Post by Grey on Feb 15, 2013 8:22:32 GMT 5
A subject vastly discussed about what is "perhaps the largest marine predator the Earth has ever seen" (Kent 2013), "the mother of all predators" (Siversson 2011), "arguably the most formidable carnivore that ever lived" (Gottfried, Purdy 1996) or "probably the apex predator of all time" (Ciampaglio 2012)..
No stupid fanboy attitude or so here, but the reasonnable explanation of the numerous passionnated (and often conflictual) discussions made about this great extinct beast (the same applied to any spectacular and often near-mythical ancients animals, especially large theropods, giants sauropods and pliosaurs...).
Differents experts, differents methods, differents results but some consensus.
The consensus is that C. megalodon reached lengths in excess of 16 meters at adult stage :
And confidently, as we're going to see, almost all authors agree it reached the 18 meters mark.
Let's take a look at the different authors and opinions.
Gottfried and Compagno established their method based on complete upper anterior tooth length in 96.
The largest tooth they owned was a 168 mm specimen.
Using their Extrapolation of Megatooth Total Length From Regression of White Shark Tooth Height Versus Body Size.
Based on a sample of 73 white sharks, the assumed closest analogue to megalodon, they resulted in a conservative total length of 15,90 m. This is probably the most reported and used method/figure in many basic information articles. Then, conservatively, the same method applied to the largest reported tooth (Bertucci) yeilds a maximum conservative estimate something a bit over 18 m.
Using Direct Sizing of Megatooth Sharks from White Shark Teeth.
On the basis of two larger females great white (6,40 m; 7,20 m (?) with both 59 mm UA teeth) and using the 168 mm upper anterior in their possession, they resulted in respectively 18,20 m and 20,20 m (?) TL for a very large megalodon.
Now, if we use a larger confirmed upper anterior tooth than the one they owned, we get larger sizes. Using Hubbell's tooth (185 mm) we get respectively 20,06 m and 22,26 m (?).
Hubbell's tooth :
Of course, using the largest reported tooth, like the one of Hubbell found too by Vito Bertucci (194 mm), we get respectively 21,04 m and 23,34 m (?).
Shimada proposed a complexe method based on crown height and specific at it allows to estimate the size of the shark based on any tooth in the dentition. I would admit I didn't get clearly how to use this method and I'd like to have the explanations of member coherentsheaf for it.
Anyway, Shimada has predicted, based on the same UA used by Gottfried (168 mm total length, 125 mm crown height) a shark estimated at 14-16 m.
As usually we don't have the measurement of the crown alone in the reports of large teeth, it is difficult to try other predictions based on larger specimens.
However, what is interesting is that this is not necessary a large UA which predicts a large shark.
Pimiento et al. in 2010, used Shimada's method and found in the Gatun nursery a sample a teeth belonging to four megalodons considered in their adult stage. One of the teeth, a small posterior, yeilded in a shark estimated at 16,8 m TL.
What I personnally think about this :
- in a sample of four adults found in a nursery, a place where it is uncommon to found large sharks, an approx. 17 m TL adult has been hinted, using a method more conservative than the others.
- the fact a small and at the first look non impressive tooth yeilds with this method in a large shark, by conservative standards, allows to think about what sizes the vastly others numerous lateral and posterior teeth (not used most of the time to calculate the size of a shark) could be suggested if we had the opportunity to test them with the method of Shimada.
However, these methods have several problems.
At first, crown or total, the teeth are not necessary larger when the shark gets larger and vice versa.
A 17 m megalodon could very well have teeth the same size or smaller than in a 15 m megalodon.
The other problem is that megalodon is actually more and more likely not a direct relative of the white shark, and thus, the white shark is perhaps not an absolute excellent model to work with.
Thus, others authors (Mikael Siversson, David Ward, Dana Ehret, Gordon Hubbell) seem to favor the tooth width method proposed by Cliff Jeremiah, though not properly published.
Seemingly, this method seems to work well with all the predatory lamniforms sharks, including the white shark. As the megalodon was primarily a lamniform shark, and finally probably not a direct relative of the white shark, this method is perhaps, in my modest opinion, the best to use.
Tooth width determine jaws size which in turns is directly related, in all lamniforms, to body size.
David Ward :
The quadrant of the jaws (midpoint to side) is about 1/10 of the total length. This would make a full grown Meg at least 60 feet long.
Renz 2002.
Mikael Siversson :
I estimate total length in lamniform sharks based on the total tooth width in the upper jaw (i.e., the combined width of all functional teeth). This gives you a good estimate of jaw size and can then be used to get a rough idea of the total length. Needless to say it works best on species know by associated dentitions (Gordon Hubbell has a seemingly complete associated C. megalodon dentition from Florida). This Florida specimen can then be used as a template for larger isolated teeth (as long as one assumes that the isolated tooth represent the largest tooth in the dentition, which produces a conservative estimate of TL). Based on tooth widths I got a figure close to 20 metres.
