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arm movement (wasRe:book review)



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.

How would this sort of manipulation fit in with T rex being a
wimpy-armed bugger? If Jack Horner is correct in his idea that the arm
was not separate from the body till the elbow, what kind of outwards
opening motion could it do?  All in and out motion towards the midline
would have to come from motion only at the elbows or wrist.  Or that
wierd Mongolian dinosaur with a fused hand/wing-sort-of-thing with a
big spike claw on the end of it (I'm at work with no dino refs-can't
look up the name)?  [ Mononykus -- MR ] Or the mighty big-clawed
dinosaur that's a relative (possibly) of Baronyx (the one that all
we've ever found was the mighty big arms)?  [ I'd say deinochirus, but
if so then you've got the affinity wrong.  -- MR ]

What kind of shoulder motion can you have without that coricoid bone   
acting as a collarbone? How much with one? How much if you compare the   
motion possible for a corocoid to a collarbone?  To a wishbone?  Is there   
much ability for a swing of the arms perendicular to the line of the body   
as opposed to the one normally found in all dinosaurs, where the swing is   
in parallel to the line of the body.  (Am I being clear here? I mean   
something like the motion to L and R, not the more regular motions of A   
and B).  Just how open can you move the arms?

.                  O(head)
.                 ()
.                 !
.           A   !    B
 .           I    !    I
 .             \  !  /
.L   <----------!---------->  R
.               / ! \
.             I   !   I
.           A   !    B
.                !
.                !
.              HH  (hips)
.                !                                -Betty Cunningham