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Post by theropod on Aug 1, 2018 17:55:36 GMT 5
Yes, that is what I am saying. The measurement and position is very unequivocally given and illustrated by Lambert et al. 2010 and 2016. D1 is the shortest preserved tooth, although it wasn’t the shortest in the entire dentition. And the 36cm teeth are from the mid-dentary, not the upper jaw, and probably weren’t the longest in the dentition either.
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Post by Grey on Aug 6, 2018 6:50:48 GMT 5
Grey: Yes, the uncertainty of position assignment is certainly a problem. The way I see it, that may well be a problem that can not be eliminated given that one insists on using isolated teeth to produce size estimates. A valuable input would be an attempt to more reliably and objectively estimate the position of a given tooth in the dentition, perhaps through morphometric methods. But the way I understood it that is not what your research deals with at all, in fact using any isolated tooth to suggest larger sizes your method has the exact same problem as Shimada’s. Hum I'm not sure to have understood this. Can I suggest you to write shorter lines ? It was always a problem in our old discussions, I'm fluent in English but it is not my mother tongue either and at times it's difficult to follow you ! The way I see it is that those isolated teeth, either the Beaumaris and the Chilean, do not seem to have stroke the people who have observed them as being teeth of a larger size for their would be position. I certainly asked this to Bianucci but he seems unconvinced by this. I know Fitzgerald, about the Beaumaris tooth, suggested 18 m as an upper range (simply using the Lambert et al. 2010 upper range) but rather guess estimated the sperm whale behind it at around 15 m (assuming the Peruvian holotype was 18 m). We should wait for a detailled description of this material. I have seen other giant teeth from Australia found later but they are, apparently, not bigger than the Beaumaris tooth. Where did Lambert et al. 2016 write the Livyatan holotype was "fully grown and old"? If anything, they mention open pulp cavities in the holotype, which in Physeter are filled in late ontogenetic stages, but they do acknowledge that this process can take place very late and adults can also have open pulp cavities. And once more, whales do keep growing significantly after attaining sexual maturity too. I’ve just recently posted a paper that found bottlenose dolphin males reached sexual maturity at an average 70% of adult mass. I’ve also already posted evidence that Physeter keep growing after maturity years ago. The average size of the whales does not just consist of animals that have stopped growing. So we can’t just nitpick only the oldest and largest adult sharks for this comparison. Regarding average and maximum size, I already acknowledged you may well be more interested in maximum size because of the second point, but as for the first and third, you suggest it is more "scientific" or "precise" to assume the single known individual was, say, among the biggest 10% of the population? Yes I referred to this quote from Lambert et al. 2016 and as you write, this do suggest a fully mature individual. Interesting points regarding the growth data you refer in odontocetes. But is there anything to suggest the holotype was still growing ? If so by how much ? I've always been inclined to compare the Livyatan holotype to the adult meg dentitions specimens from Aurora or from Chile. The Aurora set suggests 15-22 m and 17-20 m excluding outliers and juveniles in the base group. A more complicated matter comes here, the Chilean specimen is apparently even larger than the Aurora (to be confirmed...) but, statistically, why shouldn't it be assumed as an average size specimen ? Based on the dentition based method, the Aurora meg would be noticeably larger than the Livyatan holotype. I don't say there is any evidence of that but the simple fact there is zero material (like so much larger dental elements to would preclude any doubt about larger sizes) makes me doubt presently it was a strictly average-sized individual. Plus, average-size is a very ambiguous term, most sperm whale data considers the average size of bulls at 16 m, but McClain 2015 states it is 14 m. If so, even if the holotype was an average sized specimen, a slightly smaller individual could be considered as such too. This is why I only stick with the data. The holotype is estimated at 14-17.5 m based on the actual data but I don't see any data yet that would suggest it to be an obligate average-size specimen. However, I have no issue comparing it with adult meg dentitions, or even juveniles for that matter. There are far too much unknown factors here. Would the grip of the whale be that solid and prevent any powerful tail slap ? Wouldn't the shark be able to turn around, depending its actual flexibility, and bite its opponent ? The simple fact to suggest to whale would necessaril grip and try to suffocate its foe is a rather wild assumption. This is why I tend to focuse of the physical capabilities of the opponents, and I avoid most assumptions regarding behavior and specific contexts. This is why I don't have much interest in sam1 scripted fights (pun intended). Correct, the "sharkzilla" model. The teeth in the sharkzilla model are significantly smaller than the largest on records. Ciampaglio said me he used Gottfried and Shimada method but at the same time, I think the teeth in it were at most 6 inches in slant length. Simply put, consider a Bertucci's jaws-like dentition compared to this model. The volume extracted would be considerably larger. My point regarding Malta is that, a 20 m meg could be as well relatively smaller-mouthed or larger-mouthed, depending the model you use at the base. Malta as quite small teeth for its length (thus suggesting larger body size for meg) yet its mouth is still normally wide for a GWS individual. |
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Post by theropod on Aug 6, 2018 12:56:30 GMT 5
Hum I'm not sure to have understood this. Can I suggest you to write shorter lines ? It was always a problem in our old discussions, I'm fluent in English but it is not my mother tongue either and at times it's difficult to follow you ! I will try. You do realize you are at a computer though? If my lines are too long for comfortable reading, feel free to simply insert linebreaks. My point was this: You point out the uncertainty of position assignment (or wide range of plausible positions for a single tooth) as a weakness of Pimiento et al.’s or Shimada’s method. That is certainly true. But that is a problem you are going to have with any isolated tooth, unless you find a way to more precisely and reliably determine its position. So that problem does not go away, no matter what method you use for estimating overall size from the measurements of a tooth. An assumption as to that tooth’s position will always be implicit in that estimate. Unless you discount isolated teeth alltogether. Which would certainly be valid, but it is not what you are doing.
