Megalodon size

[Grey]

Good point creature386

The main purpose is that for each tooth specimen I found, I use the known methods of estimate for megalodon.

All have their own uncertainities, but all can be still used a this point.

I don't use Randall or Shimada as I lack datas on the crown/enamel length on most specimens.

I personnally favor just a little bit the tooth width by Jeremiah and the allometry by Shimada.

For Jeremiah, the problem is that same that for Gottfried and Randall, it lies in a great room on error, and the results are indicative. The good point however on the contrary to the others is that it works on others lamniforms species, and not only the white shark, which is perhaps not a perfect proxy.

For Shimada, the good point is that it is allometric, so displays a much smaller room of error, and can be used for any tooth of the dentition. The problem being that it is based on the great white only, just like Gottfried and Randall, despite we know now that megalodon is not that related and that tooth position, especially for the lateral and posterior teeth is difficult to determine.


But all can still be used. For discussing with Chuck Ciampaglio about Sharzilla, I know he used both Gottfried and Shimada for estimating the size of the shark based on the tooth they've found lying near the cetothere skeleton.

[theropod]

You could measure the crowns in those that have a scalebar.

I would include all the specimens known for direct scaling, not just two, and best the average. Allometry also has its problems, especially with animals far outside the data range. Do you have a copy of Shimada's paper? It is paywalled.

For Jeremiah, I would like to see the comparative data suggesting it works well, and for which species it does. Any idea about those?

For the Gottfried reconstruction, it defintiely has larger teeth than the great white, at least as long but more massive. The reconsturction is not necessarily accurate tough, and we don't know the exact proportions. I think we should assume similar tooth widths to Great whites. To date I think no other shark has been nominated as a more likely model, and the great white still shows many similarities in general tooth morphology.

[creature386]

Jun 24, 2013 0:16:29 GMT 5 theropod said:

To date I think no other shark has been nominated as a more likely model, and the great white still shows many similarities in general tooth morphology.

Not as a more likely model, but alternative reconstructions exist. Here one based on the suggestion of Megalodon being more closely related to Odontaspis:
theworldofanimals.proboards.com/post/502

[Grey]

I'm not skilled at manipulating pics on the net, that's why I don't try this with the pics. Everyone can do it if he wants though.

There's no question of average but of direct sizing based on one specimen. You can get similar results with smaller white sharks as long as you have their measurements of body and UA teeth. Don't harass me, harass Gottfried if you hate so much that method.

Are you sure that allometry is not better than isometry when scaling outside the data range ? It seems to me that allometry was more reliable on that matter.

I have the Shimada's paper but you can see the method's technics in the Pimiento publication in the meg profile thread. Here is the table.



Regarding Shimada, this is Mike Siversson who used it on various lamniforms species, including Lamna nasus. Certainly he prefers that method...

Yes the white shark is still a valid analogue but not necessarily that good (see Kent 2013 soon).

[theropod]

Allometry applied to something far outside the data range would imply an ongoing change of proportions. eg if I have a sample of two sharks (grossly simplyfied of course), and the 6m one happens to have teeth only 5% bigger than the 4m one, this would imply tooth size would decrease heavily. Of course it is not viable that c. emgalodon had much smaller teeth than a similar sized great white, that's the problem with allometry. If not better, isometrical scaling is certainly not worse either, and it has some degree of "solidness" because you know this simply assumes similar proportions.

Why do you take that specimen out of all the specimens? Average would simply be more reliable. We don't have individual data on all the specimens, but why do you think taking the average as proposed by Gottfried (and probably as the better method) is worse?

[Grey]

Jun 24, 2013 0:47:29 GMT 5 theropod said:

Why do you take that specimen out of all the specimens? Average would simply be more reliable. We don't have individual data on all the specimens, but why do you think taking the average as proposed by Gottfried (and probably as the better method) is worse?

But this in not worst or better ! Why Gottfried did both of these methods ? The direct sizing is for a hypothetical max size based on max sized great whites, the extrapolation (15,9 m) is the conservative maximum based on a sample of specimens. Period ! Why are you still arguing and over and over again ?

It's not me who made that method so give me a break !

Ok for the allometry question, I will dig further in it.

[theropod]

A metod based on 10 specimens is better than one based on one or two. Isn't that logical? You yourself wrote the point of this thread is not to establish a number of hypothetical maximum figures, so why do you extrapolate those, but not the normal figures? I'm arguing over and over again because I think you don't understand what I mean. Gottfried even excluded the two freak specimens in the regression.

[Grey]

Jun 24, 2013 0:58:11 GMT 5 theropod said:

A metod based on 10 specimens is better than one based on one or two. Isn't that logical? You yourself wrote the point of this thread is not to establish a number of hypothetical maximum figures, so why do you extrapolate those, but not the normal figures? I'm arguing over and over again because I think you don't understand what I mean. Gottfried even excluded the two freak specimens in the regression.

