How Did Ocean Life Become Adapted to Land?

noz92 · December 5, 2005

I understand that life is believed to come from the ocean--land life is supposed to have come from a species of fish-like animals that crawled up on land one day probably to escape predators.

I have ideas for why certain parts of land creatures would have evolved--for example, arms and legs would have been very useful for maneuvering through plants in the water, useful for hiding from predators--but other parts I don't understand how they could have been useful in the water--for example, the first land creatures obviously were able to breath on land, but what use would that have had in the Carboniferous seas?

bascule · December 5, 2005

The swim bladder of fish used to be a primitive lung. It still is in certain fish such as the lungfish.

There are fish which do come to the surface to breathe air when they are in poorly oxygenated water. That's one example of the usefulness of lungs.

There's also fish that get trapped in shallow pools of water which slowly dry up. If they can move across the land and find water again they will survive. Otherwise they perish.

Sisyphus · December 5, 2005

Yeah, I would imagine any trait at all that allowed creatures to push the boundaries of the biosphere and move towards the essentially competition-free land would reproduce like mad... if you could maneuver and respirate at all outside of water, you'd be home free, genetically speaking...

**ecoli** · December 5, 2005

Very slowly. First they would have to adapt to life partially in the water, partially on land.

Mokele · December 6, 2005

Actually, the use of swim-bladders as lungs is extremely widespread in fish, not just confined to lungfish.

And ecoli's right, it seems to have been a very gradual process. It was probably motivated by the free food on land, in the form of plentiful insects which had already invaded the land millions of years earlier. Animals capable of lunging out onto shore to catch a yummy millipede would have had an advantage, those able to actually move on land even more, and so on and so forth.

Also, it wasn't technically the seas vertebrates moved from, but rather the shallow swamps, rivers, and lagoon systems. Think of modern Lousiana bayous or Florida swamps.

Mokele

noz92 · December 7, 2005

So when would animal life have actually moved up on land?

bascule · December 7, 2005

So when would animal life have actually moved up on land?

The main fossils referred to in regards to the move from lobe finned fish to tetrapods are Ichthyostega and Acanthostega from the Upper Devonian:

http://tolweb.org/tree?group=Ichthyostega

So a little more than 350 mya

starbug1 · December 7, 2005

I understand that life is believed to come from the ocean--land life is supposed to have come from a species of fish-like animals that crawled up on land one day probably to escape predators.

I have read another theory that in some areas overpopulation was a factor in the push to go on land. And even after land animals developed there was a emerging migration of them moving back to the sea, which formed completely different species from the original ancestors that came from the sea.

shenzhou · December 9, 2005

Actually' date=' the use of swim-bladders as lungs is extremely widespread in fish, not just confined to lungfish.
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I was surprised when i learned that at least 370 species of fish in 49 families can breathe air, at least to some extent.

The best website on early land animals is the Devonian times. It covers many species and also importantly the major environmental changes which happened when vertebrates took their first steps on land.

Mokele · December 10, 2005

Oooh, thanks for the link!

herpguy · December 11, 2005

I've heard that some fish evolved into amphibians to escape predators in the ocean. The fish would swim into rivers and eventually became fresh-water fish (so they could survive while the predators couldn't) and others transformed into giant salamanders that went on land and in water. Eventually, over an extremely long period of time, the skin of the salamanders thickened into scales and created land loving lizards. Then dinosaurs came from the lizards which made birds and mammels. Primates came from mammels and here we are today.

bascule · December 11, 2005

I've heard that some fish evolved into amphibians to escape predators in the ocean. The fish would swim into rivers and eventually became fresh-water fish (so they could survive while the predators couldn't) and others transformed into giant salamanders that went on land and in water. Eventually, over an extremely long period of time, the skin of the salamanders thickened into scales and created land loving lizards.

From what I read in The Ancestor's Tale, it's presently thought that reptiles and amphibians shared a common tetrapod ancestor but did not descend directly from each other.

Wouldn't it make more sense for reptilian scales to be modified fish scales?

herpguy · December 11, 2005

Wouldn't it make more sense for reptilian scales to be modified fish scales?

It would make more sense, but things don't always have to make sense. For example, income tax.

Mokele · December 12, 2005

I've heard that some fish evolved into amphibians to escape predators in the ocean. The fish would swim into rivers and eventually became fresh-water fish (so they could survive while the predators couldn't) and others transformed into giant salamanders that went on land and in water.

Highly unlikely, for two reasons. First, fresh-water areas had numerous predators too, including sharks and giant coelocanths. Second, most of the early tetrapods were large predators in their own right, fully capable of taking on most of the other organisms in the ecosystem. Some, such as Greererpeton, exceeded 20 feet long, and were possibly the apex predators of their ecosystems.

From what I read in The Ancestor's Tale, it's presently thought that reptiles and amphibians shared a common tetrapod ancestor but did not descend directly from each other.

It's all about what you call "amphibian". If you define it is "all extant amphibians and the descants of their most recent common ancestor", yes. You could be sloppy and call the first tetrapods "amphibians", but that brings up the messy subject of the validity of paraphyletic groups in taxonomy. Honestly, sometimes Linnean taxonomy is just more trouble than it's worth.

Wouldn't it make more sense for reptilian scales to be modified fish scales?

Possibly. We don't know how soon tetrapods-amphibians lost their scales; it could be anytime between their fish ancestor and the last common ancestor of all extant amphibians. AFAIK, we don't have any fossils of tetrapods that preserve integuement, so it's sort of an open question.

Mokele

**ecoli** · December 12, 2005

Highly unlikely, for two reasons. First, fresh-water areas had numerous predators too, including sharks and giant coelocanths. Second, most of the early tetrapods were large predators in their own right, fully capable of taking on most of the other organisms in the ecosystem. Some, such as Greererpeton, exceeded 20 feet long, and were possibly the apex predators of their ecosystems.

It's more likely that a set of random mutations caused new species to find new niches in fresh water areas.

Rebiu · December 28, 2005

I for one am blown away by the concept of flying fish. They actually wiggle their tail to create thrust. I imagine could evolve into an animal that spends most of its time in the air.

sunspot · January 8, 2006

Putting aside the why for the time being, the one thing that moving to the land did do was increase the amount of oxygen that an animal could uptake per unit of time and per air absorption surface area. The main benefit, was more compact lifeforms that could support larger brains; increased the brain mass to body mass ratio. Whether the chicken came before the egg; migration to land occurred leading to direct air breathing or whether evolution in the ability to breath on land led to the migration onto land, the net result was quantum evolutionary progress.

sunspot · January 10, 2006

What is sort of interesting is that this quantum change was also practical evolution. In other words, there is no evidence that suggests that all land animals stemmed from one mutation. Yet the genetic change led to a practical and logical advancement of life. This suggests a logical potential pulling evolution toward a logically progressing future.

The question becomes, what is more fundamental than DNA and genes? The answer is the hydrogen proton. Without the hydrogen proton, the DNA would be useless as a template material. With the hydrogen proton, DNA and chromosomes become active and will define configurational potentials based on the hydrogen proton. The proton potential continues to rise into the future.