Original: Later rock paintings and engravings showing hippos being hunted have been found in the mountains of the central Sahara dated 4,000 â '' 5,000 years ago near Djanet in the Tassili n ` Ajjer Mountains .
Simplified: Later rock paintings and engravings showing hippos being hunted . They have been found in the mountains of the central Sahara from 4,000 â '' 5,000 years ago near Djanet .