Megalodon vs. Livyatan melvillei

[Grey]

And you think that is still plausible all in all as it is supposed to be an up to date model ?

[theropod]

^What’s still plausible?

[Grey]

May 4, 2019 18:58:09 GMT 5 theropod said:

^What’s still plausible?

Such a massive body plan !

[theropod]

Plausible in the sense of "likely", or plausible in the sense of "not impossible"? I certainly don’t think a body mass ten tons greater than a right whale of the same length is likely…

[Grey]

Or is it supported by the structure of the vertebra...

So this means this pretty nice artistic rendition is not realistic...

I cant wait to see the giant sculpture, they worked on it for two years.

[dinosauria101]

May 4, 2019 18:41:54 GMT 5 theropod said:

dinosauria101 : I know that picture, as I expect do most others here. No idea why people on carnivora seem to assume it implies any scientific findings on the maximum achievable gape angle though, because it does not, there has been no study on the jaw mechanics of Livyatan, there aren’t even concrete data on the gape of extant odontocetes. Livyatan certainly did have a smaller gape than megalodon, but that’s because of the extreme gape angles sharks can achieve, well in excess of most other animals, not because we know anything specific about the gape of Livyatan.


–––
Lockyer, C. 1976. Body weights of some species of large whales. ICES Journal of Marine Science 36 (3): 259–273.

Well you may have a point there, as you said, most Carnivorans don't know beans on zoology.
Here's the link to the thread (a lot less accurate than this one, but may have helpful material):https://carnivora.net/showthread.php?tid=20

[elosha11]

May 1, 2019 23:03:46 GMT 5 theropod said:

I’m going to review a few popular reconstructions based on best-fit scaling of the 3D model I posted on the profile thread to the respective images scaled to 16.8m total length.

first off, Gottfried et al.’s reconstruction:

I’m getting about 65t. Pretty good considering this was in 1996, and they didn’t have a volumetric reconstruction. Certainly still within a realistic range for a modern great white, although it certainly is in the upper range.

This one I modified the model for to match the given dorsal silhouette, and it turns out at a surprisingly mild 61t. However the tail is way narrower than it would be even in a great white, and at the same time way deeper. All in all, this one isn’t so much too bulky, but rather just badly proportioned.

Apr 5, 2019 21:37:58 GMT 5 prehistorican said:

Depends on which reconstruction you are using, either one from the internet or ones with credibility and assuming the shark isn't completely a scaled up porbeagle/white shark . BK Kent's reconstruction seems to be one with credibility as show by Grey in the recent TV doc, that was a BK Kent shaped C. megalodon. This is a photorealistic version:

This "credible" reconstruction would mass 90 tons at 16.8m (formula average would be 52t, maximum 57t). Not impossible, I’m sure you can find great whites somewhere that have those kinds of proportions, but certainly freakish.

This one’s about the same.

This one is plain ridiculous, 109 tons. Partly because this one has a very small caudal fin, which decreases the total length relative to body size (but it would obviously be way too massive even with a corrected fin).

Theropod, I'm posting my comments again from the Meg profile page, along with your model in that thread to join all of these related conversations. I do note that such conversations might be best moved to Meg size thread.

May 1, 2019 19:40:00 GMT 5 theropod said:

www.deviantart.com/theropod1/journal/How-bulky-was-Megalodon-795970644

Theropod, really nice drawings. Couple questions. I take it the 5 meter GWS is the proxy for determining the weight of the 16.8 meter Megalodon? First, I definitely agree with the length comparison. A 5 meter GWS is a large, above average GWS, but still not yet approaching maximum size, particularly for females. Whereas most research, including the recent publication by Perez, Ledder, and Grey, would indicate that 16.8 meters would be a large, and probably a bit above average size adult Megalodon (most pertinently the females) but not yet approaching maximum size. So I think the length comparison is very apt.

