Evolution of the Feather and the Origin of Birds

THE EVOLUTION OF THE FEATHER AND THE ORIGIN OF THE BIRD

This is a paper that explains about the origin of birds and the actual evolution of the feathers. The paper details about the way the feathers had first evolved and the way these birds had their origin. The common belief that the dinosaurs are the ancestors of these birds has been analyzed and the paper also deals with as to how the feathers of these birds would have developed.

The origin of feathers is unknown. Scientists have researched on this topic but none of the theories have even come close to being proved. In the past five years there have been efforts to answer as to the real evolution of these feathers. The mystery of the evolution of feathers is closely linked with the origin of birds themselves. The origin of birds has always been one of the liveliest debates in paleontology. There are various evidences that show that birds have evolved from small predatory dinosaurs known as theropods. This evidence has been accepted by most of the paleontologists, although there is still a small group, which does not believe that there is a close relationship between birds and dinosaurs. There have been discussions that lead us to believe that either the birds are dinosaurs themselves or probably they share a common ancestor. It was thought earlier that the evolution of feathers and flight were intimately linked, but the new fossils discovered in China show that feathers originated even before the evolution of flights or birds.

DISCUSSION:

bird’s most distinctive attribute is its feathers. Traditionally it was thought that the evolution of feathers was linked to the origin of flight, but studies now confirm that feathers existed even in the non-flying dinosaurs, which shows that feathers pre-dated the origin of both flight and birds. The actual progress of feathers is not fully known because of various misleads one of which actually states that the primitive feather actually came about due to the elongation and division of the reptilian scale, and the misunderstanding that feathers evolved primarily for the function of flight. Another hindrance in the concept is that of the lack of the availability of primitive fossils. Many contributions from several fields have tried to bring about a solution for these problems.

One of the foremost evidences is that there have been attempts to begin to try and find new evidence for the idea of that particular developmental process and also the complex mechanisms by which an individual organism actually grows to its full size and form and actually provides a new aspect for the evolution of the species anatomy. This had helped on the whole to contribute to figuring out the evolution of feathers. Along with the hair, nails and scales, the feathers are also integumentary appendages, the skin organs that are formed by a controlled increase in cells in the epidermis, which is the outer layer of the skin, that produces the keratin proteins. A proper feather usually has a main shaft called the rachis. (Prum, and Brush, 2003)

Thick scales on the top of a bird’s foot are called Scutes. These are also present on the back of the foot, called scutellae, and scales on the bottom of the digits, called reticulae, in a smaller size. The chemical composition of feathers is like that of the Birds scutes, scuttelae, claw sheathes, and beak sheathes, and scales around the eyes according to Alan Brush’s analysis. Also the same genes control them both. Scutes developed into feathers in a chick, when it was infected with a virus, in15-18th day of its development. Feathers development ranged from thickening of the edge of the scute, to short, fat feathers, to long, thin feather filaments. The barbs characteristic of normal feathers was found in these feathers, although the barbs were more numerous. Apparently the scutellae also develops into feathers to various degrees. (Sues, 2001)

The feather development process also throws light on the probable nature of the primitive structures, which are considered the evolutionary ancestors of feathers. According to the developmental theory, it is said that feathers evolved through a series of transitional stages, where each stage saw a novel development, a new growth mechanism. The prior stages of development paved way to a new stage, for a novel innovation in that stage, a series of which brought about the evolutionary process. Most of the lineages of dinosaurs had scutes and scutes have developed from feathers. Then maybe feathers are a primitive characteristic of the dinosaurian as a whole. We assume that the earliest dinosaurs would have had to have feathers, while later, larger dinosaurs such as hadrosaurs and tyrannosaurs could have lost their feathers, much as hippos and elephants have lost most of their hair today.

These feathers mostly resemble the non-flight feathers more than the specialized flight feathers of birds. The duck-billed hadrosaurs shows the animal’s entire body covered with scales.This is one of the best known examples.This type of scalation is not squamate, or imbricated, as it is in many reptiles, e.g., snakes, and the scutes on the feet of birds.The dinosaurs skin is consistently composed of pebble-like scales. These scales form a continuous rosette pattern which shows a field of small scales around larger scales. The larger scales are the tougher skin surfaces which also serves as a mechanical protection, other than giving the outer layer of the animal an ornamental look. The largest scales are found on the edges of the limbs.(Martin, and Czerkas, 2000)

The statement ‘feathers are a primitive feature for the dinosaurian’ is supported by the recent fossil discovery. Pelicanimimus dinosaur’s fossil skin impressions show that this dinosaur had hair-like integument, similar to Kiwi feathers. Although even before the dinosaurs evolved scutes could have evolved from feathers. This makes feathers primitive not only for the Dinosauria, but the entire Archosauria (the group formed from the common ancestor of the Dinosauria, Pterosauria and Crocodylia). Recent discoveries have proved it beyond reasonable doubt that pterosaurs had ‘fur’. Longisquama, the theropod that has the Archosauria as a common ancestor had some sort of scale like structure, which was called protofeathers by some. This evidence support the theory of many ornithologists that birds share a common ancestor with the dinosaurs, rather than descend directly from the dinosaurs (this makes the birds the fourth group of the Archosauria).

