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Post by elosha11 on Jul 18, 2016 0:31:39 GMT 5
Or a 5000 pound great white v. a 6000 pound orca? Well, his main point was not so much that odontocetes that weigh the same as sharks as a whole cannot be used as a proxy for this battle, his point was about the FKW in particular. Orca vs GWS at parity may be different. Anyway, this reminds me a lot of the debate about the reliability of accounts for the discussion of hypothetical AVA scenarios where we also sometimes ask questions like "Should we work with the best we have or are all accounts we have simply completely unrepresentative?". A similar question could be asked about analogies. I think this is indeed a case where we have to rely more more on our imagination than on actual observations because the FKW vs GWS accounts can only be used as an argument if it can be established why exactly the great white dominates (we need a causation factor that explains the correlation) and see if the same factor can help Megalodon to dominate over Livyatan. Maybe I wasn't being clear. What I was trying to say is that theropod seemed not to like the GW v. FKW analogy very much. I think it's the best one we have, but since I've seen indications from theropod in the past that he may believe Livyatan to possibly the the larger animal, I want to know whether he would think that examples where the FKW or orca was slightly larger than the shark would be closer proxy contests. I personally don't think they would be, but I'm interested in his perspective. In any event, such hypotheticals in which the cetecean is slightly bigger still have some predictive value, whether or not they are the best analogy. I agree that the evidence of FKW and great whites is sparse, which is why my initial comment expressed a desire for more evidence of interactions. Indeed, I'm hoping to get the photographer's input on the picture, perhaps there is more insight to be gleaned. But -- I do think further study/evidence on the relationship between great whites or other large predatory sharks and FKW could shed more light on our hypothetical conflict and I think it would be far from a useless, irrelevant analogy. |
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Post by creature386 on Jul 18, 2016 0:38:08 GMT 5
I agree that the evidence of FKW and great whites is sparse, which is why my initial comment expressed a desire for more evidence of interactions. Indeed, I'm hoping to get the photographer's input on the picture, perhaps there is more insight to be gleaned. But -- I do think further study/evidence on the relationship between great whites or other large predatory sharks and FKW could shed more light on our hypothetical conflict and I think it would be far from a useless, irrelevant analogy. This was not so much my point though, I was comparing discussions about the reliability of accounts to discussions about the reliability of analogies because I see some parallels: They are both extremely tempting, yet rather difficult arguments because the question of how representative they are. I was not so much objecting to the rather poor data on GWS vs FKW interactions. The bottom line is this: If we can establish that great white sharks generally dominate over false killer whales in encounters (correlation), we must find out why this is the case (causation) and look if this causation factor is also applicable in the Megalodon vs Livyatan match. |
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Post by elosha11 on Jul 18, 2016 1:40:12 GMT 5
Yes, I generally agree with your thoughts. The evidence is so sparse we cannot even make a correlation, much less prove causation. I'm not sure it's a question of "reliability" of the accounts, it's more of a question of how much inference we can take from the accounts and whether we can use them to make any predictive analogy. The "accounts" themselves had certain, very limited, but undisputed facts. (1) FKW have, on rare occasions, been seen with shark wounds from apparently sizeable sharks. That's really the only known fact right now. We do know on one occasions a 3 to 3.5 meter female FKW had shark bites on it discovered after it breached. We don't know the sex or size of the FKW in the pic I posted. Perhaps we will find out from the photographer.
All I'm trying to do, perhaps rather poorly, is draw some plausible inferences based several other factors, including where the bite is located, and which possible species of shark could have done it.
