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RE: Archaeopteryx running



 
John Hutchinson wrote:

>A good question for someone to study in more detail; I've only done a
>quick calculation with a simple models of Archaeopteryx before, and got
>expected results: pretty good at running -- roughly the same as a
>chicken, with a fair margin of error.  I am not totally convinced by the
>thrust-generator arguments, nor am I certain that Archaeopteryx could
>have run exactly fast enough, or how fast that really would be.  

This is going off on a tangent, I know...  But one of the reasons why I'm a
little uncomfortable with a cursorial origin of avian flight is that the
hindlimbs of _Archaeopteryx_ are among the *least* cursorial of any
theropod.  Ditto for dromaeosaurids (including the basal ones).  In fact,
this has come up in some of John H.'s papers.

For example, the features that Tom Holtz mentioned for tyrannosaurids, which
are inferred to have enhanced its cursorial abilities, are not present in
_Archaeopteryx_ or dromaeosaurids:  

>a) more cursorial limb proportions; b) arctometatarsi; and c) less hip
>muscle mass (as Tracy pointed out, tyrannosauroids (and >ornithomimosaurs,
and alvarezsaurids) have ilia that 
>contact on the midline; this is quite probably an adaptation to increase 
>overall muscle mass in the legs)

If Burgers and Chiappe are correct in emphasising the role of running
velocity (combined with the motion of the forelimbs), in assisting the first
birds (and their ancestors) in becoming airborne, then one would expect
hindlimbs highly evolved for sprinting.  At least, that's my take on it all.

As always, bouquets and brickbats welcome.


Tim



------------------------------------------------------------ 

Timothy J. Williams 

USDA-ARS Researcher 
Agronomy Hall 
Iowa State University 
Ames IA 50014 

Phone: 515 294 9233 
Fax:   515 294 3163