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Post by Grey on Jul 31, 2018 0:38:20 GMT 5
Yes you imply thus that this makes the holotype an average-size specimen
I've responded to this too previously.
I can provide only privately and with the guarantee to not share it for now.
Theropod, I wanted to add. You wrote that there is neither any record of sharks preying on odontocetes of similar size. That's not totally true.
Indeed there is no record of it but overall, on a general basis, sharks are the predators of odontocetes relatively close to them in size (dolphins, pygmy sperm whales). And there is the anecdotal case of a FKW killed by a GWS. That's not a strong support but this is still more quantitative than vice versa.
Anyway, I agree with your 50/50 at parity sizr, depending on the context and of various elements.
I favor the shark because of the (likely) larger size it can reach (based on current data) and the even larger bite it possesses.
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Post by theropod on Jul 31, 2018 0:49:23 GMT 5
Grey : Mean and average are used interchangeably, though more precisely the statistical term "mean" is one kind of statistical measure colloquially referred to as "average", specifically the one that is pretty much always used when quantifying the average size of a species of population. If I want to get this measure in calc, I type =average(), if I want to get it in R, I type mean(), both give the same results–you can try it if you want. Now I’m curious as to what you perceived as the difference between mean and average and what Pimiento and Balk supposedly did wrong in that regard… They did estimate the average, they say it right here: General Body-Size Patterns.—Total Length (TL) estimates for Carcharocles megalodonrange from 2.20 to 17.90 m (mean = 10.02 m, mode = 10.54 m) (Table 1). Have Pimiento and colleagues been given an opportunity to discuss the other corrections proposed by you and your co-authors? As you will recall I recently posted an incident documented in a paper of an orca ramming a Pseudorca with enough speed to throw it 10m into the air. I don’t envision ramming as that much more difficult to achieve than biting (sharks often bite small prey items at rather high speeds too…), otherwise orcas wouldn’t be doing it all the time when preying on all kinds of prey. You say you have "never read anything suggesting those isolated teeth are not from the mid-section of the jaws". Well neither have I read anything suggesting they are. The question is why you presume they must be from the mid-section of the jaws in the first place? Your null-hypothesis with any isolated Megalodon tooth is not that it was the largest in the dentition either. Have I seen the teeth? I have seen pictures of some teeth that had no wear facets, yet looked a lot like Livyatan teeth (e.g. on the shark-bitten fossil bones thread, and pictures of the beaumaris tooth), though that doesn’t automatically mean they are referrable (in fact, isolated teeth may well be entirely undiagnostic to begin with). I certainly have not seen pictures of all teeth you are referring to, nor am I claiming anything definite as to their position. I’m merely pointing out that any given isolated tooth is not necessarily the largest in the dentition, something I would have thought obvious, especially to you. If some of these teeth do have occlusal facets, then that’s another matter. I’d appreciate to have verifiable data on what we are actually discussing (that also applies to hints at embargoed research…if we cannot discuss it then why mention it?). What are the measurements of these teeth, what’s the morphology, where and when are they from? Do you have pictures that you could share? You also write "Australian teeth", so that means there is more than one? Where can I find information on these? Back then, the press releases all only documented a single tooth. A similar average size does not necessarily mean a similar minimum or maximum size, no. But who is to say whether the cetacean or the shark had a wider range of variation? Average size is more indicative of the majority of the population though, hence much more interesting from a palaeobiological standpoint (with the caveat being that the real size distribution of both would very likely have been bimodal, due to larger males or females respectively, but that’s another factor we can’t currently quantify and may as well ignore). If you are more interested in maximum size, that’s fine. But claiming anything about the maximum size of Livyatan is what I would consider jumping to conclusions… About diving deep, I think I may not be able to follow your point correctly here. Are you talking about fleeing before being bitten? I don’t think that’s the subject we are discussing, though I see no reason to presume the shark could dive deeper than the physeteroid (the limiting factor on deep diving