ASSESSMENT OF BIOMECHANICAL FUNCTION AS A POSSIBLE CONTROL ON SOFT TISSUE PRESERVATION IN EOCENE-OLIGOCENE BONES FROM THE WHITE RIVER GROUP OF SOUTH DAKOTA AND NEBRASKA

Endogenous cells and soft tissues have been found in fossilized bone material since the 1990s, and only in recent years have studies been directed at determining potential controls on soft tissue preservation. Past research has targeted oxidation-reduction conditions, fossilization rate, taxonomy, and depositional environment as possible controls on soft-tissue preservation, with little evidence of correlation. Our study aims to collect preliminary data regarding a possible relationship between biomechanical function and degree of soft tissue preservation.

The selected samples represented weight-bearing and non-weight-bearing bones from three taxa found within the Eocene–Oligocene White River Group of South Dakota and Nebraska – a brontothere, an oreodont, and a tortoise. Each fossil was subsampled for cortical and trabecular bone, briefly rinsed in 10% HCl solution to remove any attached carbonate, and demineralized in 0.5 M ethylenediaminetetraacetic acid (EDTA). The resulting demineralization products were then prepared on a wet slide for optical microscopy. The presence of preserved blood vessel fragments, fibrous matrix pieces, and osteocytes was recorded and quantified for each subsample.

Demineralization yielded large quantities of cells and soft tissues, and notable variation among the samples was detected. The relative abundances of preserved cells and soft tissues varied by taxon. Patterns observed from these samples included a much higher rate of osteocyte preservation among the tortoise samples than either mammal taxon, whereas the mammalian specimens generally yielded more blood vessel and fibrous matrix fragments. Early assessments do not indicate that biomechanical function is a significant controlling factor for overall soft tissue preservation within a fossil. Based on our dataset, taxonomy appears to have a greater influence on the preservation of cells and soft tissues than biomechanical function and the histologic attributes inherently linked with biomechanical functions.