Shark evolution Essay Example for Free

Shark evolution Essay Sharks, commonly referred to as fish are in fact quite different from the regular bony fish. Sharks have a cartilaginous skeleton, which is does not fossilize well, but despite this sharks have left a considerable fossil record. Shark evolution is in fact one of the most successful cases of phylogenic development. The evidence of sharks dates back to over 400 million years ago, almost 200 million years before the first dinosaurs, and before the evolution of any land vertebrates, in the Ordovician period, at the start of the Palezoic era. The only fossils of the oldest sharks are the scales and teeth, the teeth being quite durable and easily mineralized. The teeth in particular reveal that the oldest sharks were quite different from their modern descendants. And even through vertebrates like dinosaurs were eliminated centuries ago, sharks continue to exist today, with almost 1100 species. Among the most primitive sharks was the Cretaceous, discovered in Texas. The Cretaceous is believed to be about 65 million years old. The earliest life on earth dates back to almost 4 billion years ago, to a group called the prokaryotes, which includes the first bacteria. The prokaryotes did not even have a defined nucleus. The oldest eukaryotes, which were more advanced, and had specialized organelles evolved about 2 billion years ago. These included the famous amoeba. But the first multicelluar life form dates back to about 600 million years ago, to the â€Å"Edicarian assemblage† in Australia. Jawless fishes are believed to be the first vertebrates to have evolved, and date back to about 500 million years ago. Sharks then appeared about 450 million years ago. But even though paleontologists have considerable evidence, shark evolution posed many problems because of the fossils. With time, most of the evidence was eliminated. The scales are mostly very small in size, and have many impressions of soft tissues. But despite these drawbacks, studies reveal a rich history. The oldest shark scales go back to about 455 million years ago. But since they are quite different from those in modern sharks, most paleontologists agree that they are not from sharks. The first acknowledged fossil dates back to 420 million years ago in Siberia. These have been classified under the genus of Elegestolepis. Others, discovered from Mongolia have been classified in the genera Mongolepis and Polymerolepis. But apart for these almost classifications, little is actually known about these primitive sharks. But with the beginning of the Devonian period, shark record becomes quite varied. The first teeth of about 400 million years ago were discovered from Europe. These teeth belong to the ancient Leonodus. Leonodus had characteristic double cusped teeth. The oldest shark cranium was discovered in Australia, and dates back to about 380 million years ago, and is believed to be from a shark specie xenacanth. Earlier in fact the Leonodus and xenacanth were thought to be related because of their similar crown shaped teeth. The first partially fossilized shark shark was discovered by a geologist Gavin Young in Antarctica. But this fossil displayed an odd mix of features. Possibility exists that this too may be a xenacanth, but Young named it Antarctilamna. The Antarctilamna was 16-inches long, and was a diplodont, resembling the xenacanth. Antarctilamna’s fin though was directed dorsally. The xenacanth in contrast was exclusively a freshwater shark, and had a long fin directed rearward, just behind the cranium. But with the passage of time, sharks have endured tremendous changes of environment, and yet, have managed to survive. But like all other creatures, the species had to either adapt to the change, or end. Each time a large scale shift occurred; a number of species found the new environment incompatible and became extinct. Sharks though displayed immense diversity, and helping then expand into new habitats. â€Å"Such explosive increases in variety are termed ‘adaptive radiations[1]. ’† Over such a huge span of geologic time, sharks have has two adaptive radiations, and have survived up to five mass extinctions. Many also agree that since most shark fossils have been found either from Australia, or Antarctica, sharks may have originated in the southern hemisphere. The first radiation was in the Carboniferous period, roughly 30 million years ago. This was characterized by the flourishing of the stethacanthids. The second major radiation occurred in the Jurassic Period, about 170 million years ago. During this time both land and air was dominated by reptiles. This was the time when the hybodonts developed. Many believe that the hybodonts were the ancestors of all modern sharks, but evidence is scanty. While the hybodonts shows many obvious similarities to the modern shark, it has characteristic features not found in sharks today. One of these includes the horns behind the eyes. But now, the earliest known modern shark is believed to be the Mcmurdodus from the mid-Devonian time. The basis for this is the Mcmurdodus tooth. The tooth shows is of the same type found in modern sharks, but not in the ancient ones. But â€Å"there is a 190-million-year gap in the fossil record between the last Mcmurdodus and the first unquestionable cowshark [1]. † Even though research continues to unveil the evolution of this epic animal, a complete evolutionary record is difficult to draw. The earliest known sharks in fact were quite different from the modern counterparts. But in some respects they were very close to the modern sharks of today, having the same cartilaginous skeletons, replaceable teeth and multiple gill slits. And with time sharks have endured great geologic change, adapting to different environments, evolving to change, and have thus survived as one the most durable animals on the planet. References 1. Martin, R. Aidan. ReefQuest Centre for Shark Research. Biology of Sharks and Rays. Retrieved from (http://www. elasmo-research. org/education/evolution/evol_s_predator. htm)

