PALEOENVIRONMENTAL AND DIAGENETIC CONSTRAINTS ON THE FOSSILIZATION OF SOFT TISSUES IN CRETACEOUS DINOSAURS: EXCEPTIONAL PRESERVATION AND PROCESSES IN NORTHWESTERN WYOMING

Upper Cretaceous sandstone deposits of the Western Interior Seaway include fossil skin (integument) associated with the skeletal remains of some dinosaurs. Evidence is provided of environmental toxins, salts, cold, or dry conditions and other principal factors aside from burial rate and early diagenesis that lead to soft tissue preservation in vertebrate animals. Skin preserves as thin pyrolusite (manganese oxide) coatings on sandstone molds and casts inferred to have been deposited in nearshore marine environments. Rapid burial of organic remains in marginal-marine settings in the presence of seawater resulted in the inhibition of scavenging activity by other creatures. Seawater mixed with freshwater promoted the natural embalming of corpses and it effected changes in the microbial consortia responsible for decay leading to an increase in pH thus allowing for preferential precipitation of pyrolusite as a replacement for integument under slightly basic pH conditions. Fossilization of non-biomineralized anatomy of terrestrial animals and the circumstances under which it occurred are of great importance to our understanding of the processes that have led to exceptional preservation. Fossilization processes provide proxy evidence in the interpretation of paleoenvironments. Samples of dinosaur skin impressions, associated bone and matrix were examined using a scanning electron microscope. SEM-EDX analysis shows significant evidence of Mn on the dark portions of the skin impression. Bone material lacks any evidence of Mn, while the surrounding matrix contains only an isolated, small trace. We summarize results of field studies and laboratory analyses concerning the taphonomic history of dinosaur integument from a new occurrence from This Side of Hell Quarry located northwest of Pitchfork and Hell’s Half Acre, Wyoming. Questions addressed are: 1, How was dinosaur integument preserved? 2, What was the depositional environment that preserved dinosaur integument, and was that environment the same as that in which the animals lived? 3, How rapidly did fossilization of dinosaur integument occur? Results on the preservation of hadrosaur integument have interesting implications for the exceptional preservation of non-biomineralized tissue in a variety of animals, including other vertebrates.