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Post by theropod on Jul 18, 2016 3:15:36 GMT 5
^Theropod, I never said FKW v. great white is a perfect proxy contest, just that it's the best analogy we have and that could actually be observed, in theory. Do you have a better analogy? Well, first of all, it actually has not been observed, being observable in theory is nice, but it doesn’t become useful under any circumstances until it gets reality. Secondly, I’m not saying I have a better analogue, just that this one is brought up way too often and given way too much importance. As you wrote, you consider orca vs great white to be a mismatch and not worthy of consideration here. Certainly that is right, there is nothing anywhere close to a parity fight with these two. Now lets put FKWs into perspective. If memory serves me right, the false killer whale that succumbed after sustaining a shark bite was 3.8m long. Assume the shark that attacked it was a large female white shark around 6m long, not a certainty, but certainly not an parsimonious assumption given the prey size (presupposing that this was a predatory interaction). In that case, the size ratio here might well compare favourably to that between the 3-4m great white and the 4.7-5.3m orca that killed it. So all this is certainly very far from suggesting that sharks dominate raptorial delphinids at equal size, let alone something like Livyatan. Not necessarily. Following one plausible reconstruction, it could be (similar to an orca or pygmy sperm whale). Following others, it could also be less robust, but potentially longer. However as you know I disagree with the notion of the shark being bigger in terms of mass. I’m totally fine with going with mass parity here if there’s not a really strong argument to be made that one is bigger (and if I’m to prefer that argument to what is suggested by the current most recent published estimates, independently corroborrated by a number of other methods, and taking into account the entire range of plausible size estimates for the holotype of Livyatan, it takes more than "but the biggest estimate ever published for C. megalodon is bigger than the biggest ever published for the holotype of Livyatan"). So chiefly we’d need a comparison between two equally-sized animals, but there the problem is that extant delphinids have proportionately considerably smaller jaw s than stem-physeteroids. So I guess the delphinid should probably be a bit larger than the shark in order to make this a fair comparison, but certainly it should not be a bit smaller (as in the case of FKW and GWS). Is there any recorded case of any shark killing or "dominating" a raptorial delphinid its own size or bigger? Certainly not the first one, as a mako is a very bad analogy in terms of tooth and jaw morphology. The second is closer (as explained above), but the weight difference it takes it debatable. In any case I don’t see the relevance, since we can hardly hand-pick a whale and a shark in the sizes of our choice and let them fight, and comparisons between entire species are not just poorly representative due to mechanisms that cause one of these extant taxa to come out on top not necessarily being in place with our neogene scenario, but also data deficient to begin with. You’d need at least one properly documented account of an interaction in order to know how two species interact, not a couple of bite marks, and more would obviously be better. Maybe if C. carcharias was a well-documented predator of Pseudorca including at least a few cases where it preyed on individuals of equal or greater size. Not if all we’ve got are two bite marks of which we don’t even know for sure whether they were predatory bites, while we do know for sure that if they were the attack was unsuccessful. with the current situation, what can be really suggested from this analogy? But we don’t have any case where they did face off, so that’s purely hypothetical. Neither C. carcharias nor P. crassidens are currently at the top of the trophic chain, both are being preyed on by Orcinus. So I think that in itself is a rather obvious difference. Baird et al. 1989 documented a beached FKW measuring 462cm in total, with a 59.5cm skull. I seem to recall some other paper that also gave measurements suggesting similar proportions, but I failed to find it. Orcas also seem to have similar head/body proportions, but with the major difference that their body is also considerably more robust. I think the trend is clear, extant delphinids have proportionately much smaller skulls than stem-physeteroids. EDIT: I think I found it again, it’s this paper: Pardo, M. A., C. Jiménez-Pinedo, and D. M. Palacios. 