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Megarthropoda; Big Bugs
Topic Started: Jun 20 2010, 05:55 PM (1,294 Views)
Rhob
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I'd like to start a new effort to investigate how arthropods could have become the trophically-dominant phylum instead of vertebrates. Obviously this means that vertebrates had to be out of the way, and what better way for that to happen than for them to never have evolved in the first place? :P So my thinking is for chordates to be wiped out in the end-Cambrian event. This should lead the way to arthropods becoming dominant and giving rise to the Megarthropoda -- big bugs!

What do you guys think? Feedback/criticism/contributions welcome!
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Dean
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I think that getting rid of chordates before they have a chance to become dominant is a right step towards a world of arthropod domination, but, on the other hand, arthropods are so small because their respiratory system isn't as advanced as that of chordates. They first need to evolve something that would be as efficient as tetrapod lungs.
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Rhob
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Quite right. While in insects and some arachnids the ancestral gills have been wholesale replaced with tracheal systems, in other arthropods the gills have been adapted to breathing air. In the coconut crab (Birgus latro), the gills could be better described as full-fledged lungs because they can no longer take in oxygen from water. That means coconut crabs can actually drown.
Edited by Rhob, Jun 20 2010, 06:06 PM.
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Pando
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Instead of doing this alternative evolution you could do future evolution, with a world dominated with coconut crabs, seeing as they have semi-lungs already. Then you have to worry about the biggest exoskeleton size. Canis put it at about the size of a golden retriever.
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Rhob
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I appreciate the suggestion, but I think it would be more interesting to do an alternative evolution.
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Rhob
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Okay, so following the end-Cambrian event, what would be the same and what would be different? Most Ordovician chordates occupied benthic habitats, so other things would take their place. Trilobites were already present -- would they be even more diverse than in our timeline (IOTL)? Or would some other invertebrate group diversify instead? Obviously nautiloids and eurypterids would still exist, though they might evolve in somewhat different ways than what actually happened. Anomalocarids and their cousins apparently survived at least into the Devonian, so perhaps they'd be more diverse here as well.

Thoughts?
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Canis Lupis
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Dinosaurs eat man, woman inherits the Earth.

Ah, thanks for the reference Pando.
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Holben
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Rumbo a la Victoria

Giant scorpions look set for the top-predator niche. But even in carboniferous conditions, they didn't and probably won't grow bigger than 60cm or so. Social insects should arise much earlier, and maybe from a different family...
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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Pando
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What about 3 inch long carnivorous ants? They'd be mega for ants and could potentially remove even the apex predators.
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Holben
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Rumbo a la Victoria

Well... the largest so far have been about an inch and a half for workers, much bigger and they collapse under their own weight. But even ones that big can kill most stuff.
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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Pando
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Well, what about eusocial carnivorous cockroaches 3 inches long?
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Holben
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Rumbo a la Victoria

Yes, apart from i'm not sure how they'd become eusocial.
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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Pando
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They already swarm together, they could start living together in abandoned buildings. Then once they leave they continue to live together, and in a few million years they're eusocial.
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dialforthedevil
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50cm long woodlice as main herbivores?
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The Dodo
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With fish gone would the cephalopods be more dominant in the oceans?
In the air there would probably be fly like anthropods.
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