Megalodon size

[theropod]

Yes.

Then it’s strange you cannot open an ods-file, but I’ll attach you an excel version. Hope it works.
Untitled 1.xls (11 KB)

Copying that stuff in here in a redable form would take too long.

Yes, the litterature reference is at the bottom of the page, 1996. Gottfried wrote nothing about Megalodon in 1998.

Thanks.

No, not especially. The problem to make an exact assignment is another one.

Hence averaging the TL yeilded from the various position is a fair assumption.

why "hence"? That has nothing to do with it. Averaging the position produces an estimate that would fit for none of the positions. I’d prefer the median.

The point was another one, that the potential size ranges you get were "so big they are almost meaningless". I recall you complaining about that in certain other taxa.

You have not measured laterals, but the 17.9 m individual justly comes from a lateral.

I have measured laterals, posterior laterals.
And I just compared mid-laterals as well.

It is not logical to arbitrary decide that the average yeilded from several positions here IS an overestimate. That simply means it was most likely a very small tooth in a large shark.

That was not what I did. Whether or not a specimen may be overestimated does not depend on the average of the position and whether that’s the most reasonable or not.
It simply depends on where the used position are, and whether that region bears relatively larger or relatively smaller teeth in C. megalodon. Of course in some cases the selection of positions might actually counteract the influence that the relative tooth-lenght differences have, but that’s not the point I am arguing about.

Well you're doing a trial to the 16.8 individual. Just kidding. But the 17.9 m individual is not from a posterior but a lateral tooth. UF 245996 is also yeilded from several tooth positions and result in 13.1 m, not really an overestimate.

How do you know it isn’t an overestimate? Time travel?

In all seriousness, I am not specifically doubting any of those size estimates, I am trying to demonstrate a potential bias in this method. How that applies to each of the specimens would have to be checked for each of them.
But if you have a huge UA2 yielding a relatively small size, and tiny posteriors and posterior laterals often yielding very large sizes, that is probably partly due to this (not saying there are not also posterior teeth belonging to huge sharks, but not more than anteriors or anything in between). Accordingly, I’d suggest to stop labelling this method as conservative just because it is conservative with anterior teeth, because the estimates for posterior teeth do not appear conservative, but higher than would be indicated by the jaw perimeter (remember that big posterior lateral from a few pages back?).

No adult in the area had the time to lost an upper because they were few, not for a long time and not hunting big game in the area. And even if it lost it, nothing says that the upper was necessarily preserved and if so not collected by fossils hunters long ago who tend to ignore small, less valuable and less striking teeth. That explains this.

It does not. Why so many more posterior teeth than anterior teeth? Are those replaced more often?

Well nuff said in my last responses, in a nursery area, in a sample of 40 teeth, you're not necessarily going to find a large upper from a massive adult

You are not going to find an anterior or anterior lateral tooth, but you are going to find a decent number of posterior teeth from such massive adults?

They needed to make precise estimates here in the goal to establish life stage of the individuals. I favor other methods in others instances, not there.

The life-stage assignments themselves are rough anyway, and base on estimates done with a similar method.

We cannot make any conclusion based on two sets whereas Shimada's formula is based on numerous various individuals.

Of great white sharks, not of Carcharocles!

Some results were not logical (far too small or far too high) for individuals teeth

and who determines what is far too small or high?

, despite I did the calculation several times. That's why I think in some instances others factors that we ignore are taken into account.

How so?

In a formula that looks like this (in this case the formula for an UA1):
TL= 5.234+11.522x
where x is Crown Height and all the other numbers are given, what other factor is going to be figured in to get the dependant variable?

It’s just a matter of finding the right (and exact!) tooth position. We already saw that it matters immensely since even being off by one position can mean being off by ~100%.

If you got results that seem far too high or low, check the assignment to a tooth position. So far all my results for the samples from Gatun matched those of Pimiento et al perfectly while using the same position.

The main problem I try to explain is that you give far too much importance to the data we know about Megalodon teeth compared to the white shark applied here whereas we ignore how much we are right compared to the individuals variations used in Shimada's formula.

What is that "individuals variations used in Shimada's formula" you are referring to?
Did Shimada adjust for the relative differences between C. megalodon and C. carcharias? If so, why is the method based on great whites at all, why not just on the jaw perimeter of the known dentitions (which btw would be a good idea, a formula for estimating jaw perimeter and thus body size for each tooth position based on the tooth sets!)

I was the first to found these differences and already sent questions to Kent, without satisfying response. I'm going to try it again. The main thing is that whatever the results by Shimada would be differents compared to others methods, there's no reason to think they would be far off as they still fall in the acceptable modern size range for Megalodon and are close to those of Gottfried et al.

Well, just because a size of 11m for the holotype of Tyrannosaurus rex falls into the known size range for the species, that does not mean it is an accurate estimate for the specimen.

There's a better correlation in jaws perimeter than in crown height, this does not mean the crown height correlation is utter hogwash and deserves to spit on the datas by Pimiento et al. No professionnal did it so far, there's no reason to do it because we have measured two white sharks sets in px on Paint. We need more clues in both directions.

