The two species of stout-boded tuataras in the genus Sphenodon
are the only surviving members of a group of reptiles that is over 200 million years old. They survive today (little
changed in all those years) on some small islands off the coast of New Zealand. Tuataras have a primitive diapsid skull
(one with two openings in the temporal bone) with a pineal (median) eye on the dorsal surface complete with lens and retina
(although it can't see anything since it's buried beneath the skin). Unlike squamates, male tuataras lack a copulatory
organ (fertilization occurs as it does in birds where the lips of the cloaca are pressed together).
This lizard-like reptile has many interesting features. One is its "third eye," which has a lens and retina but no
iris. In adults, skin thickens over the eye in opaque scales. The purpose of the eye is not known.
Tuataras have a slow metabolism. They breathe about once every seven seconds, but they can go for an hour without a breath.
Perhaps that's why they can live to be more than 100 years old.
Tuataras also take it slow when it comes to breeding. After courtship and mating, nearly 10 months pass before a female
lays eggs. An additional 12 months of incubation are necessary before the young hatch!