I was suggesting that a geometric morphometric approach might present a way to more accurately determine the position of an isolated tooth. That is, if teeth turned out to cluster in a PCA depending on their position, and the corresponding positional assignment was confirmed by comparison with an associated tooth set. Certainly something I would like to look into in the future, but collecting the data will take a long time, especially since most of the tooth sets are not properly described (and the only one that is, in Japanese).
Neither did they strike them as smaller. The crucial problem here is that the people observing them, and we for that matter, have no real idea as to the position. At this point, the teeth could come from an animal smaller than the holotype, or larger, or the same size. This is actually affected by the exact same problem as with C. megalodon. A couple of isolated teeth are poor evidence of anything, we don’t even know for sure that they are the same species. You are taking the well-justified caution and reluctance to say anything about the exact size of the owner, which I share, to mean that it was smaller. In reality, it means it could realistically be smaller or larger, we simply don’t know.
Totally agreed! And until (if at all) that description demonstrates a reliable positional assignment and size estimates for the owners of these teeth, as well as the likely specific assigment to L. melvillei, they have no bearing on the latter’s average size.
I did not quote anything from Lambert, and nothing in there even directly indicates "a fully mature individual", though that is more than likely given its size. As I wrote, Lambert et al. 2016 seemingly report open pulp cavities.
In old Physeter, those get filled in.
But Lambert et al. acknowledge that it is a highly variable feature and even fully mature specimens can have open pulp cavities. Fully mature may either refer to sexual of physical maturity…
Since the vast majority of odontocete specimens in nature are still growing (McClain reported that 95% of all Physeter in their dataset were below 15m, average for males at physical maturity is 16…), where is the evidence that it was not?
I don’t think we can resolve this matter without analysing tooth histology. In all honesty, it’s strange this hasn’t been studied yet, but maybe Gilbert et al. 2018 will draw some scientific attention to it. I do get that they are hesitant about sawing open or core-drilling one of the teeth, but in my lab this is done all the time on equally rare dinosaur bones… As I am well-aware. Maybe we can compare it to other dentitions such as the Yorktown and Japanese ones too, in order to not give the appearance that we are only using the large megalodon dentitions and discounting the ones that are smaller? If it is larger than the Aurora set, then you just answered that yourself. If we have two measurements, one bigger than the other, then neither of the two is the average, the mean between the two is. But those two are not the only megalodon dentitions. to begin with. I don’t have any measurements of the Aurora or Chilean dentitions (where are those being stored btw?). It would be cool if you could share them, so that the rest of us can also have part in that discussion. You say the Chilean dentition is bigger, so you must have some measurement at hand that indicates this, right? Also btw, could you post the measurements of the Aurora dentition? I apologise if they are on your poster but I missed it, but the pdf is not working (shows just an empty page), I’ve been reading it by copying the online version (too small to read) on researchgate into a text editor…
But there are other megalodon dentitions whose owners were clearly smaller than the Livyatan holotype. And if you keep referring to isolated teeth supporting even larger sizes, you must also acknowledge that the vast majority of isolated teeth actually indicate far smaller sizes, strongly suggesting that the Aurora dentition is not average-sized. What’s your current mean estimate for Aurora, and the corresponding SD?
But average-sized is the null-hypothesis, if you want to suggest it is unusually large or small for its kind the burden of proof rests on you, as that is a decidedly less probable option based on known cetacean (pretty much any animal, really) population structures.
"Most data"? Such as? McClain et al.’s figure is probably more accurate, considering males reach sexual maturity at an average of 12m, but stop growing at an average of 15.85m (Lockyer 1981). 16m is definitely wrong.
There is nothing ambiguous about average size, it’s just have to specify what kind of sample you are talking about. As scientific studies to. For example Lockyer 1981, who clearly specified that male Physeter average 12m at sexual maturity, and 15.85 at physical maturity (and additionally, 13.65m at "social maturity"). Which is naturally why sources such as Guinness Records, obscure websites, imprecise personal statements etc. are not very useful, even under the (questionable) assumption that their data are reliable, because they don’t have any scientific rigor in reporting the underlying sources and methods.
Which applies to maximum size as well, remember your quoted pages from the Guinness book regarding sperm whale size? McClain et al. recorded 8 individuals that were larger than the largest sizes acknowledged there, by up to 3m (which would mean a mass difference of 50%!). Clearly, maximum size between these works is not the same either.
I find maximum size to be a lot more ambiguous. Maximum of what? In a sample of 1? A sample of 10? in a sample of 250? Maximum in a sample of 500000? All decidedly different things, but all of them you consider to be the same.
On the other hand, take average size. Whitehead 1993 documented a sample of 13 mature male sperm whales off Galápagos. The average (mean) size of these was 14.2m (sd ±1.0m), maximum was 16.4m. McClain et al. 2015 compiled a sample of 528 169 sperm whales. The maximum was 24m. I honestly cannot find the 14m average in there, actually, though it sounds about right looking at the data. So given your average figure, average remains pretty much constant between the two, while maximum length is 46% higher, and body mass probably over 3 times higher, in the larger sample.
Surely you don’t want to tell me that average size is the ambiguous metric here?
