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Goanna-eating goannas: an evolutionary story of intraguild predation, dwarfism, gigantism, copious walking and reckless thermoregulation

The views expressed are those of the author and are not necessarily those of Scientific American.

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It’s well known that monitor lizards (or varanids) sometimes practise cannibalism (that is, predation within their own species), and it should be no surprise to learn that big monitor species sometimes (or even often) prey on and eat smaller ones. The phenomenon whereby predators predate on other, typically smaller, predators is termed intraguild predation, and it’s a subject that’s been covered here at Tet Zoo on at least a few occasions.

This new photo – provided courtesy of Craig Stewart and John Scanlon – has been doing the rounds via email and is definitely worthy of wide attention. We haven’t been able to track down the photographer: please do say if you know or can provide a lead. Anyway, the image (definitely taken in Australia, and most likely in northern Western Australia) shows a fairly spectacular instance of intraguild predation within monitors. We can see a Perentie Varanus giganteus consuming an Argus or Yellow-spotted monitor V. panoptes.

There’s no reliable scale, but it’s obvious that the V. panoptes is proportionally huge compared to the Perentie. Eating such a proportionally large item poses potential risks for the predator (do you remember the series of articles I published on ill-fated acts of swallowing?). Furthermore – assuming that the V. panoptes was alive when the Perentie encountered it – subduing such a proportionally large animal would have been a risky endeavour. That’s about all that I can say about this remarkable photo, but I’m now left with a good opportunity to talk a little bit about Perenties and Argus monitors, two of Australia’s largest living lizards. Seeing as monstersaurians got some love the other day, it’s only fair that goannasaurians get some too.

Perentie: shy and elusive giant of the arid centre

Perentie close-up, by Richahel, released into public domain.

All monitors are awesome, but the Perentie just has to be one of the most awesome of all monitors. This is a huge lizard (the largest alive in Australia today) with a few reports describing individuals 2.5 m long in total. Anything at or over 2 m should, however, be regarded as exceptional. The Perentie has a highly distinctive, dorsally spotted livery and is comparatively long-necked. It’s an arid-land specialist of the Australian interior, though it does seem to be expanding its range southwards along the coast of Western Australia (Horn & King 2004).

While predominantly terrestrial and preferring sandy and rocky deserts as well as scrubby habitats, perenties have been known to climb, and there are peculiar (and admittedly very rare) accounts of individuals seen foraging in shallow water (e.g,. Pianka 1982). In some areas, they take shelter in burrows. These can be enormous: 1 m deep, and up to 8 m long (Pianka 1982). Perenties are well known for standing bipedally when surveying the surroundings, a behaviour sometimes known as ‘tripoding’. They’re elusive, wary, and with an air of intelligence that frequently impresses those familiar with them. ‘Intelligence’ of a sort is widespread in monitors and I hope you’ve read the stories of Komodo dragons and other monitors that enjoy human company and even engage in obvious and deliberate play behaviour.

Perentie, photographed in Western Australia by Kaiwhakahaere, released into public domain.

So, while perenties most typically walk and run on the ground, they can climb, they can swim, they can dig, and they can stand bipedally. I don’t mean to imply that this makes them ‘special’ compared to other monitors – indeed, it’s this behavioural flexibility that helps explain why monitors are so outstandingly successful.

Stomach content data shows that perenties feed on a broad diversity of arthropods, reptiles, birds and mammals, and they also eat eggs. Pianka (1994) suggested that, prior to recent centuries, perenties might have preyed on hare-wallabies and other mid-sized marsupials that are now extremely rare or extinct. Essentially, they eat whatever they can overpower, they’re consummate scavengers, and we know that they sometimes eat other monitors. But are they on record as eating monitors, or any lizards, as large as the V. panoptes prey item shown above? Horn & King (2004) refer to the swallowing of a c. 50 cm Long-nosed water dragon Lophognathus longirostris by a c. 60 cm perentie and King (1999) reported a case where a 1.5 m perentie ate another perentie that was 1.2 m long. The complete act of swallowing wasn’t witnessed in the latter case – the animal walked away with about half the length of the prey’s tail still hanging from its jaws. The photo I show here does not, therefore, represent a ‘world first’ or anything like that: we already knew that perenties did this sort of thing. Getting a good photo of it, however, is often the great challenge.

The mandatory bit about phylogeny

Within the Indo-Australian varanid assemblage, the Perentie has been found in molecular phylogenies to group together with Gould’s goanna V. gouldii and the Argus monitor V. panoptes (Ast 2001), two species we look at more below.

Reconstructed skeleton of V. priscus on display at Melbourne Museum. Photo by Cas Liber, released into public domain.

