http://scienceblogs.com/tetrapodzoology/2008/10/unhappy_with_aerosteon.php

http://svpow.wordpress.com/2008/10/31/the-aerosteon-saga-part-3-true-and-false-ad-hominems/

and points linked therefrom.

I’m not so enamored of the notion of the transition to flight via climbing and gliding off trees. Instead, IMO everybody’s ignored the “wing in ground effect” (WIGE) that can allow an airfoil close to the ground to “fly” with much less energy (less than 1/10^th?) than free flight out of ground effect. Also, an animal using WIGE can get forward impulse from its feet, rather than having to use its wings as propellers. This means they don’t need to evolve specialized adaptations for flight, just hold their feathered arms out like sails, and run. Sort of like what ostriches do. (I wonder whether ostriches don’t have much more endurance running than similar-sized mammals. IIRC there weren’t any studies of the subject when I looked a while back.)

The relevance here is that if WIGE had evolved early, many (perhaps all) theropods may have evolved from an ancestor using it. We would see multiple independent evolution of the deep sternum structure (which, IIRC, is actually needed to anchor the muscles that pull the wings up, although I don’t remember the exact logic). We would also see multiple evolution of large size, abandonment of flight (even WIGE), and growth into massive predators. It makes perfect sense to me that the Tyrannosaurs might be evolved from a flying animal. (Allosaurus is somewhat less plausible.)

In this scenario, the Jurassic “archeopteryx” might be descended from a long line of small WIGE fliers that had retained a fully workable ancestral form from the late Triassic.

This is also relevant to the pass-through lungs. It seems likely that they evolved independently (from the mammalian form) from the simple sack-lungs possessed by the small ancestors of the diapsids. Both lung forms probably (IMO) evolved during (or before) the Triassic as the need for extended exercise drove improved lungs. As with the inner ears, we shouldn’t (IMO) regard one form as “primitive” from which the other evolved, but see them as independent developments from a truly primitive form: the simple sack-lung.