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Post by Life on Apr 21, 2016 11:59:32 GMT 5
Any response to claims of Pimiento so far? Grey? |
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Post by Grey on Apr 21, 2016 12:18:24 GMT 5
I think the exact paleoecology of meg is the next in Pimiento's research.
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Post by Life on Apr 21, 2016 12:25:48 GMT 5
Very true. Teeth don’t tell you everything. There are tons of limitations to what teeth can tell us, e.g. about size, anatomy, physiology… But there are also things that teeth are comparatively good at telling us, and using teeth to draw data about their owner’s diet is among the more warranted lines of inference considering that there is a very direct link between both. And correctly so, in a way, since it does have that capability and has at least occasionally done so. As far as large aquatic predators are concerned, it’s reasonable to consider that a big-game-hunter, since even the most macrophagous apex predators still have generalist diets and largely subsist on animals smaller than themselves (the only exception that comes to mind are some orca populations that specialize in baleen whales, but see the next point). All the more so considering Pseudorca’s behaviour is nowhere near that well-studied owing to its generally pelagic habits. As you remark correctly, not even all killer whales are big-game hunters, but the species is usually considered a big-game hunter (even though it has a very varied diet); some of its members somewhat regularly hunt big game, that’s enough. AFAIK the teeth of the various types of orcas aren’t much different from one another, except when it comes to wear patterns, and some of those engage in big-game hunting, which means that the functional anatomy of the species overall is suitable for it. I.e. other’s could do it too (at least as of now, eventually O. orca will have undergone speciation), but they specialize in different prey on a cultural basis. Much like some humans don’t eat meat, but it doesn’t mean they, or humans overall, are incapable of it, or not physically adapted for it (don’t get me wrong, I don’t think there are orcas who have ethical problems with eating other mammals, but orca hunting techniques still include lots of learned behaviour that is segregated between the different ecotypes). Hence why I wrote "potentially macrophagous". You seemed interested in whether there were potential odontocete competitors, and there are. The evidence for it is relatively thin (large, robust teeth with thick enamel caps and pronounced tooth wear, with pronounced similarity to those of relatives for which we have more substantial data, e.g. Lambert et al. 2014), the evidence against it is non-existent. If they were, that would be more consistent with the hypothesis. The irony is that P. crassidens was indeed described from a fossil and considered extinct, though extant individuals were discovered later on. Owen’s description sadly seems to be devoid of inferences about its diet, otherwise that would have been a fun way to test this. But by the same logic, we cannot prove C. megalodon was a big game hunter either. The largest confirmed prey items are what? 7m cetotheres? That’s not any bigger in relation to the shark than a common dolphin or tuna is in proportion to P. crassidens. So obviously in any extinct taxon, more is being considered than trace-fossil evidence when determining its ecology. creature386: …at which a larger number of smaller individuals might be at an advantage. Lambert, Olivier; Bianucci, Giovanni; Beatty, Brian L. (2014): Bony outgrowths on the jaws of an extinct sperm whale support macroraptorial feeding in several stem physeteroids. Naturwissenschaften 101 (6) pp. 517-521. I agree with your assessment but my point is that modern raptorial delphinds do not give the impression of being (avid) big-game hunters irrespective of their biological capabilities. They don't have immense dietary requirements (due to moderate size) and can subsist on a diverse diet. Therefore, I don't think that their ancestors would be too keen about challenging Megalodon for access to available food sources during Pliocene. Megalodon, on the other hand, could not afford to be as much flexible in its dietary choices because it would grow a lot bigger at some point and would likely starve at gigantic sizes in absence of sufficient food supply. B/W Thanks for bringing that paper to my attention. It is informative. As for lack of evidence of Megalodon being a big-game hunter in the fossil record? You are wrong about this. Paleontologists have noticed bite-marks on the bones of large whales (much larger then 7m Cetotheres); bite-marks that were the result of trophic interactions with Megalodon. Of-course, these occurrences could be interpreted as scavenging attempts but we also have this example to consider: onlinelibrary.wiley.com/doi/10.1002/oa.1199/abstractMoreover, examples of Megalodon teeth suffering damage during trophic interactions: fossilcsi.blogspot.com/2014/02/megalodon-attack-bite-marks-indicate_19.html |
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Post by Life on Apr 21, 2016 12:31:43 GMT 5
I think the exact paleoecology of meg is the next in Pimiento's research. I think that she will come up with premature inferences. In one paper she says that Megalodon came into existence during Middle Miocene and in the next she says that Megalodon came into existence during Early Miocene. This is confusing. Researchers such as Robert Purdy and Mike Sivverson need to step-up now. |
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Post by theropod on Apr 21, 2016 13:33:18 GMT 5
Life If we consider the pathology described by Kallal et al. was a predation attemptk, then it was unsuccessful. But yes, it is impressive. If we consider that though, we must also consider Pseudorca attacks on sperm whales. Broken teeth are about as indicative of big-game hunting as worn teeth, wouldn’t you agree? In that case, yes, there is evidence for Pliocene physeteroids too. No idea about O. citoniensis, as I very much doubt anyone here has actually read its description.
