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Post by theropod on Dec 3, 2015 4:10:28 GMT 5
Not deeper than in smaller white sharks ? I didn’t measure it, I suggest you do so yourself if you think it is considerably deeper proportionately than a white sharks. The discussion is about whether it had such a deep caudal peduncle, not why. We don’t actually know if it had. Maybe it did, but it does not appear you can provide any evidence for it. So it isn’t more likely than that it isn’t the case, let alone the only potentially accurate representation as you claimed. I already wrote why. Gottfried et al assumed proportionately larger jaws, or a shorter shark, and also assumed massively more robust jaws because they scaled from UA height (megalodon teeth being wider and more massive for a given height, not necessarily a given width). And the drawing of Kent’s model has the jaws wide agape, of course you see more of them than you would in a shark that has them retracted in their natural swimming posture. I’m not proposing anything, as I wrote before I based the drawing on the Carcharodon from Compagno (1984). That includes what’s visible of its jaw structure, what I changed was the body depth (seemingly consistent with what the allometric trends suggest). According to the communications you shared, Siversson used isometric scaling based on tooth row length, so that means he assumes that C. megalodon’s jaws were proportionately the same size as a great white’s.
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Post by Grey on Dec 3, 2015 4:14:41 GMT 5
Not the time to respond to each point, but dude, you want a new flame war ?
Yes I m not fan of your model but in general I m not fond of all your paleo-models.
That you made relevant points is another question.
I ll respond to these points later.
But I very much prefer discussing this with the author rather than trying to reach a conclusion by your means.
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blaze
Paleo-artist
Posts: 766
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Post by blaze on Dec 3, 2015 5:31:45 GMT 5
The chapter you've shared with me, will that be all the text about megatooth sharks? because let's be honest, apart form the shape of the rostrum it does not explain why nor gives any evidence why the model is the way it is and it disagrees with it in some cases, like how the text says one of the traits of a thunniform swimmer are reduced second dorsal and anal fins but those fins in the reconstruction are proportionally much bigger than in a white shark, if reducing the size of those fins is more hydrodynamic why depict them much bigger?
We should defintely ask B.K. the whys of his reconstruction.
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Post by Grey on Dec 3, 2015 8:32:20 GMT 5
The chapter you've shared with me, will that be all the text about megatooth sharks? because let's be honest, apart form the shape of the rostrum it does not explain why nor gives any evidence why the model is the way it is and it disagrees with it in some cases, like how the text says one of the traits of a thunniform swimmer are reduced second dorsal and anal fins but those fins in the reconstruction are proportionally much bigger than in a white shark, if reducing the size of those fins is more hydrodynamic why depict them much bigger? We should defintely ask B.K. the whys of his reconstruction. Yes that's why I planned since a while to ask Kent, at least about the 25 % depth that is not directly explained in the text. I know he made some revisions after initial review but not sure if it is about the reconstructed body shape. There is also the possibility the model was not finalized and CMM is a premature depiction. My point is that Kent describes himself as a functional morphologist, a biologist armed with the equations of an engineer, so while I want more explanations for these data I'm reluctant to reject his reconstruction readily. I mail him in the day. The model is definitely in use at the Calvert Marine Museum. fossilsandotherlivingthings.blogspot.fr/2015/06/calvert-marine-museum-striking-balance.html
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Post by Grey on Dec 3, 2015 10:11:37 GMT 5
I didn’t measure it, I suggest you do so yourself if you think it is considerably deeper proportionately than a white sharks.
I'm only on mobile these times so I can't do it. But at glance their respective penduncle seem marginally deeper than in the smaller white shark to me. It would be interesting to see a comparison from dorsal views as well.
The discussion is about whether it had such a deep caudal peduncle, not why. We don’t actually know if it had.
Obviously I referred to B.K. model, not the actual shark.
Maybe it did, but it does not appear you can provide any evidence for it.
I don't have to provide any evidence, I have to get more explanation from the author. No one has any evidence about the actual thickness of the caudal peduncle in C. megalodon.
