Did you know that iguanas (and not only them) have three eyes ?
the feature is called Parietal eye, it is highly advantageous to spot the shadow of a predator coming from above, and it’s not unique to iguanas, but it can be found in frogs, lizards, sharks and other reptiles and fishes. In the Tuatara the eye is way more developed, but it regresses as the animal gets older. All these eyes can influence the pineal gland, apparently responsible for the circadian rhythm regulation.