Hey, are you mocking me ? Read my posts, you'll see that I use the normal figures !

Because Gottfried used them as exceptionnal large specimens. The 20,3 m figure was still used by Wroe later.


And these were not freak specimens, a great white over 6 m is not abnormal only very large.

[Life]

theropod

In the field of extrapolation, scientists deal with possibilities. Shark tooth size to body length dimensions are variable; norm is that larger shark have larger teeth accordingly but their are exceptions and variations to consider as well. The size estimation method developed by Gottfried at al is conservative in the sense that it is based upon these principles and issues; however, method proposed by Shimada is possibly even more reliable but results are slightly more conservative with it. So essentially both methods are good. I personally think that root width to jaw size parameter based methods deserve more credit then they are normally given but these methods haven't received much publicity unfortunately. This being said, animals are known to produce exceptionally large individuals and sharks are not an exception to this rule; white sharks are known to exceed 6m in TL, even if rarely but these specimens do factor-in. Those who have seen Cuba and Malta specimens, were stunned by their respective sizes. Photos can be deceiving and photo-analysis isn't a reliable method to figure out the size of an individual and this is why we got some under-estimates for these two specimens. However, scientists have done complete homework to determine the sizes of these two specimens and findings indicate that these specimens could be within 7 - 8m in TL. So possibility exists.

As far as extrapolations are concerned, their is always room for error in the very high-end size range but scientists do not ignore possibilities. If Peruvian findings are taken in to account, we probably have an answer, though situation in that region is unfortunate. I hope this clarifies the situation.

[theropod]

@life: Thanks,I agree with you, and the situation is clear.

Grey: I am not mocking you, you are just too fast in thinking I do. Was I that fast doing so...

A 6,5m long great white is definitely an extremely large specimen. Based on the frequency of such animals, you can call them freaks.

You still don´t understand me. You sell the direct sizing as if those were the bases for it,while obviously, those are just some exceptional specimens. I don´t want to dismiss these estimates as impossibleor the methodas necessarily flawed, just unlikely.

I never saw you using any of the other specimens, if you did, where? Apart from the two giant sharks, I only saw Gottfried´s regression and Jeremiah´s root width ratio. Please,if you regularly accuse me of overenthusiasm because I mention possibilities and probabilities, at least not do the same yourself by producing a bias in your posts!

[Grey]

I use published estimates. I use the very large specimens when calculating the hypothetical size of the large specimens, as long we assume the direct sizing based on large white shark is valid.

I use also the regression by Gottfried which gives a conservative maximum TL. I don't use Shimada because I need the crown measurements. I plan to measure it on some pics with ruler.

Me, overenthusiastic ? Yes you're mocking me...I'm in the opinion of Kent and Siversson regarding max size and weight, with possibilities of little larger sizes, depending what the skeletal structure will say.

Don't try to discredit me because I've reproached you to be an enthusiastic optimist. I've repeated many times that if I use methods, it does not mean I have great faith in.

[Grey]

The latest 7 incher found last Summer by local named Luke Walker. Don't know the exact measurements.

Using Gottfried regression, 16,86 m TL. I will not attempt to estimate the hypothetical maximum estimates as using peer reviewed technics seems to disturb some minds.





Two 16,19 cm specimens. The second one from Aurora is 11,86 cm wide.

Gottfried regression : 15,33 m TL
Jeremiah's method : 16,24 m TL.

[theropod]

Very nice tooth teeth, beautiful preservation. Is there a more exact measurement of the 7 inch specimen?

[Grey]

I don't understand either why you don't get that I simply use a technic clearly liberal and hypothetical but based on actual research. But whatever I can live without this. A 17 m TL meg based on a 7 inches tooth impresses me more than a 21 m one as it seems more real and likely (as long as you exclude Jeremiah's which results in sizes around 19 m TL based on the common width seen in 7 inchers).

Don't know the measurements of that 7 incher, I ll try to dig more on this. Without more data I suggest ~17 m TL based on Gottfried regression as a conservative TL estimate. Don't know the width either, but my own guess is minimum 12 cm, perhaps 13 cm... Keep in mind that using then Gottfried's regression for body mass, at a 17 m TL it would yeild an approx. 60 tonnes megalodon...Now that's one monster.

[theropod]

I was merely suggesting you to not just use these two exceptional specimens for the direct sizing, but you somehow took this as an attack (as usual), instead of trying to see the logic. I have no problem with the method as a hypothetical maximum, but that you made it look like this was what direct sizing suggested, while its only those two individuals of Carcharodon. And I note this seems to be the only animal in which you don't have grave problems with hypothetical maxima.