The Evolution of Birds (Or: What missing link?)

Discussion in 'Biology & Genetics' started by Trippy, Sep 28, 2014.

  1. Trippy ALEA IACTA EST Staff Member

    Messages:
    10,890
    I think it arises from consideration of the evolution of the lung. Basically, if you look at the lung fish, they are a tidal bidirectional breather when they are using their lungs, so, I believe, are amphibians (which are also capable of respiration through skin absorption).

    Please Register or Log in to view the hidden image!



    Source

    Lungs (lung fish) evolved in the early Devonian:

    Please Register or Log in to view the hidden image!



    Tiktaalik didn't evolve until nearly 40 million years after lungs evolved.
     
    Last edited: Sep 30, 2014
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. billvon Valued Senior Member

    Messages:
    12,725
    Human embryos do not have gills or gill-like structures - any more than they have pacifiers around day 24, although they might look like pacifiers to someone. The same tissue that develops into gills in fish develops into human faces and necks, but that is very different from saying we have "gill-like structures."
     
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. spidergoat Valued Senior Member

    Messages:
    51,740
    That doesn't matter. All vertebrate embryos have the same structures, and it is this commonality that is evidence of evolution from a common ancestor.
     
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. billvon Valued Senior Member

    Messages:
    12,725
    Agreed. It is evidence that we all share a common ancestor - but not that human embryos have anything like gills.
     
  8. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    Messages:
    23,198
    No one, not even Haeckel claims humans have undeveloped gills. Just that most creatures that evolved from fish do have in early embryo stage structures quite like those that in a fish do become gills.

    Please Register or Log in to view the hidden image!


    with the new sicforums, I have lost the ability to post images form sites. Not true as you can see. A simple copy without the [img} etc tags seems to have worked but if I ended that tag with the proper ] instead of } none of it appears.

    Please go to:
    http://evolution.berkeley.edu/evolibrary/article/evodevo_02
    and see image under the text quoted below.
    I'm only quoting well respected sources, like Berkeley University. I will not defend what they state - they know much more about this than I do.
    [/B]
     
    Last edited by a moderator: Sep 30, 2014
  9. Trippy ALEA IACTA EST Staff Member

    Messages:
    10,890
    No you haven't, you just need to re-learn how to use the new interface. I've edited the post for you so that the image now shows inline.
     
    Last edited: Oct 1, 2014
  10. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    Messages:
    23,198
    Sorry Trippy but somehow I seem to have insterted my post inside yours - there is a huge learning cost to the new sciforms especially as doing same thing often results in different results.

    Edited to add:
    And seems to have done this favor while I was trying a simple copy. Now I don't know if the image I wanted was posted by trippy or me - probably him. It would be most helpful it Trippy told how to get image to post - I have already lost a couple of hours trying in several posts to make image appear. If need be to post example of the means, add xxxx in the example (as I have done in some prior posts) to keep the example from working when you post it.
     
    Last edited by a moderator: Oct 1, 2014
  11. iceaura Valued Senior Member

    Messages:
    24,101
    This is strong consideration, but too far back to demonstrate - we are concerned with the presence of one way airflow in fairly advanced creatures (dinosaurs), and their immediate ancestors - the difficulty presented is in getting from advanced two way setups to advanced one way setups by plausible increments, and my observation is that we don't have to start with an advanced two way setup to get to dinosaurs and then birds - the evolution of a primitive one way setup from a far more primitive two way setup than that enjoyed by current mammals, say, followed by a few hundred million years of pre-bird refinement in that one way setup, presents fewer difficulties and more ready plausibility: as well as agreeing with what we have in the fossil record. Just a thought.
     
    Last edited by a moderator: Oct 1, 2014
  12. iceaura Valued Senior Member

    Messages:
    24,101
    I wanted to say "a few hundred million years". Is there any way to edit? When you screw up as much as I do, you need an edit function.
     
  13. Trippy ALEA IACTA EST Staff Member

    Messages:
    10,890
    FTFY

    I was led to believe at one point that there is an edit function available for users, but that it was only available for five minutes after the post was made. I guess this whole thing is still (hopefully) a work in progress.
     
  14. Trippy ALEA IACTA EST Staff Member

    Messages:
    10,890
    It was my edit - I know that for a fact because I saw the post between my edit and yours and the image was visible.

