VD's Varanid thread

[Infinity Blade]

Further proof that a Komodo dragon kills its prey through the mechanical damage caused by its teeth. NOT by venom. In fact, most large prey killed by monitors is killed more quickly than venom could even act.

One Komodo dragon actually killed a water buffalo by ripping a hole in its abdomen, effectively eviscerating the buffalo.

source->

The recently-proposed Squamate clade Toxicofera requires the abandonment of a number of well-studied macroevolutionary trends in morphology, behavior and ecology, leaving it its place hundreds of de facto convergences, and rendering much of the fossil record contradictory. No significant morphological features are synapomorphies of the Toxicofera, which is based on gene sequences in very short branches uniting snakes, iguanian and anguimorphan lizards. As currently understood, the genes support this clade, but it is sufficiently in conflict with so much other evidence that great skepticism remains warranted. One of the pillars supporting the Toxicofera (and the source of the name) is the claim that expression of venom genes in salivary glands is a synapomorphy (a shared, derived trait). This has recently been shown to be false, the genes being expressed in geckos and in multiple tissue types in various squamates. The further claim that monitor lizards (Varanidae) are venomous does not withstand careful examination. Venom gland structures are present in the lower jaw, but evidence for toxicity of monitor bites is generally lacking. Monitors kill most large prey more quickly than venom could act, and are in turn killed so quickly by most predators that little deterrent effect can exist. One potential exception is as a defense against constricting snakes, but detailed work on this possibility remains to be done.

The short story is that it is difficult to see how venom would be of much, if any, advantage as a component of predation by monitors. Monitors do not bite and hold their prey, or bite and release it after the manner of venomous helodermatids or snakes. Instead, larger prey items are shaken violently immediately after being seized, and die very swiftly from neurological and visceral trauma and blood loss. It is pointless to show that a salivary constituent causes a 30% decline in muscle responsiveness after 4 minutes (e.g., Fry et al., 2009b, Fig. 4D) if the prey item has had no blood pressure for the preceding 3 ½ minutes, and has been physically dismembered for 3 minutes.

Sweet (2016)


Also, unrelated, but from the second source posted above, here's an interesting report of black-spotted ridge-tailed monitors hunting large tarantulas.

Varanids are, however, opportunistic, and may take larger and potentially dangerous prey at times. Each of the eight V. baritji I handled in Kakadu regurgitated or defecated remains of large whistling tarantulas (Theraphosidae, cf. Selenocosmia) that occupied 4 cm diameter burrows in stony woodland, from which they ambush prey. On two occasions I observed adult V. baritji partly inserted in spider burrows, one jerking forward repeatedly. Assuming the worst, I extracted the lizard, which turned out to be in the process of swallowing the spider, all of whose limbs had been removed. From other observations, the lizards do generally consume the separated limbs as well. Even confined in a burrow these large spiders represent formidable prey.

[Supercommunist]

Young, cat sized komodo kills a feral cat's kitten.

www.reddit.com/r/HardcoreNature/comments/17hs43r/monitor_lizard_attacks_feral_cat_and_takes_her/

[Supercommunist]

God damn, looking back this thread is a graveyard.

Anyone have the OG komodo deer hunt? I think the footage was from an actual documentary. A bit blurry, but not too bad and pretty tame compared to recent stuff. I have a sinking feel it was taken off youtube.

[Infinity Blade]

This paper is very insightful in explaining how the Komodo dragon survived on the Wallacean islands between the extinction of Stegodon and the introduction of ungulates. It also explains how it survived in the presence of humans.

www.sciencedirect.com/science/article/pii/S2351989419301180#:~:text=Komodo%20dragons%20evolved%20in%20Australia,dragons%20to%20survive%20the%20Pleistocene.

[Supercommunist]

Dec 30, 2022 6:38:05 GMT 5 Infinity Blade said:

Further proof that a Komodo dragon kills its prey through the mechanical damage caused by its teeth. NOT by venom. In fact, most large prey killed by monitors is killed more quickly than venom could even act.

One Komodo dragon actually killed a water buffalo by ripping a hole in its abdomen, effectively eviscerating the buffalo.

source->

The recently-proposed Squamate clade Toxicofera requires the abandonment of a number of well-studied macroevolutionary trends in morphology, behavior and ecology, leaving it its place hundreds of de facto convergences, and rendering much of the fossil record contradictory. No significant morphological features are synapomorphies of the Toxicofera, which is based on gene sequences in very short branches uniting snakes, iguanian and anguimorphan lizards. As currently understood, the genes support this clade, but it is sufficiently in conflict with so much other evidence that great skepticism remains warranted. One of the pillars supporting the Toxicofera (and the source of the name) is the claim that expression of venom genes in salivary glands is a synapomorphy (a shared, derived trait). This has recently been shown to be false, the genes being expressed in geckos and in multiple tissue types in various squamates. The further claim that monitor lizards (Varanidae) are venomous does not withstand careful examination. Venom gland structures are present in the lower jaw, but evidence for toxicity of monitor bites is generally lacking. Monitors kill most large prey more quickly than venom could act, and are in turn killed so quickly by most predators that little deterrent effect can exist. One potential exception is as a defense against constricting snakes, but detailed work on this possibility remains to be done.

