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Post by prehistorican on Jul 17, 2018 7:46:18 GMT 5
sam1 : Where is the evidence of whales being "inherently more agile"? Yes, I’m afraid you will need to do it again. If you have done it before, reposting it shouldn’t be too much trouble. I don’t read much of carnivora any more, I simply don’t have the time. But in what I have read, I’ve never seen actual evidence to back up these claims. Claiming something is not the same as demonstrating it. prehistorican : There is no "has a robust chondocranium" here, that is entirely based on conjecture as long as nobody finds a preserved Carcharocles chondocranium. Even with a robust chondocranium, that still does not constitute an adaption for ramming though. Again, ramming a small animal despite not being adapted for it is one thing, ramming another 50 ton animal is an entirely different thing. So saying "the shark can ram too" is only relevant to this discussion if there is any evidence that large sharks actually do ram animals or objects of at least similar size. One more thing on the agility discussion. I’m not sure whether I have noted this before, but since we would expect a larger shark to have a higher cruising speed to account for its respiratory needs (Jacoby et al. 2015), and since it has to keep moving at that speed continuously, 24h a day, if anything a giant shark would realistically require larger amounts of oxidative/slow-twitch muscle-fibres than a small one. Extant sharks don’t seem to significantly outperform similarly-sized cetaceans in terms of explosive acceleration or maneuverability to begin with, but claiming a giant shark would due to its greater amount of white muscles seems like an even more hazardous claim, considering its respiratory system dictates that it would have to invest less, not more in fast-twitch muscle fibres. So you can think what you want about how much of a benefit larger amounts of fast-twitch muscle fibres would be, but I don’t think that’s relevant as the animal needs to be able to swim relatively fast, and do it continuously. Rapid acceleration is important, but respiration is even more important. So if we assume Megalodon had a cruising speed similar to a fin whale, then it can’t have had superior acceleration due to its large amount of white muscle, because in order to be able to maintain that speed it would have needed oxidative muscle fibres. That is true. I find it interesting how scientists say there is actually less red muscle in larger sharks, but I will have to find that out later. The cruising doesn't seem to be that much of a difference maybe 1-2kmh more at most and mainly from size not metabolic constraints. Need to check up on the sources again though. |
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Post by sam1 on Jul 17, 2018 11:36:35 GMT 5
Theropod - You need evidence for my claim that whales can stand in place(sharks can't) and be omni directional?(they can twist around the axis in every direction, swim sideways and even backwards(sharks can't do any of it)). Also, balance is NOT a terrestrial exclusive feature. That's ridiculous to say. The ability to hover is a feat of balance demonstrated impressively by countless fish species(archer fish for example) and dolphins.
I know a 50 ton whale can be hard to imagine doing stunts but orca can basically carry a human on the tip of its nose.
Humpback whales for example are very agile and exhibit great balance and body control.
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Post by theropod on Jul 17, 2018 16:52:45 GMT 5
sam1 Yes I do. People actually providing evidence of what they claim for a change is the only way we can transform this into an informed, evidence-based discussion. So if this is so obvious, then it certainly shouldn’t be difficult to provide some examples. Didn’t you notice the lack of objective evidence in this whole mobility-debate? Not a single piece of actual evidence for either side’s claims has been produced, just lots of statements not backed up by anything. So it really doesn’t matter whether you think your statements require evidence or not, just post it anyway. About balance, yes it is primarily important in terrestrial animals.Why do you think the vestibular system of cetaceans is so tiny (Spoor et al. 2002). Let me quote you on that: An aquatic animal is supported by water, it doesn’t have to do anything to maintain body equilibrium, prevent falling over, or adjust its center of mass. Yes, if most of its body is out of the water, as it is when dolphins "walk on water" on their tails, that’s a different story. But are you suggesting that behaviour would be of any benefit in a predatory confrontation between two 50t aquatic animals, or that a sperm-whale sized cetacean could even do it? As for the former, I think it’s pretty clear it’s not, as long as neither animal has learned to fly. The confrontation would be carried out under or at the surface, not above it. As for the latter, that’s an example of a claim I would like to see proof of. I am not saying whales are not agile or capable of well-coordinated, in fact go one page back and you will find me arguing the exact opposite. However lamnid sharks are also impressive in this regard. I’m simply asking that you provide evidence of your statements to improve the quality of this discussion, just as I have done from people arguing the opposite. prehistorican: I just noticed that I missed a correction to Jacoby et al. 2015, the 5ms⁻¹ should be 1.34ms⁻¹, so not comparabe to a fin whale at all. Should have seen sooner that 5ms⁻¹ does not make sense based on the graph.Of course any such estimate is merely an expectation, and the real swim speed may have been vastly different considering the degree of variation. Also this neither indicated that meg actually could swim "that fast" (although I’d say it certainly could) nor that it was limited to such speeds, just that in general, sharks its size should swim that fast. But the suggested scaling of swim speed is due to metabolic reasons (on average, larger sharks need to swim faster due to the scaling of gill-area to the 2nd power but body mass to the 3rd). This leaves part of my argument (swim speed similar to fin whales) moot. However the study does suggest that swim speed scales with positive allometry, so that would suggest that larger sharks need more stamina than smaller ones. Who said that there is less red muscle in larger sharks? In any case, is there any evidence that extant sharks outperform similar-sized cetaceans in acceleration? Jacoby, D. M. P., P. Siriwat, R. Freeman, and C. Carbone. 2015: Is the scaling of swim speed in sharks driven by metabolism? Biology Letters 11:20150781.
