Isotopic variation within Tasmanian bare-nosed wombat tooth enamel: implications for archaeological and palaeoecological research

Archaeologists and palaeoecologists are increasingly turning to stable isotope analysis (δ C, δ O) of fossil bioapatite to examine interactions of human and animal populations. However, relatively few investigations have focussed on the identification of natural variation in comparable modern populations, particularly within the Australian context. In this paper, we present the first modern isotopic reference dataset for Tasmanian bare-nosed wombat teeth (Vombatus ursinus tasmaniensis). Samples for δ C and δ O measurements were recovered sequentially at sub-monthly resolution from all tooth types. δ C showed little variation within a seasonal sinusoidal pattern within the sample set (n = 24 wombats; 35 teeth) due to the homogeneous C distribution of plants in Tasmania. In contrast, δ O profiles varied seasonally, representing time periods of between 0.9 and 2.1 years in 95% of the sample. Significant differences between tooth types were found from intra-individual to inter-regional scales for both dental growth rates and isotopic values. The accuracy of season-of-death assessments differed across the island; those in eastern Tasmania were accurate in all instances whereas those in the west showed substantial inaccuracies. We suggest that this may be due to the elodont form of wombat dentition and the ecologically influenced seasonally varied diet in western Tasmania. As the rate of dental growth is positively correlated with the proportion of coarse vegetation within the diet, this seasonal variation is therefore likely to change how annual isotopic signals are incorporated into the enamel. These results highlight the need to understand the degree of species-specific isotopic variation at a range of scales before applying this technique to archaeological or palaeontological assemblages