Why would the mouth of a creature evolve to be away from the head?

Question

Exhibit A: The apex predator of my world, one that can both fly and swim under water.

This deadly monster employs 4 limbs - they act as wings in the air, and fins in the water. It hunts for game in the air, in the oceans, and on land. This body of this thing is the size of a bus. This is all very amazing and this thing is ludicrously threatening with spikes all over the place, 6 eyes, and a spiked tail to boot, but I'm having trouble explaining a particular aspect of the creature.

I bring attention to its mouth:

The mouth is placed along the bottom of body, away from the head. I've yet to find an example of such a design on any creature on Earth, where the head and the mouth are completely separated.

If you'd like to see an example what kind of land creatures this thing hunts, please see my question on the Armatae Bestia.

So the question is, what could have caused the mouth of my creature to develop away from the head?

Notes:

• The creature occasionally uses its head as a weapon, like an ice pick.
• The creature is a carnivore, and does not need to chew its meals.
• The mouth is also used as a grabbing tool (hence the large amount of spikey-teeth). You can assume that the muscles around that area are strong enough to collectively hold up ~1 ton. You can also assume that the teeth around that area can be individually manipulated to a certain extent (eg: the creature can choose to only use inner ring of spikes instead of both rings to grab smaller objects, or that the creature can use only the outer ring while keeping the inner ring flush with the surrounding area in order to pick up larger objects such as logs/rocks).
• The teeth can be used to rip things apart, by "stabbing" into the target, and then spreading the teeth.
• The slit down the center of the mouth area opens up to accept food. The teeth are often used to "shove" food into that abyss.
• This creature is a solo hunter, not a pack creature. It is very territorial, and often fights other members of its species over prey and territory.

Answer 1

Not sure why, but the first thing I thought of when I saw your second image was a starfish. In fact, that may be a viable ancestor for this creature. After all, a starfish's mouth is located underneath and central:

Source

Not all starfish are soft and cuddly. Some, like the crown-of-thorns, are covered in spikes/spines:

Source

Adapting the arms into wings doesn't seem like too far a stretch, as doing so increases its mobility and, thus, its ability to find prey. The development of eyes also seems like a natural advantage: as mobility improves, you want to be able to see where you're going to avoid running into something with bigger teeth or into a wall.

So you have a six-armed starfish that's covered in spikes and evolves four arms into wings, one into a tail, and the last acquires the brain to process the increased data flow (as well as support the eyes).

EDIT:

According to the Wikipedia entry on starfish:

The starfish does not have the capacity to plan its actions. If one arm detects an attractive odour, it becomes dominant and temporarily over-rides the other arms to initiate movement towards the prey.

Having multiple "brains" can be detrimental. If two arms detect an attractive odor, which way does the creature go? Developing a single, dominant processor (i.e., the brain) is the best solution, so it can process the information from all the arms. Over time, one arm becomes more and more dominant over the others until it acquires the majority of processing power. In that arm develops the brain. Since that becomes the most likely direction for the creature to move in, it also develops the eyes, providing the shortest route from the new optical sensors to the processing unit to reduce the time it takes to see, identify, and respond a stimulus.

Answer 2

Others have already spoken of how it is most natural for the mouth of a mobile creature, particularly a hunter, to be near its head, so I won't spend too much time reiterating those points. Your question is what could cause the mouth to logically move away from the head, given this natural tendency. Here's my humble idea, take from it what you will: the mouth hasn't moved away from the head. Instead, the creature has developed a second mouth.

