Insights into molecular taphonomy and the evolution of sauropod posture garnered from Late Cretaceous fossils

Paul V. Ullmann

doi:10.17918/etd-6578

The dichotomy of this dissertation results from my fascination with taphonomy and an opportunity I received to study Dreadnoughtus schrani, a giant, new sauropod. I begin by compiling the most comprehensive literature review to date on molecular paleontology. This synthesis reveals the plethora of factors contributing to and controlling survival of biomolecules in the fossil record. However, sedimentologic, geochemical, and environmental controls on molecular preservation remain poorly understood. To examine these factors, I studied a case study site, the Standing Rock Hadrosaur Site (SRHS), and performed actualistic experiments simulating fossilization in the laboratory. My experiments tested the effect of simulated, metal-enriched groundwaters on biomolecular decay. Immunoassay results following three months of simulated burial confirm that early-diagenetic permineralization can inhibit protracted microbial attack and that acidic conditions degrade soft tissues more rapidly than they dissolve bone mineral. Taphonomic analyses of SRHS indicate the bonebed represents a mass death assemblage formed by rapid burial in a shallow floodplain lake. Demineralization of SRHS bone fragments yields abundant soft tissue structures morphologically consistent with modern analogs. Concretions aided stabilization of these tissues by cementing regions of the encasing sediment. Immunofluorescence indicates survival of endogenous collagen I in tissues from one of these bones. Rare earth element (REE) composition of SRHS bones strongly supports brief diffusion and retention of primarily early-diagenetic REE signatures. This constitutes the first confirmation that retention of early diagenetic REE signatures may correlate with biomolecular preservation. In the final two chapters of this dissertation, I examine titanosaurian sauropod anatomy and evolution. Comparisons of Dreadnoughtus with related taxa reveal that only a single feature, an accessory process on the iliac preacetabulum, is unique to the largest titanosauriforms. This implies that the appendicular expression of wide-gauge posture is not influenced by body size. Morphometric analyses reveal evolution of wide-gauge posture to be characterized by humeral narrowing, femoral broadening, medial deflection of the humeral head, and proximal migration of the deltopectoral crest and fourth trochanter. These shifts signify a minimization of muscle contraction to generate forelimb excursion and an increase in mechanical advantage for hind limb abductor and adductor muscles in titanosauriforms.

Insights into molecular taphonomy and the evolution of sauropod posture garnered from Late Cretaceous fossils

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Insights into molecular taphonomy and the evolution of sauropod posture garnered from Late Cretaceous fossils

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