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Post by Grey on Mar 2, 2014 13:48:39 GMT 5
Theropod, here is a more interesting point than the whole previous discussion : Brett has not given you the precise percentage he had used in his Parotodus estimate ? Since he agrees that carcharias remains the best model and that I know Siversson made a referal to the Parotodus research, I think the percentage Siversson used in his calculation for Meg is the same that Brett used for Parotodus.
I wonder if the 4.2 % you've found is really accurate. This really not match at all to apply this on the lower dentition of the white shark at boneclones. Theoretically, the Cardabiodon specimen and the white shark from boneclones were of a very similar length about 5.5 m with a lower jaws circumference of 746 mm. But applying 4.2 % in the lower dentition for the white shark only gives a measurement of 518 mm, far off the measurements of the Cardabiodon.
I have to repeat, there's something we lack.
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Post by Grey on Mar 2, 2014 15:55:11 GMT 5
We only really know that it’s vertebral count was in excess of 150. If the lenght/width ratio is bigger, it may have actually had fewer vertebrae. This is a related quote from Bendix-Almgreen 1983: Except for their size, they correspond in all significant fea- tures to the vertebral centra of extant C. carcharias. Given these features it seems reasonable to suppose that the vertebral centra from the Gram locality belong to C. megalodon and might be parts of the same fish from which the described tooth derives.C. carcharias has the stoutest vertebrae among extant lamniforms (although those of Cretaceous ones are even shorter), with a L/W ratio of 0.51 according to Newbrey et al.. C. taurus has 0.55, C. maximus 0.61 and Isurus oxyrinchus has 0.65. The estimated total vertebral count of C. megalodon is most similar to makos. If that was really the case, this would rather be an adaption towards speed than towards flexibility. That is right. However, this does not reject either the possibility for Meg to have had a very high count. The Peruvian skeleton has a reported number of 194 and we can suspect it is not complete.
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Post by theropod on Mar 2, 2014 16:05:16 GMT 5
If there were 4 anteriors and 12 posterolaterals in every mandibular ramus, that means there were 32 tooth positions and 31 interdental spaces. If every interdental spacing was 1 millimetre, as specified, that means there were 31mm included in the 746mm toothrow lenght. I’m wondering whether perhaps the boneclones Gws has rather atypical dentition-TL proportions. But also, 4.6% seems too little spacing for the lower jaw, since lower jaw teeth are more widely spaced than upper ones (due to their anchoring purpose, link1? link2?) If you think there’s something we lack, be specific about what it is supposed to be that we could lack. Kent specified spacing could vary from no space at all to more than 25% in lamnids, with Carcharodon the lowest and least variable (and the mako the highest and most variable, and not a good model for megalodon). He wrote the spacing in the parotodus paper was consistent with Carcharodon. An estimated 190-200 centra is not much more than in a mako shark. You are right, the previous discussion was pointless. You don’t want to understand what I write, you just want to give your very imaginative interpretations. Since it seemed so upsetting to you, I’ve deleted that last post. If you want to pose a question, always feel free to ask.
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Post by Grey on Mar 2, 2014 18:13:57 GMT 5
Perhaps there's another part of the mandible to be taken into account.
That is also what I thought, lowers are more spaced, 4.2 % seems a little low. I think possibly that the 1 mm space is applied only in Cardabiodon with its very numerous teeth. Perhaps Siversson also applied a specific percentage on Meg. Just suggesting... I thought too that maybe this GWS jaw is not normal, but I'm skeptical at the only we got measurements so far is by sheer lack of chance, atypical.
That's the fact the results don't fit which make me think we may lack smething but I really don't know. Another portion of the dentition ? Or simply we don't have the corresponding percentage ? That's the main reason why I'd urge to contact Siversson and ask him. Would be good he finally writes something about Meg, like the small tooth he found in Matrix, a clear record of Megalodon in Westerne Australia.
Kent specified spacing could vary from no space at all to more than 25% in lamnids, with Carcharodon the lowest and least variable (and the mako the highest and most variable, and not a good model for megalodon). He wrote the spacing in the parotodus paper was consistent with Carcharodon.
