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Post by Grey on Mar 7, 2014 4:05:49 GMT 5
The frozen fins of a 2120 kg great white were 79 kg. Do the math on a 60 tonnes Megalodon in which we can assume longer, thicker fins if it has indeed a more massive torso. Sharks fins have no bones but are fairly massive to support the animal. And I'm a little bit tired of these subjects which deserve no discussion as such. Your goal is just to debate about anything in that thread or never be agreed about it and just to shrunk megalodon as much as possible ? I will have to leave the forum for several months soon, when I'm back may I expect that you'll have successfully established Megalodon at 10 m adult average length with a carcharhinid-like body ? Not so private joke... And the name of this new representation would be: Isurus Megalus Lamna Pygmus  -- On a serious note, I absolutely welcome contributions of theropod (He brings a wealth of information to the table which is not common from many members).  Yes, we are just discussing about a long dead creature and theropod has proved since a long his intelligence and huge interest in these subjects. But about Megalodon, too much trying to make his own science. The example is the jaw perimeter discussion. He did a great job in his research as he found the Lowry's paper alling to calculate size from toothrow length, but then he really prematurely makes a day of his own estimates despite we still lacked some informations (which percentage to use in the calculation) and that the results were not so much corresponding with the ones by Mike Siversson who reportedly used the same method. He's not obligatory wrong, but too much believing in his suggestions when the actual evidences, rather than saying the contrary, simply suggest otherwise. On a long term, the objectivity in such statements appears questionable. Now, as I say, whatever the discussions, this is the peer reviewed works which prevail as the most up to date assessments, not opinions from some intelligent posters but perhaps not so objective about Megalodon.I sound perhaps a bit enthusiastic about Megalodon myself, but I'm enthusiastic because as a "fan" of large predators it is objectively the most widely regarded as the most spectacular top predator in history, size and brute strength wise (the only not impossible contender to date being Livyatan). If tomorrow, someone founds the evidence that Meg was a slender 13 m TL max fish specialist, I'd have no problem to revise my judgement (then I will probably focuse even more on Livyatan, though there is limited knowledge about it). Something really unlikely though. But if tomorrow, someone finds three complete Megs skeletons, all above 17 m TL confirming a robust physiology, I believe that theropod will find a way to challenge this and make it Isurus Megalus Lamna Pygmus.  Scientifically this is not a bad thing, I appreciate anti-conformist positions (more in politics and military that being said) but when this is at any cost about one particular suject, that becomes somewhat boring and suspect, hence why I've not responded to his latest long posts as I know such discussion will never come to an objective solid agreement. Now about the subject, I guess this scale reconstruction is pretty good (perhaps the pic with the young girl still a bit too large ?).  |
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Post by Life on Mar 7, 2014 10:49:35 GMT 5
Yes, we are just discussing about a long dead creature and theropod has proved since a long his intelligence and huge interest in these subjects. But about Megalodon, too much trying to make his own science. The example is the jaw perimeter discussion. He did a great job in his research as he found the Lowry's paper alling to calculate size from toothrow length, but then he really prematurely makes a day of his own estimates despite we still lacked some informations (which percentage to use in the calculation) and that the results were not so much corresponding with the ones by Mike Siversson who reportedly used the same method. He's not obligatory wrong, but too much believing in his suggestions when the actual evidences, rather than saying the contrary, simply suggest otherwise. On a long term, the objectivity in such statements appears questionable. Now, as I say, whatever the discussions, this is the peer reviewed works which prevail as the most up to date assessments, not opinions from some intelligent posters but perhaps not so objective about Megalodon.I sound perhaps a bit enthusiastic about Megalodon myself, but I'm enthusiastic because as a "fan" of large predators it is objectively the most widely regarded as the most spectacular top predator in history, size and brute strength wise (the only not impossible contender to date being Livyatan). If tomorrow, someone founds the evidence that Meg was a slender 13 m TL max fish specialist, I'd have no problem to revise my judgement (then I will probably focuse even more on Livyatan, though there is limited knowledge about it). Something really unlikely though. But if tomorrow, someone finds three complete Megs skeletons, all above 17 m TL confirming a robust physiology, I believe that theropod will find a way to challenge this and make it Isurus Megalus Lamna Pygmus. Scientifically this is not a bad thing, I appreciate anti-conformist positions (more in politics and military that being said) but when this is at any cost about one particular suject, that becomes somewhat boring and suspect, hence why I've not responded to his latest long posts as I know such discussion will never come to an objective solid agreement. Objective assessment of Megalodon is certainly important. - You made some observations - OP made some observations - I made some observations Now we shall see where this leads us to, I am expecting meaningful outcome. Dental spacing in Megalodon seems to be an interesting factor to focus upon but an observation have become apparent, thanks to your efforts: Megalodon seems to have broader and larger jaw structure at dental parity. Now about the subject, I guess this scale reconstruction is pretty good (perhaps the pic with the young girl still a bit too large ?). That poor girl... Image is nicely scaled. |
