Dunkleosteus terreli might be the most well known species of placoderm by general media. Having inhabited the devonian seas, this impressive predator possessed an unique four bar linkage jaw mechanism, which allowed not only for powerful bite, but also for a very quick opening, fast enough to essentially creating a suction force that would drag prey closer to its fearsome Jaws. This creature could fully open and close its Jaws in less than a second, and had a bite force rivaling that of modern crocodilians and the T-Rex in terms of pressure.

Given this prehistoric fish's incredible capabilities, I'd like to use a similar concept to its plated Jaws and four bar linkage system. The issue here is that what allowed the placoderm to employ such a system was the lack of a neck (skull moves while the body armor stays still), which is not the case of my land predator, which is a long snouted, bipedal tetrapod around the size of a deinonychus. To try and solve this issue without making the creature neckless, I tried to make use of 2 bony crests in the back of its head and around it's neck, which would then serve as the anchoring points for the necessary muscles and move along with the lower jaw (they're not directly connected to one another, as to allow for a greater degree of up and down neck articulation, but that can be changed Should it make the system more efficient), as seen in the rough sketch below:

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red indicates the location of the main jaw muscles, black indicates the skeleton, green indicates where the tree neck vertebrae would be, the 2 crests are represented in the crude sketch below (Sorry if it's rough, I don't have much experience in drawing and couldn't draw the back facing structure properly).

The reason for this landbound animal to need a powerful bite and fast opening is it's planet's wildlife, which, due to the denser atmosphere when compared to earth, is largely composed of gliding and flying creatures somewhat similar to pterosaurs, which mostly live and rest near the top of large trees. The dunkle predator in question makes use of its camouflaged skin to climb the trees mostly unnoticed, approaching its prey. Once it's as close as possible, it extends its 20-vertebrae, relatively long neck like a snake or a heron, performing the Jaw cycle and chopping off a limb or other body part of its soft prey, allowing an immediate amount of food and usually making the victim easier to catch. Due to its bright colored mouth and tongue, used to scare off predators, it usually keeps its jaw closed until the last moment (the atmosphere might be denser, but it's not nearly dense enough for the mouth opening to provide a strong suction).

My question: Could this attempted variant of a four bar linkage jaw arrangement still be functional? In other words: could it allow for a similar bite force and opening speed as seen in a dunkleosteus from the same proportions? I'd also be glad if an estimated maximum gaping angle possible for this jaw model was also included, as I couldn't find any information regarding the maximum gape of this fish, making it tough for me to make an estimate (though it seemed from models like it was at something between at something between 70 and 90 degrees).

Note: the reason for me choosing this mechanism lies not in the use of suction force, but in combination of a powerful bite and the extremely fast opening that would result in such auction within the water to begin with. This creature does not use a suction mechanism to hunt on land.

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    $\begingroup$ Since this developed at least once in evolutionary history, it shows its possible. However, this mechanism would be very bulky and limit range of motion in the neck. As an aquatic creature, articulation of the neck is not important and really didn't evolve in creatures until much later, which terrestrial animals rely on. You may need to address if neck articulation is important to your creature first to know if this evolutionary feature is needed. $\endgroup$
    – Sonvar
    Jun 17, 2020 at 4:33
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    $\begingroup$ Another Little problem could be, in water this high speed of opening and closing creates a suction force, which reduces the problem of moving the head to get the prey further. In air, even with a denser atmosphere, it does not (it is to small to have an Impact). So you don't just need the speed of jaw-opening and -closing, you also have to move the head in direction of the pray in this time. That reduces efficiency of this build by far. I still think it's possible, but am not realy sure if it is that usefull. $\endgroup$ Jun 17, 2020 at 4:59
  • $\begingroup$ @Sonvar the question was edited to elaborate on how it hunts. Ideally it will get close to its prey and use its neck to further close in, with the fast mechanism serving to allow for it not to require to open its Jaws before, as their insides are brightly colored (in its strategy, the neck substitutes the suction force it would have in the water, which, like Charisturcear already noted, would not be useful here, unless the atmosphere was as dense as water). The reason for choosing this mechanism is to its potential to develop more power in the jaw thanks to more attachment for muscles. $\endgroup$ Jun 17, 2020 at 14:48
  • $\begingroup$ The jaws would probably need to be shorter in order to be as fast as Dunkleosteus. You couold still have a large brain by moving the eyes and brain into the stationary part of the jaw system, and expanding it to be the skull $\endgroup$ Jun 27, 2020 at 15:12

1 Answer 1


Since it has already existed in history, the structure has a basis for existence. To work on land though, it's suction would have to move a lot more air, as the flying creatures would be able to counter any light suction (they already deal with small pressure variances while flying). Because Air has less drag, the animal would have to move a lot more air if that makes sense. The beast would have to have a supplemental air pocket, sort of like a bull frog's throat, or how many animals have the ability to use stored air to seem larger (often for warding off predators or to attract females) to move vast amounts of air to create the suction.

The maximum gape angle seems to be Allosaurus at 80 deg. but this would require a much larger suction system as it has a much larger area it needs to apply suction to. I would suggest having a gape angle at 43.5 deg, similar to the erlikosaurus andrewsi. Still extremely large, but small enough to accurately direct the suction ability.

  • $\begingroup$ The erlikosaurus andrewsi neck is also somewhat similar to what you suggested in your edit, with a strong long neck. $\endgroup$
    – Alex
    Jun 18, 2020 at 16:30
  • $\begingroup$ I'm deeply sorry if I didn't express myself properly. Though it is an interesting approach, I'm not searching for the use of suction hunting outside of the water. The denser air is simply meant to make the evolution of flight an easier task and my choice for this jaw structure lies in its ability to allow both for a strong bite as well as a fast opening and closing of the jaw to prevent its agile prey from escaping before it can bite down on it. I've edited my question so that it becomes clearer. Once again, sorry for not being clear enough. $\endgroup$ Jun 18, 2020 at 17:41
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    $\begingroup$ @ProjectApex it seems like the solution then would be a snake-like creature. They already have the ability for fast strikes, with a large jaw angle. Snakes get huge as well, in your scenario there very likely could be a snake with a body large enough to support this bone structure. $\endgroup$
    – Alex
    Jun 18, 2020 at 17:58

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