is not lung ventilation, as Physeter and Ziphiids clearly prove). If you mean after being bitten, if Livyatan bit it in the tail or fins, or even just gripped onto it elsewhere, C. megalodon would not be able to swim anywhere anymore. It would certainly be an enourmous struggle, but the shark would have already sustained major damage to its propulsion system (e.g. a bite to the caudal peduncle may very well sever the spinal chord) or at least be held in a way that would limit its movement, so I think the cetacean would be at a distinct advantage in that situation. And if the shark cannot swim, it suffocates. Hence why the first properly placed bite of either taxon would likely be decisive, whether it’s a large flesh wound caused by the shark that would cripple and exsanguinate the whale, or a crushing and gripping bite by the whale that would immobilise the shark. As for that flesh figure, I don’t doubt the fact that C. megalodon would take out bigger pieces of flesh with a bite (We’ve already had lengthy discussions as to why I find that irrelevant years ago, no need to repeat them), but keep in mind that your favoured methodology would probably put the shark with that mouth size at a considerably larger body size than 16m, since the shark IIRC was based on Gottfried et al.’s methodology which gives smaller, much bigger-jawed estimates. That’s a bit like someone scaling up my Livyatan restoration to 17.5m and estimating it at 75t, with a 3.4m skull, ignoring that both are actually based on same-sized remains, only in differently proportioned animals. So exactly as I wrote, there is no records of a shark killing a macrophagous odontocete at similar size. Even the 3.8m false killer whale (which died in the aftermath of a shark bite described as superficial, after it had beached itself, so I would not classify it as "killed by a GWS", not to mention the species of shark that attacked it is not even known) was probably a lot smaller than a white shark that could be realistically expected to attack such a prey item (I’ve already explained this, at ~400-450kg it’s very likely the white shark would be bigger than that whale, perhaps much, though not necessarily considering it did not actually kill it). As I already posted, great whites are in fact NOT predators of odontocetes anywhere close to their own size, at least as of the records of Long & Jones 1996. Bull sharks indeed seem to be though, but as we already discussed, that’s in relation to docile, non-macroraptorial Tursiops, not any macrophagous whale. I was specifically referring to macrophagous odontocetes, just as you were referring to macrophagous selachians. Non-macrophagous dolphins and pygmy sperm whales are irrelevant in this context. But I’ll note that since great whites have never been recorded killing any odontocete their own size, it’s quite unlikely that they do it with macrophagous taxa like false killer whales. And I don’t understand your use of the word "quantitative" in this context. This is not quantitative evidence in the least, considering the size of the shark in question was not even estimated.
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Post by theropod on Jul 31, 2018 1:12:47 GMT 5
sam1: The largest well-preserved tooth in the L. melvillei holotype is the first dentary tooth, 315mm long. However Lambert et al. 2016 suggest by comparison to Acrophyseter that the distal teeth were likely shorter, but they are not preserved in the holotype. Btw this tooth actually does have a wear facet, although it is much less conspicuous than on the mid-dentary teeth. So the value of this feature for determining position definitely needs more work. I think we should have a more thorough look at other morphological features in the isolated teeth that might be informative. Lambert, O., G. Bianucci, and C. De Muizon. 2016: Macroraptorial sperm whales (Cetacea, Odontoceti, Physeteroidea) from the Miocene of Peru. Zoological Journal of the Linnean Society 179:404–474.
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Post by theropod on Jul 31, 2018 2:07:42 GMT 5
sam1: That equally applies to the whale. It seems this got overlooked. Prehistorican got that figure from me, I cited it from Jacoby et al. 2015. Only that Jacoby et al. 2016 published a correction pointing out that their originally published figure of 5m/s is a calculation error, which I only later saw when I came across the online article, and the actual estimate is 1.34m/s. This is, by the way, the third time I am posting this on this thread. That does not change the key point of their paper though, that larger sharks tend to be faster, as a result of respiratory needs. No doubt there is a lot of variation there, and estimates for C. megalodon are extrapolated far beyond the data range, but at least extant sharks do not seem to become slower at larger sizes. 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.
