I skimmed the thread and didn't see anything on this, so I apologize if I am retreading old info . . .
"Here we present evidence that fossils attributed to Australopithecus anamensis (KNM-ER 20419) and A. afarensis (AL 288-1) retain specialized wrist morphology associated with knuckle-walking. This distal radial morphology differs from that of later hominids and non-knuckle-walking anthropoid primates, suggesting that knuckle-walking is a derived feature of the African ape and human clade.."Nature - Not Found
Last I saw there was some some controversy on this. I can't read that article with my limited sign-in.
message me -- can you email a copy?
We don't see knuckle walking with Ardi, and that is after the common ancestor date.
*** update ***
caffeine sent a link to the paper on line: Evidence that humans evolved from a knuckle-walking ancestor
and noted that it was 10 years old, and more recent analysis backs away from the knuckle walking, which jibes with my recollection of the controversy.
I did a search on australopithicine knuckle walking?
and found this update:
The ancestors of gorillas and chimpanzees are suggested to have become more specialised in climbing vertical tree trunks, using a bent hip and bent knee posture that matches the knuckle-walking posture they use for ground travel. This was due to climate changes around 11 to 12 million years ago that affected forests in East and Central Africa, so periods occurred when openings prevented travel through the tree canopy, and at these times, ancestral hominids could have adapted the erect walking behaviour for ground travel. Humans are closely related to these apes, and share features including wrist bones apparently strengthened for knuckle-walking.
However, the view that human ancestors were knuckle-walkers is now questioned since the anatomy and biomechanics of knuckle-walking in chimpanzees and gorillas are different, suggesting that this ability evolved independently after the last common ancestor with the human lineage. Further comparative analysis with other primates suggests that these wrist-bone adaptations support a palm-based tree walking.
So convergent evolution for chimp and gorilla knuckle walking and palm-based tree walking for Australopithicus.
Palm-based tree walking has also been suggest for Ardi as explanation for development of bipedalism.
Ardi Is a New Piece for the Evolution Puzzle
... Her wrist, hand and shoulder bones show that she wasn't a knuckle walker and didn't spend much time hanging or swinging ape-style in trees. Rather, she moved along branches using a primitive method of palm-walking typical of extinct apes. "[Ardi is] a lovely Darwinian creature," says Penn State paleoanthropologist Alan Walker, who was not involved in the discovery. "It has features that are intermediate between the last common ancestor and australopithecines."
caveat: that article is 8 years old.
ps -- questions like this are why I love this place.
Edited by RAZD, : update