animals · Creature Feature · Life · nature · Science & Technology

CFHW Creature Feature – Tuatara


Reading a mini fact file in Tori’s copy of The Week Junior a while ago, I learned a tiny bit about an unusual New Zealand lizard, the Tuatara, and found myself looking further into them because they sounded pretty interesting.

Several pages of handwritten notes later a Creature Feature was planned, and here we are.

By Sid Mosdell from New Zealand – Tuatara, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=70735190

The Tuatara is endemic to New Zealand, and once lived happily throughout the mainland, however they are now only found on 32 offshore islands (plus a very small population that was released in the mainland nature reserve Zealandia).

Their name, Tuatara, derives from the traditional Māori language and means ‘peaks on the back’ – after their cool dinosaurish spine spikes.

Talking of dinosaurs, the Tuatara are the last remaining living species of the reptilian order Rhynchocephalia, which was once globally dominant. You know, back when dinosaurs roamed the earth.

Being the last one of a whole natural order is pretty cool in and of itself, but the more they are studied, the cooler they become.

They are in fact the coolest lizard of all – literally.

They have the lowest body temperature of any reptile – fluctuating between 5.2ºC and 11.2ºC, whereas most reptiles have a core temperature of around 20ºC.

This means that Tuatara can remain active during much cooler weather than other reptiles, but also means that temperatures over 28ºC are often fatal to them. (I am beginning to think they might be my spirit animal – temperatures that high make me want to curl up in a corner and die, too.)

The Tuatara is the largest reptile native to New Zealand, with males getting up to 61cm long and weighing just over a kilo.

They vary in colour, from greenish brown and grey, to orangey-red, sometimes with yellowish patches. Their colour changes a bit as they grow and shed their skin.

Their diet mostly consists of insects and spiders, but they will also eat any frogs, small lizards, bird eggs or small chicks that they run across… and yes, small lizards includes juvenile Tuatara. They are apparently not adverse to a bit of cannibalism. Isn’t nature lovely?

Their average lifespan in the wild is about 60 years, but in captivity they have lived well beyond 100 years old, and have still been breeding at that point, too. Some scientists even think that they might live as long as 200 years if given the chance!

It is thought that their longevity might be to do with the fact that they have the slowest growth rate of any reptile – it takes them 35 years to become fully grown.

Henry, a captive Tuatara still reproductively active at 111 years old.
Photo by KeresH – Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=4514923

Okay. You might want to take a deep breath before the next section – I fell into a recent scientific paper and there were some big words and very long sentences in it. I have mostly sat and worked out what the simple version of all the Science is, and translated the mind-bending stuff into simplified facts – but there may still be some big words here and there! (And I may have got stuff wrong, though I did try and double check everything. It has all been simplified hugely because I am not a scientist, but I will link to the paper at the end if you want to check it out!)

The Tuatara has a genomic architecture that is unique in the animal kingdom – it has a mixture of features that have previously been viewed as characteristics of either mammals OR reptiles. Never before have they both been found in one animal.

It also has a spine shape that is more like a fish or amphibian – a feature unique to the Tuatara amongst all amniotes. This is thought to be because it is possibly the most unspecialised living amniote – its heart is very primitive and its internal structure is a lot like amphibians. Implying that it evolved far enough to become a reptile and then just sort of stayed there. It is the slowest evolving Lepidosaur yet analysed.

Tuatara join turtles with the most primitive hearing organs among the amniotes – they don’t have eardrums or even ear holes!

They make up for their lack of ears with their eyes though – they have three.

Yup. Three. I’ll give you a minute to scroll back up and squint at the photos and argue with me before explaining…

The two main eyes can focus independently and have excellent vision – quite probably in colour – they can see in daylight and at night, too.

The third eye, which is called the Parietal Eye, is found on the top of their head and you can only see it in hatchlings (until they are 4-6 months old) which is why you couldn’t see anything when you went to look at the photos.

This weird third eye has a lens, a parietal plug which resembles a cornea, a retina, and nerve connections to the brain. See, totally an eye, even if you can’t see it with your own.

Scientists haven’t quite established what the Parietal Eye is for yet. They think it may help to absorb UV rays to make Vitamin D, help the lizard to determine light/dark cycles in their environment, and/or help the lizard with thermoregulation.

See, wayyy more useful than ears. Maybe.

Juvenile Tuatara
By de:Benutzer:Hase – de:Bild:Brückenechse.jpg, GFDL 1.2, https://commons.wikimedia.org/w/index.php?curid=589780

In another attempt to take a title of ‘unique’, the Tuatara has a tooth arrangement not seen in any other reptiles. Their upper jaw has two rows of teeth and their lower jaw just the one. This bottom set of teeth sits neatly in-between the top two – apparently this neat system isn’t one that anything else has, even if they also have multiple rows of teeth.

When a Tuatara lays eggs, the sex of the offspring is decided by the temperature of incubation. This is known as Temperature-Dependent Sex Determination (TSD) and is quite common in the natural kingdom.

Normally the ‘hot’ eggs are female and the ‘cold’ ones male, HOWEVER, as you may have worked out by now, the Tuatara like to be different, so their system is backwards compared to most other animals with TSD.

If the egg is incubated at 22°C the juvenile is 80% likely to be male, if it is incubated at 20°C then it is 80% likely to be female. 21°C is a 50/50 chance of either, and 18°C means 100% of the babies will be female.

Told you these little guys were pretty awesome!

The Tuatara have been protected by law since 1895, but they are threatened by a number of things, which is why they no longer survive on the mainland.

Habitat destruction is an obvious one, and also poaching of both the lizards and their eggs. Although that has lessened in recent years.

One of their biggest threats comes from rats (and also mice to some extent) – these rodents are not native to New Zealand (NZ has no native mammals at all) and their introduction caused the Tuatara population to suffer massively. They eat their eggs and can even kill juvenile lizards.

Luckily, the rodents haven’t moved to many of the islands, so the Tuatara are safe there.

Well, there you have it. The Tuatara.

I hope you enjoyed learning a bit more about this interesting creature – if you have any suggestions for a future Creature Feature please let me know! I enjoyed falling down the rabbit hole of research for this, even if I did have to break the scientific papers down into chunks to figure them out!!

My Sources:

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