———. 2016: Scaling of swim speed in sharks: a reply to Morrison (2016). Biology Letters 12:20160502.And yes, you do have to explain that further. What’s so inherently wrong about a "passive" (a strange way to decribe ram ventilation btw) respiratory system? In fact, the respiratory needs are considered to be a driver of increased swimming speed in larger sharks (that observation by Jacoby et al. 2015 is not affected by the different value for C. megalodon swimming speed), which is sort of the opposite of what you propose… C. megalodon almost certainly had a metabolic rate more similar closer to mammals than to lizards though.
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Post by Grey on Jul 31, 2018 13:23:31 GMT 5
Theropod, I certainly know the difference between mean and average. I recalled the distinction to sam1 in case he did not understand it.
I did not get any response from Pimiento but one the coauthor is her student, still he has no issue to tell the data will probably need to be tweaked quite a bit.
As you know, when a sole individual dentition gives a range of TL of 12-45 m, you can rightfully doubt about it. The fact that each tooth specimen is assigned to several possible positions makes this even more doubtful.
In anycase, I question the validity to use a 14 m figure derived from isolated teeth from sharks that were possibly young adults (following Gottfried ontogeny table) with an (alleged) average Livyatan holotype that was presumably fully grown and old (Lambert 2016).
I am more interested in maximum size as :
- establishing arbitrarily the holotype as an obligatory average sized specimen without any other specimen is simply not cautious and unprecise at best (given the possible size range of this one).
- in this contest, theoretically the bigger the individuals could get within a species, the more powerful they were compared to the biggest individuals of the other species.
- getting maximum size data is easier although already quite a work to do.
Regarding the ramming contest, I simply doubt a 50 tonnes sperm whale would be as skilled at ramming an adversary than a 1-5 tonnes orca. But of course comes the question of the shark speed and mobility...
I certainly have considered the possibility of the isolated teeth coming from smaller-sized positions but :
- as yourself quote in your next message, the lack of diagnosis, partly because only the mandibular teeth are preserved, prevents most of the possible assignements.
- a good part of the preserved teeth are of very similar size, wearing facets or not.
- although not preserved, we know the upper teeth were larger than the mandibular teeth.
- anyway, tooth size is hardly relevant to state anything about size within a single species.
Nonetheless, I will explore this further.
I don't state anything about Livyatan max size, I just use the available data and recall that, so far, 17.5 m is the most optimistic estimate. The most optimistic estimate based on upper dentition metric for the Yorktown meg dentition is 21 m (Leder 2016).
Depending where it is bitten, I don't see the shark being necessary immobilized. Of course the whale would be an additional weight to drag but I doubt it would simply stop the shark swimming.
All of this is assuming a parity size
If Livyatan's ecology and diving habits are to be more compared to raptorial delphinids rather than to sperm whales, it probably wouldn't keep fighting as it needs to stay near the surface while expensing much energy during a hunt/battle and without breathing before the dive.
Regarding the flesh figure, you refer to Malta scaling. But Malta, despite having smaller teeth for its size, is not particularly small-jawed. Hence, the 20 m meg extrapolated in 1996 is not necessarily small-mouthed. As I showed, using Gottfried method, you can get 20 m figures with GWS specimens other than using Malta and Kanga.
But I was simply scaling the mechanical jaws using teeth measurements to the larger sized teeth on record, or looking at models like Bertucci's composite dentition which appears to be correct, compared with the associated adult dentitions.
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Post by sam1 on Jul 31, 2018 14:38:28 GMT 5
sam1 :That equally applies to the whale. It seems this got overlooked. Prehistorican got that figure from me, I cited it from Jacoby et al. 2015. Only that Jacoby et al. 2016 published a correction pointing out that their originally published figure of 5m/s is a calculation error, which I only later saw when I came across the online article, and the actual estimate is 1.34m/s. This is, by the way, the third time I am posting this on this thread. That does not change the key point of their paper though, that larger sharks tend to be faster, as a result of respiratory needs. No doubt there is a lot of variation there, and estimates for C. megalodon are extrapolated far beyond the data range, but at least extant sharks do not seem to become slower at larger sizes. 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.