Whitehead, H. 1993: The behaviour of mature male sperm whales on the Galápagos Islands breeding grounds. Canadian Journal of Zoology 71:689–699.
Lockyer, C. 1981: Estimates of growth and energy budget for the sperm whale, Physeter catodon. FAO Fisheries Series (FAO).
Or a slightly larger one. Your point? That is merely statistically the most likely option. You can’t tail-slap something that is holding onto your tail any more so than you can slap a crocodile biting your arm with that same arm. That remains for you to demonstrate. No, it is an assumption based on how extant raptorial odontocetes kill prey, specifically sharks. Everything I wrote is informed by the respective abilities inferred from functional morphology. I am not making up some imaginative scenario where the whale uses advanced military strategy to overcome its opponent. I am suggesting it will use its jaws to do what they do best, grip, and that this approach can very well be deadly to the shark since all the whale would have to do is hold it in place. It is not outlandish to think that the whale would know to do that, and it is certainly not outlandish to think it would be physically capable of that. |
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Post by Grey on Aug 31, 2018 21:14:23 GMT 5
Finally, I can respond.
My point is that so far, all the isolated teeth I've seen from Livyatan don't have a size and shape that hints at something interesting regarding differently sized specimens.
The quote from Gilbert 2018 about teeth still growing in full grown odontocetes within a same species further discourages to investigate more on this way.
However, I'm certainly open to any additional observation here.
In an earlier communcation, Lambert said me the holotype was an adult.
My point is that none of the descriptions of the material suggest an animal that was still growing when it died. The main difference with McClain data is that those sperm whales were killed by whalers, which has different implication than an animal that presumably didn't die after a predation event. I definitely agree that sawing one of the teeth should have been done already as it has been done for other physeteroids (Gilbert 2018).
I need to check my emails to be sure where are those sets. I know Hubbell owns severals. You can by yourself check the Aurora dentition measurements (from the Yorktown Formation) in Pimiento's thesis. Strange that you can't read it, I have it on my android as well.
The other megalodon dentitions come from animals in the 9-12 m range, so definitely in a lower ontogenic status than the Aurora and Chilean dentition. So you can compare their data with the Livyatan holotype but obviously you'll compare here immatures sharks with an adult whale.
The vast majority of the teeth are not smaller than those you can find in the Aurora dentition, even less when you discount all the teeth coming from neonates and juveniles individuals.
The first upper anterior from this is 108.5 mm wide. This is no especially large for the adult teeth.
More will be said at SVP 2018 but since the abstract will be available in few hours/days, I can put here that the mean size for the Aurora dentition, removing outliers, is 16.68 m. But I have a caveat with this that I will develop later.
There is as much evidence for the Livyatan being an average-sized individual than being quite large. However there is no indication it could be a somewhat smallish individual. My point is that finding a specimen being 2 m shorter could also make it an average-sized individual. There is a lack of data that prevents me to consider such a statement seriously.
I certainly agree there were larger individuals, I can't agree yet the holotype is an obligate average-sized individual.
This is certainly something I could revise though but current data just doesn't support that strongly. On the other hand, there are plenty of material significantly larger than the dental elements in the Aurora Carcharocles dentition.
You miss my point. It is ambiguous in the case of Livyatan itself. You're justifiably looking at the data in sperm whales populations samples. But there is no population sample for Livyatan, so no mean to rigorously assign it as an average-sized individual.
What I mean by ambigous is that the individual could be a bit larger or smaller, it could still be considered an average sized individual.
As for the maximum size, you just need to precise the sample and the context of the statement. Following my last post in the Meg size thread, it can be argued just as justifiably than the maximum size of the short-fin mako is as well 4.45 m than 5.85 m.
I highly doubt the discrepancy between the strenght of human arm and crocodile jaws is comparable to a megalodon caudal fin strength of the jaws of Livyatan.
Until I see evidence of great-toothed odontocetes doint this on a similar/larger-sized white shark, I stay skeptical at this.
The well known photograhy of a shark bite mark on the dorsal of an orca shows that even a smallish, prey item shark can do this to a much larger, powerful opponent.
Based on this, at the minimum an adult megalodon would be able to do the same, only the consequences of a megalodon struggle would be different than a small shark biting a larger orca in defense.
But only performed on sharks 2, 3 or 4 times lighter than those raptorial odontocetes.
I'm mainly skeptical about the last part of your quote. I find it doubtful that it could/would be physically capable to do that on a dangerous foe as large or larger than it is.
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Post by theropod on Aug 31, 2018 23:09:11 GMT 5
Observation: Most animals of a species cluster around the average size. Inference: a randomly sampled individual of that population is therefore likely to be close to that average size, as opposed to one of the extremes. I.e. if we have a single individual, the most likely size of that individual is average-size.
You just agreed with what I’ve been telling you all along, that isolated teeth don’t provide any solid evidence for rejecting the null-hypothesis that the Livyatan holotype is a typically-sized individual of its species.
Without histological sampling, I’m not sure he could actually know this. But I agree that it is most likely.
None of them suggest an animal that was not growing any more. The vast majority of adult Physeter individuals are still growing. It is therefore most likely that the Livyatan holotype was too.
That is complete speculation, we don’t know how the Livyatan holotype died. Whether it was disease, injury, predation, stranding or something else. But dieing of old age is very uncommon in wild animals, so I don’t get why you keep making that your deafult assumption here.
I can read it, it’s just very impractical. I cannot download the pdf file though, when I do so, I only get the first page (author information), not the actual poster.
