Tuatara

New Zealand was separated from the rest of the world over 100 million years ago. The Tuatara "lizard" has survived all that time.  It is not really a lizard.
The Kiwi, a flightless bird, is a symbol of New Zealand. However, Tuatara is an even more primitive and distinctive animal than Kiwi. 

Tuatara heaven.

Tuataras survived because no predators invaded New Zealand. Terrestrial mammals  failed to cross the Tasman Ocean, which separated New Zealand from Australia by opening about 90 million years ago. (See tectonics section). Tuataras are unusual reptiles, since they like cool weather. They do not survive well over 25 degrees centigrade but can live below 5 degrees, by hibernating in burrows. New Zealand climate was just right. 
Then humans arrived and introduced kiore, dogs, ferrets, pigs and cats...
Tuatara now only lives on predator-free outlying islands,  but can be seen on the mainland, in "protective custody."  The best place to find them is at the Invercargill Museum where a small colony of live reptiles lives in a small bush setting, behind glass. The tuataras are reproducing, which is good evidence they are enjoying the Invercargill environment (although they get a bit of help from oxytocin injections). 

Photography by John Wattie.

Tuataras do not live in lovely forest like this any more.
The Maori rat (Kiore) made it impossible to live on the mainland.
This whole picture is a cheat - a captive Tuatara melded with a misty, Whirinaki Forest background.
Nature photographers are not supposed to do that - unless they are honest and let you know it happened.
So, this is how Tuatara would have looked, before humans messed up the mainland environment.
                  

Two Species

Genetic testing has shown there are two species of tuatara: Sphenodon Punctatus and S. Guntheri.
There are also DNA subspecies, but lets not get involved with all that.

Burrows

Tuataras live separate from each other in well defended burrows. Sea-birds: petrels, prions and shearwaters, sometimes share tunnels with the reptiles. This is not safe for the birds, for wily Tuataras are partial to eggs and chickens in spring time.
Perhaps Tuatara tells the birds stories on rainy nights about him being their ancient ancestor and having every right to live with them.

Primitive reptile on the line to dinosaurs and birds.

Tuatara's relatives were the beak headed reptiles (Rhinocephalia). These spread all around the world 200 million years ago, but died out 100 million years ago. Only Tuatara survived to become  a "living fossil". Tuatara (Sphenodon) is often used by zoologists as an example of about as basic a reptile as they can find. "The diapsid reptile Sphenodon is the most unspecialised living amniote." The evolution of both reptiles and birds can be described starting from tuatara anatomy. This does NOT mean tuatara is the common precursor, just that comparative anatomical diagrams of reptiles and birds can start conveniently with this animal. The evolution diagrams showing a Sphenodon type of primitive reptile changing into a bird are the work of Svend Palm. Click on the picture to reach his fascinating web site dealing in considerable detail with evolution of reptiles and birds and the origin of flight.

Svend Palm's diagrams converted to a changing GIF file.

Teeth

Tuataras emerge from burrows, often at night, to eat any animal they can: mostly insects such as wetas, also worms, slugs and millipedes. Tuataras are too lazy to chase their prey. They just sit and if anything small is silly enough to pass by, Tuatara suddenly snaps it up. They have a  powerful bite and can hold on for long periods. Adult tuataras also enjoy eating young tuatara. The children emerge in daylight, when adults are often sleeping, which saves them from a cannibal death. Lower teeth fit into a groove between two rows of upper teeth. The teeth are actually made of bone and fastened to the outer surface of the jaw bone. Snakes' teeth are like this too (acrodont). Old tuataras are often edentulous and just eat with their jaw bones, like old people who have lost their false teeth. Loss of teeth is very serious for carnivores, like lions and is often a death sentence. Man-eating tigers in India have often lost teeth and cannot kill their faster, normal prey any more. When eating slugs, teeth are not essential and so old Tuataras get by very well. Lizards have plurodont teeth, supported by  a shelf of bone. This is one of the reasons tuataras are not lizards. Crocodiles have thecodont teeth, which are set in the bone. Humans also  have thecodont teeth sitting in sockets.

