Why the Tuatara Has Three Eyes

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There was once a thriving group of reptiles that lived during the time of the dinosaurs. Rhynchocephalia is a reptile order that evolved around 240 million years ago. These reptiles used to live around the world, but today, only one surviving species remains: the tuatara. This rare lizard-like creature is only found in New Zealand.

The tuatara has a lot of fascinating characteristics, but perhaps one of its most remarkable traits is its third eye. Sitting on the top of its head, the tuatara has a third eye complete with retina, lens, and nerve endings that connect to its brain. Scientists previously thought the eye was used to watch out for predators above, but we’ve since learned that the creature can’t actually see out of it. It’s called the parietal eye, and we don’t know exactly what it’s used for, but as the video above explains, there are a few theories.

Is the Tuatara a Type of Lizard?

The tuatara looks like a lizard, but it’s not. The species broke off from the same group that became lizards around 250 million years ago. Though they are similar, there are some key differences between tuataras and lizards. For one thing, tuataras have very long lifespans — over 100 years. They are also nocturnal, while many lizards are active during the day. And they prefer cooler climates than lizards do, too.

Why the Tuatara Developed a Third Eye

You can’t see a tuatara’s third eye, at least in the adults. The eye is covered in scales and can only be seen in young juveniles. As mentioned above, the tuatara doesn’t see out of its parietal eye, and scientists aren’t entirely sure of the reason it evolved on the animal. These are some possible theories as to the function of the parietal eye:

• Detecting the time of day and helping to set circadian rhythms
• Helping with thermal regulation
• Regulating hormones

How the Parietal Eye Works

Because the eye has a retina, lens, and nerves connected to the brain, it’s possible it was a fully working eye at some point in the animal’s evolutionary journey. But through the years, the eye lost its ability to see. However, it kept its ability to sense light.

Tuataras can’t see out of their parietal eyes because the retina is a simplified version of the retina in a normal eye. The retina does contain photoreceptors, which is why it’s believed the eye can sense the time of day. One research study showed that the tuataras use this eye like a compass and navigate by the sun. The eye is also connected to the tuatara’s pineal gland, which releases melatonin. Melatonin helps reptiles regulate heat.

More Unique Tuatara Features

The tuatara’s parietal eye isn’t the only unique feature of this fascinating creature. Following are some other differences that make the tuatara remarkable.

They have primitive teeth fused to the bone of their jaw. They work well for crushing beetles, but can’t be regrown when they break or get worn down. Other reptiles can regrow teeth, continuously replacing them as they wear down. As the tuatara ages, it has to switch to a softer diet.

They live incredibly long lives. On average, the tuatara lives for 60 years, but it can live to be older than 100. The oldest known living tuatara is Henry, a 130-year-old member of his species living in a New Zealand animal reserve. Tuataras grow so slowly that they aren’t considered fully developed adults until they are 35 years old.

They are cannibals. Tuataras are active at night, but the young tuataras only come out during the day. This is because they are in danger of getting eaten by their larger, hungry elders if they run into an adult at night.

They are still evolving at a rapid pace. One study discussed in the video found that although tuataras look a lot like ancient dinosaurs, they have evolved through the years. And their evolution has occurred at a fast rate.

Are Tuataras Endangered?

Tuataras once lived all over New Zealand, but today there are no wild populations left on the two main islands. Some live in sanctuaries and some wild populations can be found living on New Zealand’s smaller islands. Though they aren’t endangered, they are at risk.

Tuataras were once plentiful, but when rats were introduced in New Zealand around 1,000 years ago by settlers, they became the number one predator for the lizard-like creatures. Today tuataras are in danger of being eaten by rodents and suffer from habitat loss. They are also popular on the black market pet trade. Though it’s illegal because the tuatara is a protected species in New Zealand, people will pay up to $40,000 for a pet tuatara.