How do you know they are immature?
That would put the shark well within the error range of the Livyatan holotype in terms of size.
Because there is no indication for any of this! These indications you expect simply don’t exist.
The odds of finding one 2m shorter are just as high or low as those of finding one 2m longer.
Merely more strongly than any of the alternatives.
And plenty that are smaller.
No, I think you miss mine. Whether its Livyatan or Physeter doesn’t matter. But average-sized individuals are the most common, and hence the most likely. Hence, why even across several orders of magnitude of discrepancy in sample size, average size is a fairly stable proxy for size, while extreme size is not. And 1 is a very small sample size. There is nothing ambiguous about that. But if you insist to compare what can be quantified as large in a sample of hundreds of sharks to the largest individual known in a sample of exactly a single whale, we’re going around in circles.
Take a crocodile biting another crocodile’s tail then. That should be a balanced comparison, as the two are similarly strong. Strenght is not the key though. You simply cannot slap something that is firmly holding onto whatever you want to slap it with.
The question is whether the shark could dislodge the physeteroid once the latter has secured a hole. On this, I strongly suspect we disagree. Everything about Livyatan’s biting apparatus is optimized to be able to securely hold onto struggling prey. As I already showed, Orcinus can hold onto struggling Physeter. Crocodiles can also hold onto struggling prey similar to their own size with their jaws. I don’t see why Livyatan would be deficient in that regard, it’s jaws and teeth are clearly perfectly suited for that task.
I’m not questioning the ability of a shark to bite a whale, I am questioning the ability of a shark that is firmly grabbed by the tail to do so.
Do what exactly? Unless you know the exact circumstances of how the shark bit the orca, the only thing that shows is that a shark can bite an orca. Certainly C. megalodon could bite Livyatan in a variety of situations. I’m just not convinced that when grabbed by the tail it could turn around 180 degrees to bite its opponent (all while suffocating).
That is correct, but only with regard to sharks. I think I have already provided the accounts of orcas showing their physical capability to manipulate prey items larger than themselves though (Pitman et al.). Those were sperm whales, not sharks, but if a sperm whale is unable to resist being dragged away by an orca smaller than itself, then it stands to reason that a raptorial physeteroid firmly holding a similar-sized shark’s tail in its bone-crushing jaws could effectively immobilise the shark too.
This looks like we’re back to the lack of parity interactions between the two. Of course animals will always choose the easier prey, i.e. the individuals that are smaller or otherwise less capable of defending themselves. So predatory interactions will reflect that. Hence why 5m orcas kill 3m great whites, not 6m ones, and why great whites take down 3m beaked whales, not 6m ones. But by your logic, the fact that no great white shark has ever been recorded killing a similar-sized odontocete would also have to make you doubt their physical capacity to do so, even though there can be no doubt that they are physically capable of killing a similar-sized odontocetes.
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Post by Grey on Sept 1, 2018 0:36:40 GMT 5
But :
- this animal presumably didn't die prematurely so quite possibly had not much to grow more.
- a smaller or larger one could be just as well considered an average-sized.
The vast majority of the Physeter individuals are animals that were killed during their lifetime, so no wonder these bulls had to grow more afterward.
The animal in anycase was not killed by whalers so died of a more classic cause, implying there are more chances it was more advanced in its ontogenic status and growth.
There are two pages, downscroll to page 2.
- comparing with Gottfried data, which is even more conservative than ours, since the Aurora individual would be more around 13 m using their equation and 12.5 m using the upper anterior with Shimada's.
- the much smaller size of those teeth compared with the larger ones.
The range of Livyatan, using Zygophyseter and Physeter data, is 14-18 m. The range of the Aurora upper dentition only using Carcharodon is 15.1-21.3 m, with a mean of 16.7 m removing outliers. Plus, the first poster shows that comparing appropriate adult stages GWS specimens in the base sample, the Aurora meg range is 17-20 m, with a mean of 18 m.
If you want to compare the mean estimates, you can also compare 16.7 m (removing outliers) or 18 m (restricted to adult GWS base) with the 14 m (removing Physeter outliers) and 16.85 m of the Livyatan holotype.
So, on a purely statistical approach, the Aurora meg, based on dentition size compared with GWS, was larger than the Livyatan holotype either based on Physeter or Zygophyseter. Of course a larger sample of Zygophyseter would help but even the non-official estimates made from Brygmophyseter or other physeteroids on this board didn't point to something larger than the upper estimate based on Zygophyseter.
While GWS dentitions statistically suggest even possible 20 m figures for the Aurora set of teeth.
This confirms that, like Parotodus, any size prediction of Carcharocles using only isolated anterior tooth size substantially underestimate the body length, producing a short shark with absurdly large jaws.
Actually, I suspect 16.7 m is a conservative mean point since using the same method, the mean size of the C. hubbelli is smaller than the size estimate derived from one of its preserved vertebra (Ehret 2009), despite this vertebra not being the largest in the animal. Something I will ponder about...
Just like there is no material suggesting Livyatan being an obligate average-sized specimen.
All the descriptions of the holotype compare its body size estimates systematically with large individuals of Physeter about 18 m, never with the average-sized male individuals of about 14 m of this species.
Lambert et al. always find more appropriate to compare it with a large individual of its modern relative for some good reasons.
Of adult teeth ? Based on what ? Won't you rather wait for all the data to be ready before arguing about this ?
11 cm wide teeth upper anterior are always regarded as a normal adult sized tooth and anteriors below 10 cm wide are usually regarded as immatures.
