Isotopic evidence of dietary strategies and taxa-specific adaptive responses in the extinction of Pleistocene equids from the argentine Pampas

The extinction of megamammals during the Late Pleistocene in South America remains a topic of considerable debate, particularly regarding the influence of human activity. This study employs stable isotope analysis (δ¹³C and δ¹⁸O) to investigate the paleoecology of two extinct horse species, Equus neogeus and Hippidion principale, from the Argentine Pampas. Our findings reveal consistent temporal trends in the horses' isotopic values across both Pleistocene and Marine Isotope Stages (MIS) of the last glacial (MIS 1–2) and interglacial (MIS 5–6) period, with notable differences emerging in the Late Pleistocene. While both species maintained similar feeding habits for much of the Pleistocene, Equus neogeus exhibited greater δ¹³C variability in the Late Pleistocene, indicating dietary flexibility and a shift towards C₄ vegetation. In contrast, Hippidion principale maintained a more stable diet. These results suggest that Equus adapted to changing vegetation driven by climatic fluctuations, while Hippidion may have been more vulnerable to environmental changes and human presence, potentially contributing to its extinction. We expanded the spatial and temporal scope of horse isotope data by incorporating previously unstudied localities and underrepresented periods, providing new isotopic values for both species. Our study offers fresh insights into the complex interplay between climate, human activity, and megafaunal extinctions in the Argentine Pampas.