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Post by coherentsheaf on Feb 28, 2014 22:21:14 GMT 5
theropod: No idea about the mass. I culd do a guestimate but that is probably not good enough.
grey: Regarding Thalatarchon: I dont know and the paper does not give much detail. If tooth size is the only material compared, then I think this is not a reasoable estimate, as tooth size is not the best proxy. Hymalayasaurus remains are as big as or bigger than the largest Shonisaurus remains, which it is closely related to. I am looking into the reliability of body size estimates of Shnisaurus.
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Post by theropod on Mar 1, 2014 0:16:02 GMT 5
This applies to teeth as well. The only method of estimation really counteracting that is jaw perimeter, not used in the majority of estimates. And vertebral diameter is likely less variable among related sharks, considering it’s not so strongly related to dietary preferences. I think Carcharodon is a close proxy. But if you know one, I”d be interested in seeing comparable data for other lamniforms, especially Alopias, Lamna and Isurus, and also Cethorhinus. If you mean that, AFAIK there’s no reason why an estimate based on vertebral diameter shouldn’t work just as well for sharks (given postcrania are known of course). they are just a more abundant source. Certainly a partly associated vertebral collumn is far better than an isolated tooth. The more specimens are known, the more estimates you get, the higher the probability to find a big specimen. that’s why you think there’s a disparity between estimates based on vertebrae, and estimates based on dental remains. But the point is, unless the methods are flawed they should be prefectly compatible. It’s just that The sample of vertebrae is much smaller than the sample of teeth (because there are many hundreds of the latter), so that of course the largest known teeth probably represent bigger specimens than the largest known vertebrae. The one you posted was missing half its crown and we didn’t know what position it was in. You can at best make a very rough estimate, the like of an extrapolation based on its width. Maybe yours, but not mine. In the largest of a decent sample of centra that’s not such a problem. Take the specimen from denmark. Assuming it’s not from the tailfin (which without evidence we shouldn’t assume), the variation (10-23cm) seems to represent the range of size variation within the remaining axial collumn decently. The largest are likely also among the largest in the collumn. I’ve got no problem with whole megalodon dentitions, but the whole dentitions we have don’t seem to indicate an animal significantly bigger than the largest centra, somewhere in the territory of big pliosaurs and ichthyosaurs. The truly enourmous estimates all derive from isolated teeth. A large amount of the estimates you made base on a hypothetised tooth position. I’m not doubting their assignments (although noting that their size ranges are Amphicoelias-esque). But I explained why we cannot replicate that properly at the moment. well, at least these guys all are aquatic, tunniform and macrophagous, and indeed the difference seems less than with some other animals (albeit by coincidence). But I think it is irrelevant, we should estimate each animal based on the closest available analogy and compare the resulting figures (and test them well of course). If we do so, we arrive at ~16m for the largest Ichthyosaur vertebrae, ~12m for the largest Pliosaur vertebrae, and 13.55m for the largest megalodon vertebrae (though not necessarily the biggest specimens in all of those). That their vertebral size seems comparable is just a nice visible observation, not very useful to rigorously estimate their relative size.
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Post by Grey on Mar 1, 2014 1:01:16 GMT 5
No offense really, but frankly this discussion starts to be boring, I don't really know what you want to establish there. But here we go...
There is just more experience in teeth sudy than centra studies. You need to have a documented column for doing this. That's not the case. However, we have fully documented dentitions in both species so no wonder the published estimates are based on teeth. Centra are too rare and too poorly documented, period.
In the case of Cetorhinus, a quote from Kent :
I don't think meg and Cetorhinus centra are all that similar. The large meg vertebrae I've seen are pretty robust. They don't have the more tightly packed septa of the lamnids and odontaspids, but overall they're much more solidly built than those of Cetorhinus. The vertebrae of Cetorhinus are so poorly mineralized that they are almost always badly distorted during fossilization. It's very rare to see this type of distortion in meg vertebrae.
And postcrania and centra assignement is almost unknown in Meg.
If you refer to the Denmark material, 20 centra (on a total estimated at around 200) with unknown assignement is anything but better than the datas we have from teeth. If you refer to the Belgium material of 150 pieces, it's an absolute shame such a specimen has not been kept, studied and not hidden in the underground of the Museum.
