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Re: So-called Sickle Claws

In a message dated 97-08-24 04:16:23 EDT, vonrex@gte.net (Peter Von Sholly)

> I disagree.  I believe there was a large "heel pad" under the distal ends
>  of the 3 metatarsals and that all three toes bent forward from there, with
>  pads of their own, especially under the claw of digit 2, the so-called
>  killer claw.  There is plenty of room for that toe to reach the ground.  

Maybe; but the only part of the toe that would be on the ground is phalanx
II-2.  That wouldn't provide a lot of support.  It looks to me like the only
part of the second toe that touched the ground was the "knuckle" between
phalanges II-1 and II-2.

>  And what about the animal's ability to walk, run and balance?  

And why is digit II so short and directed away from the direction of
movement?  And why are phalanges II-1 and II-2 set up to articulate at up to
a 90-degree angle to each other?  And why are the muscle attachment sites on
the second toe so much more prominent than on the other toes?  And what about
that enormous, nearly semicircular claw?  Unless it was held up at least to
some extent, every step would have driven it into the ground!

(I have copies of Ostrom's drawings of the original foot in front of me--_The
Dinosauria_, p. 275)

>  You don't
>  think that would be compromised by the need to walk only on its two outer
>  toes?

It doesn't seem to be too much of a problem for ostriches!  And they put most
of their weight on only one toe!

The two outer toes of _Deinonychus_ were very nearly the same length and ran
parallel to each other.  Both were very long and robust.  The claws on these
two toes are rather flat, in sharp contrast to the claw on the second toe,
which is much more similar to the hand claws than to the other foot claws.
 The fourth metatarsal is splayed out from the third in order to increase the
area covered by the two outer toes.

These adaptations are unique to the Dromaeosauridae and appear designed for
shifting the animal's weight onto the two outer toes.