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Re: Dinosaur's hopping?

>The common ancestors of Saurischia (including Aves, if you prefer,
>though my own preference is to regard Aves as a separate class) 
>and the Ornithischia walked on all fours.  Bipedalism evolved
>at least three times in these groups, at least once is Ornith-
>ischia, once in Saurisschia proper, and once, separately, in
>Aves.  Bipedalism also evolved more than once in mammals.

   <*blink*>  Did I totally misunderstand everything I've read about
dinosaurs, or am I simply not understanding this paragraph.

   According to everything I've read, and according to the professor who
taught my dino class this past spring, the first dinosaur was an obligate
biped.  Additionally, if I remember my readings correctly, the
thecodonts/protodinosaurs, the immediate ancestors of the dinosaurs, were
also obligate bipeds.

   That would seem to mean that bipedality in dinosaurs evolved ONCE, with
quadrupedality separately evolving in each of the Dinosaurian suborders later.

   Has this opinion changed?

** "A warp core breach is imminent?     ** "Those who trade a little freedom **
** This calls for the handyman's secret ** for a little security will soon   **
** weapon, duct tape." --- Red Green,   ** find that they have none of       **
** Chief Engineer, U.S.S. Voyager       ** either." --- Jeff Poling          **