RECOVERING ENDOGENOUS CELLS AND SOFT TISSUES FROM FOSSIL BONES: DOES THE DEPOSITIONAL ENVIRONMENT MATTER?

Numerous studies have utilized demineralization assays to investigate cellular and soft tissue preservation in the fossil record. Through such investigations, well-preserved endogenous microstructures including fibrous/proteinaceous matrix, blood vessels, and osteocytes have been recovered from a multitude of diverse vertebrate fossils. To help clarify potential geologic factors contributing to the preservation of these invaluable resources, we conducted demineralization assays on fossil bones from various depositional environments to test whether burial settings influence the ability of a bone to yield original cells and soft tissues. Nine fossil bones, five from terrestrial floodplain deposits and four buried in shallow marine sediments, were selected for this study. These fossils were retrieved from a variety of localities within the Eocene Chadron and Miocene Calvert, Pungo River, and Torreya formations. The five specimens recovered from floodplain deposits of the Chadron Formation consist of brontothere ribs and limb bones, and the Miocene marine mammal specimens consist of a dugongid rib and a cetacean rib, vertebra, and auditory bulla. Bone fragments were demineralized in 0.5 M ethylenediaminetetraacetic acid (EDTA) pH 8.0 for a period of two weeks to two months, depending on the sample, with exchanges of fresh acid every other day. Microstructures morphologically consistent with vertebrate osteocytes, fibrous matrix, and blood vessel fragments were recovered in varied proportions from all nine vertebrate fossils. Most samples yielded many of at least one of these three types of microstructures. Although all of the terrestrial fossils yielded abundant blood vessels, they all derive from the same taxon; no other recognizable patterns are apparent in our recovery results. Recovery of these microstructures from all samples regardless of their burial context implies that depositional environment does not significantly control the preservation potential of endogenous cells and soft tissues in fossil bones. However, our sample size in this study was limited, so more samples need to be tested to better evaluate this hypothesis.