According to a new study, Saniwa ensidens — an extinct monitor lizard that lived in what is now Wyoming 51-49 million years ago (Eocene epoch) — had four eyes, a first among known jawed vertebrates. The third and fourth eyes refer to pineal and parapineal organs, eye-like photosensory structures on the top of the head that play key roles in orientation and in circadian and annual cycles. Saniwa ensidens had an atavistic pineal eye behind...
