Morphological differences of mandible among four populations of genus Microtus belonging to three species from Iran (M. socialis from northwestern Iran, M. paradoxus from Kopet-Dag mountains, M. paradoxus from Binaloud mountains, and M. transcaspicus from northeastern Iran) were studied by the landmark-based geometric morphometric method. No significant difference was found in the mandible shape of the two different populations of M. paradoxus, nor in their mandible overall size (by estimation of the centroid size). The three species are significantly different on the basis of the total mandible size, while the differences of the mandible shape among M. paradoxus and M. socialis in non-significant. Both canonical variate analysis and UPGMA cluster indicate a high morphometric distance among M. transcaspicus and the other taxa verifying the division of social and transcaspian voles into two different species group, socialis and arvalis respectively. Changes in the mandible shape mostly localize in the coronoid and angular processes.

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