denis
Junior Member
Posts: 195
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Post by denis on Nov 19, 2019 8:07:18 GMT 5
Everyone here is aware of these skull-body ratios, it has been discussed to death. It's far more complex than simply 1:6 across the board. I suggest you read the relevant threads on here or the actual papers/discussions among paleontologists instead of referring to some youtube videos or paleo-fiction authors. Dino Bios, it’s a blogspot where I got most of the information from. I mean that’s one, the other Wikipedia. |
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Post by Grey on Nov 19, 2019 15:23:36 GMT 5
To me, there's a kind of an irony building up in this thread. Denis seems to be pliosaur fan, and he argues for p.macromerus being much bigger than what the recent downsizes suggest. While I don't think Denis is right, what I find ironic is that Grey, a megalodon fan, basically is of the opinion that meg reached up to 20+m despite of the most recent study putting it at 12-13m on average. Now, I'm not saying the two examples are completely in the same category, but they're similar enough for this discussion to come across as a little ironic. The most recent study is nothing new and is definitely not an update of the body size department. Denis main source is Max Hawthorne, my sources are, well the actual scientific research done about as we speak. This is rather different. Again, Shimada's method applied to anterior and posterior teeth (not lateral) is certainly utter wrong. |
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Post by Grey on Nov 19, 2019 15:25:35 GMT 5
Everyone here is aware of these skull-body ratios, it has been discussed to death. It's far more complex than simply 1:6 across the board. I suggest you read the relevant threads on here or the actual papers/discussions among paleontologists instead of referring to some youtube videos or paleo-fiction authors. Dino Bios, it’s a blogspot where I got most of the information from. I mean that’s one, the other Wikipedia. What about starting to use "pliosaurus" in google scholar ? One of the best and most extensive article about pliosaurs is by Colin McHenry. |
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denis
Junior Member
Posts: 195
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Post by denis on Nov 19, 2019 15:51:37 GMT 5
To me, there's a kind of an irony building up in this thread. Denis seems to be pliosaur fan, and he argues for p.macromerus being much bigger than what the recent downsizes suggest. While I don't think Denis is right, what I find ironic is that Grey, a megalodon fan, basically is of the opinion that meg reached up to 20+m despite of the most recent study putting it at 12-13m on average. Now, I'm not saying the two examples are completely in the same category, but they're similar enough for this discussion to come across as a little ironic. The most recent study is nothing new and is definitely not an update of the body size department. Denis main source is Max Hawthorne, my sources are, well the actual scientific research done about as we speak. This is rather different. Again, Shimada's method applied to anterior and posterior teeth (not lateral) is certainly utter wrong. Not accurate. Where’s your source for your estimate. Megalodon is longer accepted to be over 20 meters buddy. How is it wrong? Most scientists agree with it. Also those teeth are more useful when estimating sizes of sharks. I think you just don’t agree with it. |
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Post by Grey on Nov 19, 2019 16:04:12 GMT 5
denis, I think this has been explained already. We are talking about a study that is going to be peer reviewed and published, a study about a far better method to estimate meg size. Many scientists are not aware of that method yet. Also, I recall you that you are here with people knowing rather well their stuff as some of them are actual researchers and specialists. No, the max of 15-18(?) by Shimada is not accurate not definitive. Yes, it seems the megalodon species could tip the 20 m mark, which is almost unparalleled among macropredators. By comparison, there is zero pliosaur specimens that is confirmed to come from a 15 m individual. In fact even 13 m is not confirmed. Because this is what the scientific literature says, not some novelist.
