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Post by elosha11 on Jul 8, 2018 21:32:19 GMT 5
Good observations, however, we just don't know enough of how these feeding interactions - whether predatory or scavenging - took place. Given its higher overall caloric needs, Megalodon may have been a less picky and delicate eater than a great white and may have fed from all parts of its prey, including the head. For instance, I can't agree that no shark would bite the jaw region because of this shark bitten jawbone from the Pliocene found in Peru:  Description is found at vmnhpaleontology.wordpress.com/2011/11/06/svp-2011-meeting-day-4/. The author thinks it was possibly a great white shark, but given the deepness and size of the bite marks, I wonder if it could have possibly been a Megalodon, prior to their extinction. In any event, it does show that sharks might feed even on the jaw/head region of a whale at times. As to the question of the fossil tooth with bite marks, your scenario is definitely plausible; it just doesn't eliminate numerous other possibilities. Fossil evidence usually will only lead one to a best educated guess, there's very little absolute certainty as to what led to the the interaction or its outcome. |
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Post by theropod on Jul 8, 2018 22:02:47 GMT 5
Off topic: Killer whales are bulkier than my Livyatan model. Of course sheer size will severely hamper its agility, but that applies to C. megalodon as well. If people envision megalodon as a somewhat (or even greatly) overbulked white shark, it’s going to have just as much trouble in that department. And even though a 50 ton animal will almost certainly take very long to accelerate to it, top speed itself is not that limited in giant aquatic animals. If even blue whales can reach or exceed 50kph, then there’s no reason why these two predators would have been especially slow either, although it would probably be really rare to see them reach , it given that their hunts would generally have been over quickly and chasing small prey for extended periods of time would have been hopeless anyway.
And has any new Livyatan of Brygmophyseter skeleton been described since I last revisited that model?
Otherwise I don’t see how its age, a whopping two years, would be relevant to its degree of accuracy.
That is only one of several possible morphologies for this animal, and there is nothing directly indicating this to be more likely than a longer, more slender version based on Zygophyseter. That being said, the Zygophyseter-version will probably be just as heavy, if not heavier. It would still be be an animal with a skull just as wide (and in any case, still proportionately way wider than an orca’s), a slimmer chest, but in exchange, 2m longer overall. That’s why I did make it a point to include an alternative, Physeter-based morphology in my chart back on DA. Although it should come as no surprise that that one is not preferrable over the others either. This meant as a size estimate and an idea of a reconstruction, but as long as that reconstruction is not supported by postcranial remains, trying to infer biomechanical capabilities from it is pointless. Especially considering there’s no real basis to even estimate how being bulky vs being more slender would positively or negatively affect the animal.
I definitely concur that feeding seems like a pretty improbable explanation for a bite mark on a whale tooth. The shark would have had to willingly bite down pretty hard on a piece of bone pretty much the size of its own jaws, for no real benefit. Even when you have a mouthful of teeth to spare, you generally wouldn’t do that. It’s also a pretty weird predation strategy. Not saying that the skull bite wouldn’t be effective, but when the goal is to immobilize and kill, the tail is certainly better. But considering that locking jaws with each other seems even more ludicrous to imagine in an underwater confrontation (or are there any animals that do that?) it still seems like the best explanation to me.
Perhaps it got mixed up, or it simply missed the target it was intending to strike.
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Post by theropod on Jul 8, 2018 22:05:33 GMT 5
elosha11: Caudal centra have facets for the attachment of haemal arches. In the specimen you posted it does look a bit like there could be one, but without a more telling photograph I don’t think anybody could be sure of that. Also there’s no transverse process, which would actually imply a fairly distal position within the caudal series.
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Post by prehistorican on Jul 8, 2018 22:29:16 GMT 5
I would favor the Megalodon in the speed and agility department due to the numerous mass of Type 2B fibers which are used all at once, compared to Type 2A muscles in Livyatan even though it also has Type 1 fibers as well. With a Type 2B fibers the movements are very explosive, extremely powerful yet fatiguable. Livyatan Type 2A fibers should have less than half the peak power production in a top speed strike (well based off of mammals and their fiber types). Type 2A can last a little loner and is moderately fatiguable. Also with numerous vertebrae, and cartilage skeleton I would definitely favor the shark in agility able to make sharper and quicker turns. Type 2B fiber is 90% muscle mass in sharks, equivalent or even slightly more than the top 100m sprinters in the Olympics. Type 2B reaches peak power production faster than style 2A and therefore I believe the shark can accelerate faster than a Livyatan of similar mass.
