Wednesday Wonders: “Megalania” (Varanus priscus)

23 04 2009
Good tidings and well-wishes ladies and gentlemen!

It greatly irks me that a worryingly-large percentage of the American population believes that dinosaurs and humans once co-existed. What’s even more depressing, however, is the fact that many of these people aren’t creationists, or even religious fundamentalists for that matter. I recall sitting through a world history course my freshman year of High School and discussing primitive homonids during the first week. At one point, our teacher divided us into groups to contemplate the question “What did early humans eat”. Sadly, mine was the only group which did not include something like “dinosaur eggs” or “Brontosaurus meat” in its answer. It would appear that I’d placed entirely too much faith in our nation’s educational system for daring to hope that the complete lack of evidence regarding the co-existence of dinosaurs and Homo saipens as well as the scientific consensus against such neighboring conditions could be considered ‘common knowledge’ amongst its people.

Perhaps this phenomenon explains the irrefutable appeal of “Megalania prisca”, now scientifically recognized as Varanus priscus. V. priscus was an Australian monitor lizard which grew to truly monstrous proportions, effectively earning it the title of “the largest lizard in the history of life” (excluding mosasaurs). Precisely howmonstrously large it was will be discussed later, but to give you an idea, take a look at this still from BBC’s “Monsters We Met” program. Admittedly, the show wasn’t one of the company’s best and was riddled with razor-thin ‘plots’ and paleontological inaccuracies, but this photograph puts the creature’s size into perspective:

Note that V. priscus skull length was around 74 centimeters (29 inches)

Note that V. priscus' skull length was around 74 centimeters (29 inches)

Varanus priscuslived during the Pleistocene epoch and went extinct around 40,000 BCE. While the animal’s sheer size conjures images of the famed Komodo dragon Varanus komodoensis, the animal’s precise relations within the genus are rather debatable. A 1996 study found the creature to be most closely related with the modern perentine,V. giganteus, based on skull roof morphology.  However, in a recent paper submitted to the Linnean society, JJ Head, PM Barrett, and EJ Rayfield suggested that V. priscus ought to be considered a sister taxon to V. komodoensis.

Alright, I’ve kept everyone in suspense long enough, s0 I’ll skip ahead to the most obvious question regarding this beast: “Just how big was it?” Unfortunately, a complete skeleton has never been found and thus, a definite answer cannot be obtained. However, several estimates have been made regarding its total length, ranging from 4.6 to 9 meters (15 to 29.52 feet, American measurement fans) in total length. While this may sound woefully imprecise, bear in mind the following factors:

-The vast majority of V. priscus remains are fragmentary or individual bones (as is the case with most fossil vertebrates). Furthermore, remains befitting of this description belonging to other reptiles have been mistakenly assigned to this animal.

-Modern Varanusspecies are a surprisingly diverse lot, ranging in proportion from the stocky, heavily-built Komodo dragon to the gracile and sinuous crocodile monitor (Varanus salvadorii, which holds the record for the modern world’s longest, though not largest, lizard). Therefore, one cannot easily utilize any such aforementioned remnants to arrive at a theoretical length without a fairly wide margin for error because there exists no universal “monitor lizard proportion formula”.  

In, “Dragons In The Dust: The Paleobiology Of The Giant Lizard Megalania“, Ralph Molnar’s definitive book on V. priscus,he notes that no living monitor sports a tail length which is less than its snout-to-vent length. Thus, using the partial remains of several specimens in comparison to several living species, he arrived at an average SVL length of 2 meters (around 6.56 feet) and thus concluded that the largest males (which tend to be the gender blessed with superior size when it comes to monitors) would have reached approximately 7 meters (22.96 feet) with most specimens attaining lengths of between 5 and 6 meters (16.04 and 19.68 feet respectively).

A skeletal mount currently on display at the Melbourne Museum in Australia.

A skeletal cast currently on display at the Melbourne Museum in Australia.

 However, M.K. Hecht pointed out that while most varanids are represented primarily by caudal (tail) vertebrae, relatively few have been found for Megalania. This suggested to him that the animal may have had a disproportionately-short tail and thus, the entire animal may have been significantly smaller in length than Molnar has indicated. Nonetheless, the sheer size of the creature’s known remains secure its place as the largest land-dwelling lizard currently recognised by the scientific community.

With regards to the question of how V. priscusmay have hunted, we must once again turn to its living relatives. The fact that modern Komodo dragons may sport several species of virulent bacteria in their saliva is well-known, as is the animal’s tendency to utilize these microscopic killers in bringing down prey by infecting the target’s blood stream with its bite, as demonstrated in this clip:

However, a 2005 research project has shown that dozens of modern lizards, including the “dragons”, hitherto thought to be non-venomous do indeed posess various degrees of venom. This suggests that all squamates (modern lizards and snakes) share a common, venomous ancestor (the incomparable Darren Naish over at Tetrapod Zoology has suggested in a recent post that even mosasaurs may have wielded venom in light of this…a truly terrifying thought!). With this in mind, it seems likely that V. priscus, like its relative, possessed a combination of venom and lethal bacteria in its bite.  

As if this weren’t enough, Molnar writes:

“In 1964, George Bartholomew, then at UCLA, and Vance Tucker, then at the University of Queensland, published the results of the first general physiological study of monitors. They found that monitors had a higher-than-expected metabolic rate, greater than in other lizards. This was later confirmed specifically for oras [Komodo dragons] in the wild, compared with iguanas…The metabolic rate of a varanid could be increased during activity until it matched or surpassed the basal rates of mammals…Other work on monitors showed that they could sustain higher levels of activity because their blood did not loose its capacity to transport oxygen during activity as quickly as did that of other lizards. The implication is that monitors could be more active and tire less quickly than other lizards of the same size.”

Molnar also notes that monitors possess some of the most advanced hearts of any lizard, describing their blood flow as “more like that of birds or mammals than like that of other lizards, in that the blood flowing to the body (systemic circulation) is supplied under greater pressure than that flowing to the lungs.” Likewise, monitors boast yet another prominent physiological distinction from their lizard brethren: while most lizards have a “trade-off” between locomotion and breathing wherein the lateral flexation of the body utilized while treading detracts from the creature’s respiratory efficiency, varanids “swallow”air (in a process known as “gular pumping” which involves utilizing the trachea instead of the esophagus) rather than acquiring it by suction. As Molnar explains, “This can be-and is-done while running to overcome the trade-off and provide more stamina. Thus, monitors can more effectively supply oxygen to their lungs during exercise and more effectively carry it to their muscles than other lizards can.”

In the name of completeness, I cannot ignore the cryptozoological aspects of Varanus priscus. For that, I shall redirect everyone to the following clip for a somewhat over-dramatized review:

I agree with most of the paleontologists interviewed…if this beast was still kicking around, it’s continued existence would be no mystery considering that the largest lizard currently known to live in Australia barely exceeds 3 meters (10 feet) in total length. Also, almost no reported sightings of living V. priscus mention its distinctive head crest which was discovered in the late 1990’s and would have certainly been a prominent feature, especially considering just how close many of these alleged victims claimed to have gotten to the animals in question.

May the fossil record continue to enchant us all!



8 responses

24 04 2009
Zach Miller

So, in closing, V. priscus is not a lizard you’d want to mess with.

Great article–I’d always been curious about this giant goana. Question, though: Seems like every monitor lizard and its mother are within the Varanus genus. In fact, I can’t think of one that’s not. Have there been any large-scale comparisons between varanids? Are they all really that similar?

24 04 2009

Howdy, Zach!

I’ve wondered about this too…I once owned a V. abigularis and noticed just how dramatically different its skull morphology was (along with that of V. exanthematicus) from your ‘typical’ monitor, most notably that the former sports a much more robust and squarish skull and its dentition is designed for an omnivorous diet while the latter creatures are famous for their narrower skulls with the teeth of a classic predator.

Tell you what, I’ll relay your question to “Ask A Biologist” and see what the organization’s herpetologists say and then post their response.

24 04 2009
I am a policeman at a all-you-can-eat. » Blog Archive » Quick scan of the net - paleontological

[…], the show wasn’t one of the company’s best and was riddled with razor-thin ‘plots’ and paleontological inaccuracies, but this photograph puts the creature’s size into Cheap Flights Brisbane to Delhi perspective: Note that V. priscus skull length was around … […]

4 05 2009
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6 05 2009
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14 08 2009
Why does the genus “Varanus” contain all known monitor lizards? « The Theatrical Tanystropheus

[…] I wrote an article about Varanus priscus (aka: “Megalania”) back in April, Zach made the following comment: “Seems like every monitor lizard and its […]

12 11 2009
Weekly Wonders: Bullockornis « The Theatrical Tanystropheus

[…] also couldn’t resist mentioning that everyone’s favorite extinct varanid quite likely devoured these birds on occasion, though this is admittedly a speculative […]

28 01 2010
Weekly Spotlight: Wonambi « The Theatrical Tanystropheus

[…] Of The Giant Monitor Lizard Megalania” (which I’ve previously cited at length here): “The squamates (snakes and lizards)… evolved large predators in Australia, including […]

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