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Ardipithecus ramidus ('Ardi')
4.4 million years ago (Ethiopia)· Fossil or site· Human ancestors & us
Well establishedStrong fossil, genetic or geological evidence.
A 4.4-million-year-old partial skeleton from Ethiopia, nicknamed Ardi, showing an early hominin that both climbed trees and walked upright.
See it on the Life map →What happened
Ardi is a female Ardipithecus ramidus, about 1.2 meters tall and roughly 50 kg, found at Aramis in Ethiopia's Middle Awash valley. Tim White's team found the first fragments in 1992 and her skeleton in 1994, then spent 15 years freeing and studying the crushed, fragile bones before publishing in 2009. She had a grasping big toe, long arms, a small brain and small canine teeth, yet her pelvis suggests upright walking on the ground.
Why it matters
Ardi suggested that our last common ancestor with chimpanzees was not very chimp-like, and that upright walking began in woodland rather than open savanna. Both points are debated.
The evidence (fossils, genes, rocks)
Over 100 specimens from at least 36 individuals at Aramis, dated by argon–argon dating of volcanic ash layers, plus fossil plants and animals showing her environment; 11 papers in Science, 2009.
Still debated
How upright she walked depends on a digitally rebuilt, crushed pelvis. Whether her habitat was woodland or more open grassland is disputed.
Connections (2)
▸Ardipithecus ramidus ('Ardi') mixes climbing with early Walking on two legsStrong evidence
The connection
Ardi's pelvis and feet suggest a creature that walked upright on the ground but still climbed easily. Her big toe was splayed for grasping branches, yet her upper pelvis was reshaped for upright walking. To her finders, this mix shows two-legged walking began in a tree-climbing ape in woodland, not in a savanna runner.
When and how
Aramis, in Ethiopia's Middle Awash valley, about 4.4 million years ago; skeleton excavated from 1994 by Tim White's team and described in 2009.
How sure are we?
The partial skeleton includes pelvis, hands and feet. But the pelvis was crushed and rebuilt digitally from scans, so readings of how she walked rest on reconstruction.
Debates and open questions
Some anatomists doubt the pelvis reconstruction and question how upright Ardi really walked; others doubt that bipedalism began in woodland, as her finders argue.
▸Ardipithecus ramidus ('Ardi') may be ancestral to AustralopithecusDebated
The connection
Ardipithecus is older and more apelike than Australopithecus, which appears about 4.2 million years ago in the same region. Its finders think Ardi's kind, or a close cousin, evolved into the earliest Australopithecus, A. anamensis, which walked more efficiently and relied less on climbing.
When and how
Middle Awash, Ethiopia: Ardipithecus at Aramis about 4.4 million years ago, and Australopithecus anamensis at nearby Asa Issie about 4.2–4.1 million years ago.
How sure are we?
Both appear in the same valley a few hundred thousand years apart and share some tooth traits. But no fossil shows the actual transition.
Debates and open questions
Some researchers see Ardi as a side branch, or even doubt it is a hominin at all. With so few fossils, the exact ancestor of Australopithecus is unknown.