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Post by Life on Mar 5, 2015 20:44:26 GMT 5
Vary large Pliosaurs (15 - 16m) may have existed, as per fragmentary remains. However, I don't find the claims of 20m Pliosaurs reliable or convincing, based on known fossil evidence.
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Post by theropod on Mar 5, 2015 21:18:31 GMT 5
^I also think teeth are a very poor basis for a size estimate. Besides those, there are just vertebrae, and those are not described in detail.
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Post by Grey on Mar 5, 2015 23:40:59 GMT 5
Most max estimates for pliosaurs level off at 15 m, some believe 18 m is plausible, one that 20 m with 25 m as max size being hypothetical. Morphometrics and growth analysis would be needed for these fragmentary remains.
There is material for an excellent PhD project.
The Megalodon size paper is under review,,I really hope it will give new insights regarding max size, though I suspect it will result in Megalodon max size at 18 m and 70 tonnes.
I know that Nat Geo is making a doc about the "10 biggest prehistoric creatures", they've filmed some footages of the kevani skull recently. The doc will be released one week prior Jurassic World.
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Post by Grey on Mar 22, 2015 22:37:36 GMT 5
I was reading McHenry's thesis again. McHenry favors the BMNH proportions (head about 19 % of the TL) rather than Tarlo's (23 % of the TL) for pliosaurids. What I find strange is that it was always said that Tarlo's old model was extremely small-headed (1/7) while it is reported big headed here. I don't success to determine if McHenry applies the same proportions for the Jurassic pliosaurids estimates than for the Cretaceous brachauchenids. Also, an early model of Basilosaurus, Livyatan at 17.5 m and Ontocetus oxymycterus.  This model of Livyatan at its upper estimate is impressive. Still a contender. Courtesy of Jaime Bran. |
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Post by theropod on Mar 22, 2015 22:51:34 GMT 5
I really like the Livyatan depiction.
As for Tarlo’s model, it’s definitely rather big-headed. But the fact that the largest pliosaur McHenry considered reliable was based on mandible lenght (which was almost 24% of Tl based on the BMNH model, i.e. considerably greater than skull lenght) further enhances this difference.
We need to determine which ratios or measurements refer to the whole head, which to the jaw, which to dorsal skull lenght and which to condylobasal lenght.
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Top Dog
Mar 22, 2015 23:49:15 GMT 5
Post by Grey on Mar 22, 2015 23:49:15 GMT 5
Was the BMNH model used for the Jurassic pliosaurids also applied to the brachauchenids ?
My point being that if the BMNHM model is already more liberal than Tarlo's, it puts doubts on the alleged 1/6 ratio (?).
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Post by theropod on Mar 23, 2015 0:48:29 GMT 5
Only for the body mass, IIRC McHenry’s brachaucheniid lenght figures were calculated based on more complete, partial skeletons.
I don’t think Tarlo’s skeletal based on a whole lot of evidence, but then, neither do I know whether the BMNH model does. But obviously, that’s the question here, hence also my previous scepticism on that ratio. More than one factor is likely at play here, for example McHenry’s estimates may seem very large skulled, for a 3m mandible and 12.7m TL, the CBL/TL ratio would be ~1/5.16, perhaps considerably less depending on where the retroarticular process is included.
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Post by Grey on Mar 23, 2015 0:58:52 GMT 5
Another potential complication, a Swedish paleontogist, specialized in plesiosaurs, told me that Liopleurodon seems to be larger headed than Pliosaurus...
For the record, he doesn't believe either in 20 m pliosaurs even we can still have surprises...
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Post by creature386 on Mar 23, 2015 1:11:14 GMT 5
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Post by theropod on Mar 23, 2015 2:17:53 GMT 5
^Posted somewhere on the board, discussed on this thread among others.
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Top Dog
Mar 23, 2015 20:55:01 GMT 5
Post by Grey on Mar 23, 2015 20:55:01 GMT 5
BTW remember the graph I shared about meg size trends ? Of course it was early results and the actual study will be available very soon now but I'm not sure anymore if the scale was in log 10 like we used it or log 2 ?
In the later case, this would make meg presumably quite much smaller than Livyatan...The author first said me to use log 10 but after said she didn't remember if it was rather log 2.
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Post by theropod on Mar 23, 2015 22:48:40 GMT 5
I recall you wrote the data had been completely revised.
Assuming log10 the typical sizes were not that huge (the highest median figure of any of the samples was short of 22t, translating to roughly 12.4m when reversing Gottfried’s weight formula, and some samples the medians were only a tenth of that), but the maximum (75t and 18.3m) roughly correspond to what is known and would be expected based on Pimiento et al.’s previously published estimates and methods.
Log2 doesn’t even give remotely plausible figures, too low even for new-born great whites (in the order of less than 30kg at at maximum), let alone adult megalodons. I probably already tried assuming a natural logarithm when determining which base to use back when I first checked the data, and even it doesn’t give realistic results.
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Top Dog
Mar 23, 2015 22:54:32 GMT 5
Post by Grey on Mar 23, 2015 22:54:32 GMT 5
Well my understanding of the log 10 is that it is indeed huge as the median figure is already larger than the largest pliosaur in McHenry's dissertation, but you see my point...
Thanks to have verified this, I had a doubt but indeed log 10 makes sense. I think the highest figure was more like 69 tonnes but given the low resolution...
Yes apparently the data is largely revised so these results are anything but definitive so far.
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Top Dog
Mar 24, 2015 3:46:37 GMT 5
via mobile
Post by theropod on Mar 24, 2015 3:46:37 GMT 5
Well my understanding of the log 10 is that it is indeed huge as the median figure is already larger than the largest pliosaur in McHenry's dissertation, but you see my point... Thanks to have verified this, I had a doubt but indeed log 10 makes sense. I think the highest figure was more like 69 tonnes but given the low resolution... Yes apparently the data is largely revised so these results are anything but definitive so far. That wasn't the overall median figure tough, just the largest one of them. The smallest of them is less than two tons. Those do not sound too high to me. |
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Post by Grey on Mar 24, 2015 4:20:35 GMT 5
Yes but a replace this in the context of the study, many immatures individuals might be included in the data set.
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