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In modern organisms the structure and arrangement of bone apatite crystals is dependent on the arrangement of the organic collagen fibers. This is reflected in the formation of different types of bone tissue, such as woven (immature) or lamellar (mature), in pathological versus normal bone, or fast-growing (woven) versus slow-growing (lamellar) tissue. Because the basic physiological processes of fracture healing are similar in extant vertebrates, similar patterns may exist in fossil taxa. The three questions of interest for this study were the following: 1) Do differences exist in modern bone apatite crystallinity between normal and pathologic bone? 2) Are differences between normal and pathologic tissue consistent in both modern and fossil bone? 3) Does the type of bone tissue affect fossilization? In this study, we use histological and x-ray diffraction (XRD) analyses to examine fracture pathologies in pedal phalanges from the theropod dinosaur Allosaurus fragilis, and two modern bird species, Branta canadensis (Canada goose) and Cathartes aura (turkey vulture). Raman spectroscopy analysis was performed on modern birds, but not fossil material. Stable isotope and rare earth elements (REE) analyses were performed on fossil material to determine if there are differences in how pathologic bone fossilizes compared to normal bone. Results from Raman spectroscopy and XRD confirm that pathologic bone is more crystalline than normal bone in both fossil and modern taxa. Stable isotope and REE analyses do not show any difference in fossilization between pathologic and normal bone, suggesting that these techniques are more suitable for examining taphonomic rather than physiological differences. / Geology

Exceptionally preserved fossils—or fossils preserved with remains of originally non-biomineralized (i.e. soft) tissues—constitute a key resource for investigating the history of the biosphere. In comparison to fossils of biomineralized skeletal elements, which represent the majority of the fossil record but only a fraction of the total diversity that existed in the past, exceptionally preserved fossils are comparatively rare because soft tissues are rapidly destroyed in typical depositional environments. Assemblages of such fossils, nonetheless, have received special attention among scientists in multiple fields of Earth and life sciences because they represent relatively 'complete' windows to past life. Through such windows, researchers are able to reconstruct original biological features (e.g. soft tissue anatomies) of extinct organisms and to describe the structures and compositions of ancient soft-bodied paleocommunities. To accomplish these goals, however, researchers must incorporate background information regarding the pre- and post-burial histories of exceptionally preserved fossils. In this context, my dissertation focuses on the environmental settings, diagenetic conditions, geomicrobiological activities, and weathering processes, which influence the conservation of original biological features within exceptionally preserved fossils and control their occurrences in time and space. An improved understanding of these critical factors involved in exceptional fossil preservation will ultimately our advance our knowledge regarding the history of the biosphere and the Earth system as a whole. Each chapter of original research in this dissertation includes an innovative and distinct approach for studying exceptional fossil preservation. The second chapter describes environmental and geologic overprints in the exceptional fossil record, as revealed by a comprehensive statistical meta-analysis of a global dataset of exceptionally preserved fossil assemblages. Moving from global to specimen-based perspectives, the second and third chapters focus on minerals (products of geomicrobioloigcal, diagenetic, and weathering processes) and carbonaceous materials replicating exceptionally preserved fossils. The third chapter examines the causes of preservational variations observed among organophosphatic tubular shelly Sphenothallus fossils in the lower Cambrian of South China using an experimental approach. (Although Sphenothallus is not an exceptionally preserved fossil sensu stricto, its conservation of original organic matrix tissues in South China provides key insights into the preservation of carbonaceous material within fossils.) Lastly, the fourth chapter presents data acquired using various in situ nanoscale analytical techniques to test the hypothesis that microstructures within exceptionally preserved microfossils of the Ediacaran Doushantuo Formation of South China are some of the oldest putative cylindrical siliceous demosponge spicules in the fossil record. Collectively, these chapters describe environmental, authigenic, diagenetic, and weathering processes that affect exceptional fossil preservation, and highlight innovative methods and approaches for testing major paleobiologic and geobiologic hypotheses regarding exceptionally preserved fossils. / Ph. D.