Environment, space, and morphological variation of projectile points in Patagonia (southern South America)

CARDILLO, M.; BORRAZZO, K.; CHARLIN, J.

Valle de Uco

Conferencia; 4th Southern Desert Conference; 2014

Universidad Nacional de Cuyo y Laboratorio de Paleoecología Humana (Mendoza, Argentina)

Introduction The aim of this work is to assess shape variation in Patagonian stemmed projectile points related to spatial and environmental factors by means of geometric morphometric and multivariate methods. The sample includes over 1000 projectile points from continental and insular Patagonia assigned to Middle-Late and Late Holocene. Previous research showed a trend of shape change related to latitudinal axis, but no information was available to some areas, especially Grande Island of Tierra del Fuego. With the purpose of extending our analysis to overall Patagonia and taking advantage of the new data set available, we focus on the correlation between environmental variables (rainfall, temperature, biomass, etc.) and morphological change. The results obtained allow discussing the role of space, environment, and resource availability in technological decision making, emphasizing the comparison between wet and dry areas. Besides authors? own research and published literature revision, most of the tips come from a broad survey program of museum collections. Materials and Methods Geometric morphometric analyses have recently became a common technique in archaeological research, although they were first introduced by several authors years ago. These techniques allow analyzing shape variation on discrete points, called landmarks, as well as groups of related points describing a surface (3D) or contour (2D), called semilandmarks). In this case we use a total of 24 points (eigth of which are landmarks). Graphic representation of these analyses allows visually explore morphological change as a continuum, which is an advantage over static or typological analyses more centered on morphological norm than on its variation. The new morphological variables obtained through a geometric morphometric analysis were used in multivariate analyses to put into test hypothesis about spatial pattering in shape variation. In this study 1445 complete or very slightly damaged stemmed projectile point images from mainland and insular Patagonia were used in geometric morphometric analyses. Aligned specimens were subjected to Principal Component analysis in order to extract general patterns of shape variation. Redundancy analysis was performed to test the relationship between independent environmental variables and shape changes. At the same time, geographical coordinates of 1320 specimens with detail spatial provenience data were used to model autocorrelation (i.e. shape contagion) between units in order to take into account spatial phenomena. Results First two Principal Components (PC) explain 82.74 % of shape and size variation of the sample. First PC describes 62%, while the second describes 20% of the variation. Correlation analysis between shape and space PC explains ca. R215 y R2 20% (p