RE: Noasaurids and An Odd Question on Tyrannosaurs...

["Williams, Tim" <TiJaWi@agron.iastate.edu>]

Mike Keesey wrote:

> The only group known to have reversed halluces (_Avialae_) also 
> appears to have hyperextendable second pedal digits (at least 
> primitively).

Yet, birds lost the hyperextensible second toe (and its accompanying
'sickle-claw') very quickly.  Perhaps both traits were an impediment to an
effective perching pes - anisodactyl perching that is, which appears to be
the primitive configuration for branch-grasping in birds.  

_Rahonavis_ is the only undisputed avian to possess both a hyperextensible
toe and a sickle-claw.  But the phalangeal proportions of _Rahonavis_'s feet
are more consistent with a terrestrial lifestyle.  By contrast,
_Archaeopteryx_ (which lacks the sickle-claw; the presence of
hyperextensibility is open to argument) has pedal digits with proportions
more consistent with perching - as do many other Mesozoic birds.


Thomas Holtz wrote:

> So what about the elements in Baryonyx, Sinraptor, Xuanhanosaurus, 
> and Scipionyx?

Another cat out of another bag.  As mentioned on the DML a while ago,
according to Rauhut the sternum of _Xuanhanosaurus_ is actually an
impression of part of the right coracoid.  Also refuted are other notions
concerning _Xuanhanosaurus_ - such that it had forelimbs designed for
quadrupedal locomotion and a hand incapable of grasping.



Tim


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



Timothy J. Williams, Ph.D. 

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

Phone: 515 294 9233 
Fax:   515 294 9359