The Genus Australopithecus

About 4.4 millions years ago, a different type of primate emerged.
The first bipedal primates are classified by Paleontologists as
hominids, and these first hominids had not yet developed the large
brain, teeth structure, and skeletal features identified as Homo.
Instead, they predate, and sometimes overlap the first Homo species
and are known as the Australopithecines. The two types of
australopithecines are gracile and robust.

This species has recently been found in the Lake Turkana region in Kenya and dates back to 4 million years ago. Though not recognized as such for 30 years, the first Australopithecus anamensis discovery occurred in the Kanapoi region of East Lake Turkana in 1965 by a Harvard University expedition. The initial find consisted of a partial left humerus. Aside from a solitary molar discovery in 1982, virtually no further A. anamensis specimens were found until the early 1990's, at which time, Meave Leakey and other affiliates of the National Museums of Kenya organized a research team for the Kanapoi region.

Around 3.9 million years ago, A. anamensis evolved into Australopithecus afarensis. It provides the first fossil evidence as the first and earliest biped. The Australopithecus anamensis tibia indicates bipedalism. It is the first species to walk upright!

The cranial capacity of the Australopithecus anamensis is unknown. Male height is around 5 feet, while the females are around 4’3”. The male weight is around 110 lbs, while the female weight is around 70 lbs. Their teeth and jaws are hominid but have some similarities to the chimpanzee. They retained ape-like crania and dentition, while also exhibiting rather advanced postcrania, more or less typically hominid-like in form. The joints on their leg bones indicate bipedal gait.

Australopithecus afarensis was named as a species in 1978 by D. Jonhanson and T. White. It is one of the better know Australopithecines because a large number of fossils have been found and attributed to this species. Fragments of more than 300 individuals of Australopithecus afarensis have been discovered so far in Tanzania, Kenya and Ethiopia. Australopithecus afarensis lived from approximately 4.1 to 2.7 million years ago in northeastern Africa.

The most famous specimen is “Lucy,” a nearly complete skeleton found in 1974 at Hadar, Ethiopia. The illustration on the right shows "Lucy" in comparison with a modern human female. She was only about 3 feet, 8 inches tall. Males were somewhat taller and twice as robust (sexual dimorphism).

A. afarensis is still very apelike but does have some characteristics of Homo sapiens . For example,“Lucy’s” overall body size, brain size and skull shape resemble a chimpanzee. However, A. afarensis walked upright like a human, not like a chimp. Evidence for bipedalism comes from skeletal fossils showing pelvis articulation and femur (thigh bone) similar to humans. Irrefutable evidence comes from the Laetoli footprints. There is no tool making associated with A. afarensis.

Many scientists believe Australopithecus afarensis was still active in trees because the fingers and toe bones of the species were curved and longer than the ones of the modern human. Also, its upper torso is stronger than ours and its arm and leg lengths are similar which also indicates the species was adapted to tree climbing.

A. bahrelghazali was discovered by Michel Brunet in 1993, in the ancient riverbed of Bahr el Ghazal in Chad, located 2,500 kilometers west of the East African Rift Valley. This is currently the first and only australopithecine specimen to be found in North-Central Africa, and is also the furthest west of any specimen found to date.

There are arguments against the case for A. bahrelghazali being its own species because of its resemblances to Australopithecus afarensis . However, the mandibular symphysis is more modern in appearance than that of A afarensis. Although the species designation of Australopithecus bahrelghazali is a new one, it is currently gaining more and more support among scientists.

Raymond Dart discovered the first australopithecine in November, 1924. The fossil was found at a lime quarry at Taung, southwest of Johannesburg, and was of an immature apelike individual. The fossil existed of the face, part of the cranium, the complete lower jaw and a brain endocast, formed when sand inside the skull hardened to rock, recording the shape of the brain.

Dart stated that the Taung individual was an earlier form of human, and named it Australopithecus africanus ("southern ape from Africa"). Australopithecus africanus appeared to be apelike in having a protruding face and small brain, but had distinctly unapelike dentition, including small canines and large, flat molars. A bipedal posture was again indicated by the central position of the foramen magnum, and by the anatomy of the spine, pelvis, and femur.

Australopithecus garhi was believed to have existed between 2 and 3 garhi
million years ago in the middle Awash region of Ethiopia. The first
parts of garhi to be discovered were the skull, teeth, and limb bones
and were found by Berhane Asfaw and Tim White. This was a significant
and surprising find because garhi had a small brain, yet used and made
tools to crack open the limb bones of animals in order to get to the
nutrient-rich marrow at the center of the bone. Fittingly, the word
garhi means surprise in the local Afar language of Ethiopia. Before the
discovery of A. garhi, the first tool users were thought to be of the
Homo genus. A. Garhi, therefore, is thought to have been a link between
Australopithecus and Homo because of the small brain/tool using
combination. A. garhi appeared to exist during the hypothetical tunnel
of time, from which species went in at about 3 million years not using
tools, not very well adapted to their environment, and with small brains
and came out at about 2 million years ago using tools, well adapted to their environment, and with large brains.

www.modernhumanorigins.com/garhi.html

http://www.ashtonfarm.demon.co.uk/early_hominid_evolution/a_garhi.htm

http:// biology.about.com/library/weekly/aa042999htm