Re: Saurischia and Ornithischia pelvis

[Darius Nau <dariusnau@gmx.at>]

Stevens et al. (2008) proposed that the prominent pubic boot would serve 
to bear a large portion of the weight when theropods were in a resting 
position, something I can’t really see an ornithischian doing.

This of course can’t be applied to sauropods to the same degree (being 
quadrupedal, their centers of mass would be more anterior and a greater 
portion of the weight would rest on the ribcage and shoulder girdle), 
but even a slight benefit in weight-distribution may have been useful at 
the extreme sizes reached by many sauropods.

Most theropods that retained this morphology were carnivores, so they 
didn’t need particularly big guts. Theropods with an opistopubic pelvis 
were (and are) often relatively small (e.g. deinonychosaurs), 
herbivorous (e.g. therizinosaurs) or both (e.g. Chilesaurus).

What remains, saurischians that were neither large, nor carnivores 
probably just retained the plesiomorphic state because the associated 
benefits were too slight to lose this feature.

Reference:
Stevens, Kent A.; Larson, Peter; Wills, Eric D.; Anderson, Art (2008): 
Rex, sit: Digital Modeling of Tyrannosaurus rex at Rest. In: Larson, 
Peter; Carpenter, Kenneth: Tyrannosaurus rex the Tyrant King. 
Bloomington pp. 193-204

Yours sincerely,

Darius Nau
--
dariusnau@gmx.at
http://www.paleo.keepfree.de

On 10.07.2015 03:15, Stuart Plotkin wrote:
> I could use some advice as to what are benefits the forward facing 
pubic bone in the saurichia vs the rear facing pubic bone in
the
> ornithischia? I was able to determine that the ornithischia pelvis 
allowed for a larger abdominal area for digestion, but what
about the
> huge sauropod bellies? What selective advantage did these pelvic 
arrangements give to the two classes of dinosaurs? Thank you