SGER: A Novel Dinosaurian Tissue Exhibiting Unusual Preservation

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ABSTRACTThe Museum of the Rockies 2003 summer field season yielded a Tyrannosaurus rex that is full of surprises. This dinosaur possesses a novel tissue type on the internal (endosteal) surface of the femur that has potential physiological and phylogenetic significance. It is structurally distinct from other fossil bone types, and may be the functional analogue of avian medullary bone, a specialized bone type that serves as short term storage for calcium reserves used in the formation of eggshells. This ephemeral bone tissue is not produced by extant reptiles or mammals, but forms in response to increased estrogen levels produced by ovulating female birds. If subsequent analyses confirm that this novel tissue is analogous to avian medullary bone, it will be the first objective means of assigning gender to a dinosaur, and provides additional information regarding the reproductive phase of the animal.The hypothesis regarding the origin of this new tissue will be tested by subjecting samples to various chemical, microscopic and molecular analyses, as avian medullary bone tissue is distinct from other bone types in living birds both structurally and chemically. For example, extant medullary bone has increased concentrations of acid mucopolysaccharides and sulfated glucosaminoglycans over other bone types, and responds in a distinct manner to high iron diamide (HID) staining.However, the presence of this novel tissue is not the only surprise observed in this dinosaur specimen. Upon demineralization of the bone, characteristics were revealed that were utterly unexpected, and again, never reported for bone tissues of this age. The demineralized matrix of the new tissue was elastic and stretchy, and had the capacity to be dehydrated and rehydrated many times without losing this characteristic. Demineralization of cortical bone also revealed the matrix to be fibrous and highly oriented, consistent with demineralized collagen in extant bone. Additionally, upon complete demineralization, pliable branching vessels were revealed within the cortical bone that are indistinguishable from those similarly recovered from extant bone after demineralization and collagenase digestion. The dinosaur vessels possessed microstructures consistent with red blood cells retained in treated vessels from ostrich bone, and these microstructures contained internal contents reminiscent of nucleated red blood cells. Finally, demineralization of the cortical bone liberated microstructures possessing external projections similar to filipodia, which are virtually identical to osteocytes observed after demineralization of cortical bone from extant birds. These microstructures also possess internal contents.This project will pursue chemical, molecular and microstructural analyses of these exceptional tissues. These dinosaur tissues have great potential to elucidate previously unsuspected aspects of molecular diagenesis, tissue/molecular preservation and processes of fossilization, not to mention the potential to independently test existing phylogenetic hypotheses and evolution. The risk of this project is more than balanced by the potential, and therefore seems to fall well within the intent of SGER funds.