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Post by Grey on Oct 13, 2017 20:53:59 GMT 5
No idea yet elosha.
One interesting point.
I don't trust a lot Shimada methodology applied to Otodus but I tested the calculation for the 41.2 mm CH L5-L7 tooth from the matrix indicating a 17.9 m TL. But this appears to be an error. Using the regression for each position I got respectively 10.81 m, 19.96 m and 28.06 m, the average being 19.6 m for this specimen.
So while I don't care too much for this methodology, the maximum TL derived from this paper should be actually 19.6 m TL.
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Post by elosha11 on Nov 10, 2017 22:09:03 GMT 5
No idea yet elosha. One interesting point. I don't trust a lot Shimada methodology applied to Otodus but I tested the calculation for the 41.2 mm CH L5-L7 tooth from the matrix indicating a 17.9 m TL. But this appears to be an error. Using the regression for each position I got respectively 10.81 m, 19.96 m and 28.06 m, the average being 19.6 m for this specimen. So while I don't care too much for this methodology, the maximum TL derived from this paper should be actually 19.6 m TL. Grey, if your analysis is correct, really great work! How exactly did your regression differ from the researchers? This seems to be a very critical point as it could dramatically change the scientific consensus on currently known maximum size of the shark. Big difference between 17.9 meter estimate and 19.6 meters. Have you thought about contacting Pimiento and the other researchers about this point? If they agree with you, they very well may amend their paper to clarify this and use your 19.6 meter estimate. It would be scientifically valuable and important to make this correction. |
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Post by Grey on Dec 12, 2017 5:11:34 GMT 5
No idea yet elosha. One interesting point. I don't trust a lot Shimada methodology applied to Otodus but I tested the calculation for the 41.2 mm CH L5-L7 tooth from the matrix indicating a 17.9 m TL. But this appears to be an error. Using the regression for each position I got respectively 10.81 m, 19.96 m and 28.06 m, the average being 19.6 m for this specimen. So while I don't care too much for this methodology, the maximum TL derived from this paper should be actually 19.6 m TL. Grey, if your analysis is correct, really great work! How exactly did your regression differ from the researchers? This seems to be a very critical point as it could dramatically change the scientific consensus on currently known maximum size of the shark. Big difference between 17.9 meter estimate and 19.6 meters. Have you thought about contacting Pimiento and the other researchers about this point? If they agree with you, they very well may amend their paper to clarify this and use your 19.6 meter estimate. It would be scientifically valuable and important to make this correction. I've sent this to Pimiento but got no response. I don't think this has much importance to her. Plus, reading her thesis, she regularly describes the sharks as being able to reach 20 m. So for the exactness, it could be appropriate to update the data but overall that's probably not too much important. I guess. |
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Post by elosha11 on Dec 12, 2017 20:54:45 GMT 5
True, that paper wasn't focused on establishing size parameters of the species, so it's probably not vital, in their view, to make any such corrections, even assuming they agree with it.
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Post by prehistorican on Dec 16, 2017 1:21:49 GMT 5
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Post by Grey on Dec 16, 2017 5:21:53 GMT 5
That's juste the figure based on Gottfried research. 16 m is the most conservative maximum size available in the literature. Gottfried extrapolated specimens about 20 m were plausible as well. According to Ferrón 2017, a 17.9 m specimen would have a cruise speed of 5 km*h and a burst speed of 37 km*h. That's not slow speed. |
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Post by Infinity Blade on Dec 19, 2017 18:41:12 GMT 5
Am I allowed to link another forum’s thread here? I wanted to ask what you all thought about Animalia forum’s Megalodon size thread discussion; either I can give a link and easily transmit you to it, or you can just Google Animalia forum.
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Post by Grey on Dec 19, 2017 20:18:28 GMT 5
Am I allowed to link another forum’s thread here? I wanted to ask what you all thought about Animalia forum’s Megalodon size thread discussion; either I can give a link and easily transmit you to it, or you can just Google Animalia forum. The person claiming vertebra are the best mean to estimate TL is actually wrong. There is a reason why fossil sharks researchers rather use methods based on dentition/tooth parameters. The reason being that you can assign one tooth to a position in the dentition but it is extremely difficult to assign one centra to a position in a vertebral column. And since complete columns have not been discovered and described, contrary to complete sets of teeth, that's even more complicated to be sure of anything using isolated centra. The Danish 23 cm in diameter centra can't be assigned to a precise position in the column while the large tooth owned by Hubbell can be assigned to a position. He critics the variability of teeth based methods but he should remark that precaudal centra diameter in the Belgian (incomplete) backbone ranges from 50 mm to 155 mm. This means any isolated precaudal meg centra, without precise placement, could result in a size range of 1 to triple. His criticism of the method based on summed tooth row length is elluding the conclusion reached by the authors; the ontogenic stage is directly related to the stability of the results. Using only adult individuals dentitions for the Yorktown dentition results in a range of possible size of 17-20 m, which is quite small and stable compared to other methods. Obviously, if one wants to estimate the most likely size range of the adult meg dentition from Yorktown, he should use large adult white sharks with mammal-eating habits rather than even smaller neonates with fish-eating dentition. And if there were 8-10 m TL giant white sharks, with available dentitions, it would be more adequate to use them to estimate meg size rather than 4-6 m TL adults. |
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Post by prehistorican on Dec 19, 2017 21:08:24 GMT 5
Nice response, even I didn't know centra were that variable.
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Post by Grey on Dec 19, 2017 21:53:04 GMT 5
Nice response, even I didn't know extra were that variable. You can copy my comment on their forum or link it if you want. |
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Post by Infinity Blade on Dec 19, 2017 23:37:36 GMT 5
Alright, but I wouldn't know how to respond because I'm not really knowledgable on extinct shark size estimation methods. Would this just be me serving as the liaison of responses between our two forums? I'd be fine with that.
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Post by Grey on Dec 20, 2017 0:03:32 GMT 5
You can, I don't see the problem.
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Post by prehistorican on Dec 20, 2017 20:11:42 GMT 5
Wait so if Yorktown was 17-20m, then how large would Hubell or Bertucci’s tooth specimen be?
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Post by prehistorican on Dec 20, 2017 21:23:49 GMT 5
“Vertebrae estimation methods based not on the diameter of random vertebra, but on the maximum diameter of vertebra in all precaudal vertebral column. And in shark's vertebral column at once several vertebrae reach the maximum diameter (see e.g. Cretoxyrhina mantelli by Shimada, 1997).
Complete columns of Otodus megalodon have not been discovered and described? Hmmm... IRSNB 3121 is almost complete vertebral column.
Estimations based on width of Yorktown specimen upper jaw and proportions of large adult great white sharks gives 15.11 m TL as well as 20.59 m TL. If estimation based on width of Yorktown specimen lower jaw gives more stable value in 18.06-23.85 m (not 17-20 m), this even does not mean that this value will be preserved when sample is increased. E.g. O. chubutensis estimations based on width of Caballos specimen lower jaw and proportions of large adult great white sharks gives 10.48 m TL or as much as 16.42 m TL.
And by the way, different results of calculations based on upper jaw and lower jaw of Yorktown specimen already indicate different proportions in comparison with great white shark jaws.
”
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Post by Infinity Blade on Dec 20, 2017 21:43:44 GMT 5
I guess prehistorican beat me to it. I was going to inform Grey about the guy's response, but now that's less work on my part.
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