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Post by coherentsheaf on Mar 4, 2014 19:00:23 GMT 5
It is established that Gottfried's equation suggests that Megalodon was overall three times the length of the equivalent white shark. I don't see how you can determine the median sizes to be lower other than by assumptions either. Gottfried's table is not perfect but has not been invalidated in more recents works. Unless you consider a 4.6 m white shark to be "large and mature", which is not, I don't see the basis of your assumption without performing a quantitive work comparable. And I'd suggest to wait for the final publication of Balk and Pimiento before arguing more. I do not know abut white shark sizes at the moment. Afaik, the only study I read trying to determine sizes during ontogeny was patently flawed by having a very small sample size and excluding specimen that were too small because they did not align with the other specimen. Empirically, a 4.6m long white shark is quite rare, so I would suppose that given the very low growth rate, that many smaller specimen are mature as well. I would suggest not to lean at the table by Gottfired at all, as it would not pass any muster.
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Post by Grey on Mar 4, 2014 19:11:37 GMT 5
What was the study ? I think there is a quantity of studies about great white growth and measurements and that the average size and maturity size is well known and established in that species. Even though some populations appear to be larger than others (Mediterranean GW are sensibly larger than the South African ones), I don't think 4.6 m overall is supposed to represent a large, mature adult especially in females.
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Post by Life on Mar 4, 2014 21:45:20 GMT 5
What’s wrong with quantitative data (anatomy and palaeontology are, above all, a quantitative science. All the more considering it often requires restoration and size estimates!), and why should this give us minimum estimates? Every lifeform has constraints, and there is no reason to presume the constraints on C. megalodon would allow it to be bigger than would be indicated by the quantitative data of extant sharks. Nothing wrong with quantitative data but importance of qualitative assessment should not be overlooked either. I understand that every life-form have constraints but following are some questions: 1. What are the constraints of Megalodon? 2. Are the constraints of GWS applicable to Megalodon? We need to be logical in our observations, not just calculative. While it is acceptable practice to use a size estimation method for GWS to estimate the size of Megalodon, underlying qualitative judgement about this practice is that this approach imposes constraints of GWS on Megalodon. In this manner, we get minimum estimates for Megalodon.
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Post by creature386 on Mar 4, 2014 22:12:11 GMT 5
What was the study ? I think there is a quantity of studies about great white growth and measurements and that the average size and maturity size is well known and established in that species. Even though some populations appear to be larger than others (Mediterranean GW are sensibly larger than the South African ones), I don't think 4.6 m overall is supposed to represent a large, mature adult especially in females. Well, this seems to hold true for at least western North Atlantic great whites. Here, great white shark specimens which were defined as large all were in the 4.6 m ballpark (most were actually even smaller): fishbull.noaa.gov/932/kohler.pdf
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Post by theropod on Mar 4, 2014 22:12:14 GMT 5
I fear I cannot follow your logic @life. Scaling from great white sharks merely assumes a comparable relationship between a given measurement (a dimension of a specific tooth, a dimension of a vertebra, or summed dimensions of either) and the total body lenght of the animal. That will never be exactly the case, but it is an approximation of its real proportions, and an approximation is the best we have (I.e. the best we can say today is that it was built roughly like a Great white or Mako shark, with a dentition obviously more comparable to the great white).
Where is the reason to presume that constraints on C. megalodon make it more likely that it grew bigger than predicted by the size of its fossils (I.e. that it had proportionally smaller mouth, vertebrae, teeth etc.) than that it was smaller?
Scaling from Great white sharks (one way or another that’s still the basis for almost all methods there are) is justified, because Carcharodon is the closest living analogue in terms of its dentition, ecology and size. We’d get the same situation if we used any other shark tough, the estimates would just have a different likelyhood and be somewhat different themselves.
Great white sharks are an order of magnitude smaller than C. megalodon. Their constraints are obviously not comparable. But what does this indicate? That it was bigger than predicted (if so, why exactly?), or that it was smaller (again, why?)? We do not know, we’ve got no indications whatsoever, therefore, how can we claim the predicted value to be a minimum estimate? It’s actually an average estimate.
Quantitative data are all that we can rely on. Fossils can be measured, and the differences and their impact quantified. That is the sole most objective way of doing it, and it works perfectly fine. This is not ethology, it’s all about measurements, proportions and physical constraints.
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Post by Grey on Mar 4, 2014 22:22:29 GMT 5
What was the study ? I think there is a quantity of studies about great white growth and measurements and that the average size and maturity size is well known and established in that species. Even though some populations appear to be larger than others (Mediterranean GW are sensibly larger than the South African ones), I don't think 4.6 m overall is supposed to represent a large, mature adult especially in females. Well, this seems to hold true for at least western North Atlantic great whites. Here, great white shark specimens which were defined as large all were in the 4.6 m ballpark (most were actually even smaller): fishbull.noaa.gov/932/kohler.pdfThat applies to that population.4.6 m is overall an average size for adults great white sharks. I don't post any source, there are plenty enough easy to find. That paper also mentions sizes in Fork Length, not Total Length.
