ECOMORPHOLOGY OF EXTINCT XENARTHRANS: ANALYSIS OF THE MANDIBLE USING GEOMETRIC MORPHOMETRICS METHODS. In the past, xenarthrans had a broad morphological diversity. However, due to the fact that extant species are dissimilar to most of the extinct ones, few ecomorphological studies have been carried out on this group. The aim of this work is to infer the diet of some extinct xenarthrans species by means of taxon free shape patterns related to diet, working with a taxonomically wide comparative sample. A geometric morphometrics analysis was developed on the lateral view of mandibles of xenarthrans, ungulates and species of other orders. Combining the results of principal component and canonical variate analyses, it was possible to characterize the shape of insectivorous species, which show a high degree of homoplasy. Omnivorous species share some morphological characteristics with herbivorous species with functional canines or high quantities of fruit in their diet. Armadillos show an extremely reduced coronoid process whereas ruminants have a much developed angular process. It was not possible to infer diet in gliptodonts, which behave as outliers in all analyses. The results obtained for most of the ground sloths and Vassallia maxima agree with those of previous studies on these species, thus supporting an ecomorphological approach on extinct Folivora. However, the PCA results suggest an omnivorous/frugivorous diet for Scelidotherium sp. and Thalassocnus natans, although they have been traditionally described as herbivorous. New analyses including the skull are needed to confirm this diet in both cases.