Our earliest vertebrate ancestors may have had four eyes

Extraordinary fossils of 518-million-year-old jawless fish, among the earliest known vertebrates, appear to show that these animals had two pairs of eyes. These fossils suggest that the creatures had two pairs of camera-type eyes, enabling them to form an image of their world. The team believes that this ancient, extra pair of eyes evolved into a set of organs known as the pineal complex, which in mammals consists of only the pineal gland that regulates our sleep cycle.