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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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