Tag: tuatara

Wellington to Puhaka Mount Bruce

April 1, 2017 • 1:00 pm

Yesterday (Friday), I went to the Pukaha Mount Bruce Wildlife Centre in the company of Phil Garnock-Jones, an emeritus professor of botany at the University of Wellington.

The Centre is about two hours north of Wellington, and on the way we passed the “Beehive“, the executive wing of the New Zealand Parliament. Built between 1969 and 1979, it’s controversial: most kiwis who told me about it couldn’t decide whether they liked it or hated it:

On the way, I saw a “kiwi crossing” sign but it went by too fast to photograph. But it looked a bit like this (landscape was different):

Only in New Zealand!

The Centre houses a largish tract of forest and also several wildlife exhibits, including kiwis, tuataras, and many birds.  Below is a kiwi chick: they’ve now hatched 100 from the radio-tagged kiwis who lay eggs on the property. Only about 5% of natural eggs survive because of predation and other factors, but when raised in the Centre, about 85% of the eggs produce kiwis that become adults. They’re raised to the point when they can fend off predators (they kick hard!), and are then released back into the forest.

Kiwis, of which there are five species (or three or four, depending on whom you ask), are all critically endangered as they breed slowly and are vulnerable to introduced predators. They are, of course, the national symbol of New Zealand, whose inhabitants are called “Kiwis.”

Here’s an adorable chick they showed for just a few minutes. It’s a North Island brown kiwi, Apteryx mantelli.

They had a white leucistic one, too, and several brown ones, but they are nocturnal and the exhibit is dark. You can’t and shouldn’t use flash, so my picture was horrible. But here’s a white kiwi chick hatched at the Centre, photographed by them. (As we’ve learned, leucism is not the same gene as albinism, and changes body pigmentation but not eye pigmentation.)

Photo by Mike Heydon

Kiwis lay the largest egg in relation to their body size of any bird: here’s how it looks via a reconstruction. Every organ must be squashed up inside! The presenter at the Kiwi House told us this is the equivalent of a woman giving birth to a six-year-old child!

More about kiwi reproduction from Wikipedia:

Once bonded, a male and female kiwi tend to live their entire lives as a monogamous couple. During the mating season, June to March, the pair call to each other at night, and meet in the nesting burrow every three days. These relationships may last for up to 20 years. They are unusual among other birds in that, along with some raptors, they have a functioning pair of ovaries. (In most birds and in platypuses, the right ovary never matures, so that only the left is functional.) Kiwi eggs can weigh up to one-quarter the weight of the female. Usually, only one egg is laid per season. The kiwi lays the biggest egg in proportion to its size of any bird in the world, so even though the kiwi is about the size of a domestic chicken, it is able to lay eggs that are about six times the size of a chicken’s egg. The eggs are smooth in texture, and are ivory or greenish white. The male incubates the egg, except for the Great Spotted Kiwi, A. haastii, in which both parents are involved. The incubation period is 63–92 days. Producing the huge egg places significant physiological stress on the female; for the thirty days it takes to grow the fully developed egg, the female must eat three times her normal amount of food. Two to three days before the egg is laid there is little space left inside the female for her stomach and she is forced to fast.

The kākā, (Nestor meridionalis) is the sister species to the kea, a bird I’ve already described. They’re more common than kea, and tend to hang around human habitats to beg or steal food. While eating lunch at the Centre’s cafe, Phil and I encountered one that flew down to the patio where we were sitting. They’re gorgeous birds, and just as fearless as the keas:

I didn’t feed them, as you’re not supposed to, but this one hopped from table to table looking for handouts. Each table also has a spray bottle of water that you can use to spray them if you want them off your table. Several people did that, but I thought it was horrible. Why would you spray one of these wonderful birds? Yes, keep your food away from them, but don’t spritz them.

This one went for the dregs of an iced mocha left at a table, using its tongue to lick the inside of the glass.

Brazen—right in front of a “Please do not feed the kakas” sign!

These people photographed the kākā but the sprayed it. Ingrates!

This guy had a tussle with the kākā over his plastic-enclosed sandwich. I would have loved to see the bird open it up.

