Actual fossils of the impossible thing.
Posted on 01/30/2002 8:06:07 AM PST by Gladwin
Modern birds evolved from ground-dwelling reptiles as their increasingly refined parenting skills led them into the trees, where they could better protect their young, proposes a researcher at the University of California, Davis.
This new theory, contradicting the two leading theories on the evolution of avian flight, appears this month in the German journal "Archaeopteryx," named after a feathered fossil with both reptilian and birdlike traits.
"The evidence indicates that a whole suite of behavioral and physical traits, including feathers and wings, evolved along with improved parenting and brood-care traits," said James Carey, a UC Davis demographer and ecologist. "Once the precursors to birds began to fly, the ecological interplay of flight and parental care may have been mutually reinforced, continuing the evolution of both traits and accelerating the rate at which the physical features of the modern bird were acquired."
The origin of bird flight is a fundamental issue in avian biology and in overall evolutionary theory. Many scientists point to the fossilized specimens of Archaeopteryx as evidence that there was a transitional vertebrate species that developed during the evolution from reptilian dinosaurs to birds. Furthermore, they suggest that the development of flight may explain why birdlike dinosaurs avoided extinction.
Until now, there have been two basic theories on the origins of bird flight. The first, the arboreal theory, is a tree-to-ground model, suggesting that birds' primitive ancestors were tree-dwellers that leapt from branch to branch. Through the ages, the ability to first glide and later fly developed because gliding slowed their fall to earth when they missed a branch.
The second, the cursorial theory, is a ground-up model that suggests that birds evolved from four-legged reptiles. According to this theory, scales on these creatures' front limbs gradually developed into feathers that gave them upward thrust when they ran and eventually enabled them to fly.
Carey maintains that both of these theories have major flaws. If the arboreal theory were accurate, birds' early ancestors would more likely have been four-legged creatures that developed membranes between their front and back legs, much like flying squirrels or bats, he asserts.
And, if the cursorial theory were true, there should have been obvious useful advantages to each form that developed between the four-legged reptile and the bird, he maintains. He is not persuaded by the suggestion that the intermediate stages of this line used their feathers, first developed to conserve heat, to swat insects from the air.
On the other hand, the parental-care theory is consistent with both the physical and behavioral changes that appear to have occurred as reptiles evolved into winged dinosaurs and finally into modern birds, Carey says.
He suggests that modern birds' very early ancestors were reptiles that established and guarded their nests on the ground, much like crocodiles. Over time, these creatures developed hard-shelled rather than leathery eggs and the ability to modulate their own body temperature in order to provide a more constant environment for their developing young. Scales evolved into feathers, better camouflaging and insulating the parents.
In time, these early ancestors of birds developed more advanced techniques for caring for their young. They started to feed their young in the nest, pumping liquid food or placing small food items in their mouths. They also began to produce fewer and more dependent offspring and smaller eggs, and began nesting in bushes and then small trees to better protect their offspring from predators.
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.
Carey hypothesizes that bird beaks also evolved in the context of parental care. The beak, he suggests, serves both as a point source of food for small hatchlings in the same way the nipple is used to feed mammalian young and also as a tool for sophisticated nest construction. This concept diverges from the commonly held notion that birds evolved beaks because they weigh less than teeth and so are better adapted for flight.
He points out that flight provided these prehistoric ancestors of birds with numerous advantages including the ability to safely place their young high in trees and cliffs, maximize their food sources through seasonal migration, and supply more and higher quality food by expanding their foraging range.
He adds that the fossil record, specifically Archaeopteryx, provides ample evidence that the evolution of parental care was the main driving force behind the evolution of avian flight. For example:
* Fossil specimens of Archaeopteryx have forelimb claws, supporting the concept that ancient bird ancestors were tree-dwellers;
* The feathers on Archaeopteryx fossils appear to be much more advanced than the creature's other birdlike traits, which is consistent with the notion that feathers evolved very early to shield the nest-sitting adults from the elements;
* The beak of Archaeopteryx is quite primitive, which is in keeping with the concept that sophisticated nest-building and feeding behaviors emerged much later in the development of parenting traits; and
* While Archaeopteryx had highly advanced feathers, its bone and muscle structure appear to have equipped it for only limited flight. This makes sense, according to the parental care theory, which asserts that flight developed long after the reptiles with their protective feathers moved into the trees.
Additionally, recent findings in Asia of feathered dinosaurs provide further evidence that feathers evolved before flight, Carey adds.
In this paper, he also discusses why flying dinosaurs with nonfeathered membrane-like wings, such as the pterosaurs, became extinct. He suggests that they perished, not because they were out-competed by birds but because they lacked the sophisticated parenting skills needed to cope with a changing environment.
Carey developed the parental-care theory of avian flight evolution while doing research supported by the National Institute on Aging, the Duke University Center for Demographic Studies and the UC Berkeley Center for the Economics and Demography of Aging.
