evolution of avian flight

[invert_nexus]

Valich,

I know. I understand. All I'm saying is to curb your enthusiasm. The threads aren't 'archived' no. But they are dead. Long dead. An occasional ressurection is not something to comment on. But three pages is. Do you understand what I'm saying about burying those threads? There are threads that were active or semi-active on the front page that were written recently and have now been pushed back three pages and will never be responded to again.

Most of those threads you ressurrected will never be responded to because you overloaded the system.

I'm not going to go on about this. This is my last post on the subject. Don't take my words too harshly. I see that you're the sensitive sort from the way that you reacted to things people said in some thread on some insecure guy being stupid. I'm just trying to get it through to you that you need to curb your enthusiasm a little.

Just a little.

It's for your own good as much as the good of the forums. I imagine that you're interested in having fruitful discussions, right? Three pages of dead threads isn't going to do that. The only ones that are going to get responded to (mostly) are going to be any that just so happened to be on the first page when you stopped. (I say mostly because a number of people use the new posts search and might respond to the threads that are buried in the normal forum view.

Now. I'd be more than happy to go back and delete those posts now that you've got the message (whether you understand me is another question. I've done all I can do.)

What say you?


On topic:

First. I'll comment on the side topic that developed. The issue of the high cost of scientific journals.

I find this despicable. 10 dollars an issue?! 100 dollars a year?! And these are non-profit organizations? Yeah. Right. And if you believe that I've got a bridge for sell you might be interested in.

Thank god for piracy.

If only Tesla had been the founder rather than his nemesis Edison. Edison the businessman. Exploiter of genius. He sold a few bridges in his day.

I find it ironic that the original issue of Science was 10 cents and the modern issues are 10 dollars.


Alright.
On to the evolution of flight.
I find the evolution of flight to be one of the most amazing manifestations of the evolutionary principle. (How interesting is it that we primates have an innate fascination with flight? We're practically born wishing we could fly. An adaptation to our ancestors' lives in the trees, I suspect.)

Not only is the purity of flight amazing, but the development of feathers in particulars is truly awe-inspiring. That such complex structures could evolve as spandrels (exaptation rather than adaptation) highlights the complexities that are possible through simple processes. I sometimes wonder which is a greater accomplishment for evolution: the evolution of flight? Or the evolution of the human mind and language? Both required multiple exaptations that were of dubious benefit to the host organism before being co-opted for the eventual purposes of the modern day.


As to the methods of flight. I'd be surprised if they didn't use some type of different mechanism. Birds depend on feathers for flight. Their wing motion is in a figure eight pattern in order to utilize the propensities of their feathers (also important are the finger feathers (that's not the term. I don't know the proper term.) that extend from the wingtips and act as propellers when the bird needs that extra propulsion.)

A flying dinosaur would have none of those mechanism and therefore would fly differently. As to how the arms would hang... Well. I suspect that their wings hang much as modern birds do. Every picture I've seen looks like your typical animal with arms outstretched. I don't doubt that there were some minor differences though.

But, I would suspect that their wing motion would be more akin to bats (except that bats are far too small to model the motions in a proper way... But still would be more of a match than birds, I suspect.)

A question to ask is how soon did feathers develop. This is still up in the air. It's possible that pterasaurs were feathered and this would change their wing dynamics drastically.

 

[valich]

The origin of flight seems to be highly controversial and has very little research but in any case birds evolved frome reptiles: "Gradually the forelimbs of these creatures became feathered and even more elongated, enabling them to better manipulate their eggs and to "parachute" from their tree nests to a soft landing. Later they would develop the ability to glide and eventually fly by flapping their wings."

There are different types of methods of flight and modern birds have diverse locomotion flight styles. I'm not sure but these may correspond to the 3 different types of winged vertebrates: dinosaur flyers, modern birds, and bat, but then you also have insects, but insects like butterflies that are more like windsurfers rather than using a powered stable flight.

In any case the main factor seems to be the position where the forelimb evolved into the wing structure and the strength of the muscles: flight ability is always limited by muscle physiology. But there are differences in the flapping motions.

To see the difference in forelimb/humerus bone position go to the link www.ucmp.berkeley.edu/vertebrates/flight/converge.html Scroll down to "Avian Flight" but its complex. I don't see it exactly. You probably need a firm foundation in anatomy, but there is a definite difference in the location of the bone structure from the humerus bone.

Also, the forelimb, hindlimb and even the tail determines a birds ability to fly. But the biggest factors are the relation of muscularpower-to-bodymass and power-to-lift ratios. I don't know what a power-to-lift ratio is. "Generally, species that are intrinsically maneuverable have large wings relative to body mass, and species that are extremely maneuverable are capable of generating high mass-specific power at slow speeds by creating large force asymmetries between the two wings."