I am not spitting on the method. It is fine for what it does. I am just aware of its likely limitations, which are due to differences between Great white sharks and mega toothed sharks, the very factor why there even is disagreement about size estimates for this creature.

[Grey]

Theropod, no need to respond, don't forget I'm basically agreed with you. But before make any statement, I'm going to investigate this further.

[Grey]

Thanks for the table.

why "hence"? That has nothing to do with it. Averaging the position produces an estimate that would fit for none of the positions. I’d prefer the median.

The point was another one, that the potential size ranges you get were "so big they are almost meaningless". I recall you complaining about that in certain other taxa.

I see no reason why arbitrary prefer the median tooth position to the average result of all position. And I think Pimiento et al. see no reason to this either.
In certain other taxa there can be better (least bad) methods or more material than in Megalodon.

That was not what I did. Whether or not a specimen may be overestimated does not depend on the average of the position and whether that’s the most reasonable or not.
It simply depends on where the used position are, and whether that region bears relatively larger or relatively smaller teeth in C. megalodon. Of course in some cases the selection of positions might actually counteract the influence that the relative tooth-lenght differences have, but that’s not the point I am arguing about.

The average size of the positions is the best alternative to chose arbitrary one particular tooth. It is true that it is tricky to accurately assign posterior and lateral teeth in Megalodon, but I see no reason to criticize the mean size resulted from the various positions when one is unable to claim which position belonged that tooth.

How do you know it isn’t an overestimate? Time travel?

Because you focused on the sizes above 15 m yeilded by posterior and lateral teeth. I make you remark that these teeth do not automatically result in humongous sizes.

In all seriousness, I am not specifically doubting any of those size estimates, I am trying to demonstrate a potential bias in this method. How that applies to each of the specimens would have to be checked for each of them.

I'm aware of the bias and agreed on that. Only, I don't try to make a revision of the whole method because of the potential error, common in any method.

But if you have a huge UA2 yielding a relatively small size, and tiny posteriors and posterior laterals often yielding very large sizes, that is probably partly due to this (not saying there are not also posterior teeth belonging to huge sharks, but not more than anteriors or anything in between). Accordingly, I’d suggest to stop labelling this method as conservative just because it is conservative with anterior teeth, because the estimates for posterior teeth do not appear conservative, but higher than would be indicated by the jaw perimeter (remember that big posterior lateral from a few pages back?).

Pimiento talks in one of her paper about UA up to 150 mm CH from Bone Valley (from Purdy). This corresponds to sharks roughly the size of the largest individuals in Gatun.
The method is conservative because I've not seen, from posterior or anterior teeth, published estimates exceeding 18 m. This can change of course.

It does not. Why so many more posterior teeth than anterior teeth? Are those replaced more often?

It possibly does. Upper anterior are easily spotted and much more often collected than small teeth. Perhaps some upper anteriors are still buried in the area and will never be found, perhaps they were collected during the last centuries, perhaps it appears the few adults simply not shed upper or numerous upper in the area. There are very numerous possibilities. We can speculate at length with this.

You are not going to find an anterior or anterior lateral tooth, but you are going to find a decent number of posterior teeth from such massive adults?

Why not ? There's no universal rule that an adult Megalodon automatically leaves behind an upper even in short occurences in shallow areas. See the previous response.

The life-stage assignments themselves are rough anyway, and base on estimates done with a similar method.

Yes, but the size estimates are essential in these studies. You doubt about the seriousness of the sizes estimates, you doubt about the seriousness of the study. I prefer to investigate it further instead of arguing.

Of great white sharks, not of Carcharocles!

I'm talking about white sharks. You argue because of two sets, I recall that Shimada's regression is based on the variations of numerous individuals.

and who determines what is far too small or high?

When I get a Megalodon at 42.2 m TL after calculation, I guess this is not an underestimate.

If you got results that seem far too high or low, check the assignment to a tooth position. So far all my results for the samples from Gatun matched those of Pimiento et al perfectly while using the same position.

Yes, and if you're unsure of the position, the best (least bad) is to use the mean estimate of all.

What is that "individuals variations used in Shimada's formula" you are referring to?
Did Shimada adjust for the relative differences between C. megalodon and C. carcharias? If so, why is the method based on great whites at all, why not just on the jaw perimeter of the known dentitions (which btw would be a good idea, a formula for estimating jaw perimeter and thus body size for each tooth position based on the tooth sets!)

I've indeed thought about that idea, the same purpose but applied to each tooth position. Would be perhaps the best method out there. But I think that the results wouldn't be too much different than Shimada's overall. Better yes, but not much different. Thats my point.

Although the megalodon dentition was obviously not identical to that of
C. carcharias (otherwise they must be considered the same species, which
is clearly not the case), Uyeno et al.'s paper, combined with the
general pattern of dentitions among all the modern macrophagous
lamniforms (see attachment), does strongly suggest that it is reasonable
to assert that we can use C. carcharias as a model to talk about the
tooth pattern at least in a general way (e.g., how tooth sizes decrease
from the front to the back of the jaws).

