3B Scientific Chimpanzee Skull (Pan troglodytes), female - Manual (Page 2)

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Chimpanzee 1
Species Pan troglodytes (Gmelin, 1788) 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 this young adult, middle-sized female chimpanzee shows a relatively low level of relief. Apart
from the pronounced supra-orbital ridges, the cerebral cranium appears somewhat smooth and could
quite readily be compared with that of the human in this respect
3 . With older animals, this would no lon-
ger be as reasonable.
In the chimpanzee’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.
The occipital condyles of the atlas 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 only at first sight to be less marked in the chimpanzee than
in other Ponginae. As is the case with all primates that have been investigated in this respect, male chim-
panzees display on average a larger brain volume, larger and differently shaped canine teeth, and a signifi-
cantly more pronounced skull relief. Mature males in all cases, and mature females relatively often, have a
sagittal crest – if less pronounced than that of the gorilla. All adult animals develop occipital crests, due to
their “front-heavy” heads.
In general supra-orbital ridges (tori supraorbitales) are formed, which are linked medially by a glabellar
ridge (torus glabellaris) to form a unified brow ridge (torus frontalis). Not unrelatedly, the frontal sinuses are
very pronounced. 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 chim-
panzee too, the enamel shows furrows on the occlusion plane next to the fissures; these are few in number
but characteristic.
Since the pioneering studies of E. Selenka around 1900, chimpanzees are considered the closest living rela-
tives of humans. They took this distinction over from the orang-utan.
2