origin of birds

I keep reading that the debate is between 'ground up' and 'trees down'. Has 'water up' been ruled out?

The big problem I have with 'ground up' and 'trees down' is that the ability to fly only helps your survival if you can do it. Half way measures get you nothing. Rabbits don't seem to be evolving towards the ability to fly.

I see a small critter about the size of a sparrow that occupies the niche currently occupied by ducks. It would lose mass in order to float better. It would grow feathers for insulation. Most importantly, the ability to fly just a few inches above the water for a distance of only a few feet would give it a real edge in surviving underwater predators.

Good question: 'Water up' has been proposed, I believe with forms like Archaeopteryx being divers that learned to fly in air (sort of the opposite of penguins). This idea is usually criticized and does not have much of a following. However, the 'ground up' got a big boost a few months ago with the proposal which I believe was called 'wing-assisted vertical running' or something like that. The idea is that birds first used wing-flapping to aid them in getting up inclines (hills, tree trunks, or whatever) to escape predators, find more food, etc. This would have provided the evolutionary impetus for improved flight abilities in a gradual manner. This idea has been received very well.

Come to think of it, chickens run a lot faster when they flap their wings. ZThis might help some of the predatory species chase down prey...kinda makes Unenlagia make more sense.

Hmmm.

I'm not surprised.

This cannot work because the predecessors of a wing-flapping animal which did not use this mechanism would be in a disastrously, cumbersome state and as such would be easy prey.

Surely the ancestors of birds glided from tree to tree to avoid capture and to get food for themselves.

I can't see why, when the trees down hypothesis explains everything

Actually gliding is most likely the preliminary stage for powered flight. Scientists have shown that gliding is an economical way to travel for an arboreal animal. It saves the glider a great deal of energy to glide from one tree to another, instead of having to climb down a tree, walk across the forest floor and then climb up another tree. In fact, gliding is so attractively economical that many living and extinct animals do it. Lizards, frogs, snakes, monkeys, squirrels, marsupials, and of course birds do it.

Rabbits are not arboreal animals. They do not save energy by gliding.

Buoyancy does not depend on mass, otherwise the Queen Mary or the Titanic would never be able to float. Buoyancy depends on reducing density, not mass.

But in order to escape underwater predators, one must be able to see them. Unless one has eyes on one's belly or feet, it is nearly impossible to see predators that are submerged. Most animals that live near the surface use a different anti-predatory strategy: camourflage. These animals usually have light colored bellies since when one looks up from underwater, one sees bright light, at least during the day. Light colored bellies would be a perfect camourflage for an animal found on the water surface. It would also be more economical than to constantly try to fly to escape an enemy that may not even exist underwater.

I would not be surprised. Wagner and Gauthier's frame-shift hypothesis has also been well received by those who believe in the dinosaurian origin of birds. If one has 'faith' (Feduccia 1999:405) in the dinosaurian origin of birds, then it would be easy indeed to have faith not only in the frame shift hypothesis, but also in the ground up origin of flight as well. 'The devil,' of course, 'is in the detail' (ibid).

Thank you for your reply

except that we don't really know that. If we did there wouldn't be any debate.

You are, of course, correct. Density, specifically bone density, is what I was thinking of.

Not necessarily. All you have to see or hear is your flock mate getting gobbled up. When a flock of birds all takes off at the same time, I don't think it's because they all independently saw the same predator at the same time.

What about that lizard (Jesus lizard?) that runs across the water. How come it doesn't swim?

According to biophysical analysis, it is next to impossible to evolve flight from the ground up. So, we do know that the ground up theory of flight is implausible. But that does not mean that everyone will automatically agree or the debate will end. Witness the debate over the origin of snakes. The fossorial origin of snakes requires that the snakes re-evolve hindlimbs from a limb-reduced ancestor. Everyone in the debate agrees that this is either implausible or improbable, yet the debate continues. Similarly, it is implausible that the 2-3-4 fingers of birds evolved from the 1-2-3 fingers of the theropod hand, especially since no tetrapod species has ever re-evolved a lost digit, but the debate over the origin of birds continues. According to Mayr (1998), sometimes scientific consensus cannot be reached despite the presence of convincing evidence because of reasons that have nothing to do with science. According to Mayr, sometimes consensus cannot be reached because some scientists have ideologies that make a theory unacceptable to them. The cladist's ideology, for example, makes the dinosaurian origin of birds the only theory that they are willing to accept.

That may be too late.

Water fowl often take off from a body of water because of the presence of hawks or ground predators, not because of underwater predators. In fact, a snapping turtle or an alligator can often surprise a water fowl from below the surface. Flight almost certainly did not evolve as an escape mechanism from underwater predators for water birds.

Who says it does not swim? Basiliscus vittatus, or the 'Jesus Christ lizard' is an excellent swimmer. See the following web site:
http://animaldiversity.ummz.umich.edu/accounts/ basiliscus/b.

an understatement

I wish I could be as certain as you are, especially given the paucity of evidence one way or another.

You make a good point about the difficulty of seeing an underwater predator. Looks like I better hang on to my day jor a little while

Ducks would need polarizing filters to see clearly underwater from above the surface. There is no evidence that any water fowl has built-in polarizing

Witness the debate over the origin of snakes. The

I'm curious