Year

2005

Degree Name

Doctor of Philosophy

Department

School of Earth and Environmental Sciences - Faculty of Science

Abstract

Previous researchers have used the extent of isoleucine epimerisation and stable carbon, oxygen and nitrogen isotope ratios of ostrich (Struthio), emu (Dromaius) and Genyornis eggshells to provide geochronological control and palaeoenvironmental information on the Quaternary sequences from which these sample types are recovered. This thesis expanded this field of research by examining isoleucine epimerisation and the stable isotopes ratios of cassowary (Casuarius), megapode (principally the Australian brushturkey, Alectura lathami) and Aepyornis eggshells. The aims of the research were to (1) increase our understanding of the ancient habitats of Casuarius, megapodes and Aepyornis in order to provide information on how these ecosystems functioned, as well as the nature and timing of the environmental change they have experienced, and (2) to document the amino acid and stable isotope biogeochemistry of avian eggshells in novel contexts in order to better understand the processes that influence these attributes. Samples of Casuarius, Alectura lathami and Aepyornis eggshells were heated at high temperatures (110, 143 and 160 ºC). These experiments were used to determine the temperature sensitivity of isoleucine epimerisation in these eggshell types, expressed in terms of Arrhenius parameters, and to characterise the thermal stability of amino acids. In the stratified archaeological sequences of Toé Cave, Kria Cave (Ayamaru Plateau, West Papua, Indonesia), Liang Lemdubu and Nabulei Lisa (Aru Islands, Arafura Sea, Indonesia) exposure to short-term high temperature heating events associated with campfires complicated interpretation of the extent of isoleucine epimerisation in Casuarius and megapode eggshells in terms of time and temperature. The extent of isoleucine epimerisation in Alectura lathami eggshells from Hay Cave (northeastern Queensland, Australia) enhanced the geochronological control for this site by clarifying the presence of temporal breaks in the sequence and providing an age estimate for a section of the sequence lacking age control. Late Holocene and Pleistocene populations of Aepyornis eggshells from the southern and southwestern coasts of Madagascar were readily distinguished by the extent of isoleucine epimerisation they exhibit. Relatively high stable carbon and oxygen isotope ratios (_13C and _18O values) in Pleistocene Casuarius eggshells from the Aru Islands were consistent with a weaker monsoon during the Last Glacial Maximum. The absence of this trend in Pleistocene Casuarius eggshells from the Ayamaru Plateau suggested the latter site is less sensitive to fluctuations in monsoon effectiveness. Supported by isotope analyses of modern megapode eggshells, carbon fixed by C3 photosynthesis was identified at the base of the Alectura food chain from the _13C values of Hay Cave megapode eggshells. The interpretation of Alectura eggshell _18O values was complicated by their wide range, and this was most likely a product of the combined effects of evaporation on oxygen isotope ratios and the protracted breeding season. The lack of variation in the _13C and _18O values of Aepyornis eggshells was attributed to subsistence on C3 vegetation and the water of perennial groundwater-fed ponds, whereas enriched nitrogen isotope ratios could be due to a number of factors including the infiltration of seawater into the littoral water table. Overall, the research presented an opportunity to examine the strengths and weaknesses of information extrapolated from isoleucine epimerisation and isotope ratios in avian eggshells in novel taxonomic and geographical settings. The high temperature experiments further documented the taxonomic dependency of the rate of isoleucine epimerisation in avian eggshells and indicated that the temperature sensitivity of this reaction is similar amongst eggshells. Although interpreting the extent of isoleucine epimerisation in eggshells from archaeological sites in terms of time and temperature was readily complicated by exposure to campfire heating events, the ability to demonstrate a close correlation with independent age control indicated that this problem is not ubiquitous in these contexts. The _13C values of eggshells broadly identified the vegetation that herbivorous birds consumed, and where the photosynthetic pathway of this vegetation was known, eggshell _13C values provided information on the _13C value of this biomass. The nitrogen isotope ratios of eggshells could be successfully integrated with existing knowledge of ancient habitats, and eggshell _ values were used to identify drinking water sources and trace climatically-significant changes in these reservoirs over time.

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