Thus, if we want predict the potential maximum size a megalodon could achieve, we have to determine the maximum width known.
Here we have some problems : width is less often reported than slant height of crown height and some very large teeth are not necessary very wide whereas smaller teeth can be very wide.
Anyway, Hubbell's tooth is 13,7 cm wide and gives a megalodon of a TL about 61,25 feet, 18,66 m long.
In all certainity, wider teeth exist. I don't know the width of the larger tooth reported by Bertucci, but MantisShrimp suggested possibly something like 14,2-15,2 cm wide.
Using this, we get 63,9 feet or 19,50 m TLand 68,4 feet, 20,84 m TL.
I've found another pic of an UA chilean tooth, broken in half by geological pressures, not pathologic, which is reportedly around 15 cm in slant height but in width, even excluding the space of the broken part, was exceeding 15 cm as well.
So if true, absolutely colossal predatory animals.
Notice. I'd like to know the measurements and especially width of this particular specimen :
Bretton Kent however, though earlier agreed that the larger megs reached or exceeded a bit 20 m TL, has revised his approach and thinks that there is no conclusive evidence that megalodon reached 18 m, though he's pretty certain the largest megalodons very likely reached this size. (Kent 2013, personnal communication).
But he thinks that given of the physiological constrainsts in sharks, the very large megalodons would have been thus primarily scavengers, because far too massive to get fast and elusive preys items, but able to scare off any other predator in the sea from their, reminding a similar proposition regarding the life history in T. rex.
However, others experts respectfully disagree with him as there is nothing as obligatory, gigantics marine scavengers known at any time, and in addition we cannot know the specific adaptions a uniquely sized predatory shark could have achieved.
Chuck Ciampaglio told me that if the bull shark was a fossil species, we couldn't predict its freshwater lifestyle.
He and Mike Siversson did the same analogy with giraffes and gigantics sauropods, which possessed gigantic necks that by our knowledge in biology we could speculate to be impossible to exist. But they exist.
In summary, megalodon was certainly very very large and a size mark of 18 m is already pretty certain. Higher sizes are quite possible or likely depending the methodology you favor.
Personnally, I don't see any reason to not favor the tooth height, though, all the methods are presumably valuable at one given time.
Ciampaglio suggested me that crown or tooth lenght were perhaps usefull at one life stage but once the shark became larger, tooth width was more adapted.
A few words about the weight.
So far, the only rigorous prediction made for the megatooth shark body mass is from Gottfried et al.
It seems that no other authors rejects it, as there is nothing better made at now and it is highly worked stuff, and though they perceived some issues :
-the method is based on the white sharks, but the white sharks often get fat when growing at large sizes. Was megalodon fat ?
- the white shark is maybe not the best model. Using a mako we get slightly lower predictions than Gottfried's predictions. Using a porbeagle, we get something quite heavier than a white shark as model (92 tons for a 18 m meg).
-often, larger animals are lighter than what would have been predicted from a smaller individual (seen among whales).
-two similar-sized sharks of the same species can have a body eight vastly varying, up to 50 %, and depending numerous factors (quantity of food in stomach, size of the liver, fat, gender...)
Anyway, I think the statement of Gottfried fits well in this fantastic creature : "a shark weighing as much as 7 or 8 Tyrannosaurus rex dinosaurs".
Something we can notice as well, is that though megalodon size has been heavily discussed, another major problem is that authors don't have all the time access to all the available, and possible, the most interesting and revelant specimens for experiment their methods and predictions (cf : Gottfried and Shimada using the same specimen in their 7 years separated works). Many teeth specimens are under private collections, and all the measurements are not all the time reported, and if so, not always correct or reliable. This is the very irritating part around.
Megalodon is almost more a property of privates all around the world than actual researchers, though some famous privates work with scientists, and actually become themselves experts (Hubbell).
I hope all of this summarizes well the whole problematic, though I might have forgotten some details and points.
Awaiting your comments and queries.
No stupid fanboy attitude or so here, but the reasonnable explanation of the numerous passionnated (and often conflictual) discussions made about this great extinct beast (the same applied to any spectacular and often near-mythical ancients animals, especially large theropods, giants sauropods and pliosaurs...).
Differents experts, differents methods, differents results but some consensus.
The consensus is that C. megalodon reached lengths in excess of 16 meters at adult stage :
And confidently, as we're going to see, almost all authors agree it reached the 18 meters mark.
Let's take a look at the different authors and opinions.
