Sharks and Dolphins

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punk rock princess
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Sharks and Dolphins

Post by punk rock princess » Mon Sep 19, 2005 4:32 pm

Hi guys!

Why do sharks and dolphins look so similar, even though one is a fish and the other is a mammal?

:?
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Post by MrMistery » Mon Sep 19, 2005 5:30 pm

Converging evolution
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Post by punk rock princess » Mon Sep 19, 2005 5:39 pm

Thanks for the hint. I've just looked up 'Converging Evolution'. Am I right in thinking that the reason why they look similar is that they share a common environment, and this is the most useful shape for that environment?

Would monkeys and humans be another example of converging evolution?

:P
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Post by MrMistery » Mon Sep 19, 2005 6:35 pm

Yes for the shape. Same environmental factors lead to similar shapes.
No for the monkey/ human analogy because humans evolved from monkeys, they did not evolve independently. This is the kind of learning we encourage, where you do the work, we just guide you. Well done!
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Post by punk rock princess » Mon Sep 19, 2005 8:13 pm

Thanks for the guidance!

:D :D :D

Would alligators and crocodiles be another example of convergent evolution?
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Post by pedro21101 » Mon Sep 19, 2005 8:31 pm

Only little correction (im so pedant), sharks are not fishes, fishes and sharks could be another example of convergent evolution. Sharks are more primitive and ancient group of vertebrates, they have only chondroit sceleton, while fishes have bone sceleton. But either posses the same shape due to environment in which they live.

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Post by Zachthemac » Mon Sep 19, 2005 9:50 pm

Would alligators and crocodiles be another example of convergent evolution?

I don't think so, since alligators and crocodiles are pretty closely related and evolve from a common ancestor.

Convergent evolution happens with two organisms that are not closely related. You can think about the evolution of wings. Birds, insects and mammals (bats) have all evolved independantly to use wings.

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Post by MrMistery » Tue Sep 20, 2005 5:51 pm

@Zachthemac
I agree
@pedro
I dissagree.
Sharks are more primitive and ancient group of vertebrates, they have only chondroit sceleton, while fishes have bone sceleton. But either posses the same shape due to environment in which they live.

Fish are divided into 2 classes(actually it's 4, but 2 of them are extinct.): class Chondrychthyes(sharks and sting-rays, with a cartilage skeleton) and Osteichthyes("boney" fish, that have more or less a bone skeleton). It is true that sharks are more primitive, but it is the same as with man and ape: we can not discuss of converging evolution because one evolved from the other.
Class Cyclostomata are not fish, they are Agnatha, but that is a whole different story
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Post by pedro21101 » Tue Sep 20, 2005 6:35 pm

No, no, no... I must disagree. Although Im not sure (this i must agree). Sharks are not fishes! In superclass Gnathostomata are several evolutional levels:
- Placodermiomorphi
- Chondrichthyomorphi - sharks, rajas,
- Teleostomi - fishes - ray finned, lobe finned,
- Tetrapoda - amphibians, reptiles, aves, mammals.
This should be in accordance with the newest zoological system.
I know on the net they name everything what has flippers fishes. Than all Gnathostomata could be fishes even tetrapoda. Cause Chondrichtiomorphi is in relation with Teleostomi as Teleostomi is in relation with Tetrapoda. But i dont want to say it definitely rather i will wait for second term where this i will study (maybe) and then i will be back! :twisted: About convergent evolution, yes it is maybe very overstated to say it is convergent evolution.

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Post by MrMistery » Tue Sep 20, 2005 7:36 pm

http://en.wikipedia.org/wiki/Shark
http://en.wikipedia.org/wiki/Fish
Wikipedia seems to agree with me. Now i am totally sure that is what it says in my zoology book, and i have asked my number one reference person(my girlfriend). But the classification may have changed. Though, it seems to much to not include sharks as fish.
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Post by MrMistery » Tue Sep 20, 2005 7:45 pm

I checked(actually my gf checked for me) the Campbell book and it says like this: "Sharks, rays, and their relatives include some of the biggest and most successful vertebrate predators in the oceans. They belong to the class Chondrichtheys, which means "cartilage fish"."
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Post by pedro21101 » Wed Sep 21, 2005 10:30 am

The system which i hold now i obtained this year, and theres so many big changes you would wonder. For example Mesozoa are classified as the first evolutional branch of the group Bilateralia(triblastica). :shock: The year before this system wasnt in use on school, so this must be really the newest version. I personally understand fishes as the most modern group of fish water vertebrates and that system it only ratifies. But now i read in one book that cartilageous sceleton of sharks originated secondarily, that their ancestors had probably bony sceleton. Im confused :roll: It can be said that fishes are all Cyclostomata and water Gnathostomata. The name fishes have not have even systematic meaning. It can only depend on user of this word how he use it and on imagination what spectrum of animals he imaginates under this word.
Last edited by pedro21101 on Wed Sep 21, 2005 10:42 am, edited 1 time in total.

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