Getting the crumbs:

Phil, like a good biologist, just sat there and photographed the bird as it sat on our table:

Here’s an Antipodes Island parakeet (Cyanoramphus unicolor), endemic to the Antipodes Islands off New Zealand. According to Wikipedia, it’s one of only five species of ground-dwelling parrots in the world:

Phil with a kõkako (Callaeas wilsoni), a very rare bird found on the North Island. It is large and has a beautiful gray color with blue wattles on either side of the beak. It’s endangered because of the usual factor: habitat loss.

A picture of the kõkako taken by Phil through the wire (he had a fancy Nikon digital SLR). Look at those blue wattles!

Here’s me with the bird; it liked me took from my hand leftover berries from the keeper’s feeding demonstration. We bonded. This was a hand-reared bird that was caught as a nest runt in the wild; it couldn’t call like a regular kõkako, but could wolf whistle like a human, clearly due to either visitors or a nefarious owner!

Here’s a tuatara (Sphenodon punctatus), a famous and iconic reptile. Found only in New Zealand, it’s the sole surviving species in the order Rhynchocephalia, which flourished during the Age of Dinosaurs: about 200 million years ago. It’s a “living fossil”, and its sister group is (lizards + snakes).

They appear to begin breeding at about 25 years of age (!) and are said to live up to 100 years in captivity, though that’s not certain. I’m sure Greg will post some more about this either here or in the comments.

[Further notes on tuatara by Greg Mayer:  WEIT readers may feel a stir of recognition when viewing this fellow, because I think we’ve met him before, in a picture taken by a friend who visited New Zealand several years ago. It looks like the same exhibit, and tuatara are, as Jerry notes, long lived, so my first guess would be that it’s the same guy. I’m not sure this is the first tuatara Jerry has seen in life, but I’d wager it’s the first one he saw in a photo, and then in life!

Tuatara are the primitive sister group of lizards and snakes, lacking the fully developed hemipenes (dual penises) characteristic of the latter two, and retaining the lower temporal arch of bone below the lower of the two openings in their cheek bones (although it has been proposed that the lower temporal arch in tuatara is a reversion to the primitive state, and not a retention of the ancestral condition).

They are perhaps best known for being the sole survivor of the order Rhynchocephalia from the Mesozoic, having changed little in skeletal morphology since that time, hence the oxymoronic but apt moniker “living fossils”.  It came as a great surprise in the 19th century when it turned out, on closer inspection, that they were not lizards. Though often misleadingly associated phylogenetically with dinosaurs and even crocodiles, they are not closely related to either, other than that they all (including lizards and snakes) are included within the great reptilian group of diapsids. (‘Diapsid’ referring to the two [di] openings [apses] in the cheekbones found in this group, which also includes birds and pterosaurs.)

Tuatara are also famous for having a well developed third or parietal eye, having both a lens and retina, though it is probably not capable of forming an image. The parietal eye is not a degeneration from a once fully three-eyed animal, but a more developed form of a rudimentary sense organ found in many vertebrates.

Once found on the main islands of New Zealand, the single species now survives only on a number of offshore islands, where they are carefully protected. These cool, windswept islands are an unusual habitat for most modern reptiles, and the tuatara have an unusual life history, sharing burrows with sea birds and living a very long time. Tuatara (plural and singular are the same in Maori, though ‘tuataras’ is often used when the word is adopted into English) have long been a favorite subject here at WEIT and you can find more by looking here.]

Two rare ducks. First, the blue duck (Hymenolaimus malacorhynchos), a “torrent duck” that lives in rapidly flowing rivers, a rare habitat for ducks. It’s highly endangered.

And the pāteke, or brown teal (Anas chlorotis), which is making a bit of a comeback:

Lancewood (Pseudopanax carassifolius, Maori name “horoeka”). This is the adult, and it’s one of those trees that develops a crown of foliage only after it reaches a certain height. The younger trees, shown below this one, have thorny, tough, and hard-to-reach foliage. It’s thought that they grow this way as an ancient remnant of their evolution to avoid browsing by the now-extinct moas.

Here’s the juvenile. Experiments using living ratites show that they lose weight if forced to browse on young lancewood, but gain weight if left to browse the older foliage, supporting the “moa hypothesis”

Koromiko (Hebe stricta), a New Zealand endemic with lovely flowers.

