|
Post by sharkboy101 on Mar 14, 2021 5:19:54 GMT 5
I know I’m a little late to the party but congratulations to Grey and all the other authors involved in the 2021 study.
Now if you excuse me, I’m gonna go to the Kronos Rising Novel Series Facebook group and ask Max Hawthorne if I can post this study in his group chat without getting blocked or insulted.
(In all seriousness I’m glad I’m not part of that cringe inducing group on FB)
|
|
|
Post by elosha11 on Sept 23, 2022 20:29:28 GMT 5
|
|
|
Post by megauf311000 on Sept 25, 2022 20:06:45 GMT 5
Hi! I have more pictures of this posterior, and I can provide them to you. First and second pictures show the morphological comparison with the l6 of bone valley dentition and Yorktown dentition. Third picture is the actual size comparison for l6 with the Yorktown adult dentition.
|
|
|
Post by Grey on Sept 27, 2022 16:59:46 GMT 5
Freakish. Can anyone say the crown width of that tooth and scale total body length using Perez et al. 2021 method ? Simple scaling with slant height and assuming UF-VP-311000 came from a 15.9 m individual (Cooper et al. 2022) suggests an alarming 23 m.
|
|
|
Post by elosha11 on Sept 30, 2022 4:02:33 GMT 5
Freakish. Can anyone say the crown width of that tooth and scale total body length using Perez et al. 2021 method ? Simple scaling with slant height and assuming UF-VP-311000 came from a 15.9 m individual (Cooper et al. 2022) suggests an alarming 23 m. Good questions. megauf311000, do you have access to the tooth or its owners so that crown width could be measured? I really appreciate your additional photos. FYI, since my FB links seem to have stopped working I added an attachment on my original post with all of the FB images.
|
|
|
Post by megauf311000 on Oct 3, 2022 3:01:55 GMT 5
Hi! I just contacted the owner and got some additional photos. CW is approximately 79mm, and I estimate the CH to be around 56mm( the owner said it’s hard to take photos with precise measurements of CH. From the photos i think 56-57mm is quite reasonable). I also got one more photo of teeth comparison with l6 of bone valley dentition.
|
|
|
Post by megauf311000 on Oct 3, 2022 3:34:53 GMT 5
Adjusted the sizes of photos uploaded, hope they become clearer. Also added two photos with shape comparison to l5 of UF311000. Huge differences in shape suggest they are not very likely to be in the same position, at least it looks more similar to l6 than l5.
|
|
|
Post by megauf311000 on Oct 3, 2022 9:20:31 GMT 5
Freakish. Can anyone say the crown width of that tooth and scale total body length using Perez et al. 2021 method ? Simple scaling with slant height and assuming UF-VP-311000 came from a 15.9 m individual (Cooper et al. 2022) suggests an alarming 23 m. Hi, Grey! size of this tooth: cw=79mm, ch=56mm. Using a crown width of 79mm, knowing that l6 of UF-VP-311000 has a cw of 62.1mm, assuming UF-VP-311000 is a 15.9m individual will return a total length of 20.2m. Quite reasonable. If we assume UF-VP-311000 is a 17.3m individual, then the corresponding total length of this individual is 22m. Nevertheless, I believe that posterior teeth are not that accurate for reflecting the sizes of individuals compared to anterior teeth. I would suggest a total length of 18m by conservative estimation. What is your opinion?
|
|
|
Post by Grey on Oct 3, 2022 13:44:04 GMT 5
Thanks megauf311000 ! Agreed, posteriors are always tricky but this is just another hint at extreme maximum size in the species.
|
|
|
Post by theropod on May 7, 2023 18:07:26 GMT 5
(On a side note, I fail to understand why your margin of error in your predictions for O. megalodon are so wide, those in Perez 2021 were less pronunced IIRC but this should be discussed elsewhere) Okay, I already explained this briefly a few times, but I’ll demonstrate with a concrete example. Let’s take the largest specimen in the sample. This is CP 63, an a1-a2 with a crown width of 113.32 mm. Based on the three most complete dentitions, this specimen would be estimated at an USCW of 2846.794, 2786.433 and 3087.190 respectively. The way you approached this, you just estimated the sizes at the upper and lower end of this range. But that’s not how a prediction interval is calculated. For that, we need to calculate the standard deviation and multiply it by an appropriate t value. The t-value is affected by the sample size (because with a higher sample we become more confident that our sample mean is close to the population mean), i.e. as should be obvious, the interval becomes wider at lower sample sizes. That means that here, with a sample size of 3, the appropriate t-value (qt(0.9^0.5,3)=2.3248) multiplied by the standard deviation (159.1062 mm) for calculating a 95% prediction interval is actually larger than the simple differences of the minimum or maximum estimates from the mean. This results in the 95% prediction range for the bilateral USCW being 3276.7-2536.9 mm. If you are sceptical, you can check the numbers. Now, to get an overall 90% prediction interval, we simply take the upper 0.95 PI based on the upper end of that range, and the lower 95% PI of the lower end, for an overall probability of 0.95^2=0.9 of falling into that range, which is 14.616--28.288 m. And this range is still likely underestimating the real uncertainty, for example because it is not taking into account that there are also uncertainties associated with the positional assignments (which are not easy to quantify). I.e., the real range would be even wider. I am a bit confused why this seems to be so hard to understand. Intuitively it should make sense that a size estimate for a single tooth will have massive error margins, just like we all intiutively understand that a size estimate based on a small jawbone frament (like the Aust Cliff specimens) has massive error margins.
