29/12/2025
Tuatara's are such cool reptiles!
The tuatara (Sphenodon punctatus) has been protected by law since 1895. While popular articles about them frequently play up the species as a ‘living fossil,’ or make big news of their parietal eye, that is a small part of what makes this reptile species interesting.
First, know that a tuatara is not a lizard. Outwardly, it looks very much like a lizard, having four stout limbs, a thick tail, and dorsal spines that somewhat resemble an iguana’s. The presence of a parietal eye is even known in most species of lizards, frogs, salamanders, and some fish, so while it is an interesting feature, it is not what sets the tuatara apart.
Tuataras are endemic to New Zealand. As the lone extant species of the order Rhynchocephalia, their distant cousins certainly did walk among dinosaurs. Rhynchocephalians are believed to have originated around 250 million years ago during the Triassic period, appear to have reached global distribution and peak diversity during the Jurassic period, and aside from the tuatara, went extinct around 60 million years ago. Fossils of some of these extinct Rhynchocephalians have been found in the United States, and recently described (2022). This is where it becomes tempting to refer to tuataras as ‘living fossils,’ but apart from the retention of several features representative of Rhynchocephalians, we don’t have the evidence to claim that tuataras have remained entirely unchanged in the millions of years that have passed since the rest of their taxonomic order died out.
As for those non-lizard features? Tuataras have very unique dentition, and the ability to chew with a very effective saw-like motion. Their teeth are also fused to their skull. Additionally, the tuatara has gastralia, which are rib-like dermal bones in the ventral body wall (belly) which do not articulate with the spine or thoracic ribs. Gastralia are known in modern crocodilians as well, but not in lizards. Tuataras are extremely long-lived, with ages up to 60 years considered to be common, and captive tuatara are known to have lived for over 100 years. They do not reach reproductive maturity until around 20 years of age, and even then, the process of reproduction has been estimated at 2 to 5 years. This leaves the species vulnerable to the faster paced threats of human activity and rats.
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More about parietal eyes:
Katie Irwin, Ashley Margret Rasys, Tathiana Roldan, Douglas B Menke, James D Lauderdale; The lizard third eye. Invest. Ophthalmol. Vis. Sci. 2018;59(9):577.
https://iovs.arvojournals.org/article.aspx?articleid=2693578
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Recently found fossil relative eusphenodontian:
David G. DeMar Jr., Marc E. H. Jones & Matthew T. Carrano (2022) A nearly complete skeleton of a new eusphenodontian from the Upper Jurassic Morrison Formation, Wyoming, USA, provides insight into the evolution and diversity of Rhynchocephalia (Reptilia: Lepidosauria), Journal of Systematic Palaeontology, 20:1, DOI: 10.1080/14772019.2022.2093139
https://www.tandfonline.com/doi/full/10.1080/14772019.2022.2093139
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The photograph used in this post shows a tuatara (Sphenodon punctatus) on the forest floor. The photo was taken by Steven Baxter, and shared under a Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) license. The image was not altered for use in this post.
View license information here: https://creativecommons.org/licenses/by-nc/4.0/
