Bone Weathering Variability in Semiarid Environments: Insights from Taphonomic Experiments in the Dry Chaco, Central Argentina

Abstract

Understanding the factors that govern bone weathering is essential for interpreting faunal preservation and site formation processes in archaeological contexts. This study presents the firstfour-years of an actualistic long-term experiment conducted in three contrasting depositionalsettings of the Dry Chaco ecoregion of Central Argentina: two open-air contexts (Arid Chacoand Mountain Chaco; n = 54, n = 76) and a sheltered context within the Mountain Chaco(n = 44). Annual observations of weathering progression were recorded for camelid skeletalelements and integrated with climatic data to evaluate the influence of environmental and anatomical variables. Using a Bayesian regression model, we assessed the relative contributions oftemperature, precipitation, solar radiation, and microenvironmental conditions to weatheringtrajectories. The model outputs demonstrate pronounced differences across contexts: rocksheltercontext showed an extremely low probability of transitioning into higher weathering stages,remaining at stage 0 across all years, while open-air settings exhibited faster and more heterogeneous weathering. Element morphology played a major role, with flat and axial bones showing higher susceptibility than long or compact elements. Microenvironmental factors—including shading, substrate, moisture regimes, and vegetation cover—proved more influential thanbroad regional climate, underscoring the need to interpret weathering within local ecologicaland geomorphological conditions. To explore ontogenetic effects, we generated exploratoryestimates of neonatal weathering stages using adult–newborn differentials from an independentexperiment. These suggest reduced survivorship of neonatal elements in open-air settings,highlighting the importance of age in mortality and taphonomic interpretations. Overall, ourfindings caution against using weathering stages as direct chronological markers and demonstratethe value of Bayesian approaches for modeling taphonomic processes. The methodologicalframework presented here provides a robust basis for expanding actualistic studies andimproving archaeological inference in semiarid environments.