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Post by theropod on Mar 7, 2014 17:59:46 GMT 5
Life I have understood your arguments, you don´t have to repeat them. The point is that I´m not referring to "dental parity" (i.e. tooth lenght parity if I got you right). That tooth lenght is not a good base for comparisons between the two has been noted previously. The data I´ve posted on relative tooth lenghts for example. EDIT: tough given that specimen is what I think it is, it may have a somewhat oddly proportioned dentition itself… in any case however this seems to apply to other specimens of C. carcharias that I have seen pictures of, although I’m not sure whether it is this extreme.Great white sharks have proportionally longer (and bigger overally) anterior teeth (except the upper intermediate), while the dentition of C. megalodon displays more uniform teeth. Thus, you are completely right in saying that compared to the tooth height of an anterior Megalodon has a more massive dentition and is overally more massive. But that becomes irrelevant as soon as one relies on a different metric that is unaffected by these differences, the complete width of the dentition for example. E.g. the lenght of the whole toothrow (or, with other methods, total jaw perimeter, which doesn’t make much of a difference for our purposes since so far we would only be estimating one from the other anyway) can be expected to be much more closely linked to the total lenght and the bulk of the shark, since if it is not that means the whole jaws would be proportionally over- or undersized. Any assumption about relatively more or less massive dentition and jaws will thus directly reflect on the TL estimate derived from it. Here´s a spreadsheet that contains all the lamnid TL-BL regressions that I could find: theworldofanimals.proboards.com/post/11847At the same lenght, Isurus does not have a less robust physiology than Carcharodon based on these. Despite its vastly different jaw apparatus. Now don’t get me wrong, I think C. megalodon had a very robust body, after all most extant lamniforms do. What I’m suggesting is that longer fins wouldn’t have made a considerable difference in terms of body mass, because the body itself would stay the same lenght. Grey: What exactly did I write now that was so upsetting to you? 79kg in a 2120kg shark corresponds to 3.7% of the total body mass. In a 60t megalodon, the fins would thus weigh merely 2.4t when scaled isometrically. That actually sounds a bit low, albeit surely far more credible than that astronomic percentage you claimed was found in Balaeonoptera. Now, you think the weight a mere enlargement of these fins will add would be massive? Even if you assume they were 100% heavier in relation to the overall weight, the difference is well below 3t, and that is being very liberal (it is just as possible the only difference would be in lenght, and perhaps only of the caudal fin), and speaking of a large specimen. In relation to the total weight, that’s basically like the difference between two theropods of similar body size, of which one has an additional metre of tail. It is absolutely irrelevant what you think I will do if a particular fossil is found. That does not reflect on me, it reflects on you, badly to be precise. Again, I urge you to post sources and details for the data you are posting (which fins?...). Still waiting for references for some of your other recent claims ( Lamna widely regarded as particularly bulky? Blue whale flippers 14.3% of the total body mass?). Regarding the method based on toothrow lenght that I used, I and Life have provided sufficient support for the small spacing between adjacent Carcharodon-teeth in the form of complete jaws. You have to look at the roots if you want to assess it in a preserved jaw, don’t expect the crowns to look as if they were in contact, which would require the teeth to overlap as they do in Carcharhinus leucas. I had contacted Kent for that very purpose and you know the response. Kallal et al. are referring to spacing between adjacent tooth tips of 6cm, and presuming the teeth to be 6cm wide. 15%, not to mention more than that (as you seem to be so keen on assuming), would be a considerable difference in that regard, and certainly does not qualify as "very nearly abut", however you put it. Newbrey et al. (co-authored by Siversson himself) assumed a vastly smaller spacing than 15% in the lower jaw of Cardabiodon ricki. I’m not the hater here for following what was actually published and pointed out by shark researchers on that matter, as opposed to following figures only used in interviews and presentations that don’t explain his methodology to a sufficient degree. If that is not enough for you, and you think you have a better one, don´t rely on the method, but stop treating me like a fanboy for doing it.
