Re: Please remind me!

[Stan Friesen <swf@ElSegundoCA.NCR.COM>]

From: Flint Weller <spatula@netaxs.com>

 > Someone asked me why, "the lizard hipped dinosaurs are said to have
 > birdlike hips".  You know, I understood this reasoning once, but after
 > looking over a few texts, I have something incomplete.

Simply put the pelvic bones of ornithischian dinosaurs *superficially*
resemble those of birds.

In birds the pubic bone is rotated to a position next to the ?ischium.

In bird-hipped dinosaurs the pubis has a posterior process next to
the ischium, and a small forward process.

 > Does it have
 > something to do with similar muscle attachments?

It has been suggested that this switch is related to increased
stomach volume.

 > Why did birds "revert"
 > back to the bird hipped form? 
 > 
They didn't revert, they evolved a similar, but different, structure
indepedently.

Note, some "lizard-hipped" dinosaurs are now known to have had a true
bird-like pelvis.

swf@elsegundoca.ncr.com         sarima@ix.netcom.com

The peace of God be with you.