Basically it's legitimate to question the extrapolation, as it's this way research progresses but it's legitimate as much to get more explanations from the author.
I simply doubt that Kent used only educated guess for his revised reconstruction of C. megalodon, hence asking him is better than arguing.
I have slightly more faith in Kent who has decades of research about the biology of this particular species than you. That's no offense, that's legit. But there are really interesting points raised in this discussion, except for your attacks I enjoy it. And I don't say at all you're wrong, maybe Kent will agree on that and say his revision needs...revision. I write him in the day, hoping he quickly responds.
I already wrote why. Gottfried et al assumed proportionately larger jaws, or a shorter shark, and also assumed massively more robust jaws because they scaled from UA height (megalodon teeth being wider more massive for a given height).
While your model is based on jaws perimeter scaling, I know. But the size figures you used for it are derived from Pimiento's results, and Pimiento's work mainly rely on Gottfried et al. 1996 regarding the paleobiology of C. megalodon. So you're mixing the data here, using a method for now untested in litterature on C. megalodon and the size figure from Pimiento.
Something to wonder about, indeed the scaling from jaws perimeter does not result in the bulging jaws from Gottfried et al. but does that mean C. megalodon did not have more massive, at least deeper jaws (if not larger in perimeter compared to the body) than the white shark ?
Whatever scaling from UA2 or from the jaws perimeter, this shark still had a heavier dentition than the white shark at parity size. The jaws in your model appear rather gracile.
And the drawing of Kent’s model has the jaws wide agape, of course you see more of them.
I obviously referred to the original sketch with the jaws closed, not the Calvert Marine Museum drawing.
According to the communications you shared, Siversson used isometric scaling based on tooth row length, so that means he assumes that C. megalodon’s jaws were proportionately the same size as a great white’s.
In one of his talk and in one of his emails (the very first one) he described C. megalodon as having a very heavy set of jaws (which does not mean proportionnally larger in perimeter).
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Post by theropod on Dec 3, 2015 19:56:23 GMT 5
My first and foremost method of estimating the 16.8m was tooth row length scaling. And I severely doubt the 14m average would be higher if all of the specimens were based on tooth row length. As you already know (sorry if that sounds like an "attack" to you) I don’t agree with your opinion regarding Shimada’s method giving lower estimates.
EDIT: The mouth in the 16.8m megalodon in my comparison is close to 1m long. The total upper jaw circumference of a 16.8m megalodon is expected to be 3.34m based on Lowry’s formula and assuming (following Kent) that the tooth-free space adds 17%. Assuming the upper jaw is a semi-circle, its radius would have to be about 1.06m. So I think I came reasonably close, especially considering that we do not actually see the entire jaw in a living shark, because it is retracted while swimming.
We don’t know. Reconstructing it with such would be another assumption without evidence, just like the immensely deep caudal peduncle.
Who sais it had a heavier dentition at the same jaw perimeter? If at all, then far less than at a given UA height, considering the summed tooth width is the same.
And again, you cannot even discern the outline of jaw cartilages in a swimming shark (or my drawing for that matter) the way you are trying to do here, you are talking about the anatomy of a structure that’s not even properly visible.
You suggested I instead use that one back then.
Yeah, well certainly it had a very heavy set of jaws, it was a very heavy animal, but does that have anything to add on the discussion?
While we’re at it, please don’t speak of attacks, I’m not the one making the constant ad-hominem allusions here. Pointing out that you made unfounded accusations is not an attack, not to mention I’ve already deleted one of those posts because I’m growing increasingly tired of it.
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Post by Grey on Dec 4, 2015 8:58:27 GMT 5
"My first and foremost method of estimating the 16.8m was tooth row length scaling. And I severely doubt the 14m average would be higher if all of the specimens were based on tooth row length. As you already know (sorry if that sounds like an "attack" to you) I don’t agree with your opinion regarding Shimada’s method giving lower estimates."
I've listed a number of points in the Megalodon size thread explaining why the CH method, as used in the matrix of data, is potentially conservative or prone to give somewhat lower results.
