Re: arm movement (wasRe:book review)

[Nick Longrich <longrich@phoenix.Princeton.EDU>]

On Tue, 5 Nov 1996, Cunningham, Betty wrote:

> Ron Orenstein wrote:
> 
> >That is to use both hands as opposite tines of a pair of tongs,
> >operating towards the midline (or together, like the arms of a
> >mantis).  In that case I would expect the lines of force to be
> >directed along the anterior (internal) digits as these reach
> >farthest forward, with the lateral digits being much less useful.
> >Such a function would explain how the outermost digits came to be
> >lost.
> 
> Squirrels have this sort of use of the arms to pinch things towards their   
> mid-line while they are eating; the hands they have are very useful for   
> manipulating the item with finer dexterity.  But if you watch closely,   
> most manipulation comes from their elbows and shoulders. not the wrists   
> or the fingers.  These seem primarily as an aid to gripping, not   
> manipulating.

        I've been thinking about dinosaur climbing, using dromaeosaurs.
What I've been tossing about in my head is this- swing the arms, palms
inward toward the trunk of a tree. Then bring the legs up, and kick in
with the hyperextendible second toe, into the bark- when you've got a
grip, extend the arms up further, latch on, and then raise the legs up
again. In this way, a theropod could climb, without having to evolve the
sprawling stance of a squirrel, but which would get the forelimbs way out
to the side- also effectively preventing the evolution of a fore-hind limb
patagia. The motions are more or less similar to what the animal would use
in killing it's prey, actually. I don't know how actually, anatomically,
feasible this would be. 

        nick L.