The later australopiths

The australopiths lived on in Africa through the late Pliocene and earliest Pleistocene, from about 3 to 1.4Myr ago, and there were as many as six species: Australopithecus africanus and Paranthropus robustus from southern Africa, A. garhi, P. boisei and P. aethiopicus from eastern Africa (Ethiopia, Kenya, Malawi) and A. bahrelghazali from Chad (Asfaw et al., 1999; Wood and Collard, 1999). There were two size classes of australopiths living in Africa at the same time (Figure 11.10), the lightly built, or gracile,A. africanus,whichwas typically 1.3 m tall, 45 kg in body weight and had a brain capacity of 445 cm3, and the heavier P. aethiopicus, P. robustus and P. boisei, which were 1.75m tall, 50kg in body weight and had a brain capacity of 520 cm3.

These australopiths show advances over Praeanthro-pus afarensis in the flattening of the face, the loss of the diastema and the small canine teeth. They show some specializations that place them off the line to modern humans. For example, the molars and premolars are more massive than in A. afarensis or Homo, and they are covered with layers of thick enamel, adaptations in this lineage to a diet of tough plant food.

The robust australopiths, species of Paranthropus, have broad faces, huge molar and premolar teeth and a heavy sagittal crest over the top of the skull in presumed males (Figure 11.10(b)). These are all adaptations for powerful chewing of tough plant food. The sagittal crest supports this interpretation because it marks the upper limit of jaw muscles that were much larger than in A. africanus or in Homo. The robust australopiths may

Fig. 11.10 Skull proportions of the australopiths: skulls of (a) Australopithecus africanus, (b) Paranthropus robustus and (c) P. boisei in anterior (top) and lateral (bottom) views. (Modified from Tobias, 1967.)

have fed on tough roots and tubers, and the gracile A. africanus perhaps specialized on soft fruits and leaves in the wooded areas.

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