Variability in oxygen isotope compositions of herbivore teeth: reflections of seasonality or developmental physiology?

Oxygen isotope compositions of herbivore tooth enamel from two areas in Kenya were measured using a laser fluorination approach. Isotope heterogeneity was found within four sets of teeth in the jaws of different individuals (∼2‰), as well as within individual teeth. The rear molar (M3) of a zebra shows a 1.4‰ variability, whereas, the middle and rear molars (M2 and M3) of a gazelle show variations of 1.7 to 2.9‰. The front molar (M1) of a gazelle is relatively homogeneous (∼0.25‰). Compositional heterogeneities are spatially correlated, and comparison to theoretical models suggests that they largely reflect different times of tooth growth coupled with seasonal changes in forage composition, rather than developmental physiology. Spatially-specific enamel analysis combined with knowledge of genus-specific diet, water turnover, and physiology allows paleoclimate seasonality to be assessed.