Ardipithecus ramidus

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By EUGENE M. MCCARTHY, PHD

ardipithecus ramidus skull
Ardipithecus ramidus cranium — frontal view
After Suwa et al. (2009) Credit: T. Michael Keesey
Ardipithecus ramidus map
Ethiopia: A. ramidus fossils have been recovered from the region circled in red.
Location of Ethiopia
Location of Ethiopia
Credit: Rei-Artur
Ardipithecus kadabba: Additional fossils, discovered between 1997 and 2001, and dating to between 5.2 and 5.8 mya, first attributed to Ardipithecus ramidus (Haile- Selassie 2001), were later assigned to Ardipithecus kadabba (Haile-Selassie et al. 2004).
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.

Tim White
Tim White
Awash River
Awash River, Ethiopia
Image: Bjorg Sandkjaer
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.

ardipithecus ramidus
Skeleton of A. ramidus
Drawing: Tobias Fluegel

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).

ardipithecus ramidus
Hand bones of A. ramidus
Drawing: Tobias Fluegel
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 could not have been consumed with any regularity. The oldest known stone tools date to about 2.5 mya (Semaw et al. 1997, Semaw 2000) — nearly two million years later than all known fossils of Ardipithecus ramidus.

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Habitat: Woodland.

Diet: Omnivorous.

Synonym: Australopithecus ramidus.

Etymology: The name of this hominid is constructed from the Greek suffix -pithecus and two words from the Afar language, ardi meaning "ground" or "floor", and ramid meaning "root" (this hominid was discovered in the Afar Depression, where Afar is spoken), plus the Latin masculine ending -us. This etymology seems to indicate that White et al. intended from the outset (White et al. 1995), when they named this creature, to convey that it is on the "ground floor" — or at the very root — of hominid evolution. Whether this is actually the case remains to be shown.

Interesting facts and information about other ancient hominids:

Ardipithecus ramidus >>
Australopithecus afarensis >>
Australopithecus africanus >>
Australopithecus anamensis >>
Australopithecus bahrelghazali >>
Australopithecus garhi >>
Australopithecus sediba >>
Kenyanthropus platyops >>
Paranthropus aethiopicus >>
Paranthropus boisei >>
Paranthropus robustus >>
Orrorin tugenensis >>
Sahelanthropus tchadensis >>
Homo habilis >>
Homo rudolfensis >>
Homo erectus >>
Homo ergaster >>
Homo cepranensis >>
Homo heidelbergensis >>
Homo rhodesiensis>>
Homo floresiensis >>
Homo neanderthalensis>>
Homo georgicus >>


Are we hybrids? Many facts suggest the answer is yes. Learn more >>
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