Suppose that at an earlier point in your creature's evolution, it had a fairly standard beak-mouth as part of its head. Suppose that it also had two strong, grasping legs below its belly to catch food, also quite standard. Think pterosaur. Here's a hypothetical evolutionary chain from that point forward:

1. Creature held its prey in its claws for an extended period.
2. Creature gradually developed a belly cavity in which it could tuck prey for a while after catching it, freeing up its claws for other uses.
3. Creature's belly cavity began to secrete a different kind of sweat than normal (does your creature sweat?) to prematurely soften up the prey, similar to saliva.
4. Creature's belly cavity developed increased sensitivity to its contents, granting safeguards similar to those granted by its standard senses of taste and smell.
5. Creature's belly cavity grew so deep that it fused with its stomach. Creature stopped using its mouth to eat.
6. Creature's grasping legs receded into its belly. Claws have rotated to resemble teeth; they can still grasp but have lost their reach. (An x-ray of your creature's belly would show vestigial leg bones around the belly-mouth.)
7. Creature's beak-mouth atrophied from disuse to whatever degree you find aesthetically appropriate. Beak can still be used as a weapon.

I'm sure this answer could use further polishing, and I'm no biologist, but hey, it's an idea.

Answer 3

The mouth leads directly to the stomach. Therefore there is no need for an esophagus. Conceivably your creature (that is the size of a bus) just swallows its prey whole. Without an esophagus there is no danger of something becoming stuck. This would also explain why the muscles are so strong in that area. They need to be strong in order to keep the struggling prey in and to help the stomach crush them till they stop.

Answer 4

Several animals have their mouth in the center of their body, however, most of them are close to their head. Squid are very similar.

You also have Star fish

What both have in common are a mouth surrounded by limbs that hold the prey close to the body. It's quite possible they are starting to eat their prey while it is still alive and thus need to be restrained. Though a water environment might also try to steal the food away to staying attached might just be a wise precaution.

Answer 5

Mouths are placed at one extreme end of the body of most earthly creatures for a very simple and practical reason: to give the creature as long digestive tract as possible. Food enters through the mouth, down to the stomach, then intestines and finally out of the excretory canal.

A creature with a simpler digestive system (and carnivores have a far faar simpler digestive tract than herbivores) can afford to have a smaller digestive tract and hence have its mouth placed away from the head region. Here are some of the important things I would like to mention about the placement of head and mouth in Earthly organisms.

Squid, Starfish And The Like

I would really not like to mention these creatures when we are talking about your predator. These creatures indeed have mouths away from their sensory headquarters (heads where most sensory apparatus are located) but you would immediately notice a few things which make them unrelated for this particular scenario:

• All of these are obligatory aquatic creatures. None of these live on land or fly in the air.

• Neither of these creatures is a vertebrate. Essentially, all vertebrates have mouths at one end of their bodies. Even for creatures which have very simple digestive systems (like obligate carnivores and filter-feeding marine creatures), the mouth is located at one end of the body. This is because all vertebrates descend from pikaia, myllokunmingia, haikouichthys and other primitive vertebrates. All of these had mouths on one end of the body (aka head).

The One Major Obstacle Placing Mouth At Other Regions

Creatures need to see and smell the food they are eating. Even when the food is served in a plate (known location) and you know it is poison or dirt-free, still it feels very uncomfortable to try and eat that food with closed eyes.

When you are a predator, the need for sight and smell gets all the more important. You don't want to ingest Artimaratia Bestea's osteoderms or the spines of a porcupine. You also don't want to ingest stones or pebbles or sand with your food. Furthermore, if you need to manipulate your food with your hands, you pretty much need to see what you are doing. When you need to tear bites of flesh from your kill, you need to see where you are biting from, to avoid eating undesired parts like intestines and stuff.

The Prerequisites Of Mouth On Other Places

• The first and foremost is that the mouth needs to be pretty much close to the head so that you can still see and smell (even if partly) your food.

• The next requirement is that your creature does not require a long digestive tract and is an obligate carnivore. This condition is already fulfilled in your creature.

• Your creature must be able to manipulate its food with prehensile limbs. Now this one is pretty serious. I don't think your creature has fingers on its flippers. even if it did, it won't be able to use its flippers as hands and use them effectively for grappling and moving about its food around its mouth.

• The surface where the creature eats, should be dirt/sand free. I think this one is easily provided.

• If you can have vision related organs around mouth, all the better.

• The group of organisms from which this predator has descended should all have the same body plan. Which means that if you have some other predators with resembling body plans, it would make it all the more realistic to your audience. Creatures are judged by their environments, not by comparison to earthly creatures.

