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Post by dinosauria101 on Apr 8, 2019 20:28:12 GMT 5
^Slightly diverging from the main point, but couldn't the shark bait the whale? The main point is discussing a battle between these animals, so I don't see how that's a diversion. How do you mean bait the whale? I mean dive under and wait for attrition (taking a breath) to become a factor |
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Post by theropod on Apr 8, 2019 21:46:40 GMT 5
Sharks use environment to their advantage. They try to stalk dolphins in murky waters and at night, pocking the right moment, such as when the pod is resting. Is such a simple concept really that hard to imagine. An animal the size of megalodon cannot easily hide in some murky estuary, certainly not until a dolphin swims right into its mouth, and as you said yourself, its potential prey would know to avoid such places. This is not just about sonar. Something the size of a bus moving through water creates sound waves, that’s a physical inevitability, and while an odontocete’s sonar only points forward, its hearing ability is perfectly fine and will be able to pick up an animal that size coming from any direction. Dolphins can accellerate quickly, they will be able to react to such an attacker coming if they detect it while it’s still a few meters away, which the attacker in turn will have to adapt to. That’s why a perfect ambush is pretty much impossible, if you can’t wait for your prey to come to you, it will detect you at least from a few meters away, since you will have to move, which still leaves you with ground to cover while the prey can react. Which is why most so-called "ambush predators" that are not crocodiles, preying mantises or freshwater turtles (animals that actually do sit perfectly still until their prey is within reach) are also good sprinters able to compensate for the prey’s escape attempts. So the point still stands, for megalodon to be able to catch a dolphin, it would require a decent level of speed and agility for a creature its size. |
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Post by sam1 on Apr 9, 2019 0:41:19 GMT 5
Sharks use environment to their advantage. They try to stalk dolphins in murky waters and at night, pocking the right moment, such as when the pod is resting. Is such a simple concept really that hard to imagine. An animal the size of megalodon cannot easily hide in some murky estuary, certainly not until a dolphin swims right into its mouth, and as you said yourself, its potential prey would know to avoid such places. This is not just about sonar. Something the size of a bus moving through water creates sound waves, that’s a physical inevitability, and while an odontocete’s sonar only points forward, its hearing ability is perfectly fine and will be able to pick up an animal that size coming from any direction. Dolphins can accellerate quickly, they will be able to react to such an attacker coming if they detect it while it’s still a few meters away, which the attacker in turn will have to adapt to. That’s why a perfect ambush is pretty much impossible, if you can’t wait for your prey to come to you, it will detect you at least from a few meters away, since you will have to move, which still leaves you with ground to cover while the prey can react. Which is why most so-called "ambush predators" that are not crocodiles, preying mantises or freshwater turtles (animals that actually do sit perfectly still until their prey is within reach) are also good sprinters able to compensate for the prey’s escape attempts. So the point still stands, for megalodon to be able to catch a dolphin, it would require a decent level of speed and agility for a creature its size. .. murky estuary? So you're just going to ignore the whole NIGHT thing and the fact how inherently mutable sea environment is..the visibility can vary wildly even in the open sea. Sometimes you can't see farther than a couple of meters..and again, at night, everything below you is a pitch black abbys. Further, I'm not at all sold on the notion that dolphin should be able to hear megalodon as clearly as you imply. Like I said, sharks are masters at silent traversing through the water. You can barely hear any murmur beyond the very close proximity. Granted, megalodon would indeed leave much more acoustic trace due to its size, but in certain circumstances I can easily imagine it being able to remain undetected up until the very last moment. Simplest example would be the pod of dolphins resting at night, at relatively noisy time..be it a passing shoal of fish, a flock of seabirds ,rain shower and thunder from above, or simply a noisy sea currents. Megalodon needs to slowly circle up from dark depths..he could remain completely silent and undetected at up to 50m..at 30m, he would take less than 3 seconds to charge straight into the pod. |
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Post by prehistorican on Apr 9, 2019 1:01:29 GMT 5
So the shark can’t keep up a short chase with a dolphin or even a whale? It just has to get lucky and hunt a distracted animal and that’s how it gets food? Wonder how fast a bottlenose dolphin is...
