Dolphins Essay Research Paper DolphinsDolphins are sleek

Dolphins Essay, Research Paper


Dolphins are sleek and powerful swimmers found in all seas. Dolphins are distinguished from porpoises by well-defined, beak-like snouts and conical teeth. There are at least 32 species of dolphins. Typical examples are the bottle-nosed dolphin, a popular performer in sea aquariums, and the common dolphin, which inspired many Mediterranean folk legends. Both often appear in open waters. Several freshwater species inhabit river estuaries in Asia and South America. The small, graceful tucuxi dolphin, also known as the buffeo, or river dolphin, has been sighted more than 1250 miles up the river. The tucuxi, the smallest dolphin, is less than 4 feet long; the largest, the bottle-nosed dolphin, reaches a length of 10 feet. That is the main dolphin that I will be discussing in this report. Dolphins once were hunted commercially, especially for the small quantity of valuable oil extracted from parts of the head and used to lubricate delicate watch mechanisms. Cheaper oils have now been found from other sources, and dolphins are no longer hunted for this reason. Many dolphins, however, become accidentally trapped and drowned in tuna nets; between 1959 and 1972 an estimated 4.8 million dolphins died in this way. The Marine Mammal Protection Act of 1972, amended in 1988 and 1992, was passed to prevent exploitation of dolphins and related aquatic animals. The National Marine Fisheries Service is the principal regulatory agency for these problems. I will now discuss the following topics about the dolphin: Basic Anatomy, its Behavior, and the relationship between humans and dolphins.

All dolphins have a similar streamlined, torpedo-shaped body. Their bodies are larger at the front than at the back. The dolphin has a short, stiff neck. The forelimbs are used as paddle-shaped flippers which helps in steering through water. The tail of a dolphin is called the fluke and it is used for propulsion. Dolphins do not have significant body hair, an external ear lobe (pinna), or a projecting nose showing. It also doesn t have externally projecting genitals, or mammary glands that show. All of these parts are reduced or tucked away to improve hydrodynamic efficiency. Their body shape differs very little in comparison with other ceteceans (whales and porpoises).

The size, shape and position of the dorsal fin varies from one dolphin species to another. The fin is not supported by any bone, but by tough fibrous tissue inside it. Dolphins can have fins that are triangular or bluntly rounded. The significance of these different styles is uncertain. Some people believe that dorsal fins help dolphins to maintain stability in the water while others believe that a well-developed fin is not essential for survival. However, the blood vessels in the dorsal fin do help to control body temperature. It acts as an exchanger of heat during intense activity or when swimming in warm water.

A dolphin has extremely smooth, firm and velvety skin, which helps them to slip through water with apparent ease. The dolphin’s smooth skin is constantly being sloughed off and replaced. It is also very sensitive to touch, and easily scarred. Almost all adult dolphins have numerous scars, nicks and notches on their skin and these help researchers to identify and study their interaction with companions, enemies and the environment. Unlike most other land mammals, dolphins do not have thick coats of hair to keep their bodies warm although new-born calves sometimes have a small amount on their beaks. To maintain a stable body temperature of around 36-37 degree celsius is particularly difficult in water, because water can conduct heat away from the body twenty-five times faster in air. Therefore, dolphins have developed a thick layer of insulating fat, known as blubber. The thickness of blubber differs between species and according to the average temperature of the water.

The tail of the dolphin is used for propulsion: it is therefore very muscular. The tail is the primary source of power when it comes to propelling the dolphin forward. Behind the anus, the body tapers into the tail stock (peduncle), which has flattened sides, and the horizontal flukes. The two flukes of the dolphin’s tail are held rigid not by bones but by tendons and fibrous tissue. The flukes feel like dense rubber to touch. Fluke profiles, viewed from above, vary considerably. Most are slightly convex at the back, but some are almost straight and others are conspicuously curved or even biconcave. Most species have a notch in the centre of the trailing edge. The two flukes function as powerful paddles and are driven up and down by the well-muscled peduncle. The long powerful muscles of the peduncle, some of which originate far forward on the back, need to be firmly attached to the skeleton. The dolphin’s vertebrate therefore have specially adapted long spines to which they are anchored. The fluke also contains prominent blood vessels that help control body temperature. It acts as a heat exchanger during intense activity or when swimming in particularly warm water.

The difference between male and female dolphins can be found out by examining the genital area which is near to the tail of the dolphin. In females, there is a single urogenital slit, which contains the genital opening, the urinary tract opening and the opening. The mammary slis of the female can be seen beside the urogenital slits. However, some males may also have mammary slits. In males, there are two openings within the urogenital slit. One of which is a small opening and the other is a genital slit where the penis is hidden. The long retractable penis emerges only when it erects.

As in all cetaceans, the forelimbs have evolved into pectoral fins. Dolphins have well-developed pectoral fins or flippers placed behind the head and below the midline. The flippers vary widely in shape, size and color from one species of dolphins to another. Flippers are important in steering and stopping. They provide excellent paddles for steering and stability. The flippers also appear to be important as organs of touch in social and sexual contexts. Pectoral fins are made of cartilage and bone. They are similar to the skeletal structure of land mammals with.

The head of the dolphin has many interesting features. The face of a dolphin is rather inexpressive. Dolphins seem to wear a permanent smile, but this is deceptive since the head, like the rest of the body, carries significant blubber under the skin. Blubber prevents major muscles on the face to reach the surface. Therefore, dolphins are capable of only a limited range of facial expressions.


Все материалы в разделе "Иностранный язык"

ДОБАВИТЬ КОММЕНТАРИЙ  [можно без регистрации]
перед публикацией все комментарии рассматриваются модератором сайта - спам опубликован не будет

Ваше имя:


Хотите опубликовать свою статью или создать цикл из статей и лекций?
Это очень просто – нужна только регистрация на сайте.

Copyright © 2015-2018. All rigths reserved.