Karamu (Coprosma robusta) another endemic plant, like nearly all New Zealand species, has at best small fruit. That’s because birds and bats were the only seed dispersal agent, as there were no endemic terrestrial mammals that couldn’t fly. These are the berries that the keeper (and then I) fed the kõkako.

Easter orchid (Earnia autumnalis; “raupeka” in Maori). Phil detected it simply because, as we walked under the host tree, he smelled vanilla (and so did I). He immediately said that there must be an Easter orchid around and, sure enough, one was right above us. The plant is known for its strong vanilla-ish scent

How many groups of plants can you see here, including the big tree hosting all the others?

The tuatara’s third eye

December 11, 2014 • 12:44 pm

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 parietal eye of the tuatara, from Alison Cree's Tuatara (Canterbury University Press, Christchurch, NS, 2014).
The parietal eye of the tuatara, from Alison Cree’s Tuatara (Canterbury University Press, Christchurch, NZ, 2014).

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

The tuatara’s parietal eye

August 7, 2014 • 10:58 am

JAC: My post on the tuatara parietal eye was short and, for some readers, not informative enough. Where did it come from? What does it look like? (By mistake I published a picture of an iguana and not a tuatara.) Greg answers some of the many questions that have surely been tormenting many of you about this bizarre feature.

by Greg Mayer

The tuatara has long been of interest to us here at WEIT, and just the other day Jerry posted a video of one hatching, along with many interesting notes on their biology, especially on the parietal or ‘third’ eye. Jerry included a picture of the parietal which, as Jon Losos, among others, noted, was not, alas (as a simple google image search indicated), that of a tuatara, but rather that of what looks to me to be a common or green iguana (Iguana iguana— which, if you learn no others, is the one scientific name you should commit to memory). Jon remarked to Jerry that good pictures of a tuatara’s parietal would be hard to find. Well, here’s the best I could find.

The parietal eye of the tuatara (Plate 20 from Dendy, 1911).
The parietal eye of the tuatara (Plate 20 from Dendy, 1911).

This is Plate 20 from Arthur Dendy’s classic 1911 monograph describing the pineal organs (including the parietal eye) of the tuatara. The upper figure is a longitudinal section of the parietal eye, and the lens, retina, and pineal nerve (equivalent to the optic nerve) are readily apparent. The two lower figures provide details of the retina.

Dendy studied both adults and embryos; the above figures are of adults. Dendy, an Englishman, resided in a number of the antipodal parts of the British Empire, and in his monograph records his good fortune in not losing some of his histological sections of tuatara embryos, “… for they were, with most of my Australasian collections, shipwrecked in transmission from New Zealand to South Africa. The boxes containing the sections were, however, salved, and reached me after being soaked for weeks in salt water.”

The following figure, from Angus Bellairs’ still useful Life of Reptiles, is based on Dendy’s top figure, and labels some of the parts for clear identification.

The parietal eye of the tuatara (Figure 114 from Bellairs, 1970).
The parietal eye of the tuatara (Figure 114 from Bellairs, 1970).

Neither of these pictures, of course, shows the parietal from the outside. I’ve read that the parietal is not externally visible in adult tuatara, but I’ve never checked on the preserved tuatara I’ve seen; Jon has seen tuatara live and up close– perhaps he will stop by again here at WEIT and let us know if he has noticed the eye on the ones he’s seen and held.

The parietal eye is also found in many lizards (which, together with snakes, are the tuatara’s closest living relatives, so the sharing of this features is not anomalous.) In vertebrates, there can be a number of evaginations (together known as the pineal complex) from the region of the brain called the epithalamus. One of these forms the pineal gland or organ, while another forms the parietal organ. Both can be photoreceptive.  In lizards and tuatara, the parietal organ 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. In lampreys, both the the pineal and parietal can be eye-like, so that some authors refer to them having a pineal eye and a parietal eye (which is why the median eye of lizards and tuatara, though sometimes called the pineal eye, is better called the parietal eye). In lampreys the position of the median eyes is indicated by a whitish, unpigmented, oval on the otherwise dark skin of the middle of the head,  In birds and mammals, the parietal organ is absent, and the pineal organ (now called the pineal gland) is buried deep in the head, and has endocrine functions.

