Animal with three eyes

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