Or perhaps, smaller-sized populations...
That's an assumption that needs real-life support. There is no qualitative data available suggesting the Livyatan holotype is something like a 14 m bull Physeter or a 4.5 m female white shark.
My point is that it is most likely near the average size but could be as well 2 m larger or smaller than the historical average size of its species. And since there are no sacred rule in science that says the first individual of a species is an obligatory absolutely average-sized individual, there is no reason to support this fanatically. This is a possibility that no one denies but that is not established in anyway.
Since this is something never observed in real-life (a raptorial odontocete grabbing the tail of a similar-size robustly predaceous shark) and given the strongly suggested highly agressive nature of Carcharocles, this appears all to be ure conjecture. Quid of the power of the caudal peduncle ? The exact gripp of Livyatan ? How much oxygen it has ? The actual flexibility of the shark ?
Even relatively small sharks appear to be able to deliver bites on an attacking orca.
Assuming the megalodon would just be unable to do anything is dubious at best.
I question the real ability of the whale to stop by grabbing its tail an opponent its size or heavier. Suffocation doesn't happen in a matter of seconds neither.
This is so much conjecture that I see no interest into this. Such a behavior has no been observed in real life at all after all, even less a comparable one.
The physical characteristics are far more interesting because based on real material.
Because the weaponry and size of Carcharodon are a key to this potential ability, I base this on the physical traits, not on some scenario no man has even observed.
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Post by theropod on Sept 1, 2018 1:23:24 GMT 5
I am well aware there are two pages, I can see them in the preview in the webbrowser (but there I cannot zoom in), but whenever I download the file, the second page is gone. As I wrote, I did look at the poster by copy-pasting the text though. Since your research is ongoing though, I’d much prefer to be informed about the current state though than the state a year ago, as well as on details that are not on the poster. So please forgive me if I sometimes ask you things that are actually on the poster, but it’s quite a pain to look it up every time, and there’s a good chance you have updated information that would be even more interesting anyway. Define "die prematurely" please. Die before skeletal, social, sexual maturity? Not die of old age? Again, do extant animals usually die of old age? I don’t think so. Did fossilized animals usually die of old age? Certainly not, this I know. We do not know how this animal died. We have no indications whatsoever. It could very well have died "prematurely", whatever you mean by that.
I don’t get your point. You are repeating this since a while, but either I keep missing your point or you keep missing mine. If we have several specimens, the calculation of their average size is straightforward. if we have two, and one is larger, the other smaller, that means the larger one is above, and the smaller one below average size. We have only this one though, that’s the one that counts. Entirely hypothetical larger or smaller specimens are irrelevant.
One individual → greatest likelihood is it representing average size.
Two or more individuals→we take the mean of those and assume it is most likely close to the population average.
Obviously as sample size increases, this becomes more and more reliable, but that does not change the fact that even if you have only a single individual, getting an average one is still the most likely option.
Isn’t every animal that is killed killed during its lifetime?
Even if it was…McClain et al. conclude stating that 95% of all sperm whales are below 15m. That means there’s well over 95% of probability of a given sperm whale not being a skeletally mature male, as they average 15.85m at skeletal maturity. There’s a lot of room for less "premature death" in there that will still mean it is overwhelmingly more likely that this individual is not "fully grown". As you keep saying, nobody ever suggested this individual to have been immature. Well, nobody ever suggested this individual to have been fully grown. The only (very weak) evidence (that is is not) are the open pulp cavities.
And in nature too, individuals of all age classes die all the time. Often, there’s even a skew towards smaller individuals, as you very well know.
And has this been quantitatively estimated (e.g. from the size of great whites at maturity, which isn’t even clearly agreed upon in the literature), or is that a guess?
If we have several dentitions, shouldn’t we compare the average size from all of them to the average size of all great whites, and by that means extrapolate size at maturity? According to Gottfried et al.’s guesstimates at least, 12m can very well be an adult shark.
But that is estimating the Livyatan holotype from several vastly different proxies, some far more conservative than others. You are only estimating C. megalodon using a single method, specifically the one that currently produces the largest size estimates. How about only comparing that to Zygophyseter-based estimates for Livyatan, i.e. 16.2-17.5m? That is the equivalent method for Livyatan.
Lambert et al. 2010 specifically state Livyatan to be comparable in size to adult male Physeter, with reference to their dataset, which includes Physeter individuals of various sizes (but none that are anywhere close to 18m). That is what they mean by "adult male", not the equivalent of an exceptionately large, 18m individual.
You have all the data, right? So either discuss away, or don’t hint at stuff that you are not willing to discuss.
What is "usually regarded" as what is not very interesting, what there is evidence for is interesting. For example, what’s the average size of upper anteriors, how much smaller than the Yorktown dentition is is, and what’s the corresponding size estimate? With a sufficiently large quantitative data basis, it would be possible to at least offer a more or less constrained extrapolation on the average size at maturity. Right now all I see is guesswork. Certainly, if we simply classify every specimen smaller than your 16.7m dentition as juvenile just on account of being smaller we won’t be getting anywhere. This would be a lot easier if there were actual anatomical features of the teeth suggesting immature stages, but those don’t exist (excepting cusplets in neonates or embryos), right?
And a shark killing a similar-sized raptorial odontocete is also never observed in real life. That does not mean the animal is physically incapable of such a feat, it just means it has never been observed, and might not happen under natural circumstances. Under natural circumstances though, a 50t Livyatan and 50t Megalodon also wouldn’t confront each other in a one on one fight to the death.