———. 2016: Scaling of swim speed in sharks: a reply to Morrison (2016). Biology Letters 12:20160502.And yes, you do have to explain that further. What’s so inherently wrong about a "passive" (a strange way to decribe ram ventilation btw) respiratory system? In fact, the respiratory needs are considered to be a driver of increased swimming speed in larger sharks (that observation by Jacoby et al. 2015 is not affected by the different value for C. megalodon swimming speed), which is sort of the opposite of what you propose… C. megalodon almost certainly had a metabolic rate more similar closer to mammals than to lizards though. "Passive" is the most appropriate word to use imo, because it best describes the respiratory principle and difference compared to lungs and gills of bony fish - the inability to control the oxygen intake via the respiratory system itself. I'll get into the rest later, don't have the time now. |
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Post by theropod on Jul 31, 2018 16:36:02 GMT 5
sam1: well I would certainly argue that a whale, while submerged, is not exactly able to control the oxygen intake via the respiratory system itself either. Grey: Yes, the uncertainty of position assignment is certainly a problem. The way I see it, that may well be a problem that can not be eliminated given that one insists on using isolated teeth to produce size estimates. A valuable input would be an attempt to more reliably and objectively estimate the position of a given tooth in the dentition, perhaps through morphometric methods. But the way I understood it that is not what your research deals with at all, in fact using any isolated tooth to suggest larger sizes your method has the exact same problem as Shimada’s. You wrote that Pimiento and colleagues did not estimate the average, but rather the mean, despite the mean being the average. So I had to assume that some clarification was necessary on that part. Where did Lambert et al. 2016 write the Livyatan holotype was "fully grown and old"? If anything, they mention open pulp cavities in the holotype, which in Physeter are filled in late ontogenetic stages, but they do acknowledge that this process can take place very late and adults can also have open pulp cavities. And once more, whales do keep growing significantly after attaining sexual maturity too. I’ve just recently posted a paper that found bottlenose dolphin males reached sexual maturity at an average 70% of adult mass. I’ve also already posted evidence that Physeter keep growing after maturity years ago. The average size of the whales does not just consist of animals that have stopped growing. So we can’t just nitpick only the oldest and largest adult sharks for this comparison. Regarding average and maximum size, I already acknowledged you may well be more interested in maximum size because of the second point, but as for the first and third, you suggest it is more "scientific" or "precise" to assume the single known individual was, say, among the biggest 10% of the population? Regarding ramming, obviously a 50 ton animal would not be as skilled at ramming something mobile as a 5 ton one, but neither would another 50 ton animal be as skilled at evading it. So in conclusion, we are currently unable to use isolated teeth to ascertain anything about the size of the whale, whether it be smaller or larger. So where is your evidence that the holotype was especially large from that? You think a bite to the tail would not impair the shark’s swimming capacity? And this seems to be treating the whale as just dead weight that would let itself get dragged around without any resistance, ignoring that it’s propulsion is no less powerful than the shark, and probably more so, considering an injured and at least partially immobilised shark. If the shark tried to swim away with the whale holding onto it, the whale will simply pull or push it in the opposite direction. Again, orcas pull sperm whales far larger than themselves out of formation. I am just talking about keeping a shark similar to its own size stationary, which would result in suffocation. I don’t refer to "Malta-scaling", quite the opposite. The flesh figure you gave, I presume is from one of those shark week documentaries, the one where the mythbusters built the giant metal jaws, correct? Wasn’t that shark based on a tooth found with a dead whale, and estimated at 16m based on Gottfried et al.’s regression? If so, then that shark has a proportionately bigger jaw than your estimates would suggest, because the more conservative estimates (the ones actually considered to have scientific merit) result in proportionately smaller sharks for a given tooth size than yours. You specifically said you scaled that up from 16 to 20 metres, not based on tooth size or questionable larger jaw mounts, but considering your own methods, that 16m shark may well have been a good deal larger with the same jaw size. It would be interesting if you could maybe do a calculation on that though.