A Mertens’ water monitor V. mertensi + Spencer’s monitor V. spenceri clade appears to be especially close to this ‘gouldii group’, while both the odatrians (a group of mostly small Australian monitors) and a (Crocodile monitor V. salvadorii + (Lace monitor V. varius + Komodo dragon V. komodoensis)) clade form successively more distantly related lineages (Ast 2001; see also Baverstock et al. 1993, Fuller et al. 1998). Megalania – that is, Varanus priscus – was suggested by Lee (1996) to be the sister-taxon to the Perentie since both share several skull roof characters. However, Head et al. (2009) argued that the characters concerned (they include a raised interfrontal suture and a rugose texture on the frontal bones) are widely distributed in monitors and sometimes size-related; they showed, via the presence of other detailed skull characters, that V. priscus seems instead to be a member of the (Crocodile monitor V. salvadorii + (Lace monitor V. varius + Komodo dragon V. komodoensis)) clade (Head et al. 2009). The as-yet-unnamed giant monitor known from the Pleistocene of Timor (Hocknull et al. 2009) belongs here as well.

Body size in varanids mapped on to Ast's (2001) phylogenetic hypothesis: from Gould & MacFadden (2004).

A few really interesting things have emerged from examination of Ast’s (2001) phylogenetic hypothesis for monitors. Odatrians are dwarfed relative to what seems to be an ancestral total length of c. 1-2 m. And the Komodo dragon is not giant due to island gigantism – it belongs to a clade that was probably large-bodied ancestrally, and was already large when it colonised Komodo, Padar, Rintja, Flores, Gili Moto and Oewada Sami (Gould & MacFadden 2004). In fact, big-bodied monitors identified specifically as V. komodoensis are now known from the Pliocene and Pleistocene of mainland Australia (Hocknull et al. 2009), indicating that the Komodo dragon was a big animal on a continental landmass before it colonised those Indonesian islands (where, today, it’s an endangered relict). Note also that V. komodoensis and V. priscus were contemporaneous on Australia. The Lace monitor might be secondarily small since it ‘only’ reaches 2.1 m and yet is surrounded in the phylogeny by the Crocodile monitor and Komodo dragon (Fuller et al. 1998, Ast 2001, Gould & MacFadden 2004).

If the gigantic V. priscus is close to the Komodo dragon as Head et al. (2009) proposed, this giant species evolved from already large ancestors and took size to an extreme. The phrase “Runaway selection for increased body size” has already been used in the literature on body size evolution in monitors with reference to both V. priscus and the Komodo dragon (Pianka 1995); this ‘runaway selection’ still seems to have occurred, just not in an Indonesian island setting, and perhaps driven by the presence of large and vulnerable mammal prey. Incidentally, Pianka (1995) was prescient enough to note that the idea of relatively large ancestral size for monitors was equally as plausible as the idea of small size and independent acquisitions of large size.

Komodo dragon photographed at ZSL London Zoo in 2009.

On not stegodont eating, and on not taking the role of big mammalian predators

There are two other things I just have to mention while I’m here. One is that the large ancestral size of the Komodo dragon lineage helps kill stone-dead the appealing but fanciful notion that this lineage spawned giants under selective pressure to prey on island-endemic stegodont elephants (Diamond 1987). Maybe Komodo dragons did meet, kill and eat miniature stegodonts; the point is that members of the Komodo dragon lineage were, however, large before this ever happened (Hocknull et al. 2009). [Image below by Conty.]

Komodo dragon (1) and Perentie (2) compared to different reconstructions of V. priscus. Created by Conty, licensed under Creative Commons Attribution 3.0 Unported license.

The other thing concerns the idea that Australia could only produce super-giant monitors because the continent’s low-energy ecosystems were unable to support big mammalian carnivores, hence the prevalence of big lizards (Flannery 1994). Since that hypothesis was first mooted, the diversity of (formerly well-forested) Australia’s marsupial predators has increased; furthermore, it’s been increasingly recognised that some of those marsupial predators were as big and formidable as placental predators from elsewhere, if not more so (Wroe et al. 1999). We now have to contemplate a prehistoric Australia where there was, after all, enough ecological and literal, geographical space to allow the evolution of big thylacines, thylacoleonids and other mammalian predators as well as the evolution of several species of giant lizard.

The goanna that walks

In case you’ve forgotten, we’re here because of that photo shown at the top. It features a Perentie and an unfortunate V. panoptes.

Argus monitor, photograph by Jeanette Covacevich, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

V. panoptes – variously termed the Argus monitor, Yellow-spotted monitor or Floodplain goanna – was only recognised as a distinct species in 1980. Prior to this, its populations had erroneously been identified as part of V. gouldii (the Sand goanna, Gould’s goanna or Bungarra). This particular situation is complicated by the fact that, after realising that ‘V. gouldii’ of tradition actually represented two species, Storr (1980) erroneously gave the name V. panoptes to the form that included the type specimen of V. gouldii. In other words, he immediately created an objective junior synonym and left the new form without a name.

