Posted: May 19, 2016 3:25 pm
Sendraks wrote:DavidMcC wrote:
... Which would include ancient vertebrate fish. The only known fish group with three eyes is the lampreys, which were certainly around at 200mYa, according to most versions of evolution.
The order Rhynchocephalia, of which the Tuatara is the last surviving member, existed 200million years ago. There were certainly lampreys around then and indeed the oldest lamprey fossils date back to 360million years ago, although I'm sure you already know that.
The existence of three eyes in basal reptile forms like Rhynchocephalia (the remains of which are found in many specialised extant forms) could be the product of convergent evolution. However, as Rhynchocephalia is a basal form, it is reasonable to conclude that all members of that order share common unspecialised features which in turn they inherited from a common ancestor, who would have been more basal still.
Yes, like the lampreys, maybe, retained by expressing the relevant genes in other ways than an imaging eye.