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Post by Life on Apr 21, 2016 13:41:41 GMT 5
Life If we consider the pathology described by Kallal et al. was a predation attemptk, then it was unsuccessful. But yes, it is impressive. If we consider that though, we must also consider Pseudorca attacks on sperm whales. Broken teeth are about as indicative of big-game hunting as worn teeth, wouldn’t you agree? In that case, yes, there is evidence for Pliocene physeteroids too. No idea about O. citoniensis, as I very much doubt anyone here has actually read its description. My friend, a juvenile Megalodon was involved in that case (estimates of TL vary from 4-8m but 6m seems to be most likely). Bite-marks on the remains of the victim clearly resemble a shark-like jaw structure being involved. Moreover, this shark went after the rib-cage area of the victim which is typical of Megalodon's attacking strategy (as noticed by Dr. Kent in his study). Still, this shark was powerful enough to bite right through the flesh and blubber of the rorqual-like whale and make contact with its rib-cage. The shark got away with a mouth-full or enough to quench its hunger for a period of time while the victim perished after a few days because of the injuries it had suffered during the attack. A great white shark doesn't takes chances like these and raptorial delphinids do not attack in this manner. An adult Megalodon would have taken that whale down fair and square. |
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Post by Grey on Apr 21, 2016 14:45:00 GMT 5
I think the exact paleoecology of meg is the next in Pimiento's research. I think that she will come up with premature inferences. In one paper she says that Megalodon came into existence during Middle Miocene and in the next she says that Megalodon came into existence during Early Miocene. This is confusing. Researchers such as Robert Purdy and Mike Sivverson need to step-up now. I think she's thirsty for publication but I don't believe she's that premature, megalodon's date for first occurence is fluctuating since a long, and 15 million years was somewhat of a consensus since a long time. 28 millions years is probably due to a reworked tooth. Regarding the size of the "large whales" prey items, I wished Purdy was more precise about this, even if Kallal et al. is an interesting case. Theropod, I don't think I would consider Pseudorca's feeding on larger whales as comparable predation attempts or then the cookiecutter shark is the most epic marine macrohunter! Given that the ‘frontal’ (read on) was over a metre long, and given the discrepancy in size between a metriorhynchid and an adult Leedsichthys, this interaction might imply that metriorhynchids acted in a similar fashion to cookie-cutter sharks: that they swam up to giant animals and took chunks out of them. As mentioned earlier, interactions of this sort have been observed in cetaceans, as False killer whales Pseudorca crassidens have been filmed biting chunks out of Sperm whales Physeter macrocephalus (Paul 1998).scienceblogs.com/tetrapodzoology/2009/07/02/biggest-ever-fish-has-been-revised/ Relative to jaw size, the teeth of the false-killer whale Pseudorca are perhaps the largest of any odontocete (with the exception of the enlarged tusk of the narwhal Monodon), but marine mammals seem to form a minor part of its diet and most prey are fish and squid (Stacey et al. 1994).McHenry 2009. But maybe the shark in Kallal et al. was graze feeding after all? |
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Post by theropod on Apr 21, 2016 16:47:30 GMT 5
Whether we call them predation attempts is a semantic issue. It’s just that the fact that a 7.4m shark bit a sizeable rorqual in the chest, and that the rorqual died a few weeks later, plausibly from infection of the wound, is no more indicative of anything than that it bit the whale, that it did not kill the whale in that attack and the whale died a few weeks later. Surely a sperm whale could potentially die from an infected Pseudorca bite, that doesn’t really say a lot about the Pseudorca’s ability to kill sperm whales.