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A soldier, conscripted or not, will face many stresses during their career. Serving for any amount of time is a trial, but some are more suited to the military than others. A drafted soldier may go through their entire mandatory term feeling miserable and insufficient, completely overwhelmed by the tasks that military professionals easily complete. These pressures and the denial of a choice of career should not be placed on any person. The idea of a two-year term of mandatory military service being implanted has been brought up. Military service should not be mandatory not only because it violates fundamental individual rights of humans, but also due to the fact that a military based on volunteers would operate much more impressively than one comprised of conscripted soldiers who would not have chosen to serve otherwise. One of the most fundamental problems with conscription is that it contradicts one of the main concepts that the United States was built on. The entire concept of conscription â€Å"violated fundamental principles of individual liberty† (â€Å"Should a Year†¦Ã¢â‚¬  n.pag.). To obligate one to serve in a field which they normally would not choose is to take away their rights as an individual to decide how best they should spend their working life. Aside from being ethically wrong on a basic level, conscription violates a literal law composed by the leaders of the United States. The 13th amendment of the Constitution of the United States of America says, â€Å"Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction† (â€Å"Should a Year†¦Ã¢â‚¬  n.pag.). This unquestionably insists that any mandatory ... ...tary full of soldiers with this problem could very easily become insufficient. In conclusion, not only does conscription contradict fundamental human rights, it is also ineffectual due to the generally lesser-quality soldiers that it tends to produce. One of the ideas that the United States was built on, that individuals should have the liberty to decide how and where to work, is violated by the idea of conscription. Most times, drafted soldiers will perform less admirably than their professional counterparts; the general unwillingness to serve on top of the usual pressures of the military can physically and mentally impact them to a greater degree. Do not tolerate the idea of compulsory military service, especially in times such as this in which it is not at all necessary. Help those who support it understand why conscription is a blatant violation of human rights.

Marco Polo

Marco Polo was no doubt one of the most influential explorers in the world. His tales of the East opened the minds of the Europeans, and his tales were a catalyst for the Age of Exploration in Europe. His influence on geographical exploration was so pivotal that many years later Christopher Columbus used Marco Polo’s book on his voyage to the New World. Marco Polo’s book, The Travels of Marco Polo, was widely published and thousands of copies were printed in different languages. However, many skeptics believe that Marco Polo never actually set foot in China, but used other traveler’s accounts of China as his own.Despite Marco Polo’s huge influence on Europe, the false and wildly exaggerated claims and the amount of Chinese Culture he failed to mention in his book made it evident that Marco Polo was really a fraud and never really made it to China. Historians have questioned Marco Polo’s credibility with his many dubious claims in his book, suggestin g that he also fabricated his story about setting foot in China. One false claim Marco Polo made was that he assisted Kublai Khan as a military advisor during the siege of Hsyiang-Yang.According to records, the Chinese siege ended on January 1273, which was two years before Marco Polo actually got to northern China. Another doubtful claim Marco Polo made was that he was the governor of Yangzhou, and served as an ambassador under Kublai Khan. Yet despite his high-ranking positions, his name does not appear in any of the Chinese records. Historians have argued that Marco Polo’s publisher, Rusticello, might have exaggerated his stories to make it more interesting, but that just furthermore questions the credibility of Marco Polo’s book.If Marco Polo and Rusticello exaggerated and lied about so many things, they might have lied or exaggerated about Marco Polo even setting foot in China. In addition to his questionable claims, Marco Polo also fails to mention important aspe cts of 13th century Chinese life and culture. Marco Polo also omits many important aspects of Chinese life and culture from his book, The Travels of Marco Polo , which would