However, “reptile” lumps together three very separate groups of animals:
- the Crocodilia, which includes crocodiles, alligators and caimans
- the Testudines, being the turtles and tortoises
- and, together, the Squamata (including all lizards, worm-lizards and snakes) and the Sphenodontia (the only living representative being the Tuatara, a unique, dragon-like reptile from New Zealand).
Snakes evolved around 120 million years ago, in the early Cretaceous. Due to their small, fragile skeletons, fossils of early snakes are few and far between, but the latest research indicates that they evolved on land from a burrowing, lizard-like ancestor, which gradually lost its limbs in order to better slip between cracks in the soil. Due to their burrowing lifestyles, the eyes of ancient snakes also became greatly reduced through lack of use; hence modern snakes had to, as it were, re-evolve functional eyes in order to take up life on the surface. For this reason, the eyes of a snake are structurally very different from other animals.
There are approximately 3000 species of snake worldwide. These are divided into two major groups: the diminutive, worm-like blindsnakes, called the Scolecophidia … and all other snakes, the Alethinophidia.
Whilst the blindsnakes do occurs in Australia, they are rarely seen.
All snakes with which people are generally familiar are Alethinophidians, which are divided further into the Henophidia (Pythons, Boas and their kin) and the so-called “advanced snakes”, known as the Caenophidia. Henophidians are regarded as more primitive than Caenophidians, primarily because (a) they retain some vestigial elements of pelvic bones and hind-limbs and (b) they have not evolved any venom apparatus.
The Henophidia contains six families of python-like snakes, only one of which, the true pythons (called the Pythonidae), has members in Australia.
The Caenophidia contains five families, members of three of which occur in Australia:
- Acrochordidae or filesnakes
- Elapidae or proteroglyphs (fixed front-fanged venomous snakes)
In total, Australia is home to nearly 200 species of snake.