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Six limbs; multi limbed fauna
Topic Started: Jan 18 2011, 06:31 PM (1,296 Views)
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I had this idea for some time now, The idea is that what if the first amphibian like creature to colonize the land had six legs instead of four. the following event are very similar to the time line that we know:

the plant life stays near the same,

Geological events are exactly the same,

and extinction events happen the same,

the only differences is the fauna has six limbs.

no what I wondered what would life be like today if evolution took this little detour?
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Are you plausible?

That still lacks a reason for the extra limbs. If they already have four fins well placed to move them over land, why use the gill opercula?
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colddigger
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I thought in another thread about six limbed alternative history it was pointed out that there was an equal opportunity for a six limbed fish to move onto land and it just happened that the four finned fish did it....?
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Dark-Matter
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colddigger: I thought in another thread about six limbed alternative history it was pointed out that there was an equal opportunity for a six limbed fish to move onto land and it just happened that the four finned fish did it....?
I think I remember that is base on a deviation from deviart.
Edited by Dark-Matter, Jan 19 2011, 03:36 PM.
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Rhob
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Hmmm...I was more thinking of something to provide an added thrust to the body. Maybe an extra pair of fins would add stabilization to the tail, which provides a lot of thrust?


If the tail provides a lot of thrust, you're talking about thunniform swimming, which is used by deep-water fish like tunas to sustain high speeds over long distances. However, I'm not sure how an extra pair of pelvic fins (essentially) will add that much more stability.

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I'd say we'd probably also be looking at freshwater fish wouldn't we? Even so, most freshwater fish also swim by lateral undulations... Perhaps a "flatter" mud living freshwater fish beats the proto-amphibian fish of our timeline onto land?

In my HabZone project - Zarathustra, on its moon Cyrus, there are freshwater vertebrates, that swim by vertical undulations, they evolve into 6 limbed "amphibious" vertebrates


Yeah, I think this is more plausible. I'm envisioning something like a modern stingray, except the pectoral fins are smaller and the pelvic fins are larger. A third pair of lateral fins at the end of the tail could then develop to produce more thrust at the end of the animal.

colddigger
 
I thought in another thread about six limbed alternative history it was pointed out that there was an equal opportunity for a six limbed fish to move onto land and it just happened that the four finned fish did it....?


To my knowledge, there's never been a species of fish with three or more pairs of lateral fins.
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Are you plausible?

Rhob
 
To my knowledge, there's never been a species of fish with three or more pairs of lateral fins.


What about the coelocanth or eusthenopteron? Don't they count?
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Rhob
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Jan 19 2011, 04:03 PM
What about the coelocanth or eusthenopteron? Don't they count?
No, those only have/had two pairs of lateral fins.
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I stand corrected. The fin I was mistaking for a third pair was in fact the anal fin.
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colddigger
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I did a little skimming and yeah, no, it doesn't seem like there are any obvious fishies who have six paired limbs. The Eusthenopteron as far as I can tell does have six fins, but the last two are top and bottom '~'

http://media.photobucket.com/image/Eusthenopteron%20had%20six%20fins/AnimaMundi1982/Eusthenopteron203.jpg


Of course... I don't include the dorsal fin........
Edited by colddigger, Jan 19 2011, 04:23 PM.
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So if you are going to have a six limbed clade of land vertebrates you'll have to take a step back and make fish with six fins. I don't think that's impossible to develop, it just makes it that much more of a fundamental change.
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Rick Raptor
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Dark-Matter
Jan 19 2011, 03:35 PM
colddigger: I thought in another thread about six limbed alternative history it was pointed out that there was an equal opportunity for a six limbed fish to move onto land and it just happened that the four finned fish did it....?
I think I remember that is base on a deviation from deviart.
Yes, this one:
http://browse.deviantart.com/?qh=&section=&q=acanthodians#/d1ho0fc

These "sectapods" are supposed to have evolved from Acanthodians.
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Dark-Matter
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That was the deviation I was talking about.
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Rhob
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From what I understand, acanthodians didn't have multiple lateral fins, just multiple lateral spines.
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