SYNCHROTRON-BASED IMAGING OF TRACE ELEMENTS WITHIN FOSSIL BONE

Previous work conducted on trace metal loading in extant and fossil tissues have revealed the exceptional preservation of soft tissue from a variety of organisms (eg. amphibian, bird, reptile and mammal). This has also permitted the identification of specific ancient biomarkers. The majority of fossils consist of hard tissues such as bones and teeth. Therefore, it is important to test the preservation of potential biomarkers in hard tissues to better understand the majority of preserved organisms.

In this study we examine fossil bone using Synchrotron Rapid Scanning X-Ray Fluorescence (SRS-XRF) that permits the elemental mapping of samples at low concentrations (parts per million) over large surface areas in a relatively short period of time (~3000 times faster than standard mapping techniques). The distribution of dilute elemental concentrations allows us to correlate specific chemistry within identifiable tissue types in both extant and extinct samples. In this study a phalanx from a large theropod dinosaur (Allosaurus fragilis) exhibiting a fracture callus and resorption cavity, and a rib from an extinct dugong (Metaxytherium sp) were mapped. The mapped chemistry was compared with morphological data obtained from thin section analysis to allow the comparison of sample bone chemistry. SRS-XRF mapping revealed both chemical variations within different bone tissues and previously unobserved histological structures not seen using conventional histological techniques. Diagenetic incorporation of trace elements can be correlated within the different tissue types present in pathologic and normal bone of A. fragilis. These include differences between woven and lamellar bone, areas of resorption, and areas of remodeling (of the callus). In Metaxytherium, details of osteon morphology can be seen in the differential uptake of trace elements. Details include the shape and extent of the cutting cone, the cement line, and the 3D morphology of the connecting canals between osteons. Comparing these results to SRS-XRF maps from extant taxa will allow us to further investigate the chemical composition of bone through time as well as identify possible trace metal biomarkers for biomolecules crucial for bone maintenance and repair.