forested and deforested streams. A total of four main trophic groups were identified. Carnivores were more abundant in forested streams, whereas herbivores, omnivores and detritivores species were the most abundant in deforested streams. The deforested streams showed higher abundance and richness of algae and periphyton consumers, while forested streams presented higher abundance and richness of invertebrate consumers. Forested streams presented longer foodchains, higher occurrence and abundance of species that have more specialized habits and are intolerant to degraded environments, whereas generalist and tolerant species predominated in deforested streams. We conclude that species composition in Amazonian streams predictably responds to the degree of forest cover. 相似文献
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A fossil assemblage collected around 3.5 m amsl from Ezeiza, Buenos Aires province, have AMS 14C ages of ca. 33,000 to ca. 40,000 yr BP, whereas in the literature is a report of a conventional 14C age of >43,000 yr BP. An OSL age from the overlying deposit corresponds to ca. 22,000 yr. The samples contain marine fossils: mollusks, balanids and corals (Astrangia). La Coronilla (Uruguay, attributed to MIS 5e) is the locality most related to Ezeiza faunistically, despite is not the nearest one. In consequence, the relationship should be addressed to a more similar age and environment than others. The fauna indicates a higher water temperature than today. In Ezeiza exclusively cold water taxa are absent, and we found seven warm taxa with their southern distribution limit displaced northwards today, plus other six at their southern distribution limit. Around 60% of all the species and more than 70% of the individuals are of warm-temperate waters. In sum, although prima facie the numerical ages would locate the deposit in MIS3, faunistic, temperature, and height evidences show that the Ezeiza mollusk assemblage belong to MIS5e. A stronger than presently Brazil warm current, reaching Southern latitudes, may explain the changes in geographical ranges. 相似文献
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Transport of crustal microparticles from Chilean Patagonia to the Antarctic Peninsula by SEM-EDS analysis 总被引：2，自引：0，他引：2
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Pterosaurs, usually known as flying reptiles, were the first vertebrate group to develop active flight. Despite being studied for more than 200 years, there are still many controversial questions regarding pterosaur functional morphology, such as the stance and gait when grounded, which rely primarily on direct examination of well-preserved articulated specimens, ichnofossils (trackways) and phylogenetic inferences. 相似文献
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Danielly Godiva Heitor Evangelista Milton Kampel Marcus Vinicius Licinio Casimiro Munita 《Estuarine, Coastal and Shelf Science》2010
Coral and reef environments in shallow waters are negatively affected by human activities in several coastal areas worldwide. It has been demonstrated that sediment influx and macronutrient discharges induce decline of coral population structure and diversity. Therefore, efforts to quantify sediment flux, sources and the biological response to sedimentation were conducted by several marine researchers. Herein, we investigated the case study of Armação dos Búzios/Brazil/Western South Atlantic, where coral colonies (mostly Siderastrea stellata) are under stress due to sediment apportionment as a consequence of regional human occupation. Classification of potential sediment source regions was based on a high-resolution aerogammaspectrometry survey for 232Th, 238U and 40K in main land near shore, used as primarily tool, in combination with sediment geochemistry. This approach allowed distinguishing three hydrographic basins (Macaé river basin, São João river basin and Una river basin) as potential sources. Hierarchical cluster analysis applied to the set of parameters identified the Macaé River as the most probable sediment contributor to the coralline site. 相似文献
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Shallow water rudist bivalves are a very suitable tool for palaeoenvironmental and palaeobiogeographic reconstructions of the Cretaceous Tethys. For this reason, we have reviewed fossil localities bearing polyconitid rudists of the late Aptian and Albian in the Himalayan area and in other Tethyan sites. The well preserved Rossi Ronchetti rudist collection of Yasin (Kohistan Himalayas) has been reinspected as a reference for the regionally distinctive Horiopleura haydeni biofacies. Two morphotypes of the genus related to different sedimentary settings were distinguished on the basis of biometric measurements. Assemblages characterized by benthic organisms of Mesogean affinity dominated by polyconitid and radiolitid rudists, together with nerineid gastropods, corals and orbitolinid forams have a distinct provincial significance. Today, various polyconitid bearing biofacies can be recognized in many sedimentary successions of the Himalayas, westwards to the Iberia region and even eastwards to the Pacific area. Their distribution allows recognition of a palaeobiogeographic pattern influenced by a thermal barrier. It also helps to understand how the accretion of the Lhasa terrane and the Kohistan-Dras intra-oceanic volcanic arc could represent a spreading centre for the “Yasin-type” Horiopleura haydeni biofacies (marked by the absence of Polyconites) in the South West Asian Province. 相似文献
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