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Is there a way to make retractable tusks anatomically plausible in a creature design without relying on an articulated bone structure? Basically, relying fully on musculature instead of articulation like a cat's retractable claw.

The tusks would be able to slide in and out of the creature's mouth through sheaths near the gums, maybe leaving the tips exposed rather than sheathing fully. An articulated structure would completely break the evolution line for vertebrates in my headworld, so I really wanted to avoid that.

Update: based on the comments and also feedback from a friend of mine, I thought about this:

  • Given the tusks would be used mainly for threat display and defense, they aren't functional for eating and/or killing prey. Their function is more comparable to appendages such as stingers and spikes. This means they don't need to be anchored in the jawbone and instead can be stored in a very thick, bulky head/throat separately.
  • The muscles would work like a mix of the retracting musculature you see in bird tongues and pharyngeal jaws, though a bit simplified. It's a matter of a muscle pulling it forward and a tendon pulling it back to the resting position naturally.
  • In order to prevent the tusks from being pushed back, they would slide in at a slight angle and lock into a crevice of the jaw, similar to how horses lock their legs to rest standing up. There would be a little muscle that pulls the tusk back to the straight alignment which allows the tendon to bring it back into resting position
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  • $\begingroup$ It would help if we knew (a) The overall size of the creature (b) the length of the skull (c) the length of the tusks $\endgroup$
    – chasly - supports Monica
    Mar 16, 2019 at 9:10
  • $\begingroup$ Can you clarify why an articulated structure is not allowed? That would help us find ways around those restrictions. $\endgroup$
    – BoomChuck
    Mar 16, 2019 at 18:06
  • $\begingroup$ Cat claws are articulated, what you want has never evolved because it would not allow the teeth to grow, the base of a tooth needs to be anchored for the tooth to function and it needs a steady blood supply. $\endgroup$
    – John
    Mar 17, 2019 at 2:44
  • $\begingroup$ Well I don't have the size and measurements for the design yet, it's only a very rough concept I have in mind for now and I felt the need to get this part sorted out before working on the facial structure. I also did explain that adding an articulation like that to the skull would completely break the evolution planning I've made for my headworld's vertebrates. There's no such thing as face claws in it and I'd rather not jump the shark -.-'. $\endgroup$
    – Lilian Silva
    Mar 17, 2019 at 3:21

4 Answers 4

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Would natural gears be acceptable? If so, the tusk could be drawn/withdrawn through a gear slider mechanism. Hope this helps :)

https://www.youtube.com/watch?v=Q8fyUOxD2EA

(Edit for clarification)

Sorry about that Lilian and Dutch (I am new here). A "gear slider mechanism" is a term used to describe a gear rotating that activates another gear attached to a rod in such a way as to slide the rod back and forth. in your case the gears could slide not a rod but a tusk back and forth, with the halting of the gears determining the length of exposed tusk. Depending on what you mean by articulated bone structure this may or may not be valid. This is partially present in nature already as bodily functions of some bugs have these partial gear shapes to aid in certain locomotions. Since it would be difficult for a fully circular gear to operate in nature these are partial gears that work in a shorter distance but no less effectively. A google search of "Gear Slider Mechanism" will bring up various simple videos of this (https://www.youtube.com/watch?v=CbFPxpRHyRI), including external and internal variations. Hope this clarified it somewhat :)

Edit again:

I drew a very crude and not to scale picture with what abysmal Paint skills I have.

