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Ardipithecus ramidus ("Ardi")
The world’s oldest and most complete skeleton of a potential human ancestor — named “Ardi,” short for Ardipithecus ramidus — has been unveiled by an international team of 47 researchers.
Their unprecedented, 17-year investigation of Ardi is detailed in a special issue of the journal Science.
The 4.4 million-year-old hominid opens up a new chapter on human evolution because “it is as close as we have ever come to finding the last common ancestor of chimpanzees and humans,” project co-director Tim White told Discovery News.
“This is not an ordinary fossil,” added White, a paleontologist in the University of California at Berkeley’s Human Evolution Research Center. “It’s not a chimp. It’s not a human.”
Instead, he said, “It shows us what we used to be.”
Placement on the Human History Timeline
The actual last common ancestor of chimps and humans probably lived between five and 10 million years ago, based on genetic and other estimates, so Ardi falls somewhere between this still unknown species and “Lucy,” the famous 3.2 million-year-old “ape-man” hominid, also found in Ethiopia, belonging to the genus Australopithecus.
“If you dig up in younger time horizons at the site where Ardipithecus was found you have Australopithecus, so we feel that we are in a position to say that Ardipithecus may have given rise to Australopithecus, which in turn gave rise to Homo (sapiens),” White said.
Ardi, who was a female, may or may not have had any direct descendants. Her species may have given rise to Lucy’s species, Australopithecus.
Bones Reveal Appearance and Behavior
Gen Suwa, one of the project’s paleoanthropologists, spotted the very first Ardipithecus fossil in 1992 while conducting a foot survey in the Afar Rift in northeastern Ethiopia. Since that time, a total of 110 specimens representing a minimum of 36 different individuals of Ardi’s species have been found within a sediment layer at the site that was precisely dated using multiple established techniques.
Ardi is the most complete of these individuals, as the skeleton includes her skull, teeth, arms, hands, pelvis, legs and feet. Based on these findings, the researchers know that she and others in her species were both tree- and land-dwelling omnivores. They had a relatively small, chimp-sized brain, long arms and short legs.
The scientists suspect Ardi used simple tools, such as twigs and leaves, but no stone tools were found at the dig site.
“Believe me, we’ve looked for them,” said White, who added that the earliest known stone tools date to 2.6 million years ago.
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