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Post by elosha11 on Jun 22, 2022 21:40:07 GMT 5
No I've lost all the pictures from KH, do you still have some of them ? Indeed I considered to show them to Cooper. He also told me about a huge upper anterior tooth at the London Museum which he measured, the size suggests an individual very similar in length to GHC-6. I think Shimada 2022 assumed an UA position for each tooth, but even excluding this one, there are at least 4 teeth in the Chilean sample that suggests 19-20 m TL... I have seen the video from Chile but unsure if this shows an actual associated dentition.. You're right, they used all teeth that had been identified as upper anteriors in previous studies by Pimiento's group. Is GHC-6 Hubbell's tooth? It's interesting that Perez states in his Calvert Cliffs Museum lecture on his and your 2021 study, that there are a number of larger teeth than Hubbell's, but he had to use that as the largest available. When you consider that they conservatively assumed it was a lateral 1 (which is apparently the widest tooth usually), rather than an UA, and consider other teeth that are presumably wider/ and bigger, it does make one ponder the question of ultimate size estimates. I still have a number of very good pictures of Peru Meg, including some that are still on this website. I have some additional ones as well. But I was really hoping you still had that picture of what appeared to be the pelvic girdle fossil of the skeleton that used to be posted here. I'll reach out to Jack Cooper about it. |
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Post by Grey on Jun 23, 2022 3:34:26 GMT 5
Yes that's the big Hubbell's tooth.
Yes, I had also shared to Victor pictures of other large teeth comparable to GHC-6.
I believe GHC-6 to be most likely L1 although I think other authors (Renz) assumed it to an A.
I've found again the pictures from Peru.
Not sure about the purpoted pelvic girdle tough.
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Post by Grey on Jun 23, 2022 3:37:40 GMT 5
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Post by Infinity Blade on Jun 23, 2022 5:38:25 GMT 5
Interesting contrast to the study I posted earlier, and which came out the month before. Interestingly Shimada is an author of both papers. |
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Post by Grey on Jun 23, 2022 10:29:24 GMT 5
Interesting contrast to the study I posted earlier, and which came out the month before. Interestingly Shimada is an author of both papers. Many of their conclusions are similar, the first only finds more diet overlap with GWS diet. But some megatooth individuals apparently were apex predators eating other apex predators exclusively. No doubt in my mind that adults Carcharodon may have been rough competitors for juveniles Otodus. |
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Post by Infinity Blade on Jun 23, 2022 19:32:32 GMT 5
Seems to line up well with the raptorial Lee Creek physeteroids being preyed on by large megatooth sharks. What an extraordinary creature.
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Post by Grey on Jun 23, 2022 21:49:59 GMT 5
Seems to line up well with the raptorial Lee Creek physeteroids being preyed on by large megatooth sharks. What an extraordinary creature. And an extraordinary food chain. I wonder how those isotopes values would compare with those of the apex mosasaurs in the late Cretaceous... Livyatan teeth certainly needs a similar work to be done. |
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Post by elosha11 on Jun 23, 2022 21:55:41 GMT 5
Interesting contrast to the study I posted earlier, and which came out the month before. Interestingly Shimada is an author of both papers. I will have to review more closely, but I am starting to think this study corrected one of the flaws I mentioned about the earlier study. if you read the Princeton article, they show one of the teeth sample tested and it is clearly a fairly large adult tooth, rather than the juvenile teeth used by Shimada in his earlier study. If they were using adult teeth rather than juvenile teeth that I believe skewed the results in the earlier study, it would, as I suspected, change the isotope analysis toward a higher trophic level. Apparently the highest ever recorded. |
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Post by elosha11 on Jun 23, 2022 22:12:32 GMT 5
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Post by elosha11 on Jun 23, 2022 22:26:18 GMT 5
Also, this study says that they reach this extremely high level of trophic interaction even when they were small in their lineage, like a 3.5 m original Otudus auriculatus. I'm puzzled by this because I don't know how such a relatively small animal could be eating massive other animals unless it was scavenging all the time. Of course, this may also indicate that the animal was extraordinary aggressive, and "punching above its weight" so to speak, similar to the idea that the small juvenile Otudus may have attacked and left marks on a much larger living humpback like whale in the fossil record Steven Godfrey originally brought to light.
Again, I have to read all this much more thoroughly, this is just my initial thoughts.
