The order Rhynchocephalia includes the fascinating tuatara, reptiles that are often described as "living fossils" due to their close resemblance to species that thrived over 200 million years ago. Once diverse and widespread, Rhynchocephalians are now represented by a single genus, Sphenodon, found exclusively in New Zealand. Tuatara possess a suite of primitive and unique anatomical features distinguishing them from other reptiles, and their evolutionary history offers remarkable insights into vertebrate evolution.
- Rhynchocephalia are an ancient reptile order dating back to the Triassic.
- Today, only tuatara of New Zealand represent this lineage.
- Tuatara exhibit distinctive jaws, skull structures, and a "third eye."
Only the tuatara represent the Rhynchocephalia today.
What are Rhynchocephalia?
Rhynchocephalia first appeared during the Triassic period.
Rhynchocephalia are a small but historically significant order of reptiles that emerged in the Triassic period, over 200 million years ago. While they were once a diverse group with many species, today they are represented solely by the tuatara, which are distinguished by their unique skull morphology, acrodont teeth, and a well-developed parietal eye (sometimes called the "third eye"). These features set them apart from Lepidosauria (lizards and snakes), their closest living relatives.
- Emerged >200 million years ago in the Triassic.
- Once diverse, now only tuatara survive.
- Unique traits: acrodont teeth, distinct skull, parietal eye.
*Tuatara* are endemic to New Zealand.
Examples of Tuatara
All living tuatara are classified under the genus Sphenodon.
There are only two living species of tuatara, both in the genus Sphenodon: Sphenodon punctatus and Sphenodon guntheri. These species are considered living fossils because their morphology has changed very little in over 200 million years. Tuatara are predominantly nocturnal, have low metabolic rates compared to other reptiles, and can live for over 100 years, making them among the longest-lived reptiles.
| Species | Distinguishing Features | Distribution |
|---|---|---|
| Sphenodon punctatus | More widespread, robust | Offshore NZ islands |
| Sphenodon guntheri | Smaller, more endangered | A small number of islands |
- Genus: Sphenodon
- Two species: S. punctatus and S. guntheri
- Found only in New Zealand offshore islands
Tuatara can survive in cold temperatures uncommon for reptiles.
Source Material
Author: American Museum of Natural History
Document: Tuatara: The Last of the Rhynchocephalians
Date Published: 2023
Conclusion
Rhynchocephalia and their sole surviving representatives, the tuatara, offer a unique window into reptile evolution and the deep past of vertebrate life. Their distinctive biology and ancient lineage make them a critical group for understanding evolutionary history.
- Rhynchocephalia are an ancient order with few modern representatives.
- Tuatara are living fossils with unique anatomical features.
- Conservation of tuatara preserves a vital link to Earth’s evolutionary past.
Tuatara do not have a modern, flexible jaw joint; theirs is a primitive condition.
Because their morphology and genetics closely resemble those of their ancient ancestors.
Tuatara are primarily found on the offshore islands of New Zealand.