The fact that Naish compared such different animals as metriorhynchids, Pseudorca and cookiecutter sharks only means we should consider it an analogy for Kallal et al.’s attacker too.
However, I think there’s a notable size-based difference here. What a cookiecutter shark does is ectoparasitism, there’s little risk to either one of them because the shark is very small. It’s an entirely different story to be flesh-grazed by a 6m animal; even though both try to do the same thing, they do it on an entirely different scale. Just like being bitten by your pet lizard is harmless, or at best a little bloody, being bitten by a komodo dragon in the same manner is life threatening–but you are also less likely to let that komodo dragon come to you and bite you.
Now I think this is straying a little too far off topic. The point I want to make is simply that we cannot exclusively rely on actual trace-fossil evidence of predation, and that large, robust, enamel-covered teeth in a cetacean, morphologically equivalent to those of (other) stem-physeteroids like Acrophyseter, for which big-game hunting has been proposed, are indicative of their owner too being able to prey on large animals.
In any case, the majority of prey items were a lot smaller than the predators, and this is a general trend among oceanic macropredators (which only the Antarctic type-A killer whale diverges from). It’s the case in Pseudorca, and it’s the case in the great white. Based on fossil evidence, it was the case in C. megalodon too. That doesn’t mean they weren’t/aren’t capable of taking large prey, and it doesn’t mean their functional morphology being adapted for that is a useless trait for our purposes.
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Post by Grey on Apr 21, 2016 17:24:15 GMT 5
Flesh grazing distinction is that it doesn't kill. The cookie cutter and Pseudorca analogy stands, no matter the respective size difference, the feeding purpose is the same. And it could be the same with Kallal case, I don't think the death of the whale is considered consequent to the bite.
Either the shark from Kallal et al. was extremely agressive with unrealistic ambitions or it was a flesh grazer with no killing attempt.
I agree on the remaining part, it seems likely there were some occurences of big mysticetes but the vast majority of the whales predated were certainly smaller than meg, if not all if some of the upper sizes estimates for meg are true. But the exact size range of the whales predated by meg in its 20 millions years of existence needs to be evaluated.
Is it possible to make a total size estimate for a whale based on a rib width? There is a notable whale rib found by Bill Heim with clear meg bite marks on it. The measurements of the rib are available. Would be interesting to get another potential size prediction for meg preys range.
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Post by theropod on Apr 21, 2016 17:29:32 GMT 5
That’s a good question. I don’t know whether it’s good for more than a ballpark estimate, rib shaft widths are rarely reported and variable throughout the individual ribs.
