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Re: Bipedalism and Arboreality.
In the case of humans, could I suggest that proto-humans were >upright<
first due to brachiating (not tree-climbing per-se but rather swinging
from branch to branch by the arms), and then retained the uprightedness
as they went to terrestrial locomotion.
In the case of theropods to birds we'd have theropod (bipedal but not
upright) going to bipedal arborial (unknown upright or not) and ending
up at bipedal bird (semi-upright) -OR- Dinogeorge's bipedal arborial
(unknown upright or not) and splitting off to theropd bipedal (not
upright) and bird bipedal (semi-upright)
Can you support a case why the bipedal arborial sequence would need to
develop semi-uprightedness? Do you see this stage brachiating as
proto-humans did, and if so, why are birds only SEMI-upright?
> >>This assertion goes against all current knowledge and research. Early
> Australopithecines spent a lot of time in the trees and modified pelvis
> and adopted a bipedal posture while still being pretty much arboreal.
> The latest reconstruction of semi-prehensile toe of afarensis feet
> demonstrates this. They combined modern pelvises and fully erect stance
> with prehensile toes.
> In fact, the more we go backwards in hominid evolution the weirder the
> locomotion gets. Tim White was working on a model of anamensis and
> specially Ardipithecus ramidus that he said "was going to challenge
> everything we ever thought about locomotion".
> So bipedality indeed seems to have a rather complicated origin in the
> trees, not on the ground.
> If we see the way Chimpanzees walk around: it seems they resorted to a
> mid-way compromise solution in an evolution race towards full bipedality:
> In 'human terms' they seem to have come to spend too much time on the
> ground too soon!<<
> Ouch. I did say that I might be making a fool of myself. Okay, I accept the
> point. Humans were bipedal before they got onto the ground and the bipedal
> stance was convenient in that is left their hands free to manipulate, and
> allowed them to gaze over the savanna to see oncoming predators. That
> arboreal/bipedal thing may be the biggest logical hole in my testament on
> bird evolution. Bipedalism _is_ a neotonous trait in humans, though. Read
> Steven Jay Gould's article about Mickey Mouse (I don't have the book handy
> and so can't be any more specific).
Flying Goat Graphics
(Society of Vertebrate Paleontology member)