At the minimum, I'd like to create a creature with a jaw structure that splits into 4 moving parts (like a +-shape or an x-shape). In order to keep food in, the cross sections will have stretchy flaps of webbing attaching them. A requirement for the 'mandibles'/jaw-sections is that they can move independently of one another, with beak like dexterity.

One earth creature that has a jaw analogous to what I'm trying to capture is a python. Their lower jaws are not rigidly attached to the skull, the lower jaw is split (but still held together by a stretchy ligament), and the jaw sections can move independently in order to 'shimmy'/push prey into their esophagus.

snake jaw

The creature I'm designing would be blind, and since it is alien, the brain does not have to be housed in the 'head'. The creature will look a lot like an ant eater, and it swallows it's food whole. I'm just not sure what the skull would look like. The best I can imagine is the mouth is not actually attached to a real skull, rather it's like a shark in that the jaw is isolated from the brain case.

shark jaw

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    $\begingroup$ I'm trying to work out if the bobbit has a two or four part jaw. $\endgroup$ – Separatrix Nov 21 '17 at 14:43
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    $\begingroup$ While I appreciate the accepted answer, you may get more responses if you hold off on awarding the answer for a while. But, it's up to you. :) $\endgroup$ – Green Nov 21 '17 at 16:26
  • $\begingroup$ @Green good point. I do appreciate your answer though. Definitely helped with designing this creature. $\endgroup$ – Tardigreat Nov 21 '17 at 16:39
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    $\begingroup$ What's the source of your images? Are you sure you're not violating their licence by reposting them here?.. $\endgroup$ – Mołot Nov 21 '17 at 19:17

Split the Maxilla and Mandible

Morphing earth-based, amphibian-descended creatures to have four jaws isn't too difficult. All the required bones are already there; it's just a matter of getting the muscles and bone shapes right. There are valid concerns with this approach since having four "fingers" attached to your face greatly reduces the strength of your bite compared to two thicker "plates".


Earth based animals almost always have a maxilla (upper jaw bone) and a mandible. Two bones make up the maxilla and two bones make up the mandible. If we separate the mandible and maxilla both into two pieces, that would give us the four moving parts requested. The maxilla and mandible already have teeth embedded in them so you'd just need to change the shape and count of the teeth to match your alien's needs.

inferior view of maxilla


Each new limb of the jaw will require minimum four muscles to control it. Two to open and close, two to move side to side. If there's articulation in the jaws then more muscles will be needed (think of how many muscles are required to move human fingers).


You'll need to be careful with how the jaws open and close. You'll also need to pick a hunting method (ambush or pursuit). Relatively long jaws like this emphasize speed of closure over absolute strength.


Yep, you can totally do it. You'll just need to be careful about the prey you choose to hunt. If the prey is too big or tenacious then your jaws will break and the creature starves.

Remember that evolution morphs what it has into new shapes or removes existing structures. It's relatively rare to get entirely new structures (bones, organs, etc) in a creature.

  • $\begingroup$ Thank you so much! Very insightful answer. I had no idea that the maxilla was fused like that. I also appreciate the explanation of how the muscles would be placed. $\endgroup$ – Tardigreat Nov 21 '17 at 16:35
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    $\begingroup$ Welcome to Worldbuilding! You wanted plausible freaky alien faces, this is how I would do it. $\endgroup$ – Green Nov 21 '17 at 16:38
  • $\begingroup$ earth primates have this pattern, earth based animals have several patterns, dinosaurs for instance have 8-9 bones in the lower jaw, even most mammals have 4 tooth bearing bones in the upper jaw. mammal jaws (upper and lower) are very different than other animals becasue they moved most of the bones into the ear. $\endgroup$ – John Jul 16 '18 at 4:00

Pharyngeal jaws might be a solution

Moray eels use them since the normal fish suction method does not work in a burrow. The inner jaws can actually reach out and pull something down the throat, that way they can eat things that are too large to swallow normally.

