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/sci/ - Science & Math

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10718506 No.10718506 [Reply] [Original] [archived.moe]

Why are there no big dog-sized spiders that hunt small mammals for food? Is there some evolutionary reason why spiders of such size are impossible, or is it just a coincidence that such things never evolved on our planet?

>> No.10718517

Bump. AFAIK there's giant underwater spiders

>> No.10718522

I'll take a guess. Perhaps at some point in history there wasn't enough large prey for them so any large ones died out or larger spiders were easier to spot for large birds and other predators and got ate.

>> No.10718527
File: 10 KB, 265x190, download (1).jpg [View same] [iqdb] [saucenao] [google] [report]

Spider crab count?

>> No.10718547

Same reason why there are no asians with B-cup tits, they are simply a lower form of life

>> No.10718550

exoskeletons can't scale that large

>> No.10718562

>no big dog-sized spiders
The oxygen content of the atmosphere is too low to oxygenate very large insect's tissues through their tracheae. If there was more oxygen in the air, then insects could be bigger. There are fossils of big insects because there used to be more oxygen.

>> No.10718619


exoskeleton mechanical limitations outside of water
passive respiratory systems limit oxygen availability and put a treshold on body activity

in the past you had larger insects, during periods when oxygen content in the atmosphere was higher.

but dog sized arachnids outside of water, seems unlikely and thank god for that.

>> No.10718620


>> No.10718647

Oxygen level in air
Not enough
4 Big spider

>> No.10718654


>> No.10718677

Weight/speed limitation.

>> No.10718798
File: 259 KB, 640x360, top10spiders.png [View same] [iqdb] [saucenao] [google] [report]

Top 10 BIGGEST Spiders in the World

>> No.10719009

Good post

>> No.10719109


>> No.10719116

This. I mean look at >>10718527 Why are crabs so much larger? What's different? The answer would be that things weigh less under water. Exoskeletons, as spiders have them, can't support the weight a spider would be if it were the size of a dog.

Is also spot on

>> No.10719158

Most large animals have 4 legs. Applies to dinosaurs and reptiles too. I think having many legs limits mobility. Spiders don't have to move around much at their size because they just live in webs. But I don't think it's possible to create webs that can hold large weight.

>> No.10720454

Are....you retarded?

>> No.10720504

There is also the fact that spiders and crabs both have open circulatory systems that are incompatible with large bodies above water.

>> No.10720563

No, why? Again, it's true that having many legs limits mobility and that would cause problems for the animal and make it susceptible to being eaten. So the only way a large spider could survive is if it made a giant web, but that's not possible.

>> No.10720571

>having many legs limits mobility
[citation needed]

>> No.10720573

Spiders aren't fast. Compare the run speed of a tarantula to, say a mouse.

>> No.10720597


>Spiders: 1 mph

>> No.10720604

Hey guys, mad genius here.

I'm just gonna let loose a series of nanites that will improve the efficiency of insect lungs again.

No need to thank me. Just doing my job.

>> No.10720613

Camel spiders can run at 10mph

>> No.10720642

The elephant shrew is the fastest mammal under a kilogram and it runs at 18 mph.

>> No.10720713

Thats because of metabolism, not limbs. Of course a mammal with a beating heart and lungs is going to run faster than an arthropod. But that has nothing do do with why there aren't giant insects anymore. Keyword anymore. As in there used to be. Because of higher oxygen in the atmosphere. You are using toddler logic here, man

>> No.10720715

The mechanism spiders use to walk doesn’t work at that size.

>> No.10720717

Not true. Eerypterids achieved alligator sizes but because they were sea dwelling

>> No.10720730

Okay, so if having more than four legs makes you faster then why aren't there any six legged cheetahs or coyotes?

>> No.10720738

Mammals can’t evolve new limbs because evolution doesn’t permit descending into fitness valleys.

>> No.10720739

Because mammals are invertebrates. Christ, you are retarded

>> No.10720741

If being an arthropod is why spiders are slow, then that would explain why there aren't any large arthropods, they would become prey.

