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Post by dinosauria101 on Feb 5, 2020 20:56:21 GMT 5
Question: do we know anything about how teeth size scales in sharks?
Do they scale with positive or negative allometry?
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Post by creature386 on Feb 5, 2020 22:31:45 GMT 5
"Sharks" are a very, very, very broad category (try applying the rules you apply to a great white shark to a whale shark), but I assume you just mean great white sharks.
Well, you can look at one of the many papers that studied the tooth height or width of great white shark individuals of varying sizes and then developed regressions for estimating Megalodon's size. Gottfried's paper would be a place to start. It's rather old, but frequently cited and good entry level material. Apart from that, you can look at pretty much any paper discussed at length in this thread here.
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Post by dinosauria101 on Feb 5, 2020 22:48:14 GMT 5
I suppose it would be good to take a look at some of those, yes.
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Post by dinosauria101 on Feb 6, 2020 0:18:06 GMT 5
Looking at some of this stuff, I can tell larger sharks have proportionately bigger teeth/jaws, which makes sense since they need more teeth to eat larger prey.
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Post by Grey on Feb 10, 2020 20:31:25 GMT 5
Looking at some of this stuff, I can tell larger sharks have proportionately bigger teeth/jaws, which makes sense since they need more teeth to eat larger prey. This is not hard data, there is anecdotal indication that teeth stop to grow in the larger sharks. The TL estimates using the dentition of larger white sharks does not indicate necessarily much larger jaws at larger size. There was probably some allometry but at which point ? Sharks generally seem to stay roughly similar in body geometry, not matter at 5 m or 12 m, active hunter or filter feeder. |
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Post by dinosauria101 on Feb 10, 2020 21:25:42 GMT 5
Hard to know, I suppose.
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Post by elosha11 on May 3, 2020 4:15:42 GMT 5
If genuine, this is an amazing 8 inch tooth. Do you have any more information about it, where it is located, where it was found, etc? |
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Post by elosha11 on May 3, 2020 5:42:21 GMT 5
Some quotes from and about Ken Shimada's study. I said he used a 6.6 CH tooth, actually the the largest of the three teeth he used was only 6.4 inches slant height. Some thoughts on this. While I respect Shimada's decision to only use museum specimens, I think he should have hedged his findings much more significantly. It's common knowledge that multiple teeth out there exceed 7 inches and some of them, like well known shark collector Gordon Hubbell's tooth measuring 7.25 slant height inch , would have probably been available to him had he asked. For instance, Leder's upcoming study might incorporate Hubbell's tooth to help estimate Meg's true max size. Victor Perez, one of Leder's co-authors visited and measured the Hubbell tooth in 2018 and confirmed its size. See www.myfossil.org/members/vperez/activity/34782/And there are likely bigger teeth out there than even Hubbell's. I know they are not available to Shimada, but to use teeth that are almost certainly well below max size to compute the supposed max size for Megaladon is counterintuitive. I also find puzzling his acknowledgement that Megalodon may have reached 18 meters, but that it was "exceptionally rare" for it to exceed the 14-15 meter range. Even among extant sharks, you will find far more smaller GWS teeth, than say 2+ inchers. And while no one would say it's extremely common to see 18-20 foot great whites, it's also not "exceptionally rare" By statistical definition, the teeth in an animal that may have lived 50+ years and shed tens of thousands of teeth of all sizes throughout its life is going to exhibit a bias in the fossil record towward smaller teeth. It is much more likely we would find teeth that are smaller than the largest ones the shark shed in its lifetime. Likewise, although hard to prove, it's not implausible for many of the larger Meg teeth to have been shed from the animal in places that are now deep oceans and less likely to be found than the shallow prehistoric ocean beds where the vast majority of Meg teeth are now found. Finally, may be that larger Meg teeth are statistically more likely to be broken or damaged and not fossilize as readily as smaller ones. In any event, here's Hubbell's 7.25 inch tooth and then two teeth which appear to be about 8 inches. Vito Bertucci -who found and sold the 7.25 inch tooth to Hubbell - also found a tooth of 7.62 inches which he placed in his Meg jaw replicate. Pics here. www.theworldslargestsharksjaw.com/Here's Hubbell's 7.25 inch tooth in the first two pics:
