Tuesday, January 18, 2011

About Australian Snakes

The term “reptile” is, in fact, a misnomer.  It is the habit of scientists to group all life-forms in terms of their evolutionary lineage – or if you like, their family tree.  In this way, we can attempt establish who evolved from whom, and who is most closely related to whom.  This branch of science is termed phylogeny.
However, “reptile” lumps together three very separate groups of animals:
  1. the Crocodilia, which includes crocodiles, alligators and caimans
  2. the Testudines, being the turtles and tortoises
  3. 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).
Contrary to appearances, these three groups do not belong to the same evolutionary lineage, and are only very distantly connected.  For example, crocodiles and their kin are much more closely related to birds than to other so-called “reptiles”.  So, never judge a book by its cover
Snakes evolved 120 million years ago.Snakes evolved 120 million years ago.
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.
Australian Scrub Python Morelia kinghorniAustralian Scrub Python Morelia kinghorni
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 
  • Colubridae  
  • Elapidae or proteroglyphs (fixed front-fanged venomous snakes)
Australia does not have any members of the mobile front-fanged venomous snakes, belonging to the families Viperidae (vipers, rattlesnakes and the like) or Atractaspididae (asps, mole-vipers and stiletto snakes), even though the Death Adder has evolved to look and behave in a very similar fashion.  When wholly unrelated species evolve to become alike in this way, it is termed ‘convergent evolution’.
In total, Australia is home to nearly 200 species of snake.

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