Teeth are more abundant so more documented, so estimates are based on them. They are the best available. Regarding centra, that's almost if we had virtually no material for estimating size.
The point is not the number of specimens teeth or centra, the point is that no one can assign a centra to a position, then predict a size. Because centras assignement is poorly studied in sharks and almost unknown in Meg which is estimated to have had a higher number of vertebra than the white shark. Why trying to make an estimate for the 23 cm vertebra ? Does anyne knows its position ? If it was the largest in the column ? The second largest in the column ? The third ? No one knows that. But if you found a document allowing to place the identify the centra and the likelihood of its size in the skeleton of a Meg, I'd interested. But I doubt such a methdology exists yet. So I don't get the purpose of that discussion.
I'm not agreed, the sides and angle of the crown gave an idea of the original shape and size. But that's certainly a matter of personnal perception and only verifiable at hand, not from a single picture on the internet...
I don't know your point as I said. You want make epic revisions based on poorly documented rare pieces such as centra ? Good luck I've nothing against of course, but until this comes, I'll favor the published methods still currently used by authors based on teeth and overall dentition.
I'd not call 20 centra a decent sample. Now the one at 23 cm is probably among the largest in the original column. Among. That's the point, that's not precisely assigned and only will result in very rough estimates.
The whole dentition from Hubbell's comes from an animal considered as a juvenile. The other from an adult. I have to recall you the sizes variations of Megalodons hinted by the works in progress...
The truly enormous estimates based on isolated teeth are themselves based on the use of Hubbell's set as template. Which estimates I made ? What is the link with the beginning of your response ? I only used tooth position using Shimada's method, not the one based on jaws perimeter. And apart for the problematic posteriors or broken teeth, most of the position were no hypothesis but likely accurate, I had even asked to Brett in one case or two.
The range is massive, that's why using the mean, though not totally satisfying, is justifiable. I'm agreed with you for the rest.
Why not but that remains then individual cases and in each we have to determine the position of the material and if it represents the largest in the column.
In the case of Megalodon, the sample bias is huge and the assignement less known than in marine reptiles anatomy. Anyway, there is really limited material for playing in Meg.
Exactly.
Now beside responding my quotes, I'd like to know what is exactly your goal ? To be fair, I've not said I'm against any estimates based on vertebra, I just recall the quick limitations of that one compared to much more documented and stable material as dentition parameters.
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Post by theropod on Mar 1, 2014 3:05:27 GMT 5
Nobody is forcing you to continue debating if you are bored by a discussion. But if you are bored, it shouldn’t be difficult to drop out.
I know the quote, and I think macrophagous lamnids are the best analogy. Still I listed it, just in case. But yes, the estimates we can already make are probably the best anyway, the best compromise between similar size and similar morphology.
That”s also the case with Ichthyosaur vertebrae, and it’s also the case with random lateral teeth.
A single tooth is a much smaller and more variable part than that. I’m not talking about associated dentitions here, I’m referring to isolated teeth.
If you have 20 centra ranging from 10 to 23cm in diameter, you probably have got some of the largest centra in the collumn among them. yes.
Teeth are virtually no material for estimating size. The only reason they are used extensively in the case of sharks is that there is a disproportionately large amount of research done on so disproportionately little material, of which teeth are the only commonly found fossil. Again, you are not talking about the quality of the material, you are talking about sample sizes.
btw, if centra are so badly studied, how do we know that? There ought to be no relevant difference between those three.
The purpose of that discussion was initially to compare the centra in megatooth sharks to those in some giant marine reptiles, to compare them with the same methodology.
A high-quality, perpendicular picture and high-quality, perpendicular pictures of an associated dentition could help you restore that piece. But line drawings and low-res shots of casts are not enough.
And certainly, just connecting the edges with an imaginary graph isn’t. with such specimens, it is best to revert to root width (which is better anyway).
I’m not making any "epic revision".
Hmm, somewhat like with those teeth (just more precise).
Yes, and it probably isn’t even 11m long, I’m not counting it.
you don’t need to.
