Florencia Gordón

Exploring Dietary Patterns in the Southernmost Limit of Prehispanic Agriculture in America by Using Bayesian Stable Isotope Mixing Models

The contribution of maize to the diet of prehispanic populations that inhabited Mendoza Province, the then-southernmost limit of agriculture in America, has been largely debated. Recently, on the basis of δ13C data, it was suggested that cacti may mimic the pattern of human isotopic values attributed to maize consumption in this region. These studies relied on a univariate qualitative approach not suitable for accurately identifying dietary contribution when multiple potential resources are available. Here, we analyzed published δ13C and δ15N data by using Bayesian mixing models to estimate the proportional contributions of different plants and animals to the protein component and total diet. The effect of different fractionation values on these estimations was also assessed. Our results pointed out the importance of C3 vegetables in the prehispanic diet of these populations and only a small contribution of maize in the later Late Holocene sample from North Mendoza. Fractionation values had a significant effect on diet estimation. Overall, our study highlights the importance of obtaining fractionation values for local resources and increasing the diversity of isotopes analyzed for both the consumer and the potential resources to get a better understanding of diet variation in this region.

Dietary patterns in human populations from northwest Patagonia during Holocene: an approach using Binford’s frames of reference and Bayesian isotope mixing models

The goal of this paper is to assess the variation in the proportional contribution of diverse resources to the diet of human populations from northwest Patagonia (Argentina) throughout the Middle-Late Holocene. Particularly, we assessed the variation among three geographic areas and two periods. We first estimated the expected proportions of terrestrial animals and plants and aquatic resources for each area according to the Binford’s frames of references approach. A Bayesian mixing method was then applied to calculate the proportion of plants and animals in the diets from stable isotopes (δ13C and δ15N) of human bone collagen. The isotope values suggest that the composition of diets differed spatially and temporally. Diets of South Mendoza were mainly composed of terrestrial animals (Rhea-Lama and rodents) with a greater incorporation of C3 plants towards the later Late Holocene; in North Neuquén, Rhea and Lama represent a proportion of 0.84 of the diet consumed; and finally, the sample of Center Neuquén is the only one with high values of Araucaria in the diet. The isotopic values obtained for the three studied areas did not fit to the expectations of Binford’s model, North Neuquén being the area that departs most from the predicted proportions of terrestrial animals and plants and aquatic organisms in the diet. These findings open up new questions about the local conditions that influenced regional variation in the diet of prehistoric hunter-gatherers.

Craniofacial variation, body size and ecological factors in aboriginal populations from central Patagonia (2000-200 years B.P.).

Previous studies have shown that ecological factors had a significant role in shaping the patterns of craniofacial variation among South American populations. Here, we evaluate whether temperature and diet contributed to facial diversification in small geographic areas. Facial size and shape of 9 osteological samples from central Patagonia (Argentina) were described using 2D landmarks and semilandmarks. Data on mean annual temperature, diet composition (δ(13)C and δ(15)N values) and femoral head maximum breadth, used as a proxy of body mass, were obtained for each sample. We then tested the association of body mass and the ecological variables with facial morphology using spatial regression techniques and a model selection approach. Akaike Information Criterion produced disparate results for both components of facial morphology. The best model for facial size included temperature and body mass proxy, and accounted for more than 80% of variation in size. Lower temperatures were related to larger facial sizes. Body mass was negatively associated with facial size and showed no relationship with the temperature. This suggests a relatively independent variation of cranial traits and body mass at the spatial scale studied here. Facial shape was not associated with the temperature or diet composition, contrasting with the patterns observed at larger spatial scales. Our results point out that the effect of climatic variables on cranial traits might be a source of morphological differentiation not only at large scales but also in small geographic areas, and that size and shape display a differential preservation of environmental signals.