| Diagenesis of bone in the fossil record is pervasive; however, the extent of this process varies with depositional environment. Diagenesis is any chemical or physical change that occurs below 200°C. This study quantifies the extent of diagenesis in shark vertebral centra through analysis of a suite of physical and chemical properties including crystallinity index, carbonate content, isotopes, and major, minor, and trace elemental concentrations. The sharks used in this study (Family Lamnidae) range in geographic location and geological age from the Cretaceous to Recent. Although shark skeletons are initially cartilaginous, the cartilage of the vertebral centra is replaced with carbonate hydroxyapatite during growth of the individual. Understanding chemical changes to biogenic apatite informs of the extent diagenesis has altered the biological signal preserved in vertebrate bones.; Modern lamnid vertebral centra establish a modern analog for comparison to fossil lamnid sharks. Rare earth element (REE) compositions, Delta 14C, and delta18O, give indications of timing of when these sharks migrate, changes in their eating habits, changes in water depth, and determination of ontogenic age and growth rates.; Fossil shark centra used in this study have undergone diagenesis; therefore how have the processes of diagenesis affected the original signal recorded in these centra? Shale-normalized REE patterns indicate that diagenesis has erased the original signal; however because diagenesis occurred at or near the seawater/sediment interface, a seawater REE signal may still be preserved in lamnid shark centra (related to the time of deposition and location). Therefore, with caution, geochemical data from biogenic apatite of fossil marine vertebrates, such as lamnid sharks, may be used to understand paleoceanography and paleoenvironment. Also, the centra from Otodus obliquus demonstrate that the biological oxygen isotopic signal is not completely erased by diagenesis. Therefore, biological signals and diagenetic signals of fossil lamnid sharks can be utilized to understand paleobiology, paleoclimatology, and paleoceanography. |
