|
|
Post by theropod on Mar 5, 2014 17:18:56 GMT 5
I got it up to this point. or 16m. Estimates are not absolute, they have room for error. An estimate merely marks the most probable value, you have to imagine probability gradients above and below that. But unless they are particularly low, they do not form the minimum. A minimum estimate is the lowest possible estimate, the lowest conceivable figure. For example, if you have a single tooth or vertebra that can not be identified, and you use the biggest in the vertebral collumn/dentition to estimate the size of the animal it belonged to, that gives you a minimum estimate. If you make an estimation based on a regression for a specific taxon, you get an average estimate. It is certainly not impossible that the animal was larger than predicted, but it isn’t any more likely than that it was smaller. That’s why we stick with the actual estimated values instead of speculating on how much bigger the animal could have got given the margin of error. None of these observations indicate our methods give us minimum estimations. Me too. But so far no better analogy than Carcharodon has been proposed. For example, Mako shark jaws look like this:  Obviously C. carcharias comes much closer as regards tooth function, and, accordingly, jaw morphology. The method itself is not difficult, it’s the tooth identification that poses the problem, but this was not the matter here. There’s a number of linear regression equations (just like Gottfried’s for UA2 height, but for each and every tooth position). You insert a given crown height measurement and the formula returns you the TL. I have used this with several of the specimens in Pimiento et al. and always got the correct result. With anterior teeth, it gives very conservative results, yes. For posterior teeth, wuite the contrary. If you use different teeth, the different proportions of Great white and Megatooth sharks come to play, and there is a more marked difference in the heights of anteriors and posteriors in great whites. I don’t know whether you’ve read my explanation, Grey did not report it correctly. These pictures appear comparable to the ones I’ve posted, but they are quite blurry. In any case if i’ve measured the one with the widest spacing even somewhat correctly (feel free to check!), their Interdental spacing is below 15%. Thank you, I’ll have a look at them. |
|
|
|
Post by Grey on Mar 5, 2014 17:43:03 GMT 5
This is not while measuring interdental spacing on pictures on the Internet that one will be able to determine with accuracy. Still, on all the jaws I've seen posted here except for one, in all I see a striking spacing between teeth.
So theropod, don't take this bad if I don't trust your measurements (or mines) done on photos and that I'd prefer to know exactly which value was used by Kent in his paper about Parotodus and by Siversson in his estimates for Carcharocles specimens (counting on he used that method, which appears likely to me as he advised me to check the method in the Cardabiodon paper).
Regarding Shimada, I've understood the point since a long. But as Pimiento et al. have no complained about this, my opinion is that the error bar is acceptable and that the method itself is reasonable. Overall, it is even more conservative than those based on width or slant measurements, as no published size estimate exceeds yet 18 m, and when asking Pimiento by mail if there will be sizes above 18 m, she said she had to check the data but did not think that there was larger figures than 18 m (now she's perhaps not that interested in max sizes so has forgotten individuals above 18 m). The error bar might be massive when one posterior tooth is possibly from different positions, but at the end the result is still in acceptable ranges. There is also one posterior (lateral) from multiple positions which yielded a size ~13 m, which is not in the largest estimates given through the study.
So, whatever how much Shimada is accurate, it is still reasonable in its results for the obvious reason it is still used. And if one prefers parcimony about Meg size estimates, he should appreciate Shimada's "modest" results.
