Why isn't the tuatara classified as a lizard?

Answer 1

The Tutara belongs to a group of reptiles called lepidosaurs along with lizards and snakes. Dinosaurs are on a different evolutionary branch called archosaurs, which they share with crocodiles. Research in the past thirty years or so has shown that dinosaurs actually had more in common with birds, their direct descendants, than with modern reptiles.

Answer 2

The main reason why tuatara are not classified as lizards are:

* Tuatara have a membranous third eyelid, which is not present in lizards.

* Lizards have external ears, but tuatara lack ears, and have no ear drum, ear holes or middle ear cavity. They do have primitive middle ear bones, but the range of frequencies they can hear is far more limited than lizards.

* Both lizards and tuatara have a parietal "third eye" on their forehead, but it is more developed in tuatara, having a retina, lens and nerve endings. It is still not used for seeing, however, and its purpose remains unknown, though there are numerous theories about it being used to regulate circadian rhythms and temperature.

* Tuatara have two rows on teeth on their upper jaw and one row of teeth on their lower jaw, which enable the tuatara to slice up its food while it is chewing. Lizards' teeth are not arranged in this way.

* Tuatara are unique in that they have abdominal rib-like bones (gastralia) that, while not attached to either the real ribs or the spine, form a protective cage on their abdomen. These ribs then have hooked projections of bone called uncinate processes, similar to those found in birds.

* Unlike lizards, the vertebrae of tuatara are hourglass-shaped.

* Tuatara prefer cooler weather, unlike lizards, which tend to prefer warmer weather.