Re: An alternative to ST and AAT

Rohinton Collins (
31 Oct 1996 20:48:10 GMT

pete <VINCENT@reg.Triumf.CA> wrote in article
> Rohinton Collins ( sez:
> The LCA, assuming it was an
> `arboreal quadruped, would be more predisposed to bipedality than the
> `since much of the time it would have stood on two feet, steadying itself
> `grasping upper branches, or reaching for fruit. The valgus angle
> `(femur/tibia angle) would most likely more closely match hominids than
> `African apes (note the orang-utan has a hominid-like valgus angle and is
> `largely arboreal) which would also aid the transformation to bipedality.
> The idea of an arboreal quadruped which spends much of its time standing
> on two feet is somewhat ambiguous. What exactly do you have in mind here?
> Do you consider the gibbon to be an arboreal quadruped? It uses all four
> limbs for locomotion, but uses the front pair quite differently from the
> back.

Fair enough Pete, I may have not explained myself well enough. What I meant
by an arboreal quadruped is an ape which uses all four limbs for
locomotion, but being arboreal, has much flexibility of locomotion and
posture (the orang-utan would probably be a good model). The chimpanzee has
a rather restricted mode of locomotion, since it is a fully adapted
terrestrial quadruped (N.B. small valgus angle). So, what I am saying is
that my LCA would have been more predisposed to the transformation into a
terrestrial biped than would be a proto-chimp LCA. And no, the gibbon is a
brachiator. I would say that a gibbon-like LCA (in its mode of locomotion)
would be unlikely because brachiation is specialised. What it comes down to
is that a more generalised LCA (in all ways, as well as locomotion) would
be more predisposed to take advantage of a new (or a forced) mode of
locomotion than a more specialised ape would be.

Clearer? I hope so. ;-)