The pineal complex was present in some of the earliest fishes, as indicated by the presence of a single median foramen [JAC: small opening in the bone] in the skull of ostracoderms, placoderms, and others. It is most eye-like in the parietal eye of lizards and tuatara, which suggests that a fully eye-like parietal or pineal was not present in early vertebrates, so that the parietal eye did not evolve from a “real” eye.

_____________________________________________________________

Bellairs, A. 1970. The Life of Reptiles. 2 vols. Universe Books, New York.

Dendy, A. 1911. On the structure, development and morphological interpretation of the pineal organs and adjacent parts of the brain in the tuatara (Sphenodon punctatus). Philosophical Transactions of the Royal Society of London 201:227-331, pls. 19-31. pdf (Dendy’s interpretations of homology are no longer all accepted, but the morphological and histological work remains fundamental.)

The Tuatara Genome Project

July 10, 2013 • 6:35 am

by Greg Mayer

We’ve had occasion to celebrate the completion of reptile genome projects before here at WEIT (including the first, the Anole Genome, and the recent turtle genomes), so it is especially notable that one of our favorite animals, the Earth’s Only Extant Non-Squamate Lepidosaur*, is now the subject on an ongoing sequencing project being led by Neil Gemmell of Otago University and the Allan Wilson Center for Molecular Ecology and Evolution (whose director is my old chum and fellow MCZ alum, Hamish Spencer). It is of course fitting that the genome project be based in the iconic animal’s native land, New Zealand. David Winter has begun a blog, Sequencing the Tuatara Genome, to document the project’s progress.

Why sequence the tuatara genome (other than just because they’re, you know, great)? This picture from David’s blog, should tell you. (BTW, back when the Anole Genome was completed, a reader asked, “What are the gaping holes in our genomic knowledge?”, and I presciently replied “Among tetrapods, the gaping holes are the tuatara,…”.)

Phylogeny of relationships of the tuatara, from David Winter's Sequencing the Tuatara Genome Project.
Phylogeny of relationships of the tuatara, from David Winter’s Sequencing the Tuatara Genome blog.

If it’s not clear, David spells it out (note that he uses the proper Maori “tuatara are“):

You sometimes hear people mistakenly call tuatara “living dinosaurs”.  In fact, as you can see in the figure above, tuatara are much more interesting than that. If you want to study a living dinosaur you only need to look out the nearest window. Modern birds descend from one branch in the diverse group we call dinosaurs, but each of those ten thousand species are dinosaurs. The tuatara, on the other hand, are the only living members of a lineage that separated from other reptiles more than 200 million years ago.

By placing modern organisms in the context of their evolutionary history, we can work out which traits were present in ancestral species, and reconstruct the changes that gave rise to modern ones. As the tuatara is the only living witness to hundreds of millions of years of evolution, its genome sequence will be immensely valuable in understanding the genetic changes that have allowed reptiles to evolve and diversify.

I urge you all to go take a look at David’s blog now, and check back in there now and again to see how things are progressing.

_______________________________________________

* I was going to say the Universe’s Only Extant Non-Squamate Lepidosaur, but I can’t quite rule out that some Vulcan survey craft, while cruising nearby waiting for Zefram Cochrane to release a warp signature, might not have decided to stop by for a bit and then taken some non-squamate lepidosaurs home (I know I would have).

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.

Tuataras and the species problem

January 23, 2011 • 11:14 am

by Greg Mayer

Tuataras are very interesting animals: endemic to New Zealand, and the sole survivors of an ancient and once more widespread order of reptiles, the Sphenodontida, whose closest relatives are the squamates (lizards+snakes). I noted some of their distinctive traits in an earlier post. When a friend went to New Zealand for a visit during the holidays, I asked him to get a picture of a tuatara if one came his way, and he obliged.

Tuatara at a North Island, NZ, zoo.

Tuataras are also of interest with regard to the ” species problem”, which Jerry recently addressed with respect to how many species of elephants there are (with follow-ups here and here). Ernst Mayr defined species in 1942 as

Species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such group.

This definition, known as the biological species concept, is the one Jerry argued in favor of in his posts (and more extensively in Speciation, his book with Allan Orr). Through most of the 20th century, a single geographically variable species of tuatara, Sphenodon punctatus, was recognized. In 1990, on the basis of morphological and, primarily, allozyme differences, Charles Daugherty and colleagues argued that a second species, S. guntheri, occurring on islands in eastern Cook Strait (see map), should be recognized. (Allozymes are proteins which are different alleles at the same genetic locus, and which are usually distinguished by protein electrophoresis.)