• For very large creatures, the part of body where the mouth is placed, should be able to move easily, without having to move the whole body. I think this one would be hard for your creature. It would look very troublesome for such a large creature to continuously move back and forth and sideways just to eat its food. But then again ... it could also be used to make it look all the more horrific. A grunting bus-sized predator, shaking heavily as it eats. That's some nightmarish stuff!

Answer 6

Like others, I also immediately thought of starfish/squid-type creatures as a starting point, however, let's generalize a bit more then.

As mentioned by several, most creatures have sense organs near/in their head. i.e. near their brain - including eyes, ears, nose, tongue and lips. For the mouth this is quite likely because of the need for quick evaluation of food as suitable/toxic. The shorter the signal pathway, the faster the analysis can be made. To be honest, this could be reasoning backwards, and it may be that the nerve clusters for the senses eventually evolved into a brain, especially since humans, for example, can essentially be viewed as highly evolved worms. We are digestive tracts (mouth to butt) that have evolved appendages that allow us to more easily acquire food.

Anyway, starting from these points, we could come up with a few options.

1) Could your creature have a second mini-brain or neural ganglion in its belly devoted to food analysis? This could then bi-pass the need for signals to go completely to the main brain, and might allow the head to evolve 'separately' for more specialized hunting purposes.

2) Perhaps the original ancient ancestor had a different structure from that of life on Earth (the worm) and thus all body types are different on your world. Perhaps an initially branched form. Maybe this was necessary because of the need to ingest, or separate, components of the environment for biochemical use? Again, this would suggest a vaguely common branched form for all creatures on your planet (similar to how, on Earth, all animals are essentially 'linear' with respect to food ingestion and excretion).

3) Perhaps the food it eats is physically or chemically dangerous and the belly-mouth is a specialized compartment to protect the rest of the creature from its harmful dinner.

4) What if this was a case of symbiotic evolution? What if the belly mouth is actually another organism that is acquired when young and forms a symbiotic relationship?

That's about all I can think of for the moment. Hope some might be helpful.

Aside: Incidentally, if it both flies and swims, how well does it do either? What are the wings made of? Are they more bat-ish or oily-feathered?

Answer 7

This immediately reminded me of the delightfully weird Opabinia regalis, an extinct arthropod from the Middle Cambrian, when evolution hadn't yet settled down into its now-familiar grooves and was still just throwing stuff at the wall to see what would stick. Opabinia looked something like a large shrimp with five (!) stalked eyes; its mouth was at the junction between its head and body, and faced backwards. It caught its prey by means of a sort of tentacle on the front of its head that looked like a vacuum-cleaner hose with a barbed crab claw on the end, and then transferred it to the mouth.

So, to answer your question directly: Because the mouth is not the primary means of grasping food. Observe how apes, and especially humans, have lost the protruding muzzles of most other land vertibrates: when we want to grasp food, we stretch out our arms instead of our necks, so our mouths don't need to reach outwards.

This doesn't quite fit the details of your description, since your guy clearly does grasp powerfully with its mouth, but let's brainstorm a bit. A large mouth is clearly built for large prey, but the lack of reach makes it ineffective against smaller, more agile targets. So what if it's adapted for dealing with prey of different sizes? Against big targets, it slams into them mouth-first and rips into them directly; against small targets, it strikes at them with its agile head to stun or kill, then swallows them whole with the mouth. If you're open to a minor redesign, a longer and pointier "nose" could be used to impale small targets for easy transfer to the mouth, Opabinia-style.

One more thought: perhaps the mouth didn't evolve away from the head so much as the head evolved away from the mouth. Its ancestor may have been stumpy and bull-necked, or even lacked a distinct head entirely; as it evolved, the upper skull stretched outwards for agility and range of vision, bringing an extended spine with it, while the mouth remained in place, or else slipped downwards to allow it to grow larger and stronger, with muscles anchored directly to the bones of the torso.

Answer 8

It originally evolved as a bottom feeder

Most modern earth-bound animals place the mouth near the sense organs for ready target acquisition, and the sense organs near the brain for faster processing.

