The aim of investigation was to determine reason of fluctuating asymmetry between selected bilateral epigenetic traits of the skull and madible of wild and farm chinchillas. Estimated values of the Wilcoxon matched-pairs test and Spearman’s coefficients of correlation for 25 bilateral epigenetic traits with the hypertrophic defects of the splanchnocranium and mandible, sex, size of the original litter of specimen, and season of the year of birth were presented. Animals born from August to December were characterised by a significant asymmetry of Foramina supra pars inferior bullae tympanicae, Foramen rotundum accessorium, and Foramina supra pars inferior bullae tympanicae accessorium on the craniums of animals from multiple birth from this time. The mandibles of these animals showed significant asymmetry of Foramina infra M₁ - M₃ and Processus condylaris. All of this may point to the occurrence of increased chinchilla sensitivity to intensified light phase of day, and this may be a factor disturbing genetic homeostatic mechanisms and adaptation to the conditions of farm breeding environment.