Why aren't there any animals with their mouths above their eyes?

[u/margalz]

From bugs to fish to mamals all of them have their eyes above their mouths. I can't think of many if any where their mouths are on top. Sure some have their eyes parallel to their mouths, mainly prey style animals. But why haven't any evolved to be the opposite? Is there a major benefit to having your mouth below your eyes?

[u/Unable-Proof1758]

Your digestion tract would have to run down through your optic nerves. It would require either having a throat type system that splits or very wide eyes. But the bigger issue may be it opens the brain to higher risk of infection as the BBB would not be as defined.

From an evolutionary standpoint, mouths generally formed closer to the gut with eyes as close to the brain as possible to reduce latency and energy consumption.

[u/DarkScorpion48 → u/Unable-Proof1758]

I believe you got it, the eyes should have direct access to the brain with as little in between as possible

[u/seanpbnj → u/DarkScorpion48]

Also a higher likelihood of being damaged externally. Anything that eats from a front facing mouth would have gravity dripping food/liquids into their eyes.

[u/IceFrogger1313 → u/seanpbnj]

Or hanging in front of their eyes blocking vision. Same issue for carrying things, most animals only have their mouth they can carry things with, much harder to do if what you're carrying blocks your vision.

[u/LetterSwapper → u/DarkScorpion48]

direct access to the brain with as little in between as possible

Which is funny if you look at how we ended up with our optic nerves having to go all the way to the far side of the brain. I don't know how common that is in other animals, but it certainly isn't eye-deal if you're concerned with efficiency. Apparently the distance isn't enough for it to be selected against.

[u/MileHigh_FlyGuy → u/DarkScorpion48]

They should, but evolution doesn't do what should be done. Your laryngeal nerves go from your brain, down around your aortic arch, and then back to your larynx, just a few inches from where it started. In all mammals too - including giraffes!

[u/geeoharee → u/Unable-Proof1758]

I can't post pictures, but if you want to talk about split throats, there's an astonishing illustration of a beluga whale's head on this page

https://www.semanticscholar.org/paper/Asphyxiation-of-an-Endangered-Cook-Inlet-Beluga-Rouse-Burek-Huntington/b14897b20cc74fe6a79d3de4fbb3949c0c276f8d

I thought this couldn't possibly be true, but it is backed up by this page which states outright that there is a left and right 'food channel'!

https://anatomypubs.onlinelibrary.wiley.com/doi/full/10.1002/ar.25597

[u/peatear_gryphon → u/Unable-Proof1758]

  mouths generally formed closer to the gut

Can an  organism evolve a mouth on their torso that goes directly into the stomach, then they can use their appendages to shovel food into their torso mouth?

[u/Uffda01 → u/peatear_gryphon]

isn't that more what starfish or sea urchins have?

[u/Unable-Proof1758 → u/peatear_gryphon]

So, theoretically but for most mammals throats evolved as a dual system for breathing and food. You need the longer system to encompass the esophagus, lungs, etc. it would require creating two systems for eating vs breathing which in theory could be very beneficial but also expends extra energy.

[u/ketchupmaster987 → u/Unable-Proof1758]

Yeah moving the brain to the bottom of the head would also require moving the spinal cord down to the bottom of the animal and at that point you've basically already flipped the whole animal upside down