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you know a jaw or mouth where the jaw full of teeth fully rotate like a drill or gear to shred their food or prey, usually show often in worm type of monster (my question is not necessary to be worm type), rather than chewing, or simple biting, or simple enclosing and opening the mouth with the circle type of jaw or row of teeth like lamprey or leech

here a gif image to help imagine it better, just focus to the blue gear, ignore the smaller one. (depend to the answers or how well this is, i may add another question related to the small one later)

the gif from pinterest

enter image description here

just to be clear my question is about full rotation not half rotate, like when the jaws move back and fort in half circle to grind or shred ( i hope its understandable)

example like this, this is the closest i can find.

the gif from Gfycat

enter image description here

  • its not necessary to be circle shape of jaw either.

  • it may or may not have tongue, i believe its dangerous if they have tongue, but i do thought to put the tongue in front or outside of the rotating jaws at least.

  • this is pure organic, so robot,cyborg, or bionic is out of the question.

so i want to know how it work or the anatomy or musculature to achieve this, preferably with image to understand it better.

or maybe there already exist an animal like that?

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    $\begingroup$ Related. $\endgroup$ – A Rogue Ant. May 26 '20 at 8:43
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    $\begingroup$ Also related worldbuilding.stackexchange.com/questions/159150/… $\endgroup$ – user69935 May 26 '20 at 12:50
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    $\begingroup$ The question is more of "why would this have evolved when fixed teeth in a reciprocating jaw motion is so much easier and more efficient?" $\endgroup$ – Carl Witthoft May 26 '20 at 15:31
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    $\begingroup$ I should point out that an oscillating ring would achieve nearly the same effect, and would not have near the biological difficulties. Bonus points for multiple counter-rotating rings. $\endgroup$ – Matthew May 26 '20 at 15:37
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    $\begingroup$ "full rotation" is revolution, and not to be seen with the naked eye in nature. I thought this was going to be about e.g., a snake's jaw, except go almost all the way or all the way but no further, because why would it. $\endgroup$ – Mazura May 27 '20 at 1:59
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The closest to what you want are gizzards stones. Necessarily so, because the rotating part cannot be a biological organ in nature - not being connected to the body, it can't receive nutrients or be protected by the immune system.

If you think it serves your purpose, move the stones upper in the digestive tract. Careful with the respiration, though.

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It's possible, albeit supremely unlikely

It's not possible with conventional biology. That said, it's possible, albeit unlikely, with a bit of unconventional biology. The main problem you face is the 'teeth ring' - the rotating outer gear you illustrate in your diagram. It's simple not possible for that to be an organic component. However, fortunately for us, it doesn't need to be a biological component.

In other words, it's possible to build a mouth around the design of slowly sliding and rotating a solid, inorganic teeth ring inside the mouth using nothing but muscles. The muscles contract to tighten their grip on the ring and then move it, and relax to loosen their grip before sliding back. (It's like using your hand to spin a disk - you grab it, move it, release it, then move back.) It'll be a bit complex, but totally manageable. The real question is how to get that teeth ring. There are two methods.

Method #1) It's a former biological component. Similar to us, this species grows enamel-based teeth. The teeth then fuse to a bone ring, and the creature then seals the bone ring so that it's now nothing more than an enamel construct. The teeth ring is then released into the mouth by way of regressive growth of the gums holding it in place.

Problems: This will require a development stage to grow the ring during which the creature can't really eat food. Additionally, should the ring break, the creature can't really do anything about it. Not to mention that, as the creature grows, it's tooth ring won't grow with it. There are various ways to handle all these problems, just thought I'd point them out, though.

Method #2) The creature creates the teeth ring carefully out of materials and inserts it in. This means that the creature can make them whenever a new one is required.

Problem: What exactly is the creature making the teeth ring out of, and how is it accomplished? Too fragile is bad, and too hard means that the creature will have a horrible time trying to make it. It'll probably end up mostly making them from rock and breaking them frequently if that's the case.

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  • $\begingroup$ i also did think about the teeth ring, but i though it can end up fell out like how fake teeth is, and i dont know how the muscle do the spinning. at least this help cover it up. $\endgroup$ – Li Jun May 26 '20 at 14:03
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    $\begingroup$ This might not totally solve the problems, but if it continually grows new rings (they'd probably need to be 'new one behind the old one'), a bit like sharks continually growing new teeth, then it could occasionally 'shed' the old one. This would give it a chance to survive if something happens to the ring, as well as making it possible for the creature to grow (the new ring is just a bit bigger than the old one). $\endgroup$ – Matthew May 26 '20 at 15:35
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    $\begingroup$ @Matthew Right, but the problem is that continual process will take up a lot of room in the mouth, not to mention that it will need to be inserted into the muscles controlling the ring, somehow. Fundamentally, it's the best solution, you just wind up with a lot of problems trying to implement it. $\endgroup$ – Halfthawed May 26 '20 at 15:44
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    $\begingroup$ Oh, sure, the whole idea is horribly impractical. I can't really see how this would ever develop when an oscillating mechanism is drastically simpler with pretty much the same benefits. Maybe if the creature was engineered by someone that prioritized 'cool factor' over common sense... $\endgroup$ – Matthew May 26 '20 at 15:49
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    $\begingroup$ With method#1, the two problems are easily solvable. Lots of creatures have an intermediate or developmental stage where their ability to gather food is limited, either by lack of teeth (such as in humans), lack of knowledge (such as in lions) or lack of simple size and mass needed to hunt. Broken and too small rings can easily be solved by constantly being in the process of growing a new ring (much like shark teeth). $\endgroup$ – sharur May 26 '20 at 16:45
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It isn't possible with our current biology for the same reason we can't have organic chainsaws: we need loose parts. Everything in an organic being is interconnected by muscles and other systems like blood vessels. For you to have a jaw that spins in a single direction indefinitely, you'd need a loose set of bones and something to rotate them. Sadly you won't find this something in an organic being, because there is no muscle arrangement that can allow for that.