2009. The false killer whale (Pseudorca crassidens) in the southwestern Caribbean: first stranding record in Colombian waters. Latin American Journal of Aquatic Mammals 7: 63–67. documenting a whale with a 437cm skeletal length and a 61.8cm skull (41.86cm wide, so comparable to Livyatan in length/width-ratio but smaller overall). Accounting for the length added by the fluke we’ve got ourselves another Pseudorca with very similar proportions. I think the evidence from literally all its relatives suggests so. Previously I’ve received a lot of hate for making any suggestion in the way of more delphinid-like morphology in Livyatan (even if it was just giving it a more prominent fin and flippers). It would be pretty weird if I had to keep reminding that Livyatan was most likely not proportioned like a dolphin. Orcinus isn’t exactly sleek but quite capable of catching penguins and salmon. Bulky body shapes in water don’t translate to poor maneuverability. Still, what about that placement makes you so sure that they are from an attack? Being possibly the result is not the same as being scientific evidence of one. And are living dolphins bearing such bite marks a good indication that this is a preferrable method of attack? If so, why are they…living? |
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Post by Grey on Jul 18, 2016 15:28:48 GMT 5
Yes, I know you were comparing meg to a fin whale, but nonetheless you posted it on this topic, are you saying you didn’t mean to imply anything related to this topic with it? In any case I don’t think the cruising speed bears any relevance. The much more important question, who sais that GWS are more maneuverable and explosive than comparably-sized odontocetes? I’d be very interested in your data. Up to now, summed tooth width has not been suggesting a large number of potential 20m-candidates. Do you have access to better data on complete megalodon dentitions that invalidate this? The cruising speed can have some relevance once we agree that the larger animal becomes faster. Given the cartilaginous, relatively flexible nature of its skeleton, I'd expect a Megalodon to be more maneuvrable than a similar-sized gigantic cetacean, maybe faster at max speed but with less stamina. I see Livyatan faster, less clumsy than a similar-sized sperm whale but nothing like a simply scaled up delphinid. Until now, summed tooth width estimates have not been published for Megalodon. That's the subject of future project. If the initial results are valid, possibly Meg maximum size could be reevaluated upward. |
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Post by theropod on Jul 18, 2016 16:09:03 GMT 5
So you think a cartilaginous skeleton automatically suggests better maneuverability?
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Post by Grey on Jul 18, 2016 16:32:18 GMT 5
Theoretically at least, that's one of its main evolutionary advantages. I think Dan Hubber agrees about that.
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Post by Grey on Jul 18, 2016 16:55:18 GMT 5
I'm not sure about the relative bulkiness of Livyatan at 16-17m. A sperm whale the same length is wider skulled and I don't think Zygophyseter is a very bulky animal (for talking with Bianucci).
On the other hand at 14m, the holotype would be even bulkier than a similar-length sperm whale.
The same thing occures with Megalodon, tooth height regressions would results in a particularly stocky, bulky shark while dentition based estimates in a longer, more classic lamnoid shape.
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Post by theropod on Jul 18, 2016 17:04:13 GMT 5
Well, I don’t see extant sharks having this sort of agility advantage over extant odontocetes at least. Neither are they the fastest or most explosive things in the ocean, as that would imply.
I wouldn’t even be so sure that large lamniforms are any more flexible than odontocetes. Why would they be, considering there should not be much of a difference in the rigidity of their vertebral collumns and that while cetaceans have bony ribs, sharks make up for that by a skin acting like an exoskeleton?
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Post by Grey on Jul 18, 2016 17:19:17 GMT 5
MAkos and great whites are certainly agile, if anything, that they're not as fast or explosive, their flexibility is their main advantage. The question is to envision this at the much larger sizes of the Miocene behemoths.
I don't think shark skin is that rigid.
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Post by theropod on Jul 18, 2016 17:23:01 GMT 5
If it’s supposed to act as a functional site for the attachment of swimming muscles is has to be rigid, otherwise that would be a terribly inefficient arrangement. Or perhaps that whole thing was a lie, I haven’t dissected a shark to check myself. But a ribcage is not that rigid either, so where’s the point?
Odontocetes are also very agile, the question is; do you have evidence that sharks are even more agile?