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Post by theropod on Nov 19, 2019 16:31:46 GMT 5
To me, there's a kind of an irony building up in this thread. Denis seems to be pliosaur fan, and he argues for p.macromerus being much bigger than what the recent downsizes suggest. While I don't think Denis is right, what I find ironic is that Grey, a megalodon fan, basically is of the opinion that meg reached up to 20+m despite of the most recent study putting it at 12-13m on average. Now, I'm not saying the two examples are completely in the same category, but they're similar enough for this discussion to come across as a little ironic. I can get the downsized source for Pliosaurus Macromerus? Yes you can. This is the most recent research work and generally considered a standard work when it comes to giant pliosaurs: McHenry, C.R. 2009. ‘Devourer of Gods’: The Palaeoecology of the Cretaceous Pliosaur Kronosaurus queenslandicus.University of Newcastle, 616 pp. www.semanticscholar.org/paper/Devourer-of-Gods%3A-the-palaeoecology-of-the-pliosaur-Mchenry/1bf35a2cbebb46f85d63793f41c8d994df59951bMcHenry estimated a total length of 12.7 m and body mass of about 19 t based on the estimated 3 m complete (2.8 m preserved) length of the Cumnor mandible. This is not set in stone, as there are obviously variable proportions among Pliosaurs, but probably the most rigorous and reasonable estimate available for a pliosaur with a jaw that size, with by far the best documentation as well as including a reliable mass estimate. However I spoke to Richard Forrest about this specimen back in 2016, and he thinks a lot of it is likely to be restored, and incorrectly at that, and the actual length of the jaw may have been up to a metre smaller, which would make this still a large but not record-sized pliosaur. I think he responded the same to other members' inquiries as well. So we have little confidence it is even that large. |
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Post by sam1 on Nov 19, 2019 18:21:27 GMT 5
To me, there's a kind of an irony building up in this thread. Denis seems to be pliosaur fan, and he argues for p.macromerus being much bigger than what the recent downsizes suggest. While I don't think Denis is right, what I find ironic is that Grey, a megalodon fan, basically is of the opinion that meg reached up to 20+m despite of the most recent study putting it at 12-13m on average. Now, I'm not saying the two examples are completely in the same category, but they're similar enough for this discussion to come across as a little ironic. The most recent study is nothing new and is definitely not an update of the body size department. Denis main source is Max Hawthorne, my sources are, well the actual scientific research done about as we speak. This is rather different. Again, Shimada's method applied to anterior and posterior teeth (not lateral) is certainly utter wrong. Certainly "utter wrong"? So there, you're basically saying you know better than one the most renowned experts on the subject, that has been studying megalodon for decades? I am supposed to just take your statement as a fact and assume Shimada made a basic mistake, because ..? |
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Post by Grey on Nov 19, 2019 20:17:22 GMT 5
The most recent study is nothing new and is definitely not an update of the body size department. Denis main source is Max Hawthorne, my sources are, well the actual scientific research done about as we speak. This is rather different. Again, Shimada's method applied to anterior and posterior teeth (not lateral) is certainly utter wrong. Certainly "utter wrong"? So there, you're basically saying you know better than one the most renowned experts on the subject, that has been studying megalodon for decades? I am supposed to just take your statement as a fact and assume Shimada made a basic mistake, because ..? Excuse me sam1, but there are certainly expérimented amateurs thzt know more than professionnals. Technically yes, I and my co-authors, and probably Mike Siversson and Bretton Kent know a bit more about the relationship between dentition and body size in megalodon : 15-16 m was probably a normal good-sized individual, depending the region and/or time. There is no contest to this, theropod, blaze, coherentsheaf,Life and elosha know actually a bit more about this than Shimada and probably other guys well aware of the study. And I have actually discussed and highlighted Shimada, he is now well aware of it and may accept the new estimate. It is a near certainty, some members of the megalodon species may have reached 20 m, making it an unique evolutionary occurence and the only macropredator eating warm-blooded prey confirmed to reach the symbolic mark of 20 m (except for the slender Basilosaurus). There is no doubt, megalodon and Livyatan possibly outclasses any other apex predators before or since because of singular events to their era. |
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Post by theropod on Nov 19, 2019 21:09:18 GMT 5
I do know enough to know that there are no certainties there at all. As I highlighted the largest specimens could be anywhere from 18 to 21 m, all based on "up to date" methods, scaling from megalodon dentitions. That’s not even considering all the vastly lower results produced by other methodologies, which even if unlikely, do exist and are not impossible, just less likely. Those are only the point estimates, each one comes with a major error bar (the range into which 50% of the sharks would fall based on normal variation in Mollet et al.’s data would be 16.7-19.8 m). There are so many inherent assumptions still in these estimates that talking of "certainty" is totally misplaced. The best an estimate for something this fragmentary can do it attempt to find the most probable value. Certainty has a very specific meaning in science. It is certain the earth is warming, because we can directly measure it. It is certain Sue the T. rex is over 12 m long, because it’s skeleton is almost complete. Claiming to be certain about megalodon’s size is like claiming to be certain about the size of Amphicoelias/ Maraapunisaurus fragillimus. Take Sarcosuchus for example. That’s an animal with fossils so massively more complete than any megalodon (let alone the ones actually potentially over 20 m long) that the comparison isn’t