I posted a half-formed theory to this group years ago, regarding the evolution of flight in birds. Here it is again, this time with a lot more detail, and a lot of loose ends cleaned up. The following is a an almost verbatim text dump from an essay I've posted on my home page. >From Sea to Sky, the Ascent of Birds ==================================== There have been many theories about the origin of aerial flight in birds; here's mine. Since Archeopteryx is generally recognized as the earliest bird fossil, it's a convenient place to start. There has been much speculation about how, and for that matter, if, it managed to fly. Let's look at what we do know... * Archeopteryx did not have the weight-saving adaptations of modern * birds, i.e... + it had not lost its teeth + it did not have the lightweight bones of modern birds + it had a real tail which, besides adding extra weight and drag, moved its centre-of-gravity well behind its wings * the wingtips did not have long primary flight feathers. * that point was moot, because the shoulder joint did not allow the wings to be raised much above horizontal * that point was moot, because there was no hole through the shoulder joint through which to pass the large tendon that gives the rapid and powerful wing upstroke in living birds * and that point was also moot, because it lacked the prominent breastbone of modern birds, onto which to attach large muscles to contract those tendons. To summarize... 1. It was too heavy to be a glider. Gliding also implies climbing up some structure in order to be able to jump off it. The desparate attempts to picture a "bird" clawing it's way up a tree are laughable. That fact that the paleo-climate of the Solnhofen Lagoon district during Archeopteryx's time was desert-like, with no large trees in the vicinity, should help kill that idea. 2. As for powered (i.e. flapping) flight, it didn't have the breastbone to which to attach muscles to contract the tendons it didn't have, which didn't pass through the holes that it didn't have in its shoulders, which didn't have the joints to allow flapping of its wings, which didn't have long primary flight feathers. 3. And in any case, the claws on the leading edge of its wings would destroy the aerodynamic airflow, and the long bony tail would push the centre-of-gravity well back of the wings. Archeopteryx never flew; deal with it. Could Archeopteryx be a flightless descendant of a bird that flew? Since Archeopteryx is the earliest known feathered and winged fossil, that seems rather unlikely. That idea would also require totally insane reverse- evolution, i.e. the shoulder joint reverting to theropod style, and the return of teeth. So we can safely conclude that none of Archeopteryx's immediate ancestors flew, either. Well, if none of Archeopteryx's immediate ancestors flew, that implies that it evolved aerodynamic feathers (picky, picky, picky) and wings for reasons other than aerial flight (picky, picky, picky). Any theory of the evolution of aerial flight in birds must address that issue. It would also be nice to be able to explain how the first attempts at flight could result in crash-landings without killing the bird, or maiming it to the point where it was unable to fend for itself, and starved to death, if it wasn't eaten by a predator. My theory starts off with a feather-covered theropod that is ancestral to Archeopteryx. For anybody who doesn't like that idea, I refer you to Sinosauropteryx, Caudipteryx, Shuvuuia, Sinornithosaurus, Beipiaosaurus, etc. Here is how I propose things went... 4. We start off with pre-Archeopteryx, a small, bipedal theropod with forelimbs like those of Coeleurosaur. It has an insulating coat of feathers. 5. Pre-Archeopteryx discovers that plants, crustaceans, and even the occasional fish along the shore are delicious. This discovery may have been accelerated by climate change which reduces food supply away from the shore. In pursuit of its food, it starts spending more and more time in the water. 6. What happens to land-dwelling vertebrates that start spending a lot of time in water? Riiiiiiiight! Their limbs tend to evolve into flippers. Our feathered, bipedal, theropod's forelimbs start looking like wings. Part way through the process, it will still have some claws on the leading edge of the flippers. Since it still spends some significant time on land, it's feet will still be that of a land animal. It's a bird, it's a plane, no it's our friend Archeopteryx. Things start making sense now. The reason that we find Archeopteryx's fossils only in a lagoon, is because it was a flightless feathered theropod that spent quite a bit of time in water. A flightless bird/theropod that spends a lot of time in water doesn't have to worry about shedding teeth to reduce weight. Claws on its wings can be used to grab fish or other prey. The fact that its feathers aren't suited for flight is moot. Their purpose is to keep the animal warm, and not get in the way when it runs around in the water. What little swimming it does probably consists of breast- stroke or dog-paddle, because it doesn't have bird-type shoulder joints. 7. A few million years pass. After spending even more time in water, adaptations continue. The feet get webbed and the shoulder joints evolve to a bird-like mode to allow raising its forelimbs above its shoulders. This allows a more powerful underwater swimming stroke; actually "flying underwater". To supply the necessary power, it needs stronger muscles, and a place to attach them to (keelbone). Now that it's wings are used for "flying underwater", "flight feathers" start to be an advantage. Since it hasn't yet flown aerially, there is no advantage to shedding its teeth. Hesperornis would be a reasonable specimen of this stage. Our flightless bird spends a lot of time "flying underwater". It learns to navigate in 3 dimensions, which will be important later. The Avian Kitty Hawk -------------------- A Hesperornis-like "flightless" bird is minding its own business one day when along comes a big fish, or whatever, that thinks of our bird friend as a yummy meal. It gives chase and the bird flees, with rapid frantic wing-strokes. Since it's an air-breathing animal, it needs to surface to breathe. It's moving as fast as it can to escape its predator, so that it not only gets to the surface, but most of its body gets clear out of the water. Since it's being pursued, it keeps flapping its wings... and flies several metres before landing back in the water, giving itself enough of an advantage to get to shore safely. Having discovered flight and its survival value, water- birds were able to able to parlay their "underwater- flying" skills to aerial flight. Crash-landing in the water after getting one or two metres into the air is a lot less likely to kill/maim a bird than crash-landing on hard land. Landing on floating logs, and then on branches of floating logs will be the next step in acquiring tree- landing skills, without killing themselves if they don't do it exactly right the first time. Birds didn't evolve aerodynamic feathers for the purpose of aerial flight, they evolved hydrodynamic feathers for the purpose of underwater flight; yeah, picky, picky, picky. Yes, I have read Elaine Morgan's book "Descent of Woman". Read into that what you will. -- Walter Dnes; my email address is *ALMOST* like firstname.lastname@example.org Delete the "z" to get my real address. If that gets blocked, follow the instructions at the end of the 550 message.