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Post by Life on Apr 21, 2016 18:16:20 GMT 5
Whether we call them predation attempts is a semantic issue. It’s just that the fact that a 7.4m shark bit a sizeable rorqual in the chest, and that the rorqual died a few weeks later, plausibly from infection of the wound, is no more indicative of anything than that it bit the whale, that it did not kill the whale in that attack and the whale died a few weeks later. Surely a sperm whale could potentially die from an infected Pseudorca bite, that doesn’t really say a lot about the Pseudorca’s ability to kill sperm whales. That example says a lot about the nature and dietary preferences of the shark [in question] at minimum. Whether the whale perished due to resultant infection or not, is a secondary thing; shark bites can result in infections. However, point is that a juvenile Megalodon sealed the fate of that huge whale. Based on this evidence, we can infer that an adult Megalodon could tackle a large whale (and likely did so). The fact that Naish compared such different animals as metriorhynchids, Pseudorca and cookiecutter sharks only means we should consider it an analogy for Kallal et al.’s attacker too. No! We cannot. None of those creatures could inflict an injury of such proportions on a whale that large. Authors can choose to look at different possibilities but careful (and critical) observation leads to one conclusion: a Megalodon juvenile was the culprit. However, I think there’s a notable size-based difference here. What a cookiecutter shark does is ectoparasitism, there’s little risk to either one of them because the shark is very small. It’s an entirely different story to be flesh-grazed by a 6m animal; even though both try to do the same thing, they do it on an entirely different scale. Just like being bitten by your pet lizard is harmless, or at best a little bloody, being bitten by a komodo dragon in the same manner is life threatening–but you are also less likely to let that komodo dragon come to you and bite you. Indeed. In any case, the majority of prey items were a lot smaller than the predators, and this is a general trend among oceanic macropredators (which only the Antarctic type-A killer whale diverges from). It’s the case in Pseudorca, and it’s the case in the great white. Based on fossil evidence, it was the case in C. megalodon too. That doesn’t mean they weren’t/aren’t capable of taking large prey, and it doesn’t mean their functional morphology being adapted for that is a useless trait for our purposes. Not necessarily true for Megalodon in particular. In several documented cases of trophic interaction between cetaceans and Megalodon, I have seldom noticed a 6 or 7 inch tooth being responsible for the damage or found stuck in the remains. Smaller teeth have been found in association with such remains much more often. Culprits seem to fit within 8 - 11m in TL range on average in such cases. I believe that we are less likely to find remains of victims of a truly massive Megalodon due to the sheer extent of damage such a monster could inflict and much greater likelihood for the victims to be entirely consumed in the aftermath of such trophic interactions. |
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Post by Grey on Apr 21, 2016 22:15:27 GMT 5
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Post by theropod on Apr 21, 2016 23:36:41 GMT 5
That’s a fascinating find. So it seems it was quite premature of us to assume giant raptorial physeteroids went extinct in the Miocene. I wonder about the exact nature of its relationship with Livyatan, but I’m not sure how much of a case for or against synonymy can be made from a mere tooth. I’m also not that convinced by size estimates other than ballparking made from it, but the notion that it was a growing individual (while not very surprising, since most adult sperm whales are still growing) deserves further elaboration. Quite a coincidence that the finding was reported today. There are photos in thes articles: www.abc.net.au/news/2016-04-21/giant-sperm-whale-fossil-found-on-melbourne-beach/7348230www.heraldsun.com.au/news/victoria/giant-beaumaris-tooth-reveals-monster-whale-stalked-our-seas/news-story/d61991da22dc111a1bc3b0e6ce9538ea?nk=db446ea4b2194ed21529c6f0ed036d70-1461263177au.news.yahoo.com/technology/a/31405184/5-million-year-old-giant-killer-whales-fossilised-tooth-discovered-at-melbourne-beaumaris-bay/Looks a lot like Livyatan’s teeth indeed. Not really, otherwise why don’t you consider false killer whales to be big game hunters on the basis of them occasionally biting very large animals? As can any bite. But I don’t consider the predator to be responsible for the work of bacteria. It seems infection did. If the juvenile megalodon had killed the whale, it wouldn’t have lived for at least another two weeks afterwards, having sufficient time to show significant bone remodeling. I don’t doubt that at all, I’m very confident that the bolded part is true. The point is that you need to infer it, you cannot directly observe that it happened. That’s not much different to inferring that an animal was a big-game hunter on the basis of its teeth (though admittedly its teeth are my main basis for inferring megalodon was a big-game hunter, I don’t really see where that a whale can die of infection is more relevant than that). We know next to nothing about the precise size of the whale, nor the size or severity of the wound, so how can you be so confident that, say a false killer whale, would not have been able to cause a similarly severe injury? Kallal et al. themselves considered a false killer whale as a potential culprit, but excluded it on the basis of its