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Author | Topic: Oldest Known Arm Bone - Land/Sea Link | |||||||||||||||||||||||||||||||||||||||||||
Dan Carroll Inactive Member |
Just tossing this one out there:
How land-living animals evolved from fish has long been a scientific puzzle. An important part of the mystery is the transformation of the fins of fish into the arms and legs of our ancestors. Paleontologists Neil Shubin and Michael Coates from the University of Chicago, and Ted Daeschler from the Academy of Natural Sciences in Philadelphia found a 365-million-year-old fossil that sheds light on this transformation. In the April 2, 2004, issue of Science, the scientists describe this bone, a humerus from the Late Devonian Period found in Pennsylvania. It’s the earliest of its kind from any limbed animal. This specimen bridges the gap between the fins of fish and the limbs of amphibians. More in link. "As the days go by, we face the increasing inevitability that we are alone in a godless, uninhabited, hostile and meaningless universe. Still, you've got to laugh, haven't you?" -Holly
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Adminnemooseus Administrator Posts: 3974 Joined: |
Thread moved here from the Proposed New Topics forum.
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Coragyps Member (Idle past 734 days) Posts: 5553 From: Snyder, Texas, USA Joined: |
It would be so nice if the paper from Science were online.....
The lineup they show of humeri from five or six critters in the Devonian fish-tetrapod series is just amazing. Even the little holes that this new bone had have analogues in Acanthostega (or someone similar - my copy is at home.)
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RAZD Member (Idle past 1404 days) Posts: 20714 From: the other end of the sidewalk Joined: |
it is on-line if you have full sign-in authority. the free service available lets you read the abstracts of recent papers.
the cover was:
Good picture of the bone and location information, the "paw" may be a little imaginative. Any Idea how this compares to structure in lungfish? Introduction to the Dipnoi
we are limited in our ability to understand by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}
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Gary Inactive Member |
I found a website with drawings of an Austrailian lungfish and the skeletal structure of its fin. Click on the links entitled "The Axial Skeleton" and "The Appendicular Skeleton":
http://home.inreach.com/cliff_lundberg/appskel.html It looks to me like the lungfish fin is totally different from the humerus of this fossil amphibian, but I don't think they are very closely related. You could also compare it to amphibian humeri, though.
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RAZD Member (Idle past 1404 days) Posts: 20714 From: the other end of the sidewalk Joined: |
thanks. I don't think they are closely related either, just that the lungfish can use their fins as rudimentary limbs. If I were going to propose a "paw" to go with the arm bone it would be more like the end of the lungfish fin:
{Rescaled photo (changed UBB code to HTML) to restore page width to normal - Adminnemooseus} [This message has been edited by Adminnemooseus, 04-23-2004] we are limited in our ability to understand by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}
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Dan Carroll Inactive Member |
Just a quick bump, to see if we have any creationist response to this.
Anybody? "As the days go by, we face the increasing inevitability that we are alone in a godless, uninhabited, hostile and meaningless universe. Still, you've got to laugh, haven't you?" -Holly
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jt Member (Idle past 5596 days) Posts: 239 From: Upper Portion, Left Coast, United States Joined: |
Hey everybody,
This is my first post, and I don't really know how things work yet, so if I do anything stupid or annoying, I'll be happy if you slap me upside the head about it (just not too hard ) Anyway, back on subject, how do lungfish benefit from their fins being like they are? Do they use them as limbs, like for digging and stuff, or do they use them exclusively as fins?
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RAZD Member (Idle past 1404 days) Posts: 20714 From: the other end of the sidewalk Joined: |
I believe lungfish can lift thier heads from muddy banks by using their fins, some better than others. I remember seeing old tv footage of some in africa, but I may be confusing them with
mudskippers (click): Lungfish have crude lungs that allow them to breath the air.
Also see http://taggart.glg.msu.edu/isb200/fish.htm There are several fish that climb out of water for various purposes. These should be compared to the bone in question to see if there are limilarities. we are limited in our ability to understand by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}
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jt Member (Idle past 5596 days) Posts: 239 From: Upper Portion, Left Coast, United States Joined: |
The structure of the foot of a primitive tetrapod is vastly different than the structure of a lungfish fin.