However, we know that in the Pre-Cambrian, many alternative forms existed, most of which are now lost. (Read Stephen J. Gould for more on this. Sadly, Halucinogenia turned out to be a red herring).

Assume this creature followed a different evolutionary pathway, and it's ancestors evolved as bottom feeding grazers. The ancestor needed to be aware of attack from above, but its food could be filtered from the substrate.

Now assume a mass extinction event leaving an evolutionary power vacuum. One would expect the remaining animals to diversify, filling in all the niches, including that of predator. Fast forward a few million years and we have highly specialised creatures yet retaining the original base body plan.

This is similar to the way that birds, humans and whales now share a body plan. Birds and humans would probably do better as hexapods with specialised forelegs, and whales could probably lose the vestigial pelvis.

Answer 9

Perhaps it could be some sort of defensive adaption, as the head is more vital/sensitive than the belly area. For example, if your creature puts its head close enough to take a bite out of a prey, the prey may retaliate and latch on to its neck. Having the mouth on the underside of the body, it would be harder for a prey to wrap around the body (like a snake would wrap around its prey, or something with hands could strangle at the neck), and it's away from sensitive areas like the eyes and nostrils.

For an illustration of what I mean about protecting the neck while feeding, see bellow:
(personal favourite for motivation)

Answer 10

Its principal food source is some sort of coevolved electric eel that tends to render predators unconscious by shock to the head (which we'll regard as a good seat for the brain since we'll put most local sensory organs apart from taste there). That works via current directly on tissues not via nerves which just saturate. Snapping of this creature's mouth works mostly reflexively, and the head is separate in order not to receive significant currents.

Answer 11

On earth, "mouth in the head" is a very common but not universal property of animals that have something that can reasonably be called a "head", and this basic plan evolved following bilateral symmetry. Wikipedia provides introductory information about the evolution of heads.

The basic mechanism is that your animal evolves bilateralism and then based on the axis of symmetry it distinguishes one end from the other by concentrating neural and sensory apparatus at one end (cephalization). So it has a head. Now, if it's going to have a long digestive tract, then the digestive tract also is going to run from one end to the other because of the basic bilaterally symmetric plan. So the only question is which end will be the mouth and which will be the anus, and the overwhelming "decision" from earth animals has been to put the mouth at the "head", that is to say at the end with the sensory organs. That's the plan from which we evolved, and AFAIK it's not observed to have been reversed.

You could in principle have a digestive tract running from front (that is, the human sense of "front", the ventral side) to back (dorsal side) instead of end to end, and remain bilaterally symmetric, but AFAIK that's not observed on earth. The animals in which this plan evolved were basically worm-like, so ventral-dorsal is a very short distance and there were probably all sorts of reasons why putting a hole through the animal in that direction wasn't any kind of improvement in evolutionary terms, whereas putting a hole in the long direction was.

The counter-examples to this plan on earth are starfish (and related animals), which probably had an ancestor with a head but have evolved away from bilateral symmetry entirely, and flatworms, with bilateral symmetry but which don't have a digestive tract at all.

Your creature looks quite bilateral to me, and therefore the flatworm approach seems applicable. No digestive tract, use the mouth to take food into a digestive cavity and then the same mouth to expel indigestible remains. Because the digestive tract is such a major piece of evolutionary "engineering", I would expect the animals on this plan to be only very distantly related to any animals that your planet might have, that do have a digestive tract.

Alternatively, you could go for a less earth-like plan, and have a digestive tract running from the mouth to an anus elsewhere on the creature: perhaps the dorsal side, perhaps further down the body on the ventral side. The key point will be that this digestive tract evolved somewhat differently from what happened on earth: for whatever reason there was no need to maximise the length of the digestive tract by running it "end to end", and so the tract didn't form all along the axis of symmetry. The difficulty then is to explain why it was advantageous to have a tract at all, if not to switch from a "batch" process of digestion, to a "flow" process that maximises capacity. Perhaps your creature and all its ancestors digest extremely efficiently and so only need a short tract, but not quite efficiently enough to only have one meal "in process" at once, and so a short tract is better than a cavity.

