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Swaping Places
Topic Started: Jan 9 2010, 11:19 PM (1,411 Views)
TheCoon
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Here's a good one: What if arthropods and vertebrates swaped places?

What if the vertebrates were the tiny critters that polinize flowers while arthropods were gigantic grazers and feroceous carnivores?
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Holben
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Rumbo a la Victoria

Elevated oxygen levels produced Meganeura and Arthropleura, so it has been seen to happen. But these were simple arthropods- it would be much harder for toaday's highly specialised arthros.
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

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Ddraig Goch
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Ar hyd y nos

Okay, so what, currently, is the most "primitive" arthropod?
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Holben
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Rumbo a la Victoria

No idea. :o

Maybe something like an annelid, if we're doing invies in general. If bigger, they would survive- we already have 3m earthworms on our planet. But the more specialised arthies wouldn't cope.
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

"It is the old wound my king. It has never healed."
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Ddraig Goch
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Ar hyd y nos

*imagines twenty-metre long earthworm* :o

By "more specialised"... how do you mean?
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Holben
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Rumbo a la Victoria

They have adapted to a tight exoskeleton, a certain weight, so biomass isn't wasted in support, and their ganglia couldn't co-ordinate such a large body.

THe twenty metre earthworm sounds plausible, though.

Maybe they should 'swape' places.
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

"It is the old wound my king. It has never healed."
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T.Neo
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If you could get high oxygen levels (sort of like in the carboniferous), much larger arthropods then those possible today could exist (such as arthropleura or meganeura).

They're still limited by their exoskeletons and finally their circulatory systems.
Arthropleura might have been 3 meters long at the biggest but it was still a low-lying organism with many small legs, and it retreated to the water to moult.

So maybe a bit larger then a cat, but the exoskeletons get them in the end.

As for vertebrates I am sure you could get really small ones if you "picozoafied" their skeletons by making them out of cartilage and cut down on the number of internal organs.

Although I agree that arthropods wouldn't have a chance against vertebrates in any sort of realistic situation.
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Canis Lupis
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Ddraig Goch
Jan 10 2010, 03:32 PM
Or perhaps something like the giant cockroaches from "The Future of the Kinds"? Although that would require elavated oxygen levels.
Yeah! I got a mention!



Anyway, I studied arthropods extensively to prepare for that section of "The Future of the Kinds". I found that the most primitive arthropod (well, at least the most primitive insect) was a silverfish.

In short, there are no possible ways for an arthropod to be successful in a swapping situation. Arthropods have always been more evolved for small sizes and the only way to get the opposite would be for the arthropod to live in water and for there to be an increased oxygen level.




Now, if you want a swap that could very well happen, I suggest you swap vertebrates with mollusks. This may just be my extreme obsession with mollusks talking, but mollusks could have easily taken vertebrate niches if verts never evolved.

The mollusks that could swap with vertebrates more easily would be cephalopods, specifically squids. Squids already possess a pen, which is all that remains of the shell. I dissected a squid last year and it looked remarkably similar to the vertebral column in the frog that I dissected as well.

I can honestly say that I am surprised no notochord-like structure has taken up the space in the pen. Cephalopods are extremely brainy. And the most effective way to control the body with this huge brain power would be a notochord-like structure.


However, gastropods are not too far behind cephalopods. Gastropods have multiple ganglia scattered throughout their body, all linked by simple chords. This, while it works, is horribly inefficient. So it is not impossible to imagine that, in some wierd take on torsion, the ganglia all line up along the center of the body and form some sort of notochord. Over time, the notochord would be covered in cartilage and could conceivably become full-fledged bone.

A skeleton could form, complete with ribs. These ribs, as Metalraptor and I posited, could form legs. In my old "The Future is Bizarre" (BTW, the first phase of that project will become part of "The Future of the Kinds"), we had a 225MYF world populated by bipedal snails we called saltokochlids. And in my version of "Rewriting Earth" (before we had the Precambrian divegence date), I had gastropods that evolved an endoskeleton and ruled the land in the absence of vertebrates.

So if there was some way to efficiently shrink vertebrates (like maybe having vertebrates never evolve, but instead having cephalochordates (which are chordates along with vertebrates) dominant), mollusks could swap with the verts very easily.
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T.Neo
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I can see cephlapods such as octopi colonising land fairly easily. They can already survive outside of water for a short amount of time provided their gills remain moist. They also posess a highly evolved (in invertebrate terms) nervous system and eyes which are in some respects better then those of vertebrates. They also posess a highly "curious" personality.

Octopi already "walk" along the seabed, unlike their swimming relatives such as squid and cuttlefish. The only issue is their lack of any support structure. Perhaps some sort of hydrostatic support?

Snails have already (somewhat) conquered land with mucus-covered moist skin, so perhaps octopi could do similar. They could also develop keratinous (or chitinous?) scales or perhaps mineralised scutes.


Altogether gastropods are far less advanced then octopi and relatives, although their one advantage is that they already breathe air and live on land.

I doubt gastropod "bone" would be chemically analogous to vertebrate bone. It would probably have a similar composition to their shells.

