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Pongo (Orangutan) male, female and juvenile skulls
Orangutan skulls of an adult male (left), female (center) and juvenile (right)
Orangutans (Pongo pygmaeus) are great apes who belong to the family Hominoidea, which also includes gibbons, gorillas, chimpanzees, and humans, as well as many fossil species. Orangutans are divided into two subspecies, one inhabiting Borneo and the other in Sumatra.
Unlike the African great apes, the ancestral lineage of the Orangutan is relatively well known, being traced back to Sivapithecus, a Miocene hominoid from Pakistan dated between 13-8 mya. Sivapithecus and Pongo share several derived cranial features including a high degree of prognathism, oval orbits, a narrow nasal aperture, and broad zygomatic arches. In these features, and in their high, rounded braincase, the skulls of Orangutans differ from that of the African great apes (Fleagle 1999).
While there is considerable sexual dimorphism in hominoid species, this is especially true of Pongo. Males, weighing about 120 kg, are about twice as large as females. The adult male Pongo (orangutan) has a robust skull and jaw with massive teeth. The huge jaw muscles are attached to a ridge at the top of the skull called a sagital crest, found in many other male hominoids, past and present, but not in females.
Male
orangutans are also unique in having two periods of maturation. The
first occurs between the ages of eight and fifteen, when males
are known as subadult and have the ability to reproduce, although they
have not reached full maturity. Fully adult males are larger than
subadult males and also have distinct cheek pouches.
Orangutans subsist mostly off fruit and leaves, although males add termites to their diet when terrestrial. Orangutans have a social structure similar to that of nocturnal prosimian primates. Most individuals are solitary and have separate home ranges. Females have relatively small home ranges and are typically accompanied by their offspring. Males have larger home ranges that overlap those of several females.
Orangutans
have very long forelimbs in relation to their hindlimbs, curved
fingers, and a reduced pollex, or thumb. Females are almost exclusively
arboreal while males often travel on the ground. When traveling
quadupedally, orangutans use a unique type of locomotion called
fist-walking.with their relatively long fingers curved into fists, the
only primate species to do so (Fleagle, 1999).
References:
Fleagle 1999:
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