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