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Post by Grey on Jun 23, 2022 23:10:14 GMT 5
The description of the bitten killer sperm whale tooth by Godfrey is also interesting in that light, plus as recalled by Infinity Blade the killer sperm whale from Lee Creek with a short lifespan, suggesting despite being orca-sized was preyed upon by something else. |
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Post by Grey on Jun 29, 2022 20:22:18 GMT 5
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Post by elosha11 on Jun 29, 2022 20:55:07 GMT 5
Absent some huge loss in natural prey base, I find it somewhat difficult to believe that cannibalism could explain a very high trophic level. This would be counterproductive for the long-lasting existence of the species, if such a large number of offspring were being picked off. Surely cannibalism did occur, as it occurs in modern shark species, but not at a significantly high level by all indications. As long as there were plenty of cetacean sources, I don't know why the shark would choose to regularly target its own species.
That said, Megalodon was probably obtaining numerous food sources, including cetaceans, pinnipeds, and perhaps other sharks.
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Post by Grey on Jul 3, 2022 8:19:13 GMT 5
Absent some huge loss in natural prey base, I find it somewhat difficult to believe that cannibalism could explain a very high trophic level. This would be counterproductive for the long-lasting existence of the species, if such a large number of offspring were being picked off. Surely cannibalism did occur, as it occurs in modern shark species, but not at a significantly high level by all indications. As long as there were plenty of cetacean sources, I don't know why the shark would choose to regularly target its own species. That said, Megalodon was probably obtaining numerous food sources, including cetaceans, pinnipeds, and perhaps other sharks. Well some of the megs studied have a lower nitrogen ratio indicating some of them definitely preyed on lower trophic prey items, but the extremely high values observed in some individuals (TL up to 9.6) is intriguing, as Boessenecker state, even an individual preying only on transient orcas could not reach that level. I guess that assuming a predation on sympatric odontocetes, themselves as high or even higher in the food chain than current transient orcas as well as predation on any smaller-sized member of the genus Otodus, Parotodus or Carcharodon might offer a temporary explanation. Another point, all the megalodon individuals appear small to mid-size, probably up to 12-13 m for the largest individuals using the SCW compared with the results using Shimada's equation, we have no data regarding the nitrogen data in really large teeth. Perhaps we could have surprises there. |
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Post by elosha11 on Jul 7, 2022 17:20:51 GMT 5
Absent some huge loss in natural prey base, I find it somewhat difficult to believe that cannibalism could explain a very high trophic level. This would be counterproductive for the long-lasting existence of the species, if such a large number of offspring were being picked off. Surely cannibalism did occur, as it occurs in modern shark species, but not at a significantly high level by all indications. As long as there were plenty of cetacean sources, I don't know why the shark would choose to regularly target its own species. That said, Megalodon was probably obtaining numerous food sources, including cetaceans, pinnipeds, and perhaps other sharks. Well some of the megs studied have a lower nitrogen ratio indicating some of them definitely preyed on lower trophic prey items, but the extremely high values observed in some individuals (TL up to 9.6) is intriguing, as Boessenecker state, even an individual preying only on transient orcas could not reach that level. I guess that assuming a predation on sympatric odontocetes, themselves as high or even higher in the food chain than current transient orcas as well as predation on any smaller-sized member of the genus Otodus, Parotodus or Carcharodon might offer a temporary explanation. Another point, all the megalodon individuals appear small to mid-size, probably up to 12-13 m for the largest individuals using the SCW compared with the results using Shimada's equation, we have no data regarding the nitrogen data in really large teeth. Perhaps we could have surprises there. Yes, both of the recent zinc and nitrogen isotope studies tested only small-to-medium-sized teeth, although the nitrogen study does seem to use overall somewhat larger teeth. Under the crown height method, the largest Megalodon tooth studied in the zinc test was only about a 7.5 m individual, which I cannot imagine would be any more than 8.5 to 9 m using the summed crown width method. I specifically critiqued that in my analysis of the zinc study. But I understand they probably do not want to do invasive testing on large, valuable teeth. It would be great if some museum would allow a 6 to 7 in. tooth to be tested. Given the diversity and presumably sizable populations of odontocetes, the evidence certainly does seem to point to megatooth sharks frequently feeding on them. In addition to various filter-feeding cetaceans. And I do agreed that megalodons and other megatooth sharks probably also preyed upon smaller sharks as well. |
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