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Post by Grey on Dec 22, 2015 1:59:20 GMT 5
Nice but you've still used the 125 mm wide tooth ? Why is there still the discrepancy with Siversson figure and sizing from actual white sharks specimens ? Edit blaze : Siversson doesn't take into account any tooth spacing.
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blaze
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Post by blaze on Dec 22, 2015 3:13:47 GMT 5
Yes, it's based on the 125mm wide tooth, as for the discrepancy maybe the jaws Siversson used were of those that are "flat" rather than in natural position? in that "fresh" white shark CT scan the width between the posterior most teeth is ~15% less than the total width of the upper teeth from either side but he says that the former measurement is 16% more than the latter in his Isurus paucus jaw, so the jaws of Isurus paucus are proportionally wider and shorter than those of the great white shark or those dried jaws are not in a life-like position.
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Post by Grey on Dec 22, 2015 3:17:26 GMT 5
Siversson justly precises the jaws are in life-like position and in a later email he precised he didn't take into account any tooth spacing. He also precises he calculates both from Isurus and Carcharodon, implying he got similar results for both.
Isn't the regression not applicable to white shark, large-mouthed lamnids ?
One thing, if we apply the posterior width indicated by Siversson, the white shark-like jaw outclasses Livyatan in sheer volume. Only the teeth appear too long but that's due to the differences in height decrease of Megalodon with the white shark.
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blaze
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Post by blaze on Dec 22, 2015 4:43:20 GMT 5
What white shark-like jaw? do you mean increasing the size of the jaw in my size chart to reach the width indicated by Siversson? the black toothrow is Hubbell's set increased 50.6%, already properly scaled for the 125mm tooth, if one wants to make it fit the width indicated by Siversson one would have to expand it to the sides, increasing width but reducing length so the volume wouldn't really change.
Given how the shape of the jaws is different between what Siversson says and that CT scan, I think it's valid to question how life-like really are the jaws he was looking at.
The regression from Tomita (2011)? using it in white sharks seems to work, the question is if it works on C. megalodon.
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Post by Grey on Dec 22, 2015 5:10:21 GMT 5
The regression from Tomita indicates different results than the 7.4 % ratio they report for the UA1 in the white shark. Are you sure the teeth are correctly scaled ? Note that between the bone clones pdf and the measurements of crown width of Hubbell's set in Pimiento 2010, there are already very different results in the summed width of all the upper teeth. The summed crown width reported by Pimiento exceeds the summed tooth width from boneclones. There is something wrong somewhere. I don't think Siversson comitted the error to use a not so naturally fashionned shark jaw since he says to have used several jaws from Isurus and Carcharodon. Scaling the data from Mollet et al. bite marks width roughly correlates with Siversson result so... Simply speaking, the 5.1 m white shark in Mollet figure has a bite width 10.63 % its body length. The 125 mm wide tooth comes from a shark conservatively estimated at 15.9 m. Using the same ratio we should get a bite width about 1.49 m, way larger than 1.05 m... I'd like to see how your jaw with a 125 mm wide, 168 mm high UA1 would compare with the Smithsonian reconstruction modified by Gottfried and Compagno which has an UA1 127 mm high. This mount is the same size as the jaws in th Calvert Marine Museum skeletal mount, see Gottfried 1996 and Purdy 2001. Despite the size difference of their UA1, your model and the Smithsonian mount seem pretty similar in size.
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blaze
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Post by blaze on Dec 22, 2015 6:31:58 GMT 5
It's the result of allometry, as I mentioned before using the width of the white shark AU1 (42.7mm) gives a UJL of 565mm, that's a ratio of 7.55% not much different from the real ratio of 7.4% and I'm pretty sure it's well within the 95% confidence interval however, given how it results in a 1203mm UJL for a 125mm wide UA1 (10.4%) it is clear that the allometric trend of the sample is for the AU1 to represent an increasingly larger percetage of the upper jaw length but Hubbell's set suggest C. megalodon bucks this trend and has a much narrower AU1 than expected for its size.
The set in the bone clones pdf and the one in table s3 of Pimiento et al.. (2010)? are they supposed to be the same set or what do you mean? the one in Pimiento et al. has a total width of 1123mm (and that's from crown width, I suppose including the root would increase it a bit) compared to 799mm of the one from the bone clones pdf (which I assume does include root as the height is explicitely said to include the root), AU1 corresponds to 9.55% and 10.39% respectively of the summed width of all teeth, suggesting the AU1 is proportionally even smaller in the larger S3 set than the one from bone clones.
The black teeth in my size chart are the photo from bone clones, made to be have the teeth touch each other and scaled to a total tooth width of 1203mm, the contour length of the tooth row of that white shark jaw is scaled to have this measurement. If we instead use the set from table s3 of Pimiento et al. (2010) (AU1 crown width of 107.3mm) and scale up to an AU1 width of 125mm we get a total tooth width of 1308mm, or ~8.7% larger than how I have it depicted, that'll increase the straight line measurements of the jaw to 114cm wide and 107cm long, still a far cry from Siversson's suggestion of 150cm.
