Sexual Dimorphism in Skulls of the Lowland European Bison,Bison Bonasus Bonasus

The research was conducted on 600 (311 male and 289 female) European bison skulls of the Lowland line collected between 1967 and 2006. The specimens came from the bison breeding centre in Białowieza (n = 67) and from the free-ranging population of the Polish part of the Białowieza Forest (n = 533). Two indices best differentiating male and female skulls were selected: one being the quotient of the orbital breadth EctEct and the length of the splanchnocranium StP, the second being the quotient of the neurocranium length BSt and the basal skull length BP. Using these indices we constructed an equation which produced negative values for females and positive values for males; 223 (74%) of the male skulls produced positive values consistent with sex, and 82 (26%) produced negative values, indicating female features. Those features were present mainly in skulls of young males (< 4 years old). 230 (80%) of the female skulls had shapes typical of the female sex, whereas 59 (20%) displayed male features.