even funny any more. Using the potentially best extant analogue ( Gavialis, equivalent to C. carcharias in the case of meg) and regression on skull length (far more substantial than summed dentition width, the best proxy we have for megalodon) produces an estimated length of over 11 m for the biggest specimen (a complete skull, not an isolated tooth). This was one of the methods employed by Sereno et al. (and the more conservative one at that). Would it hence have been justified to claim it was "certain" Sarcosuchus was over 11 m long? No, as it turns out looking at Terminonaris’ head-body proportions actually suggests less than 10 m. That’s like the difference between a maximum 20 m meg and a maximum 18 m meg. If we cannot be certain in a much more complete taxon, with a proportionately much larger extant analogue, and even using what was previously the most conservative estimate, then there is no way we can be certain that meg exceeded 20 m based on an isolated teeth and assumed isometry of teeth with respect to complete meg dentitions, and of complete meg dentitions with respect to extant white sharks. What’s our criterium for certainty? How about 95% probability? Discounting older methods (generous), we’ve got three methods, Mollet et al., Lowry et al., and Grey et al. (in prep or is it in press now). We can give each of these a 1/3 rd chance of being true. Ignoring overlap in the error margins of the methods (again, generous, as in reality the others would also have a non-zero probability of giving lower estimates) one giving the lowest results is Mollet et al.’s dataset, so looking at that we need the lower end of a 70% PI (3*5%=15%, *2*30%, but we are only considering the probability of the real size being lower here), which is 15.9 m. So at the very best, we can say we are (reasonably) certain (under the condition that megalodon conformed to a very similar morphology to C. carcharias) that megalodon grew to over 16 m. |
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Post by Grey on Nov 19, 2019 21:41:08 GMT 5
95-97 % certainty, much of the factors suggest 20 m as being reached at some points under a more likely general condition.
100 % certainty 18 m; 95-97 % certainty 20 m; 90-93 % certainty up to 21 m.
It is stastically possible for Livyatan to have reached that size but this is not indicated yet by any material. A less likely but still possible explanation was that Livyatan sp. was humpback-size, but not fin whale-size like some Physeter and quite possibly megalodon.
Other than that, no other well identified macropredator grows as big as those two.
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Post by Life on Nov 19, 2019 22:48:00 GMT 5
I do know enough to know that there are no certainties there at all. As I highlighted the largest specimens could be anywhere from 18 to 21 m, all based on "up to date" methods, scaling from megalodon dentitions. That’s not even considering all the vastly lower results produced by other methodologies, which even if unlikely, do exist and are not impossible, just less likely. Those are only the point estimates, each one comes with a major error bar (the range into which 50% of the sharks would fall based on normal variation in Mollet et al.’s data would be 16.7-19.8 m). There are so many inherent assumptions still in these estimates that talking of "certainty" is totally misplaced. The best an estimate for something this fragmentary can do it attempt to find the most probable value. Certainty has a very specific meaning in science. It is certain the earth is warming, because we can directly measure it. It is certain Sue the T. rex is over 12 m long, because it’s skeleton is almost complete. Claiming to be certain about megalodon’s size is like claiming to be certain about the size of Amphicoelias/ Maraapunisaurus fragillimus. Take Sarcosuchus for example. That’s an animal with fossils so massively more complete than any megalodon (let alone the ones actually potentially over 20 m long) that the comparison isn’t even funny any more. Using the potentially best extant analogue ( Gavialis, equivalent to C. carcharias in the case of meg) and regression on skull length (far more substantial than summed dentition width, the best proxy we have for megalodon) produces an estimated length of over 11 m for the biggest specimen (a complete skull, not an isolated tooth). This was one of the methods employed by Sereno et al. (and the more conservative one at that). Would it hence have been justified to claim it was "certain" Sarcosuchus was over 11 m long? No, as it turns out looking at Terminonaris’ head-body proportions actually suggests less than 10 m. That’s like the difference between a maximum 20 m meg and a maximum 18 m meg. If we cannot be certain in a much more complete taxon, with a proportionately much larger extant analogue, and even using what was previously the most conservative estimate, then there is no way we can be certain that meg exceeded 20 m based on an isolated teeth and assumed isometry of teeth with respect to complete meg dentitions, and of complete meg dentitions with respect to extant white sharks. What’s our criterium for certainty? How about 95% probability? Discounting older methods (generous), we’ve got three methods, Mollet et al., Lowry et al., and Grey et al. (in prep or is it in press now). We can give each of these a 1/3 rd chance of being true. Ignoring overlap in the error margins of the methods (again, generous, as in reality the others would also have a non-zero probability of giving lower estimates) one giving the lowest results is Mollet et al.’s dataset, so looking at that we need the lower end of a 70% PI (3*5%=15%, *2*30%, but we are only considering the probability of the real size being lower here), which is 15.9 m. So at the very best, we can say we are (reasonably) certain (under the condition that megalodon conformed to a very similar morphology to C. carcharias) that megalodon grew to over 16 m. Err.. You are assuming that all papers evaluated Megalodon from all possible angles, and still came up with different estimates, therefore all are equally valid possibilities. This isn't the case, WE focus on which perspectives/observations are more sound/logical/realistic and ignore the remainder. It was once argued that Megalodon was a Carcharodon but some researchers challenged this belief and it is