The immediate ancestors of humans were members of the genus Australopithecus .  The australopithecines  were intermediate between apes and people.  However, both australopithecines and humans are biologically similar enough to be classified as members of the same family--the Hominidae .  All people, past and present, along with the australopithecines are hominids .  We share in common not only the fact that we evolved from the same ape ancestors in Africa and have relatively large brains but that both genera are habitually bipedal , or two-footed, upright walkers.  By comparison, chimpanzees and gorillas are primarily quadrupedal , or four-footed.

The earliest australopithecines very likely evolved 5 million years ago or shortly after (during the early Pliocene Epoch) in East Africa.  The primate fossil record for this crucial early transitional period is scanty and somewhat confusing at present.  However, by about 4.2 million years ago, unquestionable australopithecines were present.   By 3 million years ago, they were common in both East and South Africa.  As the australopithecines were evolving, African forests were progressively shrinking and seasonally dry grasslands, or savannas, were advancing.  In this sort of environment, bipedalism would have been an advantage.

Ultimately, there were at least 2 evolutionary lines of early hominids.  One line was adapted primarily to lake margin grassland environments and had an omnivorous diet that increasingly included meat.   They were our ancestors.  The other line seems to have lived in mixed grassland and woodland environments and was primarily vegetarian.  This second line of australopithecines died out by 1 million years ago.  It is likely that all of the early hominids, including humans, supplemented their diets with protein and fat rich termites and ants.

History of Discovery

In an 1871 publication, Charles Darwin speculated that fossils of the earliest humans and their primate ancestors ultimately would be found somewhere in Africa.  He based this on the fact that the natural range of our nearest living relatives, chimpanzees and gorillas, is limited to Africa.  He concluded that we ultimately must have shared a common ancestor with those apes in Africa.  This view was mostly rejected by the scientific world of the time.  Before the 1920's, knowledge of our fossil ancestors only went back to the Neandertals in Europe and some presumably earlier human-like forms from Java.  Few researchers were willing to estimate the time period of the earliest hominids at much more than 100,000 years, and there was no inkling of anything older from Africa.  In addition, there was a bias among the predominantly European paleoanthropologists against accepting early Africans as the ancestors of all humanity.

Raymond Dart (1893-1989)

Taung Child   (Australopithecus africanus)

In 1924, Raymond Dart, an Australian anatomy professor at the University of Witerwatersrand in Johannesburg, South Africa, obtained a fossil skull that had been blasted out of a nearby limestone quarry at Taung.  It took him 73 days to chisel the skull free from its surrounding stone matrix and ultimately 4 years of spare time to free the jaw and the fossilized brain.   However, long before then, Dart recognized the importance of this find.  In 1925 he named it Australopithecus africanus (literally "southern ape from Africa").  Because of its small size, he called it the "Taung baby."   In fact, it was a child of 3-4 years old.  Despite its relatively small brain, he concluded that this species was intermediate between apes and humans.  He based this mainly on the the shape and position of the base of the brain.  It indicated that the foramen magnum, or hole in the skull through which the spinal cord passes, pointed downward and was nearly at the central balance point of the skull.  This meant that the Taung child must have been bipedal.  In addition, the canine  teeth were relatively short.  In both of these traits, the Taung child was much more like a human than a modern ape.  Most paleoanthropologists in the 1920's rejected Dart's claims that Australopithecus africanus was intermediate between apes and humans in favor of the view that it was just an ape.   Dart's claims were not widely accepted until the late 1940's.

Robert Broom (1866-1951)

Australopithecus    africanus	Paranthropus robustus

Following Dart's discovery, several other caves were investigated in South Africa.  Most of the work was done by Robert Broom from 1936 through the 1940's.  Broom was a retired Scottish medical doctor and paleontologist at the Transvaal Museum (in South Africa).   In a cave at Sterkfontein , he found an adult Australopithecus africanus.   In caves at Swartkrans and Kromdraai , he found the remains of africanus and other early hominids that were larger boned and more muscular with powerful jaws.  Broom named them Paranthropus robustus (Paranthropus means "parallel to man").   Significantly, these robust hominids also differed in having a sagittal crest, or ridge of bone extending from front to back, along the midline of the top of the skull.   A sagittal crest serves as an anchor attachment for exceptionally large, strong jaw muscles.  This skeletal feature is also present in large apes but not in africanus or humans.  Most paleoanthropologists discarded the name Paranthropus robustus by the 1960's in favor of Australopithecus robustus.  However, the current trend has been to return to the original name.

Leopard canines fit punctures in hominid skull from Swartkrans

The cave at Swartkrans was carefully reinvestigated by C. K. Brain between 1965 and 1983.   Many thousands of bone fragments, including the remains of 130 individual hominids, were recovered.  These bones were from both species of early hominids identified before as well as members of our genus, Homo.  Because many of the bones had chewing marks and at least one of the skulls had peculiar depressions reminiscent of punctures made by the canine teeth of a leopard, Brain hypothesized that some of the Swartkrans hominids had been eaten by these big cats.  The early hominid fossil bearing strata in the cave also contained 195 stones that were from another location distant from the cave.  Brain believes that 30 of them may have been used as tools or weapons.  In any case, the presence of these stones suggests that not all of the early hominids in the cave were there as a result of being the victims of carnivores.