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Post by sam1 on Aug 1, 2018 2:04:27 GMT 5
Theropod:
The inherent restriction of the shark's respiratory system comes from its passive principle which limits the oxygen intake correlation with energy burn.
The body burns energy at exponential rate with the increase of speed; the 2D surface(gill filaments and lamellae) of gas exchange area cannot keep up after a certain point.
Also, the myoglobin and hemoglobin levels of the shark is far lower than that of the whale which means a whale can store far more oxygen in its system.
This is why sperm whales casually endeavor hour long deep dive hunts employing multiple burst of speed.
They simply store and then discharge energy..like us(we don't inhale air when discharging at the high intensity), just on a whole different level.
Metaphorically - in terms of top speed performance - a shark is a jet fan engine limited by the amount of air it can suck in + the amount of drag in needs to overcome, while the whale is a rocket engine limited only by the amount of energy it can store and burn + the amount of drag.
About the GWS and Orca analogy, I think it is pretty obvious(even Grey acknowledged it) that at about 2-3t of mass, the GW is not at all comparable to Orca in terms of mobility. Simply a huge difference.
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Post by theropod on Aug 1, 2018 2:28:04 GMT 5
Sam1: And why are lungs not affected by this? The oxygen always diffuses through a surface, not just in the case of gills.
Of course most animals can just increase the breathing frequency at times of high physical activity (as do humans), to increase the oxygen concentration and accellerate diffusion, but underwater, that’s not an option, the whale actually has to make do with one lung full of air (or the oxygen therein) that has to last it for extended periods of time. So applying the same theory here, that should also pose an inherent limitation, because it’s functionally similar to "passive" ram ventilation in being unable to directly control the oxygen intake.
Yes, certainly the whale can store large amounts of oxygen in its body that allow it to maintain high levels of activity for extended periods of time underwater, but in exchange the shark receives a constant stream of oxygen as long as it remains in motion, and actually more the faster it goes.
Mako sharks are capable of swimming at considerably higher speeds than similar-sized dolphins, despite this supposed limitation on top speed. This might well be more noticeable in larger animals, but then, larger sharks would actually have to swim faster in order to maintain adequate oxygen flow. I’m not saying that their different respiratory systems and physiologies would not result in differences in locomotory abilities though. Probably the shark would excel at extremely short, powerful (non-oxidative muscle fibres) bursts and non-stop, moderate-velocity swimming (limited by the rate of oxygen intake), while the whale would essentially be limited by the amount of oxygen it can take in in a single breath and of course by the duration of its dive, probably resulting in a period of intermediate length over which it could maintain relatively high speeds, in between breaths.
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Post by sam1 on Aug 1, 2018 2:46:09 GMT 5
Couple off the bat reasons that while lungs are indeed affected, the extent is a lot different
- the lung surface area is bigger
- they can import a maximum amount of oxygen at minimum energy cost(active respiration, in other words, organism can afford intense oxygen intake while remaining still).
A Mako shark may be an example of extreme limit which exploits the maximum efficiency of available gill surface.
But are you forgetting at the scale effect?
Gills would become a lot less efficient at meg's size; tje relative mass, energy expenses, and drag would increase tremendously.
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Post by theropod on Aug 1, 2018 3:42:28 GMT 5
I would doubt the first point. While I don’t know the precise relative surfaces, at least teleost gills are considered the most efficient respiratory system in the world, owing to large surface area coupled with their countercurrent system (they need to be, since there’s much less dissolved oxygen in water than in air). The percentage of the dissolved oxygen gills can extract from water is actually a lot higher than the one lungs can extract from air. Gill surface area would also probably become proportionately larger in larger "fish" to accomodate for the cubic scaling of body mass.
