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Post by theropod on Jul 30, 2018 2:47:42 GMT 5
Grey : The difference in scales does matter, a lot. Mass and kinetic energy scale to the third power, while strength only scales to the second power. It’s for the same reason that large terrestrial animals can fatally injure themselves in a simple fall, while small ones can not.
A 50 ton animal would have a much easier time delivering a dangerous ram than a 500kg one, simply because its ram produces 100 times the force, while the cross-sectional area of its target’s support structures or tissues, which determines their strength, would only be 22 times higher. That’s also why being specifically adapted for ramming is important. It’s relatively easy to structurally reinforce a skull and head against massive forces acting in one specific direction (think woodpecker, Allosaurus…), since bone has extremely high compressive strength and additional shock-absorbing structures (cranial kinesis, horns, trabecular bone, or, in the case of whales, the junk and spermaceti chamber) can be employed as needed. Reinforcing internal organs against rupture (or ribs against breaking) to the same extent is impossible. Bottom line: even if at 500kg an animal’s ram is harmless (which I’m not sure they are, just certainly more so than at 50 tons) a 50 ton animal’s ram may very well be fatal by means of causing ruptured organs and internal hemmorrhage where the smaller animal’s ramming force might still be within the tissue’s safety factors.
Dolphins specialized for small prey are fairly docile flight animals. Of course they avoid macrophagous sharks, they have nothing to gain by confronting them. That being said there are recorded instances of dolphins attacking large sharks in defense, including two humpback dolphins chasing a sizeable white shark (Heithaus 2001). And I may be misinformed, but are there not recorded instances of dolphins killing sharks by ramming? That the dolphins don’t prey on the sharks is obvious, but they can’t be expected to, they are not adapted to prey on large animals, unlike Livyatan, and probably couldn’t even eat them if they succeeded in killing them.
According to Read et al. 1993, both male and female bottlenose dolphins mass approximately 180kg at sexual maturity (c. 10 years), but differ in their subsequent growth, with males continuing to grow considerably larger (asymptotic body masses of 265 and 190kg respectively). What’s the average size of bull sharks preying on adult dolphins (or are there recorded cases where both animals’ sizes are known or estimated?)? It would seem that bottlenose dolphins are larger than bull sharks, but not necessarily any more so than great whites are compared to false killer whales.
A macropredaceous cetacean that is actually compelled to fight is certainly a different story to me. If you envision the confrontation between bottlenose dolphins and bull sharks to be a good approximation to the confrontation between C. megalodon and Livyatan, then we will have to disagree on that. Also, as to my knowledge no shark has ever been recorded killing a macrophagous cetacean its own size either. In fact, even the pygmy killer whales has not been recorded as a prey item of any shark (disregarding cookie-cutter parasitism) in Heithaus’ review of shark-dolphin interactions, despite many sharks growing as large as, or larger than it.
If you want a fair comparison: great whites prey on beaked whales (non-macrophagous), and possibly false killer whales (macrophagous), that are 3-5 times smaller than themselves. Orcas prey on great whites that are 3-5 times smaller than themselves.
One observation regarding mobility and pectoral fins: I am not fully bought on Ford et al.’s assertion that the male killer whales’ pectoral fins significantly slow them down, especially considering their drag could be reduced by firmly holding them against the body. In fact, they might be beneficial for maneuverability. If however they do negatively affect mobility by significantly increasing drag, as Ford et al. suggest, how does that leave the suggestion of supposedly giant-sized fins in C. megalodon, especially since the shark could not just adduct its fins, unlike the whale?
As for Livyatan, unless someone finds a skeleton its flipper shape is largely speculative. Brygmophyseter has proportionately larger flippers than Physeter, though they seem smaller than in male Orcinus. Zygophyseter doesn’t have any forelimb material preserved, just a scapula. Acrophyseter lacks postcrania alltogether. In any case, if we presume sexual selection to be at play in Orcinus, with swimming performance possibly negatively affected by the result (but I remain somewhat sceptical of that, there is probably a bit of a payoff between speed and maneuverability), then knowing the sex of the specimens would also be important.
In the end of the day, I am not convinced minor differences in pectoral fin shape or size will have major impacts on speed or maneuverability, but since it’s unknown anyway, I suppose we have to do the same as in C. megalodon, reverse-engineer morphology from the probable functional requirements.
btw I wouldn’t exactly call synapse science magazine a "scientific journal" 
Heithaus, M. R. 2001: Predator–prey and competitive interactions between sharks (order Selachii) and dolphins (suborder Odontoceti): a review. Journal of Zoology 253:53–68.
