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Post by Grey on Dec 13, 2013 9:06:05 GMT 5
As ever, thanks for highlighting this kind of stuff man.
She has confirmed me that the actual results are already different, the final research will be published the next year.
The variation in size independently of the period is curious, perhaps due to a bias in the various datas at the time of this presentation. But if this trends is confirmed, the various increase and decrease of megalodon size are fascinating. Regarding the maximum size, I'm not sure they've used at this moment the largest individuals. 3 individuals in Gatun are 17 m and more, which corresponds to >59 tonnes individuals. I have the personnal feeling that the maximum size found through this study will be at around 18 m, Shimada's method seems overall, not in all the cases, more conservative, moderate than results given by the others methods.
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Post by theropod on Jan 3, 2014 17:20:04 GMT 5
@jaw-perimeter-formula: That's a very good find. However, applying this to Hubbell's set then to larger (wide) meg teeth does not correlate the results by Siversson. Using Hubbell's set of teeth, this gives a size range of 9.45-9.70 m TL, respectively with upper and lower jaws perimeter. By comparison, Siversson said in his talk he had estimated this specimen in the order of 11-12 m. Using then as template the very widest upper anterior tooth I know of, the massive tooth owned by Hubbell which has a maximum width of 15.24 cm, this results in a shark just a bit larger than 17 m, with this formula. That's big but not in correlation with Siversson largest estimates in excess of 19 m (and I don't know if he used Hubbell's tooth for that estimate either) and not even equalling the largest published size to date of 17.9 m with Shimada's method which somehow seems in most of the cases quite moderate in results. Let alone of the reported meg skeleton in excess of 18 m. Not defending Siversson's particular works but, unless I've screwed up with my calculation, the results are even more conservative than with others published estimates. I can't contact Mike Siversson at the moment and really understanding how he did his calculation for megalodon size is a pain in the ass. And this discussion should belong to the meg size thread ! What were the figures you measured/extrapolated for the jaws? Sure you added appropriate interdental spacing? Had we already reached a conclusion about how much space there had to be between the individual teeth? Most convenient would be a simple percentage by which to increase added tooth-width to account for interdental spacing. The formula appears to give higher results than the one Kent used on Parotodus, and there appeared to be a very good correlation in extant shark species used. Sadly, Sivverson doesn't seem to have documented his exact methods anywhere. |
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Post by Grey on Jan 4, 2014 1:53:21 GMT 5
I've calculated the size of the owner of Hubbell's set using the length of the whole upper dentition, like you did for Parotodus with its 131 cm upper dentition. Only using the dentition, not using the others factors.
Don't forget that Kent used the 17% added to the dentition (153 cm) to get his results for Parotodus.
Siversson had explained me how he did but not with the details. And he does not seem to respond me anymore though he suggested me to contact him again around this period of the year.
Have you tried by yourself to caculate meg size ? Keep in mind I'm prone to errors while using scientific maths.
Also Siversson said he did not use only the white shark for his calculation but also porbeagle and mako.
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Post by creature386 on Jan 4, 2014 2:25:35 GMT 5
Just asking, is there any relationship between shark size and spacing (like the spacing decreases, when the shark gets bigger, because it looks like the teeth are more closely pached in the great white shark than in smaller sharks, judging from the fact that smaller sharks yield higher results)?
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Post by theropod on Jan 4, 2014 3:04:04 GMT 5
GreyKent did that because whatever method he used included the perimeter of the whole jaw, not just the toothrow. But what is needed for this one is just the lenght of the toothrow. I'd very much like to try it myself, but I currently lack the data to even start with this approach. I thought you might have them if you tried it. Had you committed any serious calculation error, your figures would probably be off by a far greater margin. But did I get this right that you just added up all the tooth widths with nothing else? That measurement doesn't correspond to the 131cm from Kent's paper, the latter includes interdental spacing (distance between adjacent teeth at their base, not the IDD from the study which is distance between adjacent tooth tips), just not the toothless part in the back of the jaw. What I'd need is a set of measurements of maximum tooth widths for the whole dentition (I'm afraid crown widths like the set you posted earlier in this thread won't be sufficient) and precise data on how much to add for interdental spacing.