The short story is that it is difficult to see how venom would be of much, if any, advantage as a component of predation by monitors. Monitors do not bite and hold their prey, or bite and release it after the manner of venomous helodermatids or snakes. Instead, larger prey items are shaken violently immediately after being seized, and die very swiftly from neurological and visceral trauma and blood loss. It is pointless to show that a salivary constituent causes a 30% decline in muscle responsiveness after 4 minutes (e.g., Fry et al., 2009b, Fig. 4D) if the prey item has had no blood pressure for the preceding 3 ½ minutes, and has been physically dismembered for 3 minutes.

Sweet (2016)



Also, unrelated, but from the second source posted above, here's an interesting report of black-spotted ridge-tailed monitors hunting large tarantulas.

Varanids are, however, opportunistic, and may take larger and potentially dangerous prey at times. Each of the eight V. baritji I handled in Kakadu regurgitated or defecated remains of large whistling tarantulas (Theraphosidae, cf. Selenocosmia) that occupied 4 cm diameter burrows in stony woodland, from which they ambush prey. On two occasions I observed adult V. baritji partly inserted in spider burrows, one jerking forward repeatedly. Assuming the worst, I extracted the lizard, which turned out to be in the process of swallowing the spider, all of whose limbs had been removed. From other observations, the lizards do generally consume the separated limbs as well. Even confined in a burrow these large spiders represent formidable prey.

There was one study that suggested varanid venom works on mammals but not birds.

While Varanus varius venom did not have discernable effects in the avian tissue preparation assay at the concentration tested, in the biointerferometry assay both V. varius and V. salvadorii bound to voltage-sensing domain IV of both NaV1.4 and CaV1.2, similar to H. suspectum venom. The ability of varanid venoms to bind to mammalian ion channels but not to the avian tissue preparation suggests prey-selective actions, as did the differential potency within the Heloderma venoms for avian versus mammalian pathophysiological targets. This study thus presents the detailed characterization of Heloderma venom ion channel neurotoxicity and offers the first evidence of varanid lizard venom neurotoxicity. In addition, the data not only provide information useful to understanding the clinical effects produced by envenomations, but also reveal their utility as physiological probes, and underscore the potential utility of neglected venomous lineages in the drug design and development pipeline.

Couldn't access the full paper but a crocodile monitor reasource that cited the study stated that it claimed crocodile monitors had venom twice as potent as a gila monster.

However, crocodile monitor venom has already proven
twice as potent as the Gila monster (Heloderma suspectum) in an experiment (Dobson et
al. 2021).

www.eaza.net/assets/Uploads/CCC/BPG-2022/2021-Crocodile-Monitor-EAZA-Best-Practice-Guidelines-Approved.pdf

Rather odd that its venom didn't have an effect on avians given that they were thought to primarily eat birds.

A guy on deviant posted photos of his crocodile monitor bite. These photos are appear a lot less graphic than most of the ones I've seen but he claims that he was in very poor state after getting bitten.

www.deviantart.com/sethhanbury/art/croc-monitor-bite-375146934

our seven and a half foot crocodile monitor mistook my hand for a rat and latched on, then he wouldn't let go and some random girl who was near by had to pour rubbing alcohol down his throat so he would let go! i have to say i have been bit by all kinds of things but this was by far the most painful, not only does he have teeth that are half an inch long but they also have a powerful venom which sent me into shock after a few minuets, my hand was on fire and i started puking and there was a puddle of blood where i got bit. this was like ten minuets after i got bit, i was washing it off before i went to the minor emergency room.

yea and his teeth hit the bone and everything so its extremely sore right there on my wrist, but those were his top teeth and they are longer

www.deviantart.com/sethhanbury/art/croc-monitor-bite-again-375149647

People that have been bitten by gila monsters also often vomit which does suggest that crocodile monitors are venomous. Given that the crocodile monitors venom doesn't work on birds perhaps it is actually a defensive adaptation?

[Infinity Blade]

Jun 1, 2024 11:46:19 GMT 5 Supercommunist said:

Dec 30, 2022 6:38:05 GMT 5 Infinity Blade said:

Further proof that a Komodo dragon kills its prey through the mechanical damage caused by its teeth. NOT by venom. In fact, most large prey killed by monitors is killed more quickly than venom could even act.

source->

Sweet (2016)



Also, unrelated, but from the second source posted above, here's an interesting report of black-spotted ridge-tailed monitors hunting large tarantulas.

