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Post by sam1 on Apr 7, 2019 19:32:24 GMT 5
This is a model based largely on a scaled up GWS. The author of the comparison updated it later with the image I posted, based on his own research. Definitely looks far more viable to me than the image you posted(frankly looks ridiculous and completely nonfunctional. That thing would be far slower than a Greenland whale, considering all the extra drag shark has compared to the cetacean) I do not believe that Megalodon is a scaled-up great white shark but it probably had a similar physical appearance. Dental structure of Megalodon give the impression of relatively wider jaw structure (chondrocranium) than in the great white shark with teeth of similar proportions (A3 tooth factor among others), and the wider chondrocranium in turn imply a proportionally elongated body structure on the whole. This make sense in the light of relatively higher count of centrum in Megalodon. Robust dental structure of Megalodon correspond to extremely powerful muscles, and the heavily calcified remains of Megalodon in general (virtually anything preserved) imply a powerful physiology on the whole for potent ramming capacity (to stun/injure a whale with sheer impact) and shock-absorbing capacity (high tolerance for potential injuries/punishment). Nevertheless, streamlined body structure, and skin texture, would ensure that Megalodon could move really fast in short bursts - this is compatible with paleontological evidence of Megalodon being able to hunt much smaller dolphins. Endothermy is most likely. So yes, Megalodon was a biological marvel to say the least. I obviously wasn't saying that meg was based on a scaled up GW neither, if that's what you're implying. 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.
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Post by prehistorican on Apr 7, 2019 20:04:10 GMT 5
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Post by theropod on Apr 7, 2019 20:29:07 GMT 5
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. I don’t think that’s up for debate, obviously a 15m shark could never be as agile as a 3m dolphin. However it is unlikely an open-ocean predator would be able to successfully hunt cetaceans if it were slow and sluggish even for its size, like a whale shark or sun fish.
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Post by sam1 on Apr 7, 2019 23:55:27 GMT 5
Seals and dolphins can do things shark simply can't even try, such as twisting, hovering and turn in every direction from any position. Trained dolphins can do many spectacular stunts and display body control that is indeed on a whole new level. Further, both seals and dolphins can maintain high speed for hours. Finally, at several tons of weight and above, the athletic gap between sharks and mammals increases dramatically. A 5t orca for example, can jump 5+ meters out of the water, and 100t+ fin and blue whales can maintain speeds of 20km/h for hours. The biggest white sharks are nowhere near capable of leaping as high as typical 800kg specimens(up to 3m), let alone an orca. Whale sharks have been recorded at maintaining about 12km/h for several hours (IIrc) which is nothing to sniff at, and basking sharks have been recorded to accelerate as quickly and breach as high as great whites so that's impressive too..but compared to the best feats of larger mammals, they fall well short. The video you posted shows a quick and agile large shark, no doubt about that. But let's not ignore the fact that it chased a panicked juvenile. An adult seal would have easily outmaneuvered it. It very rarely happens that adult seal falls to prey to a GWS, in fact they are often seen swimming around it, sometimes even nipping at it..something it would never dared doing to an orca.
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Post by sam1 on Apr 8, 2019 0:02:24 GMT 5
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. I don’t think that’s up for debate, obviously a 15m shark could never be as agile as a 3m dolphin. However it is unlikely an open-ocean predator would be able to successfully hunt cetaceans if it were slow and sluggish even for its size, like a whale shark or sun fish. All that meg needed really, is to be stealthy and be capable of a doing a short burst of speed. Like I mentioned in above post, even basking sharks can accelerate quickly and breach. Let's say a large pod of dolphins gets surprised from below, monstrous shark surging at them like that could easily end up in a lucky catch of some careless, inexperienced and panicked individual.
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Post by prehistorican on Apr 8, 2019 1:29:44 GMT 5
So basically by luck a theoretical sluggish inagile shark makes a living by bursting into random pods of dolphins every day and the shark can't hunt the superior mammal right?
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Post by theropod on Apr 8, 2019 2:31:00 GMT 5
Exactly, and that stealth and short burst of speed are the point. Nobody is claiming it was a pursuit predator like a tuna or marlin, which extant white sharks aren’t either, but to display such a short burst of speed and sufficient agility to catch a much smaller cetacean as a 30-70 ton animal is no mean feat and would both in itself require it to be quite athletic and adapted for quick locomotion, and, in order to be effective, reasonably fast. Ferron et al.'s 35km/h based on the endotherm regression are of course only a very rough estimate, but they seem fairly realistic just to get a general idea.