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Post by Grey on Mar 7, 2014 18:13:23 GMT 5
If megalodon had indeed larger AND thicker fins to support the heavy built at this scale, the fins would probably weigh more than this figure in a 60 tonnes meg.
Perhaps the 1/7 ratio included the fluke in the source. Now a discussion about the fins is not relevant.
I don't have a bad opinion about you, you just tend to disagree with me on almost any discussion regarding this thread, like if it'd be your goal to simply no reach a consensus, and somehow to reduce megalodon size by arbitrary means.
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Post by theropod on Mar 7, 2014 19:02:52 GMT 5
If my goal was to reduce its size, you would see me reducing its size. I am not doing that.
You are also disagreeing with me, that works both ways! that our debates are so tiresome is as much your fault as it is mine.
The centra question itself was just that; an interesting observation that I wasn’t even the one to note. you were the one who started discussing it. And you see it led to some interesting conclusions. Your attitude towards debating is just too negative, that’s it. So if you don’t like it, or don’t like the answers you get, don’t do it, but stop blaming it all on me.
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Post by Grey on Mar 7, 2014 19:38:49 GMT 5
Yes but my point is that many of our discussions could be way shorter than this. The centra question did not deserve such a long debate, the jaws perimeter question has well advanced but is not finished, we still lack details, so there's no conclusion to make about the size of Hubbell's set individual yet.
All of this is of course keeping in mind that any estimate, published or not, for megalodon are only estimates that have to be taken with a large degree of caution. Which means that it is true Hubbell's set owner could be <11 m, just as it is true that it could be 11-12 m according to Siversson. You have to understand that I cannot make a day of our calculations alone based on a hazardable percentage and that I'm more interested in the exact calculation of this world authority in fossils sharks.
I disagree with you when you speculate too far beyong the available material and tools we have in hands (cf : centra). And there's really no need to discuss of our disagreement at lenght on the thread.
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Post by Grey on Mar 10, 2014 23:25:55 GMT 5
Dr. Siversson also estimated the body size of another Megalodon from a 13 cm tooth he found. This is a Carcharocles megalodon tooth, it's the remains from the largest known predator from Western Australia. Based on its size and comparing it to whole dentitions that we have found of Carcharocles megalodon, it probably grew to about 13, 14 metres, give or take a metre of so, and a weight of probably 20 tons, that's about ten times the weight of the heaviest white shark. We are going to go back to this site on Cape Range in probably August, of course after secured all the necessary permits from DEC and but I'm sure we will get that, surely... I'm going to prepare this out of the rock, but it's a nice display showing it how it was found and we have a couple more of these megalodon teeth from Cape Range in the rocks of the Miocene period.museum.wa.gov.au/explore/videos/rise-super-predatory-sharkswww.sciencewa.net.au/topics/environment-a-conservation/item/25-staring-into-the-jaws-of-shark-evolution.html/25-staring-into-the-jaws-of-shark-evolution.html?tmpl=component&print=1I've also remarked he posted several times on the fossil forum, discussing about cardabiodontids. Estimated total lengths based on maximum vertebral diameter are just that, estimates. Looking at modern macro-predatory sharks there is positive correlation between girth and the thickness of corpus calcareum. The latter is extremely thick in Cardabiodon, indicating a stocky shark. Vertebrae of the latter genus reached their maximum size in the late Albian. Estimates of total lengths in Cardabiodon can also be derived from the combined width of all teeth in the upper or lower jaw (from associated dentitions), which gives a good indication of the size of the mouth. Using lamnids as a template for vertebral diameter and total upper or lower tooth width indicates that the largest individuals of Cardabiodon reached 8-9 metres in the late Albian.
