Megalodon size

[Grey]

Dec 29, 2014 2:54:25 GMT 5 Grey said:

18 cm tooth recently found in Beaufort, South Carolina.



12.5 cm wide, crown height about 14 cm. Looks like a lower anterior tooth.

K Shimada confirmed me by mail that specimen is a lower anterior tooth.

I got precise measurements by the owner, the CH is exactly 140 mm high.

Using the a1-a2 range from the matrix, this yields a ~19.8 m long Meg. Using a1-a3, it results 21.1 m.

(theropod, looking at all the private teeth and teeth in the literature with no estimated TL, potential 20 m individuals are of course rare but they appear quite more numerous than counted on a single hand (i.e. carnivora)). There are a good bunch of very large teeth that I have not posted here. 4 teeth more than 18 cm in slant have been found this year in the US only. I have a guy who currently investigates about a Chilean 7.91 incher in a private collection...)

[Grey]

Jan 8, 2016 20:25:22 GMT 5 theropod said:

est. 91mm tall, 72mm wide (root) with a crown height of ~71mm
The preserved portion of the crown has a maximum labiolingual thickness of ~16mm.

As regards the position, when comparing the slant of the preserved crown to the teeth figured by Uyeno et al. 1989, it is an excellent match for the tooth figured in pl. 6(a), and that is what the outline bases on.
Can anyone here read Japanese?

That's a personnal tooth of you ?

Can't read the indication in Japanese, use Hubbell's dentition if you don't find it.

I have a list of body sizes estimates from teeth in the literature in preparation, one describing a juvenile specimen between 6 and 9 m (from memory) from the Grenadines and several specimens from New Zealand.

[theropod]

Yes.
I’d say it’s an anterior lateral based on the dentition, but I’d be particularly interested in whether the other tooth set corroborates that.

[Grey]

Nice piece, you've collected it ?

I'll dig about that. Isn't there a logicial allowing to translate Japanese on pdf ?

My understanding is that Hubbell set is more complete (though not properly described and published) than the Japanese.
But if there is a corresponding tooth in Uyeno that'd be good to know which position they assign it.

But you still can use some potential positions from Pimiento matrix and Hubbell's dentition.

l1-l2 : ~13m
l1-l3 : ~14.5m
l1-l4 : ~17m

[theropod]

Nope, found it on a flea market in Cologne, but I’m planning to make a trip to the locality it’s from next fall (Cadzand, The Netherlands).

I was thinking upper lateral, should have precised that. But a lot is possible, especially since its just a partial specimen.

Translation might help with a recent paper that’s available in digital form, but my pdf of that one is an old scan.

Yes, I also think Hubbell’s set is more complete, just still not properly described or figured for some reason.
I’m mainly interested because A: the photographic documentation in Uyeno et al. is much better than anything available for Hubbell’s set, B: it’s the only meg dentition recorded in the literature, even though that’s of little use without understanding what they wrote about it and C: because of the good fit that would make this a reasonable assignment. I’ve requested a translation on Paleoglot btw, but there’s no saying whether anyone is going to do it any time soon.

Pimiento & Balk’s dataset doesn’t provide a method for making size estimates, what do you mean by "use some potential positions from Pimiento matrix"?

[Grey]

Just what I did, using some range available in the matrix and make a TL estimate.

Yes an upper is possible too at this point.

Uyeno is indeed the best paper. However regarding the photos, you can get very close shots of each teeth of Hubbell set on elasmo.

[theropod]

I mean why "available in the matrix", what does their matrix have to do with it?

[Grey]

Their matrix almost always use the same ranges in 544 specimens. I personnally use ranges used in it.

[theropod]

Jan 8, 2016 20:25:22 GMT 5 theropod said:

est. 91mm tall, 72mm wide (root) with a crown height of ~71mm
The preserved portion of the crown has a maximum labiolingual thickness of ~16mm.

As regards the position, when comparing the slant of the preserved crown to the teeth figured by Uyeno et al. 1989, it is an excellent match for the tooth figured in pl. 6(a), and that is what the outline bases on.
Can anyone here read Japanese?

Note that I’m pretty sure, based on elasmo.com, that it’s not a lower lateral 4 (or more posterior), the crown seems too elongated for that.
Of course that only bases on the observation of one specimen (so it would be all the more necessary to verify it using others), who knows how variable that feature is, but lower teeth seem to be straighter and more symmetrical than upper teeth of equivalent position, and also lower posterior teeth seem to become wider more abruptly compared to the more gradual widening in the upper dentition (which is also connected to the lower anteriors being slimmer, of course).
Based on that, I’d say L1-L4 is a better fit.

