Inter- and intra-individual variability of calcium and strontium isotopes in modern Tasmanian wombats

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Palaeogeography, Palaeoclimatology, Palaeoecology


Trophic structures, i.e., the diets, food chain positions, and feeding relationships of species in an ecological community, are a fundamental yet understudied avenue of investigation into Australian megafauna extinction. Calcium (Ca) isotope analysis has been developed as a tool to reconstruct trophic levels in vertebrate palaeobiology and palaeoecology. A baseline of modern marsupial Ca isotope signatures in a single trophic level and dietary niche is required to successfully apply this tool in order to reconstruct Australian faunal food webs. We present Ca isotope data from dental enamel of modern Tasmanian bare-nosed wombats (Vombatus ursinus tasmaniensis) to constrain the Ca isotope composition of this species, an opportunistic grazer, and assess whether sex and environmental variables influence such composition. We compare these data to complementary strontium isotope data from the same samples as a proxy for geographical location. Elodont (ever-growing) wombat teeth allow for a sequential sampling strategy and thus provide high resolution intra-individual variability on a seasonal scale, creating the largest intra-individual and intra-species set of Ca isotope data in a single species so far. We show that the Ca isotope composition of Tasmanian bare-nosed wombats falls within the range for herbivores and is independent of geological substrate. Comparison with carbon and oxygen isotope data from sequential samples within the same individuals highlights that sub-monthly intra-individual variations in Ca isotope compositions may result from change in the proportions in the wombat's diet of C3 and C4 plants, or monocots and dicots. The Ca isotope compositions of male and female wombats suggest that Ca isotopes in marsupials could be used to trace nursing and weaning behaviour. The characterisation of Ca isotope values in marsupial herbivore enamel presented contributes to a modern reference set for reconstructing diet from fossil remains of extinct Australian megafauna herbivores.

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Funding Sponsor

Linnean Society of NSW



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