The earliest fossil hominids have been recovered from sites in East Africa, especially in the Great Rift Valley.  One of the most important sites there is Olduvai Gorge .  It is a 15½ mile long, eroded canyon cutting into the Serengeti Plain in Northern Tanzania.  It is only 328 feet deep, but its neatly stratified layers of dirt and rock interspersed with easily datable volcanic ash and lava layers cover the last 2 million years of geological and evolutionary history.  The remains of at least 40 australopithecines, paranthropoids, and early humans have been found at Olduvai.  When these ancient hominids lived there, it was a grassland on the edge of a lake that probably had abundant food sources. 

Mary and Louis Leakey with  a Zinjanthropus boisei palate and a modern human skull

Zinjanthropus boisei (Australopithecus boisei)

Early hominid fossils from Olduvai Gorge are known mostly as a result of the many expeditions of Louis and Mary Leakey .  Louis began work there in 1931, and his wife Mary joined him in 1935.  However, it was not until 1959 that they found their first australopithecine fossil.  Louis gave it a new genus and species designation, Zinjanthropus boisei  (literally "East African man").  Subsequently, it was recognized to be only a super robust species of australopithecine.  It is now commonly referred to as Paranthropus boisei  (or Australopithecus boisei ).  Using the then new potassium-argon dating method, the fossil was determined to be 1.75 ± .25 million years ago.  This was a startlingly early date when it was made public four decades ago.  Louis Leakey and Zinjanthropus instantly became international media stars.

Lucy (Australopithecus afarensis)

In 1974, a team of paleoanthropologists, under the direction of Donald Johanson, found an even more ancient species of australopithecine at the Hadar  site in the Afar  Desert region of Northern Ethiopia.  It was a 40% complete skeleton of an adult female whom they named Lucy.  She had been only 3.5-4 feet tall with a slender body.  She lived 3.18-3.2 million years ago.  Johanson concluded that Lucy was from a different species than had been previously discovered.   He classified her as an Australopithecus afarensis  (named for the Afar region).  Many other specimens of this species and later ones were found in Ethiopia since 1974, but none is as complete as Lucy.

Laetoli hominid footprints

About 30 miles south of Olduvai Gorge in Northern Tanzania is the Laetoli  site.  It was investigated in the late 1930's by the Leakeys, but no fossil hominids were found at that time.  After the death of Louis, in the early 1970's, Mary Leakey returned to Laetoli with Tim White, an American paleoanthropologist.  They found bones of what were likely Australopithecus afarensis dating in the range 3.7-3.5 million years ago.  They also found the footprints of 2 or 3 bipedal hominids (presumably afarensis) in a hardened volcanic ash layer.  These individuals walked in two close parallel tracks across volcanic dust at least 3.5 million years ago.  These footprints look almost like those of modern humans.  They are narrow with an arch, and they clearly show that the big toe was in line with the others.  These are all traits of humans but not of apes.  Based on the characteristics of the footprints, Mary Leakey concluded that their makers were adults who were 4 feet 9 inches and 4 feet 1 inch tall and that they walked in a strolling fashion with relatively short strides.  In addition, there are a child's footprints within those of the larger adult.

Major Australopithecine Sites

In 1995, Meave Leakey found a new, very early australopithecine species at Lake Turkana , Kenya.  She named it Australopithecus anamensis  ("anam" is "lake" in the Turkana language).  Its dentition seemed to be transitional between apes and later australopithecines.  This fits with the dating of associated volcanic ash at 4.17-4.12 million years ago.

Australopithecine fossils have been found at several other East, Central, and South African sites.  It is likely that more will be found in the near future as well.  However, it is not the intention of this tutorial to provide an encyclopedia of all australopithecine discoveries but rather to highlight some of the more important ones.

Who Were the Ancestors of the Australopithecines?

There has been a gap in the fossil hominid record for the crucial period before 4.2 million years ago when Australopithecus anamensis appeared.  New discoveries are now beginning to fill in the missing picture of evolution leading to the australopithecines at that early time.

Beginning in 1992, Tim White and several of his Ethiopian colleagues found fossils of what may be the immediate ancestor of the australopithecines at the Aramis site in the Middle Awash region of Northern Ethiopia.  The teeth of these very early hominids seem to have been transitional between apes and Australopithecus anamensis.  Among the living apes, they were most similar to chimpanzees, however, they were not apes.  These Aramis fossil hominids date to about 4.4 million years ago and may represent the first stage in the evolution of bipedalism.  Because of their primitiveness, White has given them a new genus and species designation--Ardipithecus ramidus.

Late Breaking News: In the March 22, 2001 issue of the journal Nature, Meave Leakey and six of her colleagues announced the discovery of a 3.5 million year old hominid skull found on the west side of Lake Turkana in Kenya.  This fossil may displace Lucy (Australopithecus afarensis) as the progenitor of humans.  Meave Leakey named it Kenyanthropus platyops ("flat-faced man of Kenya").  This new fossil lived during the same time period as Lucy.  However, it had a comparatively large, flat face and small teeth.  The latter characteristic suggests that Kenyanthropus regularly ate softer foods than did Lucy.  Meave Leakey suggests that more hominid fossils from the crucial time period of 3-4 million years ago must be discovered to conclusively determine the place of Kenyanthropus in our evolution.

Information provided by:http://anthro.palomar.edu