Blancan climate and feeding strategies of proboscideans and equids revealed by a multi-proxy geochemical analysis from a new locality in north-western Mexico

We present a multi-proxy geochemical analysis of proboscidean and equid teeth from a newly-documented Blancan (Pliocene–Pleistocene) locality in north-western Mexico. Eleven dental elements (six from equids and five from gomphotheres) were analysed by electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and isotope ratio mass spectrometry (IRMS) to assess preservation and reconstruct palaeoecological and palaeoclimatic patterns. All specimens show excellent microstructural integrity, with stable Ca/P and F/P ratios indicating near-stoichiometric hydroxyapatite and excellent preservation. Trace-element concentrations (Sr, Ba) and flat, PAAS-normalised REE+Y profiles indicate minimal diagenetic overprint, permitting the retention of biogenic signals. Stable carbon isotope values (δ13Cdiet,meq) reveal predominantly mixed C3–C4 feeding strategies, with proboscideans consuming proportionally more C4 vegetation than equids. The latter exhibit higher Ba/Ca and Sr/Ca ratios despite lower δ13Cdiet,meq enrichment, suggesting selective feeding or height-related browsing. Mean annual precipitation (MAP ≈ 125 mm/year), derived from δ13Cdiet,meq values, indicates arid conditions within the envelope expected for semi-arid to arid ecosystems documented for the late Neogene–early Quaternary across North America and other regions worldwide. Oxygen isotope compositions (δ18O) imply similar climatic settings amongst taxa, with interindividual variability linked to physiology, mobility or access to distinct water sources. Mean annual temperature (MAT ≈ 15 °C) agrees with independent proxies and is consistent with late Pliocene conditions warmer than present. These results provide the first quantitative reconstruction of Blancan terrestrial climate in north-western Mexico, offering new insights into mammalian ecological adaptations and environmental dynamics during the Pliocene–Pleistocene transition.