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Re: Please remind me!
> Why did birds "revert"
> back to the bird hipped form? A change of distribution in posture due to
> no tails and wishbones?
To turn your question around, the "lizard-hipped" configuration is
primitive for the Dinosauria. Among saurischians, the
dromaeosaurids, birds (surprise, surprise) and segnosaurs evolved a
"bird-hipped" configuration, convergent with the ornithischians.
Why did they do this? Umm... actually I don't know. Theories which
For birds and dromaeosaurids it was associated with a decoupling of
the tail from the hips. Birds probably inherited an opisthopubic
pelvis from their immediate ancestor - dromaeosaurids have been put
forward as the most likely candidate by many researchers.
For segnosaurs (and ornithischians) the backwards movement of the
pubic shaft was an accommodation for the larger gut - herbivores
need more space than carnivores to digest copious amounts of cellulose-
rich (and nutrient-poor) plant matter.