These small rodents in the wild weigh on average 412 grams as males, and 422 grams as females. In comparison, domesticated chinchillas weigh significantly more: males at 600 grams and females at 800 grams on average (Spotorno et al. 2004b). These numbers reveal a strong sexual dimorphism between males and females. This size difference is due to structural differences between the two sexes. Female Chinchilla lanigera are characterized by larger pelvis and viscerocranium bones. Also, males tend to have a faster growth period than the females (Lammers et al. 2001). These differences in size and development between the sexes are thought to be adaptive. Females may need a larger pelvis in order to give birth to young. The viscerocranium of the female may be larger if females consume larger food items (Lammers et al. 2001). In addition to being the larger of the sexes, females also tend to be dominant over males (Saunders 2009).
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