But he did not specify. What did he used in this "no space at all to more than 25 %". Too bad he didn't precise it to you or in his paper. Siversson or Kent, publications often lack some details that can be verified and used in that case for Meg.
I'm personnally confident with either a mako or white shark as comparison in count. Perhaps tending toward the mako as it is based on a much more analysis and revision of Gottfried works.
When Gottfried did his restoration of Meg, he used ontogenetical changes in the white shark, hence the proportion of the stockier shark with the pug-nose, in fact similar to the proportions of newborn great whites. Would be then interesting to predict an ontogenetical changes from the mako size to Meg estimated dimensions. In fact that would like the drawing made by Kent, an atypical lamniform shark ressembling to several others species. More streamlined with a longer snout though still very bulky.
You were not obligated to delete your post I could live with it. I don't want to bad interprete your approach, I have no problem with revisions for Meg size, bigger or smaller. But not at any cost. The estimates based on centra of course give smaller sizes given their sheer rarity and vastly understudied assignement. This is easy to understand why no estimate (except for the Belgium specimen) have been made based on centra for Meg despite a vast part are available to research. I have nothing against basing an estimate on the larger vertebra yeilding 13-14 m of size, but because of the uncertainties and the fact there is a very large tooth associated with it, force to cautiousness and consider this as minimum estimate for that specimen. And there's nothing wrong to compare you to Andrea Cau with Spinosaurus !
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Post by theropod on Mar 2, 2014 19:05:54 GMT 5
Estimated length.—The estimated lower jaw circumference in C. ricki is 746 mm (an estimate from summed tooth widths with 1 mm spacing between teeth) based on the revised reconstruction of its dentition (the upper row is most likely still incomplete and can thus not be used to estimate jaw circumference in a meaningful way). The estimated total length of C. ricki is 5.5 m based on the relationship between bite circumference and TL for C. carcharias (Lowry et al. 2009). It is precised the toothrow lenght is used, and that is also precised in Lowry et al. 2009. The regression is for the perimeter of the tooth-bearing part of the jaw. It must break down to the interdental spacing. Based on Carcharodon, estimates of 11m or above are not realistic for the smaller of the associated meg dentitions, although based on mako sharks they are (we’d get 11~12.4m). I recall the mako was among the analogies Siversson listed, however I don’t think the Mako shark’s dentition is a suitable analogy because it’s tooth and jaw morphology reflects a different prey and feeding style. That’s also the reason I have used the upper dentition so far, I presume Kent was mainly referring to those, and he himself used it. Applying the same percentage to an animal with fewer teeth implies fewer but larger spacings, and the amount of spacing will be proportional to the bite perimeter. I was not assuming C. megalodon had just 1mm of spacing between adjacent teeth. But it would be interesting to see whether the spacing scales isomatrically, or whether it stays constant. Sadly, no extant macrophagous shark is even close to C. megalodon’s size, so we can draw very limited conclusions from them. But the cutting purpose of the teeth constrains the space between the teeth. That’s always a problem with having just a single individual. I’m sceptical myself, but some things point out to it in this case. it’s one thing if the results don’t fit measured lenghts of actual specimens. It’s another thing if the results don’t fit other estimates. But it seems that they are well within the range you get with other methods, the odd one out is Siversson’s 11-12m figure for the subadult specimen, which is probably not based on Carcharodon. He wrote consistent with Carcharodon, which implies towards the lower bound. But since the spacing is variable, the best there is to date is the "somewhere between 0 and 15%" I’m well aware of that. well, then i think you see you misunderstood some of my points, especially the purpose of my statements. The point was not to "downsize" C. megalodon. For all I know large especimens exceeding 18m is fully valid, and that’s roughly what the consensus is about (except when using Gottfried’s methodology, but we already discussed why it probably underestimates the animal). But it has not been established (I.e., how should it be revised?) how common those large sizes were, and based on a big amount of material they appear to be relatively rare. The situation with centra and teeth both reflects this, and that is interesting regarding it’s size. Now, if you want I’ll make a second thread dealing with the average size... I’m not revising those previous estimates for specimens, and I’m surely not claiming C. megalodon was smaller than Pliosaurus.
