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Megarthropoda; Big Bugs
Topic Started: Jun 20 2010, 05:55 PM (1,295 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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Rhob
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Holbenilord
 
Ah, the old megaposting.


"Megaposting"? What is that supposed to mean?

Holbenilord
 
Well... yes, i am. Dragonfly nymphs don't have much in the way of enhanced senses.


Perhaps you should explain what you mean by "enhanced senses". My point was that they don't seem to have any problem capturing "substantial prey".

Holbenilord
 
Atrophying muscles,(so probably nerve sheaths too, slp) while becoming vestigial, become harder and their wasting away makes them strong.


What??? I guess I wasn't clear before in explaining what (pretty much) everyone else takes "atrophy" to mean. It means to weaken to the point of becoming vestigial. In no way can that be interpreted as "harden", let alone "strengthen"! Do you understand now?

Holbenilord
 
Elephants need to be the size they are to mount their guts, etc. same with big dinos. But it comes at great cost to reproduction (and therefore adaptation). So... they aren't as well off.


"Aren't as well off"? By whose standard (again)? Also, you're invoking teleological (end-oriented) reasoning to the non-teleological process of evolution. That is, evolution has no goals in mind, so to speak. To say otherwise is to rather fundamentally misunderstand how it "operates".

Holbenilord
 
The poangolin's scales DO SOMETHING, therefore not being excess. They are kept thanks to purpose.


By that reasoning, the exoskeletons of megarthropods would also DO SOMETHING, namely support the animal's internal organs.

Holbenilord
 
I see where you're coming from, but that wasn't really my argument. My appealing to 'the weastage of biomass' will in future be supplemented by a definition.


What's wrong with providing a definition now? If that wasn't really your argument, then please explain what it actually is, since I can't seem to make heads or tails of it.
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Holben
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Well... did i get through to you with my last post?

Megaposting. Clue's in the name. Link providing explanation.

Substantial prey, rather than little minnows and the like, means buffalo, antelope, etc.

'pretty much everyone else', huh? Whenever i talk to any real people about atrophying, they think of it like the atrophying nerves and muscles involved in a degenrative condition, where they harden.

My standard, ie. human standarde. They aren't well off, as when serious change comes, they die. You can't be well off when you're dead, can you?
Hope that clears up your teleology myth there.

Therefore they aren't excess biomass. I was under the impression my previous post was a warning to stay away from excess biomass.

My definition of 'excess biomass', the one i've been using at least, is biomass which is not used to further the animals reproductive success. If you invoke the appendix on me, regardless of its functions, i will have to say that because it does nothing negative, doesn't even weigh us down, it is kept for now.

Heads or tails showing up now?
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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dialforthedevil
Jun 27 2010, 04:06 AM
What about annelids,they have no true limiting factors such as an exoskeleton so surely they would get bigger?
Oceanic life would be incredible, giant sea urchins, sea slugs. Maybe even jellyfish as the top predators....
The reason bugs can get to the size of a small dog is because of their exoskeleton. The reason tetrapods can grow to the size of an Amphicoelias is because of our endoskeleton. The reason something without a skeleton can't grow more than a few inches tall is because they don't have any skeleton at all. They're just mush, and nothing can support them. Granted, they can grow to the size of a whale in the ocean if they live at the top, but annelids are stuck at their size because they either live on land or the bottom of the ocean.
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Ammonite
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On the issue of atrophy, I think both Holbenilord and Rhob are describing the same thing. Just different aspects of it. Literally, atrophy means "to degenerate." One of the effects of atrophism can be weakening, as in muscle atrophism. On the other hand, when nerves atrophy, they become harder. Which servesyour purpose, Rhob.

On the issue of dragonfly nymph senses, I am not sure exactly what they have in terms of sensory apparatus but I think the types of animals they catch - little minnows and such - have more to do with size than anything else. The fact that they are catching something, and catching it often enough to stay alive, should imply that they are doing something right.

Also, most of the selecting for sixe happens on the adult level, not the larvae level. Adult dragonflies select for mates that will inadvertantly have smaller offspring because they are selecting for smaller size in the adults they mate with. Adult dragonflies need to worry about the effects of an exoskeleton on land, not in the water. One of these effects is the chance they will be caught by a predator. In the insect world (on Earth), the smaller you are, the easier it is for you to fly and consequently the better flier you can become.

dialforthedevil
 
What about annelids,they have no true limiting factors such as an exoskeleton so surely they would get bigger?

Annelids - all worms, for that matter - have enormous potential for getting much bigger than they are now. Why they aren't substantially bigger now can be almost solely attributed to predation. I.e. Practically everything eats them. Worms don't have a chance of selecting for larger size nowadays because getting bigger only makes them easier to catch. Remove predation and worms can get much, much bigger. The flipside is that worms occupy very few niches, so even if there were no other animals there to eat them, there would be soon. Then again, this is assuming the environment is easily habitable to other animals. Put your worms on a desert world or swamp world and you may have a different story.....
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Holben
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Ammonite
Jun 27 2010, 12:00 PM
On the issue of atrophy, I think both Holbenilord and Rhob are describing the same thing. Just different aspects of it. Literally, atrophy means "to degenerate." One of the effects of atrophism can be weakening, as in muscle atrophism. On the other hand, when nerves atrophy, they become harder. Which serves your purpose, Rhob.

Annelids - all worms, for that matter - have enormous potential for getting much bigger than they are now. Why they aren't substantially bigger now can be almost solely attributed to predation. I.e. Practically everything eats them. Worms don't have a chance of selecting for larger size nowadays because getting bigger only makes them easier to catch. Remove predation and worms can get much, much bigger. The flipside is that worms occupy very few niches, so even if there were no other animals there to eat them, there would be soon. Then again, this is assuming the environment is easily habitable to other animals. Put your worms on a desert world or swamp world and you may have a different story.....
You seem to be right. ^_^

Seeing as we have 50m long worms around, it's not as if they're that small... ;)
And on the land i think we have 3m ones. Though tapeworms in certain animals can be very long too. And they aren't the worms you're thinking of...
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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