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Post by elosha11 on Mar 8, 2022 8:12:42 GMT 5
Cooler waters created super-sized MegalodonMegalodon expert leads the discovery of an intriguing pattern of the prehistoric shark A new study reveals that the iconic extinct Megalodon or megatooth shark grew to larger sizes in cooler environments than in warmer areas. DePaul University paleobiology professor Kenshu Shimada and coauthors take a renewed look through time and space at the body size patterns of Otodus megalodon, the fossil shark that lived nearly worldwide roughly 15 to 3.6 million years ago. The new study appears in the international journal Historical Biology. Otodus megalodon is commonly portrayed as a gigantic, monstrous shark in novels and films, such as the 2018 sci-fi thriller "The Meg." In reality, this species is only known from teeth and vertebrae in the fossil record, although it is generally accepted scientifically that the species was indeed quite gigantic, growing to at least 50 feet (15 meters) and possibly as much as 65 feet (20 meters). The new study re-examined published records of geographic occurrences of Megalodon teeth along with their estimated total body lengths. "Our findings suggest a previously unrecognized body size pattern for the fossil shark, notably following a geography-driven ecological pattern known as Bergmann's rule," said Shimada. Introduced by a German biologist Carl Bergmann in the mid-1800s, Bergmann's rule is a broad generalization explaining that larger animals thrive in cooler climates because their size helps them retain heat more efficiently compared to animals with smaller bodies. "Scientists constantly search for rules of life that help us predict natural patterns, and it seems that Bergmann's rule applied to Otodus megalodon," noted coauthor Victor Perez, a paleontologist at the Calvert Marine Museum in Maryland. Some Megalodon sites were previously identified as possible nursery areas of the fossil shark because those sites yield smaller Megalodon teeth on average relative to other Megalodon localities. However, the new study found that the previously identified nursery areas for Megalodon are located near the equator, where water is warmer. "It is still possible that O. megalodon could have utilized nursery areas to raise young sharks. But our study shows that fossil localities consisting of smaller Megalodon teeth may instead be a product of individual sharks attaining smaller overall body sizes simply as a result of warmer water," said coauthor Harry Maisch, a faculty member at Bergen Community College and Fairleigh Dickinson University in New Jersey. "The idea of this new study originated from casual conversation that took place during a recent fishing trip to the Florida Keys by the lead author, his family and me, stemming from a basic question: where do large fish live?" said coauthor Martin Becker, a professor of environmental science at William Paterson University in New Jersey. Despite being initiated by this simple question, "the results of this study have important implications for understanding how modern climate change is rapidly accelerating marine habitat shifts to more polar latitudes in apex predators such as sharks," noted coauthor Michael Griffiths and another professor of environmental science at William Paterson University. "The main conclusion of this study is that not all geographically different Megalodon individuals grew to gigantic sizes equally. The common notion that the species reached 18-20 m TL should be applied primarily to populations that inhabited cooler environments," said Shimada. www.sciencedaily.com/releases/2022/03/220307082337.htm----- Revisiting body size trends and nursery areas of the Neogene megatooth shark, Otodus megalodon (Lamniformes: Otodontidae), reveals Bergmann’s rule possibly enhanced its gigantism in cooler watersABSTRACTThe late Neogene megatooth shark, Otodus megalodon, is known mainly from its gigantic teeth and possibly reached 18–20 m in total length (TL). We re-examine the previously proposed body size trends and nursery areas of O. megalodon by confining the previously used samples to upper anterior teeth offering more reliable TL estimates, and by taking paleolatitudes and sea-surface temperatures into consideration. We demonstrate that individuals of O. megalodon are on average larger in cooler water than those in warmer water – a pattern attributable to Bergmann’s rule showing a latitudinal body size gradient at least for the eastern Pacific late Miocene and the western Atlantic early Pliocene assemblages. While it is still possible that neonatal O. megalodon could have utilised nursery areas, the previously identified paleo-nursery areas based on body size may reflect temperature-dependent trends rather than the inferred reproductive strategy. Thus, the gigantism of O. megalodon in cooler waters was possibly further enhanced by its cooler environment. If so, the corollary of this study is that not all populations of O. megalodon likely grew to gigantic sizes equally, where the common notion that the species reached 18–20 m TL should be applied primarily to populations in cooler environments. Citation: Shimada, K., Maisch IV, H. M., Perez, V. J., Becker, M. A., & Griffiths, M. L. (2022). Revisiting body size trends and nursery areas of the Neogene megatooth shark, Otodus megalodon (Lamniformes: Otodontidae), reveals Bergmann’s rule possibly enhanced its gigantism in cooler waters. Historical Biology, 1-10.www.tandfonline.com/doi/full/10.1080/08912963.2022.2032024
