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RE: Mats and boles, relatively? (bipedism)

Don Ohmes wrote:

> How did this "ancestral biped" come into existence? What sequence of
> selection events caused a sprawling quadruped to haul itself up onto
> its hind legs and start walking and running around?

It is more likely that bipedalism is primitive for the Dinosauria as a whole, 
and that they evolved not from sprawling quadrupeds but from quadrupeds that 
already had an erect/upright posture.  The shift to bipedalism may be 
associated with freeing the forelimbs for grasping and manipulating food - 
either vegetation or small prey.  The first ornithischians (_Eocursor_, 
heterodontosaurids) have a grasping manus, as do the first saurischians (e.g., 
_Herrerasaurus_, coelophysids).  Prosauropods have a twisted pollex (thumb) 
tipped by a large inward-pointing claw.



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