|
|
|
Post by Grey on May 7, 2023 18:15:03 GMT 5
To me this was always inherent to predictions from isolated teeth, not from the dentitions themselves. The uncertainty is less pronunced using dentition parameter than sole tooth.
|
|
|
Post by theropod on May 7, 2023 18:43:47 GMT 5
Yes, but I talked about estimates from sole teeth from the beginning. Of course I am getting smaller prediction ranges for whole dentitions than for isolated teeth too. I’m not comparing my predictions for entire dentitions to yours for isolated teeth, nor the reverse. I am comparing my prediction error margins for isolated tooth to yours for isolated teeth (such as GHC, which you do estimate in your paper). For complete dentitions, you estimated a range of 15.1 to 20.8 m, i.e. 5.7 m wide, for GHC 1 based on its upper teeth (and even wider when taking into account the lower teeth too). For the same specimen, I got a 90% prediction interval of 13.1-18.3 m, a range of 5.3 m. So I think it’s fair to say that we have similarly wide prediction margins (although I would expect the confidence intervals to potentially benefit from the larger sample size, but I think you didn’t calculate any, so it doesn’t make sense comparing them).
|
|
|
Post by elosha11 on Jan 22, 2024 19:39:15 GMT 5
Journal Reference: Sternes, Phillip C., Jambura, Patrick L., Türtscher, Julia, Kriwet, Jürgen, Siversson, Mikael, Feichtinger, Iris, Naylor, Gavin J.P., Summers, Adam P., Maisey, John G., Tomita, Taketeru, Moyer, Joshua K., Higham, Timothy E., da Silva, João Paulo C.B., Bornatowski, Hugo, Long, Douglas J., Perez, Victor J., Collareta, Alberto, Underwood, Charlie, Ward, David J., Vullo, Romain, González-Barba, Gerardo, Maisch, Harry M. IV, Griffiths, Michael L., Becker, Martin A., Wood, Jake J., and Shimada, Kenshu. 2024. White shark comparison reveals a slender body for the extinct megatooth shark, Otodus megalodon (Lamniformes: Otodontidae). Palaeontologia Electronica, 27(1):a7. doi.org/10.26879/1345 palaeo-electronica.org/.../5079- ... -body-form ABSTRACT The megatooth shark, †Otodus megalodon, which likely reached at least 15 m in total length, is an iconic extinct shark represented primarily by its gigantic teeth in the Neogene fossil record. As one of the largest marine carnivores to ever exist, understanding the biology, evolution, and extinction of †O. megalodon is important because it had a significant impact on the ecology and evolution of marine ecosystems that shaped the present-day oceans. Some attempts inferring the body form of †O. megalodon have been carried out, but they are all speculative due to the lack of any complete skeleton. Here we highlight the fact that the previous total body length estimated from vertebral diameters of the extant white shark (Carcharodon carcharias) for an †O. megalodon individual represented by an incomplete vertebral column is much shorter than the sum of anteroposterior lengths of those fossil vertebrae. This factual evidence indicates that †O. megalodon had an elongated body relative to the body of the modern white shark. Although its exact body form remains unknown, this proposition represents the most parsimonious empirical evidence, which is a significant step towards deciphering the body form of †O. megalodon. palaeo-electronica.org/content/2024/5079-megalodon-body-form
|
|
|
Post by elosha11 on Feb 8, 2024 7:47:45 GMT 5
I have now fully read this new Jan 2024 study, and find it interesting and thought-provoking, but also believe that significant additional research is needed. And, I find it remarkable that the authors failed to even mention the far larger Megalodon vertebral centra that have been found of a large but not maximum size Megalodon (the Denmark specimen) with a max vertebrate diameter of 23 cm. (Additional evidence such as the Honninger/Peru skeleton also potentially suggests that centra diameter could be substantially larger than 23 cm. I will discuss in further posts). Instead the authors' analysis exclusively relies upon the incomplete and smaller vertebral centra in the approximately 140 vertebrates found in the Belgium specimen with a maximum diameter of about 15.5 cm. In the upcoming days, I will have additional and more detailed comments, praise, and criticism of this study in further posts. But first I wanted to post some interesting and pointed criticisms/reactions of the study by Jack Cooper (and others), who of course this current study is trying to rebut. Certainly there is polite but very sharp scientific disagreement going on here. www.washingtonpost.com/science/2024/01/21/megalodon-slender-great-white-shark/
But both teams have pointed critiques of each others’ studies, a normal — if sometimes uncomfortable — part of how science moves forward. Jack Cooper, a graduate student and shark paleontologist at Swansea University in Wales who led the study that is under attack, said that his team’s work has been criticized because of its overreliance on the great white shark as an analog to megalodon. But the new interpretation originates from an analysis that also relies on comparison to a great white. He also disagreed that a thin backbone would necessarily be too narrow to support a bulky animal, pointing out that the extinct shark cretoxyrhina also had a slender vertebral column but a bulky body form. (emphasis added) Outside experts said both papers still use speculation to arrive at their different interpretations. “At the end of the day, I don’t think it brings us that much closer to knowing what megalodon really looks like,” said Robert Boessenecker, a coastal paleontologist at the nonprofit Charleston Center for