Apologies for so many questions.

I heard parietal eye was widespread in extinct forms. Could some extinct animals see as good as with other eyes? A degenerating lens in young tuatara suggests yes, and in not too distant ancestors of tuatara.

Which groups have/had parietal eye? Where it appeared first?

There are really a couple of different questions here so I'll do my best. As an aside to any reader who have no idea what we are talking about, the tuatara an ancient kind of lizard-like reptile that lives in New Zealand effectively as a youngster has a third eye on the top of its head. It is a simple black blotch that can detect light and dark and not much else, and is covered in the adults by a combination of skin and bone.

Right, back to the issue at hand, and here is the complication - we have an excellent fossil record of all kinds of extinct reptiles, synapsids and amphibians that indeed do have a pineal foramen. The foramen is the term given to the hole in the skull for the pineal eye. However, it is possible to have a pineal foramen *without* a pineal eye, so while we are happy that lots of animals *could* have had one, we can't actually be sure. Most tetrapods have one toa degree - even humans! - but it is buried deep int he brain and has evolved in the pineal gland. It basically does the same function as a pineal eye, helping to regulate your day-night and seasonal cycles. Of course it no longer has any pigment in humans and cannot tell light form dark (it never gets any light directly of course, but instead takes its cues from your normal eyes).

So in short there are lots of basal animals with pineal formane, that quite probably had pineal eyes, but we really lack and direct evidence for this as the tuatara is really our only good living example and it's hard to make a comprehensive case based on just one example. If the tuatara is unusual then we might be 'giving' pineal eyes to all kinds fof things that didn't have them, they might have a foramen, and they would certainly have had a pineal gland, but a true pineal eye? We just don't know.