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Re: uncinate processes, function?



David Peters (davidrpeters@earthlink.net) wrote:

<I checked the archives of the list, but looks like the answer to this
question was left hanging (correct me if I'm wrong), but apparently
there's no consensus yet regarding the function of uncinate processes in
everything from Ichthyostega and Sphenodon to emus and hummingbirds.

I'm playing around with a Tuatara figure and I was struck by the dorsally
convex curvature of the spine.

Wondering if that's what uncinate processes support? Are the two
characters associated in every case?>

  Well, oddly enough, unossified, cartilaginous uncinates are known in
crocodilians as well, plates that contact the following rib lower than
halfway down the ribshaft. Having seen this myself, that is, it has been
described as a pathology or abnormality by others.

  Bird spines are normally straight or curve upward. The main principle in
avian uncinates appears to be a rigidifying structure of the ribs and
dorsum to prevent flexure of the spine and destortion of the pulmonary
cavity during flight, and perhaps also to free the pulmonary region from
the ribs so as to "allow" the flow-through lungs to operate most
efficiently. The tuatara is also a fairly short-trunked lizard, and this
may related to rigidification of the of trunk to some degree....

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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