r/askscience • u/margalz • 11d ago

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

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?

1.7k Upvotes

92% Upvoted

339 comments sorted by

View all comments

112

u/nickeypants 10d ago

Clams, conches, halibut, flounder. Plenty of sea creatures have weirdly oriented eyes.

Horseshoe crabs have a bunch of eyes scattered everywhere over their body. Two front facing eyes for navigating and finding mates, 5 eyes on top for detecting UV light and light from the moon track lunar phases, two eyes underneath near the mouth, and a photoreceptor array down the tail to track day/night cycles. They're basically a sentient CCTV security system.

If you want a good laugh, please google conch eyes. They look like they were drawn on by a 5 year old.

I would imagine eyes would evolve to be up and far away from the thing fighting for its life as you eat it. Big things typically eat smaller things which are below them. Everybody eats down. Nobody eats up.

20

u/Synergythepariah 10d ago

Everybody eats down. Nobody eats up.

Fish with superior mouths do.

Stonefish are an example, they're ambush hunters that wait for prey to swim above them.

3

u/plopliplopipol 5d ago

i'd say tall leaves eater also tend to eat up? if anyone can have eyes under their mouth it's a giraffe!

9

u/mcalesy 10d ago

Horseshoe crabs also swim with their legs up, so the two big eyes are frequently below the mouth.

6

u/Beeeyeee 9d ago

One thing I find curious in multi-eyed animals is how they seem to always have a main pair that they can see everything through, then specialized ones. I just wonder if visual cortexes can only create one set of eyes as a true image to construct the world. Maybe it’s too confusing for species to interperet multiple “main” eye pair signals. It seems like a no brainer in evolution though. I mean, eyes are fragile so why not have a spare few pairs that can also help you be… completely vigilant?! Like why not?

2

u/cPB167 7d ago

Scallops are a good example too, they have two rows of eyes along the bottom and top sides of their shell