Ford, J. K., G. M. Ellis, D. R. Matkin, K. C. Balcomb, D. Briggs, and A. B. Morton. 2005: Killer whale attacks on minke whales: prey capture and antipredator tactics. Marine mammal science 21:603–618.
Read, A. J., R. S. Wells, A. A. Hohn, and M. D. Scott. 1993: Patterns of growth in wild bottlenose dolphins, Tursiops truncatus. Journal of Zoology 231:107–123.
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Post by sam1 on Jul 30, 2018 3:44:34 GMT 5
So now you're moving down from FKW and GWS to bottlenose dolphins vs bull shark to support your argument and still missing many of my points stated before. Ramming at 200kg vs ramming at 50000kg at the same speed? Seriously? Watch that slow motion of a whale shark colliding with a manta at very, very slow speed and see how its head reacted to the force. Can you even begin to coompare that to a 40t sperm whale moving at ~30km/h? Simply, a bottlenose dolphin doesn't have the tools to damage the bull shark seriously enough..its ram is not potent enough, and its jaws can't act as a secondary and finishing tool(like in my description of Livyatan and megalodon battle) Why do you need to be agressive ? Are my posts agressive ? No. The difference of scales doesn't matter. The fact is the dolphin, which is larger on average than a large bull shark, a better rammer and more mobile...still falls prey to this shark. Yes the dolphin doesn't have the massive bite but this comparison was compensated by the massive size advantage of the dolphin. The fact is no odontocete is known to have killed a macrophagous shark the same size individually and usually the cetacean is the one avoiding the fish. Definitely, knowing the ecological interactions between FKW and GWS would certainly be a better source of comparison, although as theropod said, the dolphin here appears to be a bit smaller-jawed for its size compared to Livyatan. There is no doubt though, despite their formidable dentition, that I favor any GWS like Apache or Deep Blue against any FKW. There are strong hints, based on some gigantic teeth from various positions, that C. megalodon may reach and perhaps exceeded 20 m long. That is not the case for Livyatan, neither the holotype nor any isolated teeth specimen found elsewhere in the world suggest something larger than the upper estimate of 17.5 m so far. Based on this, megalodon appears to be the species with the most powerful individuals. Again, I'm perfectly open to revise this depending on future discoveries and datas. At parity size, it is a toss up. One thing about Livyatan's alleged mobility, knowing the shape of its pectoral would also certainly help. Interestingly, a scientific journal wrote about this match : issuu.com/synapsebristol/docs/synapse_issue_9_nobleed_2Um, I was not aggressive. Like, really. Trust me. We're fine, man, I actually like you:D FYI, the beef I had with you was caused by your bashing of my Ultimate Sea predators visual chart that I put a lot of effort into and tried to be as abjective as possible. But that was long ago. I'll get back to the rest of your reply later. |
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Post by sam1 on Jul 30, 2018 14:05:47 GMT 5
So, regarding the size, I maintain that currently there is no consensus about megalodon reaching 20m. 18m seems the generally accepted figure, which indicates an average of around 13-15m.
On the other hand, I put the Livyatan holotype at ~15m, and have to assume that was the average since neither(absence of interlocking patterns) of the isolated teeth is from the mid section of the jaw which is where the biggest teeth are.
About the rest of your post, well, Theropod did a perfect job replying, nothing more to add there.
