A. africanus has a different
shape of cranium and a larger brain case than previous hominids. This skull,
known as Mrs. Ples, typifies A. africanus. 
A. africanus has a different
shape of cranium and a larger brain case than previous hominids. This skull,
known as Mrs. Ples, typifies A. africanus.
Found at the south African site of Taung,
this specimen (white background on the right) of a child is significant
because it left a record of the fossilized brain (endocast) of A. africanus.
Studies of this brain suggest it has apelike characteristics. Despite this
finding, 
paleoanthropologists
believe that significant changes to the brain had occurred by the time of
A. africanus. However, these changes are not yet apparent in the
gross organization of the outermost parts of the brain. Such changes appear
a million years later in Homo habilis. Estimates of the brain size
for A. africanus suggest that the average size was about 440 cc.,
less than a third of the 1,350 to 1,400 cc average for modern humans.
Examination of the south African fossils such as
those on the left indicated that the fossil material could be divided into
two different groups of hominids. These two crania represent the smaller
"gracile" form but a more dentally specialized, "robust"
form of hominid lived alongside of these smaller forms (see A. robustus).
A. africanus is the smaller, more generalized group. The presence of A. africanus in east Africa is less clear.
Don Johanson and his colleagues maintain that there is an evolutionary linkage
between A. afarensis and A. africanus, as well as all later
hominids. They point to similarities in the two and argue that A. africanus
is a direct descendent of A. afarensis. While it is unclear at this
point how to assess A. africanus, it is possible to identify this
group of fossils as part of a likely continuum where the development of
the postcranial skeleton for upright bipedalism and the modification of
the dentition for an omnivorous diet were main trends. Expansion of the
brain proceeded slowly in the transition from A. afarensis to A.
africanus.
This
is a specimen found at Koobi Fora that has been classified as a possible
Australopithecine or early version of a group more related to later Homo.
This particular individual has a very large brain relative to other Australopithecines
however. The 775 cc capacity is well over the normal range of about 440
to 500 cc. for other A. africanus. This specimen has been dated to
about 1.6 million years ago. Note how the eyes are positioned well below
the top of the cranium. Contrast this with the previous fossil from south
Africa and with A. boisei in subsequent parts of this journey.
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Note the small, angled forehead and prognathism
of the face on the A. africanus specimen above. The robust form of
Australopithecus has a flatter face with less facial prognathism.
A. africanus still has relatively large incisors and canines, but
they are markedly reduced from A. afarensis. A. africanus
does have larger premolars and molars relative to the size of the front
teeth. The zygomatic arch is less robust than other australopithecines,
and there is no sagittal ridge or crest.
Among the oldest of the south African australopithecines, this specimen
shows the forward projection of the face typical of A. africanus.
The temporal lines are positioned high on the side of the cranium suggesting
that developed chewing muscles attached to that area of the skull. The brain
size is small at 428 cc. This specimen is more specialized in its features
and thus has fewer "primitive" or apish characteristics that were
present in A. afarensis.
This individual had a brain capacity of about
450 cc. Notice the increase in postorbital constriction and projection of
the lower face. You might remember the relatively wide face that you could
see from the front view.
Compare the postorbital constriction of
this small brained individual with that of the next specimen. 
This is the top view of the
larger brained australopithecine introduced earlier. With the larger brain
capacity (about 775 cc.), notice the change in shape of the cranium. Contrast
this with the previous specimen of an A. africanus with about 450
to 500 cc. of brain capacity and with later Homo habilis and Homo
erectus specimens.
| TEST YOUR KNOWLEDGE This specimen has been identified as an A. africanus. What characteristics were used to make this decision? Why can't this be assigned to the A. afarensis group?  ANSWER? |
| ANOTHER TEST What the differences you can note in these two crania?  |
