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Re: Ornithischian vs saurischian hips

As Dann indicated, it seems to be related to shifts in caudal morphology. Tail-based leg muscles were being used less as the primary locomotive force (ala excellent work by Gatesy) and (in dromaeosaurs and the earliest birds) various forms of tail-stiffening was reducing the mass of the tail. Swinging the guts back between the legs probably maintained a onsistent center of gravity as the tail lost mass.

Scott Hartman Science Director Wyoming Dinosaur Center 110 Carter Ranch Rd. Thermopolis, WY 82443 (800) 455-3466 ext. 230 Cell: (307) 921-8333


-----Original Message----- From: Jura <pristichampsus@yahoo.com> To: dinosaur <dinosaur@usc.edu> Sent: Thu, 28 Jun 2007 2:11 pm Subject: RE: Ornithischian vs saurischian hips

I suppose the most obvious question to ask next is
what function did the retroverted pubis in
dromaeosaurs serve?


--- Nick Pharris <npharris@umich.edu> wrote:

Quoting "Thomas R. Holtz, Jr."

>> From: owner-DINOSAUR@usc.edu
[mailto:owner-DINOSAUR@usc.edu]On Behalf Of
>> Pedro Andrade

>> What's the functional difference between the
>> ornithischian and the saurischian hip structure,
if any?

> 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.

The other part of this that I've seen is that it
shifts the weight of
the intestines back toward the hip joint, allowing
ornithischians to
increase the size of the gut while remaining bipedal
(for a time,
anyway--given that most of the largest
ornithischians did eventually go

"I am impressed by the fact that we know less about many modern [reptile] types
than we do of many fossil groups." - Alfred S. Romer

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