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Post by sam1 on Jul 30, 2018 14:42:46 GMT 5
sam1 : I’m not putting lifestyle above morphology, although obviously lifestyle and morphology are inextricably linked. It’s not as if Megalodon was likely to have looked anything like a whale shark. Whale shark morphology is simply quite different from Megalodon’s probable morphology, and simply put, whale sharks don’t seem to have any need for speed or agility, whereas C. megalodon certainly did. Since we don’t see such major differences in speed between similar-sized, morphologically appropriate AND ecologically similar sharks and odontocetes, I fail to see why the fact that whale sharks are sluggish is evidence that the morphologically, ecologically and phylogenetically rather distant C. megalodon was too. Baleen whales are also filter-feeders, but that’s were the similarity ends. I’m not saying that all filter-feeders are slow (in fact, that does not seem to hold true for basking sharks either), but even among filter-feeders, there are varying feeding strategies and. Rorquals are lunge-feeders that have to propel themselves through swarms of prey with opened mouths, taking in up to their own body mass in water. Whale sharks either ram- or suction feed. Obviously the former ecology requires different locomotory abilities than the latter. In addition, rorquals seem to be faced with far greater predation pressure than whale sharks (or at least, I know no record of orca predation on the latter, maybe because. With the bulk of large whale sharks considered, C. megalodon was not necessarily that much bulkier (probably somewhat, but not massively). But a whale shark is simply not adapted for the same locomotory needs faced by a large macropredator, whose morphology was likely closer to other lamniforms, and even if for some reason it were, it would still be spending most of its time crusing slowly while feeding, because it simply has no reason to move quickly. Again, great white sharks are not slow animals compared to orcas or Pseudorca. Can you demonstrate some inherent reason why sharks would suffer dramatically decreased mobility at larger sizes, much more so than whales? Infinity Blade : With only one individual of Livyatan we can not scientifically conclude which taxon grew larger, but the one we have is without a doubt in the size range of good-sized to large adult C. megalodon, even at the lower end of plausible sizes. Assuming similar sizes, they are very evenly matched overall, albeit with very different strengths and weaknesses. The whale lacks the formidable cutting dentition and large gape, whereas the shark is inferior in ramming ability, ability to grip and manipulate its opponent with the jaws and has some shortcomings in mobility imposed by its respiratory system and tonic immobility (e.g. stopping, reversing, rolling and such). And the extant analogy suggesting either side to dominate in a similar-sized engagement simply does not exist, with the only cetaceans sharks take that are as large as, or larger than themselves being mysticete calves and small delphinids. elosha11 : Yes, but this has already been repeated over and over again. Literally every time agility is discussed, this comes up, as if it had any bearing on how Livyatan and megalodon compared in this regard. Since it changes nothing about this scenario, repeating it over and over again gives the incorrect impression that it did. Which I think is in fact a thing that can easily be misconstrued because the logical assumption if something gets posted repeatedly is that those who post it want to actually make a point with it. The only thing the quote from Pitman et al. can be construed to suggest is that the role of the adult male orca in prey capture is a variable one. It does not disagree with the notion that adult males are less agile than females or subadults, not does it suggest the opposite. I did think that it was important to remind that the male is quite capable of hunting though, especially since the reduced agility and hunting efficiency of the males is being highlighted this much. The way I see it, Megalodon had to be stealthy before anything else. It had to be able to close in to the prey undetected, to use up just one precious burst of energy in the final stage; having to chase the prey at that size would simply be hugely inefficient. The inherent reason you asked for, is a passive respiratory system of the shark. I'm sure I don't have to explain it further to you. Prehistorican here mentioned that meg must've been able to move at a calculated 18km/h just to be able to provide enough oxygen through its gills. Can someone give a link about that so you can perhaps review the math behind it? I have my doubts about the figure. Also, I dismiss the premise of GWS and Orca being equal in terms of mobility. Let's look at a ~2.5-3 ton orca:  Now, can you show me any footage of an ACTUALLY large(let alone a record setting 2.5t one) GWS moving at impressive speed? The sharks you see leaping in the air after seal cubs are nothing even close to the size of that orca (which still moves faster and jumps MUCH higher). But a large GWS? Here's how it fares against a sea lion: www.dailymail.co.uk/news/article-2442406/Sea-lion-taunts-GREAT-WHITE-SHARK-biting-tail.htmlCan you imagine a sea lion doing that to an Orca? Just not going to happen, ever. Generally, it seems to me that trully large great whites are far more reliant on scavenging and opportunistic feeding(to little surprise, shark attack files of GWS attacks on humans show the majority of these man killers being estimated at 4.5-5.5m) , and they are nowhere near as fast, athletic and agile as orcas. I believe there is a physiological limitation that comes into play after a certain size threshold. Akin to a, say, a reptile and mammal comparison. A lizard will be just as quick as a mammal at up to a certain size, but after that the limitations are exponentially increasing. |
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Post by sam1 on Jul 30, 2018 15:41:04 GMT 5
p.s. Another image  ..to illustrate that orca was doing that in the process of chasing down a bottlenose dolphin. It wasn't just a one-off jump but a part of the effort that lasted for "90 MINUTES" www.thesun.co.uk/news/4571393/dolphin-escapes-killer-whale-orca-baja-california/Even the most die hard shark fans know that Deep Blue GWS for example, would be incapable of doing anything remotely close to that. Not comparable at all. |