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Post by Grey on Mar 2, 2014 19:57:43 GMT 5
I remembered that part of the paper. I know that with the Mako we get this. However I'm still thinking he did use a percentage for the white shark that we ignore. Perhaps he has suggested a specific spacing for Meg. Perhaps he did base his estimate based on the several species he based his estimate. Or perhaps he modified Lowry's formula...
As the upper represents a larger part of the body that's not surprising. Siversson used it on lower because the upper was not complete. I don't remember how complete was the lower in Parotodus. Using both is valuable though.
Agreed for most, only I was not you suggestin 1 mm for Meg spacing, but a total of 4.2 %, something that does fit in the GW set we have on boneclones.
I agree that we're not going to be fine with only one individual. But here the disparity between the result of the formula and the actual size of the shark is huge. Another set would be useful.
Or based on Carcharodon with another percentage, or a range from all the species he used. That's not very relevant but even the boneclones website lists the individual at 12 m. We cannot ignore Siversson estimate he gave in public based on that upper jaw perimeter method. Which other methods fit it ?
But then, what did he applied in Parotodus ? That's quite a range and he necessarily applied a precise percentage to get his estimate. Like in Siversson paper, that is not precised.
Deleted mine.
You gave too much credential for centrum based estimates. After several pages discussing this that was a bit suspicious.
I still have a problem with that by the way because I got old mails from Gottfried where he agreed that Meg could reach 18 m despite his method. Or perhaps he was thinking about direct sizing.
There is a study in progress about that, so no conclusions at now and no need of an additionnal thread. Don't use centra there, centra reflect almost nothing so far. Too rare, too poorly documented, unlikely to be preserved in the largest Megs. For now, it appears from Pimiento interview that 18 m Megs existed at all times of its reign. Like in any animal, a maximum size is rare. But it belongs to the potential growth of the animal and is thus normal, not exceptionnal. The content of this thread suggests that from isolated teeth, sizes between 15 and 18 m are nothing exceptionnal.
I'm not of those who favor average over maximum or vice versa. I favor both, especially in the case of Meg which seems to have had huge sizes variations, a bit like Cretoxyrhina.
Good to know. Pliosaurus is perhaps comparable with some Megs populations depending the era, but again, wait...
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Post by creature386 on Mar 2, 2014 20:06:05 GMT 5
I still have a problem with that by the way because I got old mails from Gottfried where he agreed that Meg could reach 18 m despite his method. I have to admit I have little idea about this whole debate compared to you two, so this could be a stupid question, but why the "despite his method". He didn't say 17 m is the absolute upper limit and he maybe talked about larger teeth.
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Post by Grey on Mar 2, 2014 20:19:07 GMT 5
I still have a problem with that by the way because I got old mails from Gottfried where he agreed that Meg could reach 18 m despite his method. I have to admit I have little idea about this whole debate compared to you two, so this could be a stupid question, but why the "despite his method". He didn't say 17 m is the absolute upper limit and he maybe talked about larger teeth. Theropod found out that the measurements for Gottfried method was vertical height, not the slant height typically used by collectors. Basically, Gottfried's calculation is translating the vertial height of the UA2 in cm, take out one feet or two. Megs teeth, which are somewhat compact, reaching 18 cm in strictly vertical height are the largest (though in Parotodus paper, Kent indicates from Purdy that the largest authentified Meg tooth reached 18 cm). Hence, it was unlikely to find 18 m or more with Gottfried. Unless, the slant measurements indeed works (and in that case : WTF ?) or that he knew even larger teeth than 18 cm vertical height, or that he referred to direct sizing which allows to get sizes about 20 m TL.
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Post by theropod on Mar 2, 2014 20:34:27 GMT 5
But nothing indicates any percentage big enough to reach this figure with the white shark would be feasible.
In that case, the white shark wouldn’t be a suitable model any more.
Only Isurus and Carcharodon were available in Lowry et al. 2009, and of those only Isurus gives figures consistent with what he stated.
He didn’t do that in the paper.
Lower dentition had a slightly better correlation with the great white, but not significantly.
