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  1. #1
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    Jul 2006
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    Please check my paper... it's due tomorrow morning!!!

    Both the harbor seal and porpoise are mammals. Harbor seals spent most part of the time in water, while the other part is spent on land. It can move with ease in water, while spends a lot of energy to do so on land. On the other hand, porpoises spent all their time in the water. Both share the same diet of herring, codfishes, and squid, while harbor seals also enjoy sole, flounder, and octopus (Internet 1, 2). In this report, I examined the bone structures of harbor seal and porpoise and the bone structures were related to their functions. Both their similarities and differences were noted. Both have short, flattened ulna and radius; they also have very similar body shape. Porpoise have longer tail than seal. Seal have larger and clear defined carpals, metacarpals, tarsals, metatarsals, and phalanges; while porpoiseís carpals and metacarpals are nearly fused together and the hindlimb are reduced to just two bones, although it does display clear, separate phalanges in the forelimbs. Seal have large, sharp teeth in front of mouth and smaller ones on the side; porpoise have small evenly spaced teeth on the mandible and shows no tooth on the maxilla. Seal also have a long flattened bone between the ribs, while porpoise doesnít have a bone between the ribs.

    When one first observes the bone structures of both the harbor seal and the porpoise, it can be seen that both share very similar body structure. Both have long and torpedo shaped body. This shape serves both animals very well since both live under water. This body shape can help reduce drag when swimming. This type of body structure is also comparable to many other aquatic organisms. So it would only make sense for both to evolve this way. The common ancestor of seals and porpoises probably lived in water or at least spend part of the time in water since the shape of both organisms are very similar and is adapted to swimming in water; also there was no apparent radical change between the two organisms.

    The ulna and radius also showed similarities in both organisms. Ulna and radius are short and seem flattened, although itís a little bigger and longer for seal than porpoise. With such a short and flat forelimb, it is very unlikely that it is used for propulsion in water. The next best alternative function for the forelimb would be for steering. Although, one could make the case that the forelimbs in porpoise might serve no function at all since itís so small when compared to the rest of the body. However, with the forelimbs as the only limbs on the body and with no other apparent structures extend out of the body, there is little else that could help such a massive animal from moving in different directions when swimming. As for seal, besides steering, the forelimbs might also serve some function when it comes to propulsion since it is just big enough to help in such a function.

    One major difference between seal and porpoise is that porpoise have very long tail when compared with seal. The reason that porpoise have a longer tail could be because that it needed it for propulsion in water since it only has short forelimbs, which is probably serving the function for steering and nonfunctional hind limbs. The short tail for seal could be contributed to its already developed hind limbs, which is probably used for propulsion. Also its forelimbs, which is a likely source for steering. Based on these factors, there seems to be little or no use for the tail, thus it is probably reduced to the tail that seal have today.

    Another major difference between seal and porpoise is that Seal have larger and clear defined carpals, metacarpals, tarsals, metatarsals, and phalanges; while porpoiseís carpals and metacarpals are nearly fused together and the hindlimb are reduced to just two bones, although it does display clear, separate phalanges in the forelimbs. The reason the bone structure of forelimbs and hind limbs of seal are well defined might be because of the fact that it still spend part of itís time on the land. So it needs well developed limbs to move around while on land, especially the hind limbs since itís much bigger than the forelimbs. Another function for the big and well developed hind limbs in seal might be for propulsion. This makes sense since both the tail and the forelimbs are very short, so in order of seal to swim in water, the hind limbs are the only logical choice to provide that propulsion. The reason that carpals and metacarpals of porpoise are fused might be due to the fact that it that it has become a fully aquatic animal. This means that there would be no body pressure or gravitational force exerted on the forelimbs as there would be if it was a land mammal. The total reduction of the hind limbs might be because that porpoise is already using the tail for propulsion and the forelimbs for steering, so there is little use to keep the hind limbs. The common ancestor of seal and porpoise probably was able to walk on land relatively easy. This is clearly demonstrated from the limb structure of seal. Although it is less obvious in porpoise, one could still see that it probably had fully functional hind limbs before from looking at the forelimbs, which still show resemblance with the limbs of seal.

    One more difference is the fact that seal have large, sharp teeth in front of mouth and smaller, but sharp ones on the side, while porpoise have small evenly spaced teeth on the mandible and shows no sign of tooth on the maxilla. This difference is probably due to the difference between the two organismsí eating habits. The reason that seal developed large sharp teeth in front is probably due to its habits of biting or tearing its preys into pieces before eating them. One canít expect to do such a thing with out having some sort of sharp teeth. Porpoise only have small, evenly distributed teeth on the mandible is probably because that it doesnít bite in to its prey, instead, it would swallow its preys in whole and not worry about tearing it into pieces. To do that, one does not need strong teeth.

    Another difference between the two organisms is that seal have a long flattened bone between the ribs, while porpoise doesnít have a bone between the ribs. The difference is probably arise from the fact that seal spend part of itís time on land. The bone could serve as a protective and supporting structure for the mass pressure that seal have to endure every time it comes on to land. The reason that porpoise doesnít have such bone is probably because that it spends all of its time in water, where gravity isnít a big factor, thus it doesnít need such bone for supporting purposes.

    From the discussion above, one can clearly see the differences and similarities between the harbor seal and porpoise. This also demonstrated that the common ancestor of the two organisms is probably something and could live both on land and in water with relative ease. Itís not until later on that the two diverged to porpoise becoming completely aquatic, while the seal could still adapt to both environment, although it could adapt to water much better than land.

  2. #2
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    Re: Please check my paper... it's due tomorrow morning!!!

    Please dont feel like you have to correct the whole paper. Any help I can get is good.

  3. #3
    Tdol is online now Editor, UsingEnglish.com
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    Re: Please check my paper... it's due tomorrow morning!!!

    Harbor seals spent most part of the time in water, while the other part is spent on land. It can move
    spend... They

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