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.

营养结构，即饮食，食物链位置和生态社区中物种的觅食关系，是调查澳大利亚大型动物灭绝的基本但未被研究的途径。钙（Ca）同位素分析已被开发为重建脊椎动物古生物学和古生态学中营养水平的工具。要成功地使用该工具来重建澳大利亚动物区系食物网，就需要在单个营养水平和饮食生态位上建立有袋现代钙同位素特征的基线。

我们提供了来自现代塔斯马尼亚裸鼻袋熊（Vombatus ursinus tasmaniensis）牙釉质的Ca同位素数据）以限制该物种的钙同位素组成（机会性放牧者），并评估性别和环境变量是否会影响此类组成。我们将这些数据与来自相同样品的补充锶同位素数据进行比较，以作为地理位置的替代指标。Elodont（不断增长的）袋熊牙齿允许采用顺序采样策略，从而在季节尺度上提供高分辨率的个体内变异性，从而在单个物种中创建了迄今为止最大的个体内和物种内Ca同位素数据集。我们显示，塔斯马尼亚裸鼻袋熊的Ca同位素组成属于草食动物范围，并且与地质底物无关。与来自同一个体内连续样本的碳和氧同位素数据的比较表明，Ca同位素组成的每个月以下个体内变化可能是由于C3和C4植物或单子叶植物和双子叶植物的袋熊饮食中的比例变化引起的。雄性和雌性袋熊的Ca同位素组成表明，有袋动物中的Ca同位素可用于追踪护理和断奶行为。所介绍的有袋食草动物搪瓷中Ca同位素值的表征为从已灭绝的澳大利亚大型动物食草动物的化石遗体中重建饮食提供了现代的参考依据。雄性和雌性袋熊的Ca同位素组成表明，有袋动物中的Ca同位素可用于追踪护理和断奶行为。所介绍的有袋食草动物搪瓷中Ca同位素值的表征为从已灭绝的澳大利亚大型动物食草动物的化石遗体中重建饮食提供了现代的参考依据。雄性和雌性袋熊的钙同位素组成表明，有袋动物中的钙同位素可用于追踪护理和断奶行为。所介绍的有袋食草动物搪瓷中Ca同位素值的表征为从已灭绝的澳大利亚大型动物食草动物的化石遗体中重建饮食提供了现代的参考依据。