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Post by Life on Apr 9, 2019 1:43:38 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). My point was in regards to the durability of Megalodon's skeletal structure in life. Teeth and centrum are physically robust on average; calcified as in containing very high levels of calcium. [1] pubs.rsc.org/en/content/articlepdf/2015/ra/c5ra11560d[2] perso.ens-lyon.fr/vincent.balter/Articles/Martin(CG)15.pdf[3] meetings.aps.org/Meeting/MAR19/Session/C65.3[4] 2dgf.dk/xpdf/bull32-01-02-1-32.pdfCalcium is the primary source of strength in bones. 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. Great white shark's dentition for reference:-    Take a good look at the A3 and the posterior teeth. Megalodon's teeth are relatively broader on the whole.  - and would require larger jaw dimensions to accommodate them accordingly.  Scaled for you. Megalodon also had relatively higher centrum count in it (Gottfried et al., 1996). Connect the dots. You mentioned 'macrophagous predation explains tooth morphology' so below is an example.  Attributed to a juvenile Megalodon. 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. It is reasonable to assume that Megalodon's physical appearance was SIMILAR to that of the great white shark - skeletal similarities imply as much. However, this does not suggest that the Great white shark's JD - BL ratio is perfectly applicable to Megalodon as well - rather a conservative approach to estimate the size of Megalodon on pound-to-pound basis. JD = Jaw Dimensions BL = Body Length 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. Keep in mind that Megalodon was able to catch whales and dolphins from behind - chomping them in half from the rear - very high swimming speed was likely. For example: www.app.pan.pl/archive/published/app63/app004952018.pdf I obviously wasn't saying that meg was based on a scaled up GW neither, if that's what you're implying. I actually agree with your POV in regards to physical appearance of the Megalodon. In fact, following depiction is really good.  Btw, megalodon marked dolphin remains doesn't automatically make meg as agile and fast as a dolphin. Great whites catch and eat seals and dolphins all the time. Yet there's no question that both seals and dolphins are in another league in terms of agility and endurance. See above - Megalodon was able to catch dolphins from behind. When it comes to marine biology and environmental realities, size does not make much difference. Biological characteristics such as musculature, endothermy, streamlined physiology, fins, and skin texture - these are important considerations. |
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Post by sam1 on Apr 9, 2019 2:14:08 GMT 5
So the shark can’t keep up a short chase with a dolphin or even a whale? It just has to get lucky and hunt a distracted animal and that’s how it gets food? Wonder how fast a bottlenose dolphin is... I thought meg got its food from killing whales..sounds about right that a whale sized shark with monstrous teeth needs something larger than dolphins to sustain itself..are you suggesting it was primarily a dolphin killer? And that it catched them engaging in a straight line race? Let me ask you something..who is a faster runner, a hippo or a chicken? @ Life .. a dolphin bit in half from "behind".(how can such angle of attack even be determined from only a snapped vertebra and ribcage? It would literally look exactly the same if a shark bit it in half from the side) I assume that by your logic that means dolphin was caught after losing a straight line top speed pursuit to the shark? There are many more likely scenarios where the same result could occur. |
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Post by dinosauria101 on Apr 9, 2019 3:13:47 GMT 5
Excellent reply, Life! It's FAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAR superior to the vast majority of Taipan's replies to threads!