Distribution of tuataras, from Wikipedia. Circles, Sphenodon punctatus; squares, Sphenodon guntheri.

At the time, this bothered me, as I saw it as an application of the old morphological species concept, extended to genetic data: if you can tell them apart, they are different species. This is also what Jerry argued against in the case of elephants: an arbitrary amount of morphological or genetic difference, or inferred time of separation based on the amount of genetic difference, is not a sound basis for a species concept.

Recently (2010), however , further studies of tuataras have been made, including study of their DNA, and the authors of this work conclude that, as had been held earlier, a single geographically varying extant species of tuatara should be recognized (the status of the extinct tuataras from the New Zealand mainland is still up in the air). So we’re back to S. punctatus as the sole surviving species in the Sphenodontida.

This turnaround in tuatara taxonomy is also a nice example of something Jerry considered in a previous post: scientists changing their mind in the light of new evidence, and not being shy about saying so (something which, of course, should not be rare). Two of the authors of the 1990 resurrection of S. guntheri, Charles Daugherty and Jennifer Hay, are also authors of its 2010 sinking.

If you would like to sample more things tuatara, Hillary Miller, a post-doc at the Allan Wilson Centre for Molecular Ecology & Evolution in New Zealand, has been running, unbeknownst to me at the time of my initial post, an interesting series of posts on tuataras at her blog, The Chicken or the Egg.  (Allan Wilson a New Zealander who was a graduate student and later professor at Berkeley, was a pioneer in the application of biochemistry to evolutionary questions.) See also Victoria University of Wellington’s Tuatara Biology page.

______________________________________________________________

Daugherty, C.H.,  A. Cree, J.M. Hay & M.B. Thompson. 1990. Neglected taxonomy and continuing extinctions of tuatara (Sphenodon). Nature 347:177-179. (abstract)

Hay, J.M., S. D. Sarre, D.M. Lambert, F.W. Allendorf & C.H. Daugherty. 2010. Genetic diversity and taxonomy: a reassessment of species designation in tuatara (Sphenodon: Reptilia). Conservation Genetics 11:1063-1081. (abstract)

Tuataras in the news

November 23, 2010 • 1:17 am

by Greg Mayer

Tuataras are in the news today, although there really isn’t that much new about them. In fact, as Natalie Angier points out in the New York Times, they are transparently Triassic in aspect, as the following picture, of a tuatara named Henry, will attest.

Henry the tuatara, from Wikimedia.

Angier provides a review of various interesting aspects of tuatara biology– they live a long time, reproduce slowly, eat giant orthopterans, are nearly extinct, etc. What’s most interesting about them is that they are the sole living members of one of the four major groups of extant reptiles, the Sphenodontida (an order in the Linnaean hierarchy of ranks, the other reptile orders being turtles, crocodiles, and snakes+lizards); and they are found only in New Zealand, where they are restricted to a few offshore islands.  (They have recently been transplanted back to the mainland of New Zealand, whence they were extirpated centuries ago by introduced rats.)

Though they look much like lizards (iguanas or agamids in particular), and were thought to be lizards when first discovered, they are in fact not lizards, as anatomical examination reveals. They have a primitive type of skull, termed fully diapsid, which means the cheek region of the skull has two complete openings surrounded by bone, and they have at most a rudimentary hemipenis (the distinctive double copulatory organ that characterizes snakes and lizards).

Tuataras are a good example of an older group surviving on an isolated land mass, something typical of old islands like New Zealand, which separated from other parts of the former southern supercontinent of Gondwana around 80 million years ago. Tuataras had been spread about the globe during the Mesozoic (Age of Reptiles), but survived only on New Zealand.

It is distressingly common to see tuataras described as “dinosaurs”, but they are no such thing. They lived during the time of the dinosaurs (and have changed relatively little since, earning them the sobriquet “living fossils”), but their closest relatives are the lizards and snakes, together with which they form the larger reptilian group known as lepidosaurs. Dinosaurs closest living relatives are birds, which, indeed, are perhaps best thought of as actual dinosaurs themselves.