But that was not the subject of my remark. The 16.8 m estimate of yours IIRC was a mix of results from CH method and UJP. Your average megalodon is derived from Pimiento's matrix but using a reconstruction that would be provided by UJP scaling.
So you mix possibly the lower size results with the allegedly more slender body shape. All of this derived from a simple white shark drawing from Compagno. I strongly doubt this 1984 model is the only one rigorous to use.
Also, Compagno directly was involved in the 1996 reconstruction. Appart for the pug-nose head, if someone can scale up his white shark drawing to megatooth size using allometric data that's him. At least understand that I slightly more favor him using his own material and data than you.
"We don’t know. Reconstructing it with such would be another assumption without evidence, just like the immensely deep caudal peduncle."
Aren't we all assuming without evidence here ?
Even without a proportionally larger JW compared to its body, it doesn't sound ludicrous to suggest a heavier, deeper, thicker jaws structure in order to be functionnal, no ?
And the caudal peduncle doesn't sound "immensely thick to me". Such negative use of a superlative about this reconstruction from B.K. certainly shows how much you want it to be dismissed. I admit I like it but I'd like to be sure if B.K. has good justification for it.
I've asked B.K., awaiting for his response. Maybe you're right and he will suggest to not take it into account but I prefer to get confirmation first before relying on your own model.
"Who sais it had a heavier dentition at the same jaw perimeter? If at all, then far less than at a given UA height, considering the summed tooth width is the same."
You forget megalodon teeth are also much thicker. I think pretty beyond doubt the dentition was proportionnally heavier at the same tooth count.
"And again, you cannot even discern the outline of jaw cartilages in a swimming shark (or my drawing for that matter) the way you are trying to do here, you are talking about the anatomy of a structure that’s not even properly visible."
I've understood since a long. I'm 29, I like sharks since I'm 5 (oh a fanboy !), I know how they really look in life.
Still the life reconstruction from B.K., closed mouth, is larger than this. And your model does not show the commissures of the jaws as seen in living white sharks.
"You suggested I instead use that one back then."
What is the relevance of that response ? You can use both since both are from the same scientific horizon but while speaking about closed mouth I obviously referred to B.K. sketch.
"Yeah, well certainly it had a very heavy set of jaws, it was a very heavy animal, but does that have anything to add on the discussion?"
Well your model does not depict what I'd call particularly heavy jaws, nor your models seem to weigh as much as your own estimates. And I think that there is a scale issue with the diver anyway.
Yes I'm tired of this discussion as well because of speaking with you. You're only responding me for the sake of the contradiction, and your wish to have your models validated.
It's refreshing to discuss here with another member even if not of my opinion.
Now believe in your models as much as you want, I cannot care less.
I'll respond to this thread if blaze or someone else brings something new or in case of a response from the author of this "awfully fanboyistic megalodon reconstruction".
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Post by theropod on Dec 4, 2015 17:47:38 GMT 5
No, it was an estimate independently arrived at by Shimada’s formulas and upper dentition length, that’s not the same as a mixture. And what’s visible of the jaw size in the drawing scaled at 16.8m is perfectly consistent with the jaw size indicated by Lowry et al.’s formula. And as you know I have responded to all the points you gave at various occasions, and I do not agree with your conclusion. Making comparisons showcasing an opinion I don’t agree with is not what I’m for, you can do that yourself if you feel one just has to be out there. I am completely open to your suggestions as to what "model" of Carcharodon carcharias to use, but I haven’t seen any such suggestion so far. You just seem to want to dismiss, not improve. Also you are (and always have been) invited to share your concerns ragarding the drawing in question (screenshot posted further down) and explain why Compagno depicted such an un-representative great white then, and for that matter why that’s more likely than that Gottfried et al.’s megalodon silhouette is simply partly conjectural, partly based on a very different method and estimate yielding a shorter and stouter body shape. No we aren’t, as long as we aren’t assuming stuff not indicated by its best living analogue. A feature being present in C. carcharias (or another lamniform that is a good analogue) is a reason to presume