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Post by sam1 on Oct 23, 2019 22:34:47 GMT 5
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Post by theropod on Oct 23, 2019 22:52:31 GMT 5
Excellent. You wouldn’t happen to know any source on the gape angle of orcas, would you?
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Post by Grey on Oct 23, 2019 23:22:35 GMT 5
elosha11 That depends, do you think a 5 m orca would have trouble biting <4.6 m white shark? That’s about what the relative size of megalodon’s and Livyatan’s jaws would suggest as the most optimistic estimate of the shark’s size compared to the whale’s jaws. If the shark has positively allometric jaw size, or is a smaller individual than the Yorktown dentition, it ends up smaller than that. If we take the average adult size of the tooth sample, then the comparison is more like that between a 4 m shark and the jaws of a 5 m orca. An estimated 4.7-5.3 m orca has been recorded biting and holding an estimated 3-4 m great white in its jaws… And I don’t think sam1 was disagreeing that a shark bite would do massive damage to a similar-sized animal, we seem to all be pretty much agreed on that. But I’ve read suggestions here claiming the Livyatan jaws would be able to cause substantially less damage, so it’s fair to question that on the basis of how the two sets of jaws compare… I'm agreed with you regarding the jaws size ratio with orcas and GWS but I would recall this is not written in the stone until we find a preserved jaw. Meg could end up having had actually larger jaws than we would expect for its size and still growing really large... ...as much an actual preserved jaw or complete skeketon could show a much smaller shark (like Shimada's results or less) against all odds. I would recommand using the jaws structure of the Calvert Marine Museum skeleton in comparison ? The skeleton behind these jaws is 11.37 m long but the upper jaws are already an impressive 290 cm UJP. And I think this model is more scientifically robust (and robust at all) than other meg jaws reconstructions which are only scaled up from a GWS jaw set. And like said theropod, indeed meg and Livyatan quite probably ate similar-sized preys and their teeth probably made a similar amount of damage in their own kind. Meg teeth simply didn't need to be larger than they are to kill anything and a larger part of the tooth was actually the crown inflicting the deep damages, while Livyatan proportionately had less exposed enamal, a good part of the tooth was the massive root. I should emphasize on the visual horror that must have been the full bite of a large megalodon on its prey. I've seen videos of GWS almost cutting or slicing in half basically human-sized seals and these GWS were not necessarily even 4 m... The destructive and exsanguinative power at the scale of megalodon bite may have been almost or even totally unparalleled. On the other hand, not only waiting for others potentially larger specimens, I would be very curious to see a study about Livyatan biting power. I expect it to be huge, at least 15 tonnes of pressure, with a lower bound at 12 tonnes but maybe plausibly something even titanic, even exceeding or far exceeding those suggested by Wroe et al. 2008. for megalodon. How would the fight and comparison turn that time ? How a 20, or 25 tonnes potential bite pressure would play against a similar-size or even larger meg ? |
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Post by Life on Oct 23, 2019 23:33:27 GMT 5
GreyThere is no proof of Livyatan being in the league of Megalodon in big-game hunting - vastly different jaw mechanics to consider. Livyatan did not had a cosmopolitan distribution: "On the basis of the scarce fossil record, the distribution of Livyatan appears to be restricted to the Southern Hemisphere (Table 1). The absence of fossil remains of a macrophagous form of size and morphology comparable to Livyatan in the Northern Hemisphere still lacks a clear explanation." - Piazza et al (2018) To me, that sound very specialized.
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Post by sam1 on Oct 23, 2019 23:42:24 GMT 5
Excellent. You wouldn’t happen to know any source on the gape angle of orcas, would you? Have to disappoint you, sorry. Btw I remember reading a speculation about that 90° angle of sperm whales as a possible remnant of a hypercarnivorous lifestyle. The other theory was that it's a result of male competition(raking during the fights). Couldn't find that article again. |
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Post by theropod on Oct 24, 2019 0:07:16 GMT 5
elosha11 That depends, do you think a 5 m orca would have trouble biting <4.6 m white shark? That’s about what the relative size of megalodon’s and Livyatan’s jaws would suggest as the most optimistic estimate of the shark’s size compared to the whale’s jaws. If the shark has positively allometric jaw size, or is a smaller individual than the Yorktown dentition, it ends up smaller than that. If we take the average adult size of the tooth sample, then the comparison is more like that between a 4 m shark and the jaws of a 5 m orca. An estimated 4.7-5.3 m orca has been recorded biting and holding an estimated 3-4 m great white in its jaws… And I don’t think sam1 was disagreeing that a shark bite would do massive damage to a similar-sized animal, we seem to all be pretty much agreed on that. But I’ve read suggestions here claiming the Livyatan jaws would be able to cause substantially less damage, so it’s fair to question that on the basis of how the two sets of jaws compare… I'm agreed with you regarding the jaws size ratio with orcas and GWS but I would recall this is not written in the stone until we find a preserved jaw. Meg could end up having had actually larger jaws than we would expect for its size and still growing really large... ...as much an actual preserved jaw or complete skeketon could show a much smaller shark (like Shimada's results or less) against all odds. My point was about how the body of the shark compares to the jaws of Livyatan, to answer whether the latter could bite it. Baseline is that we know for sure a 3-4 m great white can be bitten by a 5 m orca, "by its back, proximal to its dorsal fin".
