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Post by Grey on Feb 13, 2014 16:51:56 GMT 5
Theropod I agree with you, the problem is that I had talked about this to Kent, but it does not seem it was the problem he had with Shimada's. That's why I'd like to verify it on others teeth set and possibly discuss it with an author. Shimada's not perfect certainly but the fact it's since three papers it is experimented and used let me believe that the results, despite the caution to keep with it, are probably not that terrible. Before make any conclusion like that, need to see further.
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Post by creature386 on Feb 14, 2014 19:45:47 GMT 5
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Post by theropod on Feb 14, 2014 21:26:17 GMT 5
You have to differentiate between social and physiological maturity. Most animals don’t simply stop growing as soon as they are sexually mature, but continue to grow, gradually slowing down. The largest part of the growth of course occurrs in the subadult and juvenile stages, but there’s still some variations in "adults" in terms of maturity.
There’s a graph on page 57 of the Great white-symposium I posted in the recommended literature thread.
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Post by Grey on Feb 14, 2014 21:38:51 GMT 5
I'm fine with the status of Megalodon proposed by Gottfried and later used by Pimiento et al. One of the purpose is justly that the range of adulthood varies between 10.5 and 14 m. But we should await the final publication about Megalodon size variation instead of speculating like it was done on the carnivora forum.
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Post by creature386 on Feb 14, 2014 21:44:50 GMT 5
You have to differentiate between social and physiological maturity. Most animals don’t simply stop growing as soon as they are sexually mature, but continue to grow, gradually slowing down. The largest part of the growth of course occurrs in the subadult and juvenile stages, but there’s still some variations in "adults" in terms of maturity. There’s a graph on page 57 of the Great white-symposium I posted in the recommended literature thread. This was about the minimum size where you could consider it to be an adult, to determine this, sexual maturity is perfectly fine. |
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Post by theropod on Feb 14, 2014 22:05:48 GMT 5
Ah yes, of course. In that case, Gottfried et al.’s figures are what you need. It is usually the most sensible to compare adult sizes, that can also be "adult" as in "sexually mature" as long as you take that figure for both. Grey: 10.5-13.9m to be exact, but it is approximate, since it also requires a bunch of other assumptions and the analogy with Carcharodon to be accurate. Sadly, all that this tells us is that they would typically reach sexual maturity at ~10.5-13.9m. The typical size at which they would stop growing (=die) is more tricky, because it depends on the span of life and the exact shape of the growth curve, I’d say ~15m(±1). However, as we see, large specimens likely reached 18m+. |
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Post by Grey on Feb 14, 2014 22:15:08 GMT 5
In the absence of extended Megalodon material, that's justifiable assumptions. What is important is to remember that we use assumptions and anaology with Carcharodon which is not the best model, but rather the least worst. I'll let the reviewers spea before argue anything on this.
If I'm correct, sharks don't stop growing their whole life, they only growth at a slower trend with age. I had asked to Stephen Godfrey his opinion about Megalodon size earlier :
"My only comment is that unlike mammals that have determinate growth, sharks do not, and so like the large Miocene tiger shark tooth illustrated in The Ecphora, as long as megalodon was alive, it kept growing, albeit at an ever decreasing rate. So I very much doubt that we have found the largest possible megalodon tooth."
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Post by Grey on Feb 15, 2014 1:22:11 GMT 5
Have checked again Balk's graphic from her talk. The smallest Megalodon, 14 MYO, is exactly 85 kg, certainly an embryonic individual like some in Gatun. The heaviest individual, 12 MYO, tips at an exactly 69 956 kg, certainly a massive female.
Like said earlier, it is sure that some periods have a smaller range of data, so we can't make any conclusion from this graph, still considering this with interest. Hoping the final publication to be published this year.
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Post by elosha11 on Feb 15, 2014 2:27:17 GMT 5
Have checked again Balk's graphic from her talk. The smallest Megalodon, 14 MYO, is exactly 85 kg, certainly an embryonic individual like some in Gatun. The heaviest individual, 12 MYO, tips at an exactly 69 956 kg, certainly a massive female. Like said earlier, it is sure that some periods have a smaller range of data, so we can't make any conclusion from this graph, still considering this with interest. Hoping the final publication to be published this year. The large female is estimated at 77.1 tons. I'm still trying to catch up on all the postings on this thread. Can someone summarize Balk/Pimiento's finding with regard to the largest teeth? I know several estimates approached 18 meters, with the longest Meg estimated at 17.9 meters. Was this based solely on tooth length or tooth width? If the former, did Balk simply use Gottfried's study on tooth length and Carharodon proportions to make her estimates? |
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Post by creature386 on Feb 15, 2014 2:41:59 GMT 5
Have checked again Balk's graphic from her talk. The smallest Megalodon, 14 MYO, is exactly 85 kg, certainly an embryonic individual like some in Gatun. The heaviest individual, 12 MYO, tips at an exactly 69 956 kg, certainly a massive female. Like said earlier, it is sure that some periods have a smaller range of data, so we can't make any conclusion from this graph, still considering this with interest. Hoping the final publication to be published this year. Don't use words like exactly, when it's about log numbers, two decimal places can already mean something and that's almost impossible to measure exactly. This is only the exact calculator result. |
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Post by theropod on Feb 15, 2014 3:04:04 GMT 5
@elosha The figures from Pimiento et al. 2013, including the 17.9m one are based on Shimada’s method (the formulas can be found in the supplementary data for the older Gatun-nursery study). The tooth belonging to that size estimate is obviously a posterior. I’ve outlined potential problems with this and other tooth-height methods here?. In short, I have serious doubts about that specimen being 17.9m, and about Gottfried et al.’s 168mm tooth (almost as big as Hubbell’s!) being from am mere 15-16m animal. The poster’s resolution is poor. I get 10^4.87=74,131kg (I’m not rounding this any further to prevent summing up errors), but it’s a matter of 55px=1, so it really is quite insufficient. Any deviation by a single pixel can already have a notable impact, i.e. the data are very rough as they are. That’s just preliminary data anyway, without knowing the details about sample sizes, we should treat it very cautiously. |
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Post by Grey on Feb 15, 2014 5:29:21 GMT 5
Theropod, I agree but it has to be extensively verified. Frankly, this finding of us about the potential issues in Shimada's is not an extraordinary finding and I would be very surprised that no shark expert has found it either. This method was also used by others paleontologists like Ciampaglio who used it (along with Gottfried's) for the Sharkzilla documentary. Again, no one seems to have complained about these potential problems. The thing is that whatever the measurements reflect the absolute accurate size of this meg individual, this size is still in the acceptable and modern range proposed for Megalodon by any method.
