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grizzly
42595.  Mon Jan 02, 2006 3:13 pm Reply with quote

Mostly harmless wrote:
Komodos have one very non-lizard characteristic: they taste the air like a snake, and this allows them to hunt at night. I keep reptiles and, although the lizards lick, they don't scent the air in the way that snakes do. As far as I know, only Komodos do that. Komodos also share one characteristic with Tokay geckoes: it's not the bite that kills, it's the bacteria in the mouth, living in the saliva.


There's been a recent discovery that will surprise you about this. Most lizards are venomous. It was thought that swellings from lizard bites were caused by infections by bacteria just because it was the prevailing belief. When it was actually tested (research was only released recently) it turned out that the swellings were caused by venom. I don't know if this is true of the Komodo though.

Quote:
PEOPLE bitten by their pet lizard can suffer a painful swelling and prolonged bleeding. Infection by bacteria in the lizard's mouth was always assumed to be the cause, but it turns out that many lizards, including some that are common pets, are actually venomous. The finding is rewriting the evolutionary family tree of lizards and snakes.

"To find the classic rattlesnake toxins in the bearded dragon - a hugely popular pet - was a huge surprise," says Bryan Fry at the University of Melbourne, Australia, who led the work.

Venom was considered the preserve of advanced snakes and just two species of lizard, the gila monster (Heloderma suspectum) and the Mexican beaded lizard (Heloderma horridum). It was thought that these lizards evolved the ability to produce venom independently of the snakes.

Now Fry's team has found that two other groups, the monitor lizards and iguanians, which includes iguanas and chameleons, are also venomous. They share nine of the toxins produced by snakes, but make others that have not been identified before (Nature, DOI: 10.1038/nature04328).

In a related paper published in the journal Comptes Rendus Biologies this week, Nicolas Vidal and Blair Hedges of Pennsylvania State University in University Park, two of Fry's co-authors, dub this new family of toxic reptiles Toxicofera. And they suggest a complete overhaul of the whole classification system is needed. "These papers threaten to radically change our concepts of lizard and snake evolution, and particularly of venom evolution," says Harry Greene, a herpetologist at Cornell University in New York.

DNA analysis by Vidal and Hedges suggests that the closest relatives of snakes are iguanians, of which there are about 1440 species, and anguimorphs, a group that includes the two lizard species already known to be venomous, and monitor lizards. This means iguanas and their close relatives probably evolved much later than was previously thought and suggests that venomous lizards and snakes are descended from a common ancestor that lived around 200 million years ago. This pushes back the evolution of venom by 100 million years, coinciding with the rapid spread of small mammals.

The paper also suggests that the method of classifying reptiles that has been used for the past 80 years, which is based partly on the texture of the tongue, should be changed. It is an unreliable method for inferring evolutionary relationships, Hedges says. Characteristics such as venom production and egg teeth, which hatchlings use to escape from their egg, are more useful, he says.

“To find the classic rattlesnake toxins in the bearded dragon, a hugely popular pet, was a huge surprise”But how could venom production in these lizards have been overlooked for so long? Fry suggests that blaming bacteria had become dogma. Komodo dragons, for example, are monitor lizards that eat carrion, and their mouths are blooming with bacteria. "It was the classic red herring," he says. Also, while the toxins produced by these lizards might kill their usual prey, they have less potent and so less noticeable effects on people.


From New Scientist 19th November

 
djgordy
42598.  Mon Jan 02, 2006 3:15 pm Reply with quote

Ciggywink wrote:


Ouroboros is also the birth name of Dave Lister, so named because he was his own father and abandoned his own 6 month old self in a cardboard box under a pool table.
.


"The Worm Ouroboros" is an early 20th Century fantasy novel by E.R. Eddison. You can read it on-line here:

http://www.sacred-texts.com/ring/two/index.htm

It is pretty heavy going because of the arcane language but well worth the effort.

