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
Upon further inspection, it appears your source provides "Obliquity to Orbit"; my source simple refers to the parameter as "Inclination of Axis." If the Inclination of Axis is measured with respect to the ecliptic instead of the Martian orbital plane, the two values should vary by the amount equal to the Inclination of the Martian orbit to the ecliptic. This value is listed as 1.85° and change, which when subtracted from your source's figure of 25.19°, yeilds a figure very close to Norton's value for "Inclination of the Axis."
In the alternative, I suppose Saturn could have swooped in on Mars while we weren't watching during the past 30 years and side-swiped it, causing the axis to change it's inclination. That would fit right in with the rest of medved's planetary weirdness.
The fact of the matter is that, no matter how stupid the Saturn thesis may sound to you, it doesn't begin to compare to evolutionism. In fact, I could even believe that we were orbitting Saturn NOW and even that would be positively brilliant compared to evolution. Nothing in the Saturn theory involves an infinite sequence of zero-probability events and nobody is demanding that the Saturn theory be taught at a fact in public schools at public expense. You have to keep these kinds of things in perspective.
A single zero probability event suffices for the honest man. The claim that there are an infinite number is a didactic device with one purpose -- to deceive. This permits the proselytizer to retort that even though every single zero probability event he is capable of itemizing is shown instead to have a probability of one there are still an infinite (not itemized) number left to substantiate his false claim.
A famous biologist (I forget who) once replied "Statistics are for losers" to a colleague who requested numerical data supporting the biologist's thesis. By this he meant that understanding how something actually works cannot be achieved by simply measuring a few parameters of the system and calculating averages and variances. Once the mechanism is described and the processes determined it is possible to predict the behavior or response of the system without resorting to statistics.
It is also well known that statistics can be manufactured to suit any purpose (e.g., "How to Lie with Statistics"). Nowhere is this fault more apparent than in the purposely deceitful use of statistics to "prove" that known events (i.e., evolution) did not happen.
A single zero probability event suffices for the honest man.
I take it you do not believe in evolution. Or are you claiming to be dishonest?
Belief does not enter into it. Understanding evolution depends only on knowledge of the physical world. The existence of the process of evolution is an irrefutable fact. Life on this planet is old and has changed continuously since its inception.
You seem not to recognize these simple facts yet you espouse preposterous conjectures with no basis in reality in order to create the appearance of statistically impossible events that preclude the natural progression of life over time. Here is a simple test of your method. Try it going backward through time. Life begets life in a continuum. Life today is clearly different than life even in the recent past. Because you will be dealing with known events (probability one)at every stage you will be forced to recognize (if you are honest) the absurdity of your zero probability argument.
Microevolution is a fact. Anything else, including the so-called theory of evolution, in all its guises, is an ideological doctrine and a belief system, like communism or naziism. Try reading through my large post above for comprehension rather than simply for making your knees jerk. The arguments involving probability are sufficiently real. Evolutionism and mathematics are incomparible. You've got world-class mathematicians like Fred Hoyle and Bob Bass claiming macroevolution is impossible and you had the Wistar symposia at which a collection of the world's best mathematicians told the evos they were FUBAR. You're beating a dead horse.
You must have posted that thing about 200 times by now. I practically have it memorized. It contains not a single valid argument and this has been pointed out to you well more than 200 times.
Crusading pseudomathematicians can write as many equations as they want. Examine their assumptions and there are always mistakes. No exceptions. Hypothesizing fictitious conditions to produce a predetermined outcome is a piece of cake for a motivated math hobbyist. Mathematicians or biologists modelling real systems however have no problem producing equations with real predictive power. Try reading Stephen Hubbell if you finally want to dispel your persistent illusion that math is incompatible with real biology.
Oh, I see. That's why the pterodactyl went extinct? It couldn't shield its young as well? How precisely would feather outweight skin in shielding against the elements? And a bird would evolve relatively complex feathers merely for the purpose of shielding young against the elements? Did it develop feathers before or after it developed the claws, before or after it started roosting in trees? Can any of these questions be answered?
I don't personaly see that many of these questions can be authoratively proven- so why spend tax money on it? Yes, we should pursue knowledge, but can we expect to discover why birds evolved wings?
This is kind of stupid. If scales are going to "evolve" into feathers in order for better camoflage and insulation, why didn't scales just "evolve" into fur and/or a fat creature with fur? I thought the reason why birds have feathers is that they enable flight while still providing warmth.
And if this theory is true, then why didn't everything develop feathers? For example, if warmth and camoflage is the criteria, then fat and fur seem to much more practical and would hold an advantage over feathers for the simple reason that fur is easier to maintain than feathers. The loss of one feather is more of a loss than the loss of one piece of hair.
The problem with the theory is that the little proto bird who just needed to keep warm and camoflaged had not a clue that one day it would also have to fly. If feathers are going to randomly appear one day (no mean trick in itself considering their complexity) for the express purpose of warmth and camoflage, then the obvious evolutionary advantage would have been to evolve as a penguin form, useless for flight, but great for warmth. Then, we're asked to believe that a different function was needed for the feathers, so the warmth feathers have to devolve and re-evolve into feathers good for another use. Not bloody likely.
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