A series of exchanges in the Bulletin of Zoological Nomenclature ensued; the outcome is that V. gouldii is now applied to the extremely widespread, sandy-habitat goanna that typically has a bright yellow tail tip while V. panoptes goes to the yellow-spotted animal of northern Australia and New Guinea. This confusing situation (which I’ve deliberately glossed over here*) means that many references to V. gouldii in pre-1980 literature actually refer to V. panoptes. Things aren’t totally resolved yet, since the substantial variation seen within V. gouldii sensu stricto indicates that it’s a species complex that will eventually be split up. And V. panoptes is already polytypic, with distinct western (V. p. rubidus), northern and eastern (V. p. panoptes), and New Guinea (V. p. horni) subspecies. [Gould's monitor show below; photo by Peripitus.]

* I didn’t even mention the name V. flavirufus.

Gould's monitor - similar to an Argus monitor, but, well, different. Photo by Peripitus, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

V. panoptes is large: males can be 1.6 m long while females rarely exceed 1 m. It occurs in diverse habitats, including mangrove edges, floodplains, wooded grassland and even urban fringes. Again, it climbs, and also forages in water on rare occasion. Again, it’s a dietary generalist, eating animal prey of all sorts. Insect larvae, turtle eggs, lizards and snakes are all recorded prey items. And it too is on record as eating members of other monitor species: V. panoptes has been observed preying on V. gouldii several times.

Me and monitors go way back - these portraits were drawn over 10 years ago. Top to bottom: Mertens' water monitor (V. mertensi), Crocodile monitor (V. salvadorii), Green tree monitor (V. prasinus), Bengal monitor (V. bengalensis). Or, I think that's right.. I've lost the labels.

Two of the best known things about this species are that it’s a consummate walker, with tracked individuals spending as much as 6.6 hours a day walking, and that it’s a fairly reckless* thermoregulator compared to other monitors (Christian & Weavers 1996). Floodplain-inhabiting V. panoptes walk long distances even during the dry season, though they do become inactive during the latest, driest part of the dry season (Christian et al. 1995). No other lizards are known to walk this much, especially during the dry season, though it has been noted that comparative data is fairly scarce (Christian 2004). Another really neat aspect of its behaviour is that it may be a communal nester: Christian (2004) described the presence of warren-like, ‘aggregated burrows’ where females might gather together to lay eggs. Whether this is a planned social strategy or the coincident use by females of the same ideal nesting sites remains unknown.

* Or, more accurately, “least careful”.

I’ve been saying for quite some time that I’d like to write about monitor lizards at length. They’re fascinating and wonderful animals, and so many amazing new things have been learnt about them in recent years. This article started life as a few short paragraphs written to accompany the photo of intraguild predation used above, but it quickly got out of hand, and here we are. Consider it a teaser; there is so much more to come.

For previous articles on varanids and other platynotan lizards, see…

Mosasaurs – historically associated with monitors or even with snakes – have been included within Platynota by some authors. This position is looking increasingly unlikely. That is, mosasaurs are probably not platynotans. Nevertheless, if you want to see some Tet Zoo articles on them, go to…

Refs – -

Ast, J. (2001). Mitochondrial DNA Evidence and Evolution in Varanoidea (Squamata) Cladistics, 17 (3), 211-226 DOI: 10.1006/clad.2001.0169

Baverstock, P. R., King, D., King, M., Birrell, J. & Krieg, M. 1993. The evolution of species of the Varanidae: microcomplement fixation analysis of serum albumins. Australian Journal of Zoology 41, 621-638.

Christian, K. 2004. Varanus panoptes. In Pianka, E. R., King, D. R. & King, R. A. (eds) Varanoid Lizards of the World. Indiana University Press (Bloomington & Indianapolis), pp. 423-429.

- ., Corbett, L., Green, B. & Weavers, B. 1995. Seasonal activity and energetics of two species of varanid lizards in tropical Australia. Oecologia 103, 349-357.

- . & Weavers, B. W. 1996. Thermoregulation of monitor lizards in Australia: an evaluation of methods in thermal biology. Ecological Monographs 66, 139-157.

Diamond, J. 1987. Did Komodo dragons evolve to eat pygmy elephants? Nature 326, 832

Flannery, T. F. 1994. The Future Eaters: an Ecological History of the Australasian Lands and People. Reed New Holland, Sydney.

Fuller, S., Baverstock, P. & King, D. 1998. Biogeographic origins of goannas (Varanidae): a molecular perspective. Molecular Phylogenetics and Evolution 9, 294-307.

Gould, G. C. & MacFadden, B. J. 2004. Gigantism, dwarfism, and Cope’s rule: “nothing in evolution makes sense without a phylogeny”. Bulletin of the American Museum of Natural History 285, 219-237.

Head, J. J., Barrett, P. M. & Rayfield, E. J. 2009. Neurocranial osteology and systematic relationships of Varanus (Megalania) prisca Owen, 1859 (Squamata: Varanidae). Zoological Journal of the Linnean Society 155, 445-457.