 
Mostly Harmless
42606.  Mon Jan 02, 2006 3:29 pm Reply with quote

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Mostly Harmless
42608.  Mon Jan 02, 2006 3:34 pm Reply with quote

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gerontius grumpus
42609.  Mon Jan 02, 2006 3:34 pm Reply with quote

gerontius grumpus wrote:
When was the last recorded sighting of dragons in England?



Just to keep this one going, it doesn't refer to mothers, mothers in law or oversize monitor lizards.

 
Psychosis_Safari
42613.  Mon Jan 02, 2006 3:38 pm Reply with quote

When was the first recorded sighting of dragons in England?...

Apologies if someone has posted anything to suggest there was one...but you can;t have a last until you have had a first, surely?

 
grizzly
42616.  Mon Jan 02, 2006 3:49 pm Reply with quote

Mostly harmless wrote:
I'm also sceptical about the chameleons, given the way they catch prey. I've kept them many times and they simply aren't geared to bite; they crunch down on prey already secured by tongue, so the prey's death is a fait accompli and poison would again be redundant. They're very pedestrian creatures and not prone to bite attacks, they use the gape as a warning.


I understand that you would be sceptical. Certainly this research is so new that it is not yet known as to how the venom is used (duck-billed platipii (sp) famously are venomous with no known use of their venom). What we should note is that the quantities of venom are firstly too small to cause any great toxic affect to a person (hence as it says in the article, the toxic affect has gone unnoticed, most likely associated with bacterial infections).

 
Mostly Harmless
42620.  Mon Jan 02, 2006 3:56 pm Reply with quote

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mckeonj
42622.  Mon Jan 02, 2006 4:04 pm Reply with quote

I think the last recorded sighting of a dragon in England was the Lambton Wurrum. Perhaps the Lady Lucinda could enlighten us further on that topic.

 
grizzly
42627.  Mon Jan 02, 2006 4:18 pm Reply with quote

I don't believe that the chameleons venom is intended for anything the size of a person's finger. The purpose of venom as I say is not known. It could be used in catching wild prey (although unlikely). It is possible that it would have a purpose in (pure wild speculation here) reproduction. I know that males of several venomous species use their venom to subdue the female during mating.

Alternatively it could be an evolutionary oddity. True it is impossible to evolve a trait when it provides no advantage in natural selection but traits can be less easily lost by a species if it has eveolved from a species that originaly had that trait (as is the case with chameleons). It is possible that even if the chameleon has no use for its venom that it wont lose it even after very lengthy periods simply because the genetic mutation hasn't occured that will stop the chameleon producing venom. If such a mutation did take place it wouldn't necessarily spread though the population and could itself place the chameleon at a disadvantage in natural selection.

 
Flash
42628.  Mon Jan 02, 2006 4:20 pm Reply with quote

I went to Komodo once, many years ago, and patted a Komodo Dragon on the head as I hadn't bothered to do any research in advance and didn't know about the bacteria-infested saliva business, which is apparently extremely nasty. Luckily this was in the morning, and apparently cold-blooded creatures are very sluggish early in the day, because they rely on ambient heat to get them going. So I got away with it.

 
grizzly
42630.  Mon Jan 02, 2006 4:24 pm Reply with quote

Flash wrote:
I went to Komodo once, many years ago, and patted a Komodo Dragon on the head as I hadn't bothered to do any research in advance and didn't know about the bacteria-infested saliva business, which is apparently extremely nasty. Luckily this was in the morning, and apparently cold-blooded creatures are very sluggish early in the day, because they rely on ambient heat to get them going. So I got away with it.


very lucky indeed

was it a wild one or in captivity on the island?

 
Flash
42632.  Mon Jan 02, 2006 4:30 pm Reply with quote

Wild. In those days Komodo was quite inaccessible; you had to go to Flores and find a fisherman who would take you there. Then you went into the village and haggled for a goat, bought it and led it out into the woods and tied it to a tree and waited for the dragons to turn up for breakfast.

Then, if you were a complete banana, you patted them on the head.

 
Mostly Harmless
42633.  Mon Jan 02, 2006 4:32 pm Reply with quote

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Flash
42634.  Mon Jan 02, 2006 4:35 pm Reply with quote

Now she tells me.

 

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