  Two others of around 7.5 to 8 inches in private collections  The last tooth above is described: To get his largest 46-50 foot estimates, Shimada used teeth with crown heights (CL) of only a little over 12 cms. Yet the two measured teeth above far exceed 12 cms in CL, they appear to be more like 15-16 cms in CL, at least a 25% increase in CL from the largest teeth Shimada used. I have no doubt HubbelL's 7.25 inch tooth would be far more than 12 cm CL as well. It must be noted that all of these teeth are UA's which Shimada believes are the only ones that will provide accurate estimates under his methodology. In short, Shimada's methodology and results are almost certainly flawed. Even while we await Leder's results, I would think any Meg researcher (obviously this would require funding and incentive) could go to Hubbell, officially measure his tooth, as Perez did and write a follow up to more accurately reflect max size under Shimada's own methodology. |
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Post by kekistani on May 3, 2020 7:09:06 GMT 5
Some quotes from and about Ken Shimada's study. I said he used a 6.6 CH tooth, actually the the largest of the three teeth he used was only 6.4 inches slant height. Some thoughts on this. While I respect Shimada's decision to only use museum specimens, I think he should have hedged his findings much more significantly. It's common knowledge that multiple teeth out there exceed 7 inches and some of them, like well known shark collector Gordon Hubbell's tooth measuring 7.25 slant height inch , would have probably been available to him had he asked. For instance, Leder's upcoming study might incorporate Hubbell's tooth to help estimate Meg's true max size. Victor Perez, one of Leder's co-authors visited and measured the Hubbell tooth in 2018 and confirmed its size. See www.myfossil.org/members/vperez/activity/34782/And there are likely bigger teeth out there than even Hubbell's. I know they are not available to Shimada, but to use teeth that are almost certainly well below max size to compute the supposed max size for Megaladon is counterintuitive. I also find puzzling his acknowledgement that Megalodon may have reached 18 meters, but that it was "exceptionally rare" for it to exceed the 14-15 meter range. Even among extant sharks, you will find far more smaller GWS teeth, than say 2+ inchers. And while no one would say it's extremely common to see 18-20 foot great whites, it's also not "exceptionally rare" By statistical definition, the teeth in an animal that may have lived 50+ years and shed tens of thousands of teeth of all sizes throughout its life is going to exhibit a bias in the fossil record towward smaller teeth. It is much more likely we would find teeth that are smaller than the largest ones the shark shed in its lifetime. Likewise, although hard to prove, it's not implausible for many of the larger Meg teeth to have been shed from the animal in places that are now deep oceans and less likely to be found than the shallow prehistoric ocean beds where the vast majority of Meg teeth are now found. Finally, may be that larger Meg teeth are statistically more likely to be broken or damaged and not fossilize as readily as smaller ones. In any event, here's Hubbell's 7.25 inch tooth and then two teeth which appear to be about 8 inches. Vito Bertucci -who found and sold the 7.25 inch tooth to Hubbell - also found a tooth of 7.62 inches which he placed in his Meg jaw replicate. Pics here. www.theworldslargestsharksjaw.com/Here's Hubbell's 7.25 inch tooth in the first two pics:
Two others of around 7.5 to 8 inches in private collectionsThe last tooth above is described: To get his largest 46-50 foot estimates, Shimada used teeth with crown heights (CL) of only a little over 12 cms. Yet the two measured teeth above far exceed 12 cms in CL, they appear to be more like 15-16 cms in CL, at least a 25% increase in CL from the largest teeth Shimada used. I have no doubt HubbelL's 7.25 inch tooth would be far more than 12 cm CL as well. It must be noted that all of these teeth are UA's which Shimada believes are the only ones that will provide accurate estimates under his methodology. In short, Shimada's methodology and results are almost certainly flawed. Even while we await Leder's results, I would think any Meg researcher (obviously this would require funding and incentive) could go to Hubbell, officially measure his tooth, as Perez did and write a follow up to more accurately reflect max size under Shimada's own methodology. You have a source on all these teeth being upper anteriors? |