Well, just because a size of 11m for the holotype of Tyrannosaurus rex falls into the known size range for the species, that does not mean it is an accurate estimate for the specimen.

For Tyrannosaurus we have much more material and much more reliable data. With Megalodon we're relying with the least bad available, including Shimada's method.

I am not spitting on the method. It is fine for what it does. I am just aware of its likely limitations, which are due to differences between Great white sharks and mega toothed sharks, the very factor why there even is disagreement about size estimates for this creature.

Everyone here is agreed about its limitations, the same than in any method. I think you just take this with too much importance. What about trying to make a revised method of your based on Shimada and propose it to the authors ?

I'm interested at searching this further but I prevent any statement like "this estimate is too much, this one too small".

In case you've missed my last edit :

For short, whatever the accuracy of Shimada regression when applied to Megalodon, it always fall in an acceptable size range for the species and it is not that important to always keep in mind others methods while Shimada is the only one to be useful while using teeth that are not UA. Otherwise, all the published sizes of Megalodon using Shimada should be rejected, which I don't agree with. This is not because upper jaws perimeter is overall better than Shimada's regression must be ignored. On a rigorous line, all the published methods are subject to potential criticism. But all the published methods are the best available. Unless studies by Shimada yeild in unreasonnable Megalodons under 1 m TL or over 25 m TL, this method is good enough.


I'm agreed with you and most of your arguments but where you tend to make your own conclusions without investigating this further, I tend to propose others reasons which can possibly explain the issues we're talking about and recall that we might ignore some others datas.

This is not a discussion of who's right here but a manner to temperate and avoid any mistatement for now. Let the paleontologists work with it, much more than we've done until now, and perhaps contact them in case.

[theropod]

Good to see the table works. I had some trouble exporting it, for some reason LibreOffice wouldn’t let me save it without crashing so I had to convert it using unoconv. Please note those are my measurements, and while I made them as precise as I could manage with the available material, it is possible there could be measuring errors of a pixel or so somewhere. Also note the exact values, should they get published in this form, will be different.

Why the median? Because that value actually corresponds to one of the tooth positions the tooth could have belonged in, (or the mean of the two intermediate ones if the sample is an even number, in which case I’d prefer to just list the two intermediate estimates), analogous to taking the average of the tooth positions and making an estimate for the resulting position.
The mean on the other hand is usually a figure that the tooth (assuming accuracy in the method) would not correspond to in life.

There are no additional tooth positions in between that it may also have belonged to (unlike, for example, in a population with a certain range of variation; for example individuals of a species that ranges from M1 to M2 in mass can usually be anywhere in between, and in a taxon ranging from R1 to R2 in femur/tibia-ration, individuals can also be anywhere, but teeth that could be an L1, L2, L3, L5 or L4 can only be one of those, nothing in between).
But I fully agree that using the mean or median (depending on the type of the data in question and the size of the sample) is the best to use in such cases of uncertainty where something belongs. That is an argument you certainly recall me using, and the reason why mean and median values are commonly used in science.

Regarding your result of 42.2m, the only ways I see you getting such a result is by the assigned position being erraneous, or your calculator having a bug. That is not a matter of additional data you’d have to figure in in the regression; there’s exactly one variable to fill, and that is tooth crown height.

Fair enough?

[Grey]

I'll give a more substantial response later. Balk has given a new talk this weekend about the size of Megalodon over time, seen on her twitter, several paleontologists congratulated her.

[theropod]

Sounds good. What’s the title of the talk?

[Grey]

I've not seen the title in the tweets only apparently she talked about body mass and the comparisons of the trends with cetacean size. It was at the North American Paleontological Convention in Gainesville (where lives Gordon Hubbell).

[Grey]

There was actually another by Pimiento too about its extinction, I will put the abstract in the Megalodon thread. She estimates its date of extinction around 2.5 millions years ago.

[creature386]

Can you post the tweet? I can't even find it.

[Grey]

There are just mentions, but I've posted the abstracts in the Meg thread.

[Grey]

A large tooth found by a scuba diver.



Using the 1 dollar bill, I've measured to tooth to be 14.2 cm wide, 17.7 cm in vertical height, with a crown height about 13.5 cm (keepig in mind the tip of the crown which seems incomplete). I was not able to measure the slant and I'm not sure of its position. I someone wants to verify the measurements.

[theropod]

Looks like an anterior to me, tending towards lower 3, or maybe 2, but it is difficult to tell that for sure.

Using the banknote as a scalebar (155.956mm in lenght):
maximum root width=141.3mm
perpendicular height=175.5mm.
slant lenght (both slants are pretty much the same)=183.1mm
crown height=136.2mm

[Grey]

Thanks you for the more precise measurements.
I'm not sure it's lower though. The tooth sounds somewhat more elongated than what we know of upper but I don't know.

[creature386]

A slant height of 183.1 mm? If this is really a lower one, then the upper 1 has to be gigantic!

[theropod]

Indeed. The teeth can be fairly variable in shape, although lower ones tend to be more slender, made for gripping and impaling. Perhaps this is just a particularly elongated upper...