Oxygen (δ18O) and carbon (δ13C) isotopic distinction in sequentially sampled tooth enamel of co-localized wild and domesticated caprines: Complications to establishing seasonality and mobility in herbivores
Abstract Dietary intake, drinking behavior, and physiology together influence the isotopic composition of herbivore tooth enamel, but the degree to which these factors influence the sequence of δ 13 C and δ 18 O values along the tooth crown remain underexplored. Analysis of serially sampled molars from sympatric wild and domesticated caprines inhabiting the Gobi steppe-desert reveal inter-species distinction in carbon and oxygen isotope ratios as as well as pronounced differences in the amplitude of intra-tooth isotopic change. For domesticated sheep, consistently high ð 13 C values visible in intra-tooth sequences and 13 C enrichment in enamel with a winter season formation period indicates pronounced graze intake throughout the year including receipt of a C 4 fodder source during the winter months. This pattern contrasts with low δ 13 C values visible in the teeth of wild caprines indicating the intake of C 3 graze and browse throughout the year. Domesticated sheep also demonstrate a wide amplitude of intra-tooth oxygen isotope variation compared to wild caprines in addition to higher summer season maxima δ 18 O values and lower winter season minima δ 18 O values. The greater contribution of graze to the domesticated sheep diet suggests 18 O-enriched leaf water strongly influences summer season δ 18 O values, while 18 O-depleted groundwater imbibed from wells is likely responsible for low winter season δ 18 O values. The oxygen isotopic distinction between wild and domesticated sheep populations affirm previous observations that the ingestion of isotopically distinct water sources impacts body water oxygen isotopic composition and subsequent expression of δ 18 O values in herbivore tooth carbonates. This has important implications for the use of δ 18 O values obtained from serially sampled teeth for reconstructing paleoenvironment, seasonality and also the movement of wild and domesticated herbivores through modern and ancient landscapes.