IMAGING FOSSIL BIOCHEMISTRY

Biomolecules have been identified within living organisms that utilize metals to help mediate or catalyze chemical transformations of organic molecules and/or perform key biological functions e.g., iron in hemoglobin and magnesium in chlorophyll. Trace metals such as copper, zinc and nickel are also essential for routine metabolic functions, performing specific roles dependent on the tissue-type in which they are occur. Therefore, the ability to resolve elemental inventories and their distribution within fossil organisms might provide valuable information pertaining to the biology, function and evolution of a species. However, in order for original biochemistry to be resolved, it must be clearly shown that the observed fossil chemistry has not been derived through geologic/taphonomic processes and that the trace elements are detectable. Commercially available techniques (such as scanning electron microscopy and electron microprobe) lack the ability to chemically image large areas and/or lack the sensitivity required to investigate the trace metal chemistry of fossils. Given the dilute concentrations of such trace-elements in biological tissues, the only reliable way to spatially resolve such inventories is through the application of synchrotron-based elemental imaging techniques. Synchrotron Rapid Scanning X-Ray Fluorescence (SRS-XRF) is a uniquely optimized method that can simultaneously detect elements in trace amounts, accommodate sizeable specimens (up to 1m²) and scan large surface areas in short time periods (~30 s/cm²) at high resolution (~2-100 microns). Complementary X-Ray Absorption spectroscopy (XAS) can also indentify the oxidation state of elements within a fossil and help determine whether they are organically derived. A series of unique fossil samples were mapped using SRS-XRF, including a 50 Mya reptile and 120 Mya bird. Results from both SRS-XRF and XAS clearly show endogenous bioaccumulated trace-metal chemistry can be preserved in fossils after tens of millions of years. The results provide a unique insight into the preserved biochemistry of these extinct organisms.