| Abstract: |
The effects of surface exposure on the isotope chemistry of bone collagen, apatite and cholesterol were studied on bones collected at regular intervals from carcasses that had been exposed to natural weathering for up to 30 years in a semi-arid savanna in East Africa. Previous work demonstrated that these bones had lost significant amounts of protein, and that the biomineral fraction (apatite) had experienced changes in crystallography and trace element concentration. Despite degradation of protein, we found no evidence for alteration of the carbon and nitrogen isotope composition of weathered bone collagen. Isotopic stability of collagen may result from the lack of dramatic changes in relative amino acid concentrations during weathering in this environment. Weathering reduced the amount of carbonate in bone apatite and slightly increased carbon and oxygen isotope variability, but there was no evidence for progressive isotopic exchange with sedimentary carbonate. While the lipid chemistry of fossil bone differed from that of fresh bone, there was no regular pattern of lipid loss with progressive weathering. In bones that retained sufficient cholesterol for isotopic analysis, delta[sup 13]C values were unaffected by weathering. We conclude that in grassland ecosystems similar to those studied here, pre-burial diagenesis, which markedly changes other aspects of bone chemistry and structure, has little impact on isotope chemistry.
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