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salt water amphibians?

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Actually, it was saltier. See here. I got the full text of the article, and there is indeed a general decline in ocean salinity since the Cambrian. At the time of the origin of tetrapods, seawater was at roughly 4.5%, now it's at 3.5%.

 

I stand corrected. But to be honest I'm lying down.

Anyway, VERY interesting article.

THANKS for the info.

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Ok, this is *way* off topic. If you want to discuss this theory, start a thread on it.

 

It was thinking about amphibians that got me thinking about the EET, but fair call nonetheless.

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In the case of crocodiles, it seems very likely. Early tetrapods are often reconstructed as having a crocodile-like lifestyle (preying on the large insects that colonized land before them), and very crocodile-like forms evolved more than once, namely Prionosuchus, Archegosaurus, and Melosaurus.

 

After they died out, a group of non-crocodile reptiles occupied the niche, the Phytosaurs, and only once they vanished did modern crocodiles take their present form (previously, they looked like reptilian greyhounds).

 

wow. that's convergent evolution demonstrated perfectly. it must be that there simply is no better design for an amphibious swamp ambush predator.

 

on crocs, there's a parallel of sorts with amphibians.

 

australia's top end has two types, the large, dangerous "salties" and their smaller, relatively harmless cousins, the "freshies".

 

while the saltwater crocs are equally at home in fresh or salt water, the "freshies" won't go near salt water if they can avoid it, presumably because they'll become prey. they've moved a long way inland in the monsoonal climate and inhabit rock pools and fresh water streams.

 

so i guess something similar might have happened with "lissamphibia". they became specialists.

 

sadly, the "freshies" are in danger of extinction because the introduced cane toads they have started eating are lethal to them. the indestructable "salties", however, can consume the toads with no ill effects.

Edited by caz

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Ok guys, there are no marine amphibians because they developed from bony fishes, Bony fishes evolved in fresh water, not marine. The skeleton of freshwater fishes evolved from fishes with no bones much like sharks, they migrated to fresh water to lay their eggs. the calcium was concentrated in their skeletons so they wouldn't loose it when they entered freshwater. Calcium is important to all animals far beyond the need for bones. The cartilage bony fish that concentrated calcium were preadapted to life in freshwater. True bony fishes developed in freshwater and later returned to the sea. Amphibians evolved from a group of bony fishes called lobe finned fishes that may have only survived in freshwater due to the highly succesful Placoderms.

 

http://en.wikipedia.org/wiki/Placoderms

 

I honestly cannot say if amphibians ever returned to the sea or not but they evolved in freshwater from freshwater fishes. the coelacanth probably evolved from a lobe finned fish who's lineage never left the ocean.

 

http://en.wikipedia.org/wiki/Coelacanth

 

The modern bony fishes, class Osteichthyes, appeared in the late Silurian or early Devonian, about 395 million years ago. The early forms were freshwater fishes, for no fossil remains of modern bony fishes have been found in marine deposits older than Triassic time, about 230 million years ago. The Osteichthyes may have arisen from the acanthodians. A subclass of the Osteichthyes, the ray-finned fishes (subclass Actinopterygii), became and have remained the dominant group of fishes throughout the world. It was not the ray-finned fishes, however, that led to the evolution of the land vertebrates.

 

http://www.lookd.com/fish/evolution.html

 

Tetrapods evolved from freshwater lobe finned fishes, the fishes you see in the rivers and oceans today are not the direct ancestors of us, Only the coelacanth and some lung fishes remain from those lobe finned fishes. the coelacanth is not a direct ancestor either but it is closely related.

 

http://www.devoniantimes.org/who/pages/lobe-fins.html

 

http://en.wikipedia.org/wiki/Lobe-finned_fish

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Ok guys, there are no marine amphibians because they developed from bony fishes, Bony fishes evolved in fresh water, not marine.

 

If origin determined the entire future of the lineage, why are there marine organisms of all other tetrapod lineages? That a lineage originated in a given environment does not constrain it forever to that environment. See Whales.

 

I suggest Clack's book, which has a good discussion on this. She specifically points out that the global distribution of tetrapod fossils means they must have been able move through marine environments (as the alternative, numerous independent origins, is even less likely).

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If origin determined the entire future of the lineage, why are there marine organisms of all other tetrapod lineages? That a lineage originated in a given environment does not constrain it forever to that environment. See Whales.