    Okay, so I'm not quite sure what the problem is, however, here is what I have worked out so far.

    The old IMG tags still work, but not all the time. Most of the images I've posted have been using the IMG tags and they've been working fine.
    When I tried to paste Billy T's image using the IMG tags it didn't work, and there was one image (I forget which) that I tried posting that also did not work. When that happens you get the generic place-holder instead of the image.

    What I have found seems to be more reliable is if you click on the image button:

    Please Register or Log in to view the hidden image!


    Enter the URL as shown:

    Please Register or Log in to view the hidden image!



    And you'll know whether or not it will post successfully because you'll be able to see the image in the post window:

    Please Register or Log in to view the hidden image!

     
  15. Trippy ALEA IACTA EST Staff Member

    Messages:
    10,890
    I disagree that it is far too back to demonstrate - perhaps you could clarify why you think this?

    Right, but those same species share common ancestors with reptiles, which in turn (as I recall) share common ancestors with Amphibians, which in turn share common ancestors with Lung fish and other lobe finned fish, including Tiktaalik - the point being that if the archosaurs were one way breathers (which is suggested by the evidence) but their ancestors (in this case lobe finned fish - a common ancestor to all tetrapods) were two-way breathers, then somewhere between Tiktaalik and the emergence of the Archosaurs - a span of 125 million years, one way breathing has to have evolved. The fact that Alligators, and Crocodiles are both one way breathers suggests that it was probably in place in some form before the last common ancestor of crocodilians and Theropods.

    Agreed - one of the points that I was making is that the split may have arisen early in the time line, at a point where lungs were still relatively simple.

    I agree to some extent with this, that's why I did the research regarding the evolution of the lung and made the comment about its evolution and its character in amphibians. The counter point that I also made was that, as near as we can tell, lungs evolved as a seperate organ to gills, rather than neccessarily evolving from gills - I suggest this on the grounds that there are lobe finned fish to this day which still have both sets of organs and are still able to use both sets of organs. This is suggestive that Tiktaalik probably had both lungs and gills (I'm sure i've seen something to that effect but I can't recall when or where).

    That is also the point I was making. It's why I mentioned the timelines and it's why I linked to the image of the crocodile lungs.

    Consider this illustration, for example:

    Please Register or Log in to view the hidden image!



    Compared to this:

    Please Register or Log in to view the hidden image!



    Then it seems to me that, at least at the macroscopic level the change that it required amounts to the seperation and migration of one of the secondary bronchial tubes. The mutations for doing this exist, and are (occasionally) expressed in humans, most of which lead normal lives - so there is no valid reason to discount the possibility that it was possible in a simpler lung that required fewer changes at lower levels (it also requires changes in the structure of bronchioles, something that's easier with simpler lungs but I don't imagine as being terribly likely to happen in humans).

    Is that clearer? The main points that I was making were that:
    1. Evidence suggests that air-sacs were present in Dinosaurs, including Tyranosaurs, and so were already in place by the time birds evolved.
    2. Evidence suggests that one way breathing evolved from two way breathing very early in the tree (375-250 MYA) and was already in place by the time archosaurs evolved. The corrollary of this is that it evolved at a time when lungs are expected to have been structurally simpler than they are now.
    3. One way breathing in alligator lungs appears to be achievable with the migration of a secondary bronchus within a lung, with one way breathing arising spontaneously as a consequence of Bernoulis law and the configuration of the junction where this secondary bronchus meets the primary.
    4. The mutations for some of these changes still occur (from time to time) within humans (along with a mutation that indicates a potential pathway to air-sacs) and generally those mutations are not detrimental.
     
    exchemist likes this.
  16. iceaura Valued Senior Member

    Messages:
    24,101
    I meant, obscurely, that going back to the first lungfish was going back too far to necessarily pertain - but I see we are in perfect agreement throughout, you make the argument much better, and no clarification is needed on any point of mine.
     
    Last edited by a moderator: Oct 1, 2014
  17. iceaura Valued Senior Member

    Messages:
    24,101
    And the edit function, if it is available at all, lasts much less than five minutes - "a moment ago" and it's not available.
     
