Rock art, Prehistory, Protohistory

The aim of this paper is to compare the tracing made at the Bronze Age petroglyph of “Barreira” in Verdoejo (Portugal) (Novoa and Costas 2004) with two different and new methodologies based on photogrammetry. This technique is oriented to reduce the different problems of subjectivity that are present in the old systems of registry, and furthermore it allows studying the rock surface without touching it.
These techniques are:
• The Virtual RTI proposed as an alternative to normal RTI method, which is a combination of reflectance transformation techniques with photogrammetry and non-contact digitising. It uses animated virtual domes, leading to a sequence of renderings of the 3D model, processed using the same methods as normal RTIs. The virtual RTI provides an advanced level of interaction with the 3D model and enhanced visualization of the surface topography (Earl, Beale, Martinez and Pagi 2010).
• Radiance Scaling is a shader applied to 3D models, which adjusts reflected light intensities in a way dependent on both surface curvature and material characteristics. As a result, diffuse shading or highlight variations become correlated to surface feature variations, enhancing surface concavities and convexities (Vergne, Pacanowski, Barla, Granier and Schilck 2010).

The importance of differences in social organization for the developing modern Homo sapiens lies in the fact that “Upper Paleolithic humans may easily have organized themselves dynamically into larger or smaller social alliances as the need arose. Such organizational flexibility would have allowed them to disperse risks of subsistence failure among larger populations better than among smaller groups with less flexible social arrangements.” (Shea 2003: 183). 

We agree that a competitive advantage would arise from more flexible and more encompassing forms of social organization and have previously modeled its implications in detail for the replacement of one group by another under conditions of difference in modes of adaptation leading to substantial differences in population density or equivalently measured as changes in population size keeping the area fixed (Read 1987) -- conditions satisfied by population estimates around 4,400–5,900 for modern Homo sapiens  in the European area for the time period of the Aurignacian (Bocquet-Appel et al. 2005) in contrast with estimates around 1,710 - 2,690 for Neanderthals (Richter 2008).  Missing so far, though, are the reasons why the mode of adaptation leading to higher population densities was open to Upper Paleolithic humans and not to the Neanderthals.  This lacuna is not resolved by imposing a definition, even in broad terms, of what constitutes so-called ‘modern behavior’  such as “behavior that is mediated by socially constructed patterns of symbolic thinking, actions, and communication that allow for material and information exchange and cultural continuity between and across generations and contemporaneous communities” (Henshilwood and Marean 2003: 635).  Definitions like this neither provide us with understanding of how the claimed new forms of social organization would come about in the first place nor what are the cognitive requirements needed for their enactment.  The missing evidence, we suggest, lies in considering what are the cognitive requisites of such behavior, the archaeological evidence for when they are in place and their possible evolutionary development.  In so doing, we also construct a better understanding of what we mean by “modern behavior” and what it means to be human.

We do not intend to re-argue all of the issues involved.  We are only adding a new interpretive reference point focusing on what may have enabled the changes that took place in the mode of social organization in the developing Homo sapiens lineage and was absent from the Neanderthal lineage and, we argue, seems to have provided the basis for what appears to be their competitive advantage vis-á-vis the Neanderthals (Shea 2003; Banks et al. 2008; Bar-Yosef 2009).

The 3D technologies have become essential in our researches on the Middle Magdalenian rock carving (18 500-17 000 cal. BP), complementary to the other traditional analytic tools. They play a noticeable role in our stylistic studies: the superimpositions of volumes and not only shapes make the form comparisons all the more accurate that margins of difference can be calculated. On the one hand, clarifying the degree of similarity between two carvings brings more data to the problem of the author(s) of the carvings, and thus it questions notions hardly tackled in prehistoric archaeology: the individual and the short time. These form comparisons prove to be very useful for other archaeological problems. Used for shape identification, they help for a better interpretation of the fragmentary representations and, beyond, for a more precise modelling of the chronological evolution of the parietal assemblages.