Hocknull, S. A., Piper, P. J., van den Bergh, G. D., Due, R. A., Morwood, M. J., et al. 2009. Dragon’s paradise lost: palaeobiogeography, evolution and extinction of the largest-ever terrestrial lizards (Varanidae). PLoS ONE 4(9): e7241. doi:10.1371/journal.pone.0007241

Horn, H.-G. & King, D. R. 2004. Varanus giganteus. In Pianka, E. R., King, D. R. & King, R. A. (eds) Varanoid Lizards of the World. Indiana University Press (Bloomington & Indianapolis), pp. 335-354.

Lee, M. S. Y. 1996. Possible affinities between Varanus giganteus and Megalania prisca. Memoirs of the Queensland Museum 39, 232.

Pianka, E. 1982. Observations on the ecology of Varanus in the Great Victoria Desert. Western Australian Naturalist 15, 37-44.

- . 1994. Comparative ecology of Varanus in the Great Australian Desert. Australian Journal of Ecology 19, 395-408.

- . 1995. Evolution of body size: varanid lizards as a model system. The American Naturalist 146, 398-414.

Storr, G. M. 1980. The monitor lizards (genus Varanus Merrem, 1820) of Western Australia. Records of the Western Australian Museum 8, 237-293.

Wroe, S., Myers, T. J., Wells, R. T. & Gillespie, A. 1999. Estimating the weight of the Pleistocene marsupial lion, Thylacoleo carnifex (Thylacoleonidae: Marsupialia): implications for the ecomorphology of a marsupial super-predator and hypotheses of impoverishment of Australian marsupial carnivore faunas. Australian Journal of Zoology 47, 489-498.

Darren Naish About the Author: Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at! Follow on Twitter @TetZoo.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Finback 10:28 pm 05/18/2012

    Yay, one of my favourite clades! I honestly didn’t know about the Australian palaeorecord for Komodos. But it’s small wonder as a group, varanids are so successful – they’ve hit a utilitarian design that suits them as opportunists, and have reasonable intelligence that benefits that opportunism; I have friends who’ve been working in the country, and been surprised by monitors entering houses to simply investigate if there’s anything interesting (read: edible) around.

    But will there be an accompanying article on supposed cryptid mega-varanids still living in Australia today? ;)

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  2. 2. andrewwright73 12:30 am 05/19/2012

    Awesome article – my absolute favourite animal! Here in Bangkok the populations of the Water Monitor have increased so much that Thai authorities round them all up and dump them outside the city (especially after one of them fell/jumped out of a tree and landed on a jogger). They still come back though and can be found in the lakes, canals, and sewers around Bangkok, living with and possibly eating various types of large catfish. There’s even a few in the patch of scrub next to my house along with the odd Reticulated Python. Moving to Saudi Arabia in August so will be keeping an eye out for Desert Monitors then I guess…

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  3. 3. Therizinosaurus 1:20 am 05/19/2012

    Clearly that first photo is a fake, Darren. If you’ve followed the dinosaur feeding literature this year, you’d know that predators very rarely eat other predators, and certainly not ones a significant portion of their size. The perentie was obviously only scavenging on the argus monitor. ;)

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  4. 4. kuartus 2:13 am 05/19/2012

    Perenties are like modern velociraptors:)

    What is the largest weight recorded for perenties?

    And what’s with the discrepancy between the size estimates for megalania? Is there any consensus?

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  5. 5. Diprotodon 2:38 am 05/19/2012

    In my experience perentie rarely tripod, whereas V.panoptes do it all the time, especially in uber flat grass plain landscapes they love.
    My guess would be the perentie vs panoptes pic was taken at a mining camp in the Pilbara. Large goannas live under the demountable buildings and scavenge bins at those camps and defend their patch against all comers- I have watched quite a few encounters between overfed behemoths at those places!

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  6. 6. Diprotodon 2:59 am 05/19/2012

    Attenborough filmed with V.panoptes showing off their tripoding moves for “Life in Cold Blood”: starts at 3:00 in.

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  7. 7. andrewwright73 5:00 am 05/19/2012

    Thanks also for the Hocknull et al. link – what an excellent article. Had no idea there was a third giant varanid intermediate to V. komodoensis and V. prisca living in the same area, and that there used to be a big relative of V. salvator in the Siwalik assemblage in India. A third separate lineage of big varanids worth looking at would have to be the still-unnamed relative of the Mangrove Monitor that became extinct on New Caledonia. Is there any more info on this one?

    One other thing – the Wroe versus Flannery debate bugs me. Flannery, in his Future Eaters book was looking purely at a late Pleistocene/Recent snapshot of Australia, when the only contenders are the Marsupial Lion, the Thylacine, and the Giant Rat Kangaroo; versus “Megalania” and Quinkana. That’s only five big carnivores, not counting aquatic crocs or snakes. Wroe, to my mind, and here I’m only going by his popular article in Scientific American, drags in the whole Australian Tertiary carnivorous assemblage, including Thylacinus potens, which wasn’t extant at the time of Flannery’s “snapshot”.

