Australopithecus
 

All members of the genus Australopithecus are found in Africa.  Their fossil record extends from 4.4 to 1.0 million years ago.  They looked a lot like bipedal chimpanzees, with long arms and short legs, as well as slight curvature in the finger and toe bones, which indicates a hand and foot structure that was still adapted for climbing trees.  While they may have spent some time in the trees, possibly sleeping there, Australopithecines were primarily terrestrial, bipedal animals, and were most comfortable walking on two legs.  However, their form of bipedalism was different from ours.  One of the species of Australopithecines was the ancestor of the genus Homo, but no one knows which Australopithecine it was.

Species of Australopithecus:

Ardipithecus ramidus (4.4 mya*)
Australopithecus anamensis (4.2 - 3.8 mya)
Australopithecus afarensis (3.7 - 3.0 mya)

Gracile Australopithecines
Robust Australopithecines
Australopithecus africanus (3.0 - 2.5 mya) 
Australopithecus aethiopicus (2.7 - 2.3 mya)
Australopithecus garhi (2.5 mya)
Australopithecus boisei (2.2 - 1.0 mya)

Australopithecus robustus (2.0 - 1.4 mya)

*mya = million years ago


Who is "Lucy"?

Australopithecus afarensis existed from 3.7 to 3.0 million years ago.  The most famous specimen of A. afarensis, and the first to be discovered, is "Lucy", which is a 40% complete skeleton that dates from 3.18 million years ago.  "Lucy" is often assumed to have been a female animal because of the nickname given to it, but there is actually no way to know whether it was male or female.  When examining skeletal remains, the gender of hominids, including modern humans, is usually identified by the width of the pelvis, the females having wider pelvises so that they can give birth to infants with large brains.  But the brain of A. afarensis was too small (about 450 cc. in adults) to require an enlarged female pelvis for birth, so the pelvises of females look no different than the pelvises of males.  Thus the nickname "Lucy" is misleading, but it is certainly easier to remember than the skeleton's ID number, which is AL-288-1.
A. afarensis is also given credit for the fossilized hominid footprints at Laetoli, in Tanzania.  The footprints are 3.5 million years old, and give definite evidence of bipedal locomotion.  They appear to be made by a pair walking side by side very close to one another, followed by a third individual walking in the tracks of the one just ahead.  Some believe that this represents an adult male and an adult female walking side by side, with an offspring following; hence the popular nickname for this group of animals: the First Family.  When these were discovered several magazines featured illustrations of hairy ape-men walking with their arms around each other.  However, as we all know, it is impossible to determine gender and relationship status from footprints, so while this explanation is touching, it is not scientifically proven.  All that the footprints tell us for sure is that A. afarensis walked upright.
A. afarensis is often assumed to be the ancestor of all species of Australopithecines arising later than 3 million years ago.  It was discovered in 1974 by Don Johansen, and is named after the Afar tribe of Ethiopia, who live in the region where Lucy was discovered.