Yes, and that’s still the best one can do with those specimens. But it’s not related to the issue at hand, that these are potentially giant specimens based on scrappy remains.
Which estimates I made ? What is the link with the beginning of your response ? I only used tooth position using Shimada's method, not the one based on jaws perimeter. And apart for the problematic posteriors or broken teeth, most of the position were no hypothesis but likely accurate, I had even asked to Brett in one case or two.
We don’t know that for sure with either, take McGowan 1996. You can make a maximally conservative or a maximally liberal assumption (obviously noone would seriously do the latter). In the case of the largest meg centra, it seems clear they are large ones for the specimen, and there will not be a large difference between adjacent large vertebrae.
the sample bias is huge with fossil taxa.
My goal was to explain how one could better make a rigorous comparison between C. megalodon and most other giant extinct animals by comparing the estimates derived from centra, since those are much more comparable in terms of their sample size, than by comparing the tentative estimates for the very largest known fragments. Furthermore, that a size estimate based on vertebrae is at least equal to one based on an isolated tooth.
I posted that elsewhere, the average of the maximum lenghts (14.56m) from the upcoming Pimiento & Balk research is also interesting to this matter. It shows you just how much those very largest specimens are not normal for the species (even among the respective maximum reported sizes for those time periods).
In conclusion, the point was to take care with enthusiastic claims about C. megalodon’s size, since how big it actually was, not counting the occasional outlier, might yet surprise us. That’s why I think it’s much more interesting to find alternate ways of size estimation, for typical specimens, or for more complete ones, and ways to compare megalodon to other giant predators, than to collect particularly huge teeth (which I think this thread contains an impressive collection of anyway, thanks to your effort) and estimate their size.
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Post by Grey on Mar 1, 2014 4:22:30 GMT 5
I simply want to be sure what do you search here. I've seen your response at the end...
Fair enough !
Sure. But we have better postcranial remains of shastasaurids than Carcharocles. Lateral teeth are certainly much easier to place than random centras. The complete dentition of Meg is known, its skeletal structure is not.
Only probably, there's no way to be sure. In fact we don't know at all. We don't know the exact assignement of Megalodons centras in the column, nor the maximum size of these centra. A single tooth is subject to many issues, but at least the direct relationship with the body is more reliable if its position is known.
Well although teeth are not perfect because of the reasons we all know very well, I cannot let you argue this. They are the least bad mean rather than the best but there has been justly extensive documentation about because of the lack of other material. But arguing that teeth are useless at estimating size is wrong, they just have to be taken with a degree of caution. Enough publications say otherwise.
There is an actual consensus among paleontologists about Carcharocles megalodon size, we can read it in abstracts or summaries ("more than 16 m", "could reach 18 m"...) and this consensus has been based on teeth studies, never on centra. And excuse me, but paleontologists specialized in fossils sharks are aware of centra since much longer than us.
About the quality of the material : centras are no better justly because of how they're rare, not at all documented in their exact assignement, position and relathionship to body length. Also a number of them are incomplete or fragmentary, added to their sheer rarity. Another point, their state of preservation is ordinary inversely proportional to their size.
We do not know, that is merely suggested in Gottfried et al, based on Carcharodon and most likely arrangement of the skeletal structure for a hydrodynamic pelagic structure, but there's no way to be sure of this. Here again, no wonder there has never been repeated atempts to estimate size with that material. That's just obvious.
Which will give very limited results because of the rarity of Megs centras and the actual impossibility to accurately and with certainty place them in a column we have never seen in any sharks species, except for some peruvian investigators.
Source for this ? Even slight size differences are important. On Mollet's page, there is always the size of the largest centrum reported from white sharks, not several centra, only the largest, which shows there's a clear maximum magnitude of width in centra. And I don't necessary talk about only three in the entire column. You need the largest centra to estimate it, not "among the largest". The largest are suggested by Gottfried to have been in the pectoral region. How much were they then ? We don't know that. If there was 10 or 15 of these largest centra you cannot state anything and make a day. As much you've been able to investigate deeply in others discussions, you far too much simplify this problematic.