 

I suggest Clack's book, which has a good discussion on this. She specifically points out that the global distribution of tetrapod fossils means they must have been able move through marine environments (as the alternative, numerous independent origins, is even less likely).

 

This is true my logic did faultier there but I did say I had no idea if amphibians had ever adapted to the sea or not. fossils seem to indicate they didn't. The plain fact is not many land animals have ever adapted back to the oceans. Yes I know whales, Plesiosaurs, turtles, seals but not many compared to the number of land animals. Paradoxically dinosaurs never adapted to marine life. If any amphibians did go back to sea they are all extinct now and left little or no fossil evidence. Evidently it's hard jump and thin skinned amphibians seem to be somewhat less than preadapted to marine conditions. As far as the global distribution drifting continents would seem to explain that pretty neatly.

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fossils seem to indicate they didn't.

 

Archegosaurus apparently did, but it's the exception.

 

As far as the global distribution drifting continents would seem to explain that pretty neatly.

 

Not entirely, early tetrapod fossils are found on what would have been opposite sides of Pangaea.

 

Evidently it's hard jump and thin skinned amphibians seem to be somewhat less than preadapted to marine conditions.

 

True, but if you'll read back, the highly permeable skins of modern amphibians are not the primitive state - early tetrapods likely had much less permeable skin, and in some cases, we know they had scales or armor.

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Where do you get that Archegosaurus lived in the ocean? It is described as living in freshwater ponds that were subject to drying up and Archegosaurus was able to wiggle over land to a new pond. No mention of marine existence.

 

Do you think it might have been possible for tetrapods to have migrated over Pangaea before it broke apart?

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Clack's book is the source. I doubt land migration would be possible - most early tetrapods weren't good enough walkers for long-distance migration, especially over the inner desert of Pangaea.

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Clack's book is the source. I doubt land migration would be possible - most early tetrapods weren't good enough walkers for long-distance migration, especially over the inner desert of Pangaea.

 

While I will have to read the book to understand your argument completely I wonder why you think migration due to long distance would be a problem. A species of salamander could migrate long distances over millions of years taking advantage of changing climate patterns. We would think the idea of a fish migrating across the Sahara Desert would be impossible but just a few thousands years ago what we know as a desert was a lush area with rivers and lakes and lots of rain. A fish could well have migrated over that area then. I am quite sure that Pangaea had changing climate patterns as well and over a geologic time span an animal could well have migrated all over it while speciating along the way. No need to swim and oceans or migrate across burning sands.

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Theoretically, it's possible, but there's no reason to assume permeable skins evolved until modern amphibians (which arose in the Triassic), especially given the marine tetrapod species I listed above, and that even freshwater poses osmotic challenges (just in the opposite direction).

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Theoretically, it's possible, but there's no reason to assume permeable skins evolved until modern amphibians (which arose in the Triassic), especially given the marine tetrapod species I listed above, and that even freshwater poses osmotic challenges (just in the opposite direction).

 

Ok, I know enough about fishes to know about osmotic pressure and even freshwater fish benefit from the addition of a small amount of salt, it lessens the stress of capture. But I still disagree with the contention that tetra pods had to be able to swim and or live in the oceans for them to have populated the Earth. The fossil record doesn't show any oceanic amphibians even thought they've been around longer than other tetra pods. Even dinosaurs didn't return to the ocean but they were world wide in distribution so the idea that Pangaean deserts would've required amphibians to colonize the oceans isn't worth it's salt >:D

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The fossil record doesn't show any oceanic amphibians even thought they've been around longer than other tetra pods.

 

Archegosaurus

 

Even dinosaurs didn't return to the ocean but they were world wide in distribution so the idea that Pangaean deserts would've required amphibians to colonize the oceans isn't worth it's salt

 

Dinosaurs weren't tied to water for reproduction, though.

 

 

Given that there is copious evidence of marine sacropterygians, I see no reason to assume, a priori, that a very closely related group was restricted to fresh water.

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Archegosaurus

 

 

Again Archegosaurus was a freshwater form not marine.

 

 

 

Dinosaurs weren't tied to water for reproduction, though.

 

 

 

Neither are reptiles, or mammals but they evolved forms that were marine. What's your point?

 

 

Given that there is copious evidence of marine sacropterygians, I see no reason to assume, a priori, that a very closely related group was restricted to fresh water.

