Cortical bone samples were collected from marsupial and eutherian herbivores at five field sites along a 1275-km south-north transect from temperate coastal to arid interior South Australia in order to address variability in stable carbon isotope composition. Collection sites were located along the eastern border of the state. Mean annual rainfall along the transect ranges from 700-800 mm at coastal Mount Gambier to 150-175 mm at Cordillo Downs in the north-east corner of the state. Bone collagen carbon isotope values become more positive towards the arid north in relation to increasing quantities of C4 grasses. Thus, stable carbon isotope analysis of bone specimens provides a method to address dietary selection and dietary variability in Australian herbivores. In addition, isotopic analyses of archaeological and palaeontological bones and teeth can be used to address changes in Quaternary climate and vegetation distributions in Australia.