Two species of the brush-tailed mice (family Calomyscidae) have been identified in western Iran: Calomyscus bailwardi and Calomyscus urartensis. Three separate karyotypes have been recorded for samples allocated to C. bailwardi; however, no formal taxonomic review of these entities has yet been carried out. Herein, molecular, morphometric, and geometric-morphometric analyses are utilized to assess the distinctness of Calomyscus samples from the Zagros Mountains in western Iran, delineating three distinct evolutionary units that may deserve species status other than C. bailwardi, in two different genetic clades. These four taxa within the Zagros folded belt – (A) C. bailwardi, from the type locality and its vicinity; (B) C. cf. bailwardi, from the southeastern part of the Zagros chain; (C) specimens from Songhor in Kermanshah Province; and (D) specimens from Saghez in Kurdistan Provinceare supported by the analysis of two mitochondrial gene sequences. Both traditional morphometrics of craniodental traits and geometric-morphometrics of the cranium and mandible confirmed that samples C and D were distinctive groups, both readily separable from C. bailwardi. Our results show that the Zagros Mountains in Iran have a high species diversity due to a complex topography that has promoted geographic isolation in the genus.

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