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Post by Infinity Blade on Sept 4, 2019 18:42:00 GMT 5
I for one didn't know what their exact objections to "Otodus megalodon" were, so no, I think it was good on theropod's part to bring them up.
Admittedly, though, I hadn't read the full paper. I assumed they had based megalodon's inclusion in Otodus was based off of morphological grounds. For some reason when I read "avoid paraphyly", I didn't think they literally meant "we're extending monophyly to genera".
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Post by theropod on Sept 4, 2019 19:23:59 GMT 5
Well, this is not strictly speaking against synonymy of Otodus with Carcharocles, just against the argument that genera should be monophyletic. There are arguments for and against synonymizing the two, I just think the end members are too different to be in the same genus and find it convenient to use the presence of serrations, which seems to be a stable distinguishing character.
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Post by elosha11 on Sept 5, 2019 6:48:37 GMT 5
elosha11: The second Livyatan depiction→ was certainly not part of the original publication (or any other that I am aware of). I have no idea why it’s seen as authoritative by some people (I recall people thought so on carnivora as well), it’s an artistically nice model, but just one more plausible reconstruction among many. As I believe I have pointed here out before, the skull model suggests nothing at all about the gape angle (nor, for that matter, does the one from the description paper). Simply depicting a skull with the jaws open does not imply the angle is the maximum the animal could achieve. My mistake then, on the second depiction. Thanks for pointing that out. I thought it came from the original publication. So I guess gape angle for Livyatan is still a relative unknown. You would think a study could be done for that, given the fairly extensive skull and jaw remains. |
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Post by elosha11 on Sept 11, 2019 7:44:51 GMT 5
Elosha, do note that these jaws reconstructions are in an unatural pose, which enhances the size visually. However I can say that Hans Sues, curator of the department of vertebrate paleontology and sharks specialists, sees Livyatan oral cavity to have been narrower than in the giant shark. Of course we will sure of anything until we find a preserved meg jaw... I'd still be somewhat surprised if a large Megalodon's jaws were less than 2 meters wide. But I definitely believe it was a wider, but perhaps slightly shorter jaw than Livyatan, with a larger overall volume than Livyatan's bite, particularly when considering the whale's comparatively thinner lower mandible. But it would be interesting to see any real study on the gape of Livyatan.   |
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Post by Grey on Sept 11, 2019 11:42:41 GMT 5
 3 m wide reconstructions usually imply measuring the width of the jaws fully widened, not the interior of the jaws themselves. As you can see above with this GWS moutj, if the distance between the most posterior upper teeth was even about 160 cm, the mouth in real life would be extremely large by any standard, including in gape and overall volume. Basically you could place two Sue-sized Tyrannosaurus skulls side by side in it. Renz (2002) described the jaws to have been 10 feet wide in outside measurements and 6 feet on the inside. It is still possible the mouth could have been a bit wider as indicated by the curvature of the teeth and the sheer size of the dentition. The Bertucci model should simply be mounted more accurately but the bite volume would still be the same. This picture below is well known but is rather appreciated for the predicted size accuracy, Brett Kent used it in his lectures. Except for the obviously GWS specific teeth shape, it shows pretty well how large would be a mouth about 150-160 cm in interior width.  |
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Post by Grey on Sept 14, 2019 20:13:53 GMT 5
I would add a correction to my last comment about the scaled up to meg GWS mouth. While the upper dentition/jaw would be that size, the lower would be quite larger.
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Post by Grey on Sept 18, 2019 5:30:51 GMT 5
Question, why is it Carcharodon that is still used in the thread title ?
I like the old-fashioned sound it has but Carcharocles is fine to me.
Something to recall I had already done.
I think we can ponder if we could say for sure that at least one individual may have weighed in the 35-45 tonnes range.
The 230 mm vertebra from Denmark when scaled with three adult great whites on elasmollet wkth vertebra and body mass figures indicated this range. One of the great whites was gutted of its liver so I extrapolated the weight of the liver.
I suspect the width of the vertebra is more correlated to the overall body mass than to the length of the shark irrespective of the variations due to external factors (amount of food recently digested, fat, liver...) i.e. a basking shark could have largest vertebra as wide as a great white being a similar weight but it will be longer due to its more slender body. At least this is what I suggest potentially interesting in that way. And it is somewhat conservative as it is not certain the Denmark vert was the largest in the individual.
But I tend to think of 35-45 tonnes as something almost certainly sure. Unless I m wrong and that the relationship is poor.