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Post by Grey on Jul 30, 2018 16:07:38 GMT 5
So, regarding the size, I maintain that currently there is no consensus about megalodon reaching 20m. 18m seems the generally accepted figure, which indicates an average of around 13-15m. On the other hand, I put the Livyatan holotype at ~15m, and have to assume that was the average since neither(absence of interlocking patterns) of the isolated teeth is from the mid section of the jaw which is where the biggest teeth are. About the rest of your post, well, Theropod did a perfect job replying, nothing more to add there. There is an abstract presented at SVP 2018 that will propose an average conservative size estimate for adult megalodon. That is not 13-15 m. Actually there is a consensus, many of the latest publications all put 20 m (as Gottfried's upper figure of 20 m for a 168 mm upper anterior is valid) and the 17.9 m individual in Pimiento matrix is actually 19.5 m, she simply made an error in the calculation (Shimada's crown height method). Even Maisey 2016 acknowledges a possible range of 16-24 m maxima. Adjusting the widest recorded teeth on Leder 2016 table, you definitely get figures exceeding the 20 m range as well. According to Erich Fitzgerald, the isolated teeth from Australia come from an animal "comparable" in size to Livyatan, not larger. I admit I've pondered about the position of the big isolated teeth from Chile. But I've asked a lot about to Giovanni Bianucci who first described those and he never suggested their alleged absence of wear from interlocking was indicative of being smaller teeth in the jaws. The few I have seen definitely have the massive shape of the big ones in Livyatan holotype. Bianucci doesn't think those teeth are from larger individuals and this is corroborated by Gilbert 2018 who reports that tooth keep growing while the body size plateaus in odontocetes. I could ask again to Bianucci though. Maybe Fitzgerald study about the Australian teeth will bring more on this. But as much as I searched, there is zero material indicating any individual larger than the holotype so far. Theropod, yes, I certainly forgotten the difference of the impact at 300 kg or 50 000 tonnes on this one. But has a 50 tonnes sperm whale ever been seen striking something mobile other than a boat ? Is there a record of Physeter killing another living being (a male rival) with it ? |
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Post by Grey on Jul 30, 2018 16:22:41 GMT 5
p.s. Another image ..to illustrate that orca was doing that in the process of chasing down a bottlenose dolphin. It wasn't just a one-off jump but a part of the effort that lasted for "90 MINUTES" www.thesun.co.uk/news/4571393/dolphin-escapes-killer-whale-orca-baja-california/Even the most die hard shark fans know that Deep Blue GWS for example, would be incapable of doing anything remotely close to that. Not comparable at all. I certainly don't doubt about this. But I doubt a 2 tonnes orca, despite such athletic skills, would be able to beat Deep Blue. The dental armament and sheer natural durability is more decisive than athletic skills. Which might explain why there is no record of odontocetes killing/preying on raptorial selacians at parity size. |
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Post by sam1 on Jul 30, 2018 19:32:26 GMT 5
So, regarding the size, I maintain that currently there is no consensus about megalodon reaching 20m. 18m seems the generally accepted figure, which indicates an average of around 13-15m. On the other hand, I put the Livyatan holotype at ~15m, and have to assume that was the average since neither(absence of interlocking patterns) of the isolated teeth is from the mid section of the jaw which is where the biggest teeth are. About the rest of your post, well, Theropod did a perfect job replying, nothing more to add there. There is an abstract presented at SVP 2018 that will propose an average conservative size estimate for adult megalodon. That is not 13-15 m. Actually there is a consensus, many of the latest publications all put 20 m (as Gottfried's upper figure of 20 m for a 168 mm upper anterior is valid) and the 17.9 m individual in Pimiento matrix is actually 19.5 m, she simply made an error in the calculation (Shimada's crown height method). Even Maisey 2016 acknowledges a possible range of 16-24 m maxima. Adjusting the widest recorded teeth on Leder 2016 table, you definitely get figures exceeding the 20 m range as well. According to Erich Fitzgerald, the isolated teeth from Australia come from an animal "comparable" in size to Livyatan, not larger. I admit I've pondered about the position of the big isolated teeth from Chile. But I've asked a lot about to Giovanni Bianucci who first described those and he never suggested their alleged absence of wear from interlocking was indicative of being smaller teeth in the jaws. The few I have seen definitely have the massive shape of the big ones in Livyatan holotype. Bianucci doesn't think those teeth are from larger individuals and this is corroborated by Gilbert 2018 who reports that tooth keep growing while the body size plateaus in odontocetes. I could ask again to Bianucci though. Maybe Fitzgerald study about the Australian teeth will bring more on this. But as much as I searched, there is zero material indicating any individual larger than the holotype so far. Theropod, yes, I certainly forgotten the difference of the impact at 300 kg or 50 000 tonnes on this one. But has a 50 tonnes sperm whale ever been seen striking something mobile other than a boat ? Is there a record of Physeter killing another living being (a male rival) with it ? Show me a recent peer reviewed study(other than the Pimiento's study) that comes up with average megalodon sizes. And why are you suggesting that I hinted at larger individuals by referring to the isolated teeth? You yourself claim they don't come from larger individuals, but that's not the point. The point is that they also don't suggest a smaller individuals, hence there's nothing to suggest the holotype specimen is a large one. And how can you choose to ignore the lack of interlocking patterns when they are so obvious and pronounced on holotype's biggest teeth? Also the shape of the front (no interlock patterns) and middle positioned teeth is basically the same, the only significant difference being the size and the before mentioned patterns. So I go with the obvious and logical conclusion - the isolated teeth are either not the biggest teeth belonging to certain livyatan specimen, either teeth belonging to another species/genus. |
