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Re: Deinonychus claws expalined as climbing adaptions



At 04:30 PM 4/27/97 -0700, you wrote:
>Each digit on this foot has a different number of phalanges.[...]
>Correct me if I'm wrong, but don't most dinosaurs' feet have a roughly similar 
>number of phalanges in the major digits? 
        The primitive theropod phalangial formula is 1-2-3-4-?, or more
properly 2-3-4-5-? when the ungual phalanges are included. I can think of no
ceratosaur or tetanuran off hand that does not exhibit this formula, +/-
digit I.

>I would at least expect to find the two
>weight-bearing digits with the same number of phalanges.
        Theropod evolution did not achieve differing toe proportions by
varying the number of pedal phalanges. Rather, the relative lengths of the
phalanges varied.

>What benefit did _Deinonychus_ get from this odd shape to the foot?
        Well, I'd say the phalangial structure is just a result of its
ancestry, and not really odd at all. That is the structure its ancestors
possessed for millions of years, and I suppose there was no reason to change it.
        Of course, the specific adaptations for the killing claw (long MT IV
and digit IV, shorter MT II and digit II, short metatarsus) are associated
with increasing the power that can be put behind the claw, and keeping the
claw clear of the ground.
        Perhaps Dr. Holtz, resident expert on the theropod metatarsus, or
Dr. Farlow, with his ken for kickers, will be moved to go into more detail
on this subject.
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      Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock TX 79409
      "The cost of living hasn't affected its popularity." - Unknown