RE: More hand rotation

["Tracy L. Ford" <dino.hunter@cox.net>]

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
GSP1954@aol.com
Sent: Thursday, August 08, 2002 8:24 PM
To: dinosaur@usc.edu
Subject: More hand rotation

Concerning Nicks oberservations on lower arm rotation in dinos and mammals.
He note that in mammals in which lower arm rotation is not possible that the
radius and ulna are locked together. It has been little appreciated that the
same is true of hadrosaurs. At the distal end there is a peg-in-notch
articulation between the two bones that, in association with a tight
proximal
fit of the radius into a sulcus of the ulna, renders the radius and ulna
immobile relative to one another. This is a running adaptation that shows
that hadrosaur arms were used primarily for locomotion rather than
manipulation of objects that their short, pad encased fingers were ill
suited
for. It also indicates that hadrosaurs remained quadrupedal even at high
speeds.

In any case, if dinosaur lower arms were inherently unable to rotate, then
why did hadrosaurs go to the trouble of locking the radius-ulna? Converesly,
if dinosaur lower arms were inherently unable to rotate, then why weren't
they all locked up? That most dinosaurs kept the radius-ulna loose suggests
the retention of some degree of rotation, albeit less than primates and so
forth.<<
In my 'ah hemmm' younger days I didn't believe that hadrosaurs walked
quadrapedally. But thanks to the wisdom of 'ah hemmm' age, I saw the folly
in this. Another thing the manus of hadrosaurs 'mimic' is a tapir, rhinos,
in some ways, deer's, etc. The toes couldn't spread apart, except digit 4,
so the 'early' belief by Osborn that they were used as paddles is incorrect
(brought on by the mummy at the AMNH). I gave a talk at the Mesa Southwest
Museum earlier this year about whether or not some dinosaurs could have
lived partially aquatic lives (Mainly brought on by the tremendous amount of
hadrosaurs and nodosaurs being found in marine deposits). My conclusion is
in the paper (when that comes out). I looked at the pes, skeleton, etc, and
I really really wish I knew about the locking ulna and radius because I
would have used that.
I probably still could, I'm waiting for the review copy to come back so I
probably could still put that in (as Paul pers. comm...?).


>>Prosauropod lower arms, for instance, articulate with the palm facing
medially. But trackways show the palm facing strongly backwards, with only a
modest medial orientation. This probably reflects rotation of the lower arm
when using them to walk compared to when they are inert. Rather like how
people often walk with palms inwards but direct the hand forward when on all
fours.<<
Interesting.

G Paul

As always Greg, you're a wealth of knowledge...

Tracy L. Ford
P. O. Box 1171
Poway Ca  92074