Based on crown height (Shimada 2003 cited in Ehret et al. 2009): mean estimated length of 10.6m (L1->10.1m, L2->9.6m, L3->10.3m, L4->12.6m)
Based on tooth width/dentition length (Boneclones measurements, mean from both tooth sets & Lowry et al. 2009, 15% IDD): mean estimated length of 9.9m (L1->9.8m, L2->9.1m, L3->9.9m, L4->10.9m)

Also I’ve found an interesting means of comparison regarding Shimada’s method. Ehret et al. 2009 report a complete dentition of Carcharodon sp., which can be compared to the megalodon dentition whose measurements are listed in Pimiento et al. (2010)’s appendix.
The last collumn (ratio) is the ratio between the ratios of crown height to sum of crown widths in C. megalodon and Carcharodon sp., i.e. it is an indicator of how much more or less tall the tooth is for the same overall dentition length. Where two teeth from opposite sides of the jaw were available for one position, the figures below reflect the mean of both.

CH CW CH/sum of width ch(meg) cw(meg) CH/sum of width ratio
44.05 34.35 0.1407798019 82.3 82.7 0.1190166305 A1 0.8454098453
42.85 36.5 0.1369447108 75.4 78.8 0.1090383225 A2 0.7962214961
31.65 31.25 0.1011505273 80.2 76.7 0.1159797542 I 1.1466055316
33.9 34.85 0.1083413231 79.2 77.6 0.1145336226 L1 1.0571554719
29.85 34.95 0.0953978907 87.8 77.5 0.1269703543 L2 1.3309555732
32.2 34.3 0.1029082774 81.6 73.7 0.1180043384 L3 1.1466943318
24.65 27.2 0.0787791627 71.7 68.2 0.1036876356 L4 1.3161809806
17.5 22.9 0.0559284116 62.2 53.7 0.0899493854 L5 1.6082950108
12.4 17.1 0.0396292745 50.6 36.3 0.0731742589 L6 1.8464698062
8.95 12.4 0.0286033877 48.2 32.2 0.069703543 L7 2.4368981689
7.1 10.8 0.0226909556 34.1 19.9 0.0493130875 L8 2.1732486022
4.7 8.7 0.0150207734 21 14.2 0.0303687636 L9 2.0217842802
3 7.6 0.0095877277 691.5 L10
312.9

37.75 28.9 0.1705058717 59.8 68.7 0.1028021317 a1 0.6029242902
42.35 31.4 0.1912827462 67.9 72 0.1167268351 a2 0.6102319079
31.55 27.95 0.1425022584 64.7 74 0.1112257177 a3 0.7805189827
28.1 27.45 0.1269196025 63 67.2 0.1083032491 l1 0.8533216851
24.25 24.65 0.109530262 66.8 67.7 0.114835826 l2 1.0484392529
19.9 21.2 0.0898825655 65.8 63.1 0.1131167268 l3 1.2584946393
14.8 17.65 0.0668473351 63.9 55.8 0.1098504384 l4 1.6433031794
9.3 14 0.0420054201 58.8 46.7 0.1010830325 l5 2.4064283219
6.8 11.2 0.0307136405 48.4 34.4 0.0832044009 l6 2.7090374056
5 9 0.0225835592 32.8 21.3 0.0563864535 l7 2.4967921609
3.6 8 0.0162601626 22.2 10.8 0.0381640021 l8 2.3470861269


Given that we can all agree that the sum of all tooth widths can be expected to have a better correlation with total length than height measurements of any individual tooth, I think it’s pretty clear that teeth of varying position could have significantly larger or smaller crown heights in megalodon when compared to a similar-sized great white.

Over the range of L1-L4 the Carcharocles dentition has proportionately somewhat taller tooth crowns (by ~20%). This is only indicative (this is a Carcharodon, but not the same species the regressions base), but once more it leads me to favour the tooth row length method (especially since it’s also congruent with the discrepancy between crown-height and jaw-perimeter estimates for the same juvenile megalodon dentition listed above).

–––References:
Ehret, Dana J.; Hubbell, Gordon; Macfadden, Bruce J. (2009): Exceptional preservation of the white shark Carcharodon (Lamniformes, Lamnidae) from the early Pliocene of Peru. Journal of Vertebrate Paleontology 29 (1) pp. 1-13.
Lowry, Dayv; Castro, Andrey L. F. de; Mara, Kyle; Whitenack, Lisa B.; Delius, Bryan; Burgess, George H.; Motta, Philip: (2009): Determining shark size from forensic analysis of bite damage. Marine Biology, 156 pp. 2483-2492.
Pimiento, Catalina; Ehret, Dana J.; MacFadden, Bruce J.; Hubbell, Gordon (2010): Ancient Nursery Area for the Extinct Giant Shark Megalodon from the Miocene of Panama. PLoS ONE, 5 (5) pp. 1-9. + Data Supplement.

