Taphonomy, geology, and paleoecology of the Sandy Site, an exceptional assemblage in the Maastrichtian Hell Creek Formation of South Dakota

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Title: Taphonomy, geology, and paleoecology of the Sandy Site, an exceptional assemblage in the Maastrichtian Hell Creek Formation of South Dakota
Author: Bartlett, Jeffrey Alan
Advisors: Victor Cavaroc, Committee Member
Mary Schweitzer, Committee Member
Reese Barrick, Committee Member
Elana Leithold, Committee Member
Dale Russell, Committee Chair
Abstract: 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 separately from the unusual small denizens of Sandy. The dinosaur faunule represented at Sandy portray a very different community than generally known for the regional Triceratops fauna of the Western Interior, and may have inhabited the Hell Creek landscape as more influential members of the ecosystem than previously recognized.
Date: 2004-04-16
Degree: MS
Discipline: Marine, Earth and Atmospheric Sciences
URI: http://www.lib.ncsu.edu/resolver/1840.16/2452

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