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



In a message dated 95-12-05 22:55:54 EST, ornstn@inforamp.net (Ronald
Orenstein) writes:

>GO writes:
>
>> 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?

Maybe this, maybe that, and maybe something else again. Maybe the ancestor of
_Deinonychus_ needed to fold its hands together to eat Kellogg's corn flakes.

When there is no evidence either way, you opt for the explanation that makes
more sense. While nobody said that evolution _has_ to make sense, it usually
does when the evidence is in and the smoke clears. Pigs _could_ evolve wings
sprouting out of their backs, but the fact that no known mammal has yet done
so gives us a clue that it probably won't happen with pigs, either.

>Why should your explanation be the better of the two in this case?  Do you
>have any evidence that the arm-tucking explanation (which makes sense to me)
>is not valid?

Why didn't any other group of bipedal dinosaurs evolve arm-tucking, if it was
so beneficial?

>Of course the two explanations are not mutually exclusive - but if the
>functional adaptation is reasonable how would you establish (short of
>linking forms or analysis (cladistic or otherwise) of other characters
>showing that D. was closer to some winged forms than those winged forms were
>to others) that the other explanation also applied?  Saying that it makes
>more sense may be good debating style, but it isn't evidence.

In _Goldfinger_ (Ian Fleming), the villain's motto is something like, "Once
is happenstance, twice is coincidence, and three times is enemy action."  So
if I see three or more different flight-specific adaptations present in a
group of volant vertebrates, I assume they didn't just happen there by
coincidence.

>>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. 
>
>Except that it might well have developed adaptations to counter this
>problem.  After all, an Ostrich is an extremely fast runner with
>fairly-large, well-feathered wings and it seems to manage.

Yeah--or it could simply lose the feathers, which according to BCF happened
in most of the large-theropod lineages.