[Grey]

That's good find.

To look at the position of your tooth, you should check also its structural thickness and the other side of the tooth. Lower teeth are particularly thick at their base.

[theropod]

Thanks for the info.
I’m a little short on other pieces to compare it to, but it doesn’t seem to taper abruptly or be thicker than probable upper laterals I know from multiview pictures (e.g. the Denmark specimen).
Actually, here’s a multiview, though it might not be scaled perfectly (I didn’t have a caliper when I made it):

[Grey]

I bet on an upper but really couldn't say if it is an anterior or lateral. Your outline reconstruction fits to something around the L3-L4 but looking at the piece alone it is hard to tell for sure. (will respond to the other discusssion later).

[elosha11]

Couple questions/observations.

Grey has diligently searched out many private collection teeth, whether UA or lateral, which plausibly could be estimated to indicate a shark 20 or more meters, by Shimada's calculation. There are certainly more than a handful at this point, and the number seems to be growing. Grey I believe has also not posted all of the large teeth he has tracked down. It's also interesting that many of these teeth come from South America, which may indicate that these were particularly good hunting grounds and/or deep enough water during the Miocene/Pliocene to support very large adult populations.

My next query is with regard to the Pimiento study. The mean size of all sharks was around 10.42 meters, and I believe the average size for an adult is implied to be around 13 meters. However, it does appears that crown heights for teeth studied in southern hemisphere were notably greater than those in the northern hemisphere, and those found in the Pacific and Indian ocean are notably larger than those found in the Atlantic.

datadryad.org/resource/doi:10.5061/dryad.6q5t4. See Fig.S.2.

But what I don't know is how many of the 544 samples were northern/southern hemisphere and likewise how many came from which ocean. Can anyone find that in the study results? Given that Pimiento's team seemed to be looking for a worldwide/across time&space median size, I do wonder what the median size would be for those from southern hemisphere alone or from pacific/indian ocean alone. It appears these oceans may have supported larger-sized populations of Megalodons, or we may simply have an example of fossil bias. If the former however, I'd have to guess the median size of southern hemisphere/Pacific sharks was somewhat larger than 10.42 meters. Not surprisingly the correlation of extremely large teeth (many of them not even reported), also comes from southern hemisphere/Pacific Ocean. And of course, if we take out the larger sample size from southern hemisphere, does that suggest an even smaller median size for Northern hemisphere/Atlantic Megs?

[Grey]

In the matrix, you can clearly see the largest teeth are from the Chilean collections. One of them has a crown width of 127mm...

However, I'm discussing with a PhD student who's working on Shimada's method and already acknowledged that it is not the best method for estimating sizes. I'm proposing him to use the method provided by Siversson to estimate TL. I've tested this lastly and I suspect, comparing summed upper dentitions from white sharks with the adult meg set from Yorktown, that the estimated size of the later could be substantially larger than what is indicated by individual upper anterior tooth height and width...

I've tested TL estimates using summed upper crown widths from white sharks specimens with known TL from Hubbell 1996 and elasmo.com (not Lowry equation since some results are in total contradiction with the summed crown width of these white sharks specimens) and tested it with Pimiento's specimens. The results are in total contradictions with those using Shimada, the largest specimens in the matrix become average specimens and some others specimens (those from Chile especially) even exceed the 17.9m largest TL in Pimiento's dataset. Even her in private discussions admitted the method needed improvement.

Yes, for speaking with proficient collectors, they all say that Chilean teeth are the very largest, even more than the specimens from South Carolina, even with the embargo, 6 inches plus specimens aren't rare. I've not read any description of the geography of the region back then but apparently it was rather deep enough to host large-sized individuals.

[theropod]

elosha11 : The data you requested:
                   formation     country   n   mean_tl
1                      Parana   Argentina   7  9.111429
2            Punta_del_Diablo   Argentina   6  9.521667
3  Basal_Black_Rock_Sandstone   Australia   2 10.035000
4                   Batesford   Australia   1 10.650000
5                 Loxton_Sand   Australia   2 12.200000
6                 Muddy_Creek   Australia   1 11.050000
7               Bahia_Inglesa       Chile  63 12.470794
8                      Onzole     Ecuador   4  8.555000
9              Rosarito_Beach      Mexico   3  5.930000
10                  Tirabuzon      Mexico   2  5.405000
11                     Ysidro      Mexico   2  7.130000
12                   Wanganui New_Zealand   1 10.420000
13                 Chucunaque      Panama  26  7.693462
14                      Gatun      Panama  40  8.052500
15                      Pisco        Peru  31 11.399226
16                Bone_Valley     US_East  38  6.711842
17                    Calvert     US_East  47  6.421489
18                Pungo_River     US_East   4 11.795750
19                   Yorktown     US_East 204 11.044461
20                 Capistrano     US_West   3 10.646667
21                   Monterey     US_West   8  9.027500
22                   Purisima     US_West   1 13.610000
23                  San_Mateo     US_West   5  9.472000
24                    Tamiami     US_West   4  9.112500
25                    Temblor     US_West  36 11.680833
26                    Topanga     US_West   3 12.380000