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Post by sam1 on Jul 30, 2018 19:43:20 GMT 5
p.s. Another image ..to illustrate that orca was doing that in the process of chasing down a bottlenose dolphin. It wasn't just a one-off jump but a part of the effort that lasted for "90 MINUTES" www.thesun.co.uk/news/4571393/dolphin-escapes-killer-whale-orca-baja-california/Even the most die hard shark fans know that Deep Blue GWS for example, would be incapable of doing anything remotely close to that. Not comparable at all. I certainly don't doubt about this. But I doubt a 2 tonnes orca, despite such athletic skills, would be able to beat Deep Blue. The dental armament and sheer natural durability is more decisive than athletic skills. Which might explain why there is no record of odontocetes killing/preying on raptorial selacians at parity size. Well, I would put money on that orca against Deep Blue shark. Killing it is probably a bit too much work(inducing tonic immobility would not be easy due to mass and strength of the shark) and hassle for a single orca that can catch its prey elsewhere. But beating it would be fairly easy, no doubt in my mind about it. But regardless, the point I was making was about mobility. It seems that GW sharks are unable to keep up with orcas after a certain size point in that regard. That fact offers a really strong hint about the grander scheme of things |
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Post by theropod on Jul 30, 2018 19:46:18 GMT 5
sam1: You do have a point. However it’s not exactly easy to determine how big the gws in any given piece of footage actually is, unless the individual is specifically identified. So are we sure large great whites don’t perform any similar athletic feats? Also, what about breaching basking sharks? Grey: No, because the point of intraspecific rival fights is to NOT be lethal. That is why Physeter probably (this was the case in the only actual observed instance, see the appendix to Panagiotopoulou et al. 2016 here→), i.e. both combatants receive the impact with a structure specifically adapted to withstand such forces, so neither can fatally injure the other without injuring itself. Also, the majority of sperm whale male-to-male aggression probably happens under water and out of view (even in the recorded instance, the whales dove before colliding). If occasionally they do kill each other, then it’s very unlikely to be observed. Impact on a similar-sized animal’s body has been simulated by using computational models though: Scaling relationships based on records of injuries sustained by humans in car crashes (Alexander, 1996; Farlow et al., 2000) suggest that twice the acceleration due to gravity (2 g=19.6 m s –2) is the acceleration at which a 39 000 kg vertebrate would suffer fatal injury. The portion of Fig. 5 above the horizontal line (2 g on the y-axis) represents accelerations above injury threshold for the target whale and below injury threshold for the attacking whale’s body. These results suggest that the momentum of the spermaceti organ of a large swimming sperm whale could seriously injure a stationary opponent of similar body mass. Further, and most importantly, the level of damping necessary to protect the attacking whale from injury would not necessarily diminish the effectiveness of the system as a weapon. About isolated "cf. Livyatan" teeth, who is suggesting that they were from bigger individuals? The null-hypothesis is that the holotype likely represents an average size for the species…and didn’t you just acknowledge that they are plausibly from similar-sized individuals, corroborating rather than rebuking that very null-hypothesis? There is really little ambiguity on the presence or absence of wear-facets, and it makes perfect sense that isolated physeteroid teeth would mostly be from the front of the tooth-row where the smaller teeth are, and where they are probably more likely to fall out. Comparing isolated teeth to the largest in the dentition without any clear indications that they pertain to the same position is certainly a flawed reasoning for suggesting the owner was smaller than L. melvillei. In fact, if physeteroid teeth continue to grow after full physical maturity has been reached (citation, btw?), that’s another reason why a smaller teeth doesn’t necessarily mean a smaller whale. Of course that all breaks down to the inherent unreliability of scaling anything from isolated teeth, but that also applies to the shark. So all things considered, isolated teeth may not be a reliable means of inferring larger individuals, but neither do they prove smaller individuals. And that "average conservative" size estimate, is it higher than the 30-60t L. melvillei holotype, and based on what specimens was it produced? Stating your opinion on how you think a shark is superior to an equal-sized macrophagous cetacean is all well and fine, but one should take care not to misconstrue that into evidence. If you consider them superior on the grounds of functional morphology, that is just an interpretation, not the evidence itself that can inform such an interpretation. Certainly, it would be much more interesting to discuss, in detail, the reasons behind it than to just state your conclusion. You keep pointing out that there is no record of "odontocetes killing/preying on raptorial selacians at parity size", but as I have already noted, there is no record of the reverse either. So that really does not constitute evidence for anything. So with that being said, could you elaborate on the "sheer natural durability" part? I think we’ve discussed the dental armament before and will have to agree to disagree on that. Carrier, D. R., S. M. Deban, and J. Otterstrom. 2002: The face that sank the Essex: potential function of the spermaceti organ in aggression. Journal of Experimental Biology 205:1755–1763.