  18. exchemist Valued Senior Member

    Messages:
    6,298
    Excellent summary. This has been a very interesting topic, by the way. For me, it illustrates yet again how far back some of the key developments actually go, compared to the rather simplistic picture I at least grew up with, of fish-> amphibians-> dinosaurs-> birds (and, separately, dinosaurs-> mammals).
     
  19. exchemist Valued Senior Member

    Messages:
    6,298
    But (a) you simply cannot apply maths to this unless you assume, implausibly, that everything else is held fixed while this is going on, and (b) your maths setup seems to misunderstand what I'm suggesting. This is that, say, 75% of the lung volume may be filled via opening A and 25% via B, while expiration may involve 75% exiting via B and 25% via A. Why is that not feasible, pray?
     
  20. Trippy ALEA IACTA EST Staff Member

    Messages:
    10,890
    Thankyou. (moderators, it seems, are unable to 'like' posts at this time - I have yet to make up my mind whether this is a good thing or a bad thing, so instead I shall thank you for your responses in thread).
     
  21. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    Messages:
    23,198
    Thanks. I don't have that bar in windows 8.1 & IE11. I used "Tools" to add "bars" looking for it. (Normally I don't have any to keep max screen.) I added "status," "favorites," "Command" & "minu" bars, but none have any thing like that. I have a chrome browser, but seldom use it. - They keep opening new window trying to sell me things is why. What browser do you use to get the chose? I also looked at "Internet options" but nothing there seem related.

    It is complex, but for benefit of others having my prior problem of getting post you are repling to appear at top of your reply (so can edit it or at least not need to pre copy from it what you want; this seems to reliable work for me:
    Right click on the "Reply" next post number you want to appear
    Select: Open
    Then you get box to type in but no quoted text at top as desired,so
    hit the main "page back" return and the when you are out of reply mode, I use my finger to hit the Reply on my touch screen.

    I think one of the right or left click buttons will also work at this point if you don't have a touch screen, but I forget which.
     
  22. Trippy ALEA IACTA EST Staff Member

    Messages:
    10,890
    It's not in any internet explorer toolbar, it's in the tool bar at the top of the text box you type your post replies in - i'll post a screen grab when I get home from work (6 hours time).
     
  23. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    Messages:
    23,198
    If you tried to fill in my "time/action" table I think you see why (I. e. you can't do it without internal conflict, I think.) but I'll try a different approach:
    here is diagram of simple two-way breather inhaling:

    At t = 0 : ---> O and then at t = 2- inhale nearly completed (lungs "O" is larger, lungs have expanded) --->O
    Now at t= 2+: <--- O and at t = 4- exhale is nearly completed <---- O
    You want to postulate this creature gets second air flow bath (two different paths for air flow between outside and lungs) but why would separate paths evolve in a two way breather? That is what I call an impossible "binary change." If the creature needed channel with greater air flow the existing single nose and tube to the lungs could INCREMENTALLY enlarge over the course of many generations - Evolution CAN do that.
    I'll use bold to indicate an enlarged airway.
    At t = 0 : ---> O and at t = 2- ---> Oetc. for the exhales
    Note the 2- is time almost 2 & the 2+ is times just a little more than 2
    At t =2+ <--- O Etc for t = 4- I.e. like second line but with arrow bold
    I.e. we now still have a 2-way breather but with greater air flow.

    If you cold make a binary change to increase the air flow
    It might be drawn as:
    Path A : ---> ....
    Path B: ---> ....

    I don't want to tell you how the 1-way final creature looks, even assuming getting new path were not a binary change, but let you use colors (first one bold to indicate it has 75% of the inhale flow and then the other bold for 75% of the exhaling flow. In all cases and at all times your one way flow must have the arrow path thur the lungs going the same way:
    ----> O ----> then:
    ----> O ---->

    The above, I think, is what you are telling me works, but I'm not sure and don't see how it would even if you could justify the entirely new flow path (A binary change) It would not have any advantage in the first born with it. Why would it be selected for?

    BTW now I see another great problem with the new sciforums. When you have made something bold or with color wrong and edit to change it the [b ] or [color= ] commads do not show, but take effect.

    For example I am now editing as don't want this or "commnds.... to be bold aand don't want any of these last two paragraphs to be in color, but as this is an edit the commands making that don't show for me to remove!
     
    Last edited by a moderator: Oct 2, 2014

Share This Page