Answer 12

It evolved from a parasite

Looking at the creature's overall body plan, it brings to mind a structure that would be more logical for a parasite than a predator. Perhaps the ancestor of this creature originally evolved to perch on and drink the blood of/gnaw at the flesh of a much bigger animal, where it wouldn't need to move much from its landing/feeding spot but would need to defend its position from other competing parasites (maybe the host animal only had a small number of 'good spots' where the blood vessels are close enough to the skin). Over time, its mouth would move to the bottom so it could constantly feed, while its head would keep watch and be used for fighting. Not needing to move much except for seeking out a new host, its walking limbs atrophied. This would also explain the spikes - a good method of repelling hands that would try to pry it from its spot.

At some point, certain members of the species started preying on smaller animals, perhaps in between feeding on hosts, swooping down and grabbing them with its mouth. Over time, this became its primary food source, while retaining the same overall body plan.

Answer 13

So, I think we've established that there's no particular reason that we need the oesophagus to run the entire length of the creature, the food could either enter the stomach directly or the oesophagus could conceivably be convoluted like the intestine. Either way it's not a constraint.

We're therefore answering the original question — WHY would the mouth move away from the head. There are some good answers here but the obvious one that I can see is to protect the EYES from the prey. Maybe the main prey species evolved a defence mechanism to attack the eyes when grabbed by this creature. This would be a bad day for any creature that needs 6 eyes for it's day-job, so it would have to quickly counter the move with an adaptation of its own.

Sometimes evolution doesn't chose the "logical" answer but the most expedient one. The mouth drifted further from the front of the face, The prey developed longer reach with it's defence mechanism and the race stopped with the mouth in the belly.

Answer 14

On your image, it appears that the head still has a snout. Why? If it has a head-like appendage without a mouth I might expect something more like eyestalks and a blowhole. What's the purpose of a chin?!

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An evolutionary mechanism that allows for more variation in body plan is to think more how Siphonophors work rather than us: we have various different organs grow from cells using the same DNA, but they produce different "parts" as separate individuals that remain stuck together.

Each zooid is an individual module, but their integration with each other is so strong that the colony attains the function of a large organism. Indeed, most of the zooids are so specialized, they lack the ability to survive on their own. This is somewhat analogous to the construction and function of multicellular organisms; because multicellular organisms have organs which, like zooids, are specialized and interdependent, siphonophores may provide clues regarding the evolution of more complex bodies.

They can have strings of mouths, or be configured arbitrarily without the locked-in developmental stages we must go through.

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Perhaps the mouth doesn't open to the stomach as is implied, but to a crop.

Or perhaps it is just a confining "bell" and other zooids lining it will eat the captive item.

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Oh, and don't forget Robert L. Forward's Saturn Rukh which has two heads, neither of which has a mouth. The mouth is a huge intake for filter feeding, leading to paired gullets.

Answer 15

I think separation of distinct concerns could come into play, namely consumption and aspiration.

You haven't gotten much into how this creature breathes but, given its environment, it is likely that it has somewhat of an unconventional air-intake system.

Maybe the mouth is a gill-like device, suitable for breathing both air and water. This would be very difficult to eat through. Additionally, it might be hard to breathe through a throat large enough to hold a city bus. It also eliminates choking danger from consuming other spiny creatures of the same world.

Perhaps your creature just likes to eat and breathe.

Answer 16

The head is not near the mouth in most animals, the head is near the mouth. The mouth is where stuff enters the body, and this is in the direction of travel. So this is where you'd naturally put forward sensors and expand nervous tissue to deal with the data. Evolutionarily speaking, in chordates (and also in many but not all invertebrates) encephalisation went hand in hand with water and food intake.

If you need to wrap yourself around your prey in order to subdue it, then it is more useful to have the mouth halfway down the body. Cf. Platydemus manokwari.

Pulmonates breathe through a dedicated "lung mouth" found somewhere in the middle of the body.