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Post by dinosauria101 on Feb 5, 2019 21:59:55 GMT 5
^Oops, I missed it. In that case I favor the shark
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Post by sam1 on Apr 5, 2019 17:16:17 GMT 5
seeing that even a 2 m longer meg doesn't look bigger should really be telling enough
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Post by elosha11 on Apr 5, 2019 19:22:14 GMT 5
View Attachmentseeing that even a 2 m longer meg doesn't look bigger should really be telling enough Ugh, I had a lengthy post ready to send and it somehow got deleted. The basic gist is that I find such drawings to be interesting, but I also find weight/shape/robusticity of Livy and Meg to be even more challenging than length estimates. I can't believe my post got deleted. Don't have time or energy to recreate it.
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Post by dinosauria101 on Apr 5, 2019 19:58:39 GMT 5
I feel you, elosha11. That happens many times when I make threads, having gathered lots of information but it all going down the drain.
Anyhow, my opinion changes to 50/50
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Post by sam1 on Apr 5, 2019 20:59:19 GMT 5
seeing that even a 2 m longer meg doesn't look bigger should really be telling enough Ugh, I had a lengthy post ready to send and it somehow got deleted. The basic gist is that I find such drawings to be interesting, but I also find weight/shape/robusticity of Livy and Meg to be even more challenging than length estimates. I can't believe my post got deleted. Don't have time or energy to recreate it. Brutal, sorry to hear. I hope it never happens to me again! I agree, the depictions will always remain speculative but that's the best we can do about these two.
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Post by prehistorican on Apr 5, 2019 21:37:58 GMT 5
Depends on which reconstruction you are using, either one from the internet or ones with credibility and assuming the shark isn't completely a scaled up porbeagle/white shark . BK Kent's reconstruction seems to be one with credibility as show by Grey in the recent TV doc, that was a BK Kent shaped C. megalodon. This is a photorealistic version: Also even though I disagree with the reconstruction of theropod1's C. megalodon (since it seems similar to Gottfried's in a sense but with an very pointy nose, and some other unlikely features), and now since the sizes are a bit outdated, his weight for the shark seems pretty accurate. It's the average of all the regressions/formulas and seems to be about what I expected, a slightly bulkier white shark which makes sense:
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Post by sam1 on Apr 5, 2019 22:32:15 GMT 5
This is a model based largely on a scaled up GWS. The author of the comparison updated it later with the image I posted, based on his own research. Definitely looks far more viable to me than the image you posted(frankly looks ridiculous and completely nonfunctional. That thing would be far slower than a Greenland whale, considering all the extra drag shark has compared to the cetacean)
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Post by prehistorican on Apr 5, 2019 22:38:19 GMT 5
It doesn't look ridiculous, simply deep bodied as other reconstructions have put it (ex: Nat Geo C. megalodon, Discovery C. megalodon). And based on the oxygen isotopes based from Ferron 2018 it would have a slow cruising speed of 5km/h but not burst speed which is 37km/h. It doesn't matter what you THINK is viable and what you think it LOOKS like rather than what IS credible and USED in reconstructions. the analogy doesn't work at ALL. "Far slower than Greenland Whale" Still slower than the shark. To say that it doesn’t look viable and COMPLETELY nonfunctional is a blatant over exaggeration even though the bulkiness seems quite expected and plausible. (And of course scientists use it).
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Post by sam1 on Apr 6, 2019 0:33:45 GMT 5
I maintain that it looks ridiculous and completely nonfunctional.. fatter than a pre-birth pregnant GWS. Unless you can give me the mathematics with the propulsory and drag numbers including the cross section figure, from this exact depiction?
Scientists use it, you say? And what are Leder, Perez and Badaut to you?
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Post by sam1 on Apr 7, 2019 1:13:30 GMT 5
p.s. alright, need to note that I did went a bit hyperbolic in my argument..if that wasn't obvious. Let's just say that I don't see any reasons to find Kent's depiction visually better and more scientificaly credible than the one I posted, on contrary. It looks out of proportion, with awkwardly big belly and somewhat cramped back with fins that seem too small for such a massive bulk. Just my opinion, until proven otherwise.
