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| Megarthropoda; Big Bugs | |
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| Topic Started: Jun 20 2010, 05:55 PM (1,297 Views) | |
| Rhob | Jun 20 2010, 05:55 PM Post #1 |
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Adult
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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? 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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| ATEK Azul | Jun 22 2010, 09:27 PM Post #16 |
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Transhuman
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Termites closest living relatives are Cockroaches and Praying Mantis's. So Carnivorous Eusocial Cockroaches or a close relative derived from an ancestor or even a convergent creature could very well exist in my opinion. |
| I am dyslexic, please ignore the typo's! | |
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| Ammonite | Jun 23 2010, 02:06 AM Post #17 |
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Adolescent
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This article from the U of C Berkely's Evolution site should come in handy here: http://evolution.berkeley.edu/evolibrary/article/_0_0/constraint_01 Arthropods already sort of ruled the Earth (at least on land) in the Silurian Period before they began to give way to amphibians and reptiles in the Devonian, but even after then they were able to reach larger sizes because Earth's atmosphere was richer in oxygen. Insects today face two problems: their respiratory system, and their exoskeletons. If this is set in present-day Earth, your insects might not get that much bigger than they already are unless you somehow increased Oxygen density in the atmosphere. An exoskeleton made of something lighter and less rigid than chitin would also help. Sorry, I have trouble believing that 12 inch tall mantises could exist on Earth today, even with all of the chordates, vertebrates or whatnot gone. If they did suddenly disappear, some other invertebrate group would probably increase in size and take over as the dominant land animals before the arthropods did, since they don't have exoskeletons and have more efficient and/or powerful respiratory systems. If you are willing to ignore this then please press on. I am quite interested myself to know what you think will happen to bees and wasps in such a world. |
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| Holben | Jun 23 2010, 03:06 PM Post #18 |
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Rumbo a la Victoria
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I deliberately have steered away from eusocials, as most of them were latecomers and the chain leading to their evolution wouldn't fit the same way. You missed the 'leg size' problem. (see Amphibination, the topic somewhere around here...) The oxygen level will be kept constant, perhaps, by lack of big plant eating. And maybe a higher amount of microbes in the soil. |
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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 | Jun 23 2010, 08:46 PM Post #19 |
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Adult
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Now that I'm back... I think we all need to keep something in mind, and that's the idea that the absence of chordates would have a major impact on the future of evolution. What does this mean? Basically, all or most of Earth's modern-day and recent arthropods go out the window. Completely. As a result, we'll need to start from the beginning -- as I've tried to do. Pandorasaurus: Sorry but this isn't future evolution. There are no abandoned buildings and the like to consider here. Ammonite: Thanks for the link. I actually read it a while ago. Yes, the biggest limiting factor for tracheated arthropods is their tracheal systems. The deal with the exoskeletons is more complicated. It seems to me that moulting is the biggest issue there, actually. I wrote a post addressing this in more detail, and can dig it up if you'd like. But the gist of it is that an exoskeleton is not (necessarily) inferior to an endoskeleton simply in terms of load-bearing capacity. Now as I mentioned in the OP, the issue with tracheal systems can be addressed by... not having tracheal systems. Lung-analogues could develop through at least two methods: direct development from gills and "re-engineering" of tracheal systems. Obviously the former is "easier" in evolutionary terms than the latter, so I think it's more likely to happen. I see more diversity occurring with exoskeletons. A lot of this will coincide with different growth strategies. It's also possible for some lines to completely internalize their exoskeletons into endoskeletons. Perhaps one or more of them will become the really big animals. So let's get started with the Ordovician period. Without "fish" (i.e. swimming chordates and vertebrates), how will life in the sea turn out differently? Will some other group compete with eurypterids and nautiloids? Will the latter become more diverse than IOTL? |
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| Pando | Jun 23 2010, 08:52 PM Post #20 |
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Obey or I'll send you to the moon
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In a world without fish I can see trilobites ruling the sea floor with some eurypterids, although most predators are cephalopods and there are a lot of gastropods that replace the herbivorous fish. |
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| ATEK Azul | Jun 23 2010, 10:02 PM Post #21 |
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Transhuman
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Beware of evolving lungs from Arthropod gills I'm pretty sure they turned part of the gills into their wings. I look forward to the products of this topic. I Would love to see that post you made especially if you can add more now. |
| I am dyslexic, please ignore the typo's! | |
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| Rhob | Jun 23 2010, 10:12 PM Post #22 |
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Adult
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That was the case with insects only, not all arthropods.