Qualitative data? Can you please explain what you mean by that?
Where is all this data when it comes to suggesting it is something like an 18m bull Physeter or a 6m white shark though?
Here we go again. I’m not supporting this "fanatically". If even you agree that is is most likely near the average size, that’s absolutely enough for me. I don’t get why we even have to have this argument if you concede this (though, truly, if you didn’t I wouldn’t understand it either). The question is why you don’t consider this in any of your further thoughts on the matter, but keep arguing that the shark is bigger when that is not supported by any hard data?
I do base this on their physical traits too. I just explained to you how the physical traits of Livyatan would make it capable of killing a similar-sized shark under some circumstances. As you are very well aware, I don’t doubt that there are circumstances where the reverse would happen too. Physical traits as in 38cm teeth more than 10cm in diameter, in the largest tetrapod jaws known (as well as, in fact the largest preserved jaws of any animal). Saying that the whale could use these jaws to grip and immobilise the shark is no more speculative than saying the shark could use its jaws to tear out a chunk of flesh from the whale’s body. |
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Post by Grey on Sept 1, 2018 2:09:48 GMT 5
That's the point. Assuming the holotype is an obligate juvenile is absolutely not reliable at this point. I rather claim it was probably around the average size of its species.
Haha. Depends what you mean. A stranding is a killing, but the animal was, presumably, not killed by a predator and with the lack of material pointing to an even larger specimen somewhere, it could be well represent a rather large individual.
The sheer enormous size of the specimen implies to be cautious about such statements.
Nothing says the distribution of size in Livyatan was exactly similar to Physeter.
Again, I have no problem with the claim that it was near the average size of the species, just the claim it was an obligate average-sized specimen is baseless at best.
Not yet, but since even the more conservative data from Gottfried points that until 14 m it can be immature. The discrepancy with the other dentition is also indicating. Aurora is so much larger than Bone Valley that it is doubtful the later is an adult, especially since much larger teeth than those from Aurora are known.
Carcharodon produces the smallest estimates in our data, not the largest. Estimates based on makos or those using Lamna are even larger and more consistent.
You can as well use the 16.2-17.5 m from the only Zygophyseter specimen sample, several adult GWS give a range of 17-20 m for Aurora.
But, sample vs sample, the more useful data comes from Physeter since there are more specimens rather than a single Zygophyseter, not even complete.
Thus, using 14-18 m, vs 15-21 m is perfectly justifiable as it is the widest range in both, and the shark includes the base species resulting the more conservative estimates.
That's the point, it's comparable to an adult male Physeter, whatever its size.
Lambert 2016 : Based on a comparison of cranial dimensions with Physeter and Z. varolai, the body length of L. melvillei was estimated to 13.5 and 16.2–17.5 m respectively, in the range of adult male Physeter macrocephalus. Size evolution is more complex within the poorly supported Physeteridae clade, with on the one hand a probable two steps size increase towards P. macrocephalus (bizygomatic width up to 2200 mm and body length up to 18.3 m in adult males, but considerably smaller in females;
So, they don't describe it or consider it as an obligdate equivalent to a 14 m Physeter and can be compared to any adult male.
There is no need to discuss this. The Aurora teeth are nothing exceptional in size.
Simply updating Gottfried life stage table based on this new data and adding new data among known great whites would strengthen that.
We are not the first to consider the Bone Valley dentition to be a juvenile, Pimiento 2010 did it too.
I mean direct evidence.
No one says it is strictly comparable to a 18 m bull. It is comparable to any male adult Physeter. Sorry but I'm not obsessive with the average-size statements.
Well, the Yorktown and Chilean associated dentitions measurements suggest larger sizes estimates than for the Livyatan holotype. And there are much larger teeth than those in these dentitions.
That's enough for now to consider the otodontid larger based on actual data, awaiting a hypothetical shrinking size for it or the finding of a 30 % larger than the holotype physeteroid...
But as of 2018, it didn't happen.
This is not fanatism, this looking at the actual material and statistical range, not wild assumptions.
My issue is that tearing out a chunk of flesh has been observed among sharks, gripping the the caudal of a similar-size shark has not.
I certainly don't doubt Livyatan has the weaponry and power to kill a foe it own size.
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Post by theropod on Sept 1, 2018 3:00:23 GMT 5
Then you are arguing against a strawman. Nobody is suggesting that the holotype is a juvenile. I’ve spent the better part of my teenage years trying to convince you that the Livyatan holotype should be assumed to be "probably around the average size of its species". Very nice to see we are on the same page about that now. That goes for C. megalodon too. Any estimate for C. megalodon actually, as it’s based on such scrappy remains. No, but nothing says it wasn’t either. Physeter is its closest extant relative. I’d be totally fine with using other odontocetes as an analogue though, it’s just that Physeter seems to have the most conveniently available data right now.
I do fully agree with that, I just don’t get what difference "obligate average-sized" as opposed to "most likely near the average size" makes for you for practical intends and purposes. Either way, we should compare it to average-sized individuals.
Yet these estimates are curiously high compared to previously published regression equations for jaw perimeter or tooth row length, even given very liberal assumptions with the latter two. Not to mention previously used methods for estimating megalodon’s size.
Who’s obsessive?
In the absence of direct evidence, use parsimony. If I found a cave bear skeleton I wouldn’t assume it had no fur, just because it’s not preserved.
