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Re: semilunate carpal
In a message dated 8/3/01 5:03:06 PM EST, firstname.lastname@example.org 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