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Re: flights of fancy (or "I'm brave, but I'm chicken****")



George attempts to recover from my devastating blow (-:

> But in some ways, humans are very good models for bipedal cursorial
> theropods! Certainly better than fish and other aquatic animals.

I know I was in a hurry, but I don't think I was *that* unclear!  I
was NOT suggesting that aquatic animals are good models for theropods.
I was trying to show that using humans to model the best means for
other animals to move/develop is a bad idea.  Let me stick to
theropods to avoid confusing the issue again.  You claim humans are
"very good models for bipedal cursorial theropods".  I say that's
absolutely gibberish.  Our moment of inertia around our vertical axis
is miniscule compared to that of a theropod according to contemporary
reconstructions.  Although many of the leg motions will probably be
similar for the two forms (although you'd want to use a sprinter NOT a
marathoner since the latter will be running heel to toe whereas the
former will be running in a more purely digitigrade fashion), the
theropod's horizontal spine, the relatively long and sigmoidal neck,
and the tail I mentioned in the last message render the analogy to
humans a rather poor one.  As I said before, given those differences
you can NOT claim that the arm movements humans use while running are
at all similar to what the arm movements would have been in a
cursorial theropod.  Since Ostrom first claimed that Deinonychus had
the semi-lunate carpal bone, people have wondered why Deinonychus
might have wanted to fold its hands in like a bird.  Maybe it was more
efficient for the animal to tuck in its arms during a high speed
chase.  Maybe that's the reason for that adaptation (exaptation?).  I
suspect that in the next twenty years or so we'll be able to make
robots well enough to test this idea just as the robotic Anomalocaris
demonstrated that those things probably did leave the W-shaped bite
marks in Trilobites.  Those of you in Ken's class, I invite you to
take this idea and run with it!

Before I run off, though, let me also add that with our vertically
oriented spine, we present a much larger leading edge surface area
than would a theropod of comparable mass.  Another reason why human
runners are not good models for theropods.

Do you feel blown away yet, George?

-- 
Mickey Rowe     (rowe@lepomis.psych.upenn.edu)