Is there any documentation of what happens to dried shark jaws besides contracting slightly? maybe they inevitably flare to the sides?
That model, I know the angle plays a role but we assume the woman is 1.64m tall than that dentition is ~85cm long, just by looking at it seems the toothrow is proportionally smaller with respect to the overall size of the jaw in that model than what is depicted in my size chart.
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Post by Grey on Dec 22, 2015 7:02:06 GMT 5
One thing to consider, Siversson sent me this explanation in 2013, Tomita is 2011 and is well within the field of Siversson. Yet he didn't rely on this regression to explain me how calculate the bite width of Megalodon... I made a mistake, I refered to the table s4, the "juvenile" associated set from Bone Valley. That's Hubbell's set. I still do note some strange differences between the respective measurements (crown width wider than tooth width in boneclones). My confidence in boneclones is rather limited, I'd rather rely on Hubbell's original set seen on elasmo.com. The s3 dentition is a set from an adult found in Yorktown. I don't know any documentation about that, I simply doubt that Siversson would omitt to use a jaw in natural position or confuse the position, especially that he precises it. I should have asked him the length of the dentition at the same time. David Ward says this in Renz 2002 : So the quadrant of the jaws in a 18 m Megalodon would be approx. 1.8 m (?). My feeling is that this regression is not applicable for much larger sharks but I'd like to see something more conclusive. Siversson also said me that estimating TL from tooth width was conservative as long as we consider the tooth used is the largest(widest) in the dentition. Is this valuable in this regression ? Looking at this shot of the Smithsonian jaw, I think it is larger than your model : I've scaled up the Smitsonian jaws at UA1 height of 168 mm. Sure there is the perspective playing and the woman might be small-sized but it looks way larger than in your chart. In fact it looks near identically as large as this chart made by coherentsheaf some times ago scaling the Calvert Marine Museum jaws at ~17 m TL.
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blaze
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Post by blaze on Dec 22, 2015 8:27:22 GMT 5
Why would Siversson use Tomita (2011) for that? the paper doesn't deal with the width of the jaws in life but with the external perimeter of the palatoquadrate, it can be made to be used for that purpose (just like you and I did at first) but if one has jaws at hand, the way he explained it to you seems like the most straightforward and sensible choice.
I will try to make a drawing of a tooth set using the proportions and measurements of the sets in Pimiento et al. (2010).
Well, there has to be an explanation, why are the proportions suggested by Siversson so different from what can be observed in the CT scan of a white shark head? either yes he committed that error or that specific jaw is abnormal, are there any other possibilities?
That quote from Ward... midpoint to side is 1/10th of total length? seems like he is suggesting the jaws of an 18m meg would be 3.6m wide.
I think so too, that's why I didn't use it to scale the jaw in the size chart.
About the jaw in my chart looking small when compared to that scaled up model, I mentioned it is probably slightly underestimated but the biggest factor seems to be that the dentition in that model is proportionally smaller than in the white shark I scaled up for my size chart, in the white shark jaw the dentition goes up to just before the jaws start flaring to the sides but in that model they fall short of that point by ~15cm-20cm.
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Post by Grey on Dec 22, 2015 8:50:25 GMT 5
Yes, though UJL could have been used by him to deduce jaw width as well.
I don't think he committed an error or that this jaw was abnormal since he says to have used several jaws. His suggestion is in contradiction with what seems to suggest the regression in Tomita but with the CT scan of the jaw, I don't see how ? The only issue is how the dentition you took from boneclones seems to fit in it.
Ward rather suggests 3.6 m is the upper jaw perimeter, not the width (is it possible to calculate the upper jaw perimeter in Livyatan ?).
The problem with the jaw in your chart is because of the teeth. While suggesting to make a comparison with Livyatan, I wasn't focused on the teeth, only the resulting dimensions of the jaw. That's why I had no problem using the Mako jaw figure first, I relied on a realistic jaw shape, ignoring the teeth.
Don't you think simply scaling the bite mark data from Mollet et al. without using the negative (unrealistic ?) allometry is more reasonnable at this point ? Basically that's what Siversson did and the results appear to be pretty similar to what we get while direct sizing great white bites. Here is also an argument in favor of Siversson using natural positioned jaws; his results appear quite close from scaling the bite marks in Mollet et al. and obviously, these sharks had their jaws in natural position while biting...
Exploring allometry using Tomita appears interesting but I suggest to simply get a jaw width and length for Megalodon and to use a white shark jaw model (ignoring the teeth problematic) for an approx. but reasonnable comparison with Livyatan.
