Carnivore teeth, especially the carnassials, are subjects to selection in the presence of dietary competition. We compared several craniodental characters in the Finnish foxes before and after arrival of an invasive species, the raccoon dog. The female foxes displayed increased adaptation to carnivory, whereas we found no significant change in the male foxes after the arrival of the raccoon dog. We suggest that the presence of a new competitor may be driving the Finnish female foxes towards more carnivorous diet.