The Earliest Hominines Term paper

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The Earliest Hominines

The first undoubted hominine discovered thus far is Ardipithecus ramidus,

which was found in 1994 and is known from 17 fragments of teeth and bone. It

dates to approximately 4.4 million years ago.

Thought to be the descendent genus of Ardipithecus is the genus

Australopithecus; individuals of this genus were bipeds while on the ground and

had ape-like brains and dexterous hands. There are at least six species of

Australopithecus: A. anamensis, A. afarensis, A. aethiopicus, A. africanus, A.

boisei, and A. robustus.

In 1924 an unusual fossil was brought to Raymond Dart, an anatomist at the

University of Witwatersrand in Johannesburg. This fossil had a curious mix of

ape-like and human-like traits. Dart named the fossil Australopithecus africanus

and claimed that, based on the forward position of the foramen magnum, the

creature was a biped.

At least four species are recognized: A. afarensis and A. africanus being

smaller and lacking the massive jaws of the two larger species, A. boisei and A.

robustus. A. afarensis and A. boisei are from East Africa, while A. africanus and A.

robustus are from South Africa. An earlier species, A. anamensis comes from

Kenya, while a single representative of a sixth species, A. aethiopicus comes from

West Turkana and is known as the "black skull" for its distinctive black staining.

Australopithecus africanus has been discovered at three South African sites:

Taung, Makapansgat, and Sterkfontein. All of these sites range in date from 3 to

2.3 mya; however, a partial foot may be as old as 3.5 million years.

Australopithecus afarensis dates to between 3.9 and 2.9 mya, and was

discovered in the 1970s and 1990s in the Afar region of northern Ethiopia.

Included in this species are the two famous finds of Don Johanson: the remarkably

complete female skeleton AL 288-1, known as "Lucy", and the collection of 13

individuals at Afar Locality 333 which has come to be known as the "First Family".

Material nearly 4 million years old from Laetoli in Tanzania has also been

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

to assess. It is believed that these two australopithcines had mental capabilities

equivalent to those of the great apes of today.

What is significant is the fact that at 4 million years ago, there existed a bipedal

hominine. Evidence supporting this fact includes: forward placement of the

foramen magnum indicating a head balanced atop the spinal column; human-like

curvature of the spine; forearms shorter than those of an ape indications of a lower

centre of gravity than apes; the Laetoli footprints; and hip and knee anatomy. On

the other hand, these australopithecines still retained a slightly divergent great toe

and shoulder girdle well suited for climbing.

Bipedal locomotion preceded any increase in brain size; in fact,

australopithecines lacked the prolonged maturation of modern humans and likely

matured as apes do. Upright walking set the stage for larger brain sizes but was

not the sole cause of these later increases.

Robert Broom and John Robinson first discovered Australopithecus robustus,

a larger, more robust australopithecine, in 1948 at the...

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