Spoor, F., S. Bajpai, S. T. Hussain, K. Kumar, and J. G. M. Thewissen. 2002: Vestibular evidence for the evolution of aquatic behaviour in early cetaceans. Nature 417:163–166.
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Post by sam1 on Jul 17, 2018 18:11:40 GMT 5
Well I'm kinda baffled now.. you need evidence that whales can keep stationary position. And that they can rotate, bend, twist and take any direction from a stationary position, using their lungs and sense of balance(point about your quotes definition taken, but balance does have different contexts, and aquatic balance is one of them..just ask a professional swimmer how important is to keep balance in the water) as a mean of shifting weight and mass effectively.
Okay. I will not give you the evidence because actually going through it just feels too silly.
The ample and obvious evidence is out there, man. Just watch some videos of whales and dolphins.
As for you view that the above mentioned abilities aren't a factor in a confrontation, well, that's just wrong.
They allow the whale to simply always confront the shark.
And shark can only change the forward moving dorection. It's somewhat(unlike the airplane, the shark can't even move upside down) like comparing the helicopter and an airplane, except the helicopter in question can do everything the airplane can.
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Post by theropod on Jul 17, 2018 19:10:14 GMT 5
Keeping stationary position is not agility, its the exact opposite of agility. What you need to provide is evidence that whales are capable of maneuvering in (relevant) ways that sharks can not, including "bend, twist and take any direction" more quickly than sharks. That wasn’t my quote, it was your quote. What "above mentioned abilities" do I claim "aren't a factor in a confrontation"? Let me get this straight, you think that a 50t cetacean is going to be fighting a 50t shark by means of walking over water on its tail like a dolphin? That’s what’s irrelevant here. And sharks do not keep balance in water now? Planes, and helicopters even less due to their lower speed, can’t fly upside down btw. You know how planes and helicopters produce lift, right? If it’s upside down, it’s in free fall (worse, to be exact). That’s at best a temporary position some are able to pass through while flying some maneuver. Point taken with regards to swimming backwards. Since you are not willing to post it, here’s a video or an Orca doing it: www.youtube.com/watch?v=qhb1FFhIEB0I would argue that the ability to reverse direction instead of having to turn around could prove very useful in certain situations that could arise in a confrontation. |
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Post by sam1 on Jul 17, 2018 20:50:23 GMT 5
I'll get back to this later, for now just a short illustration why is such a stationary abiltity a great advantage.
"Always confront the shark" means that whale can maneuver while being stationary, according to shark's position. It can always face it head on. Like a fighter keeping its guard against the other fighter that tries to run around and catch it from behind.
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Post by sam1 on Jul 17, 2018 23:00:03 GMT 5
So, about the aerodynamic(and particularly hydrodynamic) lift, you are only partially right It can be generated by the wing shape but also by its position/angle of attack. Some airplanes actually can fly upside down this way. www.scienceabc.com/eyeopeners/how-airplane-jets-stunt-planes-fly-upside-down-lift-shape-of-wings-angle-of-attack.html..and it's the exact same principle whales use to swim upside down. Expanding on this principle is the ability to twist/roll around the axis. And it is a huge advantage. Do I need to explain why? It is simply a great last resort defensive mechanism in case of close quarter engagement - rolling so the back and top side meet the bite instead of vulnerable areas. This is why you always see dolphins bitten by sharks around the dorsal fin area. |
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Post by Grey on Jul 18, 2018 19:04:45 GMT 5
This is why you always see dolphins bitten by sharks around the dorsal fin area. I don't think 'always' is adequate. Bites at the tail are just as frequent. Despite the alleged mobility superiority and a body mass even greater, bottlenoses appear to be regular prey items for bull sharks. I certainly think these athletic skills become meaningless at 30 tons plus. |
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Post by sam1 on Jul 18, 2018 19:14:32 GMT 5
How is the ability to roll in a self protective manner meaningless, and what does mass have to do with it?
And I stated that it is a last resort, close quarter engagement maneuver.
