by Greg Mayer
The tuatara has long been of interest to us here at WEIT, where we refer to it as Earth’s Only Extant Non-Squamate Lepidosaur*. We’ve been especially interested in the tuatara’s third, or parietal, eye, and our most recent post on it, which included a very nice color image of a longitudinal section of the eye, lamented the fact that we could not find any images of the eye from the outside, showing how the eye looks on the head of a tuatara. In that post I wondered whether my colleague Jon Losos, who had commiserated with us on the apparent absence of tuatara third eye photos, might not be able to help us out. Well, he’s come through– I give you the tuatara’s third eye:
The images (click to enlarge) are from Alison Cree’s Tuatara: Biology and Conservation of a Venerable Survivor (Canterbury University Press, Christchurch, 2014). It does not (at least from the photos) look very different from the parietal eye of lizards, many of which also have parietal eyes, though not as well developed internally as in the tuatara. As a refresher from our earlier discussions here on WEIT, the ancestors of tuatara and lizards did not have a “normal”, functional third eye in the middle of their heads. Read the captions in the photos above for more details on the external appearance of the eye.
Jon included the images in his review of the book at Anole Annals (the published version of the review, sans photos from the book, will be in The Journal of the Royal Society of New Zealand). Some of the issues brought up in the book that Jon notes in his review are ones we’ve dealt with here at WEIT: the perennial confusion of tuatara with lizards (and even dinosaurs!)—Jon notes from the book someone who said tuatara were “ancestral to crocodiles and turtles”!; and the proper Maori plural of tuatara (it’s tuatara, as was explained to us by WEIT readers and Maori speakers Shuggy and Jax). The most interesting thing Jon notes about the book is that it rebuts the notion of the tuatara as a poorly adapted, barely-hanging-on, survivor, arguing, among other things, that the primitive diapsid skull structure of the tuatara is a reversal, not the retention of a primitive condition. This underscores a point made by the late Carl Gans in his essay “Is Sphenodon punctatus a maladapted relic?” (the answer is “No!”).
Jon summarized his review to me this way: “It’s a great book …everything tuatara!” And, it’s got tuatara eyes!
Cree, A. 2014. Tuatara: Biology and Conservation of a Venerable Survivor. Canterbury University Press, Christchurch. Amazon
Gans, C. 1983. Is Sphenodon punctatus a maladpted relict? pp. 613-620 in A.G.J. Rhodin and K. Miyata, eds. Advances in Herpetology and Evolutionary Biology. Museum Of Comparative Zoology, Cambridge, Mass. BHL