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Re: Ceratopsians: sprawling or straight?



At 03:15 PM 12/27/97 -0500, tons wrote:
>
>I've never studied ceratopsian bones so I only have questions.  Why 
>would most dinosaurs have their limbs and feet in linear fashion 
>under their hips or shoulder girdles and ceratopsians not?

Ancestrally, dinosaurs were bipedal.  The *hind* legs, being used in
locomotion, were under the hips.  The arms were less constrained, being
used for grasping.  This means that the conformation of the front legs in
*any* group of quadrupedal dinosaurs has evolved separately (there were at
*least* three distinct origins of quadrupedality in dinosaurs, four if you
count hadrosaurs as quadrupedal).

Thus, ceratopsians would be different because they arrived at
quadrupedality in a different manner than other dinosaurs.  (Note, i am not
saying I agree with this conclusion, only that there is no evolutionary
problem with it).
>
>Would an animal that large be able to move quickly with an 
>articulation at the knee (or otherwise) that was not linear?

This is not clear,  It depends on *how* it departed from linearity.

--------------
May the peace of God be with you.         sarima@ix.netcom.com
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