Fish to amphibian transition

Discussion in 'Biology & Genetics' started by Mandana, Jun 8, 2011.

  1. Mandana Registered Senior Member

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    Why did fish to amphibian transition happen in natural history in the first place? I'm wondering wasn't the sea a more favourable place for living creatures?
     
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  3. wellwisher Banned Banned

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    I don't think anyone knows for certain, although there are theories. One simple explanation is connected to survival. Sometimes the only place left to escape might happen to be dry land, since the preditor would not follow. One fish is being chased and jumps out of the water to escape. After danger passes it wiggles back into the water.

    Say we have a fish out of water, the chemicals potentials are now different, such as the higher O2 concentration in the air, and the de-hydration potential. This is not much different that adding a chemical to a beaker of bacteria. If we use the theory of selective advantage, offspring that have genes to help better deal with the higher O2 and dehyration problems, will have an advantage, Eventually the transition allows animals that can go in water or land.
     
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  5. spidergoat Liddle' Dick Tater Valued Senior Member

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    Didn't insects transition first? In that case, there was lots of food on land.
     
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  7. Walter L. Wagner Cosmic Truth Seeker Valued Senior Member

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    Insects, probably worms, onychophores, etc. and early land-plants (liverworts/mosses, early vascular plants) were already there. Lots of food. But in other threads we've discussed the transition from shallow fresh-water fish that could raise their heads for gulps of air, and front fins that became leg-like to assist. There are lots of good transitional fossils discovered in the last few years.
     
  8. Fraggle Rocker Staff Member

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    Also, probably no predators large enough to be a threat. There are some three foot-long arthropods but I'm sure they're aquatic.
    There are fish currently in existence that can more-or-less walk surprisingly long distances.
     
  9. billvon Valued Senior Member

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    A great many possibilities:

    A lake or sea dried up. The animals in it could either transition or die.

    There were a lot of predators in the sea that couldn't survive on dry land. Any fish that could escape the sea would survive better than one that couldn't. (Mudskippers are a great way to see how this could happen.)

    There was food (plants) available on land, so fish that could survive on dry land long enough to eat would have an advantage.

    There may have been land barriers between lakes and oceans, so fish that could cross them could find new places to breed/eat.
     
  10. Michael 歌舞伎 Valued Senior Member

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    Funny enough, some animals went back to the seas - whales, dolphins, etc....
     
  11. Hercules Rockefeller Beatings will continue until morale improves. Moderator

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    Mod note: Poor attempts at strawman evolution denialism have been moved to the appropriate thread.
     
  12. Skeptical Registered Senior Member

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    There are a few good fossils which show some trends. Tiktaalik was a fish on the amphibian line. http://en.wikipedia.org/wiki/Tiktaalik Nearly 400 million years ago, it lived in oxygen poor waters. In its need to survive in those tricky conditions, it developed some adaptations which helped the later evolution into something that could, temporarily at least, live out of water.

    Lobe finned fishes like Tiktaalik appear to have been amphibian ancestors, which had fleshy, muscular fins. In the fish that lived in shallow, oxygen poor water, they used those fins to support themselves to raise their heads to the water surface, to take in water mixed with air. Evolution increased the strength of those fins, leading to proto-limbs. It is likely that they evolved vascular tissue inside the mouth to aid in gas exchange. This may have evolved into the first lungs.

    These preadaptions permitted the next stage. Brief excursions out of water, possibly to move from one pool to another. Some fossils have been found of animals that may have lived in this way. Acanthostega, which lived 365 million years ago, lived in a way that may have been similar to this. http://en.wikipedia.org/wiki/Acanthostega
     
  13. Fraggle Rocker Staff Member

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    Whales and dolphins are cetaceans, all of whom have a single ancestor. They are descended from artiodactyls, the even-toed ungulates. Probably from a primitive hippopotamus-like creature who swam all the way to the mouth of the river and liked it there.

    Warm-blooded air-breathing animals (mammals and birds) have much more powerful metabolisms than cold-blooded and/or gill-breathing animals because they have more oxygen at their disposal. Mammals who have re-adapted to aquatic life virtually rule their ecosystem. Dolphins can defeat or evade all but the largest predators, and they can even handle them because they are pack-social and work as a team. Polar bears are invincible in the water, although I don't know who wins when they enounter an orca (the largest dolphin species). Perhaps they don't swim in the same waters.

    The pinnipeds (seals, sea lions, walruses, etc.) are, like the polar bear, not completely aquatic (they sleep and reproduce on land), but it takes a giant predator to catch them in the water. The pinnipeds are descended from one common ancestor, a member of the order Carnivora and probably a primitive bear.

    River-dwellers like otters (also carnivorans, members of the weasel family) dominate their ecosystem.

    However, nothing in nature is 100%. The manatee is a grazer, not a predator.

    Penguins are near-fully adapted to marine life, but have to sleep and reproduce on land. They dominate the fish in their ecosystem, but larger mammals like orcas and seals eat them.
     
  14. Mr MacGillivray Banned Banned

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    Mudskippers are completely amphibious.

    It pays to be amphibious being a fish. Even nowadays.
     
  15. Skeptical Registered Senior Member

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    A small addition to the note above. The first known whale ancestor was probably carnivorous, at least in part.
    http://en.wikipedia.org/wiki/Evolution_of_cetaceans#Earliest_ancestors

    Quote :


    "An interesting implication is that the earliest ancestors of all hoofed mammals were probably at least partly carnivorous or scavengers, and today's artiodactyls and perissodactyls became herbivores later in their evolution. By contrast, whales retained their carnivorous diet, because prey was more available and they needed higher caloric content in order to live as marine endotherms."
     
  16. Fraggle Rocker Staff Member

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    Aren't all endotherms who have readapted to marine life carnivores? The reason being that an endothermic metabolism gives them an advantage in speed, strength and intelligence. Cetaceans, pinnipeds, otters, polar bears, penguins, all of the fishing birds. The only major exception I can think of is the manatee.

    Even endotherms who hang out in rivers rather than the sea seem to be primarily carnivores, with the hippo being the rather large exception to that rule.
     
  17. Mandana Registered Senior Member

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    Fish to amphibian

    Thanks for all your responses. I wonder why didn't all fish evolve into amphibians?

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  18. ElectricFetus Sanity going, going, gone Valued Senior Member

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    Imagine for a moment that your city is crowded, so you move to a new less crowded town, now imagine all your townsmen moved with you, now the town you left is no longer crowded, so move back!

    Same logic here with fish: you don't abandon the sea simply because a few figured out how to live on land, if you leave someone else will simply take your spot. Life always fills up ecological openings but does not make new openings by leaving, if so some other life form simply fills the spot left. Thus some fish evolved to live on land, and other fish simply dominated the sea in their place.
     
  19. Mandana Registered Senior Member

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    Fish to amphibian

    Does evolution move backward too? Like amphibians evolving into fish again?
     
  20. Fraggle Rocker Staff Member

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    The cetaceans are mammals who have evolved to be entirely aquatic. But they have not lost their lungs or their warm-blooded metabolism, because those are tremendous evolutionary advantages, even in the water.
     
  21. billvon Valued Senior Member

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    Well, it always moves forward (i.e. towards more fitter organisms.) However, sometimes that means re-developing traits that previous organisms had. Land mammals returning to the sea and becoming whales would be an example.
     
  22. Mr MacGillivray Banned Banned

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    evolution never moves forward.

    Evolution just signifies the change that comes with each generation. Or the lack thereof.
     
  23. ElectricFetus Sanity going, going, gone Valued Senior Member

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    I say Mr MacGillivray got the best answer, evolution has no direction.
     

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