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I've been a Canberran since moving here from Adelaide on the first day of 1980. I now live in suburban Duffy with my partner Louise Maher, ABC 666 radio and on-line journalist. Among my early memories is following Sleepy Lizards (Shinglebacks) around the paddocks north of Adelaide, guarded by the faithful bull terrier. I have always been passionate about the natural world, trying to understand how it works, how the nature of Australia came to be, and sharing those understandings. My especial passions are birds, orchids and mammals. I am now a full-time naturalist, running bush tours, writing books etc, doing consultancies, presenting a regular radio slot on local ABC, chairing a government environment advisory committee and running adult education classes. I was awarded the Australian Plants Society Award in 2001 and the Australian Natural History Medallion in 2006, both for services to education and conservation. As part of my fascination with our Gondwanan origins I've been running tours to South America for the past few years.

Friday, 4 January 2013

Australia; a backwater for backfangs

We have long known that Australia is fundamentally different from the rest of the world with regard to its mammal fauna and its flora. More recently we've accepted that the majority of our Passerine bird fauna is also uniquely Australian. However an aspect of our biota that is not often discussed in this regard is that the composition of our venomous snake fauna is entirely different from the rest of the world. As ever, we can explain it by seeking to understand the bigger picture. 

Some background to snake evolution first. The oldest snake fossils appear to be some 120 million years old, from Algeria. The question has been vigorously debated, but the weight of evidence seems to be swinging towards a burrowing lizard as the ancestor. Snake bones are small and fragile, so the fossil record is not as strong for snakes as it is for most other vertebrate groups, but for some 80 million years python-like or boid-like animals dominated the snake world. Then, around 35 million years ago a group of smaller, quicker snakes arose, though played only a minor role until the world began to cool about 20 million years ago, a situation which didn't suit the boids. From then these Colubrids began to dominate, until now they comprise some two thirds all the world's snakes, over 1900 species. Indeed in much of the English-speaking world they are referred to as 'typical snakes' - not in Australia though. Along the way (perhaps 15 million years ago) they developed large rear teeth which had grooves down the outer edges, along which ran modified saliva that acted as pacifying venom on prey which objected to being eaten. 
Unidentified colubrid, Manu National Park, Peruvian Amazonia.
This fellow was encountered on a river beach at night. Any identification help gratefully received!

Tree Snake, Limbe Botanic Gardens, Cameroon.
I think this one is Thrasops batesii, but again advice welcomed.
Not long after the venomous back-fanged Colubrids arose, a new group also appeared on the scene. In this group the venomous fangs moved to the front of the jaw, reduced in length and closed around the venom-delivering grooves, to form hollow hypodermic syringes. These Elapids were the ancestors of most of the most venomous living snakes; cobras, mambas, coral snakes, sea snakes - and most of the familiar Australian species, such as brown snakes, taipans, copperheads and black snakes, among which are the world's most venomous species. However, there are only about 320 species, roughly 10% of the world's snakes.
Tiger Snake Notechis scutatus, Twin Creek Reserve, Western Australia.
 The situation in Australia is dramatically different from the rest of the world. Here, the 120 Elapids represent two thirds of the snake world, while there are only 10 Colubrids, the best known of which are the Brown and Green Tree Snakes.
Green Tree Snake Dendrelaphis punctulatus, Iron Range, north Queensland.
The answer to this apparent conundrum is basically down to chance. Both groups arose in the Northern Hemisphere while Australia was isolated; it was the Elapids which made their way here when Australia got close enough to Asia, and in a continent empty of competition they spread to an extent that hadn't been possible elsewhere. By the time Colubrids made the journey, most of the good niches were gone.

The most recent group of snakes to arise, the Vipers, appeared about 10 million years ago. They have very long front fangs, to inject their venom deep into prey. Indeed, the fangs are so long that they must rotate back, to fold away along the roof of the mouth. They haven't yet found their way to Australia.
forest viper, Bokassa Mountains, Cameroon.
Again, I'm afraid I can't provide identification.
So, Australia, the land of marsupials, of banksias, of honeyeaters - and elapids.

3 comments:

Susan said...

Fascinating! And I love your Tiger shot. We have half a dozen Colubrids (one very common) and a single Viperid species (very rare) where I live in France. By far the most common search criteria that finds my blog is some version of 'are there snakes in france' and people are clearly convinced that their pets and small children are at risk. The locals love to warn incomers about the Vipers (and half of them can't tell the difference between a Viper and a Colubrid, so all too often the warnings are delivered in all seriousness). I have a lovely Western Whip Snake Heirophus viridiflavus that has set up home in my orchard -- handy supply of Wall Lizard lunch living in the woodpile. Sorry I can't shed any light on your African beauties.

Ian Fraser said...

Thanks for that Susan. Prompted by your comments I've now learnt more about French snakes; I hadn't realised there was such a relatively rich fauna. Partly I'm sure it's because I was told all about Vipers but nothing else while I was there. I spent some time (30 years ago!) at a Lycee Agricole near Limoges. My hosts in town, where I spent weekends, told me how people took an anti-venom kit on picnics! Having grown up with Eastern Browns and Tiger Snakes, I must have looked astonished (I blame my youth for such rudeness) - the danger of an allergic reaction to an unsupervised antibody injection seems greater to me than that of a Viper bite - but they were adamant. That fear, in nature-focussed people, seemed quite disproportionate.

Susan said...

Vipers (a different species to the one we get) are relatively common around Limoges. Some Australian friends who live down that way had to discourage a family of vipers from living in an earthenware pot by their letter box a few years ago I remember. I have never heard of anyone carrying anti-venom! I would look astonished too!! I don't think anyone has died from adder (the English name for vipères< bite in France since the 70s (I'd have to look it up to be sure though). It's very very rare for people to be bitten, although dogs and cats occasionally cop it.