Only verifiable at hand with an experienced eye if yes or no it would be possible. My guess is that the tooth is not that difficult to reconstruct because of the reasons listed so far, nuff said.
That was not taunting from me. But trying to establish you have a new advanced method at estimating Meg size based on isolated rare centra from unknown position in an unknown vertebral column, something that no fossil shark expert has ever tried to do, is rather epic to me. No sarcasm implied.
Well, just one sarcastic, not agressive, point : you doubted about the placement of teeth in the dentition, despite the dentition of Meg is well documented, but now you argue to be able at placing a random centra in an unknown column, with no existing documentation about this. With all my respect, this makes no sense.
Any estimate is an estimate. But yes, teeth data is more precise and with much more material to use.
Mike Siversson estimates it at 11-12 m TL (and 10.86 m using 15 % is roughly 11 m...). You have not worked on the other individual yet (which is probably only a bit larger).
I'm somewhat shocked how you argue this with such a certainty. Remember we're in the realm of estimates whatever the method. You again forget how much the calculation lacks the adequate percentage and perhaps another factor to use. We'e got massive understimates even using 4.2 % so please try to investigate further this method instead of acting like if you had found the ultimate method. I don't understand why you still persist at ignoring Siversson's estimate like if it was worthless whereas he's the only one to have several times presented sizes estimates based on that method and he's in fact the one who influed us to search about that method of calculation.
It's related in that we have better knowledge of Megalodon thanks to its teeth than to its centra, despite the problems of scaling from teeth parameters.
I don't understand why you act as if you had any tool or documented method to argue this. Seriously. They are certainly not all large for the specimen, we just know the size of the smallest and the largest. The smallest is 10 cm wide, that's only the size of the largest vertebra in a large great white. How can you claim then that in these 20 centra, there are the largest there was in Megalodon ? No one knows Megalodon column structure. The size of the associated UA tooth suggests, if Gottfried is accurate, the largest in the centra was more likely approaching 25-26 cm.
Even more in Megalodon which had a cartilaginous skeleton contrary to the marine reptiles.
The problem is that you ignore the lack of knowledge of these centra, you just take a measurement, an assumption based on a frankly limited support and you make a day. You don't even notice why rigorous estimates have not been published for Megalodon like this, except for a short mention in Gottfried's. I'm not denying this as I've myself performed such estimates but quickly realized the limits at using this. I'd be agreed with the last line if there was more documented stuff behind the centra.
Centras are considered a highly valuable material in Meg research, but not for estimating size.
One remark. You have stated during several pages that Balk and Pimiento estimates were unreliable, now you use them for establishing a figure even before the final data is collected ? Then, 70 tonnes Megs are absolutely anormal freaks but specimens under 100 kg are certainly normal ? Just kidding. Then this does not show anything yet of how common or not were the largest specimens as there is no data number of them in the graph.
Balk has strictly specified to me, again this week, how the results are not reliable yet. I don't think at all you're in position to state that she's wrong and that her results will be similar. We don't even know at which stade of her work she was then and now. I think that she knows her advancement better than us. Just thinking ! Seriously, why this tendency to want make conclusions months before any papers is even published ? Making Megalodon that smaller (which it isn't, 14.50 m TL of average maximum size is more or less about what I'd expect but again I'm patient and not make any conclusion...) is that important ?
Now if this thread has showed something, it's that sizes above 15 m, yeilded by various methods and through various teeth, not all famous for their size, are anyhing but rare. And sizes of 18 m appear just like ~6 m modern great whites, large, not anormal. Otherwise, well I guess Klaus Hönninger is a lucky man...he found the Angus MacAskill of the Megalodons... But it is just premature to state anything now. I'm opened to any possibility in the light of the future regarding Megalodon as I'm interested in truth found by rigorous way. Excuse me, but make a conclusion based on an initial graph Balk gave me, and make a conclusion of Meg size based on an oversimplified assumption of Megs centra is not rigorous. You have been much more rigorous earlier in this thread and certainly you know that.
No, centra are not of great help at this for all the obvious reasons listed above. That's a potential alternative way I fully agree as long as more data is done about centras, but that's not the miracle Method.
