Re: semilunate carpal

[Dinogeorge@aol.com]

In a message dated 8/3/01 5:03:06 PM EST, killerraptor20@hotmail.com writes:

<< Like the wingstroke of birds (which evolved from it). >>

I think, rather, that the semilunate carpal provides good evidence that the 
theropod maniraptoran forelimb derived from a forelimb that was already a 
fairly good wing. There is simply no reasonable explanation for why the 
forelimb of a cursorial, non-flying predator that used its forelimbs just to 
grasp and manipulate its prey would evolve into a form >less< useful for this 
purpose. Imagine how useless your hands would be if they could not rotate on 
their wrists and if the bones of the palms were pretty much frozen into one 
position without an opposable thumb! And if the fingers had become too long 
and too stiff to wrap around an object to hold it.

But imagine that the forelimb of maniraptoran dinosaurs was once the 
"semiwing" of a flying reptile, having evolved some of the constraints to its 
motion (such as the semilunate carpal) found in extant flying birds, that was 
diverted from its flying function >back< to a forelimb for capturing prey. 
Then all the birdlike adaptations seen in the maniraptoran forelimb acquire a 
logical explanation; they no longer appear ad hoc, in a counterintuitive way. 
The birdlike features of the maniraptoran forelimb appeared more or less 
serially along the lineage that eventually led to extant birds, but when a 
lineage branched away from this lineage in another evolutionary direction, 
the animals in that lineage exapted their inherited maniraptoran forelimbs 
for other (usually predatory) functions (but including also, perhaps, shading 
their nests).