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Post by theropod on Apr 7, 2019 4:20:25 GMT 5
Rather than endlessly debating how realistic a totally speculative megalodon reconstruction is based on the credentials of the author (argument from authority) or personal preference and guesswork about biomechanics (feely argument), we can at least attempt to quantify how bulky megalodon might have been. Basically, here are the possibilities: A: megalodon was geometrically similar to a great white, just scaled up to 10-20m total length (isometry) B: megalodon resembled a giant great white, but differed in some proportions due to the effects of size and scaling (allometry) C: megalodon didn’t remotely resemble a great white, but had a completely different body shape (in that case, insert your preferred alternative analogue here) Isometry is not such an unlikely option people sometimes make it out to be (Are you crazy, your megalodon looks like a normal great white!?!!!!), especially when attempting to be cautious, and neither is it an assumption never taken by meg researchers nor is it entirely without a quantitative basis (McClain et al. 2015 found isometric scaling in white sharks, after all). Considering that, certainly a comparison showing megalodon like a scaled up white shark could potentially be of interest. However some sort of morphological difference over these size ranges is inevitable (it’s just not clear whether it necessitates an increase in bulk), and the majority of studies have indeed found a positive allometry of body mass with respect to length in great whites, so probably we should roll with that, as others have done. Now assuming allometry, a 15m megalodon is predicted to mass 36.25t based on 6 regression equations (see references!) for great whites. A 5m white shark estimated using the same method would mass 1.2t, which scaled up isometrically to 15m gives us 32.4t. So megalodon is ~12% more massive. Since this difference must all be in the body cross-section, assuming it’s about equally more robust in dorsoventral and transverse diameters, this means you have to draw your megalodon about 6% taller and 6% wider than a 5m great white*. I chose 5m as an example and because it is a size relatively commonly attained by great whites (so it should be easier to find them represented in footage and schematics), unlike the 6m+ monsters some people prefer to see as representative of the species. You could use one of those too, of course, but then the difference between it and megalodon simply becomes smaller (the same percentage calculated above for a 15m meg and 6.4m great white is 4.5%, and that 6.4m white shark will be 2.6t, not 3.3t, which we have to account for), giving you the same end result. You can repeat this calculation for any given mass and length (estimates!) of course, these are just the masses with the most statistical basis. For providing an upper bound akin to the lower bound given by isometry, the highest bulk increase suggested by any of the regressions is Gottfried et al. 1996’s, which would make the shark about 21% (so that’s 10% height and width increase over a 5m great white in the reconstruction). I don’t see a reason to favour that particular estimate over isometry though, both respectively base on one single regression. Even so, many of the reconstructions I have seen appear to be massively more bulky than suggested by these figures, way beyond even the most robust great whites I have ever seen. Now of course we need to agree on what that "average" 5m/1.2t great white actually looks like, but I think it’s clear it is quite a bit more slender than the most robust individuals of the species. So all things considered, the difference suggested by allometry is simply not that large, certainly within the range of variation of white sharks themselves. Of course the occasional large, particularly robust megalodon would likely be even bulkier than its white shark counterpart, but that’s not really relevant to the species as a whole. Or option C, or as I like to call it, artistic freedom, which is totally fine (no reason to run around telling everyone their megalodon reconstruction sucks just because it’s speculative, when no reconstruction bases on any direct fossil evidence) but adds little to the scientific debate as long as it isn’t supported over others by any data. *This is the method I used for my last reconstruction, basing on a lateral view reconstruction Compagno’s 1984 shark species catalogue, hoping it was going to be roughly representative of a typical specimen. That assumption may or may not have been warranted, that is up to debate. That there’s no quantifiable basis for portraying megalodon as some sort of hulk is not. For example the reconstruction in prehistorican’s post is 23% deeper-bodied than the great white. Granted, that is not a very robust individual, but this difference is way over the top, the megalodon would probably be over 50% heavier than the white shark at equal length. Casey, John G.; Pratt, Harold L. 1985. Distribution of the White Shark, Carcharodon carcharias, in the Western North Atlantic. Memoirs of the Southern California Academy of Sciences, 9 (Biology of the White Shark, a Symposium.) pp. 2-14. Gottfried, Michael D.; Compagno, Leonard J.V.; Bowman, S. Curtis. 