Fishes out of Water

Some experiments with walking fishes.

Start with a fish (0) – this one is a teleost. Note the pectoral fins are right above (dorsal of) the pelvic fins.

The first tetrapods (1) evolved from lobe-finned fishes with the pelvic fins down close to the tail. A nice, stable platform on land, but boring!

What about (2)? the pelvic and analfins get repurposed as limbs. The pectorals are  lost.

Number 3 is something I see a lot of these days. The pelvic fins and the tail are limbs, which I think represents a problem with homologous structures. Any mutation that alters the development of the genes controlling the first two limbs (say, making them longer) will have to be followed by another mutation doing the same for the caudal vertebrae.  I don’t buy it. One way to get around it is if the same genes control the growth of the pelvic fins and the caudal fin, but I don’t know if that’s true. Also, the resulting limbs could be composed only of fin rays. Maybe they would be jointless spines. Maybe finger-like things. I need to draw that.

Number 4 is if the first fishes crawl on land with their pectoral fins dorsal of the pelvic fins (sorry I got them mixed up in the legend in the image). Now we have a problem where the pectorals have to be longer than the pelvics to touch the ground. One way of dealing with that is to move one set of limbs back toward the tail. Another is to repurpose the pectorals as hands. The third is to live in trees where it doesn’t matter.

And finally. The Land Flounder. He does his best.

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