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Post by creature386 on Feb 19, 2014 20:37:47 GMT 5
This whole bone identification thing is just far too hard for me. I just can't differ individual variation from tooth position.
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Post by Grey on Feb 19, 2014 23:36:42 GMT 5
Tom Holtz was at Balk talk's. In one comment he said that the average size for Megalodon was 9.26 m and 12 tons (I don't know if it was the average at one period or overall) and that the max she gave was 20 m.
If that's confirmed, I'd suggest for eventual match up to use Megalodon while precising from which particular period and to which size. Sounds like the size variations in that species over time (and regions ?) are huge, even greater than in others macropredaceous sharks, at a point that biologically we're not necessary all the time speaking about the same animal. That could induce interesting fights. Confronting a 60 tonnes Megalodon to a pliosaur has no great interest, but a 12 tonnes one might be more interesting. Of course, before stating anything, I'd suggest to wait the final publication.
2014 seems to be an interesting year in the Megalodon research, Pimiento about extinction, Balk about its size history, Boessenecker and Ehret about its extinction in the Pacific (possibly occured earlier than in the Atlantic), Kent's chapter... It only lacks a documented skeleton...
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Post by elosha11 on Feb 20, 2014 2:05:49 GMT 5
^ Let's hope the documented skeleton joins the list of developments in 2013.  |
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Post by elosha11 on Feb 20, 2014 2:15:24 GMT 5
The 9.26 meter average seems problematic to me, unless Megalodon really had an far greater range of size than other known macro-predatory sharks. I thought I read somewhere in this thread that Pimiento and Balk's research concludes that Megalodon could always reach 18 meters or more in both the Miocene and the Pliocene, but that the fossil record suggests (however obliquely) that maximum size was reached more often in the Pliocene, closer to the shark's extinction.
I wonder if the relatively small average size represents simply one epoch, whereas a larger average size was reached later, or if it confirms a fossil bias toward the frequency of smaller teeth. Who knows, but perhaps Megalodon reached mature adulthood relatively early and at a relatively small size, and then lived for 50-70 years, growing relatively slowly over that time. That is what the latest research suggests for the great white.
Incidentally, if the average Meg adult was "only" 9.26 meter but weighed 12 tons, it would suggest an incredibly robust shark. That's significantly heavier than an orca of comparable length. However, it may make biological sense since Megalodon was designed to potentially reach much greater size and should theoretically be built to pack enormous weight onto its frame.
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Post by creature386 on Feb 20, 2014 2:17:38 GMT 5
Other macropredatory animals don't have more extreme size ranges. This sample very likely included juveniles because we can't know when Megalodon matured.
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Post by elosha11 on Feb 20, 2014 2:29:15 GMT 5
^Yes, you've furthered my point. I'm skeptical that Megalodon had such a vast adult size range, which makes me believe a number of factor may have skewed the results, including the juvenile factor you mention.
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Post by Grey on Feb 20, 2014 2:30:07 GMT 5
Yes, elosha, I suspect the sample in Balk's talk includes juveniles. Tom Holtz said me that size figure is averaged overall. If Megalodon size knew variations depending the period, how to make a distinction between the adults and the youngs ? That's likely not included in the study.
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Post by elosha11 on Feb 20, 2014 2:33:49 GMT 5
If the 9.26 meter average includes juveniles, than it is still an important and legitimate average estimate of the sizes of all given sharks at any given time. But it doesn't yet answer the question of the average adult size, which should probably be significantly larger, with of course presumably smaller average size for males and larger size for females.
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Post by Grey on Feb 20, 2014 2:42:41 GMT 5
Certainly we must wait the publication. Keeping in mind that Balk and Pimiento also use the life status proposed by Gottfried with juveniles growing up to 10.5-13.9 m.
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Post by theropod on Feb 20, 2014 3:09:23 GMT 5
9.26m and 12t? That sounds far too high, no known method suggests such extreme robusticity.
If they used Gottfried’s lenght/weight formula (as they did in the material they posted so far), the result would be ~8.6t, and that regression is already on the high end as far as lamniforms go. I also currently cannot think of any published material that could provide sufficient evidence for such enourmous bulk.
Considering 9.26m is likely still within the subadult size range, yes, that figure certainly does include immature specimens. For determining an adult average, one would first have to come up with a rigorous way of telling apart adult and juvenile individuals on the basis of the available fossils.