1996. Size and Skeletal Anatomy of the Giant “Megatooth” Shark Carcharodon megalodon. In: Klimley, Peter A.; Ainley, David G.: Great White Sharks: the biology of Carcharodon carcharias. San Diego, pp. 55-66. Kohler, Nancy E.; Casey, John G.; Turner, Patricia A. 1995. Length-Length and Length-Weight Relationships for 13 Shark Species from the Western North Atlantic. Fishery Bulletin, 93 pp. 412-418. McClain, Craig R.; Balk, Meghan A.; Benfield, Mark C.; Branch, Trevor A.; Chen, Catherine; Cosgrove, James; Dove, Alistair D.M.; Gaskins, Lindsay C.; Helm, Rebecca R.; Hochberg, Frederick G.; Lee, Frank B.; Marshall, Andrea; McMurray, Steven E.; Schanche, Caroline; Stone, Shane N.; Thaler, Andrew D. 2015. Sizing ocean giants: patterns of intraspecific size variation in marine megafauna. PeerJ, 3 (715) pp. 1-69. Mollet, Henry F.; Cailliet, Gregor M. 1996. Using Allometry to Predict Body Mass from Linear Measurements of the White Shark. In: Klimley, Peter A.; Ainley, David G.: Great White Sharks: the biology of Carcharodon carcharias. San Diego, pp. 81-89. Tricas, Timothy C.; McCosker, John E. 1984. Predatory Behaviour of the White Shark (Carcharodon carcharias) with notes on its biology. Proceedings of the California Academy of Sciences, 43 (14) pp. 221-234.
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Post by DonaldCengXiongAzuma on Apr 7, 2019 11:51:15 GMT 5
I am going for vote for the livyatan slightly because it has its head to ram and it can use its jaws to attack the megalodon's unprotected gills. The megalodon"s slicing bite can do great damage to the livyathan and has a good chance of winning. Basically, it depends on who gets the first move but the livyathan gets my slight vote.
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Post by sam1 on Apr 7, 2019 13:03:18 GMT 5
I am going for vote for the livyatan slightly because it has its head to ram and it can use its jaws to attack the megalodon's unprotected gills. The megalodon"s slicing bite can do great damage to the livyathan and has a good chance of winning. Basically, it depends on who gets the first move but the livyathan gets my slight vote. Leviathan wouldn't need to attack the gills. Bitting off the pectoral fin would be far more effective. Death sentence for the shark.
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Post by Life on Apr 7, 2019 16:51:07 GMT 5
View AttachmentThis is a model based largely on a scaled up GWS. The author of the comparison updated it later with the image I posted, based on his own research. Definitely looks far more viable to me than the image you posted(frankly looks ridiculous and completely nonfunctional. That thing would be far slower than a Greenland whale, considering all the extra drag shark has compared to the cetacean) I do not believe that Megalodon is a scaled-up great white shark but it probably had a similar physical appearance. Dentition of Megalodon give the impression of relatively wider jaw structure (chondrocranium) than in the great white shark with teeth of similar proportions (A3 tooth factor among others), and the wider chondrocranium in turn imply a proportionally elongated body structure on the whole. This make sense in the light of relatively higher count of centrum in Megalodon. Robust dental structure of Megalodon correspond to extremely powerful muscles, and the heavily calcified remains of Megalodon in general (virtually anything preserved) imply a powerful physiology on the whole for potent ramming capacity (to stun/injure a whale with sheer impact) and shock-absorbing capacity (high tolerance for potential injuries/punishment). Nevertheless, streamlined body structure, and skin texture, would ensure that Megalodon could move really fast in short bursts - this is compatible with paleontological evidence of Megalodon being able to hunt much smaller dolphins. Endothermy is most likely. So yes, Megalodon was a biological marvel to say the least. I am going for vote for the livyatan slightly because it has its head to ram and it can use its jaws to attack the megalodon's unprotected gills. The megalodon"s slicing bite can do great damage to the livyathan and has a good chance of winning. Basically, it depends on who gets the first move but the livyathan gets my slight vote. Attacking gills is not easy in situations when the target is mobile. Window for this kind of attack might emerge at times but I am not aware of any case in which a cetacean taking out a shark by attacking its gills. Megalodon's gill structure wouldn't be exposed like in the Basking shark regardless.