As you can see the sample of southern hemispheric specimens is indeed smaller, only Chile is indeed in the double digits (and it indeed seems somewhat larger than the global average, but see below). Most likely some of the unusually large averages from certain localities (e.g. Loxton Sand, Muddy Creek, Topanga, Prusirima) are a result of the small sample size, just like some of the unusually small ones (e.g. Rosarito Beach, Tirabuzon, Chucunaque…).

So yes, of course, individually speaking the average of the southern hemisphere is higher and that of the northern hemisphere is lower than the global average based on these figures. But I don’t think just ignoring the sample size differences between the individual localities would be a good idea if its the overall size of the species you are interested in.

In fact the authors already suggested explanations for these differences, and I think this supports usage of the global average figure (that is the 10.02m resulting from counting every specimen as precisely one specimen):

Pimiento & Balk said:

Significant differences were found between
C. megalodon body sizes from the Northern
Hemisphere relative to the Southern Hemisphere
(Table 2). Notably, the Southern Hemisphere has
a larger mean body size (Fig. 4B) (Northern
n = 426, mean = 9.58 m, 78.30% of total sample;
Southern n = 118, mean = 11.62 m, 21.69% of the
total sample). Similarly, significant differences
were found between samples from the Atlantic
and Pacific oceans, with the Pacific having a
larger mean value (Pacific n = 188, mean =
10.90 m, 34.55% of the total sample; Atlantic
n = 350, mean = 9.53 m, 64.33%). No significant
differences were found between C. megalodon
body sizes from the Indian Ocean relative to
the Atlantic or the Pacific (Table 2, Fig. 4C);
however, the low sample size of the Indian
Ocean (Indian n = 6, mean = 11.03 m, 1.10%
of the total sample) severely limits the
statistical power.
The differences in mean sizes across hemi-
spheres and oceans could be due to both
environmental (e.g., water depth, ocean
currents, resource availability, productivity)
and biological (e.g., sexual segregation, habitat
use, home range) reasons. On the other hand, it
could also be due to sampling and taphonomic
biases. For instance, the larger mean size found
in the Southern Hemisphere could be the result
of a lack of systematic collecting efforts, as
most of the southern samples are from the
Bahia Formation (Mina Fosforita, Chile, #1 in
Fig. 2); these come from illegal confiscations
and are biased toward larger teeth (R. Otero
personal communication 2013).

Individual localities, possibly even individual hemispheres, could be affected by sampling bias, and the best way to minimise it for our overall sample is to give the minimum possible impact to those individual aberrations by taking a global mean figure of all individuals.

If you are still interested in that though, the mean size from the individual formations’ averages is 9.67m. I just don’t think that’s relevant because it gives far too much weight to individual locations whose small samples increase fluctuations, but it’s not so different from the overall mean figure anyway.

So in conclusion, yup, some localities probably did have larger averages and others smaller ones. We are already counting all of them. Due to the (very probable) danger of sampling bias affecting one or the other locality, giving greater weight to specimens from some than from others (i.e. taking the mean between averages from subsamples that have very different sample sizes) would be a bad idea at this point.

I think you may have also gotten some numbers mixed up. The overall mean is 10.02m, not 10.42. The mode is 10.54m. Pimiento & Balk don’t imply anything about adult average size, as they do not even discuss the mean size at maturity.
Nonetheless inferences can be drawn from comparing their dataset to similar datasets of great white sharks (which I discussed here→), looking at the latter’s mean size at maturity, and counting individuals larger than that as adults (for statistical purposes only. Some in that subsample are likely still immature, while others outside of it are already mature. Once more, that doesn’t imply a systemic bias, it just means you can’t count on every individual in the subsample to actually have been sexually mature, or on every one outside it to have been immature for that matter). This results in an adult average close to 14m (also extensively discussed before). None of that is Pimiento or Balk’s conclusion, their research is just the source of the dataset that makes it possible, along with McClain et al. 2015.
There is the obvious problem of the method involved, as Grey explained. Note that based on the morphometric data from Carcharodon sp. and C. megalodon dentitions it does not produce underestimates (since the majority of C. megalodon’s teeth are proportionately taller for a given overall dentition width, while only the most anterior positions are shorter).