Bites at the tail indicate, if anything, that the shark chased or tried to ambush the dolphin.
It is what's actually completely irrelevant in terms of head to head, equal terms encounter.
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Post by Grey on Jul 18, 2018 19:40:18 GMT 5
Simply said, the mobility of a 9-12 m cow sperm whale doesn't appear more impressive to me than that of a filter feeder basking or whale shark of similar size.
And I would most definitely compare a cow sperm whale to Livyatan in terms of physical constraints than to a delphinid.
I don't think Livyatan was relatively more mobile than a meg of equivalent size.
However, I do agree that Livyatan, being a true endothermic organism, may have been relatively more active (Ferrón 2017).
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Post by theropod on Jul 18, 2018 19:44:16 GMT 5
Could you please post a link or full citation to Ferrón 2017?
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Post by Grey on Jul 18, 2018 20:56:42 GMT 5
 Nota bene : yes, the body mass indication for S. sikanniensis, S. popularis and Basilosaurus are most likely wrong as he probably didn't keep in mind the slender body plan of these taxa. The table itself is highly interesting and solid to me. |
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Post by sam1 on Jul 18, 2018 22:04:58 GMT 5
Simply said, the mobility of a 9-12 m cow sperm whale doesn't appear more impressive to me than that of a filter feeder basking or whale shark of similar size. And I would most definitely compare a cow sperm whale to Livyatan in terms of physical constraints than to a delphinid. I don't think Livyatan was relatively more mobile than a meg of equivalent size. However, I do agree that Livyatan, being a true endothermic organism, may have been relatively more active (Ferrón 2017). That 12m cow can swim much faster and maintain that speed for much longer duration than any filter feeder shark. It can also maneuver while being stationary, it can roll etc, as explained, important aspects of mobility which shark simply lacks. How is that not more impressive mobility?!? You simply keep grossly underestimating the whale, even while faced with clear facts. |
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Post by theropod on Jul 18, 2018 22:25:23 GMT 5
Grey: What table? Your link only leads to an image-hosting site. If the "me" in the image legend is supposed to mean "mesotherm", then these results are quite doubtful (quantitative histological analysis suggests basal metabolic rates in the range of extant mammals and even birds for Plesiosaurs, see Fleischle et al. 2018 and Wintrich et al. 2017). Basically all the eosauropterygians in that chart should probably be classed as endotherms. So I’d really be interested in seeing the methodology behind that paper you cite. Fleischle, C. V., T. Wintrich, and P. M. Sander. 2018: Quantitative histological models suggest endothermy in plesiosaurs. PeerJ 6:e4955.
Wintrich, T., S. Hayashi, A. Houssaye, Y. Nakajima, and P. M. Sander. 2017: A Triassic plesiosaurian skeleton and bone histology inform on evolution of a unique body plan. Science Advances 3:e1701144.
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Post by Grey on Jul 19, 2018 1:30:24 GMT 5
Simply said, the mobility of a 9-12 m cow sperm whale doesn't appear more impressive to me than that of a filter feeder basking or whale shark of similar size. And I would most definitely compare a cow sperm whale to Livyatan in terms of physical constraints than to a delphinid. I don't think Livyatan was relatively more mobile than a meg of equivalent size. However, I do agree that Livyatan, being a true endothermic organism, may have been relatively more active (Ferrón 2017). That 12m cow can swim much faster and maintain that speed for much longer duration than any filter feeder shark. It can also maneuver while being stationary, it can roll etc, as explained, important aspects of mobility which shark simply lacks. How is that not more impressive mobility?!? You simply keep grossly underestimating the whale, even while faced with clear facts. I don't think it is underestimating the whale. It is simply that despite these implied mobility advantages, cetaceans, mysticetes or odontocetes, do not appear to dominate macrophagous sharks at parity. The other situation usually prevails, either involving a pygmy sperm whale, pinnipeds, dolphins or smaller/juve baleen whales. I certainly think you underestimate the sharks tonicity and speed however. Whale sharks burst of speeds have never been measured and basking sharks are known to propel their entire body above the surface with ease. The caudal and body structure of these sharks are certainly indicative of powerful swimmers. There is simply a lack of data here. Theropod, the paper is easy to check : www.google.fr/url?sa=t&source=web&rct=j&url=https://www.uv.es/everlab/PUBLICACIONES/2017/2017%2520Ferron%2520et%2520al%2520HB%2520evolution%2520gigantism.pdf&ved=0ahUKEwij-pG0vqncAhUqBcAKHZqWA0EQFghFMAo&usg=AOvVaw1V9KAeMMwXXgNUIQ7AbPevIts follow up too : journals.plos.org/plosone/article?id=10.1371/journal.pone.0185185I let you consult it and share your feedback. I plan myself to inform Ferrón about some points. |
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