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Post by Grey on Jan 4, 2014 4:10:05 GMT 5
Damn you're right, I've forgotten interdental spacing, a spacing that we ignore. Hence the relatively small estimates I got. And can't found in the Parotodus paper the combined width of all the teeth only. I'd simply advise you to contact Mike Siversson on occasion. He's perhaps tired to discuss with me.. This might not be totally accurate but I had earlier used the formula you've found above with Hubbell's set while adding 17% (of tooth-free space said in the Parotodus paper) to the upper and lower tooth rows total length, respectively. I had got a size for Hubbell's set specimen of 11.23-11.41 m while applying this with the formula. I guess the process itself is not adequate but the results are already much more similar to the estimate Siversson gave for Hubbell's specimen in his talk, as he estimated it "in the order of 12 m, maybe 11 to 12 m". My results are almost the same or just a bit smaller. You can try this with the set datas here www.boneclones.com/pdf/shark-teeth-sizes.pdfThe second corresponds to Hubbell's. I don't know if the first larger set comes from a real-life set found (three megs set have been officially found in the world), but I had tried the same calculation and found for this one a TL about 13.62 m, using upper tooth row and 17 % added so. These 17 % I added are not the tooth free space (that I ignored) but I've used this as if it represents the interdental spacing (that we still ignore). What do you think about it ? Perhaps 17 % added is bit too much but interestingly it seems to correspond to the figures given by Mike Siversson in his talk. I did the same calculation with the upper tooth row of the white shark jaws (a jaw also owned by Gordon Hubbell) in the boneclones link and I've got 5.19 m TL. Seems from my memories that it closely correlates with the original size of this animal, around 5.50 m. Again, my result is just slighty smaller. |
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Post by theropod on Jan 4, 2014 4:12:33 GMT 5
I asked Kent via E mail as to how much the interdental spacing accounts for in the toothrow measurement, but I'm not sure how soon he'll reply.
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Post by Grey on Jan 4, 2014 4:35:20 GMT 5
Check my edited last mail, a potentially interesting observation.
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Post by theropod on Jan 5, 2014 18:32:19 GMT 5
I got a response from Kent. He wrote tooth spacing in lamnids ranged from no spacing at all to over 25% (least spacing in Carcharodon, greatest in Isurus), and that variables of jaw shape complicated the whole thing. Parotodus was assumed to be like Carcharodon, which he stated was also consistent with Alopias. Grey: But aren't those the crown widths, or did I get that wrong a few pages earlier? It doesn't appear to be prudent to use an unrelated percentage, even tough it seems to be within the range interdental spacing could account for. When using the great white shark formula, it appears there's little or no interdental space to be accounted for. But were the measurements you used actually root widths? |
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Post by creature386 on Jan 5, 2014 19:40:23 GMT 5
You said Carcharodon has the least spacing and no spacing is the lower end, but wasn't Carcharodon stated to have a spacing of 17%?
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Post by theropod on Jan 5, 2014 19:41:54 GMT 5
17% was the amount the tooth-free space in the back of the mouth accounted for (which is irrelevant here, since this formula only uses the toothrow) in the total jaw perimeter. I wouldn't have asked Kent had he given the interdental spacing in the paper.
I know itÂ’s confusing, because grey used this percentage as an aproximation. IÂ’m awaiting his response regarding the used measurements, because those on page 22 are crown widths, and root widths typically appear to be a bit greater. Note that what's just a few millimetres of difference in the teeth may already have a considerable impact on the size estimate.
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Post by theropod on Jan 6, 2014 0:57:57 GMT 5
Kent sent me a Graph with the regression Grey posted on page 14 and a 95% confidence interval of 13.9-20.1m for a UA width of 14cm that gave a point estimate of 17.45m. Obviously, he urges caution about extrapolating so far beyond the data range.
