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.
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).
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.