Sex-ratio et analyse des mélanges d' Ursus spelaeus (Carnivora, Ursidae) du gisement pléistocène supérieur de Fate (Ligurie, Italie). Implications paléobiologiques

Abstract

Determination of the sex-ratio of a fossil population is essential for understanding the palaeoethology of a taxon, and this is especially true for the cave bear ( Ursus spelaeus). Classical methods for determining sex-ratios such as analyses using uni and bivariate plots are based on an arbitrary fixing of the limit between the sexes. Therefore, a more robust statistical method termed mixture analysis has been applied in this study to test all the postcranial remains of cave bear (essentially carpals, tarsals and metapodials) derived from the Upper Pleistocene site of Fate (Liguria, Italy). Results give a sex-ratio of about 35% female individuals and show a clear predominance of males. Mixture analysis appears to be a reliable method for sex-ratio determination in U. spelaeus. In this study, few dimensions have been excluded because of a significant error in sex classification. The numerous measurements identified as good predictors of sexual dimorphism in the cave bear are probably linked to the marked sexual differences in the body mass of the animal. Palaeobiological interpretations suggest that there are no available hypotheses to explain the high variability of sex-ratios documented for the cave bear in Palaeolithic sites. The individual animal behaviour appears to be the only criteria in determining their choice of a winter den. But trophic and social regulations on living populations may have influenced this choice. The association between mortality profiles and sex-ratios appears to be related to the general function of a den. The thanatocenosis of cave bears in the Fate assemblage indicates the presence of a high number of juveniles and male individuals, such that the site may have served either as a nursery or and as a male den.