Basic flapping pattern:

"During the downstroke phase of the wingbeat cycle it moves down and forward in the flight. As the wingtip ascends during the upstroke phase it follows a trajectory offset more posteriorly (towards the rear), thus completing the clockwise loop."

www.bioone.org/bioone/?request=get-document&issn=0094-8373&volume=031&issue=03&page=0382

also see "Wing upstroke and the evolution of flapping flight"
www.nature.com/nature/journal/v387/...l;jsessionid=B3082D075C8C083456CF6EB6E9E59E9B

This gets really complex. More later.

 

[one_raven]

Is there any scientific value to the hypothesis that feathers developed from reptilian scales that "split apart" to form a warmer layer of insulation as teh earth started cooling?
I have heard this and it seems to makes sense.
Is there a correlation with global weather patterns (or localized weather patterns where early bird fossils have been found)?
Are scales and feathers similar in the material they are made of, the growth patterns, the growth rates, etc?

 

[Odin'Izm]

Birds evolved from dinosaurs and were able to fly because their wings had thin membranes compared to their body size. Their bodies had hollow bones that made them much lighter, and the wings were positioned below their torso instead of above which increased the lift surface area. The positions of the muscle structure also was a key factor.

Their wings are positioned above their torso, which IS the most energy conserving mothod, as they hang from the lift created from their wings, instead of balancing on it, this makes their flight less jumpy and less turbulant. Your first sentance makes no sence what so ever, They were able to fly because they had wings, and had enough power in those wings to create positive lift.

 

[Odin'Izm]

with greater surface area for increased lift.

Surface area has little play in this, thats why they evolved away from it in favour of a refined wing shape, birds can change the shape of their wing in flight to suit the conditions, the shape of the hydrofoil of their wing changes across its entire length as windspeed, density, direction of flight,moisture change.

 

[valich]

Yes, I agree. My first sentence above makes no sense. But wing size in relation to body mass is important and that's why aves have hollow bones - to make their body's lighter (less body mass). The article that I got some of this original info from has to be mistaken because I see now from the Pterosaurian dinosaur example that their wings were on the top of their body, not the bottom. This had me confused too because if what I remember in from flight school is correct, an airplane wing generates lift by creating a vacuum on the top surface of the wing that pulls the plane up as it flies through the air. The article stated that dinosaur flyers had thinner membranes in their wings than modern birds, which also made them lighter for flight in comparison to their larger body size.

Most of the research now being done on the different ways that birds can fly are using photography on bird wing placed in wind tunnels and the terminology gets rather complex. It involves what they now refer to as locomotor modules which defer in their physical morphological shape among different bird species (morphological determinants of mobility).

see "Evolution of Avian Locomotion: Correlates of Flight Style, Locomotor modules"
www.bioone.org/bioone/?request=get-document&issn=0004-8038&volume=120&issue=04&page=0941

Reptiles have hardened epidermal scales made of keratin which are different than fish scales. The epidermis is the outer layer of the skin. Fish scales are built around the bone of the underlying dermis level of the skin, not the outer epidermis, and are sometimes - as in sharks - made of enamal and dentine, like your teeth. In fact, shark scales are thought to have evolved into teeth.

Feathers are also made of keratin and are thought to be like elaborate reptile scales, but this is really an oversimplification. They begin as solid structures that grow out of feather follicles (like hair follicles that hold your hair in your skin). These follicles are hollow cavities (pulp cavity) that extend into the underlying dermis layer of the skin. They then grow outward in a sheathed case but they do not contain any blood vessels like skin: they are not vascularized. They then develop the outward projecting barbs with interlocking connections.

Birds with "down" feathers that lie close use these for thermal insulation. They are small soft and fluffy feathers. Ducklings have total down feathers but later develop contour feathers that enable them to fly. Birds that fly use contoured feathers - not down feathers - that are more aerodynamically shaped for flight, but contour feathers still keep them dry from the rain and protect their bodies from the sun and wind. Some birds - probably most - have little or no down feathers. Down is sometimes collected from birds such as eiderducks to use to insulate sleeping bags.

I would think that the more solid and rigid contour feathers developed first from reptile scales, and then the more softer and fluffier down feathers came later?

See "Feather Types, Anatomy, and Molting" www.peteducation.com/article.cfm?cls=15&cat=1829&articleid=2776

also www.birdsnways.com/wisdom/ww46eiv.htm

 

[valich]

Surface area has little play in this, thats why they evolved away from it in favour of a refined wing shape, birds can change the shape of their wing in flight to suit the conditions, the shape of the hydrofoil of their wing changes across its entire length as windspeed, density, direction of flight,moisture change.

Yes, but it's that contour shape of the wing and the amount of surface area available to create that initial upward pulling vacuum that determines the initial lift, but muscle strength can compensate for large surface area once off the ground. In general the larger the bird, the larger the wing. But once in flight, yes the bird changes the shape of their wings to suit conditions. Muscle strength, contour and surface area are the main determinates. That's why some birds are only "gliders," while others have more stable "lift-flying features" that enable them to flap their wings at different speeds and stay airborne. Muscle strength and contour is why hummingbirds can stay airborne in a stationary position. They flap their wings extremely fast, but it is that contour surface area - the aerodynamic shape of the wing - that they use in a circular motion that allows them to still stay stationary above ground.