RE: Ornithischia/Saurischia Ilium Mass Distribution Hypothesis

["Andrew A. Farke" <andyfarke@hotmail.com>]

> -----Original Message-----
> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu] On Behalf Of
> Mike Milbocker
> Sent: Tuesday, April 27, 2004 7:30 AM
> To: cryptovolans@yahoo.com
> Cc: dinosaur@usc.edu
> Subject: RE: Ornithischia/Saurischia Ilium Mass Distribution Hypothesis
> 
> Great choice, Waylon R., the Elaphrosaurus. I wasn't able to find many
> examples of the ilium. But applying the plane view method to a side view
> of
> one example, I determined that Elaphrosaurus is Saurischian. I'll admit
> it's
> a close call, but the anterior portion of the acetabulum biases the mass
> distribution toward the head, giving a Saurischian result. However, given
> E.
> is a predator, I would have expected a much more definitive forward mass
> shift - since this seems to be the case for other large predators. I
> suspect
> the E. ilium is likely non-planar, possibly with a shelf anteriorly - I
> would appreciate any comments confirming this suspicion. Meanwhile, I'll
> continue the research.
> 
> My personal choice for a possible exception to the hypothesis would be
> Pisanosaurus, which is believed to be Ornithischian but possesses an
> anteriorly pointing pubis (a Saurischian trait). Unfortunately, the fossil
> remains of its ilium are inconclusive.

So just a few questions. . .

What happens with other ankylosaur or ceratopsid ilia (e.g., Sauropelta,
etc.)? Ilia are very "three-dimensional" elements in these taxa, with a
significant lateral projection. Could you estimate the three-dimensional
moment of inertia based on orthogonal views of the same specimen? Based on
the few illustrations (and recollections of actual specimens) of
ankylosaurs, the center of mass of the ilium could be anteriorly placed.

What's the significance of the differences between Saurischia and
Ornithischia? Is it related to posture? To muscle origin and insertion? Is
it somehow related to the position of the sacro-iliac joint? Is there no
significance at all? 

If you have a sample of ilia from the same taxon (or a group of related
taxa, such as hadrosaurines), how much intragroup variation is there?

What's the range of variation, in general?

And, what happens if you use photographs versus drawings?

How about extant birds?

Sounds like some interesting stuff so far. . .thanks for [bravely] sharing
this with the list!

Andy

_________________________________________
Andrew A. Farke, Graduate Student
Department of Anatomical Sciences
Stony Brook University
T8 040 Health Sciences Center
Stony Brook, NY  11794-8081