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Post by theropod on Jul 8, 2018 22:47:15 GMT 5
And do observations of extant cetaceans and similar-sized sharks confirm that?
Shark vertebral cartilage is just as mineralized and stiff as mammalian trabecular bone, so it cannot give it any sort of flexibility advantage (which is certainly not surprising since bones are stiff for a reason). Naturally it would be expected that a shark would be quicker in terms of yaw, while the cetacean would be quicker in terms of pitch.
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Post by elosha11 on Jul 8, 2018 23:51:27 GMT 5
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Post by theropod on Jul 9, 2018 0:31:12 GMT 5
Thanks elosha11, that does help! I was mistaken. I thought the first picture was in lateral view, but what I thought were the broken neural arch and a possible haemal arch facet, are actually the bases of the transverse processesin ventral aspect. Not a sign of a haemal arch facet in sight anywhere, so it’s probably a lumbar vertebra and not a caudal. I wouldn’t suppose anyone has a pdf of the following monograph? Flower, W. H. (1868), XII. On the Osteology of the Cachalot or Sperm-Whale (Physeter macrocephalus). The Transactions of the Zoological Society of London, 6: 309–372. doi: 10.1111/j.1096-3642.1868.tb00580.xBizarre as it sounds, it’s more difficult to find an osteological description of a sperm whale than of most dinosaurs. |
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Post by Grey on Jul 10, 2018 14:59:06 GMT 5
My referal to theropod's model age was that he could very well consider it outdated by now.
I never considered it accurate for the simple reason it is based on the Brygmophyseter skeletal mount which is considered suspicious and incorrect by Lambert, Bianucci and others. Hence why they rather used the Zygophyseter specimen as model to predict body size.
That's why, while theropod's model is not uninteresting, I'm a bit worrisome to see many people on deviant using it as a reference without any grain of salt. The model by paleoartist Alberto Gennari working closely with Giovanni Bianucci is rather the actual reference to go by.
Furthermore, this model always appeared clumsy to me.
I rather favor Biannucci and Gennari more streamlined and athletic reconstruction.
I would expect Livyatan to weigh more or less the same as a sperm whale the same length, maybe a bit less due to the less voluminous skull at the same bizygomatic width.
Or maybe to be more massive due to the heavier dentition and the overall impact on the skeleton. But based on Reynold's numbers, there is no reason to expect great differences in body mass between two individuals at the same length.
Prehistorican, I question the relevance to discuss about the weight of a "20 m Livyatan".
Not to say there is zero chance it existed, but other than the usual speculations about the larger specimens we haven't/will never found/find, there is zero, even fragmentary, material suggesting such a size figure.
Even bigger isolated teeth would be a poor indication of "larger than the holotype" as Gilbert 2018 recalled odontocetes full body size plateaus while the teeth continue to grow.
The exact inverse situation than with GWS.
Thus, a 20 m Livyatan is pure fiction as of July 2018.
Megalodon...not so much. There is actual material and methodology allowing to imply the existence of a 20 m Neogene superpredatory shark.
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Post by Grey on Jul 10, 2018 19:42:15 GMT 5
Finally I had the time to read the whole discussion.
About the bitten sperm whale tooth : has anybody suggested a simple feeding frenzy while eating the flesh of the mandible or the melon ?
Regarding the bitten sperm whale vertebra : nice investigation of its probable position. A good hint of how likely the culprit of this bite is a megalodon is the sheer depth this bone was in the body.
Even as a rotting carcass, I doubt a more conventional-sized shark would be able to reach a vertebra that deep in the body of a clearly >10 m whale.
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Post by theropod on Jul 10, 2018 21:07:48 GMT 5
Hmm. Feeding frenzy is an option, that’s true, but biting right into a tooth would imply a fairly powerful bite, more than I’d expect an animal to apply when it’s trying to strip a relatively thin layer of flesh from the bones of the lower jaw. But I suppose predators sometimes do "over-bite" while feeding. That might be a better option, I agree.
Not with a single bite, anyway. Obviously while defleshing a carcass, predators can reach the bones regardless of whether they could reach them with an initial bite, that’s the very meaning of "defleshing" after all. But you’ll see no argument from me against this being a megalodon bite mark, it’s not exactly uncommon and certainly the likeliest culprit for any shark bite marks on sizeable whales from its time period.
An "investigation" would have been finding an osteological description of a sperm whale (which sadly, doesn’t seem to have been published within the last 150 years, and the one from the 1860s, as ridiculous as it sounds, is paywalled) and making a precise positional assignment of the vertebra. Like this, there’s not much more than the obvious to state about its position. I don’t suppose you have a sperm whale osteology paper lying around anywhere (which would be interesting in any case)?
