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Post by creature386 on Nov 5, 2013 1:24:22 GMT 5
It now works, thanks!  PS: Which Compagno formula did you use for the 90,67 t figure in your table? Because I "only" got roughly 72,2 t, using his updated formula (although I could have made a calculation error):  ftp.fao.org/docrep/fao/009/x9293e/x9293e06.pdfThe other one as well yields something in that ballpark. Or do you use another formula I don't know? It would be appreciated if you could give more information about the source than just the name of the author (i.e. date). |
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Post by theropod on Nov 5, 2013 2:58:25 GMT 5
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Post by Grey on Nov 5, 2013 6:42:59 GMT 5
Article posted in the Megalodon thread, relative to the body size increase of megalodon.
Very interesting. Theropod, you can then remark it was better to wait proper research about the size patterns in megalodon instead of our conflictual discussions. As it appears something we had not expected (I think); there were actually bigger individuals in the later periods of its existence. Maximum size and minimum size did not change but larger sharks were more and more numerous, so the average size increased.
Pimiento has studied museums collections from Panama, Santiago, Los Angeles, Washington, Lima, San Diego, Gainesville and Buenos Aires.
Gainesville being Gordon Hubbell's collection... I think the paper will be very interesting. Normally this winter...
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Post by coherentsheaf on Nov 5, 2013 7:50:19 GMT 5
Article posted in the Megalodon thread, relative to the body size increase of megalodon. Very interesting. Theropod, you can then remark it was better to wait proper research about the size patterns in megalodon instead of our conflictual discussions. As it appears something we had not expected (I think); there were actually bigger individuals in the later periods of its existence. Maximum size and minimum size did not change but larger sharks were more and more numerous, so the average size increased. Pimiento has studied museums collections from Panama, Santiago, Los Angeles, Washington, Lima, San Diego, Gainesville and Buenos Aires. Gainesville being Gordon Hubbell's collection... I think the paper will be very interesting. Normally this winter... That is a very interesting result. I hope the paper will be published soon. More big specimen while maximum size did not increase suggest to me that some ecological factors kept them from attaining large sizes. This would be consistent with competition from raptorial sperm whales in the earlier ages as these animals would compete for similar resources. What seems stragne to me is the very large maximum size of the early megs. Why did not every meg grow to such a size? I would love to look at the raw data, I hope it will be included in the paper. |
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Post by Grey on Nov 5, 2013 8:48:50 GMT 5
I also had in mind the fact that a concentration of others large competitors could have an impact, but Miocene seas were extremely rich in terms of sea life and potential preys. Another possible factor, the life expectancy of megalodon during its existence. I think Bruce MacFadden is working on this since years, studying centras from Otodus obliquus to C. meg. On the website of Pimiento, she writes that some scientists suggest meg lived up to 100 years old. Perhaps meg lived older and older with time, hence more frequent in the later range. Now, the skeleton in Peru, ok it's not properly reported, but whatever its exact size, it seems huge, and it is, Hönninger said, 18 millions years old (although I had read 12 millions years old elsewhere). In any case, it's a Miocene finding, and it's certainly not on the lower bound of adult meg size.
As for the ecological factors preventing them to reach larger sizes, they are suggested in McHenry works and in Kent's chapter, relative to the size limitations of any active carnivore and the particular cardiovascular system of sharks. The largest megs (maybe +18 m) were perhaps predominantely scavengers/very opportunistic predators. A similar proposition existed for T. rex, lifestyle changing with size increase. We have to understand how meg is unique in terms of gigantism among active macrophagous top predators, and among macrophagous sharks. The physiological and ecological constraints may have been huge for this species. Bigger is definitely not always better. Meg perhaps ruled the seas like a Robert Baratheon...
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Post by theropod on Nov 5, 2013 23:36:26 GMT 5
@creature: I should check my typing better next time...
Anyway, I've corrected it (see the edited posts), used the updated formula and adding Trikas & McCosker.
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Post by creature386 on Nov 5, 2013 23:58:43 GMT 5
Actually, the other formula (the one in the table) yielded something close to 72 t too, when I used it (I can see your mistake, I just wanted to clarify that the one in the table is OK too).