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Post by Grey on Jul 18, 2016 17:29:17 GMT 5
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Post by theropod on Jul 18, 2016 19:14:24 GMT 5
And who is talking about being rigid like a stick? The question is, are sharks more flexible than similar-sized odontocetes? Right→ whales→, humpback whales→ and sperm whales→ aren’t exactly known for any of those qualities you list either but can fully leap out of the water too despite being many times the size of that basking shark. I guess there’s no need to post pictures of the various feats of athleticism known from Orcinus and Pseudorca, you are certainly aware of them, as you no doubt are regarding the extremely similar feats known from great white sharks. What’s missing is where exactly I should be getting the impression that sharks are superior. And a basking shark is a lot more elongated in built than I envision C. megalodon, let alone how you prefer to envision it. In terms of flexibility, that’s a relevant difference. Simple question, where is the evidence that sharks are more maneuverable or explosive than odontocetes? |
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Post by Grey on Jul 18, 2016 22:56:46 GMT 5
And who is talking about being rigid like a stick? The question is, are sharks more flexible than similar-sized odontocetes? Right→ whales→, humpback whales→ and sperm whales→ aren’t exactly known for any of those qualities you list either but can fully leap out of the water too despite being many times the size of that basking shark. I guess there’s no need to post pictures of the various feats of athleticism known from Orcinus and Pseudorca, you are certainly aware of them, as you no doubt are regarding the extremely similar feats known from great white sharks. What’s missing is where exactly I should be getting the impression that sharks are superior. And a basking shark is a lot more elongated in built than I envision C. megalodon, let alone how you prefer to envision it. In terms of flexibility, that’s a relevant difference. Simple question, where is the evidence that sharks are more maneuverable or explosive than odontocetes? With a more flexible cartilaginous skeleton, it is logically expected that the shark would be more maneuvrable than a comparably large cetacean. I could agree on the cetacean being faster with more stamina, the shark would be more maneuvrable. I dont "prefer" to envision it as a stocky, bulky shark. I actually tend to envision it longer and more fusiform (due to alternative size estimates) but regardless maneuvrable thanks to his cartilaginous internal structure. This is complicated though by the suggestion from B.K. that the larger sharks, will gaining in speed, would lose substantially in maneuvrability... We're in the realm of pure speculation here, including the case of Livyatan. |
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Post by theropod on Jul 19, 2016 0:25:56 GMT 5
First of all, the one thing logic does dictate is that there are certainly tightly constrained limits to how flexible that skeleton could be in an animal of that size. Animals don’t just built a skeleton for fun, it serves a mechanical purpose, whether it be composed of bone or cartilage. I’m repeating myself, but the most important structural element of that skeleton, the vertebrae, are heavily calcified even in much smaller extant sharks, to the point where their stiffness and strength equal that of bone: jeb.biologists.org/content/209/15/2920Going on, who even said that elasmobranch skeletal elements are generally more flexible than bone in the first place? For example this study tested the propterygium in 5 species of rays and found it to be similarly rigid to bone: jeb.biologists.org/content/215/12/2003So what we’re left with is the absence of ribs, which yes, might render the postcranial skeleton of sharks a little more flexible in the relevant area. On the other hand there is a strong case to be made that shark skin contributes significantly to their rigidity, considering that thrust-generating muscles are supposed to efficiently attach to it. So we’re back where we started, no indication whatsoever that sharks are actually more flexible. And flexibility doesn’t even necessarily imply agility to begin with, or anacondas would be among the most agile animals on the planet. Likewise there’s no evidence of that anywhere, you are literally making it up. I dont "prefer" to envision it as a stocky, bulky shark. I actually tend to envision it longer and more fusiform (due to alternative size estimates) but regardless maneuvrable thanks to his cartilaginous internal structure. Of course they will, getting larger something larger will inevitably lose maneuverability. It certainly didn’t take Kent’s suggestion to realize that. Could you kindly point out where I have entered the realm of pure speculation? My point is that we don’t know whether one was more maneuverable and that your speculations are dubious. My best guess would be that there would be no significant differences between two ecologically comparable animals, especially at such a size. That may be speculative, but choose to argue it or not we are left with no indication of either being more agile.
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