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Post by Infinity Blade on Mar 21, 2022 6:33:50 GMT 5
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Post by Grey on May 23, 2022 12:09:26 GMT 5
southernmarylandchronicle.com/2022/05/20/cmm-hosts-international-lecturer-jack-cooper-for-virtual-talk-on-megalodon/A great diversity of sharks have roamed the oceans for millions of years, performing various ecological roles – most famously as apex predators. Among such past sharks was the biggest shark that ever lived: the 20 m megalodon. Its enormous teeth have become iconic fossils in paleontology, found worldwide, including in Maryland. With no complete skeletons yet known, scientists are forced to use modern sharks and what little they have of the fossilized skeleton to infer this giant’s morphology and ecology. Now, a 2D reconstruction based on living sharks, and a new 3D reconstruction based on an exceptionally preserved vertebral column, have revealed unprecedented new clues about how this shark moved and ate. Are any living sharks appropriate analogs to this giant? How did the diet of whales affect their movement or energy intake? Can we even be sure what it looked like without a complete skeleton? And how does modeling an extinct apex predator help us study shark functional diversity as a whole – in the past, present or future? Jack Cooper is a Ph.D. researcher at Swansea University (Wales, UK) investigating sharks’ functional diversity and ecology through time using the fossil record. Originating from Scotland, Jack received his bachelor’s degree in Evolutionary Biology from the University of St. Andrews and his master’s degree in Paleobiology from the University of Bristol. Despite expanding his horizons to a whole range of Cenozoic sharks for his Ph.D., Jack continues to study the morphology and ecology of megalodon keenly; the biggest shark that ever lived – resulting in his first paper in 2020; and several more in development. This iconic shark is very often the center of Jack’s outreach activities. He has appeared on several podcasts, radio and news interviews, and a documentary promoting this animal’s wide and ongoing research. Additionally, he has also worked in ecotourism and conservation in South Africa, where he has caged dived with great white sharks. Jack is funded by the Fisheries Society of the British Isles and is a member of the Pimiento Research Group, which aims to understand better the extinction mechanisms sharks faced in the past and to use that knowledge to inform conservation efforts for today’s sharks. He is also a cat person.
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Post by Grey on May 26, 2022 3:39:02 GMT 5
Jack Cooper video talk with exclusive information about his future paper about 3D reconstruction of megalodon with data about the belgian column. It's one year old, can't believe I missed it.
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Post by Infinity Blade on Jun 5, 2022 21:05:57 GMT 5
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Post by elosha11 on Jun 14, 2022 21:58:10 GMT 5
On initial reading, I find this paper is somewhat puzzling. On the one hand, the zinc method for determining species' isotopic levels and its place on the food chain is very useful and a positive scientific development. But the researcher's conclusion that great white sharks and Megalodon shared the same trophic level by comparatively similar zinc contents is only supported by comparing adult great white sharks to juvenile or subadult Megalodons, all of which had teeth with crown heights (they used Shimada's method in the absence of associated dentition) with estimated body length of no greater than approximately 7.6 m. This was the largest Megalodon in the sample sizes, other teeth predicted even smaller Megalodons. I believe all of these subadult Megalodon teeth that were used in the zinc comparison were from the east coast of the United States. Those small subadult Megalodon teeth had similar zinc content to the adult great white teeth that were tested from white sharks ranging in size from about 3 to 5.5 m The paper also noted several somewhat larger Megalodon teeth from Japan, with greater crown heights, that were tested. These were by no means gigantic teeth but they had a significantly higher crown height than the East Coast teeth. And quite notably, these larger teeth from presumably larger animals, had a significantly lower zinc content than the East Coast Megalodon teeth or the great white sharks. Lower zinc content means the animal is generally higher on the food chain. The researchers had some thoughts on this. To my knowledge on my first reading, they did not directly acknowledge in their paper that they were using quite small Megalodon specimens, (you had to look at the tables and figures to get that information) but they indirectly