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Post by theropod on Nov 6, 2013 1:38:02 GMT 5
Yes, I saw what my mistake was too. The updated one should be better still tough.
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Post by theropod on Nov 6, 2013 1:48:41 GMT 5
Greater competition (and, accordingly, death-rates of relatively young individuals) during the Miocene and physiological constraints seem to be a compelling explanation, but I'm looking forward to the more detailed data.
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Post by elosha11 on Nov 6, 2013 4:14:55 GMT 5
I think another plausible factor in the proposed greater incidence of maximum size Megalodons during the Pliocene could be the larger evolving body size of its cetacean prey/scavenging. Large rorquals, bowhead whales, and sperm whales existed in greater numbers during the Pliocene. Perhaps the greater number of larger prey/scavenging items made it both necessary (and possible) for larger number of individuals to obtain great size. Megalodon would have needed to be larger, as a matter of general population, to handle the larger prey items, and concomitantly, the larger prey/scavenging represented greater food volume, which may have assisted more Megalodon obtain great size during the Pliocene.
I am, of course, open to the idea of additional influencing factors, including the lack of competition from large delphnids such as Livyatan, which appears to have died off in the early Pliocene, long before Megalodon. (It also appears that orca ancestors during this time frame were much smaller on average than the orcas of today). Even if these Meg and Livyatan did not compete or battle directly, they would have been targeting very similar food sources, which would have increased the scarcity of those resources. Still, we must keep in mind that Livyatan may have been much less cosmopolitan a species than Megalodon, which would have lessened its impact on the worldwide Megalodon population. Pimiento's study is a fascinating and I'm looking forward to studying the complete results. The more we know, the more questions that arise.
Grey, any idea when Dr. Bretton Kent's pending Megalodon chapter will be published, along with the rest of his book?
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Post by Grey on Nov 6, 2013 4:26:02 GMT 5
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Post by Life on Nov 21, 2013 15:28:05 GMT 5
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Post by Grey on Nov 21, 2013 22:39:52 GMT 5
Thanks bro, I had posted it a few pages earlier with a short discussion about. It's amazing to imagine this ancient 10 millions years old lagoon full of megalodons, from 3 m pups to the occasionnal 17-18 m adults weighing as much as a railroad car. Check this Nat Geo doc "Clash of the Americas" (check the shockshare link), about the impact of the two continents and the consequences on animal life, the last part is about Pimiento's works in the Gatun Formation. www.alluc.to/documentaries/watch-national-geographic-clash-of-the-americas-2011-online/370551.html |
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Post by Grey on Dec 13, 2013 7:09:46 GMT 5
The preliminary work presented by Balk and Pimiento about the relationship between megalodon body size and cetaceans body size change over time. She asked me to remember they are collecting more datas so the results are ever-changing.  I've to admit I don't understand what the body mass values indicate exactly. |
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Post by coherentsheaf on Dec 13, 2013 8:12:43 GMT 5
The preliminary work presented by Balk and Pimiento about the relationship between megalodon body size and cetaceans body size change over time. She asked me to remember they are collecting more datas so the results are ever-changing. I've to admit I don't understand what the body mass values indicate exactly. From the graph in figure 3B we can see that Megalodon maximum size varies through the ages. The largest maximum sizes are around 55 tonnes (in 12, 10 and 4 myo rocks) and the lowest are about 10-12 tonnes (In 7 and 14 myo rocks). The variation in maximum size follows no clear trend, with large bodied populations and small bodied populations in old and newer oceans. In figure 3A we have cetaceans with increasing body sizes through time from 2 tonnes to about 45 tonnes in the end. From figure 2 we can see the median sizes of the Megs (We can see more but I will just type out the median sizes as they appear in the plot): 4myo ago: 12600kg 5myo ago: 1800kg 7myo ago: 10 000kg 8myo ago: 18 000kg 9myo ago: 18 000kg 10myo ago: 4000kg 12myo ago: 10 000kg 13myo ago: 22 000kg 14myo ago: 1000kg Note that these are just the numbers I eyeballed from the graph. They are not the exact estimates of the researches but the error should be within about 10% up or down. |
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