it’s similar in C. megalodon. Certainly you can’t just come up with something conflicting with this if you don’t have any evidence for it, state it as a fact and call everything else BS. Yet that was pretty much exactly what you did, and your only reason for that was that my reconstructions does not agree on all accounts with Kent’s. You didn’t even stop to wonder where the reasons for that could lie, did you? There is a pronounced difference between "it doesn’t sound ludicrous" and "you have to show it like that, otherwise you are a biased hater". I certainly didn’t call it "One of the worst reconstructions I’ve seen", or "a random overnourished lamnid" the first time I saw it (was I as eager to dismiss it as you claim, or as eager to dismiss it as you are to dismiss whatever suggestion I come up with, I’d certainly have done that), I haven’t done so since, and for what I have remarked me and blaze have given good reasons. If you think I’m being dismissive, then what are you? So if it isn’t immensely thick in your opinion, then the difference can’t be that big, can it? Yet it’s sufficient for you to behave like this→. And now you expect me not to be annoyed by having to put up with that all the time, even if the objective data are entirely on my side? A deep caudal peduncle doesn’t make sense for biomechanical reasons, it increases drag where it’s no use and it wastes material that would more effectively strengthen the tail if it was instead added in width. In short, it’s a waste of energy. Why do you think it is that large, fast-swimming sharks have wide, shallow caudal peduncles while whales have deep, narrow ones? Have a close look. If anything I showed more of the jaw than I should. As you’ll notice, the jaw is also deeper, and the whole body is certainly bulkier. The mouth doesn’t look smaller than it should based on Lowry et al.’s formula (which suggests a total upper jaw bite radius of 1.06m for a 16.8m shark), but did you bother to check that? The latter has already been rebutted often enough here. You may think your eyes are better at gauging weight than actual measurements, but that doesn’t mean you are always right. Regarding the former, the jaw line in my drawing is definitely more conspicuous than it is in a regular great white, I’m sorry if you wanted it to look like in the BBC megalodon, but I won’t do that. I don’t require validation from you, it was my impression that it’s you who wished to falsify it, judging by your frequent expressions of dislike for literally everything I do. If you didn’t want me to respond to your points, you should have kept them to yourself. In any case, if you still insist on calling me a hater for this reconstruction ("random undernourished great white" lol), I’d suggest you take that up with Compagno: But of course, you’ll find some way to continue viewing me as oh-so-biased. In that case you are also the only one here to have considered any depiction fanboyish so far. You are perfectly fine with having doubts you cannot verify yourself, and you evidently feel very confident about expressing them (Does "You expect me to not consider you biased against megatooth sharks with that ?" ring a bell?). But if someone else voices doubts about a reconstruction you favour, that’s calling the author a fanboy. ALSO here are all the confirmed records of kogiids that I could find→, and it seems that they support my point, being all at least similarly bulky as the first one, or my Livyatan model for that matter. So unless you want to suggest that all of these (including the ones considered underweight) are outliers and that no normal specimen has had its measurements published, I think we can put that point to rest. So a weight/length³ ratio of 14.0 for Livyatan is not that outlandish, and is actually exceeded by Kogia (14.6) and Orcinus (15.0). Still waiting for a convincing biomechanical argumentation why Livyatan approaching an orca in robusticity is not realistic, let alone as totally ridiculous as you are trying to make it sound since years…
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Post by Grey on Dec 21, 2015 1:49:18 GMT 5
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Post by Grey on Dec 21, 2015 4:38:47 GMT 5
I think we're starting to be able to get a good indication of how wide and long would be the upper jaw of Megalodon compared with Livyatan.
Using the same ratio reported for the white shark between UA1 tooth width/upper jaw length of 7.4 %, the tooth used by Gottfried at 125 mm wide would fit in a jaw about 168 cm long and 137 cm wide (between the most posterior teeth). If I remember right (from Boessennecker article), Livyatan upper jaw length is about 180 cm and 120 cm wide.
I've never been very good at maths, but in square metre, this would suggests the upper jaw of Livyatan and the Megalodon with a 125 mm wide UA1 are approx. similar (Livyatan being very slightly smaller) ?
