Fascinating Animals: Tuatara

800px-Sphenodon_punctatus_in_Waikanae,_New_Zealand

The animal in this picture is not a lizard.

No, this isn’t some Magritte-esque ceci n’est pas une pipe kind of philosophical thing — I’ve been posting too many philosophical ramblings lately, and I’m trying to get back into posting more regular updates about not-my-personal-drama kind of things.

The animal in the above picture is called a tuatara (genus Sphenodon), and it is one of my absolute favourite animals in the world.  They are found only in New Zealand (I suspect that they may feed occasionally on hobbits), and they are incredibly ancient.  Tuatara are the only surviving members of order Rhynchocephalia, which flourished around 200 million years ago (back in the late Triassic/early Jurassic period).  This is about the time that the first mammals (some of our early ancestors, small shrew-like critters that bore little resemblance to us) were just evolving.  By that point, rhynchocephalians already looked pretty much like their modern ancestors do — check out this fossil of an extinct species from the order:

Derasmosaurus_pietraroiae

Tuatara are distantly related to modern squamates (lizards and snakes), as well as to archosaurs (the ancestors of dinosaurs and birds), which makes them very interesting to scientists — because the two groups diverged so many millions of years ago, studying tuatara may be able to tell us a lot about how modern lizards, snakes, birds, and crocodilians evolved.  Although they look similar to lizards on the outside, tuatara possess many traits that show just how ancient they are:  their brains are more similar to those of amphibians than to those of reptiles; their lungs are single-chambered and don’t have bronchial tubes; they have a remarkably well-developed ‘third eye‘ under the skin of their foreheads (something which most modern animals have lost to evolution); they have no external ear structures and their internal ears are incredibly primitive; their vertebrae resemble those of fish and amphibians rather than those of other amniotes; they have an acrodont tooth structure (their teeth are fused to the bones of their jaw rather than being separate structures); and they have sex in the same way as birds, by simply rubbing their cloacas together, because the males don’t have penises.

Unlike most cold-blooded animals, tuatara prefer cool temperatures and will actually die of heat stress if exposed to temperatures much above 80 degrees Fahrenheit for any length of time.  This adaptation to cool temperatures is likely a factor in their longevity — it’s theorized that tuatara could live to be over 200 years old in captivity (although no one knows for sure, because we haven’t been studying them long enough), and even living in the wild (with all the associated hardships and dangers) they commonly live about 80 years.  But because they live for so long, they do their living at a very slow pace:  it can take over a year for tuatara eggs to hatch, and over 30 years for a tuatara to reach its full adult size.

Like many species in New Zealand, tuatara face great risks from introduced predators.  Having lived for so many millions of years on protected islands with few natural enemies, the introduction of animals such as rats and dogs and cats has devastated tuatara populations.  Tuatara are particularly vulnerable because of their slow pace of living:  a year is a long time for eggs to remain undisturbed in a nest when there are hungry rodents about, and a female tuatara is only able to lay eggs once every 3-5 years after she has reached sexual maturity (which can take 20 years to happen).  Like most reptiles, tuatara do not protect their nests or their babies, so unprotected eggs and young are easy prey.  Tuatara are also vulnerable to the effects of global warming — not only do higher temperatures stress them out and cause harm, but their young are temperature-sex dependent:  eggs incubated at lower temperatures will hatch out female, while eggs incubated at higher temperatures will hatch out male.  As global temperatures rise, fewer and fewer females will be hatching.  So even as conservation efforts are seeing success and protection from introduced predators is becoming more stable, there is still the risk of tuatara going extinct in a grand, sad sausage party.

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