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Post by Grey on Jul 11, 2018 1:32:33 GMT 5
Yup of course I don't. I've variously searched for similar data the last years.
Or maybe asking to Boessennecker if he has any more references.
But I agree with your conclusion that it's a lumbar vert. Given the huge size of the bone, how deep it was, it can be inferred marks are from a meg.
Conversely, this can be used as another indirect evidence to support this shark species was gigantic as only an extremely large and devastating dentition could go that deep in this massive cetacean and inflict those marks.
The real question, as often : scavenging or predation ?
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Post by elosha11 on Jul 11, 2018 8:08:53 GMT 5
^Theropod/Grey - any idea just how "deep" into the flesh a shark would have to bite to reach such a vert of this size, assuming the animal was a sperm whale or other type of physteroid? FYI, there's at least one other centra on here with Meg marks on this thread just about as big as the one we're discussing. Of course, we do have to account for the possibility that the Megalodon had already taken several bites to get down deep enough to scrape this centra. In other words, it may have been more than one bite. Of it may have been the accumulation of many shark's different bites, that finally allowed a bite that scraped the bone.
All kinds of possibilities and - as stated above - we just can't know if it was predatation or scavenging. However, given the sheer number of whale bitten bones, I'm pretty confident that Megalodon could prey on pretty much whatever it wanted during the Miocene and early Pliocene. And simply due to the number of carcasses it would take to constantly support a shark the size of Megalodon, I'm somewhat certain that Megalodon was an active predator far more than a scavenger.
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Post by elosha11 on Jul 11, 2018 8:22:12 GMT 5
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Post by sam1 on Jul 11, 2018 15:52:34 GMT 5
I was just reading through this thread and find it very reassuring that only one poster("prehistorican") is showing bias, while Theropod is saving me the trouble with points I would've brought up in response.
I'll just note that, to me, this whole forensic speculation saga is, while interesting, kind of silly as there is no doubt that these animals have killed each other on countless occasions throughout their co-existence.
No need to prove or disprove it, it's just common sense and the law of probability.
We can discuss and speculate about how probable and frequent the attacks were, but again, there's no doubt that they were happening.
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Post by Infinity Blade on Jul 11, 2018 17:18:20 GMT 5
Not quite. According to Table 2 of Ford & Reeves (2008), estimates for the blue whale's speed in the scientific literature don't go any higher than 37 km/h (the more recent ones from 2002 seem even more modest at 32-36 km/h). The only whales thought to reach sprint speeds equivalent to or approaching 50 km/h (according to that table) are the sei and fin whales (48 and 50 km/h, respectively), but these were either estimates or the methodology behind them was not provided in their original sources (they were not satellite or GPS tracked). Besides, given how the sources for these figures are from 1917 and 1957 respectively, I find them to be wanting, considering how speed estimates during these years undoubtedly lacked scientific standards of accuracy we'd expect today (keep in mind, it was in the '40s and '50s when we got those ludicrously high swimming speed estimates for sailfish, which modern works do not support; Svendsen et al. 2016).
Top speed actually does seem to be limited in swimming animals in general, though not for the reason of body mass. At least in shallow depths, large swimmers (including fish and cetaceans) are limited by cavitation effects that cause tissue damage to the caudal fin; these cavitation effects begin at 10-15 m/s (Iosilevskii & Weihs, 2008). So while I don't think it's necessarily impossible that any of the aforementioned whale species could swim that fast (especially the ones more predisposed to speed), that would be bordering on the limit.
References:
John K. B. Ford; Randall R. Reeves. (2008). Fight or flight: antipredator strategies of baleen whales. Mammal Rev. 2008, Volume 38, No. 1, 50–86. Printed in Singapore.
G. Iosilevskii; D. Weihs (2008). Speed limits on swimming of fishes and cetaceans. Journal of the Royal Society Interface. 2008, Volume 5, No. 20, 329-338.
Morten B. S. Svendsen, Paolo Domenici, Stefano Marras, Jens Krause, Kevin M. Boswell, Ivan Rodriguez-Pinto, Alexander D. M. Wilson, Ralf H. J. M. Kurvers, Paul E. Viblanc, Jean S. Finger, John F. Steffensen (2016). Maximum swimming speeds of sailfish and three other large marine predatory fish species based on muscle contraction time and stride length: a myth revisited. Biology Open. 2016, Volume 5, No. 10, 1415-1419.
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