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

[Dinogeorge@aol.com]

In a message dated 9/26/99 1:36:14 AM EST, mbonnan@hotmail.com writes:

<< Okay, forget the hindlimbs, let's examine the ulna, radius, and wrist of 
 theropod dinosaurs.  It is not what we would see in a climbing mammal.  Why 
 not?  The ulna and radius, while crossed to varying degrees, are not very 
 mobile (in fact, in most cases almost complete immobile!), and therefore the 
 hand and forearm cannot be manipulated well to accomodate efficient grasping 
 and climbing.  Further, the wrist bones in the most bird-like dinosaurs 
 (maniraptorans) allow motion essentially in one plane -- that's the whole 
 deal with the semi-lunate carpal maniraptoran wrist being similar to birds. 
>>

Here you're looking at forelimbs that are derived from pretty good wings, no 
longer used for climbing. Of course you won't find many climbing adaptations 
left in such limbs! 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. The grasping 
ability gave way to a probably more useful aerial function.