I don't see the point to be enthusiastic or not, we all have interests in large, spectacular animals and Megalodon was quite possibly the largest marine top predator known to exist. And contrary to some others members I don't have a tendency to suggest and establish extraordinary sizes well above the actual consensus.
The purpose of this thread is not to determine an average size for that shark species but individual size Megalodons could attain through various methods. In that way, I have nothing against estimates based on centra, as long as we're sure this is the largest in the column, which is not the case. The thread does not exclusively include gigantics teeth specimens but also smaller ones, specimens expected to be giants turning out to be smaller or vice versa... At the end of the day I'm counting on the peer reviewed papers for valuable information, not speculations on a forum thread.
I fear that this discussion becomes a bit conflictual (though I take this easier than previously) because as intelligent you are I don't think you can admit your errors there and rather surprising ignorance of obvious facts and it's tiring to repeat and have the impress to not progress. Here you give me the impress to consider all the Megs specialists were dumb enough to not have deduced this "so much obvious method at estimate Meg size". Not interested in forum contests as what really matters, at the end, is the published reviewed works, not discussions on a thread. And I have too much respect for the members like you who contributed to the quality of this forum to continue a discussion which will yeild nothing other than the reason why I will respond, to try to prevent you to make a day of your own conclusions and present on others forums where you're active potentially fallacious informations about that shark which has already too much mistatements on the internet. Though, I repeat that doesn't matter what you can think and report elsewhere, what counts is the scientific reviewed stuff. But it'd be cool to progress a bit and try to be more objective, or we're not going to progress unlike in our previous discussions which were of a certain quality.
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Post by theropod on Mar 1, 2014 17:39:58 GMT 5
Of course, but assigning random Ichthyosaur vertebrae exactly isn’t possible either AFAIK, yet nobody protests about the use of circumstantial evidence there. We know for sure that it’s not among the smallest, since much smaller centra have been reported. Of course, only probably. But none of our estimates for megatooth sharks get better than that. As I wrote, this is under the assumption that the centra are not from the tailfin. Is there a good work on the axial collumn of great whites (or other lamnids if not)? But we have no reason to presume there were immense differences where there are none in Great whites, do we? I wouldn’t be sure of that at all. There is simply no evidence suggesting vertebrae were more variable. In fact I know a certain palaeontologist who would certainly make fun of you for that suggestion… Not useless, but an emergency solution. Extensive documentation does not remove their variability. But you certainly noticed that I did make estimates for teeth. I just consider estimates based on other remains even more interesting. That again affects teeth as well. A centrum that’s probably among the largest ones is no worse than a tooth "probably somewhere between L4 and L6" and yielding several-fold size-differences. Teeth are often fragmentary too. but vertebrae are so close to circular that in most cases it’s easy to find out their diameter even if they are incomplete. That may be the case, but see above. Either way, the 150 associated centra from belgium consitute a large part of the animal’s vertebral collumn. This specimen has to be studied extensively. That is, again, the least bad way there is. Based on pictures of shark vertebral collumns (or any vertebral collumn actually), I cannot see how there is a steep, step-like difference between adjacent vertebrae’s diameters. If even slight differences are important, why do you trust in methods in which a shifting by one tooth position can account for linear size differences of over 70%, wherein the tooth position cannot even be constrained to less than 3 candidates? In every other vertebrate, if estimating size from teeth at all, one would be conservative and assume the tooth was the largest in the dentition, yet you are totally fine with that? And at the same time think comparatively minuscule differences in width between adjacent centra are "important"? There is no point in exagerating it unless it is actually known to be statistically significant. And do all researchers just use the very largest centrum? I’m not sure: Vertebrae anterior to or directly under the first dorsal fin were taken. They used what would be labeled "anterior dorsal" in most animals, but they did not limit it to specifically the largest vertebra in the collumn. and yet: This was one of the two regression that I used, it yields 13.54m. That may be somewhat conservative, but we have no reason to presume it would be far off. Vertebral diameter remains a valid means of estimating TL in a shark. If you haven’t attempted to reconstruct its