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Post by creature386 on Feb 24, 2014 3:11:55 GMT 5
Am I right when I say that this is probably the only thread which is more than 20 pages longer than the equivalent on carnivora?
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Post by elosha11 on Feb 24, 2014 4:13:03 GMT 5
Theropod, one point on GWS that should inform your analysis on Meg size. In a post a few back you stated a well fed GWS could possibly reach two tons. A two ton shark is indeed a very big great white, but not approaching maximum size, which is between 5000-6000 pounds for modern GWS, and probably quite a bit more for the prehistoric GWS. For instance from sharkresearchcommittee.com/dist comes this quote along with a picture: "The shark was 17 feet 7 inches in length and weighed 4,140 pounds. The accuracy of the shark's weight is indisputable. The 'truck scale' used to weigh the shark was checked by the California Department of Weights and Measures and found to be accurate to within ± 5 pounds." Also see male GWS nicknamed Apache which was captured and tagged a few years ago. About 17'9" and 4225 pounds. www.underwatertimes.com/news.php?article_id=63075948121. Larger and longer specimens are recorded on Henry Mollet's website.
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Post by elosha11 on Feb 24, 2014 4:20:48 GMT 5
www.jostimages.de/haiartikel/mollet_et_al_1996cha10.pdf. This link to Henry' Mollet's methodology on measuring large GWS might prove useful, although he's using jaw perimeter rather than individual tooth rows or isolated teeth. I haven't read it yet, but thought there may be some useful info for Meg size determination.
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Post by Grey on Feb 24, 2014 4:26:18 GMT 5
Regarding the weight of the great white and in Meg, I'm as well agreed with Theropod's regression and the one from Gottfried et al, simply because of the variations and suggested increasing in bulk. I can live with that. I note though that Gottfried's regression is still used in the modern research about Meg size (Pimiento and Balk), which means that no one hs been able to strongly propose something better. But I have nothing against another rigorous alternative even if not published. At worst the regression Theropod proposed only superficially fluctuates from Gottfried's. And sharks are known to have great weight variations from a time to another in the year. But I agree that a 6 m GW under 2 tonnes is undernourrished.
But we're more focusing on TL these times.
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Post by theropod on Feb 24, 2014 23:11:14 GMT 5
He also did that in the Talk he held at the royal turrell museum, but before that he said the largest were reaching 19m.
Exactly, that one.
That looks like direct sizing to me, similar to the method he used for the vertebral diameter of Cardabiodon
I would call the regression the more reliable method, although I think 4.2% may be too little.
What could we be missing, apart from tooth specing which appears to usually be approximated by guesses? What applies to specimens also applies to methods.
Not enough for that particular specimen at least, although I do think we should use something slightly higher. Abover 15% isn’t realistic tough.
Any clue who that owner is?
Usually our default assumption seems to be that reaearchers are aware of the stuff we are aware of, no?
The proportions are a matter of speculation even with the best methods. But most likely it is somewhat similar to a great white or mako in general morphology, but with typical size-related differences that should be expected in a shark.
Indeed.
You must have sent him many mails indeed...
Sadly, assumption is the best we have got so far. Let us hope he one day published a paper on C. megalodon!
I might do that on occasion.
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Post by theropod on Feb 24, 2014 23:17:43 GMT 5
Grey: I recall reading on several occasions that TL is more useful since it is not subject to seasonal changes in bulk, the health of the specimen, whether it is pregnant etc. which all affect the weight. @elosha: Not sure what post of mine you are referring to, but I agree 2t is not the maximum weight for extant GWS, let alone extinct ones, just typical for a big female shark. The biggest extant great whites appear to reach at least 2.5t, and the largest extinct specimens were probably a lot bigger.