|
|
|
|
Post by theropod on Mar 5, 2014 17:54:00 GMT 5
There are no methods based on slant measurements. That metric is just used by fossil collectors. Where do you see that striking difference between teeth? They are spaced quite close to each other, the roots seem to (almost) touch. This is what the paper on the pathological whale rib states on the subject: As the roots of lamnid shark teeth in adjacent files do not overlap but very nearly
abut (Hubbell, 1996; Purdy & Malcolm, 2007; Ehret et al., 2009a), it is safe to assume that the roots of these teeth, if deriving from a shark, were also approximately 6 cm wide. Again, that is consistent with 5 in a total of 6 pictures of shark jaws, and consistent with what Kent wrote to me when I asked him. 13m is among the largest specimens in Pimiento et al. 2009. And you have produced several not so modest results with Shimada’s method, all affected by this point. But I wasn’t explaining it to you, we’ve discussed it extensively enough. |
|
|
|
Post by Life on Mar 5, 2014 18:05:01 GMT 5
or 16m. Estimates are not absolute, they have room for error. An estimate merely marks the most probable value, you have to imagine probability gradients above and below that. But unless they are particularly low, they do not form the minimum. Likelihood for Megalodon physiology to be more conservative then that of GWS = 0% Likelihood for Megalodon physiology to be more liberal then that of GWS = 100% How? Fossil records seem to suggest this. Therefore, estimates that we get from size estimation methods suitable for GWS are minimum and conservative for Megalodon. None of these observations indicate our methods give us minimum estimations. They actually do: Dentition of Megalodon seems to correspond to broader jaw structure in comparison to that of GWS at parity, the broader jaw structure is linked with vertebral column that represents the possibility of more liberal TL to BL dynamics in Megalodon in contrast to that of GWS. These physiological possibilities are not considered in any size estimation method suitable for GWS. Gottfried et al (1996) were smart to associate the label of "conservative" with their 15.9 m estimate for a large Megalodon using GWS as an analogue. It makes sense. With anterior teeth, it gives very conservative results, yes. For posterior teeth, wuite the contrary. If you use different teeth, the different proportions of Great white and Megatooth sharks come to play, and there is a more marked difference in the heights of anteriors and posteriors in great whites. I don’t know whether you’ve read my explanation, Grey did not report it correctly. Different proportions of GWS will obviously come in to play if teeth do not belong to same shark. Suppose that you have two specimens to consider: A1 tooth for specimen 1 P1 tooth for specimen 2 You will get different estimates for both. However, if you have multiple teeth of same shark to consider, you should get matching results for it using any of its teeth. Otherwise, you are doing something wrong and you need to consult Shimada for this matter. If I recall correctly, Shimada's method is not just an equation. Multiple researchers wouldn't have considered Shimada's method for estimating the size of sharks in their research works if this method was flawed. These pictures appear comparable to the ones I’ve posted, but they are quite blurry. In any case if i’ve measured the one with the widest spacing even somewhat correctly (feel free to check!), their Interdental spacing is below 15%. Ok. Thank you, I’ll have a look at them. You're welcome |
|
|
|
Post by creature386 on Mar 5, 2014 18:10:01 GMT 5
or 16m. Estimates are not absolute, they have room for error. An estimate merely marks the most probable value, you have to imagine probability gradients above and below that. But unless they are particularly low, they do not form the minimum. Likelihood for Megalodon physiology to be more conservative then that of GWS = 0% Likelihood for Megalodon physiology to be more liberal then that of GWS = 100% How? Fossil records seem to suggest this. Therefore, estimates that we get from size estimation methods suitable for GWS are minimum and conservative for Megalodon. This is a bit oversimplified, IMO. Especially for weight. Remember that coherentsheaf and theropod pointed out the possibility that Megalodon was more slender than the great white (and this is not even unfounded, you can find the support for this on a previous page). |
|
|
|
Post by Life on Mar 5, 2014 18:15:04 GMT 5
This is a bit oversimplified, IMO. Especially for weight. Remember that coherentsheaf and theropod pointed out the possibility that Megalodon was more slender than the great white (and this is not even unfounded, you can find the support for this on a previous page). Megalodon being more slender then GWS? How exactly? |
|
|
|
Post by creature386 on Mar 5, 2014 18:16:25 GMT 5
More slender vertebra in relation to the respective length and a higher vertebra count.
|
|
|
|
Post by theropod on Mar 5, 2014 18:20:09 GMT 5
Then estimations based on jaw perimeter of toothrow lenght would be overestimates.