In I. oxyrinchus, the upper dentition correlates better. it seems it is complete, at least they have a complete reconstructed dentition and were able to use summed tooth widths.
Yes, however we know how the tooth spacing is constrained, and we know The formula is well correlated with total lenght.
It seems strange nobody has published a paper on the morphometrics in Carcharodon dentitions yet.
The largest teeth, like Hubbell’s, turning out at 18m+ is typical and certainly not overly conservative.
That he used Mako sharks for some reason is enough of an explanation for now (that is, until Siversson explains it in more detail himself). Either way I’d far prefer the lower end of his estimate, it seems much more realistic.
We don’t know the exact number.
That you even use the term suspicious is the very core of the problem.
He must have. Even for the hypothetical largest teeth (the perpendicular height of 18cm, presumably Bertucci’s tooth) you get only 17m with his regression. But he probably did the direct sizing (with the largest reported measurement and an extreme in the variation of great whites this gives us ~19.5m) because he himself thought those results too conservative. But obviously the direct sizing while picking the specimen in many that gives the highest estimates is a very biased approach, no wonder it was never used for more than a demonstration.
Again, I am not only interested in the largest megs. Then the poster must be very outdated.
250kg lions are exceptional. 1t saltwater crocodiles are too. So are 700kg bears. All potential sizes some members of these species reach, but all not exactly normal.
Not surprising since it’s mostly teeth suggesting such sizes that even get posted here, with a clear sample bias towards the largest specimens. Then both should be interesting to you. Large specimens/species of Pliosaurus are apparently comparable to smaller populations of C. megalodon. But as a whole species, it is definitely smaller.
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Post by creature386 on Mar 2, 2014 21:10:08 GMT 5
I have to admit I have little idea about this whole debate compared to you two, so this could be a stupid question, but why the "despite his method". He didn't say 17 m is the absolute upper limit and he maybe talked about larger teeth. Theropod found out that the measurements for Gottfried method was vertical height, not the slant height typically used by collectors. Basically, Gottfried's calculation is translating the vertial height of the UA2 in cm, take out one feet or two. Megs teeth, which are somewhat compact, reaching 18 cm in strictly vertical height are the largest (though in Parotodus paper, Kent indicates from Purdy that the largest authentified Meg tooth reached 18 cm). Hence, it was unlikely to find 18 m or more with Gottfried. Unless, the slant measurements indeed works (and in that case : WTF ?) or that he knew even larger teeth than 18 cm vertical height, or that he referred to direct sizing which allows to get sizes about 20 m TL. I very well know about the slant/vertical height. It's just, with the 19.3 cm tooth, you'd still get (almost) 18 m.
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Post by Grey on Mar 2, 2014 21:26:55 GMT 5
So there's a problem somewhere. The underestimate for that shark is too great. Need to test it on another set.
Hence his use of others lamnids ?
But he did not specify Isurus, he also used others. So perhaps 11-12 m is a range (11 m being the white shark basis). He probably has his own data about nasus.
That's merely a suggestion among others.
The results I got with the lower dentition were not close to 11 m...
But he still performed his estimate based on upper total tooth width...
Still the result are ~20 % what we'd expect for the actual GW that possessed this set. Definitely the percentage is too small in that case.
I only see Mollet's website.
That's not of it being conservative (which it is still while compared with the juvenile set and the white shark) but how Siversson did it. It would be the same question if we've got size clearly above 20 m.
If added 12 m as a range in his explanation, it is that he found something at least approaching it. Perhaps the range represents the results from the various species.
THE task.
Discussing size based on centrum did not deserve such a discussion, so I got suspicion.
I'm not fond of direct sizing but I do note that the range of 11-20 m TL for Megalodon was still conserved by Compagno and Wroe in further works. That's just the extreme possibility.
I'm not sure if the 18 cm perpendicular height came from Bertucci, perhaps in Purdy's collection. Pimiento reported Purdy had found teeth from 5 cm to 15 cm in crown height.
Neither do I, the thread does not report only behemoths.
Or filled with errors.
It does not seem that +16 m or 18 m Megs are considered something exceptionnal as this the common length listed in modern litterature. As Pimiento found out, on 400 teeth, that at any period Megs reached 18 m, suggests that this was not extraordinary. Now I won't too much develop on this for now...
