The tuatara is an animal that has three eyes.
The Tuatara's Third Eye
The tuatara, a reptile native to New Zealand, possesses a unique feature: a third eye, also known as a parietal eye. While not as developed as its two primary eyes, this third eye is a photoreceptive organ. This means it can detect light and is thought to be important for regulating the tuatara's circadian rhythm, or daily sleep-wake cycle, and for thermoregulation, i.e. temperature control.
Although some other reptiles also have a third eye, it has been lost in later animal orders such as birds, crocodiles, and mammals. Nevertheless, remnants of this organ are still present in many of these animals.
Understanding the Third Eye
The third eye is an example of evolution’s earlier approach to photoreception. Here's what we know:
- Location: It is located on top of the head, usually positioned between the two primary eyes.
- Structure: Unlike the primary eyes, the third eye does not focus images and may be thought of as a light-sensing organ.
- Function: Primary functions include detecting changes in light levels and contributing to the regulation of biological rhythms.
- Evolutionary Significance: Its presence shows how animals previously approached the problem of perceiving light and illustrates the evolutionary journey of photoreception.
Why is This Important?
The existence of a third eye in the tuatara gives us valuable insights into the following:
- Evolution: It offers clues about how animals have evolved their light-sensing systems.
- Adaptation: It highlights how animals adapt to their environments using unique biological features.
- Comparative Anatomy: Studying this feature can help us compare and contrast different animal groups and their unique adaptations.
In summary, the **tuatara** is one of the rare modern animals that has a third eye. This makes them a fascinating case study for understanding animal evolution.
