Variability of the chewing surface of the first lower and third upper molars and the expression of the interorbital ridge in Maximowicz’s vole (Rodentia, Arvicolinae: Alexandromys maximowiczii) from the north-eastern part of the Middle Amur Lowland

This study represents the first comprehensive analysis of molar variability in Maximovich’s vole (A. m. maximowiczii) from the Middle Amur Lowland using both classical and complex methodological approaches. For the first lower molar (m1), we identified four anterior loop variants: the predominant ‘maximowiczii-like’ type, along with rare ‘fortis-like’, ‘oeconomus-like’, and a newly described ‘maskii’ variant (10% frequency). The third upper molar (M3) showed unexpectedly high frequencies of simple morphotypes, contrasting with previous reports of complex morphotypes from Amur region specimens. These dental characteristics distinguish Lower Priamurye populations from Upper Priamurye specimens, warranting further morphological and genetic investigation. Interorbital ridge development proved absent in juveniles, indicating its limited value as a species diagnostic character.