crown, how do you know? I have not used any new advanced method. I have used methods that have long been established for estimating a shark’s total lenght from the size of its anterior vertebrae. I doubted about placement based on guesses, without any scientific documentation going further than "lateral or anterior", and I reminded you that you considered ranges of estimates smaller than the ones from Pimiento et al. too large to be meaningful. it is not that well documented. We have a number of pictures, and a description that’s unfortunately written in japanese. I’m not arguing that. But We are not talking about random centra here. I meant the other way around. It would be 13.4m using the same method (i.e. upper bound), and it is considered an adult. As I said, Siversson’s methods for the estimate are not documented anywhere. But a method we actually know indicates it is below 11m. That is obvious, I don’t need to mention it time ang again. Of course all that is in the real of estimates (and, more importantly, the "least bad" ones). But I was already giving you an upper bound, therefore I feel somewhat confident (and as sure as I can get at the moment within the real of estimates) we can constrain its size like that. I don’t know whether he was for you, my influence for searching for such a method was Kent’s paper on Parotodus. Not worthless. But as I mentioned, his methodology is unknown, not documented, let alone properly published. It is useless to philosophize about something that we literally know nothing about. you just wrote the following: "I'm somewhat shocked how you argue this with such a certainty." But much, much less so with its teeth. As you commonly express it, the "least bad". You always immediately assume I’m making a day, when what I’m explaining is that you shouldn’t make one. Limits to the maximum size you get relative to those you get from teeth, because the sample of teeth is so huge. I’m not of the opinion that they are final data, no. But as you did as well, it can be interesting to look at what the biggest specimens in their sample were. this if of course extremely rough at the moment. Counting juveniles and neonates, your kidding is closer to accuracy than you may think. Of course not "below 100kg", since that’s the lowest reported by them, but for example "below 1t". someone you need to do the same another person does to let them see the limits this has. My point was just how uncommon those 16m+ monsters appear to be, considering even the mean of the LARGEST specimens from the respective time periods is well below that. I presume you are not prepared to argue the largest specimens are still all juveniles. good to know. For sure not. But you’re certainly not in the position to argue that they will add a bunch of much larger specimens yet. I’m just somewhat annoyed because all that ever gets reported here are maximum sizes for particularly large teeth. Remarking some more moderate figures was in order. The current data doesn’t make me confident of C. megalodon’s adult average size exceeding 15m. I’m experiencing some kind of deja vu here. Your title needs an update if your intention was to merely post estimates for some hand-picked particularly big teeth. As long as the topic doesn’t state otherwise, I will assume it to include everything related to C. megalodon’s size, not merely that. To be honest, if there’s anything here that I’m not that interested in is reading one speculative max-size estimate after another. They just aren’t that relevant. Also, why did you post Pimiento & Balk’s preliminary work here if you are not interested in it? I’m not trying to make up bias. Just keep in mind my point; as countless data show us, it gives us a biased picture to just estimate the size of the largest teeth and call that a day for concluding how big this predator was.
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Post by Life on Mar 1, 2014 17:45:09 GMT 5
Since this discussion have shifted to centrum factor, I would like to clarify some things: - Centrum length - Centrum width - Centrum quantity - Centrum position Look at this comparison between vertebral centrum of a Megalodon and GWS: The image is self-explanatory. Centrum of Megalodon are not just wider but also longer. In addition, Belgium based partially preserved specimen is incomplete not just in the context of absence of associated dentition but the vertebral column itself is incomplete and assessment is that Megalodon had noticeably higher centrum count then in GWS. All of the aforementioned factors point towards strong possibility of difference in TL to BL ratio in Megalodon in comparison to GWS. In this manner, no size estimation method is logically valid for estimating the size of Megalodon on the basis of size of its centrum. Unless a beautifully preserved adult Megalodon is found, this mystery is not going to be resolved but available data (if put together) warns us to NOT UNDERESTIMATE the proportions of Megalodon. It is misleading to consider GWS as a perfect analog for Megalodon's biology. People often overlook this fact.
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Post by theropod on Mar 1, 2014 17:55:23 GMT 5
If it had both more and proportionally longer centra, that would indicate a longer, more elongate body.
