Ardipithecus ramidus
Online Biology Dictionary
EUGENE M. MCCARTHY, PHD
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Ardipithecus ramidus (ARA-VP-6/500) — Skull, frontal view. Enlarge (Paleontological Museum of Uppsala University, Sweden) Image: Wikimedia, Conty |
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Tim White |
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| Ethiopia: A. ramidus fossils have been recovered from the region circled in red. |
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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 A. ramidus (Haile-
Selassie 2001), were later assigned
to Ardipithecus kadabba
(Haile-Selassie et
al. 2004).
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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.
Ardipithecus ramidus: Between apes and australopithecines
All specimens presently assigned to A. ramidus date to around 4.4 mya and show a mixture of ape-like and australopithecine-like features. Because 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.
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Skeleton of A. ramidus.
Drawing: Tobias Fluegel
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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, above left). In fact, this long thumb-like big toe sets A. ramidus apart from all later hominids, and not just modern humans. Ardi stood just four feet (~122 cm) tall and weighed around a 100 pounds (~45 kg).
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| 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 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 than 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 A. ramidus.
Perhaps we are not from the apes alone?
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Facts about Ardipithecus ramidus:Pronunciation: ARD-uh-PITH-ə-kəs RAHM-ə-dəs. 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. Thus the name is intended to indicate these creatures were “at the root of the ground apes.” However, this assertion has not as yet been established. |