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Post by coherentsheaf on Jul 21, 2016 1:32:47 GMT 5
With regards to the allometry, I am not sure what you mean. Did you do logistic regression? If you want consistent estimates, use perfect data sets where all of the variance is explained. Else there will necessarily be a difference in slope  |
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Post by theropod on Jul 21, 2016 2:03:24 GMT 5
Something like lm(log(physeter$skull_length)~log(physeter$total_length)) and lm(log(physeter$total_length)~log(physeter$skull_length)). In one the skull ended up becoming slightly bigger, in one it got slightly smaller.
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Post by Grey on Jul 28, 2016 7:14:52 GMT 5
I'm not sure to have posted this one before. Approx. 15cm x 15cm, one can wonder where was this tooth in the dentition, how large was the dentition, how large were the largest teeth in this very dentition and how large was the animal behind it. Teeth like this are solid hints the current maximum size published for Megalodon are probably conservative.  |
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Post by Grey on Aug 7, 2016 6:17:49 GMT 5
The abstract of the study I'm co-author SIMPLIFYING THE METHODS - BODY LENGTH ESTIMATES FOR CARCHAROCLES MEGALODON USING ASSOCIATED TOOTH SETS AND JAW WIDTH RELATED DATA FROM GREAT WHITE SHARKS AND MAKOS LEDER, Ronny M., Florida Museum of Natural History, Vertebrate Paleontology Department, Dickinson Hall, 1659 Museum Rd., PO Box 117800, Gainesville, FL 32611, PEREZ, Victor J., Geological Sciences, University of Florida, Gainesville, FL 32611 and BADAUT, Teddy, Independent affiliate, Thoirette, 39530 / 39240, France, leder.ronnymaik@flmnh.ufl.edu Since the first time a Megalodon shark tooth was found and identified as such, the question of the actual size of one of the Neogene top predators was the subject of imaginative speculation and scientific investigation. Both the results and the methods that are used to determine the size led to enormous dimensions in each case but are still quite diverse and bear a high potential for uncertainty. The problem with the recently most used estimation methods like those from Gottfried (1996) and Shimada (2002) is that they make body length estimates based on isolated teeth rather than entire dentitions. After testing the validity of the body length estimates from Shimada, which is the most accepted at the moment, by using several associated dentitions from C. megalodon, we noticed an extreme variability of the body length estimates depending on the tooth position in the jaw (Perez et al, 2016). In fact, especially estimates from lateral teeth were extremely variable and estimates from posterior teeth also varied significantly. The circumstance that we have this huge range in estimates makes it obvious that the teeth proportions of Megalodon don't correlate with that of the living Great White Shark. Subject of the studies presented in this poster is the use of the sum of the crown width of teeth from associated tooth sets as a measure for the related width of the entire jaw. Then we use this relation for a body length estimate based on the jaw proportions derived from appropriate data from modern Great White sharks and Makos. Moreover, this study is a positive example of successful collaboration between professional and amateur paleontologists, one of the priorities of the NSF funded FOSSIL project. gsa.confex.com/gsa/2016AM/webprogram/Paper285189.html |
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Post by creature386 on Aug 7, 2016 19:22:47 GMT 5
You co-authored a paper? Wow, congratulations!
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Post by coherentsheaf on Aug 9, 2016 0:32:10 GMT 5
very well done! Congratulations. Now we have a published author on Megalodon on the forum!
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Post by Grey on Aug 12, 2016 23:23:02 GMT 5
Thank you guys, although I admit the main work is done by colleagues. Hopefully the new data will be stronger than the previous methods.
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Post by Life on Aug 22, 2016 9:06:06 GMT 5
GreyCongrats. You can be a part-time paleontologist.
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Post by Grey on Sept 30, 2016 16:48:35 GMT 5
The poster has been presented. The conclusions are very interesting.
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Post by theropod on Sept 30, 2016 17:08:48 GMT 5
Congratulations, I hope it went well!
Were you at the conference?
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Post by Grey on Sept 30, 2016 22:53:06 GMT 5
Thank you. Nope I'm back in the army and couldn't be available but the lead author sent me the poster. I wait a little before sharing it. Hopefully it will result in excellent papers. It proposes new body length estimates for the Yorktown adult dentition, the Bone Valley juvenile dentition and a chubutensis dentition from Peru.
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Post by Grey on Oct 13, 2016 19:15:10 GMT 5
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Post by elosha11 on Nov 12, 2016 21:27:22 GMT 5
So I'm curious to hear everyone's thoughts on Grey and his collaborators initial conclusions, as shown in the poster in the link above.^ To summarize, the research team used three sets of associated dentition, two from an adult and juvenile Megalodon, and one from C. Chubutensis. They then compared them to the associated teeth of great whites and makos of various sizes as the probable closest living analogue to megatoothed sharks. The team concentrated on the sum of the crown width of the teeth, rather than on crown height or slant height. The methodology was "based on simple cross multiplication of summed tooth width
– body length relation from living species with summed tooth width of fossil associated tooth sets."
When compared to the size and proportion of adult great white and mako associated dentition, the adult Megalodon associated teeth from Yorktown, (which are by no means the widest known teeth), yielded an estimated BL of around 18 meters. The juvenile was estimated at 12 meters and the C. Chubs adult was estimated at 11 meters. These preliminary findings would suggest that teeth that are much larger than the Yorktown set come from larger sharks that may have significantly exceeded 18 meters. The study's initial conclusions appear to suggest that Megalodon's maximum BL may be underestimated.
My initial thoughts are that using a full set of associated teeth and summed tooth width seems to be a more developed source than relying on single teeth such as an anterior or a lateral, the latter of which the study suggests are particularly inaccurate measures. I also found it interesting that the study completely "disregarded" interdental spacing since it is unknown in extinct megatoothed sharks and only accurate for freshly examined great whites. But it seems problematic to completely disregard spacing since we know it does occur and does have an impact on the overall jaw size. But the study claims that simply using crown width without accounting for interdental spacing still yields stable estimates for jaw size.
Any thoughts/critiques on this methodology?
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Post by Grey on Nov 12, 2016 21:49:32 GMT 5
Additional meg sets are needed, to know the exact relationship between crown width>summed crown width>body length.
Interdental spacing is not necesserary as the purpose is to deal with only the material available and it is strong enough.
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Post by elosha11 on Nov 13, 2016 21:05:18 GMT 5
Is the study anticipating introducing other associated tooth sets in the official publication? That would be great.
I'm still uncertain why some type of interdental spacing wasn't used. I understand they can't predict how much space was between the teeth, but we know such space existed between the teeth. The poster states the sum of the teeth provides stable estimates of jaw size. But without accounting for interdental spacing, doesn't it slightly reduce the size of jaws? Perhaps a calculation that includes very conservative calculation of spacing would yield more accurate findings.
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