Nomenclature, measurements, landmark scheme, and morphotype analysis of the first lower molar in narrow-headed voles. A Nomenclature for the description of the first lower molar of the narrow-headed vole. AC: anterior cap; LRA: lingual reentrant angle; LSA: lingual salient angle; BRA: buccal reentrant angle; BSA: buccal salient angle; T: triangle; PL: posterior lobe. B Measurements of the first lower molar (m1) applied in this study: L: length of the tooth; AC1: length of the anteroconid complex; AC2: length of the anteroconid mesial cap; B1: width of the tooth; B2: width LRA4–BRA3; B3: width BRA3–LRA3. Note: some literary sources (e.g., van der Meulen and Zagwijn 1974; Nadachowski 1982) denote the same measurements by different labels, i.e., AC1 = a; B1 = W; B2 = b; B3 = c. C Landmark scheme after Wallace (2006). D Morphotype measurement after Smirnov et al. (1986) and Ponomarev and Puzachenko (2017).