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



Darn, I really wanted to make a clean break yesterday...

But "Nicholas R. Longrich" <longrich@phoenix.Princeton.EDU> draws me
back:

> Wouldn't a camptosaur, hypsilophodontid, duckbill, bonehead,
> dryosaur, fabrosaur, ceratosaur, allosaur, kangaroo, jerboa,
> basilisk, or any other animal that spends a lot of time on two legs
> find folding arms just as useful [as Deinonychus would -- MR]?

In the first place, your argument is weak in principle, much like the
one of Greg's I criticized recently (the fact that George is also
using similar arguments doesn't mean you should consider such
arguments to be good chains of reasoning).  Just because evolution
found a solution once doesn't mean it will find it multiple times (or
even twice).  Jared Diamond had a wonderful piece on this in a column
for _Natural History_ about five years back.  In talking about the
probability of finding extra-terrestrial intelligence, he suggested it
might not be that likely.  Just because *we* evolved it doesn't mean
anything else has or will.  He analogized it to woodpecking in birds
(which also appears to have evolved only once despite its obvious
benefits to the lineage that evolved it).

More importantly, though, nearly all of the animals you suggest were
facultative bipeds.  It thus seems clear that the evolutionary forces
which would/could have molded their forelimbs would have been very
different from those that molded the forelimbs of dromeosaurs.

In response to my claim that _Deinonychus_ forelimbs don't look like
modified wings to me, George responded:

]  The forelimbs of _Deinonychus_ are DEAD RINGERS for the forelimbs
] of _Archaeopteryx_, bone for bone for bone.

Geez, doesn't anybody read what I write any more?  I said MODIFIED
wings.  Because _Archaeopteryx_ and _Deinonychus_ share their forelimb
structure, it is clear that between the two of them said structure is
plesiomorphic.  Thus you can't determine based on the evidence we've
been talking about whether a) _Archaeopteryx_ took that forelimb and
added feathers to it so that it could fly, or b) whether that shared
forelimb had feathers (and other adaptations) which _Deinonychus_
either shed or just didn't use for flight.

] If I had to rely on catching roadrunners for a living, I'd be
] extinct. But just think--maybe roadrunners would be _even faster_
] without their feathers (but then they wouldn't be ale to fly).

It's not just a question of speed.  Don't you read what I write,
George?  Look back over the past couple of days for a refresher,
please.  Now, I hope to really be out of here.  Ron, Tom, please keep
it up!

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