addressed it by stating the test teeth samples could be deemed accurate because they believe the specimens they used had reached their fully developed morphology to consume the same prey as any other Megalodon, i.e., ones that were much larger. I would find it somewhat surprising if 5 to 7 m Megalodons were feeding at the same trophic level as a 15+ m full-size adult. I don't think anyone would expect a 2 m great white to be consuming the same type of prey as a 5 m adult, and the evidence today bears that out. They also acknowledged that the larger Japanese teeth yielded lower zinc content, but rather than posit that a reason could be that larger mature sharks are higher on the food chain, they simply speculated that the Japanese teeths' lower zinc content could mean they were consuming a different prey base then those on the East Coast. It must be noted that there were only two Japanese teeth in the sample, just like they were only seven or eight from the East Coast, so any conclusion based on this limited sample must be provided with due caution. I am sure that testing is very expensive and time-consuming, but I will also note that the sample size used is very small. I think about seven or eight Megalodon teeth were tested and about the same number of teeth for Otudus Chubutensis, which were also not all that large, with crown heights yielding nothing more than around 7M for the largest one. They also used samples only from museums I believe, which makes sense because those samples are presumed to be well cared for and undoctored. And I am sure that there is a resistance to using much larger teeth because of not wanting to damage a valuable specimen with invasive testing and sampling. Yet I believe that there may be a glaring issue with using subadult Megalodon teeth, when the limited evidence from Japan suggests that the larger the teeth gets, the higher the animal is on the trophic chain. Those two Japanese teeth from larger specimens had substantially lower zinc content in the tested great white shark teeth. If in fact, larger and adult sharks had substantially lower zinc content than great whites, this would suggest adult Megalodons fed on a higher trophic level than great whites and would significantly undermine - but certainly not completely discredit - the researcher's hypothesis. In general it's a good paper, but I don't like how the researchers somewhat bury the evidence undermining their eye-catching headline. Even if it is true that that full-sized Megalodons fed at a higher trophic level than great white sharks, it does not necessarily mean that great whites had no role in their extinction. Personally, I am very skeptical that great whites acting alone could have had much to do with Megalodon's extinction. But if you combine their presence and other smaller sharks' presence with numerous other contemporaneous environmental and evolutionary factors such as habitat and nursery loss, many whales going extinct and others adapting to migrate to very cold regions for lengthy periods of the year, then possibly great whites, other smaller sharks, and perhaps smaller ceteceans, such as orca ancestors could have had some influence on the Meg's demise if they were better at pursuing the remaining prey base than their much larger cousin, or could outcompete or kill juvenile Megs that may have been vulnerable from loss of nurseries. Until a statistically viable number of adult Megalodon teeth have been tested, I would put a significant caveat by this study. Unfortunately, although the zinc analysis itself seems to have been done rigorously, the authors' ultimate conclusion may have fallen into the correlation proves causation trap. |
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Post by Infinity Blade on Jun 15, 2022 3:40:49 GMT 5
On initial reading, I find this paper is somewhat puzzling. On the one hand, the zinc method for determining species' isotopic levels and its place on the food chain is very useful and a positive scientific development. But the researcher's conclusion that great white sharks and Megalodon shared the same trophic level by comparatively similar zinc contents is only supported by comparing adult great white sharks to juvenile or subadult Megalodons, all of which had teeth with crown heights (they used Shimada's method in the absence of associated dentition) with estimated body length of no greater than approximately 7.6 m. This was the largest Megalodon in the sample sizes, other teeth predicted even smaller Megalodons. I believe all of these subadult Megalodon teeth that were used in the zinc comparison were from the east coast of the United States. Those small subadult Megalodon teeth had similar zinc content to the adult great white teeth that were tested from white sharks ranging in size from about 3 to 5.5 m The paper also noted several somewhat larger Megalodon teeth from Japan, with greater crown heights, that were tested. These were by no means gigantic teeth but they had a significantly higher crown height than the East Coast teeth. And quite notably, these larger teeth from presumably larger animals, had a significantly lower zinc content than the East Coast Megalodon teeth or the great white