About the second point, undoubtedly true (I already mentioned that in my last comment though), but obviously only relevant if the animal can actually freely increase its breathing frequency, which a whale can not do underwater.
Excursion: Despite the disadvantage of being limited by swimming speed (it would be interesting if someone with a more in-depth education in physiology than me could do a calculation on whether this would actually be a limiting factor at C. megalodon’s size), ram ventilation also has its advantages as compared to mammalian lung-ventilation.
Notably, it provides a constant flow of oxygenated water in one direction (allowing for the countercurrent-system to constantly provide the optimal diffusion gradient). In that regard it’s actually similar to the highly efficient unidirectional airflow system of birds…which is also a system considered a key adaption in allowing the largest body sizes ever reached by terrestrial animals (Sander et al. 2014), so certainly a relevant adaption in allowing to sustain high aerobic capacity at large body sizes.
No I am certainly not forgetting about the effect of scaling, and I explicitely wrote so in my last post.
The thing is that most of what you say about gills can also be applied to lungs. Lungs may enclose a 3-dimensional volume of air, whereas gills are comparatively open structures, but nonetheless they also have to extract oxygen via a surface that would scale at the power of .67 with mass, so inherently the two have the same problem. Yes, mammalian lungs can more efficiently ventilate without the whole body having to move (though if you move anyway, you may as well combine the two, as some terrestrial mammals have done as far as I know), so they can mitigate this by always providing fresh air with the optimum oxygen content. But "fish" in turn mitigate this by using countercurrent mechanisms, increasing the diffusion efficiency. All I’m saying is that more research would be needed to actually compare the two and determine if the limitations you propose are actually A: tight enough to become the limiting factor on mobility at the sizes we are talking about and B: that much tighter than those on the whale itself. Personally I’m not convinced large marine animal’s speed is really limited by their respiration system as opposed to musculoskeletal constraints, and often the sheer lack of a selective pressure necessitating higher speeds.
At least in extant, actively swimming sharks, ram-ventilation seems to be quite adequate to sustain their activity levels, apparently better than the "active" ventilation seen in slow-moving species such as rays.
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Post by sam1 on Aug 1, 2018 4:09:09 GMT 5
Is the alleged oxygen extraction percentage absolute or relative? Are you taking into account the properties of air and water?
Again, regardless of that the absolute amount of oxygen a whale can store far surpasses that of a shark.
Im afraid you're not really seeing the rocket and jet engine top speed analogy.
Jet engine's thrust depends on the amount of air it can convert into energy, and it also shuts off the moment the air intake is cut off. A rocket engine is just a charge that gets discharged. Its performance doesn't depend on anything other than the amount of energy it has charged up(and air resistance). It is inherently more powerful principle.
So your notion that a whale is moving underwater and can't breathe isn't relevant in the sense of how much speed(energy) can it achieve. It has the energy stored. Whereas in the case of a shark, the energy depends of the water-oxygen conversion. The faster it tries to move, the less effective the conversion is.
