Bernard Castelein / Guianan brown capuchin (Sapajus apella) chewing on branch, Pampas del Yacuma Protected Area, Bolivia

Alex Hyde / Brown / Tufted Capuchin (Cebus apella) family group in cloud forest, Manu Biosphere Reserve, Peru.

Ben Cranke / Black-striped capuchin (Sapajus libidinosus) using rock as a tool to break open palm nut, Parnaiba Headwaters National Park, Piaui, Brazil. August.

Ben Cranke / Black-striped capuchin (Sapajus libidinosus) using rock as a tool to break open palm nut Parnaiba Headwaters National Park, Piaui, Brazil. July.

Ben Cranke / Black-striped capuchin (Sapajus libidinosus) using rock as a tool to break open palm nut, Parnaiba Headwaters National Park, Piaui, Brazil. July.

Roland Seitre / Capped Langur (Trachypithecus pileatus) in tree, India

Gabriel Rojo / Snow-capped Lanin volcano, Lanin National Park, Argentina, with Monkey puzzle trees (Araucaria araucana) in foreground

Pete Oxford / Brown Capuchin (Cebus apella) stabilizes itself with its prehensile tail while using a heavy rock hammer to crack open palm nuts placed in small pits in the anvil rock surface, Cerrado habitat, Brazil

Pete Oxford / Brown Capuchin (Cebus apella) stabilizes itself with its prehensile tail while using a heavy rock hammer to crack open palm nuts placed in small pits in the anvil rock surface, Cerrado habitat, Brazil

Pete Oxford / Brown Capuchin (Cebus apella) pair using rock and anvil to crack open Piassava Palm (Attalea funifera) nuts, Cerrado habitat, Piaui State, Brazil

Pete Oxford / Brown Capuchin (Cebus apella) using a rock to crack open a Piassava Palm (Attalea funifera) nut, Cerrado habitat, Piaui State, Brazil

Pete Oxford / Brown Capuchin (Cebus apella) using a rock to crack open a Piassava Palm (Attalea funifera) nut, Cerrado habitat, Piaui State, Brazil