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Post by theropod on May 3, 2020 16:22:07 GMT 5
I think all this is somewhat brushing under the carpet that Shimada is accounting for such larger teeth, he merely does not consider them, to use a legal term, admissible evidence due to them not being in the public trust (as discussed before this is in line with common practice and is for example recommended by the SVP and a requirement for publication in some journals). He is even very liberal with the size of the largest teeth here by acknowledging teeth possibly up to 20 cm in tooth height, which is far larger than Hubbell’s or other properly documented teeth: Anecdotal accounts indicate that the largest teeth of O. megalodon may measure as much as
about 20 cm in TH and 15 cm in CH (e.g. Renz 2009, p. 90–92). Assuming that such gigantic teeth are upper anterior teeth, and if the least conservative linear function (A2) is used, the calcula- tion would yield 1,813 cm TL, or about 18 m TL. That is also where his 18 m estimate came from. So it is not fair to accuse him of willingly ignoring larger tooth specimens. If there’s anything he can be accused of on that account, it is using such a poorly documented figure for the largest teeth instead of using the largest private specimens with properly verified measurements, for which Hubbell’s tooth would be an obvious contender (but I also think I know why that was not an option, see below). But this has the effect of inflating the estimate, not lowering it. It should also be pointed out that Hubbell’s tooth (184 mm or maybe 187 mm in slant length, judging purely from the photo elosha11 posted above around 175 mm in tooth height and 126 mm in crown height) isn’t necessarily much larger than the largest publicly held specimens Shimada (and Gottfried et al.) acknowledge (162 mm in TH and 117 mm in CH for FMNH PF 11306 and 120 mm CH for NSM PV-19896). Vertical tooth height is a smaller measurement than slant length, about 92-97% in a number of teeth that I’ve measured. So are likely only talking about something on the order of a few percent here that Hubbell’s tooth would be larger than the largest tooth Shimada had access to (we can’t say with absolute certainty, as I am not aware of any perpendicular tooth height measurement being explicitly published for Hubbell’s tooth, and if it were it wouldn’t have been in a source Shimada would have been allowed to cite anyway.), I don’t think it is proportionate to get so hung up over that rather minor issue, especially considering he actually acknowledges possible maximum sizes well in excess of what Hubbell’s tooth would indicate. As for the common or average size, I think I have already demonstrated how using entire meg dentitions as a size proxy, thereby removing the methodological problems with Shimada’s paper, most megalodon specimens were likely indeed smaller than those 15.3 m Shimada estimates, and that is while acknowledging some specimens may even have reached 18-21 m.  1.0 here is the size of the Yorktown dentition. That itself may well be a 15 m specimen, in which case it’s obvious, but even assuming it is a 17 m specimen, that would still mean 0.9 on this scale equates to roughly 15 m, and the vast majority of teeth clearly belong to smaller idividuals than that. In a natural population the bias towards smaller teeth is the same as the bias towards smaller individuals, as the probability of any given shark losing a tooth is proportional to the probability of any given shark being present. More smaller sharks obviously lead to more smaller teeth, which is because since there would be mortality throughout the lifespans of these animals a given cohort would get thinned out the older and larger they got, but if you were there to catch and measure 100 random sharks, that would give you a similar average size to if you were to sample 100 random teeth. So Shimada’s statement that a "vast majority of O. megalodon must have been <15 m TL", while intentionally vague, is likely correct. Honestly it is hard to suggest it is anything else, otherwise why are these teeth the largest ones in museum collections? Similarly, it is also correct to note that the vast majority of Great White Sharks are <6 m, even though with many thousands of sampled sharks of course there is quite a number of 6-7 m individuals on record. The obsession with focusing on the largest, most mature fraction of the population and ignoring all else that is present in AvA circles has not penetrated large parts of academia yet. There is much to be said about the method Shimada used to estimate size, which frankly lacks novelty and doesn’t account for various major problems, but I’m getting the impression that there is a lack of criticism of the methodology in favour of a criticism of the results here.
