Re: Gliders to Fliers? (Was Re: Ruben Strikes Back)

["Matthew Bonnan" <mbonnan@hotmail.com>]

Dinogeorge said:
If you look at the earlier, less derived theropods, such
> as ceratosaurs and dilophosaurs, you find the forelimbs retain a grasping
> function, which is greatly diminished in the more advanced and birdlike
> theropods. Sam Welles once told me, very emphatically, that _Dilophosaurus_
> most definitely had an opposable pollex digit on the hand that when used 
> with
> the other two large digits could grasp and hold things. I could never
> understand why theropods would have >lost< this marvelous and useful 
> ability
> until I realized that the hands of the more advanced theropods are derived
> from the fairly good wings of their volant ancestral forms.

Herrerasaurus is 3 meters long.  Dilophosaurus is much larger.  Grasping 
hands be damned!  How do such large animals clamber through trees?  Where 
are the adaptations in the feet of either of these dinosaurs?  
Dilophosaurus, and the smaller ceratosaurs Coelophysis and Syntarsus, lived 
in very arid, desert-like environs.  Where were all the trees to do the 
climbing in?  The downward and posteriorly directed shoulder, again, limits 
mobility in the arms.  And while there is certainly a grasping function in 
the hands of many theropods, it is not comparable to the more supple hands 
of most tree-dwellers.  The motion you get in most theropods is more of a 
raking motion.  Plus, the arms of Dilophosaurus are relatively reduced, 
getting closer to the condition seen in Allosaurus and the later tetanurans.

None of this speaks to me of an arboreal lifestyle.

Matt Bonnan

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