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



In a message dated 95-12-05 14:55:18 EST, rowe@lepomis.psych.upenn.edu
(Mickey Rowe) writes:

>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'm afraid you were...

>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.

I wouldn't think of using humans to model aquatic mammals.

I said, in "some" ways. Not perfect. Jesus, doesn't anybody read what I write
anymore?

>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.

Using hyperbole here doesn't help the situation and makes it sound as if
you're raving. "Gibberish"? I hardly think so.

>Our moment of inertia around our vertical axis
>is miniscule compared to that of a theropod according to contemporary
>reconstructions.

So consider a human runner with a large log horizontally strapped to his or
her midsection.

>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),

See? It's not "absolute gibberish" after all.

>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?).

No, the reason is more likely to be that _Deinonychus_ had a volant ancestor
somewhere in its family tree. Why is this so difficult to accept?

>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.

As I said above, I never claimed that humans were perfect models for running
theropods. The point I was trying to make is that a running animal that
evolves feathers on its forearms would be in the position of a human runner
trying to run while wearing a long-sleeved coat--that feathers in those
locations would tend to hamper rather than help. Perhaps I'm wrong, and
feathers on the forearms and hands _would_ help a running theropod capture
more prey, but I don't think anything you've said in this posting or in the
previous posting is terribly convincing of this thesis.

>Do you feel blown away yet, George?

Nah. Buffeted about a bit, but nothing unusual for this group...