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Post by elosha11 on Jul 7, 2016 21:09:32 GMT 5
^Yes, Grey already pointed out it was in centimeters and I acknowledged my mistake. I simply didn't notice the tape measure was in centimeters before. So really it's not a very large tooth at all.
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Post by theropod on Jul 8, 2016 14:42:17 GMT 5
Sorry, I missed that.
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Post by Grey on Jul 12, 2016 22:56:00 GMT 5
A poster of the study will be submitted at the GSA of Denver in September, I'm co-author. I don't know yet the preliminary results but they've made a number of GWS dentitions measurements at Hubbell's private Museum.
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Post by elosha11 on Jul 14, 2016 11:28:20 GMT 5
elosha11Great to hear from you, I'm of course curious about the investigations of your contact. However, the rule in the first picture is in metrics. It looks more like a 7cm wide tooth, I don't think Argentines use inches. I can't see the pictures in your second post. Anyway I've done a quick research about this Museum and found this; if what the ruler in this picture is accurate, this is amazing :  www.anbariloche.com.ar/noticias/12/06/2016/53494-el-tiburon-mas-grande-que-existio-el-megalodonThis reminds me of the French paleontologist who told me to have observed a 22cm tooth in a Museum in Angers, long ago... Before going enthusiastic, contacting the Museum is needed, I had contacted several Chilean and Peruvian Museums while investigating about Livyatan teeth. I've often been disappointed by the "fish stories" about giant Megs, pliosaurs or Livyatan teeth before. But 23cm for the ruler seems quite precise. I note their reproduction of the Meg jaws is massive and sounds quite rigorously built although the teeth are reproductions.  Some news, the study about Megalodon size based on dentition size is now involving Dr. M. Siversson as well. The team is progressing. I've received confirmation from the reporter who wrote this article that the 23 centimeter Argentinian tooth above is only a man-made model and is not based off any specific tooth. It's instead just trying to provide a theoretical maximum size based on teeth that may or may not exist. Disappointing and the article really should have stated specifically that it was only a model. The reporter did state that the jaws in Museum are partially based on a 17 centimeter tooth that the Museum has been seen and measured. |
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Post by Grey on Jul 14, 2016 11:56:27 GMT 5
Yes I got the same response from the Museum and they showed me the measurement of their largest tooth casted in the jaws.
Anyway, the tooth was more about 21cm and if what I suspect is true, anything larger than that would suggest truly absurd sizes...
I have the abstract of the study, I'll post it when the book is out.
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Post by coherentsheaf on Jul 14, 2016 12:34:04 GMT 5
So that likely puts the largest Megalodon on the order of magnitude of 100 000kg give or take? That is very interesting in the sense that there are no other predators anywhere close to that size. Why is it different? I have a few ad hoc hypothesis:
-We have much larger sample sizes for Megalodon than for other giant predators due to the abundand teeth, which make it more likely that very large individuals are preserved. However even the much rarer vertebrae suggest sizes as large or larger than known from other taxa.
-Megalodon directly preyed on filter feeders, skipping steps in the food net, so it had a larger pie available, which could be a factor. Where the large filter feeders like Pachycormids free of similar predators?
-It could be a case of runaway arms race- whales got larger forcing Megalodon to get larger, however the data we have fail to support a clear trend if I recall correctly.
-There were some physiological constraints on other predators which were ahrd to overcome. Here however it is significant that filter feeding sharks do not seem particularly large compared to other giant filter feeders.
What are your thoughts on this?
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Post by creature386 on Jul 14, 2016 15:10:14 GMT 5
I'd prefer the hypothesis one, as it seems to have the least unnecessary extra assumptions. The vertebrae problem probably refers to the 18-19 m Megalodon skeleton, doesn't it? Well, given that it is only one skeleton (where an extreme average is more easy to get) and the fact that we can make some statistics about Megalodon's size (and the skeleton deviates from any average), it is quite reasonable to assume that it's an extreme case. Perhaps large vertebrae survive easier than smaller ones?
Maybe these are unnecessary extra assumptions as well, but all other explanations also need to account for why the size of the skeleton differs so significantly from the average tooth-based size.