have been hard to leave out as an European if he really set foot in China. Marco Polo claimed that he spent many years traveling around China, serving as â€Å"The Eyes† of Kublai Khan.Yet during the time he spent traveling South China, he fails to mention anything at all about tea drinking, which was popular in southern China during Polo’s time. He also fails to mention the binding of a woman’s feet, which would have fascinated the Europeans due to how strange and different it was. This raises suspicion, since Marco Polo vividly describes other aspects of Chinese culture and life with so much detail; yet he fails to mention the slightest bit about tea drinking and feet binding, strongly proving that he only borrowed descriptions from other travelers.Other aspects of Chinese Culture and life he omitted from his book were the use of chopsticks, Chinese writing, Chinese books and printing, and porcelain; all important aspects of Chinese life and culture. However, the most alarming thing Marco Polo failed to mention was the Great Wall of China. Though some historians might argue it was in tatters during this period of time, it still remained China’s greatest architectural achievement, and shouldn’t have been missed out from Marco Polo’s book if Marco Polo actually went to China.Marco Polo may have missed out on many aspects of Chinese culture and life, but his book never ceased to amaze the Europeans from the moment it was published. Marco Polo’s book told of a land to the east never known to the Europeans before, and opened up the Europeans’ medieval minds whether or not those accounts of China actually belonged to him. At first, Europeans found his tales hard to believe, but instead of rejecting Marco Polo’s stories, they embrac ed it as a romantic fantasy.Nonetheless, The Travels of Marco Polo became Europe’s most widely read book, due to the fascinating and detailed descriptions of Kublai Khan’s wealth and his magnificent empire. His descriptions of China was that of a country with thriving towns, and with cities far richer than any place in Europe in terms of goods, services and technology. Marco Polo may not have included everything about Chinese culture, but he still managed to amaze the Europeans with descriptions of paper money, at the same time introducing Europe to coal, a substance they had never heard of before.Marco Polo may have opened up the minds of European and his stories may have been a major cause of the Age of Exploration, but in the end evidence proves that he was merely a useful â€Å"recorder of Information†, as deemed by Frances Wood, Marco Polo’s No. 1 critic. Despite Marco Polo’s book about China, which fascinated readers all around Europe, the am ount of false and dubious claims in Marco Polo’s book combined with the amount of important aspects of Chinese life and culture omitted from the book strongly proves that Marco Polo was not a credible source and never really set foot in China.His false statements and wild exaggerations in his book have caused historians to question his credibility, and the amount of omissions in Marco Polo’s book are simply too great to confirm that he really set foot in China. Nonetheless, Marco Polo was a huge influence to Europe, whether or not his tales were fabricated from other travelers, and remains one of the most famous explorers to this day. Marco Polo Marco Polo was no doubt one of the most influential explorers in the world. His tales of the East opened the minds of the Europeans, and his tales were a catalyst for the Age of Exploration in Europe. His influence on geographical exploration was so pivotal that many years later Christopher Columbus used Marco Polo’s book on his voyage to the New World. Marco Polo’s book, The Travels of Marco Polo, was widely published and thousands of copies were printed in different languages. However, many skeptics believe that Marco Polo never actually set foot in China, but used other traveler’s accounts of China as his own.Despite Marco Polo’s huge influence on Europe, the false and wildly exaggerated claims and the amount of Chinese Culture he failed to mention in his book made it evident that Marco Polo was really a fraud and never really made it to China. Historians have questioned Marco Polo’s credibility with his many dubious claims in his book, suggestin g that he also fabricated his story about setting foot in China. One false claim Marco Polo made was that he assisted Kublai Khan as a military advisor during the siege of Hsyiang-Yang.According to records, the Chinese siege ended on January 1273, which was two years before Marco Polo actually got to northern China. Another doubtful claim Marco Polo made was that he was the governor of Yangzhou, and served as an ambassador under Kublai Khan. Yet despite his high-ranking positions, his name does not appear in any of the Chinese records. Historians have argued that Marco Polo’s publisher, Rusticello, might have exaggerated his stories to make it more interesting, but that just furthermore questions the credibility of Marco Polo’s book.If Marco Polo and Rusticello exaggerated and lied about so many things, they might have lied or exaggerated about Marco Polo even setting foot in China. In addition to his questionable claims, Marco Polo also fails to mention important aspe cts of 13th century Chinese life and culture. Marco Polo also omits many important