Where I may have some further question is the weight estimate of 1195 kg average for a 5 meter GWS. Knowing you, I would assume such a figure is backed by research or at least some rational inferences. However, I note that on elasmomollet.org's GWS size page, there are 15 GWS sharks with weights calculated/estimated from between 4.67 meters (obviously shorter than the proxy model) up to 5 meters. Out of those 15 sharks, 10 of the 15 GWS have higher weights than 1195 kgs, including some of them well below 5 meters. A number of them significantly exceed such weight such as 1400 or 1500 kgs. Two of the 5 below 1195 are well below, something like 800 or 700 kgs, but as I said, the median average (and quite possibly the mean, I haven't yet checked) would seem to indicate a larger overall weight than your proxy model. These 15 sharks were weighted from all different parts of the world and over many different years, so it more likely represents a more typical size representation for such individuals. I know that 15 sharks in this context, isn't a huge comparison sample, but it's not small either, particularly when taking into account both geography and time differentials.

I suspect that GWS historically have averaged a bit heavier weight than 1195 Kgs at 5 meters. How much, I don't know. But it seems rather common for 5 meter animals (and even those below 5 meters) to exceed 1195 kgs in weight. I suspect that something like 1300 kgs might be a little closer to the truth. Which in turn, would result in a modest increase in bulkiness of your Meg model. Maybe something like 54,000 for the mean model and closer to 60,000 kgs for max size estimates.

BTW, what would your current model predict for the weight of an 18 meter Megalodon, which is a fairly commonly cited estimate for max size Megalodons? Personally, I think the largest specimens probably exceeded 18 meters, but I'm comfortable using 18 meters as a baseline for max size.

I'm going to post this same comment in the Meg v. Livyatan thread, since we have the same discussion there. But I note that such conversations should likely be transferred, or at least copied, to the very comprehensive Megalodon size thread, since that is probably the most pertinent thread for it. Obviously, the size of the shark matters in the question of interspecific conflicts with Livyatan, so I do acknowledge the info can also readily be posted in that interspecific thread.

UPDATE: I now see where you got your data on GWS average weight at 5 meters on your deviantart linked page, in which you state:

There have been six published regression equations for deducing white shark mass from total length (Fig. 1), which provide the data I am relying on here.
Megmass - by theropod1

While that seems rigorous, it does still appear to be a bit counter to the higher overall weights suggested by the 15 sharks posted on Mollet's elasmomollet.org website, as referenced above, as well as the weight at 5 meters suggested by the NOAA data in my post below

[elosha11]

Just found this. The National Oceanic and Atmospheric Administration's very useful white shark weight/length calculator supports my above assertion as to a heavier weight for GWS at 5 meters. They calculate a 5 meter white shark will have a fork link of 184 inches. Here's their pound estimate, which is exactly 1300 kgs, as I mentioned above.

With a Fork Length of 184 inches
a White Shark will weigh about 2866 pounds

Here's their calculator page. They go into quite a bit of detail as to their analysis, and it appears pretty carefully researched. Caveat, it's only dealing with North Atlantic sharks, not a world population, so it's not entirely comprehensive. Here's the site: www.nefsc.noaa.gov/nefsc/Narragansett/sharks/calc.html

FYI, they have a chart link converting weight to feet but it appears to be broken on their site. I found another link with what I believe is part of the chart.

[theropod]

elosha11 : The method used on the NOAA site is one of the regression equations (Kohler et al. 1996) whose mean I took. But it is not the only one there is, see here:

link→

I would strongly suggest that the "mean" collumn presented here represent the best currently available estimate while using the great white shark as an analogue.

The results differ because that website used only a single equation, while I used the mean of all six that I am aware of. Kohler et al.’s method itself does not predict exactly 1300kg at 5m, what it predicts is 1293kg, the website just rounded and converted into wacky imperial units (the fork length for a 500cm TL shark would be 183.61 inches, not exactly 184), explaining the slight difference.

Here is the equation from Kohler et al. 1996:

BM[kg]=7.5763E^{^-6}*(0.9442*TL[cm]-5.7441)^{^3.0848}

The red part is fork length predicted from total length, the green part predicts body mass from that fork length, both equations are taken directly from the paper

The results for a 5m shark are as follows:

Fork length: FL[cm]=0.9442*500cm-5.7441=466.36cm

Body mass: BM[kg]=7.5763E^{^-6}*466.36cm^{^3.0848}=1293.9kg

This is the exact calculation, using the exact values and units from the paper and without rounding or conversions.

So as you can see, I took this method into account, it’s just that there are others predicting accordingly lower values (in fact, all of them). There is some variation between the individual equations.

