Re: Gliders to Fliers?

[Josh Smith <smithjb@sas.upenn.edu>]

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.

This is NOT to support George's arboreal theropod ideas, but where the
hell is the evidence that all of the early ceratosaurs were living in
hyper arid environments with no trees??????

Petrified Forest Member of the Chinle Formation?  There is evidence of
abundant and widespread plant life all over in these rocks. LARGE trees.

Red Beds DO NOT necessarily indicate hyper aridity and these theropods
are not being recovered from the aeolian deposits.  True, we do find
coelophysoidish teeth in cross-bedded aeolian sands in the Bay of Fundy,
but they were not exclusively there.