Stable Sr isotopes of fossil dental enamel reflect diet and digestive system differences among sympatric herbivores

Abstract

Reconstructing the trophic (paleo)ecology and associated physiological traits of both extinct and extant taxa is essential for understanding the functioning of (past) ecosystems. In this context, novel metal stable isotope proxies offer promising tools for investigating ancient diets and, to some extent, the digestive adaptations of animals. In this study, we analyzed the stable strontium isotope composition (δ⁸⁸Sr), alongside δ¹³C, δ¹⁸O, and ⁸⁷Sr/⁸⁶Sr ratios, in fossil dental remains of herbivorous mammals from the Early Pleistocene site of Tighennif, Algeria (∼1.2–1.0 Ma). Traditional carbon and oxygen isotope data indicate an environment dominated by C₃ vegetation, while the ⁸⁷Sr/⁸⁶Sr ratios suggest either a relatively homogeneous strontium baseline or limited geographic mobility of the animals. Our results demonstrate that δ⁸⁸Sr is sensitive to diagenetic alteration, with enamel samples retaining biogenic signatures comparable to those of modern mammals, whereas dentine exhibits δ⁸⁸Sr values shifted toward positive geogenic end-members. δ⁸⁸Sr patterns may reflect trophic niche differentiation among herbivores and potentially indicate distinct digestive physiologies, offering a novel alternative proxy for dietary and ecological reconstructions in the fossil record.