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Re: Archaeopteryx and Flight
>Brings up a good point. If wing-like structures were to evolve
>on cursorial animals, it would, as with racing cars, be connected
>with an instinct to use them to _decrease_ lift rather than increase
>for just this reason. That contradiction would seem to make the
>cursorial hypothesis much harder to believe.
I'm hardly the first one to point this objection out. I have never bought
the cursorial model. Not one of the various gliding animals alive today
(excluding fishes) is terrestrial, including at least two lines of frogs, a
snake, two lines of lizards and four lines of mammals (anomalurids,
squirrels, gliders and the colugo). Although a number of lizards will run
bipedally not one of them has foreleg modifications for doing anything other
than getting them out of the way (the frilled lizard, for example, tucks
them in at its sides). Yes, I know, we have no real analogue to a small
therapod around except birds which evolved from flying ancestors, but I
still find a running dinosaur hard to imagine as a proto-bird.
A SLIGHTLY more likely possibility for a terrestrial protobird might be a
therapod that performed leaping displays involving ornamented forearms
(something like a crane dancing); or, possibly, a glider living in hilly or
deeply-gorged country where leaps from precipices might be possible. But
the arboreal model still seems most likely to me, at least on the grounds
that it ties in with adaptations in living vertebrates.
As for Archaeopteryx, I do not find the habitat argument at all convincing.
Modern chachalacas live in scrubby country, but their relatives the
curassows and guans are forest birds and the group probably evolved there.
I suspect Archaeopteryx did likewise, and we simply don't have a good
representation of Jurassic fossil forest dinos (in fact, maybe that also
explains why we don't have many Jurassic dromaseosaurids - they were living
in trees in the forest, in areas where fossilization was unlikely. Well,
that works for me.).
Ronald I. Orenstein Phone: (905) 820-7886 (home)
International Wildlife Coalition Fax/Modem: (905) 569-0116 (home)
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