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Author | Topic: Walking Catfish | |||||||||||||||||||||||||||
lpetrich Inactive Member |
How a Walking Catfish Walks (Clarias spp.). It's more like wiggling than walking, or at least so it seems to me. But it does give a hint as to how the earliest land vertebrates could have walked if they did not have limbs fully adapted for walking.
[This message has been edited by lpetrich, 12-04-2003]
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Quetzal Member (Idle past 5872 days) Posts: 3228 Joined: |
Walking catfish are very cool. However, isn't the current hypothesis that legs, etc, developed in shallow-water bottom dwellers before they decided on froggy goes awalking? If that was the case, I like the Ambystomatidae family of salamanders as a better modern example, especially this little guy (Ambystoma mexicanum):
Innit cute? Note the fully developed limbs and hands, coupled with the feather gills of an obligate water dweller. This species (and a few others of the family) remains neotenic, although the majority of the 30-odd species in the family metamorphose into land dwelling amphibians. Here's a pic of one of the metamorphosed A. mexicanum - very rare, and indistinguishable from A. tigrinum:
fixed pic width, hhmm doesn't seem to do anything to page width tho - The Queen [This message has been edited by AdminAsgara, 12-05-2003] [This message has been edited by AdminAsgara, 12-05-2003] {Bumped the width of 2nd photo from 60% to 80%, page width was fine at 60%, and (in preview anyhow) also at 80% - AM} [This message has been edited by Adminnemooseus, 12-05-2003]
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Adminnemooseus Administrator Posts: 3974 Joined: |
I assume there is html to scale that 2nd photo down, but I don't know how to do it. Admin or AdminAsgara, care to take a shot at it?
Then I can see how it's done. Now, back to our fishy topic, already in progress. Adminnemooseus
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roxrkool Member (Idle past 989 days) Posts: 1497 From: Nevada Joined: |
Now if those are perfectly good examples of current and observable transitional life forms, I don't know what is!
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mark24 Member (Idle past 5195 days) Posts: 3857 From: UK Joined: |
rox/Quetz,
Now if those are perfectly good examples of current and observable transitional life forms, I don't know what is! But are they? If they are neotenic then probably not. The limbs/digits are "inherited" from the non-neotenic form that was terrestrial. A truly great imtermediate would be a non-neotenic fully aquatic amphibian with limbs & digits that is not secondarily aquatic. This would clearly show that limbs & digits could evolve before terrestriality. Anyone? Mark ------------------"Physical Reality of Matchette’s EVOLUTIONARY zero-atom-unit in a transcendental c/e illusion" - Brad McFall
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Chiroptera Inactive Member |
You mean, like a mudskipper?
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mark24 Member (Idle past 5195 days) Posts: 3857 From: UK Joined: |
No, they can come out of the water & don't have digited limbs.
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Chiroptera Inactive Member |
Hmm. Maybe I don't get your point. You want a
fully aquatic amphibian but won't allow an amphibian to come out of the water? And why are digits important? Anyway, I suspect that the example you are asking for is pictured in your avatar?
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roxrkool Member (Idle past 989 days) Posts: 1497 From: Nevada Joined: |
But isn't it all relative? Aren't there an infinite number of possibilities a transitional form can take? (Okay maybe not an 'infinite' amount.)
And does it matter which direction evolution is moving? Or did I misunderstand?
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mark24 Member (Idle past 5195 days) Posts: 3857 From: UK Joined: |
Chiroptera,
Sorry, I never made myself clear. Quetzal pointed out that current theory suggests that early tetrapods gained limbs & digits before leaving the water. I pointed out that a neotenic salamander probably isn't a good example of a transitional because it gained it's limbs from a terrestrial ancestor. In that sense they are atavistic structures rather than structures that evolved for a purpose under water, even if the early tetropods did in fact look like that.
Anyway, I suspect that the example you are asking for is pictured in your avatar? Indeedy! Mark ------------------"Physical Reality of Matchette’s EVOLUTIONARY zero-atom-unit in a transcendental c/e illusion" - Brad McFall
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mark24 Member (Idle past 5195 days) Posts: 3857 From: UK Joined: |
rox, see post 10.
Mark
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Quetzal Member (Idle past 5872 days) Posts: 3228 Joined: |
There are, actually, quite a few of the salamanders which are fully aquatic in both larval and adult forms. I like the hellbenders (ex, Cryptobranchus alleganiensis) of the Cryptobranchidae subfamily (Urodela):
Although you can't really see it in this adult pic, the little guy has fully functioning gills. Does this work? PS: Notice the resemblance to your avatar? [This message has been edited by Quetzal, 12-04-2003]
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mark24 Member (Idle past 5195 days) Posts: 3857 From: UK Joined: |
Quetzal,
Does this work? No, a fully aquatic ampbhibian is a fish. Thanks, Mark [This message has been edited by mark24, 12-04-2003] {quote:ampbhibian (!?!?!?) - Adminnemooseus } [This message has been edited by Adminnemooseus, 12-04-2003]
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Quetzal Member (Idle past 5872 days) Posts: 3228 Joined: |
You have a good point. Salamanders are probably not "transitional" in the sense of demonstrating the sequence from water to land. They're pretty derived, and separated out from the Anurans sometime during the Mesozoic (IIRC). I'll see if I can remember any other extant critters that are closer to the mark, but anything around today would be pretty much at a long-evolved (i.e., derived) state. IOW, your objection concerning the terrestrial/aquatic line - at least in amphibians - would probably still apply.
OTOH, I think that fishies coming up on land like lp's catfish or Chiroptera's mudskippers blur the terrestrial/aquatic distinction more than a bit. There's also some of the Blenniidae that can live out of water for awhile and even one that lives in intertidal pools and deliberately jumps out of the water to escape predators - and can sit around for up to ten minutes (I can't remember which species). IMO, while they may not represent transitionals in the sense your avatar does, the DO show that things are still coming ashore...
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Quetzal Member (Idle past 5872 days) Posts: 3228 Joined: |
Erm, I thought you wanted a fully aquatic tetrapod? The hellbender sure seems to be in the running. Maybe you could define a little more clearly what you're asking?
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