EVALUATING A NON-DESTRUCTIVE METHOD FOR ASSESSING SPECIMEN PRESERVATION

Fossils preserve irreplaceable information about our planet’s past climate, ecosystems, and organisms. Unfortunately, many techniques that reveal this information, such as stable carbon (C) and oxygen (O) isotopes, are only useful if a fossil is chemically unaltered. Typical methods for detecting alteration, like benchtop X-ray fluorescence (XRF), Fourier transform infrared spectroscopy, and scanning electron spectroscopy, measure the relative amounts of carbonate and phosphate (CO₃/PO₄) or calcium and phosphorous (Ca/P), or the size of carbonate crystals. The sensitivity of these techniques is poorly understood, and most are in themselves destructive, requiring removal of chips or powdered material for analysis.

In this study, we checked if alteration can be detected non-destructively with a handheld XRF device that measures elemental concentrations, including Ca/P. We evaluated preservation of fossil teeth from large mammals from Big Bone Lick, KY using Ca/P, CO₃/PO_4, and C and O isotopes both before and after chemically treating the teeth to remove material from the burial environment. Ca/P in bones and teeth should be 2.2 (with a range of 1.3-2.3), while CO₃/PO₄ should be 0.2-0.5. Specimens with values outside of these ranges may be altered.

Scanning whole teeth distinguished specimens with high (altered) and low (unaltered) Ca/P. However, high Ca/P was not detected on cleaned surfaces (with exterior surface of teeth removed) or powder. CO₃/PO₄ did not differ between groups with high or low Ca/P either before or after chemical treatment, although treatment did significantly reduce carbonates in all specimens. O isotopes did not differ between groups, while C isotopes were higher and more variable in specimens with unaltered Ca/P. This did not change after chemical treatment.

While more research is needed, our results suggest that it is possible to detect alteration of fossils using Ca/P via handheld XRF, and that this method may actually be more reliable than others. Being able to confidently assess preservation non-destructively will allow researchers to avoid unnecessarily damaging of chemically altered fossils that can be used for other research and teaching.