A somewhat valid analogy could be drawn from the whole-species average of the great white. Does anyone know how large it is when including not just adults but also juveniles/subadults?
And from Pimiento & Balk’s poster I don’t see much of a marked size trend. Note that upper and lower bounds may or may be strongly affected by sample biases (which I think is a more likely option that its size range fluctuated randomly between periods).
The median size is highest 13ma, 9ma, 8ma and 4ma, so definitely the sharks could grow generally big, during the Miocene as well as the Pliocene. The upper size on the other hand is highest 12ma, 10ma and 4ma (all in descending order).
To be able to properly compare the latter, one has to make sure the samples are approximately equal.
Otherwise it’s like checking a million products from manufacturer A and only a thousand from manufacturer B, and deciding that A’s products had generally worse quality just because there was a bigger absolute number of flawed items found.
As long as the research is not finished and everything documented, I don’t think the maximum and minimum sizes will be of much use for intra- and interspecific comparisons.
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Post by elosha11 on Feb 20, 2014 3:25:08 GMT 5
Yes, I agree that 12 tons seems too high for a 9.26 meter Megalodon. Even under the assumption that it was comparatively more robust than a great white, I doubt it was quite this large at 9 meters. I wouldn't say it is an impossible size range, but probably implausible given our current knowledge of lamniforms. Even 7-8 tons would be a very large and robust animal at 9.26 meters, probably comparable to an orca.
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Post by Grey on Feb 20, 2014 3:33:48 GMT 5
Guys that's whithout a doubt 12 short tons. They based it on Gottfried et al. It's also Tom Holtz observation, I don't know if he read this, heard this from her or interpreted this. But all of this is based on Gottfried's regression. Let's say that Holtz talks about something around 10 m, 10 tonnes. For the remaining part, I agree to wait the final publication, but it's not bad to get clues from the research in progress. What can be mean by this is not that average adults Megalodons were that large, but that if we were travelling in time during Miocene-Pliocene, we are most likely to found at first a Meg that size. To my knowledge, they're examining >400 teeth specimens. I guess that's enough as data. Then we'll see how they've performed it, I'm confident with Pimiento for distinguish adults and youngs, she's behind the nursery paper... And there are reviewers comments before publication... I agree we must wait, but we already see big fluctuations between various Megalodon populations, and one might admit than in interspecific conflict a 12 tonnes shark is not the same thing than a 55 tonnes one (against a big foe, of course the attack of a 12 tonnes shark would be the same than a 55 tonnes one for a human diver). A colleague of Pimiento just sent this new finding to her, a Pliocene specimen, if that is a UL4 (or UL5 ?) like I suspect, it probably comes from a giant.  |
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Post by creature386 on Feb 20, 2014 20:50:06 GMT 5
To be able to properly compare the latter, one has to make sure the samples are approximately equal. I don't know about the sample size, but (as I said before) some samples have far smaller size ranges, so the larger/higher results can be sample bias. By the way, it would be great if there one day was of Gottfried's publication because although some stuff is outdated or flawed, we still take a lot of data from it (it had a reconstruction and probably the best method of it's time). Also, most of the unpublished stuff would be mentioned in such a comprehensive publication. |
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Post by theropod on Feb 20, 2014 21:40:09 GMT 5
Agreed. Over 400 teeth in total, but perhaps that’s 60 teeth from 12ma and just 20 from 9ma, which would be the reason for the vast difference in the reported scope of variation... 12 short tons would still be 10 886 kg, still 27% too heavy for a 9.26m specimen. So there must be a misunderstanding somewhere. Either it’s 9.98+m, massing 10.886t, or it’s 9.26m, likely massing ~8.2t (8.6 going with Gottfried et al.). I tend to trust the latter because the 9.26m is a far more precise figure, less likely to be a personal guess or misunderstanding. Considering that the sample includes immature specimens, that is not surprising. Grey: Why do you think it’s such a posterior lateral? It seems it could be an anterior lateral (=among the broadest teeth in the dentition) just as well. Here identification gets even more complicated since it’s missing a good piece of crown. |
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Post by Grey on Feb 20, 2014 21:53:38 GMT 5
Looking at its structure, the anterior laterals does not show such a curved side as in that tooth and have a larger crown. The tip is missing but the remaining part allows to get how the structure of the tooth looked alike. Not sure of course but it does not look to me an anterior lateral, L4 or L5 does not sound too far fetched.
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