LAUSR

Abstract We examined sexual dimorphism and variability of craniomandibular morphology in the Japanese giant flying squirrel (Petaurista leucogenys) using different statistical analyses. Among 31 measurements using 33 adult skulls (19 males and 14 females), females showed slightly larger mean size for all traits. Univariate analysis revealed that females were significantly larger than males for the greatest length of skull, zygomatic breadth, and mandibular length. Discriminant functions indicated well distinctiveness between the sexes. Moreover, six additional mandibular measurements were taken for estimating the mechanical advantage of the primary masticatory muscles, of which females showed significantly larger incisor resistance arm and moment arms of the superficial masseter (most ventral fibers) and the anterior deep masseter than males. These traits could increase the surface area for the attachment of masticatory muscles and thus have a role in biting mechanism. These suggest that larger females have relatively greater absolute bite force, which may contribute to obtain more access for greater ecological resources. Additionally, the coefficients of variation did not differ significantly between the sexes. Patterns of variability tended to differ in the cranial dimensions based on longitudinal and transverse axes, but not obviously in the major subdivisions of the skull. The observed variability patterns suggest the existence of developmental factors and higher integration to maintain functional relationship related to their lifestyle. Finally, we identified craniomandibular dimorphism in P. leucogenys as a size related phenomenon mostly associated with resource benefits, despite similarities in variability caused by morphological constraint.