Okay, I'll dig it up and post a link to it in this thread. |
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| Ammonite | Jun 24 2010, 12:36 AM Post #23 |
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Adolescent
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Then how do you plan on developing wings in your arthropods? |
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| Nemo Ramjet | Jun 24 2010, 07:03 AM Post #24 |
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Newborn
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One serious obstacle to large-bodied arthropods would be their exoskeletons. How to take care of the molting problem? Perhaps they need to return to water every once often to support their squishy, freshly-molted bodies. Then you could have a world of arthropod crocs - growing big and vicious, but every once often returning to the water to grow. They would be very vulnerable in the intervals... Or you can go for a totally novel invention - like brand-new <internal> skeletons. How would that derive from an exoskeleton, however? You can have indented grooves along the legs for structural strength. In time, the grooves could pucker in, becoming more and more like fake bones. Imagine then that the interior part of the groove is not shed anymore, but begins to accumulate inside the leg, growing stronger and thicker with every molt. Eventually the outside parts of the exoskeleton would not be needed and wither away, leaving only the "fake bone" inside. I don't know how compatible this would be with the muscular anatomy of arthopods, but if it works, you can have very cool results... |
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| Holben | Jun 24 2010, 11:13 AM Post #25 |
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Rumbo a la Victoria
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Arthropod crocs... hmmm. Very interesting. Their sensory organs would have to be adapted quite a bit, but perhaps they could act as a nymph stage? An internal skeleton... perhaps nerve sheaths could atrophy and expand, or something... they could have an exoskelton 'flip', like what happened to the cuttlefish pen. The groove idea is interesting. But wouldn't excess exoskelton be broken down, to conserve biomass? On lungs- scorpions and spiders have BOOK LUNGS, allowing far more efficient oxygen distribution. Ahhhh.... wonderful scorpions...
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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 | Jun 24 2010, 09:03 PM Post #26 |
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Adult
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Well, I didn't think I was supposed to know already?
Wow, the one and only Nemo Ramjet has decided to grace this humble thread with his presence! I am honored. ![]() Returning to the water is, of course, a readily available option. I think a lot of the evolutionary history of insects was based on staying in the water until the last molt. Another option is burrowing, which is what coconut crabs do. When large, a coconut crab takes an entire month to finish molting -- most of that time is apparently spent separating the old exoskeleton from the new one. I wonder if there's any way to speed up that process? Anyway, if burrowing or submerging isn't possible, maybe some kind of nest or cocoon could be made instead. Larger sizes on land might provide more of an impetus to alter the mechanics of molting. Maybe the hardening of the exoskeleton can begin before the old one is (completely) shed. Or maybe the growth pattern can change so the sclerites grow out, either constantly or periodically. That would sorta decouple the sclerites from the non-sclerotized parts of the cuticle, I think. Your suggestion with the internalized exoskeleton is interesting, Nemo. One issue with it, however, is where to put the old cuticle that's inside the body. Unless you're saying that the exoskeleton there would be completely invaginated, at which point the "molting" would just add successive layers from the inside out. That would definitely be interesting -- the question is how to get to that point. ![]() Actually, there's already a precedent for this with apodemes, internal extensions of the exoskeleton that serve as extra structural and/or muscular support. Or did you know about that already?
How would their sensory organs have to be adapted quite a bit? Adapted quite a bit to what, exactly?
"Atrophy" and "expand" are basically antonyms. Just so you know.
Tell me, how does nature define "excess biomass"?
Yep, plus there's the type of lungs that evolved in the ancestors of the coconut crabs. Both types are derived from ancestral gills, which in turn derive from more ancestral appendages (or projections thereof). |
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| Holben | Jun 25 2010, 02:48 PM Post #27 |
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Rumbo a la Victoria
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All the aquatic bugs we know would have trouble finding substantial prey, with their compound eyes and the weak hearing/ generally sensory organs they have. Ambushing would be a challenge. Well... they work here, don't they? You get what i mean? Atrophy as in harden... EXCESS BIOMASS, the holy law of evolution. Same way the weak falls by the wayside. Excess biomass will be punished by being hunted down and the species purified. Only the leanest survive on the biggest scales. |
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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 | Jun 27 2010, 01:05 AM Post #28 |
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Adult
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Really? Are you discounting, for example, dragonfly nymphs and water bugs for some reason?
My understanding of "atrophy" is that it means to reduce or become vestigial.
Would you consider elephants to be "lean"? How about the giant dinosaurs? I was reading about pangolins earlier today. I suppose, by your reasoning, you'd consider the pangolin's scales to be "excess biomass". Tell me, then, why do pangolins have them? Hopefully you see my point. Nature and evolution don't have a one-size-fits-all standard for "efficiency". Appealing to "conservation of biomass" is to assume otherwise. |
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| dialforthedevil | Jun 27 2010, 04:06 AM Post #29 |
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Frumentarii Administrator
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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.... |
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| Holben | Jun 27 2010, 08:08 AM Post #30 |
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Rumbo a la Victoria
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Ah, the old megaposting. Well... yes, i am. Dragonfly nymphs don't have much in the way of enhanced senses. Atrophying muscles,(so probably nerve sheaths too, slp) while becoming vestigial, become harder and their wasting away makes them strong. 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. The poangolin's scales DO SOMETHING, therefore not being excess. They are kept thanks to purpose. 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. |
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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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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!









7:14 PM Jul 10