RE: Ornithischian vs saurischian hips

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu]On Behalf Of
> Pedro Andrade
>
>
> Not sure this has been discussed here before:
>
> What's the functional difference between the
> ornithischian and the saurischian hip structure, if any?
>
Well, there would be a number of them. (And it is important to keep in mind 
that there is a LOT of variation in each group. Pelves
of _Lesothosaurus_, _Stegosaurus_, hadrosaurids, and ceratopsids are all 
ornithischian, but have very VERY different structure, for
instance!).

The classic one, though, deals with the orientation of the pubes. The 
traditional saurischian orientation (pubis subvertical to
anterior) is the primitive condition: heck, in that sense, WE have 
"saurischian" pelves. In ornithischians (except possibly for
_Pisanosaurus_) the pubis points backwards. This would allow an increased 
volume for intestines without having them expand too much
laterally, which would in turn allow the digestion of more plant material.

                Thomas R. Holtz, Jr.
        Senior Lecturer, Vertebrate Paleontology
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
        Mailing Address:
                Building 237, Room 1117
                College Park, MD  20742

http://www.geol.umd.edu/~tholtz/
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