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Post by Grey on Mar 1, 2014 19:08:25 GMT 5
To my knowledge, vertebral column are more documented in marine reptiles than in Carcharocles. And even if they are not, you have then to complain why and how they've estimated sizes in these species, not in the case of Megalodon. In the case of MoA as I showed, the vertebra based estimates make sense as the vertebra are known and assigned and thus comparable with others related pliosaurs. But since the associated vertebra were not themselves associated with another substantial element of the skeletal structure, like the skull, as it is the case in MoA, how to be sure where these centra were placed in the body ? We cannot. No paper since 1983, the date of publication of this material has mentionned an assignement for that piece. The best was the mounted column in Belgium, where only the precaudal part was probably missing. But there's no way to determine where to place the 23 cm centra in the column and there's no reason to think that it was the largest in the individual. As I wrote, this is under the assumption that the centra are not from the tailfin. I don't know I've not seen any reference, but that's possible. How's that differences ? They are variable just like teeth. I remember an article where Hubbell said that either teeth or vertebra are not very reliable in that way. And to be sure you can make an estimate you have to be sure the centra is the largest : reasonnable assumption in a mount of 150 vertebra where only the precaudal is missing (and even then Gottfried expressed uncertainties in his conclusion), much less reasonnable with 20 centra associated with a tooth quite large, just useless wih a single isolated centra. And as the largest centra are much less preserved, that's most of the time a lost cause. And they are not more interesting. At best they are equally interesting. But centra are extremely rare, much less preserved, much more difficult to assign. The only attempt of assignement was in the Belgium skeletal of 150 pieces (I don't remember if it was attempted in the angustidens). It is not more interesting because of their quick limitations. How to determine a centrum is the largest ? How to place it if isolated or in a small associated group ? We can't. Fragmentary teeth are not used. Fragmentary vertebra lose their external parts and are easily crushed. That posed problems to Gottfried too : That's clear. Then no wonder to not have the largest centra in an individual and to get a smaller size than expected, especially when associated with a 12 cm wide tooth. I plan to send a mail to the Institut Royal des Sciences Naturelles de Belgique about that. No you need to know if that's the largest centra or if you know perfectly the each vertebral assignement in Megalodon. I don't think one person on Earth knows. Drawing models won't help. You still need to know the assignement of the vertebra to determine this, which is not the case. I agree with that a shark having a maximum vert of 23 cm would be that large. I don't agree at saying that the largest centrum of the Denmark material was the largest in the shark. It is impossible to determine this. It would be important if that was the largest in a part as large as the Belgium column which is 3/4 complete. I don't know, I guess I've said. That we cannot assign and that were likely not the largest in the whole column. That only works with uncertainties in the Belgium material : in a partially preserved Megalodon. Big deal. There is scientific documentation allowing assignement, even though, here again, one need to examinate the material properly, not watching it on the internet to do it accurately. I don't get the last part. Three complete Megs dentitions. One uncomplete column stored in the archives the Belgium Museum. Meg dentition is more documented. And when I say we are documented, I think about the researchers, not us here on the forum. Well that's at last a good point. I thought for a while you were arguing this too. I know it's an adult, it's reported in Pimiento abstract. Siversson method is the one we are using only he uses another percentage that we ignore. In a mail where I asked him the method, he said me to read the recent paper about Cardabiodon where the method is featured. And that's Lowry et al. Which upper bound ? You just added a percentage depending the finding of the day. I have nothing against "your" results (they're mines too) but I want to know how Siversson did use that method to get sizes of 11-12 m for Hubbell's specimen and 19 m for the largest Megs. I don't understand why you don't have understood that Siversson is using Lowry et al. 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).And ? We use independantly the best in Meg and in marine reptiles. In marine reptiles we have more substantial remains and better understanding of the arrangement of the bones. In Meg we have documented various estimates based on dental or dentition elements. Make a day at what ? At using the most useful methods which are not related to centra ? Limits because centra are too much rare, difficult to assign and unlikely to be the largest in the individual. There is no report with maximum size in the species. You simply get constant underestimates while doing this. Yeah. You expect Megs under 1 tonnes to be in the range of the maximum size ? You really want to shrunk that shark ! How do you know the one above 16 m are so much uncommon ? There is no data about the number of specimens in that boxplot. We just see trends and median, in a non definitive graph. You again make that a day. So wait the publication ! Have I ever said something as such ? I've said the contrary, that I don't expect larger specimens than 70 tonnes and I'm not even sure that one is valid. Shimada gives rather conservative length figures, I doubt one Meg will excess 18 m in the sample. I'm not interest in average size, I let this to Pimiento and Balk. I'm interested in potential individuals size. Of course I report rather big or very big specimens, not only though. Contrary to you I wouldn't expect anything yet. Personnally the current data tells me that Megalodon sizes knew some much variations through ages that I'm sometimes wondering if there wasn't several subspecies. But contrary to you I prefer to wait before claim, no offense but that's true. The title needs no update, I report here potential sizes for Megalodons individuals. Never said I was not interested in Pimiento and Balk, I'm not interested at discussing extensively it when the paper is anything but finalized. And I report it here, well, for keeping aware you fellow members of the board. That's wrong ? There's no biased picture, we just report the sizes of large teeth. No need to recall that all Megalodons were not that large, especially and apparently depending the era. Period.