Now why not speculate just a bit more. The 230 mm vert was apparently associated with a partial tooth that was estimated to be a 120 mm wide upper anterior (I suspect this to be a slight overestimate). Scaling the vert diameter at the 139 mm wide Hubbell tooth suggests then conservatively a body mass range in the 55-70 tonnes.
This seems quite reasonable.
In addition, we know Livyatan skull width roughly corresponds to a 15 modern Physeter. Based on the idea that 15 m Physeter will weigh 34 tonnes (a real 16 m one weighed 41 tonnes) that physical constraints may restrict the body at certain size to have an overall similar bioplan, we can say that based on the width of its skull that the Livyatan holotype weighed at least around 34 tonnes.
If the body is more related to skull width and that Livyatan was really around 17.5 m long, it suggests around 40-45 tonnes, not the 54 tonnes suggested by direct isometry, which would oversize the actual skull width.
If it was 16 m it may have approached the 40 tonnes region.
We're really talking about uncomparably large active raptorial hunters.
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Post by dinosauria101 on Sept 18, 2019 14:51:43 GMT 5
Question, why is it Carcharodon that is still used in the thread title ? I like the old-fashioned sound it has but Carcharocles is fine to me. Wasn't Carcharodon supposedly more accurate? I was under that impression when I changed it |
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Post by Infinity Blade on Sept 18, 2019 17:04:47 GMT 5
Edited. If megalodon was an otodontid, there's no way it could have been a species of Carcharodon. I can't make such changes to the poll without deleting it entirely, though.
I also reposted pictures in the OP, since they just became small boxes with question marks (at least from my perspective). The meglaodon one is the same, but I don't remember what the Livyatan picture was, so I posted a different picture. I hope it's to everyone's liking (particularly with regards to accuracy).
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Post by theropod on Sept 18, 2019 17:27:48 GMT 5
Infinity Blade Since dinosauria101 apparently only just made that poll, no idea what happened to the old one, and only a single person seems to have voted, I suppose it wouldn’t be a terrible loss if you deleted it and made a new one with the correct taxonomy. I do like that there’s a 50/50 option now though, I don’t think we used to have one.
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Post by Infinity Blade on Sept 18, 2019 17:33:44 GMT 5
Okay then, edited accordingly.
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Post by dinosauria101 on Sept 18, 2019 17:34:47 GMT 5
Tweaked the title a bit too
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Post by elosha11 on Sept 19, 2019 18:37:23 GMT 5
Grey, interesting post above. With regard to this quote How wide is the diameter of the vert when you use the 139 mm wide Hubbell tooth? I'm curious if it matches up well with the 26 cm verts Klaus Honninger claimed to find as the largest in his 18.26 meter Megalodon skeleton. If I recall, he claimed the skeleton had huge associated teeth, larger than 7 inch UA's I believe. For whatever one thinks about Honninger's overall credibility, his pictures of the vertebral centrum do look like very large Meg verts, further supported by the fact that they look very similar to the Denmark verts. And the 26 cm centrum diameter he provided seems quite plausible.
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Post by Grey on Sept 19, 2019 22:26:53 GMT 5
Conservatively, the 139 mm wide Hubbell tooth could confirm vertebra around 26-27 cm. I suspect the complete tooth would have been a tad smaller than 120 mm wide. And the Danish vertebra was not necessarily the biggest though it was surely on the large side.
As for the Honninger, yes these pictures were definitely large centra... as for the size itself, Honninger himself often gave contradictory figures.
But it is reasonable that Carcharocles had vertebra 26 cm in diameter and more.
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Post by Grey on Sept 20, 2019 4:57:45 GMT 5
I remember to have read on the fossil forum that the fossil centra of the genus Otodus/Carcharocles looked much like those of the modern Carcharodon, Isurus, Lamna, Odontaspis and Carcharias but apparently one noticed some greater similarities between the meg vertebra and those of the sand tigers.
Anyway, a relatively close phylogeny is generally expected between those two lineage and if the overall body shape was probably different at some extend, possibly the size of the largest vertebra was similarly correlated to the body length.
A 2013 study (Hansen et al.) about a fossil sand tiger determines that a 333 cm individual would have its widest centra at 41 mm.
Applied to the biggest Belgium vertebra scales up at around 12.6 m TL and for the Danish vert at around 18.7 m.
Of course the different tail shape may add perhaps 1.5-2 m compared to the more moon-like caudal expected for the genus, but this is further hint that maximum TL of 16 m may not be realistic for the genus.
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