Re: Palms in

["Matthew Bonnan" <mbonnan@hotmail.com>]

Larry Febo said:

> It is also suspected now that T. Rex also cared for it`s young in such a
> way. How then did it "bring home the bacon"?....Either many trips, or it
> used it`s mouth,....(perhaps regurgitated food).  I still think a better
> explaination for such  restricted movement in theropods in general is a
> cause of their being secondarily flightless. Once specialized for flight,
> such bone structure would be hard to unmodify for other uses.

One might be tempted to say this (restricted movement due to secondary 
flightlessness), except the poor pronation/supination "problem" is 
encountered in most archosaurs.  The radius and ulna do not cross either in 
crocs or birds.  Crocs pronate their manus by having flexed elbows and a 
laterally-facing shoulder joint that allows a great deal of circular motion 
while walking.  If you were to change a croc shoulder joint so that it faced 
down and back like in many dinosaurs, the croc would not be able to pronate 
its manus and they would, more or less, face palm-side in as in many 
dinosaurs.  Birds never really do pronate their manus, and instead their 
palm only faces down when the arms are abducted (moved away from the body).

Matt Bonnan
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