Sketch of the oral jaw and the pharyngeal jaw of a moray eel source

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    $\begingroup$ I always wondered what the inspiration for the jaws in "Alien" was. Thanks! $\endgroup$ – pojo-guy Nov 21 '17 at 22:24
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    $\begingroup$ @pojo-guy: Actually, the original "Alien" movie quadrilogy and much of the Alien expanded franchise predates the discovery of the moray eel's pharyngeal jaws in 2003. Imagine how surprised the Alien's designers were back then. $\endgroup$ – MarqFJA87 Apr 28 '18 at 22:48

At this rate why does it even need to be a bone jaw.

Why not make it like an octopus / Cthullu with tentacles feeding a food hole.

The evolutional advantage of a functional jaw is a structure capable of processing large hard food chunks into smaller bits more easily process able by the bodies digestive system. the two part jaw is physically efficient at this because its a lever/vice capable of exerting large amounts of energy on a small surface area. So more jaw parts actually results in a weaker bite. So if you make the jaw more about fitting or stuffing stuff into the mouth you can have as many sections as you want, ignoring the bite of course.

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    $\begingroup$ Octopuses (and other cephalopods) still have two part beaks. $\endgroup$ – Joe Bloggs Nov 21 '17 at 14:40
  • $\begingroup$ I know, hence the usage of "like", regardless I added an evolutional explanation that should be more descriptive. $\endgroup$ – anon Nov 21 '17 at 14:47
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    $\begingroup$ That's a great question. My objective isn't bite force or total maneuverability (that's more of a secondary feature), but the ability to keep the 'mandibles' stiff without exerting metabolic energy. The creature initially evolved by swallowing it's food whole somewhat passively as it swam. (it also breathes cutaneously through the throat/mouth lining) It's only vital functions were to close (in order to keep live food in), open as wide as possible (for display, like a sarcastic fringehead, and to swallow large meals) and later, to grasp onto objects. $\endgroup$ – Tardigreat Nov 21 '17 at 14:57
  • $\begingroup$ So like the demigorgon from stranger things $\endgroup$ – anon Nov 21 '17 at 15:02

The human premaxillary bone is fused to our maxilla.
But fish have split premaxilliary bones.

Many lines of fish use the premaxillary bones to protrude the mouth, swinging them down and laterally.

fish anatomy diagram http://blog.hmns.org/wp-content/uploads/2010/05/archy-teleost-puckerBlckF.jpg

These premaxillary bones are hinged at the midline. Here is another image to show how these structures can support the edges of the mouth to maximize gape.

fish diagram http://slideplayer.com/slide/3468357/

That will do for the upper "jaw" as regards opening wide.
It is interesting to me that as far as I can tell, the lower jaw is solid. Even fish that want a big gape like bass or tarpon do not so it by splitting the mandible. Maybe they need a firm anchor. I cannot think of any reason why your creature could not have a split premaxilla and then split the mandible too.

I think the main reason for such a big gape is that they can suddenly do it and suck in prey. I was not able to find a good skeleton of a paddlefish or other big filter feeder to see the skeletal underpinnings of their fixed gape.

Fish have two sets of tooth bearing structures too - oral and pharyngeal jaws.


With the shark picture you use, I'm surprised you didn't come up with the goblin shark, next to the moray eels (and Ridley Scott's Alien) the best known "extendible-jaws" creature. That's "goblin", not "gobbeling" shark as my kid says quite topically.

As an aside, the remark about a "bobbit" (polychaete worm Eunice aphroditois) is off; it uses bristles like others use pincers. I'm attributing its mention to its appearance in Blue Planet II recently, where I was puzzled by Attenborough using its 'popular' name that refers to a 1990s incident/meme!

  • $\begingroup$ I know of the goblin shark! Such an interesting deep sea creature. Another alien design I was constructing had similar attributes to the goblin shark. Thank you for mentioning it. $\endgroup$ – Tardigreat Nov 22 '17 at 12:50

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