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Post by Grey on Feb 25, 2014 9:21:53 GMT 5
I know, the point is that either he means the figure he got was "exactly" 19 m or a bit more, below 20 m. Why are you suggesting this ? This quote just succeeds the one where he explains that he uses jaws perimeter. There is nothing to think he used some basical direct sizing when estimating Meg size as we know he effectively uses Lowry's formulas. Me too. I just suggest that Siversson uses it too for Megalodon but get different results because we lack some factor or because indeed he does not add 4.2 %. The only way to know would be asking him. Not by guess only based on modern templates. I think too we probably don't have the exact spacing to use. But it is possible too we ignore something else in the whole calculation or dentition. The fact is that using what we have so far, either for the 5.50 m Hubbell great white, the Hubbell's set estimate at 11-12 m and the largest Meg at about 19m, we get constant underestimates. In any case, I won't use Lowry's formula extensively until I get all the appropriate data to use it. What I want to know is which percentage is the most likely to use, I don't want to assume arbitrary something between 0 et 15 %. In tis purpose I'd want to know what did use Siversson in his calculations. He did not say me who's the guy but he said he had found again him after a strange coincidence and will send me a photo of the tooth once he has seen it again. Only they are both very busy and did not find yet the time to see each other. Not necessary when it comes to private collections, and knowing that a large tooth is in a collection and how large it is doesn't mean it was used. I's possible that he used Hubbell's big tooth but nothing confirms this. By proportions I meant dimensions, size... I think that despite we lack a documented skeleton, we have a pretty good idea of how Meg was based on Kent's model revised from Gottfried's model (the main revision being the snout, short and pug-nosed in Gottfried's, more typical in Kent's). Not as much as to Brett. But perhaps he's just busy. No need of a published paper about Meg from him for that (though I agree that would be the best option), he can just explain it through mail contact, like he already explained his calculations for mouth size. I don't know for a paper but I know a BBC doc with him researching Meg remains had to be shot last year. There was also a report about a trip in 2012 from the Western Australian Museum. In 2012, palaeontologists at the Western Australian Museum plan to explore 15-20 million-year-old rocks in the Southern Carnarvon Basin in search of fossil remains of Carcharocles megalodon and its favourite prey, baleen whales. Video clips and photographs will be uploaded on the Museum’s web site so you can follow the search for the ultimate super predator. museum.wa.gov.au/explore/blogs/museumfish/white-shark
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Post by Grey on Feb 25, 2014 11:59:03 GMT 5
I agree. Now what matters about body mass derives directly from the paleobiology in Meg, length measurements alone don't matter much if the animal was a robust fusiform organism or a serpentine shaped one, the biological and ecological constraints are not the same. Like determining that a mosasaur individual and a Ginsu shark individual have the same length but certainly not the same weight. But in the case of Meg, we have a fairly good idea of its body shape (thunna-like most likely, carcharinid-like is a second less likely option) and datas, published or not, about its plausible body mass.
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Post by theropod on Feb 25, 2014 17:58:55 GMT 5
He sais "about 19m". That can be either a bit above or a bit below the 19m.
He speaks of "comparing it for example to that of a white shark, or mako shark, or a porbeagle shark..." and then "probably in the order of 12, maybe 11-12m". That does not sound particularly precise, like the point estimates given in papers (such as his own) that use the jaw perimeter method, or any of the methods in fact. It sounds very much the estimate for Cardabiodon from earlier in the talk, based on vertebral size comparison to vertebrae of a large white shark specimen.
Also, Porbeagle sharks were not even studied in Lowry et al. 2009.
I recall you once cited some generalised ratio between jaw quadrant and TL from one of Kent´s mails. It seems more likely he used something like that, or direct sizing like with Cardabidon verts.
There is no other factor than the interdental spacing that we could be missing here. But it doesn´t seem his estimate for the Florida dentition is consistent with Lowry et al.´s formula for great white sharks, thus we should consider he may simply not have used that regression on it.
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Post by Grey on Feb 25, 2014 18:12:46 GMT 5
Theropod, your assumption of Siversson using direct sizing or generalised simplistic method is wrong, he explains in the talks he uses jaws perimeter when talking about Megalodon size and explained it to me several times in mails. We see that he also estimated his Cardabiodon specimen by this method. The estimate based on vertebras is another point.
I did use total tooth width in the upper jaw based on an associated dentition (Gordon’s collection) and adjusted for the largest known teeth. Based on tooth widths I got a figure close to 20 metres.