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blaze
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Post by blaze on Dec 22, 2015 11:39:30 GMT 5
Using the measurements of Hubbell's set in Pimiento et al. gives a total toothrow width of 69cm, scaling up to a 125mm AU1 results in one of 105cm, this is much smaller than that suggested by the larger set (131cm) probably because of the difference in how much the AU1 contributes to the total width (12% vs 9.6%), either way both measurements are much too big to fit into a jaw suggested by Tomita's regression which is only 129cm and that's for the external perimeter (on either side) of the whole palatoquadrate. The dentition I took from bone clones does not seem to fit in, it fits because I scaled the white shark jaw to have the same total tooth width suggested for the 125mm wide tooth, the bone clones teeth then were scaled to fit that same measurement.
Ward clarifies quadrant as midpoint to side, I don't see how that suggest he means perimeter, that reads like an straight line measurement.
The teeth are no problem to my size chart, I already did exactly what you suggested, I'm not basing jaw size on Tomita at all, I just took that white shark jaw, measured the total upper tooth width in it and then scaled accordingly, no allometry or regression equations used. The difference between the proportions suggested by that CT scanned head and what Siversson suggest is not something of my making, it might be that juvenile white sharks have narrower mouths than adults, in such case then I just have to flare out each side of the jaw up to 150cm.... it could also be that bite marks are not that good representation of the actual jaw size, I remember reading here arguments from other experts about that, I'll search for them.
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Post by elosha11 on Dec 22, 2015 20:28:26 GMT 5
Curious, as all of these depictions seem far smaller than the Meg jaws recreated by researchers at Houston Museum of Natural History, D.C., etc. Is this the depiction for an "average" size Megalodon jaw, i.e. 10-12 meters? I cannot believe an 18+ meter shark would have jaws nearly this small and narrow.
For what it's worth, Honniger reported his Meg skeleton has jaw remains of I believe around 2 meters, and reported that it was only partial remains, suggesting a perhaps bigger structure. There have been others too that have supposedly found fossilized Meg jaws in Peruvian desert of well over 2 meters. Whether this is true and can ever be verified is anyone's guess.
EDIT - sorry I was looking at the jaws depicted on page 58 of this thread, hadn't yet seen the posts on page 59. Will review and comment further.
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Post by Grey on Dec 22, 2015 21:45:24 GMT 5
The jaws in Houston are in flat, unatural position, that's why they're not considered here. Plus, the placement of the teeth can be debatable (decreasing size). Natural jaws are still wide but more elongated. The jaws were made by Cliff Jeremiah who's certainly knowledgeable in shark anatomy but is not scientist. I tend to disregard anything reported by Honninger as long as there is nothing documented or properly photographed from Peru. The jaws I used from the Smithsonian, as well as its corrected version from Calvert are in natural position and were made by actual paleontologists specialized in fossil sharks. That's why I used them as comparison here. Their only potential issue is that they're based on the white shark configuration with the bended, small UA3. Megalodon had all its UA close in size, so these jaws might slightly underestimate the tooth row length. But we can roll with them in the purpose of this discussion, they can allow to be conservative. I tend to use the data from Siversson and scale it to the CT scan used by blaze but disregarding to put the Meg dentition in it. I only look at the surface (width + length of the dentition). Using the CT scan jaw and the indication by Siversson results for the 125 mm wide tooth from Gottfried et al. 1996 to fit in a jaw approx. 134 cm wide between the most posterior teeth and 125 cm long (using the CT scan proportions). Comparatively the uuper jaw of Livyatan is 93 cm wide between the most posterior teeth and 133 cm long. I don't conclude anything but this basic scaling implies the Megalodon specimen from Gottfried et al. 1996 (conservative TL 15.9 m) has a larger upper jaw perimeter than the Livyatan holotype. This would support large adult Megalodon as having theoretically the largest predatory bite among vertebrates. The scaled up jaw mount with the lady I made may reflect the theoretical size of the jaws. However Livyatan seemingly would have a slightly larger or equivalent (need to see the surface in square) bite than the Yorktown adult Megalodon. blaze you don't think it's the most reasonnable way to go for now ? About Ward, B.K. said me the same thing, multiply this by 2, you get the upper jaw perimeter (along the curvature of the jaw). Approximately, the jaw perimeter represents about 20 % of the shark TL.
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Post by neogeneseamonster on Jan 16, 2016 17:03:20 GMT 5
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Post by spartan on Apr 24, 2016 0:05:52 GMT 5
Do we have "hard numbers" for the angles of their respective bite gape? Physeter seems to have a rather large gape for a cetacean, but I don't know how telling this is due to their vastly different jaw morphology.
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Post by Grey on Apr 24, 2016 0:07:58 GMT 5
Gottfried et al. suggests the gape in megalodon would be up to 75 degrees, reflected in the Calvert Marine Museum reconstruction.
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