Comparative Taphonomy and Paleoecological Reconstruction of Two Microvertebrate Accumulations from the Late Cretaceous Hell Creek Formation (Maastrichtian), Eastern Montana PDF Download

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Category :
Languages : en
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Author: Laura Elizabeth Wilson
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Category : Hell Creek Formation
Languages : en
Pages : 212

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The CM assemblage is dominated by tabular, low density elements such as cycloid scales and fish vertebrae. Dense, equidimensional elements such as teeth and ganoid fish scales dominate the JPC assemblage. Transport distances, hydraulic equivalencies of dominant skeletal elements, amount of hydraulic sorting and reworking, and degree of time-averaging varies between deposits and significantly affect taxonomic distributions. Chi-squared tests and rank order analysis results demonstrate that relative abundance of taxa can be determined for portions of the assemblages despite different taphonomic processes. Most notably, relative abundance of hydraulically equivalent skeletal elements from morphologically similar organisms can be compared regardless of accumulation in non-isotaphonomic deposits. Statistical comparisons were made among osteichthians using ganoid scales, caudates using vertebrae, ornithischians using teeth, and testudinates using shell fragments. Results show that portions of the assemblage analyzed using hydrodynamically equivalent elements are not significantly different.

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Category : Chordata
Languages : en
Pages : 160

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Languages : en
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The Sandy Site is a multispecific terrestrial deposit in the fluvial sediments of the Upper Cretaceous Hell Creek Formation. It captures a diversity of Late Cretaceous dinosaurs and other vertebrates. Over three thousand bones represent at least fifty genera of birds, pterosaurs, terrestrial and aquatic tetrapods, and fish. Ten of the eleven dinosaur families found throughout the formation have been recognized at this quarry. Detailed taphonomic observations included abrasion, bone completeness, skeletal representation. These and a number of qualitative features indicated two distinct bonesets in the assemblage. An allochthonous suite included bones of tyrannosaurs, hadrosaurs and ceratopsians, which possessed taphonomic signatures similar to exotic aquatic vertebrate specimens. Smaller, unusual dinosaurs comprised a parautochthonous group with mammals, birds, pterosaurs, and small herpetofauna. Sedimentologic data suggest a fluvial crevassing event as the most likely depositional setting. Crevasse channel deposition fits with the Sandy microstratigraphic package and structures present, the narrow time resolution, and the dual nature of the taphocoenosis. A direct cause of mortality cannot be identified, but that agent and the subsequent burial of the taphocoenosis apparently occurred in two steps. Comparison with other sites indicates that Sandy was a product of fortuitous set of repeatable events, and that similar depositional environments produce mixed assemblages with multispecific parautochthonous components. The autochthonous assemblage presents a Sandy paleofauna different from conventional reconstructions of the Hell Creek Formation. Smaller dinosaurs prevailed in this setting, in marked contrast to the dominance of a few megafaunal taxa presented in previous reconstructions. The original faunule has a size structure similar to modern mammal communities. The regional ecology may have been mosaic rather than homogeneous, where large dinosaurs lived near but s.

Author: Paul D. White
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Category : Dinosaurs
Languages : en
Pages : 166

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Author: Jeffrey Alan Bartlett
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Category :
Languages : en
Pages : 143

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Keywords: paleoecology, taphonomy, Maastrichtian, Cretaceous, Hell Creek Formation, South Dakota, dinosaur, Sandy Site, vertebrate, paleontology.

Author: Pat Shipman
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ISBN: 9780674530867
Category : Science
Languages : en
Pages : 222

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Pat Shipman sets forth the taphonomic methods of analyzing how animal remains are acted upon and altered, both by biological and by geographic phenomena, in their passage from the biosphere of bones and carcass into the lithosphere of fossils. She explains the role of disease, predation, accidents, postmortem destruction, and transport in the life history of a fossil, and provides an introduction to the relevant geological concepts and to faunal analysis.

