What reptile from New Zealand has a 'third eye' on its head?

The tuatara is a New Zealand reptile with a light-sensitive “third eye” on top of its head.

This structure is called the parietal eye, or pineal eye, and is associated with the parapineal organ. It is not a fully functioning eye for forming ordinary images, but it can detect light and is thought to help regulate biological rhythms such as daily and seasonal cycles. The structure is covered by skin in adults, so it is not usually visible as an obvious eye.

Tuatara are the only living members of the reptile order Rhynchocephalia. They are not lizards, even though their body shape can make them look lizard-like. Their lineage separated from that of lizards and snakes more than 200 million years ago, giving them an unusually ancient evolutionary history.

Tuatara are endemic to New Zealand and survive mainly on protected offshore islands and managed mainland sanctuaries. They can be active at surprisingly low temperatures, and some individuals live for more than a century. The “third eye” is also found in some lizards, so it is not unique to tuatara, but it is one of their best-known features.