Re: cursorial flapping -Reply

["Nicholas R. Longrich" <longrich@phoenix.Princeton.EDU>]

        One preadapation towards flight that arboreality may cause is 
developing the arms and putting them in the right position. I don't know 
how constrained the movement of theropod arms are, but whenever I see 
squirrels, I notice how sprawled out the legs are when they run over the 
ground. When they get up in the trees, the arms spread wide to grip the 
trunk. This puts the arms and legs in a perfect setup to develop a 
glide-plane. One problem is that the motions employed are the opposite- 
squirrel arms produce most of their power pulling backwards, while birds 
produce their power an a forward, downward stroke. But what might develop 
these muscles would be clmibing forward down the tree, instead of up, 
and, once glide-plains are developed, the muscles to hold these in place. 
The problem of course remains the flapping.
        
        Various other points- for "predator free" evolution of ratites, 
after the dinosaurs went exinct, things were pretty "predator free" for a 
while. And flightless Cretaceous forms may have evolved opportunistically 
after the end of the Jurassic, it may be that predators were not doing 
especially well for a few million years.        

        Fliht in general is a good adaptation. There are over 9000 
species of bird and 1000 species of bat. Pterosaurs preserve under 
only very rarely due to their delicate construction and paper-thin bones, 
but we have over a hundred species of 
them, implying great diversity. Birds were probably more diverse than we 
think in the Cretaceous, as well. And it is very possible  that why the
 insects have done as well as they have (as opposed to say, arachnids
 or other arthropods) is because they can fly. I'm guessing that the 
flying groups far surpass the nonflying groups in diversity among the 
insects. Well, actually, I don't think weevils can fly, can they? Change 
that to "flying and secondarily flightless insects".

        I live on an archipelago, and at home, I see the crows flying 
over the water quite frequently, sometimes in large numbers, and they 
enjoy foraging on the ground, in trees for berries, or in the tidepools 
for whatever the heck it is they eat down there- fish, isopods, snails, I 
don't know. This seems like a lifestyle that Archaeopteryx might have
 enjoyed.