Identifying Darwins fish

I'm doing an artist's perception of what I consider to be the Darwin fish made famous in bumper stickers. I started with Acanthostega, (which I think is the actual 'Darwinfish' but I've made a slight change in reducing the length of the rear legs to mere lobe fins with seven digits in the rays. The front limbs have no apparent elbows or wrists and bear eight digits in the fin. The reason for the change is that I was going for a more unclear distinction between amphibean and fish. I also moved the rear fins forward just a smidge to acheive this illusive effect. What I have now is a 34' clay sculpture of a creature that is immediately recognizeable as both a fish and as a tetrapod and the distinction between them is uncertain.

This slight change means that it is no longer acanthostega, but what would it be? As I understand it, Sauripteris still has heavy scales and panderichthys still had rayed fins. Does anyone know of any creature fitting this description that is known in the fossil record? All I can find is skeletal fragments of possible contenders and would not know even which of them would be most likely (if any) to be it.

I'm also a bit sketchy on exactly when tetrapods would have lost the fishy scales, which appears to be the only division I know of between them. I think that's how they determined the difference between the modern lungfish that are fish and those that are amphibean, isn't it? Would this creature still have scales or not?

I hope others will help on a number of details. I will just mention one that you may not have thought of: I hear that some mercenary person has copyrighted the Darwinfish design that goes on cars. I think your design is safe, but be careful what you call it.

This is great news. I would like to see possible ways that the fish ancestors of acanthostega evolved into a tetrapod. A possible explanation I have is that initially the fish ancestors of acanthostega fed on small fish which sheltered in amongst the reeds/ roots at the edge of a body of water. Strong fins would be an advantageous to moving in amongst this vegetation. Then moving on the bottom and launching an attack from there may have become even more advantageous. So the strong fins started to move nearer to the underside of the fish. As there is less oxygen in the shallows they may have started taking air and evolution slowly developed lungs. Now that they had lungs, and strong limbs near their underside, they could start to venture onto the land where a huge untapped resource of insects were already established. And from there .....the world.

This is just my initial proposal for what may have happened. I would like to see any other hypotheses. I think we have enough brain power in sci.bio.palaeontology to crack the case within a week.

Check out, oddly enough, www.darwinfish.com.

(Snip)

Before I learned about Acanthostega and the like, I pictured a similarity between walking catfish and axolotls, presuming as others had that feet formed after leaving the water. Now my image is the same as yours.

I wish I knew more about these transitions than I do. I have a series of questions: Where can I see fossils of Sauripteris, or at least read something that will describe what is known of its appearence? Did any of these proto-tetrapods have seven fingers on the front fins or six fingers on any fin? All I know so far is that most had eight on the front, seven on the back and suddenly they have five all around.

I think there is something better than the above hypothesis. If the creatures were living in the shallows then it is highly likely that they would encounter the ground beneath the water, more often than a fish in open water, they could then use it as a base from which to push from - this is the physical situation which led to strong fins/ limbs moving to the underside of the fish. This evolutionary process would have been accelerated if these particular fish ancestors of ours had started to venture out of the water for short periods of time. The evolution of lungs and strong limbs would have provided a positive feedback mechanism for each other, and if there was an abundant supply of food on the riverbank or shoreline then this too would accelerate the evolution of tetrapods from fish.

Nobody knows exactly how it happened. There is very little evidence of any of the transitions. Mainly because they were transitions and were superseded very quickly.

For this I can only point you towards http://www.google.com.

(There are many scientific sites produced by a search from there.)

I think the evolution of five fingers, on all four limbs, is structural design. Physically, it is better to have five strengthened points rather than six, seven or eight unwieldy digits. Evolution and natural selection could do this in a few generations. At the moment, I can't think why five digits were not streamlined even more.

I must reaffirm that what I write here is only a rough guide and maybe not even a guide at all, but by analysing the situation I think we can get fairly close to the truth of the evolution of tetrapods from fish.

Here is the transcript of a programme I watched regarding this matter:

I really must thank you for that link! I'm going to tentatively name my fish livoniana even though we don't know what the body looked like completely and when/if the rest of it is ever found, I'll either arrogantly brag about my success or do my Homer impression; Doh!

I wish you the best of luck. If you work it out logically, I think you can get fairly close to the actual physical shape of those fated marine creatures.