aspects of Chinese life and culture from his book, The Travels of Marco Polo , which would have been hard to leave out as an European if he really set foot in China. Marco Polo claimed that he spent many years traveling around China, serving as â€Å"The Eyes† of Kublai Khan.Yet during the time he spent traveling South China, he fails to mention anything at all about tea drinking, which was popular in southern China during Polo’s time. He also fails to mention the binding of a woman’s feet, which would have fascinated the Europeans due to how strange and different it was. This raises suspicion, since Marco Polo vividly describes other aspects of Chinese culture and life with so much detail; yet he fails to mention the slightest bit about tea drinking and feet binding, strongly proving that he only borrowed descriptions from other travelers.Other aspects of Chinese Culture and life he omitted from his book were the use of chopsticks, Chinese writing, Chinese books and printing, and porcelain; all important aspects of Chinese life and culture. However, the most alarming thing Marco Polo failed to mention was the Great Wall of China. Though some historians might argue it was in tatters during this period of time, it still remained China’s greatest architectural achievement, and shouldn’t have been missed out from Marco Polo’s book if Marco Polo actually went to China.Marco Polo may have missed out on many aspects of Chinese culture and life, but his book never ceased to amaze the Europeans from the moment it was published. Marco Polo’s book told of a land to the east never known to the Europeans before, and opened up the Europeans’ medieval minds whether or not those accounts of China actually belonged to him. At first, Europeans found his tales hard to believe, but instead of rejecting Marco Polo’s stories, they embrac ed it as a romantic fantasy.Nonetheless, The Travels of Marco Polo became Europe’s most widely read book, due to the fascinating and detailed descriptions of Kublai Khan’s wealth and his magnificent empire. His descriptions of China was that of a country with thriving towns, and with cities far richer than any place in Europe in terms of goods, services and technology. Marco Polo may not have included everything about Chinese culture, but he still managed to amaze the Europeans with descriptions of paper money, at the same time introducing Europe to coal, a substance they had never heard of before.Marco Polo may have opened up the minds of European and his stories may have been a major cause of the Age of Exploration, but in the end evidence proves that he was merely a useful â€Å"recorder of Information†, as deemed by Frances Wood, Marco Polo’s No. 1 critic. Despite Marco Polo’s book about China, which fascinated readers all around Europe, the am ount of false and dubious claims in Marco Polo’s book combined with the amount of important aspects of Chinese life and culture omitted from the book strongly proves that Marco Polo was not a credible source and never really set foot in China.His false statements and wild exaggerations in his book have caused historians to question his credibility, and the amount of omissions in Marco Polo’s book are simply too great to confirm that he really set foot in China. Nonetheless, Marco Polo was a huge influence to Europe, whether or not his tales were fabricated from other travelers, and remains one of the most famous explorers to this day.

Analysis Of The Movie The Graduate Essay - 1611 Words

Edward Brambila English 2—Prof. Sosner 12/16/2016 The Art of Symbolism in â€Å"The Graduate† The movie â€Å"The Graduate† is a struggle story of a fine caliber that falls under the genre of comedic drama. Some might even argue that it was one of the best films of its time and even till this day. The way the movie blends characters is anything but superficial and its use of symbolism to describe said characters leaves little more to be desired. While some may not like the movie and say it falls short the movie has proper use of symbolism through the use of multiple props, it also uses symbolic statements as a way to strengthen Dustin Hoffman’s character’s archetype and clue in on specific details which in turn shows us the relationships between him and other characters. Of the many symbolic details the first two we encounter at the very beginning of the film are cluing us in on the character of Dustin Hoffman who is known as Benjamin Braddock. The two details happen almost simultaneously, one being the song â€Å"The Sound of Silence† by Paul Simon and Art Garfunkel and the other is the symbolic action of him sliding across the screen on an airport conveyor belt. The first detail, the song, suggests that the character Benjamin or Ben is lost in the world. He has no idea where to go from this point in his life forward. He is lost in the â€Å"darkness of life† and is directionless. The second detail is the conveyor belt which forcibly moving him along. This conveys the fact that throughoutShow MoreRelatedBrothers Grimm and Beautiful Mind1109 Words   |  5 PagesA Beautiful Mind Film Analysis A Beautiful Mind Film Analysis This movie is based on the true story of the brilliant mathematician John Forbes Nash Jr. He made remarkable advancements in the field of mathematics at a young age and had a very promising future. 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