If feathers are primitive for the whole group, there is no reason to think that birds had to descend from dinosaurs. The feather structure for the Archaeopteryx is very noticeable when compared to its moden structure. The multifaceted structure of feathers in these proves that the feathers rose only once in these birds and they formed all the major features of the birds even before the dichotomy of birds into Sauriuare, the Archaeopteryrx and the enantiornithine birds, and the Ornithurae, which consists of all the modern birds and the Early Cretaceous Chayangia.

For nearly a century now, many debates have been had as to the exact origin of these birds and two theories have come up to support the idea. According to the arboreal theories, it was the creatures that lived in trees, which first started to fly. It had all supposed to be started with a gliding stage.

This concept has been promoted by the belief that flight is more effective at higher speed. Also the flight stroke that is ultimately gained in a higher altitude from the ground is simpler. But there is also another theory that helps to explain that animals that live on the ground probably have better flight as the start of with running on the ground. The fact that these terrestrial animals, the bipedal theropods have all the parts that birds used in flight stands to signify that these animals were probably responsible for the evolution of birds. And also the particular aerodynamic models of these earliest birds also help to prove that these could be used for helping the legs to get enough speed to help them in a take off while running. (Prum, 2003)

The diffrence that can be seen between the way the Archaepteryx used its wings for flight and the actual modern bird does not seem to be very different. It has basically got to do with the ‘triosseal pully system’ and the fact that they should be able to flap their wings over their back, which lets them fly from their ground. If the Archaeopteryx was actually on the ground and it had a horizontal back then the dorsal gleniod would be absent and then these birds would have been prevented from flying. The fossil record that is available of these feathers does not help in any way to actually lead us to the origin of these feathers, that cannot be really figured from these living birds. Alongside, the dinosaurs that are known to be the ones who were the ancestors of these birds are not of too much help either. The supposed feathered dinosaurs the Protarchaeopteryx and the Caudipteryx are actually flightless birds.

In the Washington Post, an article was published by John Schwartz in which was stated though most paelontoligist feel that the fierce Tynasourus Rex looks like a chicken, because of the anatomical similarities seen between this ancient reptile and the modern bird. But researchers have come to realize that the fossils of some particular creatures found in China resemble the ancestors of the modern bird. These help us to give us critical clues about the structure, function and evolution of the modern birds and their intricate appendages.Several reports of feathers and feather-like structures in various theropod dinosaurs from the Yixian Formation of Liaoning province in northeastern China have been found in recent years. A series of layered lake sediments and volcanic ashes is what is called the “Yixian Formation.” The Yixian Formation is of Early Cretaceous age (dated at 125 million years ago). Remarkably preserved fossils of an amazing array of terrestrial, flying and aquatic animals are found in this deposit. The sedimentary rocks retain traces of soft tissue sometimes even identifiable gut contents, as by nature they are fine-grained. (Schwartz, John)

From the Yixian Formation, Sinosauropteryx, one of the theropod dinosaurs showed fiber-like structures which generated from the back of the head, neck, back and tail. Some researchers considered it to be feathers, while others believed it were frayed internal fibers of collagen, which is a structural protein found in connective tissue. Two other theropod dinosaurs from the same deposits, Caudipteryx and Protoarchaeopteryx anyway undoubtedly possessed true feathers. Small feathers covered the body in both the cases. Feathers were also attached to the second (longest) finger of Caudipteryx and it also had a fan like arrangement of feathers on the end of its tail. Its skeletal structure does not support the claim of the opponents of the theropod-bird connection, who believe that Caudipteryx was actually a flightless bird. Protoarchaeopteryx also bore a symmetrical fan of feathers. A nearly complete, articulated skeleton of an unidentified dromaeosaur, whose body is covered with densely covered feather like structure, is one of the latest remarkable findings from the Yixian Formation.

Feathers originated and were initially present in non-flying theropod dinosaurs is clearly realized by the exceptionally preserved fossils from the Yixian Formation which strengthen the case for the theropod-bird connection. This clearly shows that feathers evolved for some purpose other than just flight, maybe it acts like a thermal insulation or say a behavioral display (or both), which is still retained in today’s birds. Theropod’s feets are inherently webbed. Biologist’s recent experiments of studying webbed toes may have provided an important clue. The webbed toes become free at a certain point in the development of fetus. Ducks are an important exception to this. Dr. Hongyan Zou and Dr. Lee Niswander wondered about this particular exception and on conducting experiments they realized that it was the absence of some protein in the feet of the ducks that let them to remain to be webbed.

