Résumé
Morphological diversity in the sciurid family was analysed by applying geometric morphometry (Fourier transform) to the mandible outline. The results obtained showed that phylogeny and ecology had a prominent role in shaping the mandible. Three distinct extreme forms are recognised illustrated by Marmota, dwarf tree squirrels and dwarf flying squirrels, respectively. Contrary to the mandible of the dwarf flying squirrel, the dwarf tree squirrel mandible does not have a developed coronoid process, while Marmota mandible is rather elongated. Tooth morphology, as well as chewing direction, studied by microwear analysis were only slightly variable and had no clear impact on the shape of the mandible. A study of the mandible of the Early Oligocene European squirrel Palaeosciurus goti did not contradict a preliminary interpretation (based on its limbs) that it had been a ground dweller, despite the fact that its mandible still exhibits a primitive outline.