Sadly your design can't work unless you have mechanical teeth on an organic creature. There is simply no muscle arrangement that allows for this kind of spinning, so with our biology we can't have mouths with rotating teeth, nor organic chainsaws, nor animals that fly like helicopters.

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    $\begingroup$ Not true - see my comment at Adrian's answer $\endgroup$ – Carl Witthoft May 26 '20 at 15:30
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    $\begingroup$ @Carl Witthoft not only you're trying to fit a microscopic concept into a mac4oscopical one, you're incorrect, as neither bacteria nor eucariotic cells spin their flagella in a unidirectional orientation, they rotate it, and not like we see in a gear. In a macroscopic organism (what the asker wants) it's not possible for a movement in a gear-like fashion to exist. $\endgroup$ – ProjectApex May 26 '20 at 16:19
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This species could evolve from a predatory creature that feeds on much larger creatures. It would kill its prey using a long conical fang, and cut up its prey using a saw-like structure, and . Its prey might evolve to have sticky blood which traps the predator's fang. To avoid this, the predator may evolve to drop its fang to escape, and regrow it. They might later evolve to be able to reattach their fang. It may also gain an extra spine at the end of its saw, as a backup if it must discard its tooth. A mutation may cause development to change, leading to the saw-spine growing into the fang. This would allow the creature to disconnect its fang and hold it, and spin it using the saw. The saw could degenerate into a piston, with the spike becoming a large peg, and the entire system becoming optimised into a drill.

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The only known biological gears in the real world are the thighs of some insects:

Planthoppers are the first animals found to possess a biological form of a mechanical gear, used in locomotion. (Crocodiles possess a heart valve with cog-like projections, but they have no cog-like function.) The first formal description of this mechanism was in the species Issus coleoptratus. The gears keep the legs in synchronization, allowing the bugs to jump accurately at an acceleration of nearly 400 gs in two milliseconds. The existence of the gears in planthoppers had been known for decades, but zoologist Gregory Sutton and his co-authors only recently characterized their functional significance by doing high-speed photography of the insects at Cambridge University. The gears are found only in the nymph forms of all planthoppers, and are lost during the final molt to the adult stage. It is suspected that gears are lost in the adult after the last molt because if broken they would be irreparable, crippling the insect for life. Prior to their discovery, it was assumed only humans had made and used gears.

The insect gears are not completely circular, but rather portions of a full circle. They only move back and forth, instead of doing full rotations. But an animal in your world could develop the same mechanism in the mouth, which would develop in order to synchronize jaw parts during a cobra-like strike. A quarter billion years of evolution and some layers of flesh over this mechanism could have the gear parts evolving to eventually become full circle and loosened from the rest of the skull. To have them spin only one way the teeth of the gear could be sloped - each gear will only turn one way. Back and forth muscular contractions around the gears can then keep them spinning.

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    $\begingroup$ How do you supply them with nutrients, repair them, etc.? $\endgroup$ – Matthew May 27 '20 at 19:18
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    $\begingroup$ @Matthew nutrients, the same way many tissues get nutrients in our body: by diffusion. The outermost layers of our skin is not very irrigated in most of the body, you can have cuts without bleeding if you don't cut deep enough. Yet it is alive. As for repairs, it's live tissue. It can repair itself. $\endgroup$ – The Square-Cube Law May 27 '20 at 20:16
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Obligatory Symbiosis

Everyone has brought up some excellent points about how tissues need to be connected for an organism like this to function. On a macro scale, that’s true, so why make it be one organism at all? If you want a rotating jaw with teeth, have the rotating jaw be a separate organism that depends on the host, and that the host depends on.

There are plenty examples of obligatory symbiotic relationships in nature, e.g, lichens, or any number of animals that have a gut microbiome without which they can’t survive, and which can’t exist without them.

There are also examples of macro animal symbiosis,Ike the urchin crab which carries an urchin around for protection, and thus also helps the urchin move to new feeding grounds.

So have a second organism that symbiotically sets up shop inside your creature’s mouth. A good design might be similar to a strain wave gear: image or meaning strain wave gears Note how the gears mash together! That would be perfect for your purposes.

The internal ‘jaw’ helps the host chew up tough food from its hunts, and in return, the host gets it access to food by doing the hunting.

Your host organism could look like any number of things. The symbiotic jaw would likely look like a very ridged and rough version of a bivalve, in a more oblong and spherical design: enter image description here

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Well, I'm not an engineer or biologist, so I'll present only the raw idea without resolving many issues addressed to full design.

Instead of the common mechanical approach, it might be worth experimenting with electromagnetism (see: electric eels), which could help to rotate the jaw.

The teeth could form in the following way - when the species are young, their teeth are stationary, but their rings of teeth are 'removed' in a similar way that human teeth are during growth. However, that loose bone (ring of teeth) would still stay inside a mouth and be placed inside the new, second set of teeth-bone which would simply be like an annular rail that holds teeth inside the maw. Maybe there could be some sort of fluid that helps with friction-related issues too.

On the other hand, although I'm not claiming it's impossible in a proper setting, the evolution of these species creates a huge problem in itself. Even with a high level of genetic engineering, I would still support the idea that it's easier/cheaper to just design/maintain a mechanical counterpart.

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