Tuatara: mouth Tuatara in 3D: red/cyan anaglyph: Click for bigger version

Reproduction

The female buries up to 19 soft shell eggs in soil, but not often.
Life is slow in the cold blooded reptile world and egg laying occurs about once per 4 years.
Even laying in soft soil is a contested activity, for other females may dig up the eggs to lay their own. No interest is taken in the eggs, which are left to hatch by themselves just over a year later.
Males are bigger than females and have bigger spines down their backs. "Tuatara" apparently means "old spiny back" in Maori. Males can mate every year. Females taking 4 years is a bit frustrating for them. So males fight vigorously over receptive females, and often show combat scars. The winning male  inflates his throat and raises his spines while slowly circling  the lady tuatara, lifting his body up and down in a comical fashion with each step. Eventually the girl nods to indicate she is impressed and he is acceptable for father of her eggs. The juveniles mature slowly over 9 years (in captivity) to 20 years (in the wild). Tuataras live for 60 to 100 years.
     These ancient reptiles are like modern humans in life span and aggression
           - but will humans last over one hundred million years?

Gender

The sex of Tuataras is decided by soil temperature around the eggs.
Warm soil causes males, cool soil leads to females.
Other reptiles show this peculiarity too (crocodiles, turtles).
Most other animals have gender decided by X and y chromosomes.

Third eye

Tuataras have three eyes, but the third eye is only tiny. It grows on top of the head, under the skin in adults, and has a retina with nerve connection to the pineal. The pineal gland, in the middle of the brain, produces melatonin; which influences sleep and hibernation. The amount of light falling on the third eye may trigger these biological cycles. There is a tiny extra hole in the skull for the third eye: called the parietal foramen (although it is in the middle). We will review the big temporal foramina shortly, since they are not eye sockets.
Some scientists say the third eye has no function at all.
Tuataras hibernate - or at least are dormant in their burrows in winter. On a warm winter day, they will come out to enjoy the sun. This seems more a function of temperature than of light (since they live underground). Maybe the third eye has little to do with hibernation after all?

Diapsid skull

From Kardong, 1998

The "simple" form of skull just has two big holes in its side, which are for the eyes. Turtles have anapsid skulls like this and were thought of as "primitive". Zoologists now suspect that is a mistake, because being easier for artists to draw a turtle's skull does not mean turtles are low on the evolutionary chain.

The next skull is synapsid, with one hole low in the temporal area. Mammals, including humans, have this arrangement and so it is far from primitive.

Modern reptiles, apart from turtles, are diapsid. They have two temporal holes behind the eye holes, giving even more bone for attaching the big jaw muscles. Tuataras show this complex arrangement very well and their skulls look like baskets as a result of it. No wonder they can bite hard. 

The attachments for biting muscles are: Two bone arches, plus the side of the little brain box, plus the struts joining the arches. The brain box is little, because tuatara is not very clever and most of tuatara's skull is for eating, not thinking.

"Basket heads", with big holes in the bone reduce weight. Dinosaurs were very successful reptiles who developed light, hollow bones and needed a light weight, diapsid head. That is where tuataras get the reputation of being related to dinosaurs.

The bone arches behind the eyes have the jaw closing muscles attached. The arches bulge outwards slightly so the muscles have room to thicken as they contract.

It is said the jaw elongated when reptile precursors, living in water, developed an appetite for big fish and had to open their mouths wide. The long nose was also useful for poking out of the water to breath. (Crocodiles evolved from these). But a long jaw is harder to close and so the powerful biting muscles needed the bone arches to attach them to the skull.

 Pre-reptiles had to develop lungs from gills, to breath air rather than water, before emerging onto land as amphibians. Later they had to develop eggs that could survive out of the water, by having an amnion. Only then could they live separate from water and stop being amphibians. Tuatara eggs have an amnion.