What’s also no mean feat is for said 30-70 ton animal to be stealthy. How exactly do you see this going down, the dolphins won’t realize a 15m shark is swimming 5m below them until the last second when they can’t move a metre out of its way any more? There’s not really a way of that happening. An animal that size rapidly swimming towards a prey item also won’t go unnoticed that long, especially not by an entire pod. So obviously megalodon most likely functioned as an ambush predator, but when dealing with small prey there’s little chance it could catch it completely without having to chase it or at least adjust its direction rapidly to counter the prey attempting to evade it. This is not a crocodile that can remain hidden and motionless while its prey comes within biting distance, it’s a huge animal that has to remain in motion constantly and is hunting prey with excellent hearing in open water. Unless megalodon could make itself look (and sound!) like a piece of giant kelp, there’s no way it could have functioned as a predator without at least a certain level of agility. And we already know many of megalodon’s prey items were quite small compared to itself, hence at a decided natural advantage in that department. So no, its ecology strongly precludes a sluggish physiology. That doesn’t mean it would need to be as fast or agile as a dolphin, that’s what the ambush is there to make up for, but it cannot replace agility alltogether (which it doesn’t in most other ambush predators, lions or tigers aren’t slow or sluggish animals either).
And I am very well aware that basking sharks are pretty athletic. That doesn’t mean they can perform the feats of a small dolphin, it just means they are agile, fast-moving animals to the extent that one can reasonably expect from an animal their size. A blue whale can’t make a backflip through a loop suspended 10m in the air either (or, for that matter, hope to compete against a dolphin in a contest of maneuverability), that doesn’t diminish its athleticism.
I think you are confusing cetaceans with sardines or krill there, a pod of dolphins isn’t something you can just blindly swim into to regularly catch one by blind luck. Maybe with a lot of luck that could happen occasionally, as a reliable hunting strategy it could not. And even less with other cetaceans, that probably didn’t travel in large, dense pods.
Anyway, how the heck did we come here, I was agreeing with you that meg wasn’t as agile as a dolphin, after all. I don’t buy the whole automatic mammal superiority story either though, as you are well aware.
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Post by sam1 on Apr 8, 2019 3:18:54 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. Also, they can traverse through water with minimal movements which, along with their keen sensory helps them to approach close undedected. It is known that dolphins along the south African coast avoid murky waters precisely because of sharks.
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Post by dinosauria101 on Apr 8, 2019 7:33:53 GMT 5
^Slightly diverging from the main point, but couldn't the shark bait the whale?
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Post by sam1 on Apr 8, 2019 13:39:47 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?
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Post by creature386 on Apr 8, 2019 15:59:18 GMT 5
Wouldn't dolphins have sonar to deal with murky water though?
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Post by sam1 on Apr 8, 2019 16:24:00 GMT 5
Wouldn't dolphins have sonar to deal with murky water though? Echolocation only detects what's in front of the dolphin, or in the direction its head is pointed towards. In order to scan the area below, dolphin needs to dive or look down. Again, they don't use their sonars continuously and can't be perfectly alerted all the time..especially during the resting phases.
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Post by creature386 on Apr 8, 2019 17:49:16 GMT 5
My initial thought was that sight has the same "looking down" restrictions. Then I realized that dolphin eyes are arranged in the right way to avoid precisely that problem (that, and sight requires less of a conscious effort than sonar). That being said, when googling for "dolphins avoid murky water", all I found were (admittedly pop-science) articles ( example) telling how little of an obstacle murky water presents to them. I'm interested in theropod's take on this.
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Post by sam1 on Apr 8, 2019 18:14:46 GMT 5
Google search won't give you a better result than the research paper on GWS predation on dolphins in Suth African waters. That's my source. I'll post PDF screenshots later.
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Post by sam1 on Apr 8, 2019 19:06:26 GMT 5
..For some reason one screenshot doesn't get through. Anyway, I'll just quote instead because the online link to the article is very scarce. But you can easily find the direct PDF link through Google search.
"There is circumstantial evidence that Natal bottlenose dolphins actively avoid encounters with large sharks. They consistently avoid dirty, discoloured water (Ross 1977). This behaviour may be an attempt to minimize confrontations with some species of big sharks, large numbers of which have been seen just inside and on the borders of discoloured wate r (pers. obs. VGC and GJBR) during aerial surveys conducted along the Natal coast.
"..Bottlenose dolphins are likely to have adapted both behaviourally and physiologically to this predation pressure to minimize its effect on the population. The avoidance of turbid water and the efficient camouflaging of the young calf (Cockcroft & Ross in press, a) are possible examples of these adaptations."
Source: "Shark predation on Indian Ocean bottlenose dolphins Tursiops truncatus off Natal, South Africa" South African Journal of Zoology. V.G. Cockcroft, G. Cliff & G.J.B. Ross 1989
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