Tuataras are great! (But they’re not lizards!)

June 5, 2012 • 8:30 am

by Greg Mayer

(see Update below)

This morning’s Science Times has a short piece on chewing in tuataras, based on new work (abstract) by Marc Jones of University College London and colleagues that is in press in the Anatomical Record. We’ve sung the praises of tuataras before here at WEIT. But the Times piece repeatedly refers to tuataras as lizards! As all budding herpetologists learn early in their careers, the tuataras of New Zealand are the sole survivors of an otherwise extinct order of reptiles, now usually called Sphenodontida.

Tuatara (Sphenodon punctatus) at a North Island, NZ, zoo.

The story of the discovery of the tuatara, and the realization by Albert Gunther that they were not lizards, is one of the most exciting in 19th century natural history. Clifford Pope (1955) put it this way:

The discovery of the tuatara was just as startling to the scientific world as the capture of a dinosaur would have been. In fact, the ancestors of this little reptile reached their highest development before the reign of the dinosaurs…

Tuataras are related to the Squamata (lizards + snakes), but are more primitive. Major groups of reptiles are often distinguishable by the opening(s) in the sides of their skulls. Tuataras and squamates are both diapsids– they have two holes (an ‘apse’ is a hole), but squamates have a more derived condition in which the lower temporal bar (the bone along the bottom edge of the lower hole) is lost, thus freeing the quadrate bone at the back of the skull to become movable, thus making the skull kinetic (having joints within the skull for movement of skull parts). This kinetic ability is taken to its most extreme in snakes, where the skull can basically come apart and the various parts move independently (allowing snakes to eat things which are much bigger than their heads).

Tuatara skull by Arthur Weasley, from Wikipedia.

Bone 9 is the jugal, which is the largest part of the lower temporal bar. Bone 12 is the quadrate, which is mobile in squamates. Squamates also have hemipenes, paired male copulatory organs, which tuataras have in only a very rudimentary form. The following video allows you to see the differences between a tuatara and lizard skull. Note how strut-like is the bony framework of the Komodo dragon (a lizard) skull compared to the tuatara.

Tuataras can’t seem to get any vernacular name respect. In addition to being called lizards, they’ve also not infrequently been called dinosaurs (including in the otherwise great Nature film, Land of the Kiwi), a misnaming we’ve mentioned before here at WEIT.

UPDATE. Reader truthspeaker asks about the tuatara’s “third”, or pineal eye (which is perhaps better called the parietal eye). Located on the midline on the top of the head, the parietal eye is also found in many lizards. (Remember, although tuatara [to use the proper Maori plural] are not lizards, the squamates (lizards+snakes) are their closest relatives [together they are the extant lepidosaurs], so the sharing of features is not unusual or exceptional.) There can be up to four evaginations (together known as the pineal complex) from the region of the forebrain called the epithalamus, one of which, the parietal organ, can be photoreceptive, and can have a lens and a retina, forming the parietal eye. The eye is overlain by a translucent scale, easily visible in many lizards. It cannot, as far as is known, form an image. It’s also present in lampreys, where it appears as a whitish oval on the otherwise dark skin of the middle of the head. The pineal complex also has endocrine gland functions (e.g. secreting melatonin), and the combination of photoreception and melatonin secretion has led most people to consider that they are involved in circadian rhythms, but I’m not aware that the whole story has been well worked out.

The point reader Frank makes in the comments about the word “primitive” being better applied to characters rather than taxa is well taken, and, indeed, my point about the primitiveness of tuatara is that they retain the (primitive) fully diapsid skull, and do not have the derived state of the copulatory organ.  When applied to taxa, primitive is often intended to indicate a preponderance of primitive characters, as in the term “primitive sister group”, even though, by definition, if extant, sister groups have been evolving for exactly the same length of time (and thus might be expected to have similar numbers of derived states among neutral characters). Primitive might also be used to refer to the chronology of branching sequence in phylogeny (a more primitive taxon having branched off earlier). But it is best to always be “tree thinking“, and to look at a phylogeny from multiple perspectives, although at any particular time some particular approach may be of more interest. One of my favorite New Yorker cartoons depicts a corporate boardroom, around which many captains of industry are seated. In one chair, though, sits a dog, who speaks up: “May I offer a different perspective?”