sharks. Lower zinc content means the animal is generally higher on the food chain. The researchers had some thoughts on this. To my knowledge on my first reading, they did not directly acknowledge in their paper that they were using quite small Megalodon specimens, (you had to look at the tables and figures to get that information) but they indirectly addressed it by stating the test teeth samples could be deemed accurate because they believe the specimens they used had reached their fully developed morphology to consume the same prey as any other Megalodon, i.e., ones that were much larger. I would find it somewhat surprising if 5 to 7 m Megalodons were feeding at the same trophic level as a 15+ m full-size adult. I don't think anyone would expect a 2 m great white to be consuming the same type of prey as a 5 m adult, and the evidence today bears that out. They also acknowledged that the larger Japanese teeth yielded lower zinc content, but rather than posit that a reason could be that larger mature sharks are higher on the food chain, they simply speculated that the Japanese teeths' lower zinc content could mean they were consuming a different prey base then those on the East Coast. It must be noted that there were only two Japanese teeth in the sample, just like they were only seven or eight from the East Coast, so any conclusion based on this limited sample must be provided with due caution. I am sure that testing is very expensive and time-consuming, but I will also note that the sample size used is very small. I think about seven or eight Megalodon teeth were tested and about the same number of teeth for Otudus Chubutensis, which were also not all that large, with crown heights yielding nothing more than around 7M for the largest one. They also used samples only from museums I believe, which makes sense because those samples are presumed to be well cared for and undoctored. And I am sure that there is a resistance to using much larger teeth because of not wanting to damage a valuable specimen with invasive testing and sampling. Yet I believe that there may be a glaring issue with using subadult Megalodon teeth, when the limited evidence from Japan suggests that the larger the teeth gets, the higher the animal is on the trophic chain. Those two Japanese teeth from larger specimens had substantially lower zinc content in the tested great white shark teeth. If in fact, larger and adult sharks had substantially lower zinc content than great whites, this would suggest adult Megalodons fed on a higher trophic level than great whites and would significantly undermine - but certainly not completely discredit - the researcher's hypothesis. In general it's a good paper, but I don't like how the researchers somewhat bury the evidence undermining their eye-catching headline. Even if it is true that that full-sized Megalodons fed at a higher trophic level than great white sharks, it does not necessarily mean that great whites had no role in their extinction. Personally, I am very skeptical that great whites acting alone could have had much to do with Megalodon's extinction. But if you combine their presence and other smaller sharks' presence with numerous other contemporaneous environmental and evolutionary factors such as habitat and nursery loss, many whales going extinct and others adapting to migrate to very cold regions for lengthy periods of the year, then possibly great whites, other smaller sharks, and perhaps smaller ceteceans, such as orca ancestors could have had some influence on the Meg's demise if they were better at pursuing the remaining prey base than their much larger cousin, or could outcompete or kill juvenile Megs that may have been vulnerable from loss of nurseries. Until a statistically viable number of adult Megalodon teeth have been tested, I would put a significant caveat by this study. Unfortunately, although the zinc analysis itself seems to have been done rigorously, the authors' ultimate conclusion may have fallen into the correlation proves causation trap. For the record, I don't actually think this is conclusive evidence for great whites having a role in megalodon's extinction (far from it). I actually asked some of my Twitter followers what they thought, and this is what one said, which I think is a reasonable response. |
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Post by elosha11 on Jun 15, 2022 5:24:28 GMT 5
Yes, I believe the paper has a lot of good scientific value overall, and I'm not blaming the authors entirely for popular media's rather sensationalist headlines, (they have to sell copy first and foremost). However, I think the authors could have been a little bit more forthright about the size parameters of the teeth they were examining, and issued the appropriate caveats based on that. I also really don't understand their rationale that juvenile and subadult Megalodons are assumed to be feeding at the same trophic level as much larger adults.
The headlines took their cue of "great whites drove Megalodon extinct" from the authors' own conclusions as to the great whites' possible role in Megalodon's extinction, which may or may not be correct, and at least for now, should be viewed quite critically.
