Researchers currently believe the evolutionary split between humans and apes occurred 5-7 million years ago; to date, nobody knows which species provides the "missing link" between humans and apes. Many believed it was australopithecus (or, "southern ape"), dubbing it and its cousins: "ape-men". Unfortunately, further research would prove otherwise.
The species under the genus australopithecus represent some of the earliest known relatives of modern humans. The different species are (listed in order of their presumed evolution):
Australopithecus Anamensis Fossils
Australopithecus Anamensis
Originally discovered in Kenya (1965), anamensis existed about 4 million years ago, and provides first evidence that hominids were bipedal (walked on two legs).
Australopithecus Afarensis
Roughly 3-4 million years old and standing 3-4 ft, afarensis is still more ape than human, particularly in the face/jaw. Afarensis also has long, powerful fingers which are specialized for tree climbing. "Lucy" (Ethiopia, 1974) is the most famous afarensis fossil; when discovered she was the oldest, most complete skeleton of an early hominid
Australopithecus Africanus
Although originally believed to be between 2.5-3.5 million years old, recent study places africanus closer to 2-2.5 million years old, making it much younger (and, presumably, more evolved) than previously thought. Africanus is the first of the genus to be discovered and represents one of the last known hominids before modern human (it is among the first to be more human than ape, and believed to be a direct descendent of modern man).
Africanus stands 3.5-4.5 ft tall, weighing upwards of 100 pounds (slightly larger than a modern chimpanzee). It boasts a larger brain than afarensis, human characteristics in the face, and modern hands (adapted for manipulation instead of climbing).
In addition to the "Taung Child" (1924), South Africa claims numerous other significant finds, such as "Mrs. Ples". The most complete australopithecine skull ever discovered got her name because she existed in the Pleistocene era (recent study suggests "Mrs." is really a "Mr."!).
Australopithecus Garhi
First discovered in Ethiopia (1997), garhi represents one of the many questions marks in evolution theory. It is thought to have existed 2.5 million years ago, making it a contemporary of Africanus. The mystery: garhi has a smaller brain than Africanus and retains much of the primitive facial structure of afarensis. Nevertheless, its mouth is more comparable to modern humans than Africanus. Researchers have long assumed that evolution occurs in a linear fashion, with younger species possessing more "advanced" features than older ones. Garhi complicates this assumption as it seems to be a evolutionary step backward.
New age estimates for Africanus suggest it is younger
than garhi, which could account for some of garhi's more
primitive characteristics. Garhi may represent a genetic dead-end--a
line that never made it. It could also be a very early species of modern
man. That's
the fun part:
NOBODY KNOWS!!!
LATE-BREAKING NEWS
As of January, 2003, new research has anthropologists reconsidering their notions regarding australopithecus. An Australopithecus (species undetermined) discovered in 1998 (Sterkfontein, South Africa) provided a wealth of information regarding australopithecine anatomy. Additional bone fragments from this discovery have since been extracted and examined, revealing an australopithecus that was much more human-like than previously believed, particularly in the body and legs/feet. The new data suggest australopithecus was a full time biped, but likely spent most of its life in the trees.
If true, australopithecus would have modern anatomical features believed to have taken millions of years to develop. This would place the split between humans and apes much further back on the evolutionary scale. These modern features also seem to confirm a new analysis of the famous "Mrs. Ples" fossil, which indicates "Mrs. Ples" is up to 1 million years younger than previously believed (and a male!). This places Africanus further up on the evolutionary scale which, in turn, implies a more advanced physiology.