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.
The primitive tetrapod foot has at least 29 bones (35 for the one on the left) laid out in an asymmetrical pattern. There are over 30 joints in each foot below (33 and 34). Each digit of the foot needs at least a ligament for it to be functional. Every joint in the digits has a severely restricted range of motion; they can only bend in one direction. The other joints in the foot have a greater range of motion, but are still restricted in some way; they cannot bend in all directions. The foot has at least 5 sets of joints that could be controlled individually, without affecting the entire appendage. The foot is attached to the skeletal structure, and is capable of supporting the weight of the animal.
When the two are compared side-by-side:
| Lungfish Fin Tip-----
| Tetrapod Foot
|
---|
Bones:
| 8
| 29-35
|
Joints:
| 5
| 33-34
|
Joint range of movement:
| free or none
| highly restricted
|
Controlability
| rough
| fine
|
Structural support:
| none
| strong
|
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]