I estimate total length in lamniform sharks based on the total tooth width in the upper jaw (i.e., the combined width of all functional teeth). This gives you a good estimate of jaw size and can then be used to get a rough idea of the total length. Needless to say it works best on species know by associated dentitions (Gordon Hubbell has a seemingly complete associated C. megalodon dentition from Florida). This Flrida specimen can then be used as a template for larger isolated teeth (as long as one assumes that the isolated tooth represent the largest tooth in the dentition, which produces a conservative estimate of TL).
Estimating TL based on eg crown height is a very unreliable method as tooth height does not in itself determine the size of the mouth (some sharks have tall and narrow teeth). The number of teeth in the dentition, their combined width and the space between the individual teeth do however strongly correlate with the size of the mouth. This is not rocket science. The latter method does however rely on a complete dentition being available and that the dentition has been reconstructed correctly. I could not possibly care less if people prefer Shimada’s or Gottfried’s methods. You can read more about TL estimates based on tooth width in a paper that will be in press very soon (and available as free download) in Acta Palaeontologica Polonica (about Cardabiodon). In the case of C. megalodon the dentition indicates TL’s approaching 20 metres. That's clear. He did it as seriously as in Cardabiodon, except that he did not publish anything about Meg. And it sounds likely the exact figure he got was about 19 m or a bit more, less likely below.
We probably ignore the exact percentage to use but I won't deny that it is possible we forget a factor in the calculation. The best would be asking directly.
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Post by creature386 on Feb 25, 2014 19:03:26 GMT 5
But it doesn´t seem his estimate for the Florida dentition is consistent with Lowry et al.´s formula for great white sharks, thus we should consider he may simply not have used that regression on it. You don't know if he only used the great white shark, maybe he used the average of the great white shark and mako shark results.
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Post by theropod on Feb 25, 2014 21:27:41 GMT 5
I don’t know what he did, but he does not explain anywhere that he used a published regression equation, let alone the one from Lowry et al. 2009. The paper on C. ricki where he does that is very recent, not even fully published actually, but a preprint. I’m not convinced he used an identical method back in his talks.
For all we know, he could have just used direct sizing based on specimens from the species he mentioned, just as he did with Cardabiodon in the same talk (where he did it although linear regressions for the same thing were available). We do not know his methodology from those talks, excluding the basic measurement they use for reference.
But from all the explanations it is apparent he does not assume a massive interdental distance, and that we should not do so either. Mostly, it is apparently not even found worthwile elaborating on it, and so far all the examinations we did suggested a spacing of <15%. So if (some of) Siversson’s older figures do not agree with that, we have to consider that his method back then may not have been the same.
I for my part tend to trust the method that I know.
Ergo the estimates I trust are ones using Lowry et al’s formula with a spacing of ~15% or less
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Post by Grey on Feb 25, 2014 22:36:37 GMT 5
His methodolgy is jaws perimeter, used in his papers and clearly explained in the mails that he counts the multiple points. There are no older figures, there are estimates he has given on Cardabiodon in his paper, and the ones he gave to megalodon. The direct sizing he gave from the vertebra has nothing to do with the estimates he gives for Megalodon taking into account jaws perimeter data. By the way Lowry are not the only data about that, there are tose of Mollet too.
The only figures we have for Megalodon from an authority is that one, it is then legitimate to find out how he did exactly, that he used Lowry's formula (most likely) or not. And not playing to arbitrary apply 15 % one day, 5 % the other day...while doing the calculations. We can only certain while asking him. But I won't dismiss Siversson's estimates for Meg that he states himself as the latest.
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Post by Grey on Feb 27, 2014 13:36:41 GMT 5
Quite big, measured 17.4 cm on the slant, 17.1 cm on the other side and seems to tip at 12.5 cm in width I guess. Arguably an upper.
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Post by creature386 on Feb 27, 2014 16:15:10 GMT 5
Remember that not only upper is important. Posterior or anterior is just as important. I am not sure about it, but it looks a bit asymmetrical to me, so I don't think it is an anterior tooth.
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