EUGENE M. MCCARTHY, PHD Google+ Profile
Remains of this extremely ancient hominid were first discovered in 1992. Anthropologist Tim White, of the University of California, Berkeley, led the team making the find.
White et al. (1994) initially assigned the material to Australopithecus, but later claimed that the creature they had found was different from australopithecines — different enough to deserve a new genus, Ardipithecus, of its own (White et al. 1995).
Specimens. The first fossils recovered were pieces of the cranium, a mandible, teeth, and arm bones. Additional fragments recovered in 1994, together with the previous finds, added up to about 45 percent of the skeleton. This was the now famous "Ardi", a 50-kilogram (110 pound) female. Ultimately, the material recovered included most of the cranium, as well as the hands, feet, and pelvis. All of this material was unearthed from Pliocene strata at a site named Aramis, near the Middle Awash River, in the Afar Depression, Ethiopia (see map at right).
Later, between 1999 and 2003, a team headed by Sileshi Semaw, of Indiana University, discovered fragmentary remains from nine separate Ardipithecus ramidus individuals at As Duma in the Kada Gona valley on the western margin of the Afar.
Between apes and australopithecines. All specimens presently assigned to Ardipithecus ramidus date to around 4.4 mya and show a mixture of ape-like and australopithecine-like features. Because Ardipithecus ramidus shares certain characteristics with apes, some experts think it's an ancestor of chimpanzees instead of humans. A growing consensus, however, seems to consider it close to a common ancestor of both apes and humans since its teeth are intermediate between those of earlier apes and Australopithecus afarensis.
Small brain. The brain size of this hominid is on the small side, even for an ape. The cranial capacity is between 300 and 350 cc — smaller than that of the typical chimpanzee, and considerably smaller than that of a gorilla. It is smaller, too, than the usual australopithecine's — less than a quarter the size of a modern human's.
Bipedalism. According to an analysis of the postcranial material presented in a package of articles published in the journal Science, Ardipithecus ramidus was bipedal when on the ground, but went on all fours when climbing trees, as is, of course, the case with modern humans. However, unlike modern humans, this hominid had a big toe that could grasp branches (see figure, left).
Diet. Wear patterns on dental remains indicate Ardipithecus ramidus was omnivorous, eating a broad range of foods, but that it did not eat many items that were fibrous, hard, or abrasive (Teaford and Ungar 2000). However, since stone tools (and fire) were still far in the future, meat must not have been consumed with any regularity. A recent paper (Harmand et al. 2015) reports the discovery of the oldest known tools, but dating to between 3.11 and 3.33, they are at least a million years younger thatn Ardipithecus ramidus. mya. Previously, the oldest known stone tools were only from about 2.5 mya (Semaw et al. 1997, Semaw 2000) — nearly two million years later than all known fossils of Ardipithecus ramidus.