The Pliocene Environment and Hominin Diversity 159Using patterns of tooth eruption in young australopith-
ecines such as Taung, paleoanthropologist Alan Mann and
colleagues suggest that the developmental pattern of aus-
tralopithecines was more humanlike than apelike,^12 though
some other paleoanthropologists do not agree. Evidence
from the recent discovery of the young A. afarensis speci-
men (Lucy’s baby) will help scientists to resolve this debate.
Our current understanding of genetics and the macroevolu-
tionary process indicates that a developmental shift is likely
to have accompanied a change in body plan such as the
emergence of bipedalism among the African hominoids.
Other South African sites have yielded fossils whose
skulls and teeth looked quite different from the gracile aus-
tralopithecines described above. These South African fossils
are known as Australopithecus robustus. They are notable for
having teeth, jaws, and chewing muscles that are massive (ro-
bust) relative to the size of the braincase. The gracile forms
are slightly smaller on average and lack such robust chew-
ing structures. Over the course of evolution, several distinct
groups of robust australopithecines have appeared not only
in South Africa, but throughout East Africa as well.Robust Australopithecines
The remains of robust australopithecines were first found at
Kromdraai and Swartkrans by South African paleoanthro-
pologists Robert Broom and John Robinson in the 1930s
in deposits that, unfortunately, cannot be securely dated.
Current thinking puts them between 1 and 1.8 mya. Usually
referred to as A. robustus (see Table 7.1), this species pos-
sessed a characteristic robust chewing apparatus including a
sagittal crest running from front to back along the top of the
skull (Figure 7.11). This feature provides sufficient area on
a relatively small braincase for attachment of the huge tem-
poral muscles required to operate powerful jaws. Present in
robust australopithecines and gorillas today, the sagittal crest
feature provides an example of convergent evolution.as was a partial foot skeleton (Figure 7.10) described in
1995.^9 The other South African remains are difficult to
date. A faunal series established in East Africa places these
specimens between 2.3 and 3 mya. These specimens are all
classified in the australopithecine species named by Dart—
A. africanus, also known as gracile australopithecines.
The reconstruction of australopithecine biology is
controversial. Some researchers think they see evidence
for some expansion of the brain in A. africanus, while oth-
ers vigorously disagree. Paleoanthropologists also com-
pare the outside appearance of the brain, as revealed by
casts of the insides of skulls. Some researchers suggest that
cerebral reorganization toward a human condition is pres-
ent,^10 while others argue the organization of the brain is
more apelike than human.^11 At the moment, the weight of
the evidence favors mental capabilities for all gracile aus-
tralopithecines as being comparable to those of modern
great apes (chimps, bonobos, gorillas, orangutans).
gracile australopithecines Members of the genus Australopith-
ecus possessing a more lightly built chewing apparatus; likely had a
diet that included more meat than that of the robust australopith-
ecines; best represented by the South African species A. africanus.
robust australopithecines Several species within the genus
Australopithecus, who lived from 2.5 to 1.1 million years ago
in eastern and southern Africa; known for the rugged nature
of their chewing apparatus (large back teeth, large chewing
muscles, and a bony ridge on their skull tops for the insertion of
these large muscles).
sagittal crest A crest running from front to back on the top
of the skull along the midline to provide a surface of bone for
the attachment of the large temporal muscles for chewing.Figure 7.10 Drawing of the foot bones of a 3- to 3.5-million-
year-old Australopithecus from Sterkfontein, South Africa, as
they would have been in the complete foot. Note how long and
flexible the first toe (at right) is. This is a drawing of the StW
specimen referred to in this chapter’s Original Study.
(^9) Clarke, R. J., & Tobias, P. V. (1995). Sterkfontein member 2 foot bones of
the oldest South African hominid. Science 269, 521–524.
(^10) Holloway, R. L., & de LaCoste-Lareymondie, M. C. (1982). Brain
endocast asymmetry in pongids and hominids: Some preliminary findings
on the paleontology of cerebral dominance. American Jour nal of Physical
Anthropology 58, 101–110.
(^11) Falk, D. (1989). Apelike endocast of “ape-man” Taung. American Journal
of Physical Anthropology 80, 335–339.
(^12) Mann, A., Lampl, M., & Monge, J. (1990). Patterns of ontogeny in
human evolution: Evidence from dental development. Yearbook of Physical
Anthropology 33, 111–150.