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Post by Grey on Jul 14, 2016 15:46:54 GMT 5
I wouldn't say that Meg reached 100 tonnes for certain but that's theoretically possible once the species reached 20m or more, which seems more and more likely (although we never know, the study and data are not prepared yet). I know that Mike Siversson rather thinks that the absence of gigantic vertebra (30-35cm) would suggest that Meg was slightly less heavily built than a white shark. But I rather think that the absence of such large centra is more due to sampling bias, since even the large teeth are relatively rare despite being shed constantly by the shark. But even if it reached 20m with a somewhat lighter build than a similar-sized white shark, a 60-70 tonnes macro-predator would be rather unheard of in the fossil record, the very only potential exception being the poorly known raptorial sperm whales. My thoughts of this : - of course there is a sampling of large teeth from Meg far larger than other macropredators. However, for discussing it various times with collectors and scientists (Kent and Godfrey)it is unlikely we have found the biggest tooth from the biggest Megalodon ever neither. - a recent paper I've read about the Mio-Pliocene mysticetes seems to confirm than almost all, if not all, were significantly smaller than Meg (and Livyatan) and that really gigantic mysticetes only occured after Meg's extinction : rsbl.royalsocietypublishing.org/content/12/7/20160186- Meg and the gigantic raptorial sperm whales are the largest marine macropredators known in the fossil record, this is very certainly due to the massive radiation of cetacean taxa in the Early Miocene. - Kent gave a possible explanation about why Meg would/could have grown so large, a giant cartilaginous skeleton would be cheaper to build than a bony skeleton. Farlow also suggested than the slightly lower metabolism of the shark would have allowed it to grow larger for the same amount of food source than its competing odontocetes. - Regarding the pachycormids, McHenry said me that a 10m pliosaur was armed enough to take on a fish twice its mass so they may have been subject to predation, at least in their early times of life. Evidence of failed predation by a pliosaur exists on one specimen. -of course, there is always the implication that the very largest Megs were more opportunustic scavengers than the smaller ones. Maybe the much more cetaceans filled Miocene seas had far more potential carcasses to feed these giants. |
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Post by coherentsheaf on Jul 14, 2016 23:21:03 GMT 5
Hm the pliosaurs can take pachycormid twice its size claim... Really? How would they kill it efficiently? Crocs sometimes manage to kill similar sized animals (mostly by drowning) but it is quite some effort for them. I dont think that pliosaurs with the kind of jaws present in the largest species so far would easily prey on giant pachycormids.
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Post by elosha11 on Jul 14, 2016 23:52:22 GMT 5
Regarding one point Grey made. I agree that Megalodon and Livyatan most likely primarily fed on whales significantly smaller than them. I also agree that such smaller cetaceans were the predominant prey/scavenging for both predators throughout their entire existence. But -- at least for Megalodon, we have evidence of bone damage on a huge vertebrate of what looks like a sperm whale. Also an old NG documentary showed bite marks on what they described as a bowhead whale flipper, which they estimated to be at least 40 feet long. If those prehistoric bowheads were like present day ones, it would be extremely robust at 40 feet long. So there is some evidence that Megalodon fed on some very large species as well as the much smaller and more plentiful cetotheriids.
EDIT - There's also the possible attack by perhaps a juvenile Meg leaving bite marks on what may be the ribs of a pretty large rorqual. We know the whale was living at the time of the bite because the bone showed signs of healing. Of course, there's a lot of " may be's" in that example.
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Post by jhg on Jul 15, 2016 2:07:02 GMT 5
I always thought of 16 metres and 50 tonnes.
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Post by elosha11 on Jul 15, 2016 2:18:49 GMT 5
I always thought of 16 metres and 50 tonnes. That would be a very conservative maximum size. There's quite a bit of evidence suggesting a maximum of 18 to 20 meters. The current consensus seems to be about 18 meters, but there's evidence - both published and unpublished - suggesting even larger sizes. Weight is even harder to determine but 50 tons max weight is probably an underestimate, whereas 100 tons is really pushing it on the upper end. Hard to really predict unless we somehow get a full adult skeleton with associated teeth. Believe it or not, such a skeleton may actually exist in Peru, but for various political and other reasons, it is not accessible at the present time. |
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Post by Grey on Jul 15, 2016 7:15:17 GMT 5
I always thought of 16 metres and 50 tonnes. This is the maximum conservative size suggested by Gottfried et al. At the same time they suggested potential size up to 20m. Current research may suggest upper sizes avove 18m. Which is, I understand, hard to believe for a predatory shark. |
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Post by Supercommunist on Jul 15, 2016 14:15:23 GMT 5
Hm the pliosaurs can take pachycormid twice its size claim... Really? How would they kill it efficiently? Crocs sometimes manage to kill similar sized animals (mostly by drowning) but it is quite some effort for them. I dont think that pliosaurs with the kind of jaws present in the largest species so far would easily prey on giant pachycormids. For what its worth, theroc has posted an image of a young gracile alligator preying on a similar sized bass.  |
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Post by neogeneseamonster on Jul 15, 2016 18:23:31 GMT 5
Hm the pliosaurs can take pachycormid twice its size claim... Really? How would they kill it efficiently? Crocs sometimes manage to kill similar sized animals (mostly by drowning) but it is quite some effort for them. I dont think that pliosaurs with the kind of jaws present in the largest species so far would easily prey on giant pachycormids. For what its worth, theroc has posted an image of a young gracile alligator preying on a similar sized bass. Did the alligator actually killed and ate the bass? (I'm just curious because I've seen some footages similar to this one but not actual killing) |
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