Author: Benjamin Andrew Scherzer
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Category : Debris avalanches
Languages : en
Pages : 216

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In the summer of 1998, a bonebed of juvenile dinosaur material was found in beds of the Two Medicine Formation along the Sun River in Teton County, Montana. Initial inspection of the "Sun River Bonebed" indicated unique dominance by juvenile remains and unusually high concentration of fossil material. Modern exposure of both the bonebed and surrounding strata allowed for a detailed taphonomic study of the assemblage. In the summer of 2004, the bonebed was excavated in a fashion that recorded depthwise taphonomic data of fossil material and surrounding sediment, and allowed for three-dimensional reconstruction of the bonebed. The lithology of the surrounding beds was documented for 120 m immediately below and 40 m immediately above the bonebed to interpret the overall depositional environment of the area. Lastly, the paleobiologic and sedimentologic interpretations made for the bonebed were compared to bonebeds of similar fauna in the Two Medicine Formation. Taphonomic attributes of the fossil material indicate a mass death assemblage of late juvenile lambeosaurines subject to post-mortem bioturbation and possible fluvial transport. A number of elements from the assemblage exhibit a rare form of taphonomic modification known as "wet rot," currently documented in only one other dinosaur bonebed. Sedimentologic and additional taphonomic data in the assemblage indicate entrainment of the vertebrate material in a cohesive debris flow and ultimate deposition in the respective flow deposit. The sedimentology of the surrounding beds indicates ultimate deposition in an ephemeral fluvial environment. The restricted age class representation of the assemblage lends credence to existing paleobiologic interpretations of hadrosaurids in the Late Cretaceous of Montana, and the Sun River Bonebed is significant in its exhibition of "wet rot" modification and in being one of a restricted number of documented debris-flow hosted vertebrate bonebeds.

Author: Jon P. Christians
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Category : Edmontosaurus
Languages : en
Pages : 214

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Author: Daigo Yamamura
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Category : Fossilization
Languages : en
Pages : 204

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Although a great deal of paleontological information is derived from analyzing fossilized skeletal remains, the fossilization process of vertebrate skeletal remains is poorly understood. Depositional environment, taphonomy and diagenesis of an assemblage of vertebrate skeletal elements from a sandstone in the Late Cretaceous Hell Creek Formation are investigated in order to decipher relations between sandstone diagenesis and skeletal element fossilization. Fieldwork included taphonomic data collection, section measurement and description as well as sample collection. The rock and fossil bone samples were analyzed by petrography, cathodoluminescence, scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The depositional environment including the fossil assemblage is interpreted as a crevasse splay based on the facies association of repeating sequences of mudrock and fine sandstone overlying channel and levee deposits. Taphonomic data suggest the bones were exposed on the surface up to 15 years before burial, and the assemblage is time-averaged. Although sandstone including the fossil bones indicates physical compaction, fossil bones do not exhibit signs of compaction. Barite is an unusual authigenic mineral found in fossil bones, suggesting collagen degradation during early diagenesis facilitated unique diagenetic microenvironment within bones. Calcite and siderite cements were precipitated multiple times, suggesting alkaline pore-fluid conditions were common during diagenesis. However, oversized pores and highly altered grains indicate that porefluids were acidic during late diagenesis; acidic pore-fluid conditions are likely due to the organic acid produced by degradation of organic molecule at higher diagenetic temperatures. Fossil bone minerals are altered due to 1) early pore-fluid infiltration combined with dehydration/rehydration processes, 2) saline pore-fluid infiltration and 3) increased temperature and pressure during deeper burial. This study demonstrates that petrography, XRD and SEM/EDS together can help decipher the diagenetic history of fossilized bones. In order to maximize the information, not only the fossil bones, but surrounding rocks need to be analyzed because surrounding rocks record different sets of diagenetic processes such as calcite precipitation in the vadose zone, siderite precipitation in the phreatic zones, acidic pore-fluid condition during mesogenesis.