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Post by creature386 on Mar 4, 2014 22:26:01 GMT 5
And how do we know this population is particularly small? To me, they aren't easy to find at all and my browser can't open many of the ftp files (no idea why, earlier it was able). Is the average figure on Wikipedia reliable? Most of the sources cited were rather for the 6.4 m shark than for the average range given there.
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Post by theropod on Mar 4, 2014 22:28:43 GMT 5
a quote from that paper:
The mean lenght of 2.04m is interesting for comparison. Obviously, there appear to be differences, perhaps because it’s not a global average... Lamna nasus appears bigger than I tought it was.
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Post by Grey on Mar 4, 2014 22:29:17 GMT 5
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Post by creature386 on Mar 4, 2014 22:29:50 GMT 5
theropodI wasn't saying 6.4 m is reliable because it has five sources, I was just saying most sources weren't about the average size. GreySo, it would be like 5 m in total length, right?
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Post by Grey on Mar 4, 2014 22:31:18 GMT 5
There are still large specimens that have reliable size figures.
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Post by Grey on Mar 4, 2014 22:34:09 GMT 5
theropodI wasn't saying 6.4 m is reliable because it has five sources, I was just saying most sources weren't about the average size. GreySo, it would be like 5 m in total length, right? Something in that neighborhood I'd guess.
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Post by theropod on Mar 4, 2014 22:39:50 GMT 5
Why do you have to guess? The paper gives a figure, fork lenght represents 92% of Tl in lamnids, or more exactly, 0.9442TL-5.7441 in the great white. I.e. if you want to get the TL from FL all you have to do is calculate FL/0.9442+5.7441 A Fork lenght of 4.6m corresponds to a TL of 4.93m. creature386: I wasn’t specifically adressing you. I’m quite confident in Carcharodon reaching that lenght, it’s what was reported for a specimen from Cuba. Just adressing the topic at hand, size at maturity and maximum size are both difficult to verify. EDIT: Kohler et al. give 332 and 454cm as the fork lenght at maturity, translating to 357 and 487cm TL. Average for both sexes would be 407cm. Note however that other authors give more conservative estimations of the size at which maturity is reached, such as 366-427cm (Bigelow & Schroeder 1948, cited following Caillet et al. 1985). So a 4.6m great white is most likely a mature specimen. Great white sharks that size are commonly among the largest in samples, and are regarded as large white sharks in research works (e.g. Casey & Pratt 1985). For a male, that’s already a very big size, though not necessarily for a female. And certainly it’s not a small great white. For what it’s worth (not much), if you take that "Meg=GWS*3" assumption (which seems to basically assume an 18m megalodon is analogous to a 6m great white) the corresponding figure if 13.8m for meg. That’s somewhat consistent with the few actual adult individuals reported thus far (the Yorktown and the Uyeno et al. dentitions, and the specimen from Denmark). We can expect average size of mature Megalodons to be somewhere between 13 and 15m based on the methods available.
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Post by elosha11 on Mar 5, 2014 3:18:07 GMT 5
I haven't had time to read from my last comment on page 41 to this page now, so with that caveat, let me briefly comment.
It is premature to claim that the Denmark specimen with 20 vertebral centra ranging from 10 to 23 cms, and with an associated 16 cm tooth, was around 13 - 14 meters in length. First, there are only 20 centra, so approximately only 10 percent of the skeleton. To claim 23 centimeters was the maximum sized centra is ignoring ninety percent of the missing evidence. The fact that the centra ranged so drastically from 10 to 23 cms, may mean that we only have a scattered, random assortment of associated centra We need to review the paper about these fossils, but it seems to suggest that we may not even have any ordered, sequential centra at all from those preserved. Again, I'll have to find the paper to confirm and we definitely need to add that paper to Megalodon profile if it isn't already there. I think there's a reasonable chance that the 23 cm is a large centra, but not the largest in the vertebral column. Judging by the size of the 16 cm anterior tooth, my very rough guess would put this shark at around 15-16 meters, based again on a composite of all the tooth size methodologies discussed here. This would be further corroborated if Klaus Honninger's calculation of a 18-19 meter Meg skeleton with 26 cms centra (which may or may not be the largest) is confirmed.
Second, using GWS as proxy for Megalodon seems to have more and more limited use, but the GWS is the best analogy. I think 4.6 meters may represent a reasonable size for a modern female GWS, perhaps even "average." Anything exceeding 5 meters is a big shark. But -- you absolutely must keep in mind that GWS size and overall population is depleted and limited due to human interference. In other words, you could likely find far more frequent 6 meter + GWS 50,000 years ago then today. Just like prehistoric GWS, Megalodon was privileged to have no human interference with its environment, life cycles and food sources.