>> No.10720742

as has been said scientists say it has to do with oxygen levels. i think having more than 4 legs is probably just mechanically to complex for creatures with internal skeletons, but not exoskeletons. really makes you wonder though if there could be races of intelligent insects or other bug-like creatures on some planet out there that kept a high oxygen level longer. i have to wonder if it's probably typical that the oxygen levels get lower in a planetary life-cycle and the insects always get smaller...

>> No.10720745

So the logic here is that six legged cheetahs would be faster?

>> No.10720747

*vertibrate. Fuck you got me so triggered, now I'm retarded

>> No.10720750

Yes, but it would also require a larger and more complex body plan and that much more energy to fuel.

>> No.10720751

Potentially, but the energy costs may not be worth the increased speed and developing a new limb to run around with would involve crossing a fitness valley, which evolution doesn’t do.

>> No.10720758

and more specifically i think i've seen it said that bugs basically have different types of venous systems, which is why they need more oxygen, which is what limits their size. but you have to wonder why having an exoskeleton apparently always means you have to have that other type of venous system.

i think it's really interesting to think about this kind of stuff in the context of life on other planets. obvious some planets would have different variables at play that could lead to other variations being emphasized but i personally think that what we have on earth is probably pretty common, that most other planets with life have very similar designs. i think especially things like fish, land animals having 4 legs, sharks and crocs specifically i think are probably everywhere. think about it- sharks and crocs are basically mouths with torpedo-like bodies that are perfectly designed for their environment. i bet sharks and crocs are common across the universe. they're like the quintessence of predator design.

>> No.10720763

So basically four legs is the optimal amount of legs for an animal to have. Maybe that's why there aren't any large spiders.

>> No.10720767

also i dont believe in a 6 legged cheetah being faster. look at how a cheetah runs in slow motion. i has like a gallop or whatever, where maybe only one or two feet are touching the ground at a time. it's basically lunging its whole body forward with its hind legs and landing with its front. another pair of legs would just get in the way of that. there's a reason land animals dont have 6 legs. the skeletal design would be complex, as well as muscular. the other 2 pairs of legs have something like an axle that goes across. how would the middle pair have that? it'd be going through the rib cage and internal organs.

it wouldn't add anything and it would just make the design overly complex for no reason.

>> No.10720781

No, more may be superior, but they have to be justified by a benefit to fitness without crossing fitness valleys. Myriapods for example varry widely in the amount of legs they have, some having less than ten and others hundreds. There’s no fitness valley to cross because evolving another pair of legs only means growing another body segment. Mammals in comparison have complex skeletal systems and musculature that isn’t so modular.

Some species of spiders actually LOST a pair of legs by them evolving into pedipalps, which are extra sensory organs and secondary mouthparts. Scorpions are the same, with a pair of legs evolving into their pinchers.

>> No.10720785

No, its literally because of the air. Stop being stupid on purpose

>> No.10720793

I dunno, it seems like 4 legs is more efficient. If a large animal had 6 legs then it wouldn't be able to eat enough to live.

>> No.10720801

It might be able to, we just don’t know. Arthropleura was a giant millipede with dozens of legs longer than six feet in length.

>> No.10720808

Yeah, but back then everything was bigger, maybe the decrease in oxygen just made everything shrink.

>> No.10720812

There's something deeply beautiful and elegant about that system.

>> No.10721051

I'll reiterate previous comments of the exoskeleton not scaling with something befitting this board: exoskeletons are a surface and volume scales faster than surface area, with the increased thickness of the surface layer required to compensate presumably causing biological complications.

>> No.10721075

because everyone is like, doing there

>> No.10721077

like the dog is not really far

>> No.10721106

It would take far too much energy to support the body of the spider if it was that large, so it would not be viable.
Giant underwater crabs are basically what would happen if it was possible though, as they don't have to deal with weight as much.

>> No.10721114

Spiders have lungs though, sorta. They don't rely on through-skin diffusion like insects.

>> No.10721118

No this is anti-science heresy. It's settled science that alien life is incomprehensible to our human chauvanist minds. Think articulated gasbags, wandering herds of lichen, arboreal jellies, and superintelligent shades of the colour blue.

>> No.10721119


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