3B Scientific Orangutan Skull (Pongo pygmaeus), male - Manual (Page 2)

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English
Orang-Utan 1
Species Pongo pygmaeus (Hoppius) 2
Subfamily Ponginae Allen, 1925
Family Pongidae Elliot, 1913
Superfamily Hominoidea Simpson, 1931
Infraorder Catarrhina Hemprich, 1820
Suborder Simiae Haeckel, 1866
Order Primates Linnaeus, 1758
The skull of the mature, very large male orang-utan presents a very marked relief. The cerebral cranium
and the facial bones (viscerocranium) have a rough appearance and are marked with bumps, ridges, etc.,
which were formed in response to the requirements of the masticatory and neck musculature. They are in
no way comparable with those of the human.
In the orang-utan’s skull too, the disproportionate size of the face/jaw part (the facial bones, i.e. the
splanchnocranium or viscerocranium) in relation to the cerebral cranium is noticeable. This relationship,
however, only develops in the course of postnatal growth – particularly at the time of the second dentition.
On the sagittal suture, that is down the middle of the skull, a bony sagittal crest (crista sagittalis) develops,
becoming more pronounced towards the back. It is formed from the parietal bones and serves as the ori-
gin of the temporal muscle
3 , which increases in size as it approaches the crest. At the back of the head
(the occiput) the sagittal crest joins the occipital crest, which develops as the neck musculature becomes
stronger.
The occipital condyles of the head joint and the great occipital foramen they enclose (foramen occipitale
magnum) are located in the posterior region of the skull. Here too, the obvious contrast with the newborn
or infantile animal is evident.
The sexual dimorphism of the skull appears at first sight more pronounced in the orang-utan than in, for
example, chimpanzees, but less so than in the gorilla. As is the case with all primates that have been inves-
tigated in this respect, male orang-utans display on average a larger brain volume, larger and differently
shaped canine teeth, and a significantly more pronounced skull relief. In any case, all mature males, but
almost no mature females, have a sagittal crest. All adult animals develop occipital crests, due to their
“front-heavy” heads. In orang-utans, however, these crests are noticeably smaller than in the African
Ponginae.
Generally only supra-orbital arches develop. Related to this, there are no frontal sinuses. This development
takes place in connection with the formation of the permanent teeth and then with the wear of the teeth
with continuing abrasion from chewing
4 .
The upward branch of the lower jaw (ramus mandibulae) is relatively low. Typical of the Ponginae is the
more or less parallel arrangement of the premolar and molar teeth. In front of them are the incisor teeth.
The sexually differentiated, dagger-like canine teeth extend distinctly beyond the occlusion plane. For this
reason, in the upper jaw between the canine tooth and the first premolar, there is a gap, or diastema, into
which the lower canine tooth engages.
The anterior teeth engage one over the other like shears, which makes it easier to bite off a piece of food,
while the posterior teeth have broad, shallow crowns, suited to grinding; this constitutes-in the case of
the molars–what is known as the dryopithecine pattern, which is also displayed by humans. In the orang-
utan too, the enamel shows typical furrows on the occlusion plane next to the fissures. These are set close
together, and their arrangement is so characteristic that even a lay person can identify an orang-utan tooth
from them alone.
Since the pioneering studies of E. Selenka around 1900, orang-utans are no longer considered the closest
living relatives of humans.