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Post by creature386 on Mar 1, 2014 20:30:45 GMT 5
If it had both more and proportionally longer centra, that would indicate a longer, more elongate body. I thought we usually don't use vertebrae for bulk? Also, hasn't Gottfried said Megalodon had less elongate centra than a basking shark?
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Post by Life on Mar 1, 2014 21:35:46 GMT 5
If it had both more and proportionally longer centra, that would indicate a longer, more elongate body. I thought we usually don't use vertebrae for bulk? Also, hasn't Gottfried said Megalodon had less elongate centra than a basking shark? Basking shark does have long centrum but low count (109 - 116). Morphology of centrum depends upon where it is located. As apparent from the image I posted, Megalodon had very big centrum (bigger then that of any shark), and with count of 200 or more.
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Post by theropod on Mar 1, 2014 21:49:49 GMT 5
If it had both more and proportionally longer centra, that would indicate a longer, more elongate body. I thought we usually don't use vertebrae for bulk? Also, hasn't Gottfried said Megalodon had less elongate centra than a basking shark? Wasn’t that Kent? If a species has both elongated centra, and a larger vertebral count, that makes its vertebral collumn more elongate. Compared to a close relative (commonly used as a model for its body shape), and without any additional factors figuring in, that likely also means a more elongated body. But couldn’t it be that: either A: C. megalodon didn’t have such a large vertebral count at all or B: the proportionally longer centrum in the picture is a result of either crushing or a different position in the collumn? I doubt all the vertebrae in the animal are proportioned the same.
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Post by creature386 on Mar 1, 2014 21:51:17 GMT 5
You're both right about the vertebral count thing. Gottfried has said that as well, I don't remember if Kent did.
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Post by Life on Mar 1, 2014 22:10:42 GMT 5
I thought we usually don't use vertebrae for bulk? Also, hasn't Gottfried said Megalodon had less elongate centra than a basking shark? Wasn’t that Kent? If a species has both elongated centra, and a larger vertebral count, that makes its vertebral collumn more elongate. Compared to a close relative (commonly used as a model for its body shape), and without any additional factors figuring in, that likely also means a more elongated body. But couldn’t it be that: either A: C. megalodon didn’t have such a large vertebral count at all or B: the proportionally longer centrum in the picture is a result of either crushing or a different position in the collumn? I doubt all the vertebrae in the animal are proportioned the same. A) Megalodon DID had very high vertebral count, large macro-predators among sharks have very high vertebral count. This may have some biological implications such as possibility of decent maneuverability and bending ability at large sizes. B) That centrum is not crushed. Here is another example: www.flmnh.ufl.edu/rentmegalodon/images/walkthru/megalodon08.jpg (much smaller but matching morphology). As far as variation in centrum is concerned, this depends upon its location within the shark and also on the size of the shark. Megalodon would logically go through lot of ontogenetical changes during its course of life from neonate to adulthood. Upon approaching adulthood, Megalodon would have acquired very robust morphological features.
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Post by theropod on Mar 1, 2014 22:28:51 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.
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