Three statistical methods for sex determination in extant and fossil caprines: assessment of the Rupicapra long bones

摘要

Sex determination of fossil remains in archeopaleontological contexts is a necessary step in order to gain insights in archaeological and paleobiological parameters such as prey selection and sexual dimorphism. Species with higher sexual dimorphism are more reliably sexed while the sex determination of less dimorphic animals is not attempted. In this study, we compared the accuracy of three different methods in the sex determination of a modern known-sex sample of chamois (Rupicapra pyrenaica parva) from the Cantabrian range (Northern Iberian Peninsula), which is a small-sized ungulate with low sexual dimorphism when compared to other animals in which sex determination has been attempted (i.e., Ursus spelaeus, Capra pyrenaica). The three methods applied were mixture analysis (MA), cluster analysis (CA) and principal component analysis (PCA). Within CA we applied three different analysis: one agglomerative hierarchical method (AH) and two optimal partitioning methods (k-means and robust k-means); and within PCA we applied normal and robust variants of the analysis. The performance of the CA and PCA methods was better than the MA. More specifically, we used the k-means analysis to the early Upper Pleistocene sample of chamois from Valdegoba cave (Burgos, Spain). The results show that chamois males double the number of females in this site, while the pattern in modern living chamois populations is the opposite. Moreover, the proportion of adults represented in the Valdegoba chamois sample is the 80.25% of the minimum number of individuals (MNI), well above the w50% expected in modern living populations. However, it is difficult to ascertain if Neandertals, the main accumulation agents of the site, were selecting young male chamois adults, or if neither sex was preferentially targeted, and males were hunted more frequently due to their solitary nature. Finally, the size of the chamois males at the site was larger than that of modern chamois males, while females are equal in size to those of present day. This discrepancy implies larger sexual dimorphism for the Pleistocene chamois sample from Valdegoba.