Not a lizard, and not a snake - but some of both

Did you know that there is still a species alive on earth that roamed the planet alongside the dinosaurs?

It’s called the Tuatara. The tuatara is the last surviving species of the Sphenodontians, a group of animals that developed and thrived during the upper Triassic – nearly 220 million years ago. If you were to look at it, you might think the tuatara is a lizard – a triangular head, four squat legs with long spiny toes, leathery skin, and a long tail. However, while the tuatara is a reptile, it is equally closely related to both lizards and snakes. It is the only surviving species on earth that fits this description. Other relatives of the tuatara were the beak-headed reptiles (also known as Rhinocephalia), but the rest of them died out 100 million years ago.

The tuatara is sometimes referred to as a living fossil. Despite its ancient origins, the appearance of these animals has not changed very much in the last 200 million years. This means that they can be used to study what their ancient relatives looked liked. Because of this, they are of great interest to scientists who study the evolution of lizards, snakes, and diaspids (the group that includes both birds and crocodiles).

Interestingly, though the overall appearance of the tuatara has remained unchanged for millions of years, it now seems that they undergo relatively rapid molecular changes. By comparing DNA extracted from tuatara bones approximately 8000 years old to modern tuatara DNA, scientists now believe that this animal has the fastest rate of DNA changes ever measured. At an average rate of change of slightly over 1.5 subsitutions per nucleotide per million years, it beats out the previous record-holding fast molecular evolver, the Adelie penguin. The fact that the DNA of the tuatara changes so rapidly, while its overall body hasn’t changed in millions of years, is remarkable.

Tuataras live only in New Zealand. And though I refer to the tuatara as one species, there are actually 2 closely related subspecies of tuataras – S. punctatus and S. guntheri. S. guntheri is also know as the Brothers Island tuatara, and it is extremely rare, much more so than its S. punctatus relative. In reading up on these creatures, I came across a few interesting facts:
-They have the slowest growth rate of any reptile we know of. In fact, they keep growing until the reach about 35 years old, but only attain a final size of 20 inches.
-They can live to be over 100 years old, though their average life span is around 60 years.
-They can hold their breath for nearly an hour.
-They are nocturnal – for the most part. Adult tuatara hunt at night, but young tuatara will hunt during the day. This is because a really hungry adult will eat a young tuatara if it can catch it. In addition, because they are cold-blooded, they will bask in the sun during the day to regulate their body temperature.
-They have an extra eye besides the two in the front of the face. Called the parietal eye, it is found on the top of the head, and is visible only in the very young. After about 6 months of age, it becomes covered with opaque scales and pigment. Its function is unknown, though scientists have suggested it to play a role in circadian rhythms or the absorption of UV light to aid in the production of vitamin D.
-The hearing organs of the tuatara are very primitive, and look very similar to that of turtles. There is no eardrum, or even an earhole. The cells that respond to sound are relatively poorly specialized, and respond only to low frequency sounds.

If you have a few minutes, and want to see some pictures of these cool little creatures, you can check out the website of the Kiwi Conservation Club at:
http://www.kcc.org.nz/animals/tuatara.asp


The image of the tuatara was taken from:
http://www.wpclipart.com/imgpage.html?http:
//www.wpclipart.com/animals/T/Tuatara.png