Sulfur isotopes in hunted ungulates reveal Palaeolithic human mobility patterns in Northern Iberia

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Abstract This research addresses a central question in Palaeolithic research: how hunter-gatherer mobility was structured across space and time in the Cantabrian Region (northern Iberia), which has human occupation evidence spanning from the Middle Pleistocene through the Holocene. A multidisciplinary framework integrating primarily δ³⁴S isotope values, combined with δ¹³C and δ¹⁵N, palaeoproteomics, Bayesian age modelling, palaeoclimatic reconstruction, isoscape mapping, and ecological diversity was developed. A total of 905 animal bone collagen samples, with evidence of anthropogenic modifications, from 16 key archaeological sites from the Mousterian to Mesolithic (Marine Isotopic Stage 5 to 1, between 100-7 ka BP) were analysed, permitting the reconstruction of spatial patterns of resource exploitation and human mobility. The δ³⁴S isotope values show weak, inconsistent relationships with climatic proxies, suggesting that sulfur signatures are primarily driven by geographic and ecological factors rather than climate. Strong spatial trends are observed, with higher δ³⁴S values in coastal zones and lower values inland. Diachronic trends reveal marked shifts in human mobility: smaller ranges during the Mousterian, increasing mobility through the Châtelperronian and especially the Aurignacian, followed by reduced mobility in the Gravettian and Solutrean, and renewed territorial expansion during the Magdalenian and, likely, the Azilian. In contrast, the Mesolithic is characterised by decreased mobility and thus increased territoriality in both coastal and inland contexts. Faunal isotope values and isoscape predictions reveal that some animals were acquired beyond local foraging ranges during the Palaeolithic, particularly in inland regions with lower δ³⁴S values. Isotopic niche analyses indicate partial interspecific overlap consistent with ecological flexibility. Macromammal and micromammal diversity exhibit contrasting patterns, with a significant negative correlation in Simpson and Shannon indices. Macromammal diversity correlates negatively with δ³⁴S values, linking increased hunting diversity to expanded catchment areas and longer-distance foraging, whereas micromammal diversity shows positive correlations with δ³⁴S, δ¹³C and δ¹⁵N reflecting stronger climatic influence. Overall, these results demonstrate that hunter-gatherer behaviour in northern Iberia during the Middle and Late Palaeolithic was highly dynamic, combining logistical and residential strategies that shifted in response to changing environmental conditions, resource distributions and cultural adaptations.

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