    Basically, when humans first arrived in Australia (the “Flannery” snapshot), the Australian large carnivore assemblage was far less diverse than any assemblage elsewhere, and two of the five were big reptiles, which again, didn’t happen elsewhere. Even Madagascar had two Fossa species. Ergot I guess I support the low-energy ecosystem = low large carnivore diversity arguement.

    Again, great article, awesome links!

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  8. 8. naishd 6:00 am 05/19/2012

    Thanks, everyone, for great comments. First thing I want to say is that this article was not meant to be ‘A complete guide to everything you ever wanted to know about the biology and evolution of Australian varanids/Komodo dragon history/Perentie biology’ – in fact, I tried (I really did) to avoid going off at tangents. So, I deliberately avoided discussing the papers on venomosity in Komodo dragons and V. priscus… though perhaps I should have cited them as they include very relevant comments. If interested in the predatory behaviour of big varanids, be sure to see…

    Fry, B. G., Wroe, S., Teeuwisse, W., van Osch, M. J., Moreno, K., Ingle, J., McHenry, C., Ferrara, T., Clausen, P., Scheib, H., Winter, K. L., Greisman, L., Roelants, K., van der Weerd, L., Clemente, C. J., Giannakis, E., Hodgson, W. C., Luz, S., Martelli, P., Krishnasamy, K., Kochva, E., Kwok, H. F., Scanlon, D., Karas, J., Citron, D. M., Goldstein, E. J., McNaughtan, J. E. & Norman, J. A. 2009. A central role for venom in predation by Varanus komodoensis (Komodo Dragon) and the extinct giant Varanus (Megalania) priscus. Proceedings of the National Academy of Sciences 106, 8969–8974.

    There’s a 2012 paper by Fry et al. on how Komodo dragons filled a mammal-like niche in Australia, but I don’t yet know the citation. Any help appreciated.

    Sam Sweet has brought my attention to the very interesting…

    Sweet, S. S. & Pianka, E. R. 2007. Monitors, mammals, and Wallace’s Line. In Horn, H.-G., Bohme, W. & Krebs, U. (eds) Advances in Monitor Research. Mertensiella 16, 79-99.

    …. it also includes a discussion of the evolutionary interaction between monitors and predatory mammals.

    Finally, I also wish that I was previously aware of this published article on intraguild predation in the Perentie…

    Macdonald, S. 2007. Observations on the stomach contents of a road-killed Perentie, Varanus giganteus in Western Queensland. Biawak 1, 21-23.

    This very neat short paper describes a case where a dead Perentie was found to contain both an adult Black-headed goanna V. tristis and adult Ridge-tailed monitor V. acanthurus. The V. tristis contained a skink tail and a gecko in its own stomach contents. You can see Macdonald’s paper for yourself (and a ton of other neat stuff on monitors) in the issue here.

    Thanks to Stephen Zozaya for help.


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  9. 9. naishd 6:35 am 05/19/2012

    Onto other comments…

    With regard to giant crypto-goannas (comment 1), I don’t think there’s much to these stories. With perhaps one exception, they all come from Rex Gilroy… not a reliable source (I’m sure that many of the accounts in his books are fictional). As Ralph Molnar notes, the stories only came in long after ‘Megalania’ became known to the public.

    Therizinosaurus/Mickey (comment 3): yes, with all due respect to my friend and colleague Dave Hone, I’m not happy with the comments in the paper concerned, given the ubiquity of intraguild predation (even among large animals, like crocodilians, big cats, canids, hyenas, eagles etc.).

    Kuartus (comment 4): I think that mass record for Perentie is 17 kg. I don’t know that there is a ‘consensus’ for V. priscus, since there are so many unknowns about its body shape. However, even if it was Komodo-like in proportions, as now seems most likely, estimated lengths range from 4.5 m (Wroe) to 7 m (Molnar). Molnar’s methodology seems fairly sensible to me.

    More comments later…


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  10. 10. cmchenry 7:02 am 05/19/2012

    Great article, lots of juicy content. Some quick comments;