Well, I disagree. I think the most likely size estimates would put the Livyatan holotype at a very similar size to those dentitions (Yorktown at least, you still haven’t specified how big the chilean dentition actually is).
Not on raptorial odontocetes of equal size.
I don’t get what’s so outlandish to you about the suggestion of grabbing the tail, it seems like one of the most obvious targets of attack for obvious reasons. Strictly going from their functional morphology, of course.
Then what was all the fuss about?
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Post by Grey on Sept 1, 2018 3:18:20 GMT 5
There is difference between claiming it is an averge-sized individual, with a precise data, and claim it was more or less around the average size of its species.
You don't understand. I mean to be cautious when one argues the holotype is an obligatory average-sized specimen.
The data from Carcharocles dentitions suggest a specimen theoretically 15-21 m was not particularly large since significantly larger teeth specimens are known than in this dentition. The very lack of material hinting at a significantly larger Livyatan specimen can, understandably, suggest that the holotype coud have been quite large for its species. That is a possibiity.
While there is no doubt there were significantly larger megalodon specimens based on dentitions metrics than Aurora.
I disagree, because of the lack of additional specimens and by caution, we should compare it to any adult bull Physeter. And this is what is done in the literature.
There is nothing curious here. This is the decoupled scaling predicted by Kent (1998). There was no real data for jaws perimeter as those used unknown parameters (such as tooth spacing). Here we limit our method to the material available, comparing summed dentitions. Yes, Kent probably underestimated the size of Parotodus a little as well.
Kent himself wrote that those previous methods based on single tooth likely underestimated the size of the animal.
The term might be rude but can't we just compare the data with the data and not assume unverifiable statements such as this ? I'm fine with comparing the holotype with any meg dentition specimen so far.
There is strong scientific support for the fur on the living bear, not for assuming the Livyatan holotype is necessarily to its species what a 14 m Physeter is to its own.
Sorry but that's wrong. The total size range for Livyatan is 14-18 m, for the Aurora it is 15-22 m using GWS from any base group, 17-20 m restricting to adults.
Even using only Zygophyseter data, Livyatan is approaching but not as large as the Aurora specimen. There is some overlapping size but statistically, the Aurora meg is larger.
There is no data yet for the Chilean, it is possibly larger.
The claim that simply grabbing the tail of a similar size opponent would end the encounter is simply dubious and virtually unverifiable.
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Post by theropod on Sept 1, 2018 3:42:06 GMT 5
A 16.7m great white would be predicted to mass 50.6t (minimum, Casey & Pratt 1985: 45.3t, maximum, Gottfried et al, 1996: 55.7t). That is a perfectly reasonable size for the Livyatan holotype.
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Post by Grey on Sept 1, 2018 7:57:39 GMT 5
Yup but you exclude the lower range of Livyatan and the whole range of both. My point is that the Aurora dentition possibly extends up to more than 20 m, not Livyatan so far.
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Post by theropod on Sept 2, 2018 22:54:48 GMT 5
On the issue of longevity, I’ll give you an example of what I mean.
For simplicity’s sake, I’m only comparing to the male population of Physeter here, but this also applies to females (although I don’t think you are keen on suggesting any possibility that the Livyatan holotype might be a female, which are much smaller than males in nearly all extant odontocetes).
Discounting juveniles that are below the size at which they can be considered ecologically mature, T. rex is known from tens of adult (i.e. sexually mature) specimens, all of these are body fossils, which means that the individuals all died, and did so of natural causes (I think we can dismiss the possibility of time-traveling whalers that, once they ran out of whales, moved on to the late cretaceous to prey on tyrannosaurs).
Of these individuals, Sue and Scotty are the only ones that that have entered a phase of negligible growth (they have an EFS), i.e. they are the equivalents to 15.85m bull Physeter. All the others were still at least somewhat actively growing, as proven by their histology.
T. rex was the apex predator and one of the largest animals of its ecosystem, so adults were almost certainly immune to predation, just like was likely the case for L. melvillei. Still, there’s no way around accepting that almost all specimens died before achieving their full size (Erickson et al. 2005), and hence they must have died of something other than old age, be that starvation, thirst, injury, disease, intraspecific confrontation, defensive behaviour by prey, "lethal taphonomy" (such as miring or drowning, the terrestrial equivalents to stranding) or any given combination of these factors.
We can make the same analogy with Allosaurus (with the caveat that as of my knowledge, there is actually not a single Allosaurus with an EFS, but it’s growth pattern was found to be similar to tyrannosaurids by Bybee et al. 2006), this is definitely not an exception. Myhrvold et al. 2013 found only 3 of the 14 dinosaur taxa they analysed even have specimens 90% or more of the predicted final size based on growth models. T. rex is even among those few that do, and yet it’s a prime example of an animal that generally dies before reaching full size.
Of course dinosaur growth trajectories aren’t necessarily the same as odontocetes’. It’s certainly possible the latter reach full size earlier during their maximum life span, and it’s plausible that some theropods never fully stopped growing (but vertebrates whose growth does not slow down at some point are unheard of). But what we do know is that both of these reach ecological, sexual and social maturity well before physical maturity (i.e. before being fully grown or at least close to full size), and that both their adult populations overwhelmingly consist of individuals that haven’t yet reached this full size.
So if sperm whales or, by inference, Livyatan, that died of natural causes are most likely fully grown individuals, how do you explain that taxa like T. rex or Allosaurus, whose adults were also not subject to high predation pressures from other predators, have an adult body fossil record mostly consisting of individuals that had not reached full body size or anything close to it. We know that many large sauropods, for instance, hadn’t yet reached their maximum possible body size. A 50 ton Apatosaurus is clearly an adult for any practical concern, yet it is not osteologically mature, and hence not fully grown.
