Australopithecus aethiopicus (2.7 to 2.3 million years ago)
Australopithecus aethiopicus may be an ancestor of
two later species, Australopithecus robustus and Australopithecus
boisei. The species has a peculiar mixture of primitive and highly derived
traits relative to earlier species.
Brain size of A. aethiopicus is
comparable to that of modern apes and the much-earlier A. afarensis.
Other skull traits appear to be novel adaptations, some of which probably
allowed A. aethiopicus to exploit tougher food sources. The massive
face was flat or concave with no forehead.
A very large sagittal crest (a
ridge of bone running along the top of the skull) and other heavily reinforced
areas of the skull would have provided strong points of attachment for chewing
muscles. Powerful chewing muscles, paired with the species' extremely large
and thickly enameled molars and premolars, suggest that A. aethiopicus
ate very tough, grainy foods that required a great deal of processing.
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