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Re: flapping from gliding



Nick Longrich wrote:

>      The point: The arboreal hypothesis has two main strengths. a)
>the leap between gliding flight->powered flight seems to me to be,
>both conceptually and evolutionarily, an easier one, than the one
>between a running or leaping predator and powered flight.

I think this alleged "conceptual ease" exists only if you are already
predisposed to believe this idea.  To me, the evolutionary path from
running to wing-assisted running to full powered flight seem just
as conceptually easy, in fact more so.

>b)It's based on evidence obtained by looking at both fossil and extant
>life forms and looking at the real world. 

Certainly not, unless you look at the evidence very selectively and
ignore counter-examples.  Consider extant flightless birds. I believe
all of them are good runners.  If you believe that modern flightless
birds are descended from previously flighted forms, then you acknowledge
that the reverse transition has taken place.  Why then is the transition
in the other direction conceptually hard?

Besides, pterosaurs must have descended from walkers/runners, not gliders.
The further back you go in the pterosaur family tree, the better adapted
they are for running.  It is the more advanced forms that start to shorten
their legs and become less well adapted.  One of the most primitive
pterosaurs known, Preodactylus, has long hind limbs and was well-adapted
for walking if not running.  Scleromochlus, considered by many to be
the dinosaur/pterosaur ancestor.  It was not capable of flight,
but seems to have been adapted for jumping and hopping.  It could not
have been a glider since it lived in a non-arboreal desert environment.

>       I think if there's any reason we are so taken with ground-up
>theories, it's because we're ground living ourselves and that's how
>we ourselves did it.

Not at all.

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