Humans nearly have the tuatara skull arrangement. Thick, very strong fibrous tissue runs from the top of the zygomatic arch up to an arching ridge of bone on the side of our big brain box, so covering the temporal muscle. The fibrous sheet is not there as a protection, but acts as an extra muscle attachment. Temporal muscle fibres are stuck very firmly to this membrane (temporal fascia). In the case of  tuatara, part of this temporal fascia has solidified into bone, making the second arch, and turning the reptile into diapsid, while we are only synapsid.  Our single zygomatic arch has the powerful, jaw closing, masseter muscle attached to it.

Transformation sequence from Tuatara skull to a Bird skull

NB:
This is not evolution, it is just a zoological concept from primitive reptile (such as tuatara) , through dinosaur to bird
by Svend Palm.

Some reptiles are classed as diapsid but actually show the two skull openings very poorly or not at all, which shows how counting holes in the head is an intellectual exercise for zoologists rather than a practical thing for simple folks like us.  Birds are classified as diapsid but some people say the holes are actually different and most of us can't even see any holes in a bird skull. The bony arches, which define the holes for casual folk are not important to zoologists, only the holes themselves. Holes with no donuts. Don't you feel the subject has been simplified by this concept?  Forget about euryapsid skulls, they are a primitive marine dinosaur condition.    Tuatara skull replica

The only reason I brought all this confusion up is to show you:  how nice a fenestrated tuatara skull looks,  how its brain box is much smaller than its head  and why the university people wisely call tuataras "diapsid".  Many of us bird-brains need this knowledge like we need another hole in the head...

Sprawling tuatara, resting on his tummy. Run your mouse cursor over him to see the head turn.

John Wattie photography

Lizards have legs splayed sideways and can't get off the ground. They move by wriggling, with just a little help from the limbs. Some lizards have no legs and slither around like snakes. This is closely related to the swimming motion used before the early reptiles emerged from a life in water.

The tuatara skeleton shows how the pelvic and shoulder girdle articulations allow the animal to elevate its tummy off the ground. Not that he does this often - too tiring. Much of a Tuatara's life is spent sprawling. Svend Palm's diagram.   The difference in the pelvis and shoulder girdles is another reason the "Tuatara Lizard" is not a lizard!

Pelvic Girdle The pelvic girdle changed more extensively. Sphendon has a sprawling gait, but many dinosaurs walked on their back legs. In dinosaurs the front legs became fairly useless and often atrophied.  For diagrams showing the hips and shoulders of tuatara and how they changed in birds see Svend Palm.

Shoulder girdle In the reptilian line leading to birds, the front legs turned slightly to allow tree climbing, by grasping the trunk. This clasping motion was a short step to the flapping motion needed for wings. The pectoral girdle in birds seems to have hardly changed from primitive reptiles (Sphenodon) to modern birds. The clavicles and sternum fused into a furcula, giving a solid base for the powerful pectoral muscles needed for upper limb clasping and later wing flapping.

Here is a New Zealand lizard (a copper skink). He can lift his head, but his tummy is still on the ground. (Photograph by John Wattie)

DigiMorph of sphenodon punctatus: University of Texas in Austin uses Computed Tomography to build digital models of skeletons, including the Tuatara. This CT model is by  Jessie Maisano, who kindly gave permission to use the picture. The reptile bone names have been added by John Wattie. Note how they are different from human anatomy names. For comparison, a bird skull is also provided from DigiMorph to show the difference from reptiles. Another New Zealand icon, it is the extinct Moa skull, which has the holes but not the hole margins...  Pitch yaw and roll movies are provided, if you click on the Moa to reach the DigiMorph web site. A high speed connection helps to download the quick-time movies, which give an excellent 3D impression.            The industrial CT scanner used in Austin had a slice width of 20 microns. This is much less than the 700 microns used in high resolution medical CT scanners but is needed to show fine detail in small bones. In a similar fashion, John Wattie and Tim Sheehan have used a medical CT scanner to show an aortic aneurysm in 3D.  http://nzphoto.tripod.com/animal/tuatara.htm