more speculation on the origin of flight

[Cory Pittman <cory@cet.cet.com>]

Tracy Ford wrote:

>And what of the possibility of not having a gliding phase? If the animal 
>is a good glider why evolve into a flying animal? IMHO there was no 
>gliding phase.

If my memory is correct, modern gliders that have often been mentioned
as analogs for bird ancestors are primarily herbivores or insectivores
that use gliding (at least partially) to escape from non-gliding
predators. For such species, I agree there would be little selective
pressure to go beyond gliding since all that's necessary for a
successful escape is to get to the next tree.

However, I wonder if this was true of hypothetical gliding Theropods? To
speculate a bit, what if one assumes that there were several sympatric
gliding species of various sizes, some of which preyed on others? If a
predator could follow its prey into the air, it seems like an "arms
race" would be set up that might generate selective pressure favoring
assisted gliding and, eventually, sustained flight.

I'm not suggesting that a gliding phase was essential (a similar
scenario could be constructed using assisted running/leaping in
cursorial Theropods). However, I wonder if some sort of "arms race"
might be essential (or nearly so) as part of the equation for pushing a
lineage across the boundary to sustained flight?

Once some degree of sustained flight was achieved, other factors (access
to more widely scattered food sources, greater ease of dispersal,
greater ease in migration, ability to move nests to offshore islands,
etc.) could come into play to drive refinements. 

Hard to prove, of course.:)

Back to lurking.

Cory Pittman
cory@cet.cet.com