 

 

Why would the distribution of fish have anything to do with the distribution of amphibians? I have already said that lobe finned fishes were marine and freshwater but amphibians evolved from the freshwater versions.

 

 

http://en.wikipedia.org/wiki/Sarcopterygii

 

 

Archegosaurus were freshwater forms, they were associated with freshwater deposits not marine.

 

 

BTW I will be the first to admit this is an extremely difficult thing to nail down, I'm betting that very little real information exists on the overall ecology of these animals.

Edited by Moontanman

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Again Archegosaurus was a freshwater form not marine.

 

Cite a source for that, please. I've cited mine, and she's the world's leading expert on the subject.

 

Neither are reptiles, or mammals but they evolved forms that were marine. What's your point?

 

My point is that you cannot look at impermeable-skinned animals with amniotic eggs for clues about animals which had more-permeable skins and anamniote eggs.

 

Why would the distribution of fish have anything to do with the distribution of amphibians? I have already said that lobe finned fishes were marine and freshwater but amphibians evolved from the freshwater versions.

 

Because it shows that there wasn't some major barrier for sarcopterygians becoming marine. And since tetrapods are just derived sarcopterygians (and, at the time we're talking about, only minimally derived), there's no reason to presume they weren't just as adaptable as their fishy cousins.

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While I think there is reason to think they were exclusively freshwater I will wait until I read the book you cited before I argue any further. I have burnt the Internet up looking for info and all I could get was a few tantalizing clues and generalizations. I see no reason to continue with out more information. I'll continue to search and read the book.

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It's an excellent book, and she's a very good writer, much better than most scientists.

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I have become suspicious of the whole Wegener idea of plate tectonics - continents have to wiggle and rotate in freakish ways order for it to be correct. Using occams razor, the EET is far simpler - and works - exactly. The continents fit together exactly!

 

Sorry, Occam's razor is exactly why nobody seriously considers EET a scientific theory. Plate tectonics fully explains the observed phenomena, while EET requires some as-yet unexplained and unobserved mechanism for causing the expansion. Far simpler to follow PT, which is supported by numerous different observations.

 

If EET made testable predictions that diverge from PT, and the observations supported it, there would be more serious adherents.

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Sorry, Occam's razor is exactly why nobody seriously considers EET a scientific theory. Plate tectonics fully explains the observed phenomena, while EET requires some as-yet unexplained and unobserved mechanism for causing the expansion. Far simpler to follow PT, which is supported by numerous different observations.

 

If EET made testable predictions that diverge from PT, and the observations supported it, there would be more serious adherents.

 

Plate tectonics does not fully explain the observed phenomena. That's my point.. At least, it does not do so as well as EET. Apart from the (admittedly crucial) missing info on the mechanism of expansion EET seems to fit with the data.

 

If a potential mechanism was discovered, would it change your view? Is the lack of a mechanism your only issue?

 

Maybe this needs a separate thread?

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with EET there would be no mountains(except volcanoes) and there would be no fossils of sea creatures at the summit of everest.

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Maybe this needs a separate thread?

 

Yes.

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with EET there would be no mountains(except volcanoes) and there would be no fossils of sea creatures at the summit of everest.

 

I don't think that's true. Mountain ranges are formed when expansion causes continental plates to buckle (as the curvature of the eart decreases). I'd suggest reading up on EET. In fact, EET gives an explanation of why fossils of sea creatures ARE found at the summit of everest rather than on the sea bed!

 

If people actually WANT a thread on this I'm happy to start one. Is there already one?

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No, please, go ahead and start one.

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Plate tectonics does not fully explain the observed phenomena. That's my point.. At least, it does not do so as well as EET. Apart from the (admittedly crucial) missing info on the mechanism of expansion EET seems to fit with the data.

 

If a potential mechanism was discovered, would it change your view? Is the lack of a mechanism your only issue?

 

Maybe this needs a separate thread?

 

I'm still waiting to hear what observations are not explained by PT that are explained by EET. You can measure the rate of plate movement today, but AFAIK nobody has measured any corresponding increase in the Earth's diameter.

 

In the absence of a plausible mechanism to explain expansion, EET is just a bizarre hypothesis. Without a mechanism, it is difficult to come up with testable experiments, for observations that could support or rule out the viability of the hypothesis.

 

So far, I haven't heard anything that really supports the idea, and much that says that it does not merit consideration as a serious theory.

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How wierd. I replied to this yesterday, but my post has disappeared???

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