Orangutan (meaning forest man in a Malay language); two subspecies recognized, although there is some movement to consider these separate species. Inhabits tropical rain forests of Borneo and Sumatra. Primarily arboreal, but do descend to ground, particularly the males; diurnal; quadrumanual climbers; on ground, locomotion is a form of quadrupedalism referred to as fist walking. Sexually dimorphic in body size and several morphological features including canine size, skull anatomy, and the presence of large cheek flanges on the side of the face, and throat sacs used in loud vocalizations in the adult males; these last two features develop about five years after puberty. Body mass ranges from 35 to 50 kg in females, 60 to 90 kg in males. Dental formula: 2.1.2.3; primarily frugivorous with leafy supplements; some data suggests differences in diet between males and females. Noyau social behavior.