I am well aware you have expressed your distaste for theropod analogies (pun fully intended) in the past, but they are still valid analogies that you cannot just wave away by saying that they are different animals. If other apex predators and animals without natural predators generally don’t seem to die of old age, why do you think it is likely that Livyatan did? Where is the evidence suggesting this, if you insist to keep repeating that we should assume this as the most likely?
Again, Livyatan’s holotype is generally implied to have been an adult, that is all. You are making assumptions about that statement (one that doesn’t base on real evidence to begin with) that are entirely fictional. Adult in this context likely means no more than ecologically or sexually mature, and seeing how there is no histological study on this specimen, this is probably assumed simply because it defies imagination that an animal rivalling large male sperm whales and large individuals of C. megalodon in size would be a juvenile.
And I fully agree with that assessment. That is not the same as suggesting that the individual was fully grown, died of old age, or was likely an unusually large, old specimen for its species. There is nothing in its morphology and no histological evidence suggesting this. There is even a little bit of evidence (open pulp cavities reported by Lambert et al. 2016) to the contrary, but it is fairly weak and I am not proposing we use this to dismiss any possibility that the specimen was old or large. Again, I am not saying it is impossible this is an old, fully grown whale. It is possible. All I am saying is that it is more likely that is isn’t; the most likely thing is that it was a normal-sized adult, which brings us back to it being the equivalent of a ~14m bull sperm whale, not a 16m+ one, and not an 18m Megalodon either, unless you can demonstrate that 18m was the average size of the species.
On your last post, as for the "whole range of both", I don’t think I really need to explain why mean estimates are preferable, do I? If your range of estimates is 15-20m, but the mean is actually 16.7, the mean is the best way to capture that estimate, since just the individual maximum and minimum estimates alone don’t contain any information on the overall distribution of estimate. I recently posted an example of this, estimates within a range can cluster around a mean, or median, or both, but there can be other estimates that diverge further than is the norm, and in effect that makes these figures less relevant than those that plot closer together. You will certainly have done your homework and already excluded extreme outliers from the dataset if they exist, but that does not mean there aren’t some estimates that diverge more than others. That’s why the sample mean isn’t simply the mean of the largest and highest value in a sample. I have asked you this before and I’m asking you again: what’s the standard deviation of your current estimates for this specimen? That would be a better way of comparing ranges if you insist on doing that, as it at least captures the average variation in the estimates and not just the extremes.
I have already acknowledged I am excluding the lower end of the estimate’s range for Livyatan. As I explained, that is because I think the method is less reliable, just like I’m excluding other, less reliable, but lower estimates for C. megalodon. Both reasonably complete genera of stem-physeteroids suggest body masses around 50t are reasonable, and I happen to think that those provide the better method for size estimation, just like I think your most recent estimates for megalodon are based on a better method than earlier ones (which would have suggested that the average size was very similar to the lower estimates of Livyatan, and which I happily compared to these estimates).
I’m not expecting you to agree with this at all, just to understand my position. Likewise I could agree to disagree if you would prefer the Physeter-based estimates for Livyatan over those from Zygophyseter and Brygmophyseter and only include those, even though my own opinion is that comparing those to the highest existing estimates for megalodon is not a balanced approach.
Bybee, P. J., A. H. Lee, and E.-T. Lamm. 2006: Sizing the Jurassic theropod dinosaur Allosaurus: assessing growth strategy and evolution of ontogenetic scaling of limbs. Journal of Morphology 267:347–359.
Erickson, G. M., P. J. Makovicky, P. J. Currie, M. A. Norell, S. A. Yerby, and C. A. Brochu. 2004: Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. Nature 430:772.
Lambert, O., G. Bianucci, and C. De Muizon. 2016: Macroraptorial sperm whales (Cetacea, Odontoceti, Physeteroidea) from the Miocene of Peru. Zoological Journal of the Linnean Society 179:404–474.
Myhrvold, N. P. 2013: Revisiting the estimation of dinosaur growth rates. PloS one 8:e81917.
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Post by thalattoarchon on Sept 16, 2018 0:20:20 GMT 5
Probably I have to ask. What are known about the interactions of large macropredatory sharks with the same-sized toothed whales? I know some data that great white sharks are known to prey on belugas in past but I do not remember the sources.
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Post by theropod on Sept 16, 2018 13:59:14 GMT 5
We've debated this quite extensively a few pages back.
There seems to be no record of predation by great white sharks on same-sized toothed whales, the largest recorded prey item in the literature were 3m long ziphiids, which were en by sharks estimated at 5m or more (long & joness 1996). There are (rare) accounts of white shark predation on juvenile right whales and adult northern elephant seals, so it seems that Odontocetes may represent a more challenging prey than these taxa. So based on the sizes (great whites grow quite a bit llarger than belugas) predation on belugas may be plausible. However seeing how their natural ranges don't really overlap much, if at all...
There is a record of predation on odontocetes of equal or larger size for bull sharks, and it seems this taxon takes relatively larger pres than white sharks do (Heithaus 2001).
None of the cetaceans so far recorded falling victim to sharks are themselves macroraptorial feeders comparable to Livyatan, whereas the sharks in question definitely are. There are no records of any shark killing an orca, false killer whale or even pygmy killer whale.
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