    1. Not that I’d want to question a Scanlon ID, but how sure are we that that’s a panoptes being swallowed by the giganteus? That tail tip looks very yellow. I haven’t seen panoptes in the Pilbarra (c.f. comment 5), but that tail does look a lot like gouldii that I’ve seen in the Kimberley.
    2. Good to see so much space devoted to panoptes, they really are awesome animals. Pretty much the dominant terrestrial predator in the floodplains of the Australian Wet-Dry tropics. Their mobility is incredible – we radio tracked one this year that moved 4 kms (straight line) in one day, and then two days later walked back to the original site. Also, those warrens are pretty amazing, would love to know what’s going on with those. I’ve seen them swim as an escape strategy, and they so have a strongly keeled tail similar to that of mertensii, but I’ve never seen one climb a tree. It does do the tripedal stance a lot (as does gouldii) – that’s really cool. They are big – not quite as big as a varius, but big and really strong.
    3. Given that pretty much all of the ‘gouldii’ group and the odatrians are endemic Australians, it seems likely that they diverged close to or in Oz. But I do wonder what the ‘varius’ group’s story (komodoensis, varius, salvadorii, prisca) is. Did they diversify in the Sundas, with varius, prisca, and komodensis reaching Australia? Or did they (along with the gouldii+odatria clade) diversify in Oz and then head back to New Guinea , the Sundas, and maybe even Asia? On the subject of varius, they are a real handful. I’m not convinced about the ‘varius as secondarily small’ idea- it’s a big animal. Perenties are long, but they’re very gracile. I would guess that varius would outweigh them .Yes, salvadorii are long, but the tail is a very large part of that and they are not as robust as a varius.
    4. Thanks for the link to the Sweet et al paper. I just read Sam’s papers on niche separation between two pairs of odatrians (tristis vs scalaris, and glauerti vs glebopalma), awesome work and if he’s reading this just want to say that I love your work.
    5. Some sad news for panoptes – as of this year, cane toads have just entered the East Kimberley. The Kimberley is one of the last great wilderness left and is home to a guild of 11 varanids – probably the most diverse reptile predator guild on the planet. Panoptes is at the top, and along with mertensii and mitchelli we expect it to be heavily impacted by toads (see Doody et al. on the impact of toads upon these species in the Northern Territory). It’s the top predator in the riparian zone across the Australian tropics, it’s about to be knocked for six in the Kimberley, and we still have so much to learn about what it is doing (how far they do move, are those warrens really communal nests, etc?,). Makes me weep.
    Good to see you covering this totally awesome group of lizards, made my day.

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  11. 11. naishd 7:32 am 05/19/2012

    Thanks for that great comment, Colin; brilliant stuff.

    It occurred to me last night that the goanna being swallowed might be a gouldii, not a panoptes. But, by looking at lots of photos, I managed to convince myself that the former has a bright yellowish tail-tip with an adjacent bold, dark, more proximal part, while the latter has a dull yellowish tail-tip and a browner/less bold proximal part.

    Size of varius vs salvadorii: former gets to 14 kg, apparently… which is greater than most published masses for the latter (max 14.4 kg). So, yes, I take your point! I was following Gould & MacFadden.


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  12. 12. cmchenry 8:54 am 05/19/2012

    Narrow banding on the proximal tail, strong yellow distally with no banding… – I’ve only seen panoptes and gouldii in the Kimberley, and both species vary considerably across Australia (much more splitting to come?!) – but my money is on Gould’s. I’ll send you some pictures.

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  13. 13. Christopher Taylor 8:58 am 05/19/2012

    I am very familiar with perenties: on the offshore island that is our field site, perenties are pretty much the only large carnivore. There is nothing quite like wandering along with your eyes on the ground trying to find a pit trap, then looking up and finding yourself right in front of one f***ing big lizard. Who will be just placidly looking back at you. Because perenties could not give a shit about anything, really, and they are not about to exert themselves on your behalf.

    During a rather nasty drought period a couple of years ago, my colleagues say one perentie meandering through the accomodation camp with the tail of another perentie still hanging out of its mouth. I believe there are photos.

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  14. 14. David Marjanović 9:17 am 05/19/2012

    If you’ve followed the dinosaur feeding literature this year

    Which paper?

    Perenties are like modern velociraptors:)

    No. Jurassic Park “velociraptors” are way too much modeled after monitors.

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  15. 15. David Marjanović 9:20 am 05/19/2012

    Because perenties could not give a shit about anything, really, and they are not about to exert themselves on your behalf.

    So, they’re the sauropsid response to the honeybadger? :-)

    Link to this
  16. 16. cmchenry 9:30 am 05/19/2012

    Chris – which island? (BTW – are you still based in Melbourne/)

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  17. 17. Christopher Taylor 10:25 am 05/19/2012

    Barrow Island. I’m based in Perth; I’ve never been in Melbourne.

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  18. 18. John Scanlon FCD 12:28 pm 05/19/2012

    Lots of comments, great.

    I’m not married to the idea of it being V. panoptes rather than gouldii in the Perentie’s pharynx, but the colour pattern and bulk (relative to what can be seen of length) do seem to be consistent. I’ve seen a lot more panoptes than gouldii at this point, a large number of them in the Murchison district early last summer; locals (traditional owners) call them Bungarra, so this common name apparently should not be restricted to Gould’s. Every goanna scat I’ve checked has contained only invertebrate remains, which means I haven’t been checking for long enough.

    I recently had to write some stuff on body size of V. priscus for a book chapter (and went with Molnar, in not considering individuals up to 3.8 m SVL as ecologically unimportant) but forgot to reference Gould & McFadden, though I’d definitely seen it.