Reader DV wonders what the famed Chicago herpetologist Clifford Pope (whose perhaps most famous paper we considered earlier here at WEIT) meant by “highest development”. Since he is no longer with us, I would venture three possibilities, none of which are idiosyncratic to Pope. First, he might have meant highest species richness– there’s only one species of tuatara now, but there were many more species of sphenodontids in the past. Second, he may have meant greatest adaptive diversity, i.e. not necessarily number of species, but number of distinctive ecologies and ways of life (there was an aquatic group in the order, pleurosaurs, in the Mesozoic). Third, he may have meant that the most distinctive, derived features of their morphology appeared at that time, and have not changed (much) subsequently (i.e. they are “living fossils”). At the time Pope wrote, rhynchosaurs (a fairly diverse early Mesozoic taxon now thought to be allied to archosaurs [birds and crocs among extant taxa]) were thought to be related to sphenodontids, and this might also have influenced his notion of “highest development”.

Pope’s book, by the way, The Reptile World, is still a great store house of reptile natural history, and worth a read. There have been advances in both classification and our knowledge of natural history since it was published, though, so I would also recommend Harry Greene’s Snakes, Eric Pianka and Laurie Vitt’s Lizards, and Andy Ross’s Crocodiles and Alligators.

Finally, Ichthyic (by implication) and Paul Coddington note that the proper plural of  “tuatara” is “tuatara” (like “deer” and “deer”). As part of an earlier consideration of the tuatara (note my avoidance of the plural!), in response to a question I posed, reader Shuggy provided the following details:

I’m not a native speaker, but my Māori (2 years university, 40 yrs informal) is good enough for this. You show the plural by using a plural article; ngā tuatara, or a number; he tuatara e rua, two tuatara.

But to tell the truth, most non-Maori-speaking New Zealanders, which means most New Zealanders, would say two tuataras too.


O’Hara, R.J. 1997. Population thinking and tree thinking in systematics. Zoologica Scripta 26:323-329. pdf

Greene, H.W. 1997. Snakes: The Evolution of Mystery in Nature. University of California Press, Berkeley

Pianka, E.R. and L.J. Vitt. 2003. Lizards: Windows to the Evolution of Diversity. University of California Press, Berkeley.

Pope, C.H. 1955. The Reptile World. Knopf, New York.

Ross, C.A., ed. 1989. Crocodiles and Alligators. Facts on File, New York.

30 thoughts on “Tuataras are great! (But they’re not lizards!)

  1. >>the ancestors of this little reptile reached their highest development before the reign of the dinosaurs

    What does “highest development” mean?

    1. I’m no biologist, but I’m guessing what is meant is that their morphology hasn’t altered much since the before the Triassic.

      That wouldn’t stop their genome changing in other ways of course. Just not in ways that result in obvious morphological changes.

      But I’m guessing you are right – terms like “Highest”, “progress”, “advancement”, are meaningless in the context of evolution.

      But perhaps Professor Coyne can put us right.

      Cool article though.

      1. Yes, primitive and derived are best used for particular characters, NOT for entire lineages (which have all been evolving for the same length of time since the origin of life on Earth). As an example, the platypus is a “primitive” mammal in terms of its egg laying and diffuse mammary glands, but “advanced” in terms of its venomous hindleg spur and its incredible sophisticated “bill” that can detect electric fields.

    2. “highest development” and “more primitive” bother me in this article which is otherwise very interesting and informative. These terms imply a progression in evolution, perhaps a teleological progression, which should not be there. Tuataras have had the same length of time to evolve as any close relative they split from – are they then “more primitive” even if their phenotype is not noticeably changed for millions of years? Hasn’t this point been argued on WEIT before?

      Larry Moran at Sandwalk, highlights today this topic with reference to the imagined view of a platypus of humans. Perspective is everything – the example is from Ryan Gregory at Genomicron. Who is more primitive, Platypus or human, if we are all here today?

        1. In computer alchemy (it’s not a science!) Primitives are the commands and methods that must first be invoked. You cannot initiate that HyperText Transfer Protocol (http) without first establishing a physical connection (air gaps) and logical connection (Internet Protocol and Transmission Control Protocol). Obviously primitive does not mean unsophisticated, it means this must occur before any other action. Moreover, subsequent actions are not necessary as things can be done at these primitive levels. ARP, the protocol that allows you to find computers by name not by numerical IP address, is done solely at link layer.
          There are limitations to the language and as such I am always amused by the fabric rendering and the donning of ash-cloth over such minor inconsequential events. I read primitive for what it is, the earliest form or the base on which all is built. I also recognize that complexity and advanced or highest development are not synonymous (tapeworms!).