more closely spaced tooth tips. Which reminds me, Pseudorca sp. is another macrophagous cetacean known from the Pliocene according to Kallal and colleagues. But in the light of what grey just posted, that seems to be of secondary importance. Primarily we are less likely to find them because there were very few megalodons that size (given you and me are talking about the same thing when saying "truly massive"). And do sharks ingest the entirety of large tetrapod prey items? In that case, shouldn’t there be an abundance of extremely large, extremely bony coprolites? Also, aren’t you suggesting that "truly massive" megalodon must have fed on proportionately smaller prey by saying that it would be more likely to consume it in its entirety? It certainly isn’t going to do that with a whale its own size. Could you name some examples, I’m not aware of a huge lot of such associated remains, much less ones where there are data on size. |
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Post by elosha11 on Apr 22, 2016 17:40:08 GMT 5
Extremely interesting. It seems like either Livyatan or a very similarly sized raptorial sperm whale lived into the Pliocene. If this tooth is Livyatan, it also suggest the species was capable of trans-Pacific travel, as it is about a 15,000 km straight trip from Peru (where Livytan skull was found,) to Australia, where this tooth was found. And given the migratory habits of Livytan's presumed cetacean prey, it makes a lot of sense that it would a pelagic species, and not one inclined to only South America. The tooth looks extremely similar to Livyatan's, and in fact given its robustness and length, which far exceeds that of other known raptorial sperm whales, I'm inclined to believe this is another example of the Livaytan soecues. The 18 meter length and claims that it was still growing are both speculative and likely an exaggeration, made in the excitement of the discovery. A larger 36 cm tooth associated with the whole Livyatan skeleton yields a 13.5 - 17.5 meter range, so a smaller 30 cm tooth should not yield a larger size estimate. Nor can I figure out why the scientist quoted states it was 18 meters long and still growing, unless he's accounting for the fact that larger Livytan teeth have been found. But in that case he should have clearly stated he believes this to be a Livyatan tooth and said that this animal was likely a bit smaller than the published range of the holotype. If he wants, he could then surmise that the species might reach up to 18 meters. It always annoys me when scientists themselves make exaggerated or sensationalized claims to make their discovery more impressive. To me, the size isn't the most impressive part, although it does suggest a quite large Livyatan. The most exciting thing is that it shows Livyatan likely lived longer than what was previously predicted (and may have become extinct from the same factors that doomed Megalodon) and that it suggest that the species may have covered a far greater territory than previously thought. I would be inclined to put these articles in the Livyatan profile thread, but perhaps that is a bit premature. |
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Post by elosha11 on Apr 22, 2016 17:52:16 GMT 5
Life If we consider the pathology described by Kallal et al. was a predation attemptk, then it was unsuccessful. But yes, it is impressive. If we consider that though, we must also consider Pseudorca attacks on sperm whales. Broken teeth are about as indicative of big-game hunting as worn teeth, wouldn’t you agree? In that case, yes, there is evidence for Pliocene physeteroids too. No idea about O. citoniensis, as I very much doubt anyone here has actually read its description. My friend, a juvenile Megalodon was involved in that case (estimates of TL vary from 4-8m but 6m seems to be most likely). Bite-marks on the remains of the victim clearly resemble a shark-like jaw structure being involved. Moreover, this shark went after the rib-cage area of the victim which is typical of Megalodon's attacking strategy (as noticed by Dr. Kent in his study). Still, this shark was powerful enough to bite right through the flesh and blubber of the rorqual-like whale and make contact with its rib-cage. The shark got away with a mouth-full or enough to quench its hunger for a period of time while the victim perished after a few days because of the injuries it had suffered during the attack. A great white shark doesn't takes chances like these and raptorial delphinids do not attack in this manner. An adult Megalodon would have taken that whale down fair and square. I agree that this was likely a juvenile Megalodon and that it was an impressive bite. But we have to be careful about drawing too firm of conclusions because we do not know and will never know, the exact circumstances of the attack. The whale could have been sick and dying already, and the Meg could have been part of a larger group of sharks/other predators attacking it. We see that today with tiger shark groups attacking sick baleen whales. The rorqual could have died from its sicknesses, from this bite, or from multiple bites from multiple predators. Or it could have died from something else all together. All we have is a fraction of a rib to go on... Or the whale may have been perfectly healthy and the Meg's bite led to its eventual death days/weeks later. Or it could have died from completely unrelated causes. All we know is that likely a juvenile Meg took a bite out of sizeable rorqual whale which did significant damage. It suggest a very powerful and lethal bite to so damage even a large whale, but that's really all we reasonably infer. |
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