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Post by Grey on Jan 6, 2014 3:34:24 GMT 5
I knew that Brett was going to respond this. He's very cautious while using any actual method even if he considers jaws perimeter to be the best method in the absence of a compete skeleton. That's the same reason he's not confident with the proposed upper estimate of 17.5 m for Livyatan. Briefly what thinks Brett of meg size : I think 18 m or slightly more is plausible, and if megalodon got much larger than this they would probably need to be largely a scavenger (for reasons mentioned in the chapter). I know that this statement of the largest, oldest megs being perhaps mostly scavengers will be discussed among fossils sharks specialists (several would be skeptical at this even though they'd need to read the whole chapter), but I have personnally no problem with it, something similar had been proposed for T. rex. A changing lifestyle with growth is interesting. Now, were megs really reaching that large for that we assume the largest exhibited such a lifestyle ? It would be interesting to use also Isurus and Lamna, as Siversson did, and see the results there. Perhaps Siversson simply has a stronger idea of the spacing in meg teeth ? Just like Kent, Siversson several times gaves me valuable informations not available to scholars. But the frustrating truth is that we'll really approach any conclusion once the skeleton is collected and studied. But having discussed at length with Hönninger, I'm confident this skeleton is 18 m or a bit more. That's why I'm always skeptical when sizes significantly under 18 m are yeilded by a very large, record-sized tooth. The graph he gave you is exactly the same that mine about tooth width or are there new datas specific to meg in it ? Yes theropod, earlier I had used crown width, from Pimiento's paper data. But lastly I've used the tota tooth width, indicated in boneclones papers. What's the problem there ? You've used what ? Did Kent indicate you how much he added of interdental spacing for Parotodus to get 131 cm or he simply said he used the same than in Carcharodon ? Regarding the inderdental spacing in meg, the closer I know of is from the balaenopterid healed bone bitten by a suspected juvenile meg. The spacing between the teeth marks is about 6 cm. But this does hardly indicate the spacing between the basis of each teeth. Yes , the 17% here are not related, that's the freespace at the back of the jaws, but I've loosely used it for interdental to check if the results were similar to those of Siversson estimating meg size. They apparently are. In other words, to use also others lamniforms such as Isurus and Lamna, and to know the most likely spacing between each teeth in megalodon (asking to Siversson). Also, I find strange that Carcharodon may not have interdental spacing at all. The great white set owned by Hubbell has a total upper teeth width of 74.7 cm, only counting the teeth width. Using this with the formula, it results 4.44 m TL. But the actual shark was 5.52 m TL. You need to add almost 25 % of spacing to get 5.53 m. At least based on that specimen, using only the upper teeth width results in a significant underestimate. So I'm not sure that Carcharodon has no spacing at all, even though there might be some variations. |
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Post by theropod on Jan 6, 2014 15:55:44 GMT 5
The same regression, with slightly more precise parameters (the previous ones seem to have been rounded). He wrote it based on a dataset from Hubbel 1996. Its not the same picture since it shows the estimated size of Carcharocles. I had used nothing so far, because I thought I had no sufficient data. The boneclones-.pdf looked to me as if it gave the same figures that you had labeled as crown width, just rounded. If those are the total widths, were from were the grown widths previously posted? I got a summed upper-jaw tooth width of 1598mm, which would give us an estimate of ~9.45m (potentially a few % more? >>see the update further down this post>>). By comparison, a point estimate for the UA1 with KentÂ’s regression would indicate ~10.6m, of course with considerable error bars. I'll try the Isurus regression with a higher spacing later. The method seems well in agreement with the method used on Parotodus (7.6m for a 131cm toothrow), but if Siversson really estimated (ie. it wasn't a guess) the owner of the Hubbel tooth set at 11-12m we should wonder why. ThatÂ’s strange regarding HubbelÂ’s great white (were did you take the data from?). You should ask that to him or Kent. Is it a complete, measurable specimen? Update: I tried with the above figure for the tooth set and 25% of spacing for both the I. paucus and I. oxyrhinchus regressions The results are 12.5 and 11m respectively. I agree this most likely has to do with the spacing. However I think based on tooth morphology the mako sharks are not a good model. I would say the reality is likely somewhere in between the two, it appears unreasonable that Carcharocles had interdental spacings as large as in makos, and neither do the teeth of the two share a similar morphology:  but I also find it hard to believe there was no space at all between the teeth. For what its worth, jaw restorations typically show some spacing, and there seem to be Carcharodon individuals that have a bit of it too. |
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Post by theropod on Jan 6, 2014 16:05:03 GMT 5
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