Panagiotopoulou, O., P. Spyridis, H. M. Abraha, D. R. Carrier, and T. C. Pataky. 2016: Architecture of the sperm whale forehead facilitates ramming combat. PeerJ 4:e1895.
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Post by theropod on Jul 30, 2018 20:01:59 GMT 5
Actually something that may sometimes get overlooked regarding bite potency and related issues:
While I disagree with this conclusion on the grounds that the two are not functionally comparable and the respective damage would be of a very different kind, I can accept why someone might consider the shark’s wider jaw and slicing dentition to be the more advantageous for killing. In fact, I certainly would agree that there are cases were a bite capable of causing massive exsanguination would be advantageous over one causing massive crushing and puncturing injuries–and vice versa in other cases.
But the whale actually does not have to use its bite itself for killing. Simply getting a firm grip on its opponent with the jaws is enough to end the fight as there’s little that could dislodge it once that happened (that is exactly the kind of thing that dentition and jaw shape is built for, after all). Let me call back to mind the account of orca predation on sperm whales, where the orcas were quite proficient at pulling sperm whales out of formation with their jaws, and the male took a sperm whale (supposedly larger than the killer whale itself) in its mouth, violently shook it, and swam off with it. Again, proportional to its overall body size, Livyatan has much larger and more powerful skull, jaws and teeth than orcas, so if anything it should be more capable of performing such feats. The point being that once Livyatan managed to firmly bite something, there’s probably pretty much nothing that could make it let go. This is not a bite-and-release-type jaw morphology, it’s built to hold onto what it bit.
Then, even if the no doubt potentially massive crushing injuries caused by the bite were insufficient (e.g. severing the caudal spinal collumn or crushing the skull hardly seems out of the question), it could simply suffocate the shark by immobilising it, possibly facilitated by using tonic immobility.
So I don’t think which predator takes out the larger chunks of flesh with its bite, besides grossly oversimplifying the different jaw function of the two, would be such a determining factor in this fight.
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Post by sam1 on Jul 30, 2018 20:43:23 GMT 5
^ that's exactly why I claimed before(as a side note) that the gripping bite of Livyatan might have potentially been just as deadly as the slicing bite of the Megalodon.
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Post by Grey on Jul 30, 2018 22:27:27 GMT 5
There is an abstract presented at SVP 2018 that will propose an average conservative size estimate for adult megalodon. That is not 13-15 m. Actually there is a consensus, many of the latest publications all put 20 m (as Gottfried's upper figure of 20 m for a 168 mm upper anterior is valid) and the 17.9 m individual in Pimiento matrix is actually 19.5 m, she simply made an error in the calculation (Shimada's crown height method). Even Maisey 2016 acknowledges a possible range of 16-24 m maxima. Adjusting the widest recorded teeth on Leder 2016 table, you definitely get figures exceeding the 20 m range as well. According to Erich Fitzgerald, the isolated teeth from Australia come from an animal "comparable" in size to Livyatan, not larger. I admit I've pondered about the position of the big isolated teeth from Chile. But I've asked a lot about to Giovanni Bianucci who first described those and he never suggested their alleged absence of wear from interlocking was indicative of being smaller teeth in the jaws. The few I have seen definitely have the massive shape of the big ones in Livyatan holotype. Bianucci doesn't think those teeth are from larger individuals and this is corroborated by Gilbert 2018 who reports that tooth keep growing while the body size plateaus in odontocetes. I could ask again to Bianucci though. Maybe Fitzgerald study about the Australian teeth will bring more on this. But as much as I searched, there is zero material indicating any individual larger than the holotype so far. Theropod, yes, I certainly forgotten the difference of the impact at 300 kg or 50 000 tonnes on this one. But has a 50 tonnes sperm whale ever been seen striking something mobile other than a boat ? Is there a record of Physeter killing another living being (a male rival) with it ? Show me a recent peer reviewed study(other than the Pimiento's study) that comes up with average megalodon sizes. And why are you suggesting that I hinted at larger individuals by referring to the isolated teeth? You yourself claim they don't come from larger individuals, but that's not the point. The point is that they also don't suggest a smaller individuals, hence there's nothing to suggest the holotype specimen is a large one. And how can you choose to ignore the lack of interlocking patterns when they are so obvious and pronounced on holotype's biggest teeth? Also the shape of the front (no interlock patterns) and middle positioned teeth is basically the same, the only significant difference being the size and the before mentioned patterns. So I go with the obvious and logical conclusion - the isolated teeth are either not the biggest teeth belonging to certain livyatan