          1. Unfortunately, in this case, using the word higher does propagate a myth about evolution – that it implies long-term improvement (which would require look-ahead)

  2. Jerry, once again you have written about this interesting set of creatures and noted some of their unusual characteristics, but you have failed to mention that some of them have a third eye in the middle of their foreheads.

    A third eye, man.

  3. Note that Greg wrote this, not I, but I’ll call it to his attention. Yes, the “pineal eye” is a famous feature of this species.

    Ten to one Greg will post an update.

    1. As a modern mammal, we evolved from synapsids, which originally had a single “apse” in the skull. But that closed up and is gone in the lineage that led to modern mammals. I guess these animals figured they needed a temporal opening like they needed a hole in their heads.

        1. Do you mean Sir David, or Lord Richard?

          “Sir Attenborough” is a grammar fail, even in USian.

      1. errr… the ‘apse’ did not close up in the synapsid line leading to mammals — we have it as the space between our cheekbone and the cranial vault. [Actually the posterior part of this opening, since it became continuous with the orbital opening in early mammals.

  4. FWIW,

    We have a decent sized group of tuatara right by where I live, both in the Wellington Zoo, and in the protected “Zealandia” natural reserve area. Even one at the local uni campus which is nearly always viewable.

    happy to to take anyone who comes through on a tour.

    1. I believe the picture I posted above (taken by a friend) is of a tuatara at the Wellington Zoo.


      1. well, there ya go 🙂

        Welly zoo is a quite nice, small zoo, focusing on high quality exhibits as opposed to huge numbers of them.

        they’ve recently partaken in some serious renovations; lot of money being pumped into new exhibits. Not sure what the outcome will be, but I am now noticing corporate sponsor logos everywhere, for better or worse.

  5. Well, if you’re going to call them “reptiles” you may as well call them “lizards”, too. One good paraphyletic group deserves another, or something like that. 🙂

    (Also worth pointing out in the interests of pedantry that lizards are paraphyletic whether tuataras are included or not. As a paraphyletic assemblage, whether one particular taxon is included or not is fundamentally arbitrary.)

    1. I’m happy to consider snakes as highly evolved lizards, because their ancestors were clearly lizards for a long time before the whole elongation and limblessness stuff happened. In this sense, ‘lizards’ just means ‘squamates’, and it’s monophyletic. Including snakes within ‘lizards’ emphasises an important and interesting part of their evolutionary history.

      NOT being a squamate is the most interesting aspect of Sphenodon‘s evolutionary relationships, so calling it a lizard is a badly missed opportunity for education.

      1. Well, I agree that snakes should be included within the lizards. But if “lizard” is just another name for “squamate”, the statement that tuataras are not lizards becomes decidedly non-profound. “Lizard” in this sense just means “any member of Lepidosauria that is -not- a tuatara”. So, OK, tuataras aren’t lizards. That’s not the most interesting aspect of their evolutionary relationships, it’s an arbitrary nomenclatural decision.

        1. In any case, that’s wandering a bit. The gist is:

          Mainstream -academic- use of “reptile” and “lizard” is inconsistent, unhelpful, and just plain wrong. There just isn’t a coherent and generally accepted usage to appeal to. So… probably not the best context in which to insist on nomenclatural purity from the popular science guys.

          Now, you’re right, problems with how “reptile” and “lizard” are used can be fairly straightforwardly addressed, but right now it’s still just a mess…

  6. I had a couple of tuatara in my apartment during my post-grad years (left over from another researcher’s experiments). They were great fun. One of them was very tidy, the other dug up everything and flung it all about. The untidy one was aggressive and would often pose “attentively” and “bark” at people.

    One day, there was a knock at the door and a couple from England introduced themselves as tourists who had lost their way. They wanted to know how to get to the local wildlife park because their daughter was mad keen to see a tuatara. By amazing coincidence they had likely knocked on the door of the only house in the country where tuatara could be found. I invited them in, their daughter got to handle a tuatara, not just look from a distance.

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