If a 6 m orca has a 92 cm skull, a 5 m one’s would be around 77 cm. I think we can all agree that if an orca for a given skull length can bite something, a Livyatan likely could as well. The jaw perimeter (370 cm) you estimated for the Yorktown individual is 26 % greater than the skull length of Livyatan. That means the shark scaled down to match the skull size comparison with the orca would have a ~96 cm ujp (or 26% that of the Yorktown individual).
To find out how large that shark would be, we can either use the jaw perimeter regression, in which case it is around 4.6 m, or we can use isometry, as in your method, in which case it is 4.5 m. The average implied by the tooth sample would be 4 m and 3.9 m respectively.
I have relatively little problem envisioning a 5 m killer whale biting a 4 m or likely even a 4.6 m white shark effectively. It follows that the Livyatan holotype, whose jaws are relatively speaking just as large, would also be able to bite an average sized and Yorktown-sized megalodon, respectively. Would you agree?
Of course the assumption of isometry might not be accurate, who knows. However all evidence points towards positive allometry in jaw size, I have so far seen no evidence at all for negative allometry. Meaning the shark belonging to those jaws might be smaller for a given jaw size (not really the point I was making, but certainly relevant to it, as that would make the shark’s body smaller than estimated here, therefore easier to bite). Of course if we estimate a shark from its jaws, if we make the jaws proportionately larger we get a smaller shark, or the reverse. The jaw size is the constant here, that doesn’t change. The average jaw size of megalodon won’t change either, as it’s simply the 86.5% the size of the Yorktown dentition that comes from comparing teeth directly to that specimen. But the shark to which that jaw belonged could be 13 or 15 m, depending on the estimate. I’m using the upper estimates here.
Good, do you have suitable pictures and/or dimensions of those jaws?
Also, if you find this reconstruction credible, which shows significantly larger jaws than as of your estimates, would you agree that the positive allometry suggested by data for jaw perimeter and tooth row length in white sharks is plausible?
I would tend to say scaling up from a gws jaw set is perhaps the only scientifically robust thing to do…
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Post by theropod on Oct 24, 2019 0:15:51 GMT 5
sam1: It would be somewhat surprising if that explanation were correct (hypercarnivory=bigger gape), since adaptations for strong bite force (muscles with large moment arm, high fiber-pennation) generally tend to limit gape. Sperm whales don’t need to be able to bite very hard, so they can more easily afford morphology that allows very wide gapes (long, parallel-fibred jaw muscles with small moment arms). Of course gapes can vary very widely between hypercarnivores, but something with such massive and massively rooted conical teeth and extremely robust skull morphology strikes me as more adapted for extreme bite force than extreme jaw gape. I would be quite surprised if orcas (or Livyatan) could open its mouth to 90°. That’s comparable to an Allosaurus. The only mammals other than sperm whales that seem to achieve such high gape angles are sabre-toothed feliforms and some metatherians. So I think tooth raking makes more sense in this case. But still, very interesting that sperm whale jaws open this wide, I didn’t expect that.