    There are available names for species between komodoensis and priscus in size from Timor (hooijeri) and Central Australia (warburtonensis) – possibly the same as each other, though the material may not be adequate to test this.

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  19. 19. Tomasz Skawiński 1:06 pm 05/19/2012

    There’s a 2012 paper by Fry et al. on how Komodo dragons filled a mammal-like niche in Australia, but I don’t yet know the citation. Any help appreciated.

    Maybe that is the paper in question? There is a short discussion on the “varanids as the mammalian analogues” hypothesis.

    Frye BG, Casewell NR, Wüster W, Vidal N, Young B, Jackson TNW. 2012. The structural and functional diversification of the Toxicofera reptile venom system. Toxicon (in press).

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  20. 20. Therizinosaurus 3:41 pm 05/19/2012

    David @14- I direct you to the exchange between Hone and I here-

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  21. 21. Andreas Johansson 12:26 pm 05/20/2012

    In the size comparison chart, is each square 1 m? I’d presume so (Molnar’s priscus is about 7 squares long), but then the woman is unusually tall, which would seem to somewhat defeat the purpose of adding a human silhouette.

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  22. 22. naishd 6:28 pm 05/20/2012

    Andreas – yes, each square must be 1 m. So, the human figure is something like 1.8 m tall. I don’t see this as a problem, even if it is a woman.


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  23. 23. Cameron McCormick 10:58 pm 05/20/2012

    So, the human figure is something like 1.8 m tall. I don’t see this as a problem, even if it is a woman.

    In the US, a woman over 20 who is 1.73 meters tall is in the 95th percentile. Maybe 1.8 m is common in the Dinaric Alps (where the average is 1.71 m), but for most human populations it’s probably in the top 1%.

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  24. 24. Heteromeles 1:51 am 05/21/2012

    The silhouette is from Texas, and has big hair.

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  25. 25. David Marjanović 1:55 pm 05/21/2012

    Ah, yeah, that! Thanks!

    for most human populations it’s probably in the top 1%

    Sure; here in Berlin, however, women who measure 1.80 and more are common.

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  26. 26. shocknull 12:47 am 05/22/2012

    Hi all,

    A couple of comments re: palaeobiogeo of large-bodied varanids. The fossil record for these biggies goes back into the early-mid Pliocene in both Oz and India, perhaps as far back as the late Miocene (not confirmed). Many of the islands that make up the indonesian archipelago were underwater during this time and it would seem not available for varanid colonisation. Although they are mostly made up of chunks of both Gondwanan and Laurasian bits, many of the palaeogeoreconstructions assume or infer emergence. When you look at the basin sedimentology over much of the Neogene these blocks were not depositing siliclastics therefore little evidence for emergence. Much like New Guinea. It is more likely that we had two independent lineages of large-bodied varanids, one in central Asia and one in Australia. The question to be solved in SE Asia was did the komodo group disperse onto Java or was this an eastward dispersal of the Indian taxon (sivalensis). Unfortunately the fossil record in India for large varanids amounts to 3 specimens (so far as I know), however, with my experience in Australian collections there could be many Swalik collections with varanid bits floating around misidentified or just not identified.

    As for the Timor taxon, this will remain undescribed until we can find more of this beastie. Although it resembles warbartonensis, so do many specimens in the ‘not-komodoensis and not-priscus’ size ‘gap’. The only clearly priscus specimens come from the late Middle Pleistocene to late Pleistocene. I would suggest that the central Aust specimens are sampled across the Plio-Pleistocene with few having good chronological constraints. warburtonensis is a dorsal vert so pretty uninformative other than intermediate size. Athough size does seem to be quite a valid identifier for many of the large taxa with clear sizes in the Pliocene, Mid Pleistocene and Late Pleistocene.
    More cranial and appendicular remains of central Aust varanid fossils are needed.

    As for priscus size, one of the projects I’ve been steadily working on is describing and illustrating in detail all material referable to the large varanids in Australia. A lot of specimens were not recognised in Aust museum collections, being mixed in with mammal, crocodile, bird, turtle and even fish collections. So, Molnar’s review of Meg was a great start, however, since then the number of elements known has probably doubled. The process is a long one as it has taken a long time to gather the material and undertake comparative analyses and get the things photographed and illustrated. Reconstructing skulls etc. Watch this space.

    My estimates of TotalL of Meg based on a 1:1 ratio of SVL = Tail Length is 5-6m with a 6m specimen being exceptional. At best I can get at 2.5mSVL from the skeletal remains with no exceptionally large individuals in any collection. In fact, small individuals are the exception. More in the pipeline on this.

    Anyway, hope that keeps the discussion going. Great to hear there is so much interest in varanids.


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  27. 27. naishd 3:27 am 05/22/2012

    In case anyone didn’t realise, comment 26 is by Scott Hocknull, lead author of the Hocknull et al. PLoS paper cited above (and co-describer of Australovenator, Wintonotitan and Diamantinasaurus, and star of the ING cassowary episode…). Thanks much for the very interesting comment, Scott.


