Posted: May 19, 2016 3:50 pm
Sendraks wrote:DavidMcC wrote: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.
There is nothing to suggest that basal reptile forms evolved from Lampreys, which is referred to convergent evolution. Indeed the evolutionary relationship between lampreys and jawed vertebrates is sketchy at best.
Nothing is straightforward at hundreds of MYa. The lampreys certainly seem to be more related to sharks than other fish, I admit.
However, I am arguing that the lamprey (which pre-dates any reptile in most versions of the evolutionary time-line), effectively "invented" the three eyes, so the tuatara could have inherited the genetic structure for it indirectly from lampreys, via Rhynchocephalia, and maybe other intermediate species, because, no doubt the lamprey was not a direct ancestor of any reptile, though it would have been the closest you get in known or extant species to being the "inventor" of the three eyes. It certainly predated Rhynchocephalia, in most versions of the evolutionary time-line (they change from time to time,sometimes drastically).