Zinc isotopes in Late Pleistocene fossil teeth from a Southeast Asian cave setting preserve paleodietary information

Stable carbon and nitrogen isotope ratios of collagen from bone and dentin have frequently been used for dietary reconstruction, but this method is limited by protein preservation. Isotopes of the trace element zinc (Zn) in bioapatite constitute a promising proxy to infer dietary information from extant and extinct vertebrates. The ⁶⁶Zn/⁶⁴Zn ratio (expressed as δ⁶⁶Zn value) shows an enrichment of the heavy isotope in mammals along each trophic step. However, preservation of diet-related δ⁶⁶Zn values in fossil teeth has not been assessed yet. Here, we analyzed enamel of fossil teeth from the Late Pleistocene (38.4-13.5 ka) mammalian assemblage of the Tam Hay Marklot (THM) cave in northeastern Laos, to reconstruct the food web and assess the preservation of original δ⁶⁶Zn values. Distinct enamel δ⁶⁶Zn values of the fossil taxa (δ⁶⁶Zn_carnivore < δ⁶⁶Zn_omnivore < δ⁶⁶Zn_herbivore) according to their expected feeding habits were observed, with a trophic carnivore-herbivore spacing of +0.60% and omnivores having intermediate values. Zn and trace element concentration profiles similar to those of modern teeth also indicate minimal impact of diagenesis on the enamel. While further work is needed to explore preservation for settings with different taphonomic conditions, the diet-related δ⁶⁶Zn values in fossil enamel from THM cave suggest an excellent long-term preservation potential, even under tropical conditions that are well known to be adverse for collagen preservation. Zinc isotopes could thus provide a new tool to assess the diet of fossil hominins and associated fauna, as well as trophic relationships in past food webs.