Although the dinosaurs are gone, extant vertebrates provide clues to the development of photoreception among the clades that probably preceded and then radiated into the dinosaurs. The ancient order Rhynchocephalia, which includes Sphenodon as its only family, with two surviving species, had its heyday between 200 million and 100 million years ago. While this order is reptilian, these creatures were not lizards, but their own order.

Approximately 100 million years ago as other members of Rhynchocephalia were succumbing to extinction, Gondwanaland was breaking apart and New Zealand and its islands were breaking free from Australia, thereby isolating this last member of Rhynochocephalia, Sphenodon, presumably without competition. The tuatara survives virtually unchanged, as a fossil relict and provides us with a glimpse of vertebrate evolution from perhaps as long as 200 million years ago.

In the early Jurassic (approximately 200 million years ago) tetrapods were radiating into lizards, turtles, crocodiles, dinosaurs, and eventually birds and mammals. Sphenodon was in an order of early reptiles and provides us …