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Post by sam1 on Aug 1, 2018 14:18:15 GMT 5
About the isolated raptorial SW teeth..I was aware of the size of the smallest *preserved* Livyatan teeth, just wanted to hear it from Grey to clear out if he is having base for his arguments (apparently not, as you also have noticed after all).   And the single Beaumaris whale tooth shown above is 30cm. Based on the appearance, it could've come from different parts of the jaw, the least likely parts being the section where the very largest tooth are positioned (apparent lack of interlock patterns and seemingly more curved top of the tooth, like those in the front part of the jaw), and the back of the jaw(different shape of the tooth) |
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Post by theropod on Aug 1, 2018 16:19:24 GMT 5
sam1: No offense, but I do not get the impression that you yourself are fully aware of the sizes of the Livyatan holotype’s teeth, at least if you made, or are going by that picture you posted. The largest preserved holotype teeth (the ones reaching 36cm) are in the dentary, not the maxilla. The maxillary dentition only has parts of the roots preserved (which are similar, to slightly larger in diameter, and slightly greater length would appear likely based on that and Acrophyseter deinodon). In A. deinodon, occlusal facets are most pronounced in the middle third of the tooth row, which likely includes some of the longest teeth, but in L. melvillei, the smallest preserved tooth (first dentary tooth), which is 31.5cm, not 25 as you claim, also has a small facet. Going, again, by A. deinodon, the posteriormost teeth are likely the shortest in the dentition (despite being quite thick), and these are not preserved in Livyatan. Now, the 30cm Beaumaris tooth could very well be from something the same size as the holotype, I don’t disagree with that. It does not seem to have an occlusal facet (there is actually a picture from the other side in one of the articles), and its robusticity seems to match what we would expect from one of the distalmost teeth. But a more detailed morphological analysis and morphometrics would be needed for a reliable assessment. Your rocket analogy was not lost on me. What you are ignoring is that despite a rocket being potentially capable of greater peak power output, it is also inherently limited by how much fuel it can store internally (which is a lot more limited than in the jet engine, as the rocket needs to carry its entire reaction mass, which in turn lowers efficiency) and it can not just burn it all at once either given that it needs to maintain thrust for a certain amount of time. There’s a reason rocket engines aren’t in general use aboard aircraft nowadays. The whale can not use up its stored oxygen all at once either, it needs to stay submerged for a certain amount of time. Since you seem to like technological analogies so much, why do you think submarines need to use slower electric propulsion when submerged, as opposed to at the surface where they can use more powerful combustion engines? The whale’s respiratory system and oxygen storage would certainly give it more control over how much oxygen it can use at peak as opposed to the shark, but it is still limited by its own limited oxygen intake, unless it is at the surface. And you still need to demonstrate that the theoretical limitations you propose for shark respiratory systems actually apply at these scales. It’s entirely possible that the oxygen uptake provided by gills at the shark’s speed is more than sufficient to sustain that speed. Of course the whale can store more oxygen. The shark does not NEED to store oxygen, it’s taking it in continuously, just like a jet engine doesn’t need to store oxygen. The "alledged" oxygen uptake percentage in teleost gills is ~60-80% of that in seawater iirc (from one or two of my functional anatomy textbooks), whereas humans have only around 25-30%. Does that answer your question? I don’t know the percentage in shark gills or whale lungs. The point is that gills can obviously extract oxygen very efficiently, which argues against them being particularly limited. What you don’t seem to be getting is that the faster a shark moves, the MORE effective its respiration becomes, not less. Moving faster is the ram-ventilation-equivalent of breathing faster. Obviously moving faster also requires more energy, i.e. more oxygen, but it might be able to make up for that by simply increasing gill surface area. Whereas the amount of oxygen the whale can use is simply limited by its stored oxygen divided by the time it stays submerged.
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Post by sam1 on Aug 1, 2018 17:03:31 GMT 5
Alright, I was not aware that the smallest preserved tooth in the holotype was the very front one(if that's what you're saying)..I only knew that it is 31.5cm, not which exact tooth it is. So the depiction I made was just a visual estimate. It just doesn't look as if the first anterior tooth in that picture is only 4.5cm shorter than the biggest one, especially since it should have smaller root as well. But yeah, my bad then.
The rocket and jet engine analogy was, as stated for a reason, in the context of top speed alone.
And I have strong reasons to suspect that, again as stated initially, gills cannot keep up with the exponential energy requirements of body size and drag increase.
Let's also not forget that the pectoral fins and opened mouth of a 50t megalodon moving at proposed 30km/h would definitely add up in a major way. Hydrodynamical properties of a megalodon are most likely significantly inferior to that of the whale..yeah I know you're thinking mako shark while reading this, but again, the scale! What I'm thinking is the GWS, WS, Basking shark and the fact that on larger scale, sharks seem to be significantly slower than their cetacean counterparts. There's just no evidence in the wild to support the supposed maintaining of propulsory capabilities theory.. unlike in the whales.
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