Note, given the difference in tooth row lenth between the white shark and Megalodon (slightly longer tooth row for the same UA1 width for Megalodon), the figure for Megalodon might be slightly underestimate.
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Post by Grey on Dec 21, 2015 5:53:54 GMT 5
After further observation, I realize my calculations are way off, upper jaw length being not a straight line... Plus Boessenecker indications for Livyatan are rather rough, looking at the suppl. data and the figure of the skull might be more accurate. Nevertheless, finding the upper jaws size in Megalodon and Livyatan will be very much determining. I suggest to look further at this, theropod blaze, it sounds feasible. Siversson already gave me a method to calculate the width between the most posterior teeth based on Hubbell's associated set. It suggests the set was from an upper jaw 89 cm wide (between the most posterior upper teeth so). The tooth in Gottfried 1996 at 125 mm wide suggests an upper jaw width about 137 cm. The issue is that the upper jaw length in the paper doesn't correlate with that width figure but with the complete palatoquadrate. It could respond to the question if Livyatan solelely has the biggest tetrapod bite or it even beats Megalodon for the biggest maw. Not sure about but just using Siversson's data to the 125 mm wide tooth and using the figure of a mako upper jaw in Tomita's paper, I get the straight line of the dention length for this Megalodon would be about 132 cm long, for 137 cm wide. Looking at the upper dentition of Livyatan in Lambert et al. the straight line of the dentition lenght appears to be about 143 cm and the most posterior teeth to be about 96 cm wide. Based on this, the 125 mm wide tooth would be from a more voluminous upper jaw than Livyatan's holotype (summing the lenght and width values in the respective jaws) but this is based on the uncertainty of the mako figure I used from Tomita. I don't claim anything conclusive, just opening some avenus for work. But somehow, the 125 mm wide tooth stuied in Gottfried would fit in an upper jaw that would compare like that with Livyatan.
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blaze
Paleo-artist
Posts: 766
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Post by blaze on Dec 21, 2015 13:42:43 GMT 5
I used the data on the paper you shared to recreate the regression equation, if that 125mm wide tooth is an AU1 then the estimated upper jaw length would be 129cm, remember however that this length is defined as "length along the jaw curvature starting at the symphysial articulation to the lateral quadrate-mandibular joint." so double this length equals the full external perimeter of the palatoquadrate, measuring that Mako jaw drawing in GIMP, the straight-line measurements would be 108cm long and 127cm wide with a width across the posteriormost teeth of 81cm.
How did Siversson came up with that width for the Hubbell set?
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Post by theropod on Dec 21, 2015 15:55:44 GMT 5
That jaw length is remarkably similar to the values you get from Lowry et al.'s regression if you add Kent's 17%, even using the relatively crude half-circle approximation, but we'd expect a much greater width by that method (supposedly due to the mako analogue being narrower).
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Post by Grey on Dec 21, 2015 16:21:31 GMT 5
I used the data on the paper you shared to recreate the regression equation, if that 125mm wide tooth is an AU1 then the estimated upper jaw length would be 129cm, remember however that this length is defined as "length along the jaw curvature starting at the symphysial articulation to the lateral quadrate-mandibular joint." so double this length equals the full external perimeter of the palatoquadrate, measuring that Mako jaw drawing in GIMP, the straight-line measurements would be 108cm long and 127cm wide with a width across the posteriormost teeth of 81cm. How did Siversson came up with that width for the Hubbell set? Are you sure ? The paper indicates the upper jaw length of the white shark is 7.4 % its UA1 width, hence I get 168 cm of upper jaw length for the 125 mm wide tooth. Your results suggest a white shark with a 45mm wide UA1 only has a maximum between posterior teeth of only 29 cm ? Mollet et al. 1996 I don't see how 81 cm of width can be plausible with a 125 mm wide UA1. If we scale the 5.1 m white shark with a 48 cm wide bite at 15.9 m (the conservative TL for the 125 mm wide tooth in Gottfried et al.) you get a bite near 149 cm wide, of course there are individual variations without using a regression but that's far from the 81 cm you've found. Haven't you rather used the regression resulting for Protolamna in the paper, understood to have a relatively smaller mouth compared to the larger lamnids ? Siversson : If we use Gordon’s associated meg dentition as a template and assume a jaw shape similar to that in modern lamnids (white, mako, porbeagle) then you would end up with an upper jaw width (measured between the most posterior teeth in a functional position) of roughly 150 cm for a tooth with a slant height of 7’’. Megalodon might well have had a more rounded curvature and a significantly wider posterior jaw width (as measured above) but I very much doubt it would be as much as 2 m for a 7’’ slant height tooth.