now increasingly apparent from years of research/examinations of fossil records that Megalodon was actually a chronospecies - continuation of megatoothed shark lineage since Otodus obliquus - otodontids to be precise. So WE completely disregard the Megalodon- Carcharodon connection now and embrace latest knowledge. Of-course, WE do not utterly disregard physiological similarities between Megalodon and Great White (superficial or not) since these similarities have their own value but WE keep in mind the fact that these two are different sharks with distinct adaptations. Similarly, estimating the size of Megalodon on the basis of size of Anterior teeth only - is a traditional consideration. These methods literally impose physiological considerarions of the Great White on Megalodon and Grey et al (in progress) are expected to challenge this practice with a previously overlooked set-of-observation(s). Do you recall those strange-looking sculptures in the Megalodon versus Livyatan thread? They are not realistic even at a brief glance. There is no need to compute average of everything. WE do not ignore old information but it is better to consider more sound observations in view. |
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Post by sam1 on Nov 20, 2019 0:11:43 GMT 5
Certainly "utter wrong"? So there, you're basically saying you know better than one the most renowned experts on the subject, that has been studying megalodon for decades? I am supposed to just take your statement as a fact and assume Shimada made a basic mistake, because ..? Excuse me sam1, but there are certainly expérimented amateurs thzt know more than professionnals. Technically yes, I and my co-authors, and probably Mike Siversson and Bretton Kent know a bit more about the relationship between dentition and body size in megalodon : 15-16 m was probably a normal good-sized individual, depending the region and/or time. There is no contest to this, theropod, blaze, coherentsheaf,Life and elosha know actually a bit more about this than Shimada and probably other guys well aware of the study. And I have actually discussed and highlighted Shimada, he is now well aware of it and may accept the new estimate. It is a near certainty, some members of the megalodon species may have reached 20 m, making it an unique evolutionary occurence and the only macropredator eating warm-blooded prey confirmed to reach the symbolic mark of 20 m (except for the slender Basilosaurus). There is no doubt, megalodon and Livyatan possibly outclasses any other apex predators before or since because of singular events to their era. Man..now you excuse me, but I definitely take Shimada as bigger authority on the subject than you. And what, are you suggesting it didn't occured to him to choose between the anterior and lateral method? That he did not have actual reasons for his decision?? From what I understand (correct me if I'm wrong) his rationale went along applying the GWS average/maximum teeth/TL analogy. The obvious thing is, a GWS jaw is typically a showcase of differently sized anterior teeth that are almost never aligned and placed in perfect order. And there is often an anterior utlier that sticks out in shape, position, and size. I may be merely speculating here, but this characteristic seems less pronounced along the lateral part of the jaw. So taking one isolated tooth and simply extrapolating from that does not look like a realistic method at all..it doesn't take into account that if megalodon was anything like the GWS, or any other shark for that matter, it had wildly different teeth within the jaw. And the only way to go is to take a holistic approach and make conclusions from that. I'm sure there are some isolated GWS teeth that would, by limited estimation methods, suggest a much greater maximum size than what is actually scientifically confirmed. p.s. apologies for derailing and hijacking the thread. You can move this discuasion to a more appropriate one |
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Post by theropod on Nov 20, 2019 1:12:41 GMT 5
I was not assuming that, I was ignoring the remainder as well. Not quite correct, all size estimation techniques, including the one Grey is proposing, still rely on Carcharodon, because there is nothing else to use. Except if you want to use the mako shark, which seems to obviously be the inferior proxy for every reason imaginable (morphology, ecology, size), and suffers from all the same problems. Precisely this one: Which assumes isometric scaling between dentition width and total length of Carcharodon. Using isometric scaling from white sharks does in no way "challenge this practice" of using the white shark. And at any rate, there is nothing better to use, we can only not impose physiological considerations of the white shark on megalodon when we have hard data to suggest otherwise. Which we do in terms of body temperature, but precious little else (certainly not body proportions). Sorry, those are definitely massively overestimated levels of confidence. Revert back to the Amphicoelias/Maraapunisaurus fragillimus example. Or various giant footprints for that matter. If you are 90 % certain that meg reached 21 m based on an isolated tooth, then you must also be 90 % certain the Plagne trackmaker was a 200 ton sauropod? Or take again the example at hand, Pliosaurus macromerus. So McHenry 2009 estimates 12.7 m? So based on that, you are what, at least 90% confident that it grew to over 12.7 m? And that’s an almost 3 m long mandible, not a single 15ish cm tooth. And even with the former, as this case demonstrates, there can be major problems. Now in additions to the problems we now know about, one more thing that never even seems to get considered is that not all pliosaurs have the same head-body proportions, and that having only a mandible we don’t know exactly what kind of proportions this one had. So if you had 20 other Pliosaurus specimens, and you ran a regression on them, and the lower end of a 90% PI was 12.7 m, then yes, probabyl you could reasonably say you are pretty certain the specimen was that large. But McHenry based the proportions on a museum model he thought to reflect them accurately, without any such statistical analysis. So while it might have been appropriate to say the estimate was the best one available, it is by no means certain that it was this large.
