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RE: Saurischia and Ornithischia pelvis

On 2015-07-13 15:28, dale mcinnes wrote:
Ummmm ... could not the forward/ downward projecting pubis
[ancestral position] been selected for in very early and small
for flight to prevent yaw. No known triassic birds yet but, would this
be some indication that more was going on than we know of ? If the
was still reptilian, perhaps, like training wheels on a bike, this
could have
spurred the latter [brain] towards this kind of experiment [flight] ?
No hard
evidence. Just thinking out loud here.

Keep in mind: WE have forward pointing pubes. As do parareptiles. As do lizards (hence the name). It doesn't have to be "for" anything.

If you are looking for the time when selection favored the forward orientation of the pubis, you need to look in the fish-tetrapod transition, not in Triassic archosaurs.

The retroversion begins (depending on the exact phylogeny and optimization of the character) in the ancestors of alvarezsaurs and pennaraptorans, or at the base of eumaniraptorans. In no case do we have evidence of an old-fashioned allosaur-style pubis orientation when birds first showed up.

And I think people are conflating the actual question (orientation) with the not-related issue of a pubic boot (a distal expansion of the pubis, regardless of the orientation). The original poster asked about the position of the pubis.

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Geology Office: Geology 4106
Scholars Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
Fax: 301-314-9661

Faculty Director, Science & Global Change Program, College Park Scholars
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
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                        University of Maryland
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