There was one study that suggested varanid venom works on mammals but not birds.

While Varanus varius venom did not have discernable effects in the avian tissue preparation assay at the concentration tested, in the biointerferometry assay both V. varius and V. salvadorii bound to voltage-sensing domain IV of both NaV1.4 and CaV1.2, similar to H. suspectum venom. The ability of varanid venoms to bind to mammalian ion channels but not to the avian tissue preparation suggests prey-selective actions, as did the differential potency within the Heloderma venoms for avian versus mammalian pathophysiological targets. This study thus presents the detailed characterization of Heloderma venom ion channel neurotoxicity and offers the first evidence of varanid lizard venom neurotoxicity. In addition, the data not only provide information useful to understanding the clinical effects produced by envenomations, but also reveal their utility as physiological probes, and underscore the potential utility of neglected venomous lineages in the drug design and development pipeline.

Couldn't access the full paper but a crocodile monitor reasource that cited the study stated that it claimed crocodile monitors had venom twice as potent as a gila monster.

However, crocodile monitor venom has already proven
twice as potent as the Gila monster (Heloderma suspectum) in an experiment (Dobson et
al. 2021).

www.eaza.net/assets/Uploads/CCC/BPG-2022/2021-Crocodile-Monitor-EAZA-Best-Practice-Guidelines-Approved.pdf

Rather odd that its venom didn't have an effect on avians given that they were thought to primarily eat birds.

A guy on deviant posted photos of his crocodile monitor bite. These photos are appear a lot less graphic than most of the ones I've seen but he claims that he was in very poor state after getting bitten.

www.deviantart.com/sethhanbury/art/croc-monitor-bite-375146934

our seven and a half foot crocodile monitor mistook my hand for a rat and latched on, then he wouldn't let go and some random girl who was near by had to pour rubbing alcohol down his throat so he would let go! i have to say i have been bit by all kinds of things but this was by far the most painful, not only does he have teeth that are half an inch long but they also have a powerful venom which sent me into shock after a few minuets, my hand was on fire and i started puking and there was a puddle of blood where i got bit. this was like ten minuets after i got bit, i was washing it off before i went to the minor emergency room.

yea and his teeth hit the bone and everything so its extremely sore right there on my wrist, but those were his top teeth and they are longer

www.deviantart.com/sethhanbury/art/croc-monitor-bite-again-375149647

People that have been bitten by gila monsters also often vomit which does suggest that crocodile monitors are venomous. Given that the crocodile monitors venom doesn't work on birds perhaps it is actually a defensive adaptation?

Hmm, well, with regards to the effects people feel after being bitten, this may not really mean much.

Handbook of Venoms and Toxins of Reptiles

It is also important to note that the medical effects/sequelae of bites from any species do not constitute evidence of "venomousness" from the perspective of biological function. Human bites, dog bites, rodent bites, etc. all can produce local effects that are caused by physical trauma and concomitant wound inoculation with bioactive components of saliva. The effects can be evocative of mild–moderate envenomation and on occasion, can precipitate anaphylaxis (Weinstein et al., 2012; Trummer et al., 2004; Watson et al., 2018).

The apparent potency of lace monitor and crocodile monitor venom is interesting, though. I'm starting to wonder if it just varies between species. The study you posted actually mentions this as well.

Dobson et al. (2021)

Helodermatid lizards were long thought to be the only venomous lizards. However, studies in many “omics” fields have provided evidence for venom in other anguimorphan lizard lineages, including varanid species, such as the legendary Komodo dragon (Varanus komodoensis) [24,37,38,39,40,41]. The majority of varanid lizards are active predators that exhibit extreme differences in size between species: from the 20 cm V. sparnus to the over 2 m V. komodoensis [42,43]. This disparity in size is also accompanied by variations in diet, hunting behavior and habitat [43,44,45]. Differences in selection pressures due to the variety in the habits of these lizards have led to considerable variation in their venom compositions and activities, rivalling that of the diversity seen within genera of venomous snakes, consistent with active evolution under purifying selection pressure [37,38]. Previous studies incubating varanid venoms with human fibrinogen revealed extensive variation in fibrinogenolytic activity, and other effects include the induction of hypotension [37,38,39,40]. Variable venom activity is reflected in the severity of bites in reports, ranging from minor injuries to hospitalizations requiring medical treatment [46,47,48,49].

Komodo dragon bites on humans, for instance, show no evidence for any effects from venom.

