Paper No. 6
Presentation Time: 2:50 PM
ONTOGENETIC VARIATION IN ELEMENTAL RATIOS (SR/CA AND BA/CA) OF TOOTH ENAMEL TO ASSESS DIAGENETIC ALTERATION
PEEK, Stephanie, Geology and Geophysics, University of Wyoming, Dept. #3006, 1000 E. University Ave, Laramie, WY 82071-3006 and CLEMENTZ, Mark T., Geology and Geophysics, University of Wyoming, 1000 University Ave. University of Wyoming, Dept. 3006, Laramie, WY 82071, speek@uwyo.edu
Diagenetic alteration of bioapatite in the fossil record is one of the biggest obstacles in the use of biogeochemical proxies for paleoecological reconstruction. This is especially true in the study of elemental concentrations, particularly the ratios of strontium and barium to calcium (Sr/Ca, Ba/Ca) which are commonly used to define dietary preferences and trophic relationships within terrestrial foodwebs. However, diagenetic alteration of Sr/Ca and Ba/Ca ratios of bone has been observed over very short time scales (< 10 yrs). As a result, tooth enamel, which is more resistant to alteration because of its large crystal size, low porosity, and low organic content, is favored in archaeological and paleontological research. Yet, inter- and intra-tooth variations in the Sr/Ca and Ba/Ca ratios of enamel are poorly understood. Here we looked at modern specimens to investigate the potential utility of this method as an assessment of diagenetic alteration in fossil material, developing methods to better refine paleoecological reconstructions of ancient terrestrial ecosystems.
During ontogeny, differences in the magnitude and effectiveness of biopurification (processes that result in preferential incorporation of Ca into skeletal material over Sr and Ba), result in differences in the Sr/Ca and Ba/Ca ratios of tooth enamel, which are fixed at the time of mineralization. Additional biopurification occurring across the placenta and mammary glands should result in a difference in the Sr/Ca and Ba/Ca ratios from early- and late-forming enamel within the same individual. Results from the teeth of three steers have demonstrated that Sr/Ca and Ba/Ca ratios follow predicted trends based on diet and physiological differences through ontogeny. Enamel forming in utero and during nursing has significantly lower values than enamel forming after weaning, observed both through bulk sampling (inter-tooth variation) and sub-sampling of teeth forming during the weaning process (intra-tooth variation). This expected difference in elemental ratios of tooth enamel within a single specimen can be used as a check for diagenetic alteration; it has the potential to open up new applications for Sr/Ca and Ba/Ca in the fossil record and to supply additional life history information on diet as well as timing of weaning and tooth formation.
