Animal physiology, biomineral diagenesis, and the isotopic reconstruction of palaeoenvironment

Our ability to relate the isotopic compositions of vertebrate tissues to the isotopic compositions of diet and drinking water is affected by diferential routing of dietary macromolecules, animal physiology, and factors related to organismal age and body mass. The correlation between the isotopic composition of precipitation and that of vertebrate tissue is additionally affected by the compression of the meteoric water isotopic values and the influence of food delta18O and deltaD values in consumer tissues. Diagenetic alteration of tissue values may further obscure biogenic isotopic information. These factors affect our ability to reconstruct information about seasonality and environmental conditions in the past, and to relate these conditions to events of archaeological and palaeontological significance. This work addresses these concerns as follows: The relationship between seasonal variation in precipitation deltaD and delta18O and the SD and 8180 values of sequentially-sampled dentin collagen was investigated in an ethnographic sample of ovicaprids raised in a traditional Mongolian pastoral regime. The results of this study suggest that dentin collagen delta18O and deltaD isotopic values reflect seasonal variation in the isotopic composition of diet and ingested water, although the amplitude of seasonal isotopic variation is compressed in the tissue.;The effects of ontogenetic status on the isotopic composition (deltaD, delta 13C, delta15N, delta18O) of rodent tissues were investigated in a controlled feeding study using rats of different ages consuming isotopically identical diets but drinking isotopically different waters. The data suggest that ontogenetic differences in the isotopic composition of bone collagen could pose problems for model-based palaeoenvironmental reconstruction; and that apatite carbonate and phosphate, bone collagen, and hair keratin are differentially sensitive to different delta18O inputs.;The effects of diagenetic alteration on fossil tissue delta 18O and delta13C values were investigated in a study of the carbonate delta13C and delta18O and phosphate delta18O of a fossil faunal assemblage from the Kromdraai hominin site. It was determined that diagenetic alteration of fossil isotopic values; as revealed by a series of isotopic comparisons between dentin, apatite, and depositional context; may affect interpretations of ecological relationships between taxa and of diachronic changes in the Kromdraai locale over time.