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Post by spartan on Oct 24, 2019 0:20:51 GMT 5
  For visualization. And it makes sense for them to have such a wide gape, males use their jaws heavily in intraspecific combat. |
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Post by theropod on Oct 24, 2019 0:24:50 GMT 5
GreyThere is no proof of Livyatan being in the league of Megalodon in big-game hunting - vastly different jaw mechanics to consider. Livyatan did not had a cosmopolitan distribution: "On the basis of the scarce fossil record, the distribution of Livyatan appears to be restricted to the Southern Hemisphere (Table 1). The absence of fossil remains of a macrophagous form of size and morphology comparable to Livyatan in the Northern Hemisphere still lacks a clear explanation." - Piazza et al (2018) To me, that sound very specialized. Didn’t you suggest just a few pages back that a physeteroid tooth from the norther hemisphere bearing a purported meg bite mark was likely to be Livyatan? spartan: Yes, but even that is nowhere close to 90°. 90° is really a massive gape angle, especially for a mammal (though it appears somewhat normal for sharks, speaking of which, can we get some reliable information on how far shark jaws can open, since dried specimens are often preserved in an inaccurate articulation?). |
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Post by sam1 on Oct 24, 2019 0:49:24 GMT 5
sam1 : It would be somewhat surprising if that explanation were correct (hypercarnivory=bigger gape), since adaptations for strong bite force (muscles with large moment arm, high fiber-pennation) generally tend to limit gape. Sperm whales don’t need to be able to bite very hard, so they can more easily afford morphology that allows very wide gapes (long, parallel-fibred jaw muscles with small moment arms). Of course gapes can vary very widely between hypercarnivores, but something with such massive and massively rooted conical teeth and extremely robust skull morphology strikes me as more adapted for extreme bite force than extreme jaw gape. I would be quite surprised if orcas (or Livyatan) could open its mouth to 90°. That’s comparable to an Allosaurus. The only mammals other than sperm whales that seem to achieve such high gape angles are sabre-toothed feliforms and some metatherians. So I think tooth raking makes more sense in this case. But still, very interesting that sperm whale jaws open this wide, I didn’t expect that. Yeah it would seem to make sense from a biomechanical standpoint that bigger gape is detrimental to bite force but there's really no actual indication of that in nature. A hippo is a mammal with highest recorded bite force, and it reaches a gape of an unparalleled 150° Among big cats, tigers have the widest gape yet again the greatest total BF if I'm not mistaken. Hyenas also can open the jaws as much as a typical dog. |
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Post by theropod on Oct 24, 2019 1:15:21 GMT 5
True, forgot all about hippos. They certainly have very strong bites in absolute terms, but have they ever actually been measured? I would not count on them being particularly strong for their size, their bites are probably the highest of any terrestrial mammal simply by virtue of being the largest terrestrial mammals with any propensity for biting. According to information creature posted, lions have the highest gape angle among big cats, and it’s just 65°: theworldofanimals.proboards.com/post/48246But yes, I’m not saying bite force across taxa is always that clearly correlated with gape angle, but it would seem unlikely that raptorial odontocetes were as or more suited to high gape angles than extant Physeter. |
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Post by Grey on Oct 24, 2019 1:16:45 GMT 5
Theropod, Yes I always considered that as well. Anything is still possible. When someone asks me how maximum large was megalodon, I respond either 17 m (tooth height method and/or strong allometry in the dentition region, potentially with a heavy built structure ?) or somewhere quite above 20 m (isometric, more athletic ?). Made a long by coherentsheaf (scaled here at 17 m).  Yes but a scaled-up more robust GWS set then...like the CMM jaws there. |
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Post by theropod on Oct 24, 2019 1:26:37 GMT 5
Yes, probably good reconstruction, but what jaw perimeter or dentition length does that correspond to?
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Post by sam1 on Oct 24, 2019 1:27:22 GMT 5
True, forgot all about hippos. They certainly have very strong bites in absolute terms, but have they ever actually been measured? I would not count on them being particularly strong for their size, their bites are probably the highest of any terrestrial mammal simply by virtue of being the largest terrestrial mammals with any propensity for biting. According to information creature posted, lions have the highest gape angle among big cats, and it’s just 65°: theworldofanimals.proboards.com/post/48246But yes, I’m not saying bite force across taxa is always that clearly correlated with gape angle, but it would seem unlikely that raptorial odontocetes were as or more suited to high gape angles than extant Physeter. I just have to say 65° seems very wrong, no matter the length of the PDF. I mean look at this images.app.goo.gl/7tsSSPS8wFTP3K1q8images.app.goo.gl/Y4PAmxzfY9h4xsuHAimages.app.goo.gl/FkGqNcoY6xSdZkgz9images.app.goo.gl/42FYdv7wZ5bgcvk2A |
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Post by Life on Oct 24, 2019 1:28:44 GMT 5
GreyThere is no proof of Livyatan being in the league of Megalodon in big-game hunting - vastly different jaw mechanics to consider. Livyatan did not had a cosmopolitan distribution: "On the basis of the scarce fossil record, the distribution of Livyatan appears to be restricted to the Southern Hemisphere (Table 1). The absence of fossil remains of a macrophagous form of size and morphology comparable to Livyatan in the Northern Hemisphere still lacks a clear explanation." - Piazza et al (2018) To me, that sound very specialized. Didn’t you suggest just a few pages back that a physeteroid tooth from the norther hemisphere bearing a purported meg bite mark was likely to be Livyatan? It surely does, but how it ended for the unfortunate whale anyways?  It might be that Livyatan was subject to enormous competitive pressures from the Megalodon, and was unable to establish cosmopolitan presence consequently. --- This thread offer a deeply unrealistic projection of the implied strength and capabilities of Livyatan actually - fossil records do not measure up to the hype factor. I get the excitement factor in relation to Livyatan but can WE tone down the hype factor a bit and draw inferences from the fossil records at hand? |
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