Re: Gliders to Fliers? (Was Re: Ruben Strikes Back)

[Stanley Friesen <sarima@ix.netcom.com>]

At 06:03 PM 9/25/99 -0700, dbensen wrote:
>You say that the protohumans were bipedal at their earliest stages?  I thought
>that they hadn't really become good at walking on their hind legs until fairly
>late in their development (?)

They were not *good* at it, at least compared to humans.  But they most
certainly *were* obligate bipeds from the very beginning, at least on the
ground.  (Note there is some suggestion that some species of
_Australopithecus_ may have retained the ability to brachiate).
Anatomically, they were *badly* suited to quadrupedal locomotion when not
climbing a tree.

>I may be making an idiot of myself here, but aren't most monkeys quadripedal,
>even though they live in trees?  In fact, most monkeys, especially the 
>old-world monkeys, always run on four legs when on the ground.
>
Again, there are different sorts of arboreality.  Some retain
quadrupedality, others do not.

Forms which spend most of their time moving along the top of sub-horizontal
branches tend to stay quadrupedal (this covers most monkeys, squirrels, and
cats).  Forms which spend much of their time on sub-vertical branches (like
indris), or *under* branches (like apes) tend to have their ability to
locomote quadrupedally on a horizontal surface seriously impaired.

The 'nuthatch' idea is not that far off - nuthatches spend their time on
*vertical* branches.  And they have significantly different feet than
passerine birds, indicating different stresses during locomotion.

--------------
May the peace of God be with you.         sarima@ix.netcom.com