This paper offers a functional analysis of structure and variation trends in the dentition of species of the tribe Lemmini Simpson, 1945. The striking differences in the structure, trends in variation and rate of evolution between the Lemmini and all other members of Arvicolinae can be understood from the quite different functioning of the masticatory apparatus. The polarity of character states in the dentition of the Lemmini is discussed. Suggested polarity is supported by the palaeontological and functional evidence. The distinctive means of increasing the efficiency of the masticatory apparatus seen in Lemmini not only reflects definite genetic history but can also be explained by their very unusual food specialization and the demands it imposes on the mechanics of their masticatory apparatus.