Primates process protected fruits by holding them in the hand(s) and removing the peel with the incisors. The ability of primates to consume unprotected fruits is restricted by competition from birds whereas texture prevents birds from consuming peely fruits.
1994, P. W. Lucas, “Categorisation of food items relevant to oral processing”, in D. J. Chivers, P. Langer, editors, The Digestive System in Mammals: Food, Form and Function, Cambridge, Cambs: Cambridge University Press, →ISBN, part III (Form), page 208: