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Post by spinosaurus1 on Apr 25, 2014 3:06:08 GMT 5
"From time to time, I’ve been accused of being a fossil killjoy. I pulverize childhood dreams like Diatryma crushed seeds (and not little horses). I’m not sure how true that is. I’ve yet to quantify how much of my writing destroys dreams versus geeking out over new discoveries. But today I have to own up to being a downer. In case you hadn’t heard, Australia’s extinct, giant monitor lizard wasn’t as monstrous as traditionally thought.
In 1858, when paleontology was still a young science, the anatomist Richard Owen read a paper before London’s Royal Society on some astonishingly large lizard bones that had been collected from Ice Age deposits in Australia. Specifically, Owen described a trio of vertebrae that measured three inches long and two inches high. These were far bigger than any lizard then known – the Komodo dragon wouldn’t be recognized by science for another 54 years – and, through a bit of rough anatomical math, Owen expected that this huge “land lizard” would have reached 20 feet from snout to tail.
Owen dubbed this gargantuan lizard Megalania prisca, and he had a little fun imagining that such a lizard might still clamber through the bush. “Whether among the vast and unexplored wildernesses of the Australian continent any living representative of the more truly gigantic Megalania still lingers, may be a question worth the attention of travellers,” Owen told his audience, although the hard-nosed scientist did concede that the lizard was most likely extinct. Either way, Owen concluded, the huge saurian “must have been carnivorous, and, by its bulk and strength, very formidable.”
While the fossil trail took some confusing turns as Owen and succeeding generations of researchers puzzled over fragments of Australia’s prehistoric reptiles, by 1975 paleontologists had settled the image of Megalania as a truly gigantic monitor lizard that ripped into Volkswagon Bug-sized wombats between 4 million and 30,000 years ago. This was late enough that the first people to arrive on Australia may have encountered the lizard, and Megalania was definitely not a squamate to be trifled with. The skeletal reconstructions put up at the Museum of Victoria and other institutions looked like Komodo dragons pumped up to almost 20 feet long. Despite all that had changed since 1859, Owen was right about one salient point – Megalania was one formidable lizard.
But Megalania ain’t what it used to be. For one thing, the lizard’s bones are so similar to those of other monitor species – belonging to the genus Varanus – that paleontologists have taken to calling it Varanus priscus. And while it seems likely that the big lizard was venomous, recent size estimates have shrunk this “dragon in the dust.”
Let’s have a look at the traditional baseline first. In 2004, working with the relationship between vertebrae size and body length, paleontologist Ralph Molnar proposed that mature Varanus priscus could have been between 23 and 26 feet long, depending on the anatomy of the tail. But other researchers think such sizes are major overestimates. In a 2002 study that critiqued “the myth of reptilian domination” in prehistoric Australia, anatomist Stephen Wroe reanalyzed old body size data and calculated that the lizard probably averaged about 11 feet in total length and, citing earlier estimates from Molnar, wouldn’t have grown much longer than 15 feet.
Size estimates in a 2012 paper by paleontologist Jack Conrad and colleagues came out in between the extremes. While describing a new, large Varanus species that once lived in Greece, the researchers also took a look back at Australia’s ever-contentious lizard. Without the tail, the Varanus priscus specimen in their study had an estimated body length of almost seven feet, meaning that this individuals total length was almost certainly longer than the 11 foot average Wroe suggested. Especially large specimens, Conrad and coauthors noted, could have had bodies almost 10 feet long with the tails trailing behind, although these animals still would have been smaller than the monstrous lizards paleontologists used to reconstruct.
The entire back-and-forth over the lizard’s size is only a small part of the story, though. Since Owen’s days, paleontologists have viewed Australia as a place where the Mesozoic clung to life – a land full of marsupials where reptiles tenaciously clung to predatory dominance. That view is changing into a more complex Pleistocene vision, with the island continent’s huge monitor playing the role of ambush predator among a variety of carnivores – mammalian and reptilian – that stalked the Australian Ice Age. At 11 feet or 20, it’d be difficult not to be impressed by a lizard of such scale, but the rapacious role of the long-lost monitor has yet to be pulled from the scraps the reptile left behind."
phenomena.nationalgeographic.com/2014/03/19/australias-giant-venomous-lizard-gets-downsized/
if this is true, then megalainia's average length was very comparable with a komodo dragons maximum length and would of reached lengths up to 15 ft or more. what do everyone think of this?
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Post by Infinity Blade on Apr 25, 2014 4:18:03 GMT 5
You can look at my reply in the Carnivora variant of this topic.
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Post by Grey on Apr 25, 2014 4:38:28 GMT 5
Ausar can you post your reply here, I don't have access to Carnivora.
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Post by Infinity Blade on Apr 25, 2014 4:49:34 GMT 5
"IMHO, this "downsizing" is questionable at best. If I'm analyzing this correctly (so you have the right to correct my basic summary of the article if you think it's wrong), it goes like this: it starts out with Brian Switek admitting he's been called a "fossil killjoy", then goes on saying V. priscus was originally thought to be an utterly amazing, giant predatory varanid in the 1800s and thought to be that way for a long time. Then it said that it's phylogeny became a problem (and as far as I'm aware, still is). It then says it was estimated to be ~11 feet at one point (2002), ~23-26 feet two years later (you do the math), and somewhere in between those two ranges years later (2012). Then it goes on to say that there's been back-and-forth problems with its size and briefly talks about the nature of Pleistocene Australia.
It doesn't really explain how what's thought to have been its size was reduced or how one estimate is better than the other, it just explains the conflict between size estimations. There is still uncertainty with its size as far as I'm aware, and btw, look at the comment below the article as well, if anything."
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blaze
Paleo-artist 
Posts: 766
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Post by blaze on Apr 25, 2014 5:35:53 GMT 5
The comment in the article is spot on, when I first saw it last month I thought there have been new findings or something but no, nothing new at all and neither of the studies compare apples to apples. coherentsheaf made several good comments criticizing Wroe's estimates on cf and how they were full of methodological flaws. The most obvious to me is how Wroe used Hetch's estimate average SVL of 2.3m and determined that it meant a total length of 3.45m and then proceeded to scale up Komodo dragons to that length as if komodo dragons had tails only 33% of their total length, that simple mistake there results in he underestimating the mass by almost 240%(!). |
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Post by Vodmeister on Apr 25, 2014 12:22:43 GMT 5
Another prehistoric animal being downsized? Now there's a surprise. Kaprosuchus, Smilodon Populator, American Lion, SA GSFB, Deinosuchus, Ngandong Tiger, Predator X, Livyatan, Liopleurodon and now Megalania. I probably missed a dozen more.
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Post by Vodmeister on Apr 25, 2014 12:23:12 GMT 5
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Post by Life on Apr 25, 2014 13:43:38 GMT 5
A point about debating ethics: Do not redirect discussions towards other forums in your responses such as "You can look at my reply in the Carnivora variant of this topic." Always post information (relevant to the discussion at hand) and cite external sources where necessary.
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Post by coherentsheaf on Apr 25, 2014 15:15:52 GMT 5
Here is what I wrote about Wroes 2002 estimates. (His later estimates are more than 500 kg as a lower bound - something which the above article fails to mention and should therefore probably be dismissed out of hand)
"
ll estimates of size I could locate are on page 3. The first one is directly scaling up a 10 feet komodo dragon to a length of 4,5m. Since there is not much context given for this estimation I can only say that this estimate is probably an underestimate since in most genera larger animals tend to be more robustly built. However this calculation does not commit the same critical flaws we will see in later ones.
Next he tells us that while the total length is not given by Hecht but we can get it by using Hechts methodology. I assume that means that tail length= total lenght*(1/3). This would result in the average total length of 3,45m, as given in the paper. So far no mistakes, but a very unrealistic assumption, since extant varanids usually have longer tails.(Molnar 2004) Now he goes on to scale up komodo dragons to this length arriving at the first of his ery low estimates. This is flawed methodology since komodo dragons have tails that are about the same length as their body. Since monitor tails are quite slim this difference in relative tail length leads Wroe to massively underestimate Megalania`s mass (pun intended).
For example if we take the average SVL for large dragons on Komodo of 146cm and their average mass of 67kg and scale them up to an average SVL of 230cm in Megalania ( the one assumed by Wroe, but not made explicit) we arrive at a total mass of 260 kg. (which in turn is probably an underestimate).
...
