BONE HISTOLOGY AND DIAGENESIS OF ARCTIC CENTROSAURINE CERATOPSIDS FROM THE KIKAK-TEGOSEAK QUARRY (NORTH SLOPE, ALASKA)

The Prince Creek Formation contains the largest number of Late Cretaceous Arctic dinosaur fossils in the world and the only bonebeds on the Alaskan North Slope. One of the more studied bonebeds is the Kikak-Tegoseak Quarry, which is dominated by the ceratopsian Pachyrhinosaurus perotorum. Although previous studies have interpreted taphonomy of the site using sedimentological and paleontological data, less is known about the diagenetic characteristics of this assemblage. This study investigates the histological and molecular structure of P. perotorum ribs utilizing petrographic studies of bone thin sections, X-ray diffraction (XRD) and Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy, in order to assess the extent of diagenetic alteration. Histological analyses identified most bones as representing adults, based on heavily remodeled cortical tissue, and one as a young juvenile, based on the lack of lines of arrested growth (LAGs). XRD results show fossil bone has been altered to carbonate fluorapatite from hydroxyapatite. ATR-FTIR spectra indicate that histologically determined adult bones have lower carbonate (ν₂CO₃) phosphate (ν₃PO₄) absorbance ratios (0.015-0.023), while the juvenile specimen had the highest ratio (0.057). Adult float specimens had intermediate ratios (0.039-0.055). In all bones, the ν₁PO₄ peak shifted to higher wavenumbers signifying a more crystalline apatite lattice structure than is typically observed in modern bone, but peak positions varied from 964-971cm^-1. XRD results represent a common fossilization signature. The reduced carbonate in the adult bones reflect a more stoichiometric apatite, which is consistent with ontogenetic trends in human and in modern animal bone. However, differences attributable to diagenesis cannot be ruled out. Variable crystallinity within all bones potentially relates to variable pre-fossilization weathering/exposure time.