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RE: semi-lunate carpal questions



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Chris Fisher
>
>
> My deepest apologies if I am dredging up a controversial topic.
>
> I have 2 questions:
>
> 1. In maniraptorans, does the semilunate carpal restrict the dorsoventral
> movement of the manus? In other words, does the development of
> this element
> (from fused distal carpals 1 and 2?) restrict the ability of the hand to
> move "up" and "down", and limit it to moving mostly "sideways"
> (laterally)?
>
> 2. In maniraptorans, does the semilunate carpal restrict the
> movement of the
> fingers?
>
> Any help would be hugely, greatly appreciated.

Time for a little maniraptoran role-play... :-)

Hold your hands in front of you, palms facing inwards (i.e., hands
parallel).

Moving only at your wrists, move your hands up and down.  This is the motion
permitted by the semilunate carpal: a lot more degrees of motion than we can
get with our hands, though.

Moving only at your wrists, move your hands inward (so your palms face
towards you and your arms make something approximating an right angle like a
wrist).  If you were a maniraptoran, you would have popped your wrists WAY
out of joint.  This motion is not possible for a maniraptoran.

Put your hands back in the starting position.  Moving only at your fingers,
curl your fingers inward.  This motion (albeit in slightly different planes
and different degree angles) is permitted by a maniraptoran hand.  As you
can see, this is essentially indepedant of the wrist.

For additional fun and elucidation, play with chicken wings or turkey wings
the next time you have chicken or turkey.  The motion possible at the wrist
is proscribed by a modified semilunate carpal.  Pop the manus off of the
forearm of the chicken wing to see the pulley-shaped morphology.

Hope this helps.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796