He goes on to use an equation by Blob, to estimate the weight of V.prisca with SVL of 230cm (which compared to modern day Dragons would be a massive animal.) and arrives at 96 kg, the size of a large dragon. This low weight is unsurprising since Molnar claims that this formula is wrong. He sources personal communication with Blob and provides a presumably correct formula, namely log(mass)=3.435*log(SVL)-6.009. (SVL in mm and mass in g)Given in an SVL of 2,3m this would result in a mass around 350kg.
In summary, Wroe "estimates" are a collection of bizarre methodological flaws. "
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Post by theropod on Apr 25, 2014 15:32:28 GMT 5
Downsizing and noting that not all individuals of a species were equally massive are also different things. The same applies to Deinosuchus for example.
I don’t recall Livyatan being downsized. Liopleurodon also hasn’t really been downsized in the way Kaprosuchus or the Ngandong tiger have, it’s just that now more people comprehend that the BBC’s 25m figure was made up–but it was never an official estimate (and not even based on Liopleurodon actually).
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blaze
Paleo-artist
Posts: 766
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Post by blaze on Sept 27, 2014 23:50:07 GMT 5
I think we can say goodbye to 1 tonne Megalania, while it is true that Conrad et al. (2012) didn't estimate its size based on the largest known dorsal we can easily use their methodology to do so ourselves, they say that the svl in komodo dragons is 39.93 times the length of their posterior dorsals, applying this ratio to QM F2942 which is 66.5mm long we get an svl of 265.5cm which suggests a total length of 5.3m. Using Blob's revised equation for varanid mass from svl provided by Molnar (2004) we get a mass of ~570kg and Pianka (1994) for varanid skull length from svl gives 45cm.
How the heck did Molnar and Hetch estimate svls of 3.5m and 3.8m respectively for the owner of this dorsal?
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Post by coherentsheaf on Sept 28, 2014 0:31:44 GMT 5
I think we can say goodbye to 1 tonne Megalania, while it is true that Conrad et al. (2012) didn't estimate its size based on the largest known dorsal we can easily use their methodology to do so ourselves, they say that the svl in komodo dragons is 39.93 times the length of their posterior dorsals, applying this ratio to QM F2942 which is 66.5mm long we get an svl of 265.5cm which suggests a total length of 5.3m. Using Blob's revised equation for varanid mass from svl provided by Molnar (2004) we get a mass of ~570kg and Pianka (1994) for varanid skull length from svl gives 45cm. How the heck did Molnar and Hetch estimate svls of 3.5m and 3.8m respectively for the owner of this dorsal? By the same methodology, linear scaling as detailed in Molnar (however not not explicitely using posteriors and using a lace monitor nstead of a komodo dragon). Conrad et al. on its own is not conclusive a, however you can analyse its result conjunction with Hocknulls data which suggest V.priscus to be 2 about times the linear dimensions of V. komodoensis, which again suggests a similar result to Conrad et al. However both Molnar and Hecht use more comparative measurements to come up with large result, for example the dentary QM F6562 results in a restored svl of 3.1m, or the occiput BMNH 3996 results a svl of 3.1, or the large phallanx in table 9 in Molnar was estimated at 3-3.5m. These SVLs still get you to 1 tone ad beyond. Several things could be the issue here and have tried a comprehensive write up several times though I thought it time consuming in the end as my fazit has ot change much: it seems to me that Megalania was similar in size or larger than a modern saltwater crocodile, and if the ecological distribution of sizes was analogous to modern oras then giant Megalanias were probably a consistent ecological factor. |
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blaze
Paleo-artist
Posts: 766
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Post by blaze on Sept 28, 2014 1:28:29 GMT 5
Does Molnar give the measurements of the megalania and varanus material he used?
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Post by coherentsheaf on Sept 28, 2014 1:51:37 GMT 5
Does Molnar give the measurements of the megalania and varanus material he used? Molnar used the specimen QM J16156 with a purported SVL of 0.54m, a length that he clams to be 51.4 times the average vertebra width (Note that QM 2942'S 68.8mm are width not length.) |
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Post by coherentsheaf on Sept 28, 2014 2:10:25 GMT 5
Further information that is likely interesting: 56% Of dorsals wuld according to Molnar be between 1.4 and 2.9m suggesting an average of about 2.15m and a standard deviation bigger than 0.8 m. Given the empirical distribution tails of Komodo Dragons from these data QMF 2942 is by no eans a exceptionally rare individual but whatevs.
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