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Archaeopteryx and Flight

The possible evolution of flight from a cursorial habit could be hard to 
make, however, most people are assumming that Archaeopteryx was running and 
catching things. Some cursorial birds do this, many don't. Many hop and fly 
for short distances to avoid things (whether they are sources of possible 
danger or just bushes) but rarely run. Crows and gulls are a good example of 
this type of bird in action on the ground. I suspect the basic problem would 
be the amount of lift that could be generated by a proto-bird that lacks a 
keeled breast bone. The muscles would be much weaker without one and would 
not be capable of generating much lift. This, I think, is the crux of the 
arguement and shifts it in favour for a glider as being the evolutionary 
branch for flying birds. Once into a tree the glider does not have to 
generate a large amount of lift to get off the ground (and thus does not 
need large muscles to do this), it just has to be able to keep it's wings 
extended and let gravity do the rest. From this, the logical progression 
would be flapping to generate lift so as to travel farther or higher. This 
advantage should have been sufficient to drive the development of a keeled 
breast bone for the attachment of larger muscles. So, in all, I think the 
glider is the most likely scenario for the development of Avian flight.

And I'm sorry for the giant Jurassic dragonflies statement in a previous 
posting. It was only meant to illustrate that insects are a valuable source 
of food for many animals. I'm also sorry about that dreadful stegosaurus 
illustration I sent, it looked somewhat better on my screen.

Miles Constable
Toxic Chemicals Biologist by necessity,
By-stander and Observer of Paleontology by interest