Stable isotope analysis of bone collagen and tooth enamel of modern Australian faunas

Stable isotope analysis of bone collagen and tooth enamel of modern Australian faunas to investigate dietary inputs: implications for palaeo-diet and palaeo-environmental reconstructions.

R. Fraser, T. O'Connell* and R. Grün ...................
*University of Oxford

 

Fossil mammal faunas are a major source of palaeoecological information: the diversity and abundance of species from well-dated deposits can provide proxy data for past vegetation and palaeoclimates. The isotopes of carbon, nitrogen and oxygen within fossil bones and teeth, are an additional source of diet and climate information. Whilst the use of stable isotopes in palaeodiet research is used extensively overseas in the archaeological and ecological fields, it remains vastly under utilised when considering Australia's fossil faunas.

There is uncertainty about how stable isotopes reflect diet and climate in the Australian context,

therefore this project has begun by measuring the 13C and
15N of bone collagen and the 13C and 18O of tooth enamel from modern marsupial herbivores; kangaroos, wombats and koalas. By analysing these tissues from modern species with known dietary preferences, from distinct geographic, floristic and climatic regions, we can investigate the existing relationships between diet, environment and the isotopes measured.

13C in tooth enamel

.Isotopic analysis of enamel CO3 within the hypsodont (continuously growing) teeth of grazing wombats has revealed variations in 13C over the growth of the tooth, as shown in Figure 15. These incremental changes along the time series represented display what is likely to be seasonal changes in 13C plant values of the animal's plant diet. The range of 13C values within a tooth series varies between geographic areas. The large ~8 range of the wombat shown in Figure 15 may be due to the greater seasonal variation in C3 and C4 grass types in this area. Figure 16 shows a tooth series with less delta13C change (only 1.5), this wombat lives in a predominantly C3 grass area with little seasonal variation. As the distribution of C3 and C4 grasses is predominantly determined by temperature and season of rainfall, the isotopic series provided by wombats' teeth might indicate the magnitude and type of climatic or plant seasonality at that location.

13C of kangaroo and koala tooth enamel CO3 has also been measured. The sampling of separate teeth within an individuals' tooth row revealed significant differences in 13C between teeth; up to a 5 variation was observed in modern kangaroos. Ultimately, this modern baseline data will aid the interpretation of isotopic values found in fossil faunas. Gaining an insight into the diets of Australia's extinct megafauna, and the diets of extant fauna, such as the kangaroos, over time in response to changing climate and vegetation regimes will increase our understanding of ecological change.