Friedman et al. (2023)

A 43-year-old zookeeper was bitten on the leg by a Komodo dragon and suffered local tissue damage with no excessive bleeding or systemic symptoms to suggest envenomation. No specific therapy was administered other than local wound irrigation. The patient was placed on prophylactic antibiotics and on follow-up, which revealed no local or systemic infections, and no other systemic complaints

See also Boyd et al. (2021)-> that also documents a Komodo dragon bite. Their treatment accounted for any potential venom, but at the time they wrote this they still considered there to be no unequivocal evidence for envenomation by varanids, implying they found no evidence of envenomation in their patient. This suggests to me that maybe Komodo dragons specifically don't really have (or need) any sort of potent venom.

[Infinity Blade]

Squamate scavenging services: Heath goannas (Varanus rosenbergi) support carcass removal and may suppress agriculturally damaging blowflies

Human-induced environmental change has caused widespread loss of species that support important functions for ecosystems and society. For example, vertebrate scavengers contribute to the functional health of ecosystems and provide services to agricultural landscapes by removing carcasses and associated pests. Widespread extirpation of native Australian mammals since the arrival of Europeans in Australia has removed many scavenging species from landscapes, while scavenging mammals such as European red foxes (Vulpes vulpes) have been introduced. In much of Australia, squamate reptiles are the largest native terrestrial scavengers remaining, where large native mammals are extinct and conservation management is being undertaken to remove invasive mammals. The contribution of reptiles to scavenging functions is not well understood. In this study, we investigated the ecosystem functions provided by large reptiles as scavengers to better understand how populations can be managed to support ecosystem services. We investigated the ecosystem services provided by vertebrate scavengers in Australian coastal mallee ecosystems, focusing on the heath goanna (Varanus rosenbergi), the only extant native terrestrial scavenger in the region. We carried out exclosure experiments, isolating the scavenging activity of different taxonomic groups to quantify the contribution of different taxa to scavenging services, specifically the removal of rat carcasses, and its impact on the occurrence of agriculturally damaging blowflies. We compared areas with different native and invasive scavenger communities to investigate the impact of invasive species removal and native species abundance on scavenging services. Our results indicated that vertebrate scavenging significantly contributes to carcass removal and limitation of necrophagous fly breeding in carcasses and that levels of removal are higher in areas associated with high densities of heath goannas and low densities of invasive mammals. Therefore, augmentation of heath goanna populations represents a promising management strategy to restore and maximize scavenging ecosystem services.

onlinelibrary.wiley.com/doi/full/10.1002/ece3.11535

[Supercommunist]

Komodo being aggressive with an adult buffalo.

[Infinity Blade]

Supercommunist You're gonna f*cking love this. Komodo dragons have iron-coated enamel on their tooth serrations and tips. You might've seen it on Twitter already, but I had to share it on WoA.

Iron-coated Komodo dragon teeth and the complex dental enamel of carnivorous reptiles

Komodo dragons (Varanus komodoensis) are the largest extant predatory lizards and their ziphodont (serrated, curved and blade-shaped) teeth make them valuable analogues for studying tooth structure, function and comparing with extinct ziphodont taxa, such as theropod dinosaurs. Like other ziphodont reptiles, V. komodoensis teeth possess only a thin coating of enamel that is nevertheless able to cope with the demands of their puncture–pull feeding. Using advanced chemical and structural imaging, we reveal that V. komodoensis teeth possess a unique adaptation for maintaining their cutting edges: orange, iron-enriched coatings on their tooth serrations and tips. Comparisons with other extant varanids and crocodylians revealed that iron sequestration is probably widespread in reptile enamels but it is most striking in V. komodoensis and closely related ziphodont species, suggesting a crucial role in supporting serrated teeth. Unfortunately, fossilization confounds our ability to consistently detect similar iron coatings in fossil teeth, including those of ziphodont dinosaurs. However, unlike V. komodoensis, some theropods possessed specialized enamel along their tooth serrations, resembling the wavy enamel found in herbivorous hadrosaurid dinosaurs. These discoveries illustrate unexpected and disparate specializations for maintaining ziphodont teeth in predatory reptiles.

www.nature.com/articles/s41559-024-02477-7


In fact, it's probably widespread in reptile enamel (even crocodilians have it to some extent), but it's most pronounced in the Komodo dragon and its closely related ziphodont species.

The authors play with the idea that theropods may have had it too, but unfortunately they can't tell from fossils. The fact that they can't find evidence of it in Megalania teeth or fossil crocodilian teeth suggests that fossils don't preserve it well. However, some theropods had specialized wavy enamel strengthening their serrations, so even if they didn't have it, they had this adaptation (or they had both and were a step-up compared to modern Komodo dragons and crocodilians).

[Supercommunist]

Yeah I saw on twitter. Really cool info. It helps explains how komodos are able to inflict cuts on each other despite their tough armor. I wonder if it also has implications about saber tooth cat teeth. Beavers have iron in their teeth so clearly this adapation isn't a reptile only thing.