Morphology and morphometry of the nuchal plane of breeding chinchilla [Chinchilla laniger, Molina 1782] skulls allowing for sex and litter size at birth

The aim of the investigation was to determine the effect of sex and litter size at birth on the values of selected metric traits of breeding chinchilla skulls. Eighty-six chinchillas of both sexes, aged 12 months, kept under similar nutrition and care conditions, were used in the study. The skull's weight was determined, as well as 14 craniometrical traits of the braincase and the splanchnocranium. The volume of the rteurocranium and the area of the foramen magnum surface were determined, and the cranial index was estimated. The basic statistical measurements and the simple, parietal, and semi-parietal correlations between selected traits of the nuchal plane were estimated. The sex and litter size at birth were not the source for variations in the traits: A-P, B-P, A-N, N-P, Zyg- Zyg, Eu-Eu. A significant effect (P≤0.01) of sex of the chinchilla on the height of the squama occipitael bone and the foramen magnum index was found. The inherence of the statistical significance in parietal and semi-parietal correlations for the selected nuchal plane of the skull confirms the necessity of making allowances for sex in craniometric research, as well as for litter size at birth in the case of estimating the values of the metric traits in the skulls of animals coming from multiple litters.