CONTROLS ON SOFT TISSUE AND CELLULAR PRESERVATION IN LATE EOCENE AND OLIGOCENE VERTEBRATE FOSSILS OF THE WHITE RIVER AND ARIKAREE GROUPS

Abstract

Previous studies on microtaphonomy have identified multiple different organic microstructures in fossil vertebrates from a variety of time periods and environmental settings. This study seeks to investigate the potential taphonomic, paleoclimatic, and geochemical controls on soft tissue and cellular microstructure preservation. To this end, fifteen vertebrate fossils were studied: eight fossils collected from the Oligocene Sharps Formation of the Arikaree Group in Badlands National Park, South Dakota, and seven fossils from formations in the underlying White River Group, including the the (Oligocene) Brule Formation of Badlands National Park, and the (Eocene) Chadron Formation of Flagstaff Rim, Wyoming; Toadstool Geologic Park, Nebraska; and Badlands National Park, South Dakota. A portion of each fossil was demineralized to identify any organic microstructures preserved within the fossils. I investigated several potential soft tissue preservation factors, including taxonomy, paleoclimate, depositional environment, and diagenetic history as shown through bone apatite crystallinity and trace element alteration. Soft tissue microstructures were preserved in all fossil samples, and cellular material was recovered from most fossil specimens. Soft tissue and cellular preservation was found to occur independent of taxonomy, paleoclimate regime, depositional environment, and apatite crystallinity. The period of fossilization and diagenetic trace element addition, as shown through rare earth element (Lanthanum) diffusion profiles, may be connected to organic microstructure preservation, as longer estimated diffusion periods were correlated with poorer preservation of bone histology and greater cellular degradation in some of the fossil samples.