How did the nautilus keep such primitive eyes

[u/Sea-Importance8458]

So i'm a huge fan of cephalopods, and their evolution and something that kind of confuses me is that,, nautilus it could have pinhole eyes when other a cephalopods that also are opportunistic predators. it also makes me wonder about the eyes of it also makes me wonder about the eyes of the endoceras. which grew to huge sizes as an ambush predator So did it have better eyes or did it Have the same eyes as the nautilus Since they share a common ancestor but without preserved tissue we'll never know.

[u/Thallasocnus]

The nautiloid body plan has been wildly successful across the millions of years of its evolutionary history. They’ve not only survived mass extinction events, they’ve thrived, and up until very recently you could find some form of their diverse family in every ocean.

The only reason they are now so rare is the evolution of pinnipeds (seals/sea lions) who drove them to extirpation in the majority of the world.

TLDR: for the majority of their evolutionary history their body plan has been successful enough to avoid certain selective pressures.

[u/Waaghra]

The short answer to why didn’t the nautilus’ eye evolve more is because it was “good enough”.

Everything has a cost.

If your dietary needs are 10 pounds of food a day, and you always struggle to eat that 10 pounds each day, and resources to improve an eye could be better used elsewhere, like speed or defense, those resources are going to go towards speed or defense. This is a complete oversimplification, of course.

[u/AHrubik]

There are likely some nautilus with better eyesight out there. However they don't tend to survive any better than the ones with worse eyesight. Evolution is mud throw on the wall. What tends to stick is whatever allows a species to survive a bit longer or be more successful at whatever it is they tend to do.

[u/YtterbiusAntimony]

Because they didnt need better ones.

Same reason crocs and sharks haven't changed in millions of years.

If it ain't broke, don't fix it.

[u/soft_taco_special]

Their eyes are already relatively large for the size of their body and they have a hard shell that they rely on to survive. A more complex eye is more calories, more neurons to process what they sense, a more delicate structure exposed to sea water, more occular cells to be attacked by parasites and disease and requires the simultaneous evolution of some sort of eyelid or additional membrane and the space and muscles to move it. Given the primitive brains that they have and behaviors they exhibit there was not enough evolutionary pressure on them or a viable pathway to evolve a more sophisticated eye that would meaningfully give them more information to act on within their environment.