Реферат: The Earliest Hominines Essay Research Paper The

ascribed to A. afarensis, despite suggestions that the wide variation in size of

individuals may mean the presence of 2 species. It is likely, however, that A.

afarensis size differences represent sexual dimorphism similar to Miocene apes and

intermediate between the greatly dimorphic modern gorillas and the less dimorphic

chimpanzees.

Other East African sites have yielded fossils similar to A. afarensis or A.

africanus. These sites are all 2 million or more years old. The individuals ranged

between 3.5 and 5 feet, with weights of between 29 and 45 kg.

Australopithecus afarensis and A. africanus are considered to be “gracile” or

smaller australopithecines. These two species possessed small incisors, short

canines in line with the other teeth, and a rounded dental arch. No gap between the

canines and incisors in the upper jaw (diastema), as seen in apes, was present. The

molars and premolars were larger than those of modern humans, but were similar

in form. Tooth wear indicates that these species chewed as humans do, but with 2

to 4 times the force. The diet was largely tough, fibrous vegetation. A. afarensis

individuals tend to show more sivapithecine features, such as a less-rounded dental

arch, less shearing tooth wear, slight diastema, and some canine projection, than

the later A. africanus individuals. These sivapithecine features suggest a Miocene

sivapithecine-like ancestor.

Some sex differences have been noticed in these two australopithecines: males

seem to develop a bicuspid first lower premolar while females do not; and females

seem to possess skeletal features better suited to tree-climbing than males. These

differences suggest that males and females may have had slightly different foraging

strategies, with males spending more time on the ground and females exploiting

trees.

Cranial capacity of A. afarensis was 310 to 500 cc and that of A. africanus was

428 to 510 cc (roughly the size of a chimpanzee and 1/3 that of a human);

intelligence, however, is more a factor of the ratio of brain to body size.

Unfortunately, the vast rang of body sizes in these forms makes this ratio difficult