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Post by theropod on Apr 7, 2019 19:21:24 GMT 5
@life: Of course all the preserved remains of C. megalodon are heavily calcified, because calcification is a prerequisite for preservation. That all the preserved remains are heavily calcified does in no way allow us to draw conclusions about the degree of calcification in the shark’s skeleton, because we wouldn’t be finding any that are not calcified to begin with. If we were finding significantly more preserved skeletal elements in megalodon than in fossil white sharks, that might imply its skeletal had better preservation potential and was thus likely more mineralized, but preserved remains of C. megalodon don’t include elements not also known to be preserved in Carcharodon (e.g. Ehret et al. 2009, Kriwet et al. 2014).
Teeth allow some (highly speculative) inferences about the morphology of the jaws they came from, but those are rather limited without having an actual jaw preserved. Only macrophagous predation explains the tooth morphology, and this is of course supported by ample trace fossil evidence, allowing us to make a functional and ecological analogy to the jaws of the great white shark that has a similar feeding regimen. But "teeth with similar proportions" are where the comparison breaks down, because you need to specify how they are compared, they do not have particularly similar proportions at all. An anterior or anterolateral megalodon tooth is shorter and probably thicker than a great white tooth the same mesiodistal width, wider and thicker than one the same apicobasal length, and shorter and probably narrower than one the same labiolingual thickness, it all depends on what metric is being normalized. And when overall size is already based on the tooth width (cumulative tooth width, dentition length, jaw perimeter or whatever), the jaws cannot be proportionately broader nor narrower, because the total length is estimated from the estimated jaw width. The chondocranium of megalodon is an entirely different issue and also entirely unknown. Shark jaw apparata are a totally separate unit from the chondocranium, so being able to make some inferences about one doesn’t translate to doing so about the other. That being said the same things also apply here, if overall size, including that of the chondocranium, is estimated based on the width of the jaws or dentition, then everything also stays in proportion. It’s shape can be variously restored, whether you prefer your megalodon with a pointy nose or a pug nose, none of that has any factual basis.
Swimming speed is again something we can say nothing specific about. The only estimates for it (like the much cited 35km/h burst speed estimate and Jacoby et al’s 5km/h cruising speed) base on respiratory and metabolic scaling of cruising and burst speeds respectively, and are of course prone to extreme error margins (the 95% confidence interval in Ferron et al. 2017 under the assumption that megalodon was endothermic ranges from around 15 all the way up to around 80 km/h). In other words, literally everything is possible, from as slow as a right whale to as fast as a mako shark, which is not surprising since both of these are also endothermic species. That’s because the estimate bases on a very general scaling relationship, not concrete biomechanical evidence. It’s metabolic assumptions that these estimates for swimming speeds base on, not the other way around, as there is again no direct fossil evidence whatsoever for estimating swimming speeds in C. megalodon. Swimming speed estimates were only used to independently test hypotheses about metabolism, because the higher swimming speeds implied by endothermy are more consistent with an active predatory ecology.
Ehret, D.J., Hubbell, G. and Macfadden, B.J. 2009. Exceptional preservation of the white shark Carcharodon (Lamniformes, Lamnidae) from the early Pliocene of Peru. Journal of Vertebrate Paleontology 29 (1): 1–13. Ferrón, H.G. 2017. Regional endothermy as a trigger for gigantism in some extinct macropredatory sharks. PloS one 12 (9): e0185185. Jacoby, D.M.P., Siriwat, P., Freeman, R. and Carbone, C. 2015. Is the scaling of swim speed in sharks driven by metabolism? Biology Letters 11 (12): 20150781. Jacoby, D.M.P., Siriwat, P., Freeman, R. and Carbone, C. 2016. Scaling of swim speed in sharks: a reply to Morrison (2016). Biology Letters 12 (8): 20160502. Kriwet, J., Mewis, H. and Hampe, O. 2014. A partial skeleton of a new lamniform mackerel shark from the Miocene of Europe. Acta Palaeontologica Polonica 60 (4): 857–876.
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