USING GEOCHEMICAL TECHNIQUES TO ASSESS DIFFERENCES IN CRYSTALLINITY BETWEEN NORMAL AND PATHOLOGIC BONE IN MODERN AND FOSSIL SPECIMENS

In modern organisms the structure and arrangement of bone apatite crystals is dependent on the arrangement of the organic collagen fibers. This is reflected in the formation of different types of bone tissue under different conditions and rates of growth. Woven (immature) bone is typical of fast-growing juvenile or pathologic tissue, whereas lamellar (mature) bone indicates slower growth and higher degrees of bone remodeling. Because the basic physiological processes of bone growth and fracture healing are similar in extant vertebrates, similar patterns may exist in fossil taxa.

This study examined fracture pathologies in pedal phalanges from the theropod dinosaur Allosaurus fragilis and the modern birds Branta canadensis (Canada goose) and Cathartes aura (turkey vulture), in order to determine whether differences exist in bone apatite crystallinity between normal and pathologic bone, and whether any differences were consistent in modern and fossil material. Histological and x-ray diffraction (XRD) analyses were performed on both dinosaur and bird material; bird specimens were also analyzed by Raman spectroscopy. Carbon and oxygen isotopes in the carbonate fractionation of fossil bone and Rare Earth Elements (REEs) were analyzed in the fossil material to determine if there are differences in how pathologic bone fossilizes compared to normal bone. It was hypothesized that normal (mature) bone would have a lower crystallinity than pathologic (immature) bone due to the higher degree of mineralization and rates of osteogenesis (laying down of new bone tissue) seen in pathologic bone growth versus normal bone remodeling, and that these differences in crystallinity would have an effect on bone fossilization.

Results from Raman spectroscopy and XRD confirm that pathologic bone is more crystalline than normal bone in both fossil and modern specimens. Stable isotope and REE signatures in pathologic and normal bone are not significantly different, suggesting that these techniques are more suitable for examining taphonomic rather than physiological differences.