RE: Ornithischia/Saurischia Ilium Mass Distribution Hypothesis

["Jaime A. Headden" <qilongia@yahoo.com>]

Mike Milbocker (mmilbocker@psdllc.com) wrote:

<The drawing you sent(above)has the head on the left side. I think you'll
agree the left side of the ilium in the drawing is heavier/taller than the
right side. Therefore, Alvarezsaurus is Saurischian - which agrees with
orthodoxy. The palaeos drawing shows it strongly Saurischian, if the mass
ratio is any measure.>

  Based on comparison to other alvarezsaurs, all alvarezsaur ilia known
have a slender pubis peduncle and a broad, short, and nearly absent or
fully absent ischiadic peduncle, and the postacetabular ala is broader and
longer and deeper than the preacetabular ala. This is true in
*Alvarezsaurus,* and the reference citing this as being reversed is wrong.

  Similarly, the preacetabular ala os most ankylosaurids has an area
largely 2-3 times that of the postacetabular ala, if not more, given the
position of the acetabulum is well posterior to the two-thirds point of
the iliac length and the bredth of the preacetabular ala exceeds that of
the postacetabular ala in all ankylosaurs I have seen to date, especially
in ankylosaurids and the "polacanthids" such as *Mymoorapelta,* and even
nodosaurids as in *Sauropelta.* Exactly how was it determined that these
ilia were caudally-heavy, rather than cranially heavy?

  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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