specimen, either teeth belonging to another species/genus. I had detailed on carnivora why Pimiento's average size is quite likely not valid (basically most of the results in her matrix are probably off by a good margin). Reading our poster (Leder et al. 2016) renders the results of this matrix obsolete. Her study actually deals with mean size, not actual average size. But it is most likely off in terms of accuracy. The simple fact the teeth in the matrix are assigned to several positions is problematic as it suggests a huge size range for Actually all the teeth found in Australia (I've seen the pictures) are smaller than those in the holotype. Hence the animal was probably not as large. From discussing with Bianucci and Lambert a number of times in years (some of the discussions are on the forum), it doesn't appear from them that either from those wears or those isolated teeth they come from larger individuals as you imply. But I certainly can ask again to Bianucci since he directly examined the Chilean teeth. |
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Post by Grey on Jul 30, 2018 22:54:46 GMT 5
sam1: You do have a point. However it’s not exactly easy to determine how big the gws in any given piece of footage actually is, unless the individual is specifically identified. So are we sure large great whites don’t perform any similar athletic feats? Grey: No, because the point of intraspecific rival fights is to NOT be lethal. That is why Physeter probably (this was the case in the only actual observed instance, see the appendix to Panagiotopoulou et al. 2016 here→), i.e. both combatants receive the impact with a structure specifically adapted to withstand such forces, so neither can fatally injure the other without injuring itself. Also, the majority of sperm whale male-to-male aggression probably happens under water and out of view (even in the recorded instance, the whales dove before colliding). If occasionally they do kill each other, then it’s very unlikely to be observed. Impact on a similar-sized animal’s body has been simulated by using computational models though: Scaling relationships based on records of injuries sustained by humans in car crashes (Alexander, 1996; Farlow et al., 2000) suggest that twice the acceleration due to gravity (2 g=19.6 m s –2) is the acceleration at which a 39 000 kg vertebrate would suffer fatal injury. The portion of Fig. 5 above the horizontal line (2 g on the y-axis) represents accelerations above injury threshold for the target whale and below injury threshold for the attacking whale’s body. These results suggest that the momentum of the spermaceti organ of a large swimming sperm whale could seriously injure a stationary opponent of similar body mass. Further, and most importantly, the level of damping necessary to protect the attacking whale from injury would not necessarily diminish the effectiveness of the system as a weapon. About isolated "cf. Livyatan" teeth, who is suggesting that they were from bigger individuals? The null-hypothesis is that the holotype likely represents an average size for the species…and didn’t you just acknowledge that they are plausibly from similar-sized individuals, corroborating rather than rebuking that very null-hypothesis? There is really little ambiguity on the presence or absence of wear-facets, and it makes perfect sense that isolated physeteroid teeth would mostly be from the front of the tooth-row where the smaller teeth are, and where they are probably more likely to fall out. Comparing isolated teeth to the largest in the dentition without any clear indications that they pertain to the same position is certainly a flawed reasoning for suggesting the owner was smaller than L. melvillei. In fact, if physeteroid teeth continue to grow after full physical maturity has been reached (citation, btw?), that’s another reason why a smaller teeth doesn’t necessarily mean a smaller whale. Of course that all breaks down to the inherent unreliability of scaling anything from isolated teeth, but that also applies to the shark. So all things considered, isolated teeth may not be a reliable means of inferring larger individuals, but neither do they prove smaller individuals. And that "average conservative" size estimate, is it higher than the 30-60t L. melvillei holotype, and based on what specimens was it produced? Stating your opinion on how you think a shark is superior to an equal-sized macrophagous cetacean is all well and fine, but one should take care not to misconstrue that into evidence. If you consider them superior on the grounds of functional morphology, that is just an interpretation, not the evidence itself that can inform such an interpretation. Certainly, it would be much more interesting to discuss, in detail, the reasons behind it than to just state your conclusion. You keep pointing out that there is no record of "odontocetes killing/preying on raptorial selacians at parity size", but as I have already noted, there is no record of the reverse either. So that really does not constitute evidence for anything. So with that being said, could you elaborate on the "sheer natural durability" part? I think we’ve discussed the dental armament before and will have to agree to disagree on that. Carrier, D. R., S. M. Deban, and J. Otterstrom. 2002: The face that sank the Essex: potential function of the spermaceti organ in aggression. Journal of Experimental Biology 205:1755–1763.