Around 95% certain that megalodon reached over 16 m is the best we get (and that level of confidence is already optimistic for reasons I outlined), and that’s not even considering the high, but unquantifiable, probability that megalodon exhibited morphological features we cannot predict using white sharks as an analogue, which influences the size estimate in an unknown direction and to an unknown degree, but further increases our uncertainty. Basic maths. sam1 I suggest you read Shimada’s paper(s). His method is quite simple. He computed a linear regression for shark total length based on the crown height of each tooth position, based on 12 great white sharks. This is the first point where alarm bells should ring, because 12 is a tiny sample size, especially for something as variable as teeth. Hence there is likely a lot of statistical noise influencing those formulae. Secondly we know from the handful of semi-officially known (and the one officially described one, sadly exclusively in Japanese…) dentitions that appear to represent single individuals that there are major differences. Anterior teeth of great whites are proportionately taller, so proportionately taller tooth==>>proportionately smaller jaw==>>proportionately smaller body for a given tooth height. With Shimada’s most recent paper limiting the analysis entirely to anterior teeth, that obviously tends to result in underestimates (the method as a whole does not, in fact the mean size based on Shimada’s method applied in Pimiento & Balk’s dataset gives results that are perfectly consistent with using dentition size. What’s triggering certain posters here so much about Shimada’s new study is basically that he published the same method almost two decades ago, he merely made some minor corrections and tests now but basically not much about it changes. Admittedly this would not have warranted its own publication, but those being so upset by this (if really it is about publication ethics, and not the not liking the results part) should contemplate whether any paper almost entirely dealing with estimating the size of something this fragmentary really warrants the publication then, let alone dozens as there are for megalodon. Correct. Teeth are a small and variable part of an animal and a larger tooth can very easily be the result of individual variation in tooth size rather than necessarily coming from a particularly gigantic shark. This error bar is completely ignored here. In fact it is getting worse due to the fact that we have a very limited number of meg dentitions, and no properly available measurements for any of them, to quantify said variation. We know that even ignoring that factor, the error bars are enormous, see my last post (which assumed jaw size as a given, ignoring any variation you’d get from using an isolated tooth to estimate it); only 50% of sharks would be predicted to fall in a 3 m wide total length interval (in fact the 95% prediction interval, i.e. what we could actually be fairly certain of under normal standards, ranges from 14 to 23 m, and that’s only the variation in total length for a given jaw size, not that of jaw size for a given measurement of a single tooth or something like that). And yet people are trying to sell estimates like "over 20 m" as a near certainty. Statistically that is mind-boggling. There’s a reason coherentsheaf always used to say the only thing he was sure of was that meg was over 10 m long… |
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Post by sam1 on Nov 20, 2019 1:48:19 GMT 5
I've read Simada's paper, but my understanding was that his sample was considered within the context of known maximum size for the species.
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Post by theropod on Nov 20, 2019 1:54:33 GMT 5
I don’t know what exactly you are getting at. He didn’t have a "sample" really, unless you mean the one of great whites used for the regressions. He surveyed what were the largest teeth he could find and made an estimate from those. Of course the largest teeth someone can find, bearing in mind there must be many thousands of teeth in collections, pretty much corresponds to the maximum size. I’m usually using the largest specimen in the Pimiento & Balk dataset as a stand-in for maximum size.
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