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Post by sam1 on Apr 9, 2019 3:42:07 GMT 5
The main point is discussing a battle between these animals, so I don't see how that's a diversion. How do you mean bait the whale? I mean dive under and wait for attrition (taking a breath) to become a factor That's actually the main advantage of the shark. In a prolonged underwater battle it definitively would become an ever increasing factor. |
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Post by dinosauria101 on Apr 9, 2019 3:45:35 GMT 5
Yeah, I'd also say it's one of the main factors aside from weapons and/or size that gives the shark a fair chance (though I still say 50/50)
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Post by theropod on Apr 10, 2019 1:09:24 GMT 5
My point was in regards to the durability of Megalodon's skeletal structure in life. Teeth and centrum are physically robust on average; calcified as in containing very high levels of calcium. I did get your meaning, containing high levels of calcium was what I was talking about. Megalodon’s skeleton may or may not be more heavily calcified than that of white sharks, specific studies on that would be needed. The fossil evidence (specifically what you mentioned, "virtually anything preserved") does not provide obvious or previously noted evidence of an unusually high level of calcification in C. megalodon as compared to other sharks such as C. carcharias. If that was not your implication, then fair enough. I was under that impression because you wrote it corresponded to its (more) robust teeth. Well, actually hydroxylapatite is the primary source of strength in bones, which is only about 40% calcium by mass, or 20% by molarity (to be exact bone mineral is carbonated hydroxylapatite, but I don’t know how much the carbon adds so I’m ignoring it). Calcium on its own is no more use for strength than the iron in blood, otherwise muscles would be stiff like bones. But I get your meaning. Shark skeleton biomineralization is also apatite, not only calcium. [1] Is a study on the occurrence of fluoroapatite rather than hydroxylapatite in (apparantly) all fossil teeth, although I find the conclusion discounting a diagenetic explanation a little premature. [2] is a study on calcium isotopes to reconstruct trophic positions of elasmobranchs. [3] is ultrastructural research on megalodon teeth. [4] is the description of the danish associated megalodon specimen. I can’t find anything that would suggest exceptional levels of biomineralization for megalodon in these studies, in fact none of them seem to be more than tangentially related to the degree of skeletal calcification at all, as three of them mostly deal with tooth mineral and the other one with isotope ratios. So I’m not exactly sure what you are trying to tell me here, that megalodon had tooth enameloid is not exactly a shocking revelation, that tooth ultrastructure may be related to fracture resistance (as has been previously noted in many other animals) is certainly an interesting piece of information but not at all relevant to what you were discussing before, and that megalodon occupied a high trophic level based on calcium isotope ratios has been previously discussed here (as has, of course, the danish specimen). Relative…relative to what? That’s my point. They can hardly be broader relative to their width. Of course they are broaded relative to some dimensions, that’s because they don’t have the exact same proportions. But what is tooth length so important for? Relative to (anterior or anterolateral) tooth length, yes. Centrum count alone allows no direct implications for total length of body proportions, so I don’t see how that is a dot to connect to anything. Besides, centrum count in C. megalodon can not even be reliably estimated. Note that Gottfried et al. first express doubts about whether an anterior part of the belgian vertebral column is missing, but then only provide an estimate under the assumption that it is. Dental similarities imply this, and nobody is contesting that. Skeletal similarities are extremely limited due to the non-existant nature of most megalodon skeletal elements. No, but it is a starting point. Megalodon may have been longer or shorter than is implied by the size of its teeth and the proportions of white sharks, but any such assumption would be baseless. Of course as I said previously, the level of uncertainty with body size estimates, especially those based on isolated teeth where the uncertain tooth position, variability of individual teeth, variability of the dentition width with respect to jaw size, and jaw size with respect to total length and variability of body mass with respect to total length are all added up, is pretty extreme in general–again, in both directions. But weren’t we discussing body shape, not size? I thought size was fairly well agreed to be best predicted based on the jaw size derived from summed tooth widths? As Sam correctly points out, this is no evidence of the precise angle of the attack, depending on the size of the attacker there are multiple feasible bite angles, either from behind, below or above. This includes attack angles frequently employed by white sharks when attacking odontocetes, specifically those outside the fields of detection of the eyes and the sonar. Even an attack from behind would not necessitate