In the case of modern animals, don't forget their life history and biology is affected by human interferences, hence far more rare maximum size reached in these species.
Yes there's a sampling bias, but not only. And smaller teeth can also indicate very large sizes. We have also mostly discussed Hubbell's specimen.
Maximum is far easier to determine by available means. Average is deeply worked by Balk and Pimiento with a large sample of teeth from various world locations. So let's wait their work (and the comments of others paleontologists about).
If Pimiento's indication is right, yes. But I have nothing against segregate smaller Megs specimens from larger like differents breeds or subspecies in match up and comparisons with other large marine predators. Though the bite force of a 18 m Meg and a 13 m Plio are certainly comparable.
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Post by Grey on Mar 2, 2014 21:28:44 GMT 5
Theropod found out that the measurements for Gottfried method was vertical height, not the slant height typically used by collectors. Basically, Gottfried's calculation is translating the vertial height of the UA2 in cm, take out one feet or two. Megs teeth, which are somewhat compact, reaching 18 cm in strictly vertical height are the largest (though in Parotodus paper, Kent indicates from Purdy that the largest authentified Meg tooth reached 18 cm). Hence, it was unlikely to find 18 m or more with Gottfried. Unless, the slant measurements indeed works (and in that case : WTF ?) or that he knew even larger teeth than 18 cm vertical height, or that he referred to direct sizing which allows to get sizes about 20 m TL. I very well know about the slant/vertical height. It's just, with the 19.3 cm tooth, you'd still get (almost) 18 m. But that tooth was itself measured in slant (as far as I know), not perpendicular height. Perhaps like suggested Theropod, it was the one reaching 18 cm in vertical height, which gives it smaller than 18 m TL.
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Post by creature386 on Mar 2, 2014 21:37:28 GMT 5
Yeah, but I have suggested a slant height of 18 cm for the 16.8 cm tooth.
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Post by Grey on Mar 2, 2014 21:44:57 GMT 5
Yes, so ? (I don't like spamming so I fill the post with useless things like this line^^).
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Post by theropod on Mar 2, 2014 21:53:38 GMT 5
Probably. With a bigger percentage of spacing, that would again indicate he used a method based on makos, which have such larger spacing because their teeth serve for gripping. Which I agree with Kent is not what C. megalodon was built to do.
Hence why I doubted that he necessarily used Lowry et al. In any case, you don”t get this based on the white shark, still the best analogy imo.
Unlikely since we don’t reach 11m even based on 15% of spacing, while he used a smaller percentage with the white shark regression in his paper on Cardabiodon.
Based on white sharks or based on mako sharks?
Because I actually get an estimate of 11.2m when using the lower tooth width +15% with the white shark formula, and 12.2m for I. oxyrinchus, but only 10.6 using I paucus. So apparently, the lower dentition in C. carcharias is a good deal shorter than the upper, and it seems the two species of mako have very different upper to lower dentition proportions.
No, they used lower tooth width.
Not necessarily. as I wrote the shark might simply be an outlier. One with a large spacing, probably, and perhaps relatively elongated, i.e. with a relatively smaller mouth.
But we cannot know that for sure based on a single specimen that’s not extensively described. It is just made very likely by the other data we have.
Then please stop having such "suspicions" about your fellow members and accept the fact that others have other opinions on what deserves discussion. You do not have to participate if you consider something unworthy of discussion. But you cannot have the last word in every debate, whether you think it has a right to exist or not.
...Or a tooth comparable in size to Bertucci’s. In any case, the tallest tooth on record (though not necessarily the biggest).
Not only, but mostly.
Are you suggesting that Pimiento & balk made a poster filled with errors for the SVP meeting?
The two are not exclusive. the lenghts listed in the literature are mostly in the format "could exceed 16m" or "could reach 18m".
So where did they state that? Their poster tells us something very different, and not long ago you remarked to be surprised that at any time the largest exceeded 18m because you thought Shimada’s method was conservative.
Maximum size we can only approximate, and only if the sample is good. We don’t have that luxury with the majority of animals.
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