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Post by elosha11 on May 3, 2020 21:01:18 GMT 5
@kekistanti. I don't have a source saying these are UA, but I think Hubbell has stated on youtube somewhere that his tooth is a UA, and given the size and shape of these teeth, I have no reason to believe they are laterals or lower teeth. Some here know more about the exact shape of each type of tooth, so if anyone wants to point out why they think the teeth I posted are not UA's, I'd consider it. But they certainly have the size and general shape of UA's which are known to be overall largest Meg teeth. theropod. I don't think you and I are really saying anything all that much different. I'm not accusing Shimada, nor am I upset with him with only using largest museum specimens. I do wish he would have contacted Hubbell, at least, who seems perfectly fine with scientists measuring his tooth. I'm also fairly sure that the crown height of the Hubbell tooth is above 126 mm, although it's a bit hard to see exactly in the pic where the CL ends and the root begins. Maybe Perez measured the CH and would know... However, it looks like the crown runs from about the 40-50 cm mark on the ruler to the 150 cm mark (11.5-12 cms) but the tooth then extends beyond the end of the 150 cm mark for at least another 1-2 cms. So I'd ballpark around 12.5 to 14 cm CH. The other two posted teeth, if accurate, seem much closer to 15-16 cms CH. I'll also note that IF that 8 inch SH tooth is valid and accurately measured, it exceeds 20 cms in SH. And there are multiple teeth posted on this thread that are likely to have CH greater than 12, but there's no way to know for sure. However, I agree with you the CH height methodology seems outdated. I also agree that most Megs under the mean average would necessarily be <15 meters, but there's ample evidence under any methodology that some of them well exceeded that size into the 18+ meter range. Shimada's study seems really more geared toward what a large, but not really max size, Meg would have looked like. A 14-15 meter Meg may have been a relatively large adult, similar to how a 14-15 foot great white is a relatively large adult, but not one approaching max size. However, the way he framed his arguments has led to inaccurate descriptions of 14-15 meter being max size. I also agree with you on the fossil bias toward small teeth, in fact you're stating some the same points I raised in my initial post. My guess is that a max size Megalodon would be as common as any other large shark or cetacean, not common but not really infrequent either. Moreover, I hesitate to use the relative rarity of a 6 meter GWS as an analogy, as the fossil record indicates they may have reached 6+ meters more commonly in prehistoric times before man's impact on the ocean environment. Megalodon, and all other large prehistoric marine animals' sizes, were obviously not constrained by humankind's activities. And I think he should have been more forceful in explaining that there are almost certainly much larger teeth than what he used. You almost get the impression with his reference to "anecdotal" larger teeth that he's skeptical that 7+ inch SH teeth exist, even though it's common knowledge for the past 50 years at least that multiple such teeth exist. And I do agree that most Megs swimming in the oceans at any one point in time (or as an aggregate number for the entire history of the species) would have been < 15 meters. That simply accounts of the fact that for the majority of a Meg's life (those that lived a full age), it would have been below 15 meters. Let's say we have a very large Meg that reaches 19 meters and lives 50-60 years. Probably 75-80% of its life will have been spent as an animal below 15 meters, meaning that a far greater amount of teeth that it lost over the course of its life would have been from an animal less than 15 meters. This is also why stating Megs average (mean) length being around 10 meters is useful, but often deceptively used by those who have an agenda to downsize Megalodon. That figure was computing the mean, and took into account the shark's length at all stages of life. In Pimiento and Balk (2015), they reiterate the sizes, and give the following information: - Neonates reach sizes up to 4 m (13 feet) - Juveniles range from 4 to 10 m (33 feet) - Adults range from 10 m and up (33 feet and up) You can do that for any species. Great whites' mean is probably only 10 feet when you take into account all the neonates and juveniles, but no one suggest this means it would be highly unusual to find a great white shark 18 feet or larger or that a 15-16 foot adult is not common. If you took the mean for humans, we probably average 4.0 feet in height (ballpark guess) based on babies, children, young adults, normal-sized adults, and very tall 2+ meter adults, but no one would seriously claim this means the average adult is 4 feet tall, or that the average adult GWS is only 10 feet long. Mean is a useful number for the whole species, not for adult sizes. Meg skeptics have often these studies to inaccurately misstate the statistic in order to downsize Megalodon's adult size. In fact, you could do the same thing with a sperm whale or a Livytan, a Mosasaur or any apex ocean predator and get a mean far smaller than actual common adult sizes. |
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Post by theropod on May 3, 2020 23:28:21 GMT 5
elosha11 I measured that in the picture you posted, that is how long the crown is. Of course this is likely to by imprecise by a number of millimetres, but I would strongly doubt that tooth is 14 cm in crown length. Edit: I measured again and got pretty much the same result.  scaled so that 1mm=10px And as people here have made a point of posting only particularly large teeth on this thread, that is by no means surprising. I can of course go through our collection and post the largest tooth I can find in there, but I doubt people here would even be interested. But didn’t Shimada explicitly acknowledge teeth this size, even bigger actually, to exist? Honestly I don’t think I am, because the point I was making there was precisely that there is no such fossil "bias" towards smaller teeth.
