Re: Scapular movement in Dinos

[Dann Pigdon <dannj@alphalink.com.au>]

NANNOTYRAN@aol.com wrote:
> 
>   Is there any decent argument against scapular rotation in quadrepedal
> dinosaurs?  GSP illustrates his dinosaur skeletons showing a fore-and -aft
> motion of the scapula, presumably to give the animal extra push in it's back
> stride.  He mentions that the corocoid would "slide" up and down a
> cartilaginous sternum that would make this theory possible.  As an animator,
> this is a wonderful thing to work with, but with the upmost respect for
> dinosaur science, I don't want to accept this explanation without some other
> viewpoints to ponder.  I see plenty of arguments for a moving scapula, the
> muscles all appear to attach that would indicate such a motion, but I'm a
> little hard up for evidence against it.  A number of computer animation tests
> that show a 10-15 degree of movement work wonderfully with the limb
> proportions and trackway evidence.
>  Do the books say scapulas move to sell copies, or is it a valid argument?
> 
Here's an observation, although by no means take it as "evidence" of
any sort. Since most dinosaurian quadrapeds seem to have ultimately
evolved from bipedal ancestors many of them tend to have a marked
difference in limb size, favouring the hind limbs (sauropods excluding
brachiosaurs / camarasaurs, stegosaurs, ceratopsians, etc). When this
is the case then the swinging scapula would be the only way such a
creature could achieve a moderately fast run without ending up
face-first in the dirt. I believe this was the guts of Greg Paul's
arguments concerning ceratopsians.
        This all hinges on whether these creatures were actually 
capable of running fast (I imagine diplodicids and the like were not
particularly swift). But take a look at a protoceratops skeletal 
reconstruction. There seems to be a marked difference in limb sizes
favouring the hind limbs, no doubt remanent of their psittacosaur-like
anscestors. Since we can be fairly sure that they were preyed upon by
velociraptors (V.mongoliensis) I find it hard to believe they could
not achieve at least a moderately fast run in order to escape. Of
course those beaks and jugal spikes may have served as a deterant, and
perhaps they may have found adequate safety in numbers, but from a
personal point of view faced with a pack of dromaeosaurs I'd prefer
the "run like hell" option than standing my ground.
-- 
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        Dann Pigdon
        Melbourne, Australia
        http://www.geocities.com/capecanaveral/4459/

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