Remember that 150cm figure I gave you is not the total width of the jaw but the transverse distance between the most posterior teeth in the upper jaw. It is a relatively straight forward calculation. You first measure the total width of all upper jaw teeth (left or right) in Gordon’s associated meg dentition. These teeth measure about 77 cm in total width. You then apply this number to lamnids (I used white sharks and makos). For example I have a I. paucus jaw where the total width of all upper left teeth is 173 mm and the transverse width between the most posterior upper jaw teeth (the jaw is dried in natural position) is 16% larger. This method slightly underestimates the transverse width as the jaws contract slightly when they dries. Applying x1.16 to the Gordon’s associated med dentition results in a jaw width (transverse measurement between the most posterior upper jaw teeth) of 89 cm. The slant height of the largest tooth in that dentition is about 105mm. Using a 7’’ slant height tooth gives you 178/105x89=150cm. Still a very, very large mouth.
Note that Siversson is himself rather cautious. Applying this to the 125 mm wide tooth indicate something around 137 cm, quite a discrepancy with your results. Look at the white shark specimen in the paper, UA1 42.7mm wide=UJL 578mm. Applying this to a 125 mm wide Meg tooth results UJL about 169 cm. Not saying you're wrong but your posterior teeth width figure of 81 cm sounds very small in a white shark-like body supposedly almost 16 m long, almost 1/20. This would mean a dentition just about as wide as in Pliosaurus kevani and much less long, though P. kevani would be significantly smaller than this shark. I admit my calculations aren't the most precise or reliable but I'm quite skeptical. Maybe one of the issues is that the upper jaw length in the figure is only indicative, not put at scale. I've used the figure only accounting the dentition width and length, not the upper jaw length. My calculation is based on the ratio said for the white shark, the bite marks size reported and Siversson's method to estimate bite width in Megalodon. I've only used the Mako upper jaw for the scale of the dentition, not the upper jaw length (which I doubt is at scale in it). In both case, I only measure the distance of the bite, not including the total width of the jaw structure. Finding a similar figure for the white shark dentition would be nice. Beside my measurements of Livyatan upper jaw do appear correct ?
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blaze
Paleo-artist
Posts: 766
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Post by blaze on Dec 22, 2015 0:04:46 GMT 5
Well, that's what the regression equation gives, using a percentage doesn't account for allometry but trying to use it to estimate something so clearly outside of the range of the sample has to have an effect. Plugging the width of the white shark AU1 in the sample results in an estimate UJL of 565mm, a little lower than the real value of 578mm, could it be that the equation results in a disproportionate increase of AU1 in respect to the rest of the jaw? is a proportionally larger AU1 at larger body sizes the trend seen in extant sharks? if that's the case C. megalodon seems to be going the other way around, looking at the tables with tooth measurements from Bone Clones, in the white shark AU1 is the widest tooth in the dentition but in C. megalodon the widest is the 5th, if in C. megalodon AU1 is disproportionately narrow that will result in underestimates using that equation. I will try to get a jaw size using an image of a CT scan of a white shark head, the specimen is rather small but seeing as Siversson used a similarly small shark for that scaling you mentioned then it shouldn't be inherently more wrong. edit: Here it is: Width at the posteriormost teeth is 105cm, length of the dentition is 98cm, I assumed no interdental space so this is a conservative estimate, in Livyatan length of the dentition is 133cm and width at the posteriormost teeth is 93cm.
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