Zinc isotope ratios (δ66Zn) in fossil enamel from Tam Hay Marklot cave show no significant correlation with carbon (δ13C) or oxygen (δ18O) isotope values, indicating that variations in dietary plant type (C3 vs. C4) and climate/hydration status do not interfere with the trophic-level signal conveyed by δ66Zn, thereby supporting its validity as an independent dietary proxy.

When animals eat plants, their bodies retain more of the heavier zinc isotope, making their teeth have a higher ratio of that isotope. When animals eat meat, they get zinc that already lost some of the heavier isotope, so their teeth have a lower ratio. This difference stays locked in tooth enamel as it forms and doesn’t change after death, even if the animal lived in a hot, wet environment or ate different kinds of plants. That’s why scientists can tell if an animal was a plant-eater, meat-eater, or both, just by measuring the zinc in its teeth — without being misled by climate or plant type.