Panagiotopoulou, O., P. Spyridis, H. M. Abraha, D. R. Carrier, and T. C. Pataky. 2016: Architecture of the sperm whale forehead facilitates ramming combat. PeerJ 4:e1895. Interesting about the whole ramming subject. Here I question the actual ability to ram into an adversary that was presumably quite mobile. But we enter into the realm of pure speculation. I've never heard or read anything suggesting those isolated teeth are not from the mid-section of the jaws. Firstly, there is originally more than 10 of those isolated teeth (about 20 if we count the Australian teeth). Have you seen them, recorded their sizes and examined their shape ? I've observed, IIRC, 4 or 5 of those teeth (pictures taken in private collections) and I'm confident some of them had the wears. I agree this is an interesting point that I plan to work on but I think you jump to conclusions. So far, I didn't get such an indication from Bianucci. I certainly agree that based on the fact that odontocete size stops while the teeth keep growing (check Gilbert 2018), this does not make the isolated teeth as coming from smaller or larger individuals. But I'm reluctant to state anything about an alleged average size without at least another individual. Of course, if teeth really much larger were discovered, I doubt this would be still valid... Anyway, as we have seen before, a similar average size wouldn't necessarily indicate a similar maximum size. Regarding the average size, embargo on anything before my coauthor presents it to SVP. Interesting about the grippling bite. One thing the shark can do against it : simply diving deep. Regarding the comparative bite, it was conservatively estimated, through experiment through a reconstruction, that the jaws from a 16 m megalodon would be able to take about 940 kg or so of organic substances. Simple scaling to 20 m suggests a bite able to take more than 1800 kg. From my observation of the Livyatan jaws, as powerfully built and impressive they are, I don't think they are able to do a similar task. |
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Post by sam1 on Jul 31, 2018 0:02:02 GMT 5
Show me a recent peer reviewed study(other than the Pimiento's study) that comes up with average megalodon sizes. And why are you suggesting that I hinted at larger individuals by referring to the isolated teeth? You yourself claim they don't come from larger individuals, but that's not the point. The point is that they also don't suggest a smaller individuals, hence there's nothing to suggest the holotype specimen is a large one. And how can you choose to ignore the lack of interlocking patterns when they are so obvious and pronounced on holotype's biggest teeth? Also the shape of the front (no interlock patterns) and middle positioned teeth is basically the same, the only significant difference being the size and the before mentioned patterns. So I go with the obvious and logical conclusion - the isolated teeth are either not the biggest teeth belonging to certain livyatan specimen, either teeth belonging to another species/genus. I had detailed on carnivora why Pimiento's average size is quite likely not valid (basically most of the results in her matrix are probably off by a good margin). Reading our poster (Leder et al. 2016) renders the results of this matrix obsolete. Her study actually deals with mean size, not actual average size. But it is most likely off in terms of accuracy. The simple fact the teeth in the matrix are assigned to several positions is problematic as it suggests a huge size range for Actually all the teeth found in Australia (I've seen the pictures) are smaller than those in the holotype. Hence the animal was probably not as large. From discussing with Bianucci and Lambert a number of times in years (some of the discussions are on the forum), it doesn't appear from them that either from those wears or those isolated teeth they come from larger individuals as you imply. But I certainly can ask again to Bianucci since he directly examined the Chilean teeth. Pimiento study doesn't interest me any more. It gives an average size that even I think is incorrect and I also know your opinion about it. No need to repeat yourself. Anyway, that is why I asked for another peer reviewed such study. Can you provide it? So since you say the isolated teeth are smaller than any tooth from the Livyatan holotype I assume you can say what are the dimensions of the holotype's teeth? What are the exact figures for the smallest teeth in the holotype jaw? Finaly, for the second time, I am not implying that those teeth are from bigger individuals. Read my post again. And Theropod's reply was along the same line as well. |
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