Even today with GWS populations at an all time low, a 5 to 6 meter GWS is unusual, but not really infrequent. Just in the past 3 or 4 years, you can find probably close to a dozen reports of such sized animals. My preliminary guess is that it would not be very uncommon for Megalodon throughout the Miocene and Pliocene to reach relatively large size, maybe 15-16 meters average in times of plenty and 18+ meters for very large adults (and not necessarily just the females).
Will comment more when I have time to fully catch up on this thread.
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Post by Life on Mar 5, 2014 7:51:14 GMT 5
I fear I cannot follow your logic @life. Scaling from great white sharks merely assumes a comparable relationship between a given measurement (a dimension of a specific tooth, a dimension of a vertebra, or summed dimensions of either) and the total body lenght of the animal. That will never be exactly the case, but it is an approximation of its real proportions, and an approximation is the best we have (I.e. the best we can say today is that it was built roughly like a Great white or Mako shark, with a dentition obviously more comparable to the great white). Where is the reason to presume that constraints on C. megalodon make it more likely that it grew bigger than predicted by the size of its fossils (I.e. that it had proportionally smaller mouth, vertebrae, teeth etc.) than that it was smaller? Scaling from Great white sharks (one way or another that’s still the basis for almost all methods there are) is justified, because Carcharodon is the closest living analogue in terms of its dentition, ecology and size. We’d get the same situation if we used any other shark tough, the estimates would just have a different likelyhood and be somewhat different themselves. Great white sharks are an order of magnitude smaller than C. megalodon. Their constraints are obviously not comparable. But what does this indicate? That it was bigger than predicted (if so, why exactly?), or that it was smaller (again, why?)? We do not know, we’ve got no indications whatsoever, therefore, how can we claim the predicted value to be a minimum estimate? It’s actually an average estimate. My point is very simple: when we use a size estimation method (valid for GWS) to estimate the size of Megalodon, we (logically) impose the constraints of GWS on Megalodon which leads to less reliable estimates of the size of the latter shark. This procedure is acceptable due to GWS being closest living analogue to Megalodon but should we consider estimates for size of Megalodon obtained through such procedure as absolute? This is the point. If a size estimation method (valid for GWS) gives 18 m total length (TL) for the largest known Megalodon tooth, their is still room for error in this case, this individual could be 20 m long in life. So if Grey asserts that 20 m TL is possible for this individual, he is not being unreasonable. Size estimation methods that are used to estimate the size of Megalodon are basically developed to estimate the size of GWS; these methods impose same constraints on Megalodon which are actually valid for GWS but this assumption can be false due to observations such as Megalodon dentition not being as compact as that of GWS (differences in dentition) and possibility of difference in TL - BL dynamics (differences in composition of vertebral column and vertebrae themselves); these are the observations that should not be logically overlooked. It doesn't matters if paleontologists around the world use GWS to estimate the size of Megalodon in current times (many do this under constraints of published literature and this approach being regarded as an acceptable procedure) but we aren't obligated to blindly adhere to such procedures. Someday, somebody, is likely to question this approach just like Megalodon's alignment with Carcharodon genus had been. In the end, we are (or I am) interested in finding out the truth about Megalodon and not what world thinks about it. UPDATE: Regarding Shimada, theropod suggests that it is prone to (relative) overestimates using posterior or lateral teeth, and underestimates with anteriors teeth, considering that Megalodons had more compact teeth at parity than the white shark. Only, I don't see how all the team of Megs experts who used that method have not considered this. Also, Shimada highest estimates, for now, do not exceed 18m, which means that, while not overly conservative, is more modest estimates that based on the largest or widest teeth yeild in sizes approaching 20 m. theropodAre you sure that you are using Shimada's method properly? It is the most difficult method to understand and use, IMO. Shimada's method is almost as conservative as that of Gottfried et al (1996), slightly more to be precise. However, Shimada's method is not restrictive in its approach to estimate the size of shark. Kent certainly knows what he is talking about. and we can observe it: here the adjacent roots have very little, if any, space in between. some of them definitely touch. same here. and here This last one has much greater spacing, which is where I took the 15% from. that’s of course a ballpark estimate due to our obvious inability to measure it precisely from an image with perspective, but that’s the best we have for now. A precise average spacing would be preferable, but it is not available. The figure from Newbrey et al. is within the range of reasonable possibilities. The shark from bone-clones must have been close to the upper end as far as spacing goes, and a bit longer than would be predicted, or, it has abnormally big spacing. Or, less likely, there’s a total sampling bias and Kent is wrong too. I hope I’don’t have to repeat it again. If you dismiss this I’m certainly not the one who belittles someone... Be very careful when you consider jaw structures like these for size estimations. These jaw structures are often artificially inflated or not properly prepared. This is correct jaw structure: This one as well: The jaw structure in the top image represents a reportedly 6m long GWS. Important readings:
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