There are more smaller teeth because at any given point there are more smaller individuals, both immature and mature, than there are larger ones. Because all sharks start out small, but not all reach "maximum size". That is not a bias, it reflects the real condition in the living population. Just like randomly sampling and measuring living white sharks.
If 4-5 m white sharks are twice as common as 5-6 m ones, then you will be likely to catch twice as many of those. That is also not a bias.
If we are only interested in adults, as we usually are, then we can single out those individuals that are mature, but that doesn’t mean the smaller ones won’t still be more common among those individuals, because even 5 m adult great whites are far more common than 6 m. That is not a bias, that is how common the individuals really are.
So yes, 15m is likely a relatively large adult for megalodon, Shimada incidentally is correct on that account even if he did get there using a very different method (sometimes there is something to be said for the amount of scientific caution in one's conclusions that allows one to be right with them even with methods that are likely flawed, sometimes thers isn't, but this is one of the times when there is, because honestly nothing less cautious would really be warranted when estimating something from a bunch of teeth). But it is not comparable to "14-15 ft great whites", which really arent very big adults at all, only slightly above the average length at maturity actually.
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Post by elosha11 on May 4, 2020 18:51:54 GMT 5
theropod. Thanks for measuring. To be clear I was estimating a range of 12.5-14 cm based on the tooth's right side CH, closest to the ruler. I tend to think it less than 14 cm also, but I think it's likely a bit more than 12.6 cm. However, your measurements may also be correct. I will see if I can contact Perez to see if he measured CH. In any event, the two other teeth I posted (and yes I know they are not currently testable) seem to indicate substantially greater CH. Of course we can't use them officially because we cannot attest to their accuracy or even authenticity. Yet there are quite a few teeth with greater SH than 6.6 inches out there, and quite likely greater CH than what Shimada used. Shimada is well aware of this, so my only quibble is that he could have more strongly worded the caveats to the size of his sampled teeth. You may disagree with that and point out he did say other larger teeth might suggest 18 meter animals. I simply think the way he worded it makes it all too easy for people to interpret it as him stating that 14-15 was likely a max size for normal Meg specimens and I think that's not true, even using his own, likely flawed, methodology. And it is even more unlikely to be true using an associated dentition analysis. My comments in bold following yours for easier reading.
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Post by theropod on May 4, 2020 20:43:07 GMT 5
Just to clarify, I did of course measure both sides, the crown isn’t longer on the other side either. Crown height is supposed to be measured perpendicular to the line between both sides of the crown base, so there would be no point measuring in the vertical plane if both sides weren’t aligned, i.e. if I’d gotten a longer measurement from one side than from the other.
A physical measurement would of course be preferable, but I think it is almost impossible for that tooth to have a crown much more than 13 cm tall.
The other pictures you posted do appear to have longer crowns than that, yes.
Well, Shimada did not use that wording and neither did I. However conversely this argument can not be used to suggest that 18 m was a totally normal size either. It is just as uncommon as the figures based on the population would suggest.
It is arguably a sizeable GWS, but not sizeable for an adult. Mean size at maturity for great whites of both sexes is likely about 4 m, even higher for females. 15 ft is about 4.6 m. I think there are mentions of great whites that weren’t even mature at that length. That is not the equivalent of a 15 m megalodon, more like a 12 m one.
So this would be akin to calling a 12 m megalodon "sizeable", which is arguably correct in some contexts, but not for an adult, considering there were very likely individuals that weren’t even mature at this length.
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Post by kekistani on May 6, 2020 2:38:40 GMT 5
theropod elosha11 Found it! Hubbell states that this tooth is an upper anterior at 0:28
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