As for elasmollet, many of the sizes you cite there are not even reliably measured, certainly not with great precision, and it seems like most of the sharks you referred to weren’t even weighed (e.g. the one originally estimated at 8m "However, judging from the picture it's more likely slightly longer than 5 meters and weighed around 1300kg."–that is an important difference to a shark exactly 5m long and weighed at exactly 1300kg, even a shark of 5.1m would already mass closer to 1.3t than 1.2, even with a 5.0m one at 1.2t), instead there are lots of guesses based on photos, which I wouldn’t consider particularly robust evidence for anything. Not to mention that list may not be especially representative in terms of sampling in the first place.

I’m afraid I can’t follow you on why you think that would cast any serious doubts on the weight predicted by six regression equations from scholarly publications based on large samples or (presumably at least mostly) reliably measured sharks. Among them, they presumably have ten times as many white sharks in that approximate size range around 5m than the elasmollet summary, and presumably those white sharks were actually scientifically measured and documented and not just guessed at based on photographs.

In fact the mere notion that someone could visually estimate a 5m shark to within 100kg of its real mass from a photo (or visually estimate it to within 10cm of its real length with any confidence for that matter) is ludicrous, we can do a little experiment on that if you want. And that’s not even considering such considerations as that a shark pulled onto land would suffer deformation due to gravity, or that there’s camera perspective and distortion to make the task of size estimation even more difficult. You can give an approximate size estimate based on a suitable photo, and an approximate weight estimate, at least on a comparative basis, or if, like I did here, you use a volumetric model as a template (which I highly doubt was done for any of the sharks on the list) to make an approximate absolute weight estimate, but it’s very unrealistic to be exact to the degree that could reliably distinguish a 1.3t and 1.2t shark, even with the latter method (as you can see from the variations we got with the reconstructions including a dorsal view, there are some factors you cannot realistically account for with just a single picture, you can merely give a best estimate, based on the most realistic body shape).

In other words, this doesn’t run counter the evidence you listed, that evidence is simply contradicting the majority of scientific data on great white shark length-mass relationships. I have listed some reasons as to why this might be the case; one is a regression that is evidently on the high end, but which I did incorporate and gave the same weight to as to all the others, and the others are rather anecdotal reports with poor reliability.

That being said (and going back to one of the reason I think the visual weight estimation based on a photo isn’t sufficiently reliable), you probably wouldn’t even be able to visually tell the difference between a 5m 1.3t and a 5m 1.2t shark (see the models for 57 and 52 ton megalodons, which is in fact a greater difference than that between 1.3 and 1.2 tons), least of all in my size chart.

Besides, which is the more important point, none of this has any bearing on the bulkiness of my meg model, I used the mass estimate derived for a 16.8m megalodon to estimate its bulk directly, whether a 5m white shark is 1.2 or 1.3t is totally irrelevant to that.

PS: You can move this conversation wherever you like, I couldn’t decide where it was most appropriate as we don’t have a "meg body shape"-thread yet and we already have so many threads discussing meg I didn’t want to open a new one just for reviewing some reconstructions that were mostly discussed here. I’m sure we have previously discussed bulk and body shape on this one as well, but it would seem equally appropriate for the meg size thread.

[Grey]

The pictures of the 15 m updated model are enbargoed until the 23 May.

[dinosauria101]

May 12, 2019 0:22:03 GMT 5 Grey said:

The pictures of the 15 m updated model are enbargoed until the 23 May.

Grey I know this is a little off topic, but do you think theropod should allow creature386 to share some great Megalodon info with Carnivora? I myself am rather against that idea and if possible would like some backup

[Grey]

Euh yeah I have authority on this !

[dinosauria101]

^And I definitely agree with you; like I said Carnivora is not worthy of such good information

[dinosauria101]

^As I said, that likely crossed the line

[elosha11]

While I totally agree that theropod can post whatever he wants, wherever he wants, and/or authorize others to do so on his behalf, I ask that we all try to remain as civil as possible and respect each other's opinions, even if we think they are misplaced. Let's also please keep pejorative comments out of our dialogue, we want WoA to be a place where all can voice their opinions and be subjected to either validation or respectful disagreement. Thanks.