Extant large members of the order Carnivora show high variability in feeding adaptation. Morphology of their teeth and skull is a primer to predict diet in both extant and extinct species. Here I present a complete geometric morphometric survey of mandible of large (>7 kg) Carnivora in order to make paleoecological predictions for selected Plio-Pleistocene taxa. Mandibular size and shape data support a strong differentiation between families but also convergence due to functional adaptations to hunting prey. Linear discriminant function analyses are performed in order to obtain dietary predictions on fossil taxa with statistical accuracy. There is a high level of discrimination among dietary categories, especially when subsets of predator and non-predator carnivores are analyzed separately. New insights emerge for Plio-Pleistocene fossil taxa whose paleoecology was previously inferred. Mandibular size and shape data are accurate dietary predictors in large carnivores, with size being more relevant to clarify adaptations in killing prey of different size classes.