Using vertebral diameter to infer total lengths seems to be a less reliable option when the corpus calcareum is very thin (as in anacoracids) or of diminishing thickness towards the centre (as in Cetorhinus).In these posts, he said he was going to work on Danian otodontids. |
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Post by Grey on Mar 17, 2014 9:28:14 GMT 5
theropod I propose that specimen. It's a Chilean, apparently a posterior, UL 6 IMO. It's width is 3.5 inches, 8.89 cm. I suggest to use Gordon Hubbell's tooth set as a template to assign that tooth a calculate approximatively how large was the individual. As we have disagreement or rather, we still don't know the exact percentage of tooth spacing to use as in Kent's or Newbrey's paper, I'd suggest to consider Hubbell's specimen was about 10 or 11 m as estimated by Siversson. This seems fair enough to me in the absence of additionnal data for the calculation with Lowry's formulas. I'd not be surprised if we come up with a large Carcharocles, Hubbell said that the very largest teeth come either from South Carolina and Chile. My rough estimate based on the complete dentition is that it comes possibly from a Carcharocles in the 17-19 m range, more or less 18 m. It is plausible that 7 inchers (slant) are lying somewhere belonging to the dentition that tooth belonged.
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Post by theropod on Mar 17, 2014 23:46:40 GMT 5
In this case I agree with the identification, at least if there isn’t too much perspective in the photo. What’s the source of the image and the measurement?
CB-11 (1974mm in total tooth width) has L6s measuring 71 and 78mm wide (average is 74.5mm)
CH-31 (1598mm in total) has L6s 52 and 56mm in width (average is 54mm)
I.e. the tooth is about 19.3% and 64.6% bigger respectively, resulting in total upper jaw tooth widths of 2355.6mm and 2630.8mm.
Now, I don’t think there is much of a point in using direct sizing based on some rounded range here, when a regression equation doing the same is available, since that range is actually loosely based on Lowry et al. It merely results in less precise and objective estimates.
But assuming these two specimens were "13-14m" and "10-11m" respectively, you’d get estimates between 15.5m and 18.1m, not 17-19m.
On the other hand, if you use Lowry et al.’s formula with 15% interdental distance, you get 16m and 17.8m, so we can say that the ranges overlap fairly well here.
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Post by Grey on Mar 17, 2014 23:55:08 GMT 5
The tooth is from a private collector I discussed with.
I've asked to not use Lowry as long as we don't know the exact spacin percentage used in the published estimates from it, I intentionnally asked for a direct sizing from Siversson estimate. I was also focusing on Hubbell's set, not the other, but that's a good thing to use it too whatever.
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Post by theropod on Mar 18, 2014 0:00:04 GMT 5
Well, either way you do not get 19m from it.
It doesn’t make a difference if the figure you use for direct sizing suffers from the same problem.
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Post by Grey on Mar 18, 2014 0:01:44 GMT 5
You may remark in your calculation that the mean is respectively 16.8 m and 16.9m, a very similar ~17 m TL. But remains to be known precisely how to work with Lowry to get more solid figures that the one I proposed.
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Post by Grey on Mar 18, 2014 0:07:38 GMT 5
Well, either way you do not get 19m from it. It doesn’t make a difference if the figure you use for direct sizing suffers from the same problem. I've said that was rough, I've just used one side in Hubbell's set, hence approaching 19 m. |
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Post by theropod on Mar 18, 2014 2:07:25 GMT 5
You may remark in your calculation that the mean is respectively 16.8 m and 16.9m, a very similar ~17 m TL. But remains to be known precisely how to work with Lowry to get more solid figures that the one I proposed. In both cases that’s slightly lower than the lower bound of the figures you gave. |
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Post by Grey on Mar 18, 2014 2:30:43 GMT 5
I gave a rough range, you gave a more precise range, that's why I've asked you. I've not complained against your range but against using Lowry. Period.
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