More info. This is basically the "Gular sac" of a cone snail with the "radula harpoon" being replaced by a tusk fired with a combination of the "ballistic energy" of both the potential energy barely being held back by the tendons and the modified natural counter rotating mechanical gear of certain jumping insects (Planthoppers) used an "Internal gear slider mechanism". These two types of potential energy could result in a lightening fast and powerful thrust of a tusk that would not be pretty to be hit by. Essentially a sharpened jackhammer that would hit once and slowly build the potential energy back up for the next strike. This all is of course poorly explained and probably not feasible for an obvious reason im missing entirely but this would be pretty d--n awesome if it was accurate and compact enough to fit in the throat,base of jaw, roof of mouth...etc. all the quotated words are google searches or at least they were for me. Im done haha

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    $\begingroup$ Please add some more details. The link to the video alone is not helpful, and the link can be dead at any moment. $\endgroup$
    – L.Dutch ♦
    Mar 16, 2019 at 9:23
  • $\begingroup$ With the extra details added in, this looks like a perfectly acceptable answer. Welcome to WorldBuilding.SE! $\endgroup$
    – F1Krazy
    Mar 16, 2019 at 13:10
  • $\begingroup$ I think I know what you mean, it's the kind of movement you see in locomotive wheels. It's just really hard to picture a way to apply this to the creature(the video doesn't go into detail on how the "gears" move nor where they are located), but this is still a really unique suggestion. ^^ $\endgroup$
    – Lilian Silva
    Mar 16, 2019 at 15:33
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The Onychodus, a prehistoric fish, had a pair of laterally compressed tusks at the front of the lower jaw. These tusks were not attached to any other bone, but fit into a pair of deep cavities on the palate and were free to move. The lower jaw was connected with the upper jaw in a way that made the tusks thrust out as a dagger when the head was raised. So yes, it is possible.

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  • $\begingroup$ Interesting suggestion, though these teeth aren't quite what I was looking for. I'm specifically referring to the idea of a long tusk being able to literally slide in and out of an opening rather than compressing itself down into the jaw. $\endgroup$
    – Lilian Silva
    Mar 16, 2019 at 5:09
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Moray eels have a second set of jaws (pharyngeal jaws) in their mouth which they can retract with muscles. Or rather, the retracted position is the normal condition, and they can extrude the jaw to grab an unfortunate victim. But still, the mechanism is the same.

enter image description here

So, since these are only tusks, you can do away with a few of the muscles that morays use to open and close their jaws. In the end, you only really need 5 of the eels' muscles - 3 for protracting and 2 for retracting. Those muscles are the levator internus and externus and the rectus communis to pull the tusk out, and then the dorsal retractor and pharyngocleithralis for pulling it back in.

So, there is the mechanism by which your creatures will retract their tusks without any osteological articulation. Needless to say, the muscles involved don't have to be literally homologous with the fish muscles of the same name, they just need to resemble them and function similarly.

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    $\begingroup$ Oh I hadn't thought of that. It's a good comparison for the mechanism I'm looking for, I'd probably modify it so the tusks aren't necessary stored in the throat and instead on a very bulky lower jaw. A friend of mine also added her own comments on this idea that could help and I'll edit my post to show it later ^^. $\endgroup$
    – Lilian Silva
    Mar 16, 2019 at 15:23
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Well as you mentioned, cat’s claws function in a similar way. It is not too great of a leap to assume this would be possible with tusks. Plausible is a different story though.

However, i suggest retractable gums rather than tusks. The tusks themselves would stay in place, attached to the jaw. The muscles in the gums would contract, and pull upwards, revealing the tusks which could now be used. The tips of the tusks may protrude past the gum line, assiting in eating, but when the tusks are needed to attack, the gums would be able to move to unsheath the tusks (similar to how you move your lips to bare your teeth).

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  • $\begingroup$ I actually have used that to make Toothless's(from How to Train Your Dragon) retractable teeth plausible and also for some headworld creatures of mine. Unfortunately this would only work well with very short tusks, though, which isn't what I'm seeking. Thanks for the suggestion nonetheless! $\endgroup$
    – Lilian Silva
    Mar 16, 2019 at 15:17
  • $\begingroup$ @LilianSilva Ah well, even if it doesnt help you, at least it might help someone else, maybe if someone was designing plausible vampires. $\endgroup$
    – Liam Morris
    Mar 16, 2019 at 15:41

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