Paleontology who was not involved in the new study. Dana Ehret, curator of natural history at the New Jersey State Museum, said that it was good to see biologists who study modern shark biology join the discussion of ancient sharks, and, for him, the interesting thing is that both papers suggest that the megalodon was probably longer than scientists once thought. Jack Cooper says the new publication doesn't supply sufficient evidence to support a more svelte Megalodon. He's a graduate student in paleobiology at Swansea University in the UK. He's part of that other group that measured the spine and came up with the longer estimate of Megalodon's length. Cooper says the new publication presents an argument his group already considered. "It does reaffirm that we would need to find a complete skeleton to know for sure what Megalodon looks like," he says. "But if you're going to present an alternative hypothesis, you should use a lot of statistical work to try to make your case." Cooper agrees this is an important riddle to solve, once more fossil evidence becomes available. That's because Megalodon likely kept its most essential organs warmer than the surrounding seawater, which would have allowed it to swim further and faster. Knowing its size and body shape tells us how much it likely had to eat to maintain such a lifestyle. "And that can tell us quite a lot about what made it vulnerable to extinction about 3 million years ago," says Cooper. At the end of Megalodon's reign, sea levels were changing, ruining coastal habitats. This would have meant less food, possibly contributing to the giant shark's extinction. Cooper says the reasons behind Megalodon's vanishing could help us respond to the plight of today's sharks, many of which are endangered on a planet again in flux. www.npr.org/2024/01/26/1226649080/that-giant-extinct-shark-megalodon-maybe-it-wasnt-so-mega
[/b] The authors of the previous study are not convinced by the new findings, however. Lead author Jack Cooper, a researcher at Swansea University in the U.K., along with his colleagues Catalina Pimiento, also at Swansea University, and John Hutchinson, at the Royal Veterinary College, say the new study is more of an alternative hypothesis that suffers from "circular logic" — where an argument assumes its conclusion is correct, and uses the conclusion to support the argument "Moreover, they don't actually provide a new length estimation in their work," they told Live Science in an email. The new study, they added, ignores the fact that the previous analysis considered multiple living examples of sharks alive today, and that one of their models also showed an elongated body when based on great white sharks alone. "Importantly, the 'elongated body' interpretation is based on a single observation, a comparison with a single analogue, and lacks any statistical tests to support its hypothesis," they said. "More critically, several aspects of the study are impossible for future researchers to verify or replicate as the authors do not provide the raw data." www.livescience.com/animals/extinct-species/controversial-study-claims-megalodon-didnt-look-like-a-50-foot-giant-great-white-shark
[/b] But the researchers behind the 2022 research are not convinced by the new hypothesis. “While alternative hypotheses should be and are welcomed in science, this particular proposal suffers from a circular logic,” says paleontologist Jack Cooper of Swansea University in Wales, who was not involved in the new study. The new study says that the great white shark is an inappropriate analogue for O. megalodon, Cooper notes, but the new research also uses the great white shark for its comparisons of body form to the exclusion of other sharks. The 2022 study, by comparison, considered other lamniform sharks in addition to the great white and created a three-dimensional model. The 2022 study also produced an elongated O. megalodon model as one of its possible outcomes, as well, but researchers ruled it out based on data from a broader array of lamniform sharks. Lacking a complete O. megalodon skeleton, such disagreements may seem difficult to resolve. “However,” Cooper says, “sharks have generally remained geometrically similar throughout their long evolutionary history, which means living sharks can be informative in reconstructing extinct ones.” Even when the shark’s record is mostly teeth and isolated vertebrae, scientists can still generate a rough idea of the megatooth’s shape based on physiology, what it likely fed on and other details gleaned from the fossil record. Working out the shark’s form is critical to understanding how the megatoothed shark lived during its long tenure in Earth’s seas. “The body plan of megalodon is a key part of understanding its wider ecology, such as how fast it swam and what it needed to eat,” Cooper says. A longer shark would swim differently, for example, or have organs like the liver and spiral intestine related to the shark’s feeding and digestion. O. megalodon thrived for about 20 million years before vanishing, even as its preferred prey survived. Understanding the shark’s form can help experts uncover the carnivore’s evolution and extinction. For the moment, however, Cooper and colleagues are not swayed by the new reconstruction. All researchers are agreed that O. megalodon was not simply a supersized great white, but what kind of shape the enormous shark took as it slid through ancient waters is only just beginning to come into focus. www.smithsonianmag.com/science-nature/was-megalodon-slimmer-than-previously-thought-180983628/
|
|
|
Post by elosha11 on Aug 26, 2024 7:19:57 GMT 5
|
|