|MadSci Network: Zoology|
Tuataras are said to have "third" or pineal eye, with cornea, retina, lens etc., but it is hidden under the skin. It is thought that this is actually rudiment of something more developed - perhaps remnant of real third eye. The idea of three-eyed monsters seems quite strange and interesting. BUT I havent found any reliable mention of extinct group of animals having three fully functional eyes. Did they exist or not?
Re: Did some (extinct) animals use they 'third eye' for seeing?
Try the links in the MadSci Library for more information on Zoology.