First, the fin. The tip of a lungfish fin has 8 bones laid out in a simple geometrical pattern. There are no more than 5 joints, and the joints cannot be individually controlled. The rest of the fin is made up of a backbone-like segmented chain of about 12-14 bones. This backbone allows the fin to be flexible, which is useful for swimming. Two long, narrow bones come off of each bone segment to give the fin shape. The spine of the fin is flexible, and can bend along its entire length. The small bones coming off the fin do not have flexible joints, though. The fin is minimally controllable, only the main set of joints can be moved, and they are moved as a group. These fins are not connected to the skeletal structure, only to soft tissue. This prevents the fish from using the fins to support itself on land; at most the fish could drag itself, but not lift itself off the ground.
When the two are compared side-by-side:
All the stuff above does not prove that the lungfish did not evolve into the first amphibians. However, it does show that lungfish would have to have quite substantial skeletal changes to become amphibians. Lungfish are nowhere near being a conclusive link between fish and amphibians. Had amphibians evolved from fish, it likely would have been through the lungfish. But there would be links. If there was a sequence of similar lungfish that had fins become attached to the skeleton, then develop fibula, tibula, and tibia, then develop ankle bones and multi-segmented proto-digits, that would be worth consideration. That would not even be all the way to an amphibian, but it would be worth considering as evidence. In the chain between the fishes and the amphibians, the lungfish would provide merely a starting point, but any chain between the starting point and the ending point is completely absent. There is no evidence for the evolution of amphibians from lungfish, only speculation. P.S. can an administrator fix all the blank space in here? thanks (added in edit)changed images to ImageShack.Thanks Gary! (/added in edit)
I tried hun, two of your images aren't available to link img to, damned geocities sites , can't fix all the space above table...percy will have to let me in on the secret - The Queen [This message has been edited by AdminAsgara, 04-28-2004] [This message has been edited by JT, 04-29-2004] [This message has been edited by JT, 05-01-2004]
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jt Member (Idle past 5596 days) Posts: 239 From: Upper Portion, Left Coast, United States Joined: |
deleted duplicate post - The Queen
[This message has been edited by AdminAsgara, 04-28-2004]
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RAZD Member (Idle past 1404 days) Posts: 20714 From: the other end of the sidewalk Joined: |
thanks. lots of good work there (although can't see two of your pictures).
Looks like convergent evolution to me. I knew from cladistic tree that lungfish were off the tetrapod lineage, my point was only that an early foot would look more like a fin than a foot. I have also tracked my old source back and it was mudskippers and not lungfish I saw ... and that's a hoarse of a different cholera.
They say as you get old that memory is the second thing to go (and I can't remember what the first was ...) we are limited in our ability to understand by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}
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jt Member (Idle past 5596 days) Posts: 239 From: Upper Portion, Left Coast, United States Joined: |
Thanks for the compliment.
I guess I'll go research mud-skippers... P.S. The Queen...Thanks for getting rid of some of the whitespace. My computer displays the pictures, I have no clue what that's about. Thanks for adding the links, I'll start doing that
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Coragyps Member (Idle past 734 days) Posts: 5553 From: Snyder, Texas, USA Joined: |
Of course, too, guys, we need to keep in mind that the modern lungfish has had the same 360 million years to diverge from some lobe-finned ancestor that frogs and people also have. Jennifer Clack's Gaining Ground has a couple of cladograms that have lungfish more distant from tetrapods than coelacanths - but she goes on to say it's really not at all settled. She also has some pictures of skulls of modern lungfish, and they are very unlike Devonian ancestral lungfish, which aren't much like Devonian "tetrapodomorphs."
Confusing stuff, says I.
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jt Member (Idle past 5596 days) Posts: 239 From: Upper Portion, Left Coast, United States Joined: |
Coragyps,
Is the fin structure of those "Devonian ancestral lungfish" different enough from modern lungfish to make a difference to my argument? Could you post some pictures or links? thanks (added in edit) By the way, this picture, which is what I based my argument off of, is of the supposed evolution of amphibians from fish, so the fish fin in the image is of the "ancestral" fish. My argument still stands. Also, which I didn't say earlier (because of a brain fart), this is the standard view of where amphibians came from, so most of what what I was saying applies to the evolution of amphibians in general, independent of the starting species [This message has been edited by JT, 04-28-2004] [This message has been edited by JT, 04-28-2004] [This message has been edited by JT, 05-01-2004]
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