the ability to achieve top speeds on par with the prey animal, but as I already explained to sam, I agree that megalodon probably had a respectable burst speed in order to be able to close the gap to its smaller prey items fast enough to achieve sufficient levels of hunting success (which we know it must have had as such prey items, i.e. animals much smaller and more agile than itself such as small cetaceans and pinnipeds, seem to have been an essential component of its diet). That does not mean it must have been as fast or as agile as a dolphin, or seal (or Eurhinodelphinid). Again, as correctly pointed out, white sharks are nowhere near as agile (though possibly on par in top speed in most cases) as most of their prey either. Minor nitpick, but Xiphiacetus is not a dolphin, though true delphinids were around at the time and I would not be surprised if there were dolphin remains with megalodon bitemarks somewhere. It does, just not as much as on land. Larger animals can obviously be faster in water than on land, that is because they don’t require adaptions for weight support that are detrimental to locomotory efficiency. But the fastest aquatic animals–sailfish, marlin, swordfish, tuna, mako–are still all in a relatively constrained, and far more moderate, size range, even though that optimum size appears to be considerably (~10 times) larger than in terrestrial animals. Body mass still scales at a higher power than muscle strength, which puts limits on the realistic speed because the thrust needed to accellerate the body to that speed is still a function of its mass, even in water. |
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Post by elosha11 on Apr 11, 2019 0:34:43 GMT 5
Not sure if this has been mentioned but the Godfrey paper on the odontocete bitten caudal bones suggests the shark was either Megalodon or C. Chubutensis. The attacker's estimated length was around 11 meters and the cetacean was around 4 meters. So a subadult, but still a sizeable shark. I will have to read through the various posts and comment further. Here's two more examples of possible Meg predation on dolphins from the good old shark bitten fossil whale bones thread. Just click the links.. theworldofanimals.proboards.com/attachment/download/238theworldofanimals.proboards.com/attachment/download/241 |
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Post by Life on Apr 12, 2019 2:43:13 GMT 5
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Post by Grey on Apr 12, 2019 4:41:33 GMT 5
Currently, size of the body and the oral cavity are the main determining factors known for this match.
All in all, estimates show both to be in a similar size range, but it is definitely true that current estimates and material available suggest megalodon to have been able to grow larger with a predatory apparatus more voluminous.
Or course there is only one good specimen of Livyatan and I'm perfectly open to the possibility of larger specimens but the extend and magnitude of this is unknown, even more since this only specimen of Livyatan is in a size range quite wide (14-18 m).
To my knowledge, none of the isolated teeth found in various parts of the world referrable to the genus are indicating animals larger than the Peruvian specimens. There are reported 40 cm teeth (straight or along the curve?) from Chile but Lambert et al. doesn't seem to consider it evidence from a larger individuals, furthermore the Peruvian specimen upper teeth may well have approached 40 cm in length, simple scaling the diameter between the widest lower teeth and upper tooth would indicate that.
Nonetheless, admitting those isolated alleged 40 cm teeth would correspond to the lower 36.2 cm teeth and using the upper estimate of 17.5 m, would suggest 19.4 m.
Our study using the parameters of upper dentitions among lamniforms suggests a conservative size of 21.3 m from the big tooth in Gordon Hubbell's collection.
Moreover, teeth comparable or larger or very large from more posterior positions do exist.
Something often stated for many extinct taxa is true as well for O. megalodon, we probably didnt find the very largest teeth from this genus, and thus the largest possible individuals.
So all in all, there are more reasons, some explained by sampling bias but not only, to consider megalodon to have been marginally the larger of the two, and quite probably the mightier. Even if this statement could very well change or not.
Something else to note, Boessennecker 2019 reports killer sperm whales to go extinct before O. megalodon.
So claims of superiority of macroraptorial cetaceans over O. megalodon driving it to extinction, either by competition or physical superiority, appear to be unfounded.
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Post by prehistorican on Apr 12, 2019 4:51:06 GMT 5
I believe that one of the scientists said that the recent arrival macroraptorial whales didn't affect the distribution or amount of teeth throughout the time period of C. megalodon, and therefore probably also not the population.
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Post by prehistorican on Apr 12, 2019 6:06:50 GMT 5
There are larger/wider teeth for C. megalodon, but unfortunately I believe they are private. I wonder if there is the same for Livyatan but there seems to be far less remains.
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