With BL you mean body lenght? In that case, it’s just a longer tail.
It does, because relative to the size of its mouth the anterior teeth of C. megalodon are smaller, not because size estimations in general (most give considerably higher results) are underestimates.
What I’m referring to is not indiidual variation tough, it is a very marked trend in the relative sizes of teeth in the two.
One equation for each tooth. It’s quoted in Pimiento et al 2009 and in Ehret et al 2009.
So far only two subsequent studies used the method for C. megalodon. It was supposed to be a method for C. carcharias, for which it is perfectly fine, but there are differences between the two that have to affect the method.
you wrote this in your last post:
That’s the exact problem here, differences between the two taxa (for once, this is a difference that we actually know) left unaccounted for.
CB-11 CH-31 KO-009 (C. carcharias)
A1 142 138.3529411765 171.7670682731
A2 138 134.0294117647 170.4457831325
A3 118.5 129.7058823529 114.9518072289
L1 129 132.1764705882 147.983935743
L2 137 130.9411764706 150.6265060241
L3 124.5 124.7647058824 144.0200803213
L4 108 113.0294117647 117.59437751
L5 105 96.9705882353 71.3493975904
L6 93.5 72.8823529412 47.5662650602
L7 84 64.2352941176 33.0321285141
L8 57.5 42.6176470588 22.4618473896
L9 45.5 30.2647058824 17.1767068273
These are their respective tooth-heights at toothrow-lenght parity.
That’s the case because it is a method based on and used for Great white sharks, not C. megalodon. In the light of evidence, we have to be careful with just applying this to a shark that has different proportions.
|
|
|
|
Post by Grey on Mar 5, 2014 18:30:52 GMT 5
There are no methods based on slant measurements. That metric is just used by fossil collectors. Where do you see that striking difference between teeth? They are spaced quite close to each other, the roots seem to (almost) touch. This is what the paper on the pathological whale rib states on the subject: As the roots of lamnid shark teeth in adjacent files do not overlap but very nearly
abut (Hubbell, 1996; Purdy & Malcolm, 2007; Ehret et al., 2009a), it is safe to assume that the roots of these teeth, if deriving from a shark, were also approximately 6 cm wide. Again, that is consistent with 5 in a total of 6 pictures of shark jaws, and consistent with what Kent wrote to me when I asked him. 13m is among the largest specimens in Pimiento et al. 2009. And you have produced several not so modest results with Shimada’s method, all affected by this point. But I wasn’t explaining it to you, we’ve discussed it extensively enough. The slant measurements method remains a method, whatever it is not that rigorous or published compared to others. I see quite a spacing between the teeth, especially in the anterior part, except in one, in none of these jaws the spacing is negligible or near to 0%. But I really don't want to discuss it at length. I want to know the exact value used by Kent and Siversson, not precised in their paper, talk or mails. Kallal just points on that in absolute terms, the spacing in that species is not great, even 15 % is not massive on the whole dentition. 13 m is among the largest in Pimiento because the vast majority is from small teeth belonging to juveniles. But 13 m does not sound like an overestimate and several other figures are larger, two others are in the same neighborhood and all the other smaller. In anycase the results are justifiable and well within the modern range from other methods. The results I've produced myself with Shimada's are all discutable as my measurements were rough added to the potential errors I've made (something that you should keep in mind yourself in your calculations). I don't have the teeth at hand nor the experience to assign them with certainty. Pimiento et al. do have the experience and material. Let's agree to disagree for now. |
|
|
|
Post by Life on Mar 5, 2014 18:33:02 GMT 5
More slender vertebra in relation to the respective length and a higher vertebra count. I didn't get this logic That single large vertebra is from an adult Megalodon:  Do you get slenderness vibe from it? Megalodon is expected to have 200+ vertebral count in it (sizes would vary position wise). In contrast, GWS neither have extremely elongated vertebrae (sizes still vary position wise) and nor matching count. This observation seems to indicate the possibility of more liberal TL to BL dynamics in Megalodon in contrast to that of GWS. |
|
|
|
Post by Grey on Mar 5, 2014 18:36:24 GMT 5
More slender vertebra in relation to the respective length and a higher vertebra count. I've discussed at length with Kent, Ehret who have studied and handled megs centra. They've never suggested that Megalodon's centra were more slender and that the shark by itself was slender. The problem with weight estimates based on white sharks is not related to centra but that the largest great whites get fat with age, we don't know if that was the case for Megalodon, and the actual proportion of its liver, wich has a massive impact on the weight. But based on the fact this shark preyed on highly caloric organisms, probably even more so than the white shark in proportion, I wouldn't surprised if the largest, oldest Megs were fatty too. |
|
|
|
Post by creature386 on Mar 5, 2014 18:38:35 GMT 5
Slenderness was the wrong word, from what theropod said, they appear to be proportionally longer (so I should have said in relation to width).