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Note: This story has been adapted from a news release issued by University Of California - Davis for journalists and other members of the public. If you wish to quote from any part of this story, please credit University Of California - Davis as the original source. You may also wish to include the following link in any citation:
http://www.sciencedaily.com/releases/2002/01/020130073659.htm
The present consensus is that feathers did not evolve directly from scales but are a novelty -- probably a cylindrical follicle producing a conical papilla that evolved into a branched structure. The biochemistry, 3-D structure, and genes are different for scales and feathers. Birds retain scales on the bottom of their feet that are chemically identical to reptile scales. Bird scutes, claw-sheathes, and beaks are chemically identical to the feathers. The genes for feather proteins are located adjacent to and in the same relative position on a bird chromosome as the scale genes in the Crocodile, for example.
Feathers evolved originally as insulation. Exaptation for flight occurred much later. A recent example of exaptation is the use of the wings as glare shields by the African Black Heron. Clearly the wing structure evolved without any anticipation that it could be used for the purpose of shielding a patch of water from the sun, yet that is what the bird uses it for as it feeds in the shallows.
Antifunctional? I love it when creationists make up words to sound like they know what they're talking about.
How would a set of gradually improving feathers or bones be "antifunctional" every step of the way towards flight?
They don't need everything to fly, they just need everything on your checklist in order to fly well. The idea is that they flew poorly at first, and eventually got better at it.
And the idea that evolution has been somehow disproven or dscredited is ludicrous.
No, males and females share most of the same DNA. In our case, we have twenty-three pairs of chromosomes. Males and females have essentially identical DNA in 22 of the pairs, the other pair is made up of X- and Y chromosomes.
You need everything on the list just to fly poorly. Picture some bird with half-formed flight feathers or with the flight feathers but not the system which lets them rotate open like venetian blinds on upstrokes. He wouldn't get off the ground.
dinnertime and the end of this as a new species.
Take for example mules, half-horse and half-donkey.
If a man has a minor (or even major) mutation, he may still be able to mate with a "normal" woman and produce viable offspring.
Simply--how can an organism survive without lungs when it is busy evolving a circulatory system? You're seriously telling me that the organism can do both at once, along with the nervous system, immune, sexual...all at once?
To which I'm told--you ain't no scientist.
Evolution, however, is a fabulous means of description, without its religious dogma. It is so effective at categorizing and classifying that I think it must have assumed some other proportions in the minds of the witch doctors...
Quite a few. Most evolutionists think it would have taken millions of years to make leaps like this.
And what about the inbetween mutations? Where are they? There would have to be some (actually many) around.
They could have died off if they couldn't compete with the newer animals. A modern bird would be able to fly much, much better than a half-bird half-lizard creature. The half/half creature would die out if it couldn't compete with birds (if predators could kill it more easily than a modern bird, it would die out, and eventually become extinct).
Remember, too, that the jenny (the offspring of a horse and a mule) is sterile.
Yes, sometimes mutations preclude animals from mating, just as sometimes mutations leave humans sterile. The thing is, the sterile ones die off very quickly, whereas the fertile ones are able to keep passing on DNA.
Better tell that to the bats, bees, honey gliders, flying squirrels, flying fish, pteradactyls, pteranodons, etc., etc. There is even an arboreal snake that does a pretty good job of simulating flight. With your argument the Wright Brothers shouldn't have been able to fly until they were provided with a Pratt & Whitney Jet Engine and a Boeing airframe.
Better tell that to the bats, bees, honey gliders, flying squirrels, flying fish, pteradactyls, pteranodons, etc., etc.
Irrelevant. We're talking about evolving into a flying bird and a gliding squirrel or lizard is not remotely close to a plausible 90% point for getting to flying bird status. For a bird or anything trying to evolve into a bird to fly, even badly, all features would need to be in place.
You could "fly" yourself if you wanted to. Especially if you first climbed a tall tree and relied on gravity for acceleration. At least you could accomplish a steep dive without any wings, feathers, hollow bones, enlarged respiratory system, or big breast muscles. Because you don't know what the first proto-bird looked like it is a bit presumptuous of you to assume that it could not do at least as well as you as a "flyer" of sorts. This proto-bird may have been very well adapted for steep dives, perhaps it hunted this way. Perhaps it had sufficient control surfaces to adjust its trajectory while diving. It really doesn't take very much to begin to fly.
Now to your second mistake. No living thing "tries" to evolve. Becoming a bird is what happened to the progeny of those collections of breeding individuals for whom survival depended on falling without damage which led to diving with accuracy which led to gliding for distance which led to soaring aloft which led at last to flying. The best at each stage tend to leave more progeny than the less accomplished and the process accelerates when a species moves to an unoccupied niche (i.e., the sky is the limit).
Very small changes in gene expression (ie one non-functioning gene) can have large consequences. For example, whether a baby develops male or female genitals is determined by three chemicals: anti-mullerian hormone, testosterone, and 5-alpha-reductase. If one of these chemicals is not produced then the baby will have problems. For example, genetic male babies who cannot produce 5-alpha-reductase due to a genetic mutation do not develop a penis and scrotum.
Likewise, it's possible that a small genetic change in reptiles could produce scales that look like feathers. I don't know enough about reptiles and birds to say for sure.
Actual fossils of the impossible thing.
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