Stable carbon isotopes in deep time : the diets of fossil fauna and hominids (original) (raw)

This thesis describes the development, testing and application of a technique for extending carbon isotopic dietary tracing millions of years in time,. using the mineral phase of calcified tissues (apatite) as alternative sample material to collagen. The results reported here provide empirical evidence for the validity of the technique. Investigation of the isotopic relationships between diet, collagen and apatite, using a large sample of modem fauna with known diets, confirms that the isotopic relationship between collagen and apatite changes with trophic level. Thus, both collagen and apatite reflect dietary 13 C/ 12 C ratios, but the results support the hypothesis that different a.Spects of diet-protein and energy, respectively-are reflected by these tissues. IsotopiC analyses of apatite in archaeological dietary studies have been controversial due to argument about the effects of diagenesis on • the 13 C/ 12 C ratios. A comparison of apatite 13 Cj1 2 C ratios from a chronological ~eries of fossil browsers with those of modem browsers reveals a difference between the two which may largely be attributed to diagenesis. This difference increases predictably with time and cannot be eliminated by an acid pretreatment which removes calcite and a more soluble mineral phase. Despite the alteration, browsers and grazer,s are clearly distinguishable using enamel 13 Cj1 2 C ratios, ~ven after 3 rna. The technique is applied to three studies of the diets of extinct taxa. Firstly, the extinct springbok, Antidorcas bondi, is shown to have been a grazer, in contrast with the intermediate diet of its living relative, A. marsupia/is. Secondly, a comparison of two fossil baboons with browsers and grazers from Swartkrans Member 1, dating to approximately 1.8 rna, shows that the C 3-based diet of Papio robinsoni is clearly distinct from the graminivorous (C 4) di~t of Theropithecus darti. Thirdly, results for Australopithecus robustus enamel specimens from Swartkrans indicate an intermediate diet, mainly C 3-based, but with a significant C 4 contribution, derived either directly from C 4 grasses or indirectly via animal foods. Thus a comparative approach using 13 C/ 12 C ratio analysis of enamel offers a significant new tool for obtaining unique information about human and faunal diets of great age.- ,.