Reconstructing Middle and Upper Paleolithic human mobility in Portuguese Estremadura through laser ablation strontium isotope analysis

Significance

Laser ablation MC-ICP-MS allows in situ strontium isotope data to be obtained for incrementally formed bioapatites such as enamel with extremely high spatial resolution. Here, we provide a large-scale application of the method comparing the mobility and subsistence behavior of Middle and Upper Paleolithic humans in the same landscape. These remains and the fauna analyzed alongside come from the Almonda karst system (Portuguese Estremadura). Data suggest that regional Middle Paleolithic individuals roamed across a subsistence territory of approximately 600 km ², while Upper Paleolithic individuals moved seasonally and exploited a smaller territory of approximately 300 km ².

Abstract

Understanding mobility and landscape use is important in reconstructing subsistence behavior, range, and group size, and it may contribute to our understanding of phenomena such as the dynamics of biological and cultural interactions between distinct populations of Upper Pleistocene humans. However, studies using traditional strontium isotope analysis are generally limited to identifying locations of childhood residence or nonlocal individuals and lack the sampling resolution to detect movement over short timescales. Here, using an optimized methodology, we present highly spatially resolved ⁸⁷Sr/ ⁸⁶Sr measurements made by laser ablation multicollector inductively coupled plasma mass spectrometry along the growth axis of the enamel of two marine isotope stage 5b, Middle Paleolithic Neanderthal teeth (Gruta da Oliveira), a Tardiglacial, Late Magdalenian human tooth (Galeria da Cisterna), and associated contemporaneous fauna from the Almonda karst system, Torres Novas, Portugal. Strontium isotope mapping of the region shows extreme variation in ⁸⁷Sr/ ⁸⁶Sr, with values ranging from 0.7080 to 0.7160 over a distance of c. 50 km, allowing short-distance (and arguably short-duration) movement to be detected. We find that the early Middle Paleolithic individuals roamed across a subsistence territory of approximately 600 km ², while the Late Magdalenian individual parsimoniously fits a pattern of limited, probably seasonal movement along the right bank of the 20-km-long Almonda River valley, between mouth and spring, exploiting a smaller territory of approximately 300 km ². We argue that the differences in territory size are due to an increase in population density during the Late Upper Paleolithic.