Term Paper: Evolution of the Feather

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[. . .] 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… [END OF PREVIEW]

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