Globally, I consider Shimada's method to be good, somewhat globally conservative (I don't know of any estimate with it reaching the 20 m mark yet) and useful as it determines if a posterior tooth belonged to a big one or not, an adult or not, whatever the degree of the size accuracy. And it does not seem this method has been criticized for that matter as it's been several papers it is regularly used. Some might prefer others, I know that Dana Ehret, despite prefering tooth width estimates, used Shimada's in several papers. In my case I accept all rigorous methods. And I ask to be cautious while arguing about these issues in Shimada's, perhaps we ignore others factors, the details in the calculation and again the fact that none of these sharks experts has expressed that particular criticism about that method. One alternative : instead of arguing on the board, just contact and discuss with them.
Yes, one px difference has a great impact on the plot, that's why I've posted the lowest figure at 20 px, instead of 21 in my first post. However, that the graph is preliminary suggests only to be cautious with the median figures in the graph, but the highest and lowest peak are not to be discussed as they represent the largest and smallest individuals in the plot. It will change only if they found smaller or larger individuals in the final paper. And I doubt they'll find an even smaller individual than 85 kg, and I'm not sure that Shimada's method in the total sample will figure out a Megalodon significantly higher than 18 m (so ~70 tonnes).
However, I recall that I don't think this highest peak around 70 tonnes is based on the 17.9 m specimen, as this one from Gatun is 10 MYO, and the 70 tonnes peak is in the 12 MYO plot.
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Post by theropod on Feb 15, 2014 16:27:03 GMT 5
They must have included something bigger than that specimen, based on Gottfried et al.’s formula a lenght of 17.9m would imply a weight of 69t.
Based on my measurement from the graph (74.131t), the individual with that body mass would have been 18.27m long.
That those data are preliminary affects upper and lower bounds even more. If the sample gets enhanced, specimens are going to be added on either side of the median, and will probably expand the size range in the sample. The median will remain RELATIVELY stable, unless there is a massive bias in the data collected so far.
Fair enough on the first part, as long as you keep it in mind. As soon as we find some additional white-shark dentitions with measurements we can verify it more extensively. Don’t forget you were the one to first note this discrepancy.
And it’s not as if scientists always complained as soon as there is a problem with a method, many flaws have simply been overlooked over the years (European Torvosaurus), undoubtedly by numerous researchers, and it’s not as if a method that was not rebutted was automatically considered flawless.
This method was probably used simply because it provides the most convenient way of estimating the shark’s size based on every position in the toothrow. But at the same time, the resulting figures are also highly uncertain (even ignoring the difference between GWS and meg dentition). For example, the size figures in Pimiento et al. 2010 (and thus 2013 too) are the mean figures of tooth-position-ranges that frequently suggest a 2- to 3-fold difference in terms of TL (that is, literally, even worse than Amphicoelias fragillimus).
For example, the specimen estimated at 16.8m, based on a crown height of 28.1mm, could have been a lower lateral 4-6, i.e., it could ahve come from an individual of 9.4m, 14.8m, or 26.0m.
I would not claim this method to be generally conservative. It is obviously conservative with anterior teeth. For all we know, not with posteriors. I have yet to see other rigorous methods to yield estimates of 20m or above.
They are certainly well-aware of the limitations, for that very reason there are people who favour tooth width and jaw perimeter (Siversson, Kent, Jeremiah etc.).
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Post by creature386 on Feb 15, 2014 16:49:42 GMT 5
And it’s not as if scientists always complained as soon as there is a problem with a method, many flaws have simply been overlooked over the years (European Torvosaurus), undoubtedly by numerous researchers, and it’s not as if a method that was not rebutted was automatically considered flawless. But the European Torvosaurus mistake didn't happen because of a wrong method, but because of a misquotation. I believe it would be easier to find a wrong method (especially for people dealing a lot with methods and citing them in their own works, like Kent did with Pimiento) than to look at every single source to see if all was cited correctly. |
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Post by theropod on Feb 15, 2014 17:28:46 GMT 5
That was simply an example for an error that was overlooked. An example for a bad method ("wrong" in this case is a problematic term) would be Therrien & Henderson 2007, but as it happens, due to the existence of more complete remains, there is not a small number of methods that are used over and over again in theropods.
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