This same process was also carried on with different other birds and little fury animals to realize that these it was the lack of this protein that actually caused scutes on the feet to develop into feathers. From the experiments conducted by Zou and Niswander and Alan Brush, it comes to our notice that scutes evolved from the feathers. But the actual origin of these feathers has not been proved. It does not help in removing the hindrance to the dinosaur theory. By suggesting that the feathers did not evolve from scales, scutes, they do not make things easier by suggesting that these actually developed from feathers. Moreover, dinosaurs also had these particular features. There are also other discoveries that suggest that these dinosaurs may also have had feathers. But whether these feathers were present in the archosaurs group or whether they belonged to a group that resembled them is a question that makes us wonder all the time. But by the suggestion of these researchers and the findings of the new dinosaurs Sinosauropteryx, it brings a little closer to make us realize that there is a relationship between the dinosaurs and the birds. (Poling, 1996)

From the various specimens that were discovered in China it could be realized that these have been the best find of ages. From this we have come to realize they are different in various forms of stratigraphic positions, phylogenic implications and their completeness. These findings yielded Confuciusornis, a skeleton of the bird, and also Liaoningornis, which had a keeled sternum, which brings to realization that these were the earliest signs of flight in the bird’s structure. This keel extended to the front of the sternum and also present was coracoidal sulci. The most recent works on these show that the late Cretaceous enantiornithines did not have endothermy.

There were also certain other fundamental anatomical differences present in the two avian groups that explain the reason why these have different ways of representing their way of locomotion. This was because that along with the fact that they had curved claws and the fact that these Liaoningornis spent a lot of their time on trees. But still the whatever the arguments be, the oldest available evidences for feathers are still only those of the Archaeopteryx, which belonged to the Jurrasic of Germany. Moreover, most of these also have some feathers on the specimens and they are being preserved in some strutural detail. But still there is no real evidence for the contour feathers, except for a berlin specimen which shows them on their legs. Though this is the place where most of these feathers are found, as they were first found in the Confusciosornis, the oldest fossil found in record. But at the same time, unfortunately there were no traces of these contour feathers in the Archaeopteryx specimens. (Hou; Martin; Zhou, and Feduccia; 1996)

CONCLUSION:

The debate on bird’s origins and the significance of shared characters with the dinosaur will continue. Although this debate will include one new factor, the similarity of dinosaur feathers to bird feathers. If the feathers of Sinosauropteryx are proved to be very close to that of birds it may add doubt relating to the dinosaurian ancestry of birds into the fold. All the basic features of feathers must have been in place before a basic dichotomy into Sauriurae and the Ornithurae occurred.The oldest feathers are identical to todays modern feathers, even to its microscopic detail even down to its basic features of the feathers should have been the same before the dichotomy into the Sauriurae and the Ornithurae occurred. This makes us realise that this division must be much older than the Archaeopteryx and probably even much earlier than that period. The actual date as to the Jurrasic Cretaceous is still not been decided upon, though the Confuciusornis and the Liaoningornis have been dated to be younger than the Archaeopteryx, but older than various other birds and hence until a conclusion is reached as to the exact date of these no conclusion can be drawn relating to the origin of these birds or the evolution of their feathers.

Bibliography

Martin, Larry D. And Czerkas, Stephan A. (September 2000) “The Fossil Record of Feather Evolution in the Mesozoic” American Zoologist, volume 40, issue 4,-page 687

Prum, Richard O. (January 23, 2003) “Paleontology: Dinosaurs take to the air” Nature, volume 421, pp.323-324

Sues, Hans-Dieter. (April 26, 2001) “Paleontology: Ruffling Feathers” Nature, volume 410, pp. 1036-1037

Hou, Lianhai; Martin, Larry D; Zhou, Zhonghe and Feduccia, Alan. (November 15, 1996) “Early Adaptive Radiation of Birds: Evidence from Fossils from Northeastern China” Science, volume 274

Prum, Richard O. And Brush, Alan H. (March 2003) “Which Came first, the Feather or the Bird?” entitled, “New Evolution Research Ruffles Some Feathers” Scientific American, volume 288, issue 3,-page 84

Schwartz, John. “Paper Contradicts Increasingly Popular Theory that Birds Descended from Dinosaurs” Washington Post (No DATE HAS BEEN MENTIONED)

Poling, Jeff. “Feathers, scutes and the origin of birds” (1996) retrieved from http://dinosauria.com/jdp/archie/scutes.htm

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