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  28. 28. Owlmirror 1:12 am 05/23/2012

    Off-topic, but: TetZoo ver 2 has been moved to a new theme/style/system — and all of the old comments are gone.

    Is there any chance that there is a backup of them that can be restored?

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  29. 29. naishd 4:05 am 05/23/2012

    Err… what? Better go look..


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  30. 30. David Marjanović 5:03 am 05/23/2012

    They’re gone on Pharyngula, too. I’m told they’re still – or again – there on ERV, so I suppose they’re going to reappear. However, new comments can already be made, and a few are there. A few even reference older comments that aren’t visible.

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  31. 31. naishd 5:07 am 05/23/2012

    I can no longer access the publishing platform, so can’t destroy spam. I expect the site to get flooded with nonsense over coming months.


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  32. 32. David Marjanović 5:13 am 05/23/2012

    So I overcame my disgust and hovered over the slimepit. All comments of at least the last two subthreads, 4935 on the latest one alone, are there (paginated). I suppose the NatGeo overlords deal with the smallest blogs first. There’s even a whole new post, so the publishing platform appears to be accessible, too.

    (…If you don’t know why it’s called the slimepit, click on the link once. You’ll probably never need to do that again in your entire life; and you definitely won’t want to.)

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  33. 33. David Marjanović 5:14 am 05/23/2012

    …and the slimeys have already complained about spam. Apparently the new and worsened commenting system makes spamming easier.

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  34. 34. David Marjanović 5:20 am 05/23/2012

    When I’m already babbling off-topic… the Middle Jurassic abelisaurid… I’m getting one of those moments when I suspect that “all important divergences among dinosaurs happened on one afternoon in the Late Triassic”. (Who said that?)

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  35. 35. naishd 5:24 am 05/23/2012

    I think I first heard (from either Jerry Harris or Tom Holtz) that Larry Witmer said this. I said it back to Larry while we were both looking at Sankar Chatterjee’s ‘Maleri Formation pachycephalosaurs’ at SVP 1999. I can’t remember his reaction, he might have hit me.


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  36. 36. David Marjanović 7:46 am 05/23/2012

    Ah. I knew about the connection to the Maleri Fm “pachycephalosaurs” (what has become of them, BTW?), but I knew Chatterjee himself hadn’t said it…

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  37. 37. Vpanoptes 11:38 am 05/23/2012

    Hello -
    Darren – many thanks for a very interesting article. Just a few quick comments/additions to CMCHenry’s post.

    1) Yes, panoptes is an awesome beast. I spent two years radiotracking them pre- and post-cane toad invasion in Kakadu NP. They are capable of very long-distance movements (longest one I have on record was 12 km+) and some males seem to have huge home ranges (up to several km2). Females have (comparatively) tiny home ranges (up to several ha2).
    2) The situation with cane toads is pretty depressing. In approximately 1 year of following a population pre-toad I had one mortality out of 70 animals. Post-toad the mortality was approximately 70% in 10 months. It’s not pretty, but that’s another subject.
    3) Tree-climbing is pretty rare, depends on whether you count the ones that scramble up the inside of semi-hollow gums, or take the outside route to perch high above the reach of your noose and mock you from above.

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  38. 38. Jerzy v. 3.0. 5:01 am 05/24/2012

    About intraguild predation: interesting is this imbalance on Komodo: it supports large predator with limited prey – because adult Komodo dragons can feed on juvenile Komodo dragons. Apparently some other ecosystems work this way too.

    I wonder if it could be applicable to Mesosoic ecosystems? Mid-sized carnosaurs feeding on juvenile carnosaurs before being able to attack full-grown sauropods?

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  39. 39. David Marjanović 9:10 am 05/24/2012

    About intraguild predation: interesting is this imbalance on Komodo: it supports large predator with limited prey – because adult Komodo dragons can feed on juvenile Komodo dragons.

    Why “because”? How limited is the prey?

    And how often does this actually happen? After all, the juveniles are in the trees where the adults can’t go.

    I wonder if it could be applicable to Mesosoic ecosystems? Mid-sized carnosaurs feeding on juvenile carnosaurs before being able to attack full-grown sauropods?

    Nah. Ornithischians, juvenile sauropods!

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  40. 40. Hai~Ren 9:57 am 05/25/2012

    Talking about intraguild predation in varanids, I wonder if Komodo dragons prey heavily on water monitors where they are sympatric, and if this means that large water monitors end up spending more time living in habitats like mangroves. After all, Komodo dragons patrol the beaches and waterholes that would be ruled by water monitors elsewhere.

    There was a study done on niche partitioning in water monitor and Bengal monitor, and water monitors will apparently prey on juvenile Bengals. Walter Auffenberg also mentioned that “In my experience with mixed collections of both species in captivity, adult salvator often attacked and severely injured even full-grown bengalensis… – so much so that I stopped placing them together.”

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