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Archaeopteryx and Flight



Miles Constable at Edmn <ConstableM@mail.edm.ab.doe.ca> wrote:

> There are some things to consider in an animal evolving a novel (for 
> Therapods at least) mode of locomotion. There are at least two reasons that 
> I can see for flight, the first is to grab the abundant flying insects of 
> the period (dragonflies were huge and Archaeopteryx was a small dinosaur),

Don't the huge dragonflies, stoneflies and other large insects date from
the Carboniferous period -- when there were no aerial vertebrate predators?
By Archaeopteryx's time in the Jurassic there would already have been
insectivorous pterosaurs and the bugs smaller, faster and smarter.  But,
maybe there still were plenty of bugs to go around!

> the second is to avoid being eating by the other larger Theropods. There is 
> an equal advantage, from an evolutionary sense, between being better at 
> getting food and to being better at not being eaten.

Yes.

> So, even if they were 
> not living in heavily forested areas, there is a definate advantage in being 
> able to leap into the air, gliding and quite possibly making a sudden change 
> in direction to avoid another hungry Theropod.

The arboreal glider hypothesis is reasonable because intermediate wings
would be useful as gliding apparatus, and provide a clear path for improving
efficiency until true flight is possible.

The ground-runner hypothesis is harder to swallow because uses for
undeveloped wings are less obvious.

How about intermediate forms whose wings support only a portion of the
animal's weight, being able to pursue prey and escape from predators by
running towards and over the soft mud flats.  The partial lift from their
small wings could have saved them from sinking & getting stuck.

----
  Mike Bonham        bonham@jade.ab.ca
``Organization is the enemy of improvisation.'' -- Lord Beaverbrook