|
|
|
|
Post by Grey on Mar 5, 2014 18:40:07 GMT 5
More slender vertebra in relation to the respective length and a higher vertebra count. I didn't get this logic This vertebra is from an adult Megalodon: Do you get slenderness vibe from it? Based on that pic, it is sure that compared to Carcharodon hubbelli, this Meg centra is anything but slender, rather much thicker. But here again there is the problem I've discussed at length with theropod : we can agree on this only if that centra was from the same positions than the centra from the Carcharodon skeleton in the pic, which we don't know. But quoting Kent in mail : The vertebral centra in megalodon are consistent with a robust, fusiform body, and are very different in shape from those found in eel-like (i.e., anguilliform) swimmers. |
|
|
|
Post by Life on Mar 5, 2014 18:48:18 GMT 5
Slenderness was the wrong word, from what theropod said, they appear to be proportionally longer (so I should have said in relation to width). I am sorry, this doesn't makes any sense. theropodWhat are you trying to assert in this respect? Based on that pic, it is sure that compared to Carcharodon hubbelli, this Meg centra is anything but slender, rather much thicker. But here again there is the problem I've discussed at length with theropod : we can agree on this only if that centra was from the same positions than the centra from the Carcharodon skeleton in the pic, which we don't know. But quoting Kent in mail : The vertebral centra in megalodon are consistent with a robust, fusiform body, and are very different in shape from those found in eel-like (i.e., anguilliform) swimmers. GWS would have some elongated centrum in its body but nothing seems to indicate that GWS is as heavily built as Megalodon even at parity. Teeth alone confirm this situation. Their is no such thing as mixture of slender and robust physiology in a single shark. All megatoothed sharks are more heavily built then even the largest known smalltoothed shark in history. Just look at the remains of O. obliquus, it puts GWS to shame in a comparison of physiology and Megalodon is the largest megatoothed shark in history. To even assert otherwise is absurd. Megatoothed sharks were the real heavyweights among sharks, they were true big-game hunters. |
|
|
|
Post by theropod on Mar 5, 2014 18:57:26 GMT 5
You meant what I was stating about the vertebrae?
Obviously, if the centra are proportionally longer, and there were more of them, that implies a more slender vertebral collumn.
The estimated vertebral count for C. megalodon is 190-200, not 200+
What remains are you talking about? Nothing I have seen of O. obliquus puts the great white to shame, other than the size reached in large specimens.
What suggests that C. megalodon was bulkier than predicted by regressions based on extant lamniforms? Especially, what suggests it was both bulkier and longer?
|
|
---which-are-up-to-six-centimetres-long---are-very-similar-to-sharp-blades-Shark-teeth-have-proved-to-be-especially-durable---as-fossiles-even-for-millions-of-years.jpg)
