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Re: Saurischia and Ornithischia pelvis
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.
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
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
> ornithischia? I was able to determine that the ornithischia pelvis
allowed for a larger abdominal area for digestion, but what
> huge sauropod bellies? What selective advantage did these pelvic
arrangements give to the two classes of dinosaurs? Thank you