How do you guys feel about the Toxicofera hypothesis?

Maybe this is old news but I just found a neat article about an argument for lizard taxonomy, namely the fact that many lizards are venomous but not classified as such (if I’m understanding this correctly), which is Fascinating! I don’t know a whole lot about taxonomy or lizards but I stumbled into it when looking at gila monster information, so for the more informed I’m wondering your opinions and the legitimacy of the paper!


Hmmmm interesting. I was always told that there are only three venomous lizards in the world.

I think this hypothesis has been relatively poorly received overall if I remember, but there are some very dedicated proponents of the idea. It certainly made big headlines, it lends itself to sensationalism, but it also is plausible enough and not completely out of left field.

@elpatitojuan2 I had only known of two! Are we counting Komodo dragon?

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Yup, including komodo. I saw in a documentary many years ago that they were indeed venomous opposed to the theory of killing prey with bacteria.


I feel like people keep going back and forth on this! I heard that it was bacteria as a kid, then (I think related to Toxicofera hypothesis or at least around the same time) that, as you said, it’s venom, and now some people say they are mildly venomous (or not at all) and the bacteria is doing most of the work. Confusing!



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Komodo dragons have been well known to use venom for at least a decade by now. It’s disputed just how powerful it is if I remember correctly, but they definitely do produce it. The bacteria theory is entirely outdated, but a lot of people still do believe it.


Cool, thanks for the info, that definitely clears the picture some! I’d always heard they bite a wound on a living animal repeatedly over days and let it fester, is that true? Is there debate about whether venom plays a role there, if it is true? Or do they kill most of their prey the old-fashioned way, or some other way?

Welcome here btw

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I’m not incredibly well versed in their hunting methods, but from what I know, not purposefully if it does happen - it’s more incidental that if prey manages to escape they’ll often succumb to the venom and be scavenged by the komodo afterward. I haven’t read up on their hunting too much though!

Thanks for the welcome!

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This 2010 paper argues that venom production is the basal state of the suborder Anguimorpha. Many members of that specific branch of Squamata order may have lost their venom over time however.

The Toxicofera clade appears to be active, based on molecular evidence according to Wikipedia:

There is little morphological evidence to support this grouping, however it has been recovered by all molecular analyses as of 2012.[2][3][4]

I see a number of sites saying that iguanas have atrophies venom glands that produce a harmless venom, but they all seem to be using the exact same wording, indicating that they’re copying that information from somewhere else.

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You can watch on YouTube, they eat the preg alive with no problem, living deer screaming, they don’t care as any other predator so they don’t just wait for their death, but if prey runs away, they can find it later.


From the research I’ve read the bacterial infections, when they happen, are generally not a result of bacteria in the mouth of the Komodo, it’s a result of the conditions the animal they bit were in, in particular the introduced water buffalo, which are the animals that the bacterial infection issue is most relevant to.

Here’s a good overview from 2013:

the team managed to swab the mouths of 10 adults and 6 hatchlings.

They found… nothing special. All the microbes they found were common in the skin and guts of their recent meals. There were no virulent species at all, and certainly nothing capable of causing a quick, fatal infection. And the species that were there weren’t particularly abundant. “The levels of bacteria in the mouth are lower than you’d get for a captive mammalian carnivore, such as a lion or Tasmanian devil,” says Fry. “Komodos are actually remarkably clean animals. This is another nail in the coffin to the idea of them using bacteria as a weapon.”

Fry thinks that bacteria do help to kill the largest of the dragon’s victims, but not in the way that Auffenberg suggested. When the dragons tackle natural prey—medium-sized mammals like deer or pigs—the victims die very quickly from blood loss. The venom helps, but it’s the wounds that are important. But water buffalos are a different story.

These creatures were introduced to Komodo by humans. They’re too big to kill outright and always escape the initial attack. In their natural environment, they’d disappear into wide marshlands, but there’s nothing like that in Komodo. Instead, the buffalos seek refuge in rank water holes, stagnant and contaminated with their own faeces. In this microbial wonderland, their wounds soon become infected. “It’s the same as if you dumped a whole bunch of cow dung in your pool during the peak heat of summer, shaved your legs with a very old razor, and then went and stood in the water for a day,” says Fry. “You’d end up with some very tasty infections!”


@pliantscience @draginous

Komodo dragons attempt to kill their prey outright when they attack. Biting and “following” prey waiting for it to die of venom/sepsis is not actual hunting behaviour. When such prey does get away (but succumbs later), is a failed hunt on the dragon’s part.

Here’s an excellent overview on the hunting behaviour of Komodo dragons: The Komodo Dragon: Even Deadlier Than You Thought


From what I’ve seen the hypothesis is still only that … actually a bunch of hypotheses. One idea that seems interesting is that the Squamata clade may have an exaptation (or pre-adaptation) for venom based on the makeup of their salivary or other oral glands developed early in their history. So all squamates might have the hardware that would allow them to more easily develop some sort of venom but not all do, or their venom is relatively benign and may be poorly understood by researchers. Lots of unknowns, probably too many to make any conclusions about taxonomy based on whether a lineage is classified as venomous or not.

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Well, on a tangent, if I may…

Cat bites can be very toxic and swell up very painfully in minutes. It is said to be due to bacteria; but how can bacteria reproduce so quickly to make such a reaction?

In my experience, a ‘normal’ cat bite is not that bad, maybe like getting a good prick from a thorn. But, the bite from an aroused, fluffed up, hissing cat can have an instantaneous toxic effect with much pain and rapid swelling. My personal theory for the difference in reaction is that the cat’s stress hormones cause the release of something toxic in its’ saliva that is not normally present.

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One thing to remember about cats is that their canine teeth are more like needles, which can have the potential for penetrating deeper into the skin and epidermis than e.g. a dog or similar animal. This deeper penetration may be a factor for cat bites being more ‘infectious’.


I’ve always considered house cats to be venomous animals best handled with heavy gloves and a noose pole.


A very tangential dragon story. (Couldn’t resist sharing)

A few years back, my son was working for an online service which helped foreign students get into North American colleges, by working with college recruiters to be sure all the forms and paperwork were properly prepared and submitted.

My son was assigned some of the tougher cases which included an applicant from the Komodo Islands. Everything had been processed and ready to go correctly except one final pack of forms that was getting dangerously close to the deadline limit.

He finally managed to contact the applicant, who explained that the reason for the delay was that the village that he lived in had been in a lockdown as a large dragon was seen cruising the streets and that meant he was not able to get to the post office for three days.

My son said the college involved was very understanding and granted a submission extension. I think that they just really enjoyed hearing a genuinely original excuse.

I mean, it’s a far cry from the ol’ “dog ate my homework” cliche.

Oh, and the applicant was accepted.

Sorry for the hijack of this discussion. Please, back to regularly intended discussions and studies of lizard venom.


Maybe, but it seems different to me. A shallow Vs deep thorn prick isn’t instantly “reactive” like a bite from an aroused cat can be. Even a hard playful bite doesn’t instantly swell and ache (usually) as a bite from a hissing puffed up cat.

I’ve always considered house cats to be venomous animals best handled with heavy gloves and a noose pole.

My husband loves our cats dearly, but he won’t touch them :rofl: cuz they always swat his hand.

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