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Post by Life on Jun 18, 2022 18:48:04 GMT 5
Size provides "competitive advantage." It is absolutely logical to assume that the Megalodon could eat anything it could catch. Paleontologists continue to find and/or identify remains of different animals that were consumed by the Megalodon - big/small/fast/dangerous. www.newscientist.com/article/2279774-sharks-were-almost-wiped-out-in-an-extinction-19-million-years-ago/So what happened 19 million years ago? Nobody knows for sure. It would be better to focus on how water properties affect sharks including their reproduction. I will finalize my review when I have time. |
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Post by Grey on Jun 19, 2022 18:30:33 GMT 5
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Post by elosha11 on Jun 21, 2022 1:00:54 GMT 5
I attended Jack's zoom lecture on June 15th that you told us about. He actually mentioned the Denmark fossils in that lecture in response to a question that I had about studying them, and he also said there that he thought most, if not all of it is gone. He was hoping at least some of the larger ones would still be there. I know it's only one centra, but I wonder if the large one that Hubbell has would be available for study, like his 7.25 in tooth. |
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Post by Grey on Jun 21, 2022 3:19:21 GMT 5
I attended Jack's zoom lecture on June 15th that you told us about. He actually mentioned the Denmark fossils in that lecture in response to a question that I had about studying them, and he also said there that he thought most, if not all of it is gone. He was hoping at least some of the larger ones would still be there. I know it's only one centra, but I wonder if the large one that Hubbell has would be available for study, like his 7.25 in tooth. I wonder if MacFadden and Pimiento have worked on that vertebra.. At least we have a rather good description of the Danish material. If Jack's works are correct, if the Belgian column is definitely 11.1 m, it would mean the Danish original backbone could have been 16.5 m on its own, and a shark at >23 m...which still falls within the upper range of the upper estimate of GHC-6 in our 2021 article as Jack recalled. By the way, the actual highest TL estimate for meg in the recent literature using the SCW method is an individual in Shimada's 2022 paper about Bergmann's rule, calculated at 19.9-21.7 m in the supplementary data. I couldn't watch Jack's lecture given the hour in France, he told me it would be released publication of his article. You may have seen some very interesting informations. I'm interested in exactly how they scaled the column to the white shark skull. |
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Post by elosha11 on Jun 21, 2022 15:52:59 GMT 5
I attended Jack's zoom lecture on June 15th that you told us about. He actually mentioned the Denmark fossils in that lecture in response to a question that I had about studying them, and he also said there that he thought most, if not all of it is gone. He was hoping at least some of the larger ones would still be there. I know it's only one centra, but I wonder if the large one that Hubbell has would be available for study, like his 7.25 in tooth. I wonder if MacFadden and Pimiento have worked on that vertebra.. At least we have a rather good description of the Danish material. If Jack's works are correct, if the Belgian column is definitely 11.1 m, it would mean the Danish original backbone could have been 16.5 m on its own, and a shark at >23 m...which still falls within the upper range of the upper estimate of GHC-6 in our 2021 article as Jack recalled. By the way, the actual highest TL estimate for meg in the recent literature using the SCW method is an individual in Shimada's 2022 paper about Bergmann's rule, calculated at 19.9-21.7 m in the supplementary data. I couldn't watch Jack's lecture given the hour in France, he told me it would be released publication of his article. You may have seen some very interesting informations. I'm interested in exactly how they scaled the column to the white shark skull. I didn't know that about the tooth used in Shimada's 2022 study. Can you point out to me which figure or table that information is located in? Did they use a larger/wider tooth than the Hubbell tooth, and what was its position in the jaw? I also forgot that your 2021 study assumed the Hubbell 7.25 in tooth was a lateral 1 tooth, which is apparently the widest tooth in the shark's jaw. This is an assumption which provides a more conservative overall length. I heard that recently on Perez's lecture on the Calvert Cliffs Museum website, but I'm sure that is also mentioned in the 2021 study. If that tooth is a slightly more narrow anterior tooth, that would mean the shark estimated range would go up as well. Have you shared with Cooper any information or photos about the Peruvian Megalodon skeleton? Despite all of the K.H. sketchiness, the size of those vertebral centra at 26 cm is tantalizing. Also, @life recently posted a video from Chile, which seems to indicate perhaps a Megalodon's remains were found there including an associated dentition. Cooper mention that he may be going to Peru soon to examine some teeth there. I wonder if we should try to help him track down any of these things. |
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Post by elosha11 on Jun 21, 2022 16:16:51 GMT 5
I found that tooth in the supplementary material. What a massive difference between the crown height method and the summed crown height method. The only thing missing in this data is what position the tooth is. Any ideas? I do know that both the Perez method and Shimada's method think that single upper anterior teeth are the best length predictors, assuming absent an associated dentition. The farther back you go in the jaw's tooth positions, the less stable the length predictions.
1 Catalogue number CH CW TL (CH) TL (SCW: Large) TL (SCW: Small) Ma Stage Formation Locality Country Ocean Latitude
13 MNHN CP 62 100.86 128.5 11.93 21.653126435346778 19.881311521471332 7.6-6.8 Messinian Bahia Inglesa ('Unit 5') Mina Fosforita Chile Pacific 27S
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Post by Grey on Jun 21, 2022 22:28:52 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..
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