Re: Dinosaur Hand Shakes

[Dinogeorge@aol.com]

In a message dated 97-08-15 01:43:57 EDT, jamolnar@juno.com writes:

<< >This sounds all right except for the opposable thumb, of which I'm not 
 >so
 >sure. Did you hear this somewhere (other than from Dr. Bakker)? AFAIK, 
 >only
 >dromaeosaurs had "opposable" "thumbs". >>

The late Sam Welles insisted that _Dilophosaurus_ had an "opposable thumb,"
and he's the one who studied the material. He demonstrated exactly what he
meant, using his own hands, to Tracy Ford and me back in 1993 in Albuquerque.

On the other hand (heh heh), I'd question whether dromaeosaurids had
opposable thumbs. Their grasping technique, such as it was, was more likely
to have either hand oppose the other. The semilunate carpal limits the
movements of the digits and links the movement of the hand to extension and
flexion of the entire forelimb. The thumb does seem to have been capable of
moving independently of the other digits, but only in a limited fashion and
not in a manner suggesting opposability to them. Also, the elongate manual
phalanges make for lousy grasping because they're too long for the hand to
really wrap around an object. The hands seem to be built more for tearing,
raking, and slashing, especially with those huge claws.

The hand-wrist-forelimb articulation of dromaeosaurids is quite inexplicable
as any kind of a functional improvement on the better grasping ability of
earlier theropods such as _Dilophosaurus_. But if one sees the dromaeosaurid
forelimb as having once passed through several early stages in the evolution
of an avian wing, then one can understand its functional limitations much
more clearly as being left over from its previous function as an organ for
flight. The detailed structure of the dromaeosaurid hand and forelimb is
powerful evidence that dromaeosaurid ancestors were once fairly decent
fliers, especially in light of how the forelimb developed in their close
sister group, the avialan birds.