I can see them suspending their organs and such on the shell or remnants of it. A notochord/spinal column seems too hard to evolve from scratch to me. I also see legs derived from muscular appendages of the "foot" as more plausible then rib-derived ones.
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Holben
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T.Neo
Jan 11 2010, 08:00 AM
I can see cephlapods such as octopi colonising land fairly easily. They can already survive outside of water for a short amount of time provided their gills remain moist. They also posess a highly evolved (in invertebrate terms) nervous system and eyes which are in some respects better then those of vertebrates. They also posess a highly "curious" personality.
Terrestrial cephalopods again?

Well, what niche would they fill? They eat crusteceans and fish, to my knowledge. On land, woodlice and beetles wouldn't satiate a 30cm-long octopus.

A mucus like covering? And moving with all eight limbs? Waste of biomass and strength. Their calcite skeleton is very weak as well, and they would be intensely vulnerable to predation.

Just for a start.
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

"It is the old wound my king. It has never healed."
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SIngemeister
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Holbenilord
Jan 10 2010, 03:51 PM
No idea. :o

Maybe something like an annelid, if we're doing invies in general. If bigger, they would survive- we already have 3m earthworms on our planet. But the more specialised arthies wouldn't cope.
Annelids have hydroskeletons, so not quite limited by the same factors as arthropods.
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Holben
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Rumbo a la Victoria

So, as i said, bigger annelids. Their hydroskeletons are also very flexible- and i'll also assume they'll spend most of their lives underground after 'the swape'.
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

"It is the old wound my king. It has never healed."
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T.Neo
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Quote:
 
Well, what niche would they fill? They eat crusteceans and fish, to my knowledge. On land, woodlice and beetles wouldn't satiate a 30cm-long octopus.


Well, they'd clearly evolve to take up new niches.

And you can get pretty big insectivores.

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A mucus like covering?


Snails do it.

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And moving with all eight limbs?


Yep. Arthropleura moved with all... 300 or something. 8 isn't that bad (and it'd be like crawling anyway since without bones it wouldn't get much support.)

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Their calcite skeleton is very weak as well, and they would be intensely vulnerable to predation.


Calcite mixed with chitin? Octopi don't have skeletons anyway, so they'd have to evolve one from scratch.

Well, since after the "swap" there wouldn't be any predators; the octopi would be the apex organisms in their environment.
Edited by T.Neo, Jan 11 2010, 01:12 PM.
A hard mathematical figure provides a sort of enlightenment to one's understanding of an idea that is never matched by mere guesswork.
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Rhob
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Holbenilord
Jan 11 2010, 12:49 PM
Terrestrial cephalopods again?

Well, what niche would they fill? They eat crusteceans and fish, to my knowledge. On land, woodlice and beetles wouldn't satiate a 30cm-long octopus.

A mucus like covering? And moving with all eight limbs? Waste of biomass and strength. Their calcite skeleton is very weak as well, and they would be intensely vulnerable to predation.

Just for a start.
Yes, cephalopods prey mainly on smaller crustaceans, mollusks, and fish. Most of them seem to prefer crustaceans.

There's no reason that all octopuses that venture onto land must be 30 cm long. Many species are much smaller than that. On the other hand, while woodlice and beetles are smaller than crabs and fish, there may be more of them. So an octopus would simply need to eat them more often (which it would if simply driven by hunger).

Given the nature of cephalopod anatomy, the easiest way for them to get out of the water may be through tree climbing. Some people have written about terrestrial cephalopods arising around mangrove swamps and the like. Freshwater environments have overhanging plants, tree branches, and (in the tropics) external root systems quite often. Members of one or more cephalopod species could pull themselves up onto them to evade predators.

I suspect that terrestriality would favor increasing dexterity on the part of cephalopod arms and/or tentacles. For example, a cephalopod could "fish" while hanging on a tree branch or external root out of the water, dipping one or more of its arms into the water to grab passing prey items. Perhaps it would also use its arms as lures to attract the prey.

While cephalopods are vulnerable to attacks, their evolutionary "strategy" has been to try to prevent attacks from occuring in the first place. They're masters of camoflauge. So there's no reason to think that they couldn't blend in with the things they're hanging on. Or they could even make themselves look like bird droppings!

Thinking about it this way, it seems like many species cephalopods could fare rather well out of the water. What holds them back, as far as I can tell, is their osmoconformity. Only one species is known to tolerate low-salinity brackish water -- the brief squid of Chesapeake Bay. Still, who knows what the future could hold here? :)
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Holben
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Tree octopi? :lol:

You want 'em in the mangroves, so they can go between water and trees like an amphibian?

Really, the sheer amount of competition...
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

"It is the old wound my king. It has never healed."
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Rhob
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Holbenilord
 
Tree octopi? :lol:


Sure, why not?

Holbenilord
 
You want 'em in the mangroves, so they can go between water and trees like an amphibian?


I don't necessarily want them anywhere. But they already seem somewhat pre-adapted for arboreality with their grasping tentacles (much better for pulling than for pushing).

Quote:
 
Really, the sheer amount of competition...


Many cephalopods live in some of the most competitive environments on Earth -- coral reefs. So you were saying...? :P
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