Abstract
We present the first high-resolution carbon and oxygen isotope profiles of carbonate in modern wombat
(genera Vombatus and Lasiorhinus) tooth enamel and demonstrate that the carbon isotope ratios (δ13C)
clearly preserve seasonal changes in diet and local environmental conditions. Our baseline study of δ13C in
tooth enamel and bone collagen from wombats that inhabited semi-arid, savannah, temperate and alpine
environments in eastern Australia documented an offset of 5.2±0.4‰ and 12.9±0.3‰ from the animal's diet,
respectively. Marsupial wombats are obligate grazers, whose teeth grow continuously. Sequential microanalysis
of δ13C and δ18O along the length of wombat incisors yielded a time-series of isotopic variation. The
microprofiles of wombat tooth δ18O are highly variable between and within sites. Notwithstanding, the δ18O
values were relatively high in wombat teeth from arid and semi-arid sites, and significantly lower in those
from southern temperate and coastal regions. In contrast, the δ13C of wombat tooth enamel correlates well
with the local environmental setting and the seasonality of C3 and C4 grass growth. In areas with marked
seasonal changes in the proportions of winter C3 and summer C4 grasses, wombat microprofile δ13C values
varied by up to 8‰. Importantly, at sites with predominantly C3 or C4 grasses all year, variations in
microprofile δ13C values are small (b1.9‰), indicating that the relatively large seasonality in δ13C we observe
in wombat teeth must be primarily controlled by changes in diet, rather than animal-specific factors.
This study shows that microprofiling of δ13C in wombat incisors, in particular, provides a high level of
isotopic detail which is not available from time-averaged isotope records from bone collagen, or bulk analysis
of isotopes in tooth enamel. Wombat teeth are common in the Quaternary fossil record and, as such, they
have the potential to be outstanding archives of palaeoecological information. For example the δ13C of fossil
wombat teeth could be used to define the changing proportions of C3 and C4 grasses inwombat diets through
the Quaternary, which in turn reflect changes in the seasonality of precipitation, summer temperatures, and
possible ecosystem modification by human activities.