Gottfried and Compagno established their method based on complete upper anterior tooth length in 96.
The largest tooth they owned was a 168 mm specimen.
Using their Extrapolation of Megatooth Total Length From Regression of White Shark Tooth Height Versus Body Size.
Based on a sample of 73 white sharks, the assumed closest analogue to megalodon, they resulted in a conservative total length of 15,90 m. This is probably the most reported and used method/figure in many basic information articles. Then, conservatively, the same method applied to the largest reported tooth (Bertucci) yeilds a maximum conservative estimate something a bit over 18 m.
Using Direct Sizing of Megatooth Sharks from White Shark Teeth.
On the basis of two larger females great white (6,40 m; 7,20 m (?) with both 59 mm UA teeth) and using the 168 mm upper anterior in their possession, they resulted in respectively 18,20 m and 20,20 m (?) TL for a very large megalodon.
Now, if we use a larger confirmed upper anterior tooth than the one they owned, we get larger sizes. Using Hubbell's tooth (185 mm) we get respectively 20,06 m and 22,26 m (?).
Hubbell's tooth :
Of course, using the largest reported tooth, like the one of Hubbell found too by Vito Bertucci (194 mm), we get respectively 21,04 m and 23,34 m (?).
Shimada proposed a complexe method based on crown height and specific at it allows to estimate the size of the shark based on any tooth in the dentition. I would admit I didn't get clearly how to use this method and I'd like to have the explanations of member coherentsheaf for it.
Anyway, Shimada has predicted, based on the same UA used by Gottfried (168 mm total length, 125 mm crown height) a shark estimated at 14-16 m.
As usually we don't have the measurement of the crown alone in the reports of large teeth, it is difficult to try other predictions based on larger specimens.
However, what is interesting is that this is not necessary a large UA which predicts a large shark.
Pimiento et al. in 2010, used Shimada's method and found in the Gatun nursery a sample a teeth belonging to four megalodons considered in their adult stage. One of the teeth, a small posterior, yeilded in a shark estimated at 16,8 m TL.
What I personnally think about this :
- in a sample of four adults found in a nursery, a place where it is uncommon to found large sharks, an approx. 17 m TL adult has been hinted, using a method more conservative than the others.
- the fact a small and at the first look non impressive tooth yeilds with this method in a large shark, by conservative standards, allows to think about what sizes the vastly others numerous lateral and posterior teeth (not used most of the time to calculate the size of a shark) could be suggested if we had the opportunity to test them with the method of Shimada.
However, these methods have several problems.
At first, crown or total, the teeth are not necessary larger when the shark gets larger and vice versa.
A 17 m megalodon could very well have teeth the same size or smaller than in a 15 m megalodon.
The other problem is that megalodon is actually more and more likely not a direct relative of the white shark, and thus, the white shark is perhaps not an absolute excellent model to work with.
Thus, others authors (Mikael Siversson, David Ward, Dana Ehret, Gordon Hubbell) seem to favor the tooth width method proposed by Cliff Jeremiah, though not properly published.
Seemingly, this method seems to work well with all the predatory lamniforms sharks, including the white shark. As the megalodon was primarily a lamniform shark, and finally probably not a direct relative of the white shark, this method is perhaps, in my modest opinion, the best to use.
Tooth width determine jaws size which in turns is directly related, in all lamniforms, to body size.
David Ward :
The quadrant of the jaws (midpoint to side) is about 1/10 of the total length. This would make a full grown Meg at least 60 feet long.
Renz 2002.
Mikael Siversson :
I estimate total length in lamniform sharks based on the total tooth width in the upper jaw (i.e., the combined width of all functional teeth). This gives you a good estimate of jaw size and can then be used to get a rough idea of the total length. Needless to say it works best on species know by associated dentitions (Gordon Hubbell has a seemingly complete associated C. megalodon dentition from Florida). This Florida specimen can then be used as a template for larger isolated teeth (as long as one assumes that the isolated tooth represent the largest tooth in the dentition, which produces a conservative estimate of TL). Based on tooth widths I got a figure close to 20 metres.
Thus, if we want predict the potential maximum size a megalodon could achieve, we have to determine the maximum width known.
Here we have some problems : width is less often reported than slant height of crown height and some very large teeth are not necessary very wide whereas smaller teeth can be very wide.
Anyway, Hubbell's tooth is 13,7 cm wide and gives a megalodon of a TL about 61,25 feet, 18,66 m long.
In all certainity, wider teeth exist. I don't know the width of the larger tooth reported by Bertucci, but MantisShrimp suggested possibly something like 14,2-15,2 cm wide.
Using this, we get 63,9 feet or 19,50 m TLand 68,4 feet, 20,84 m TL.
I've found another pic of an UA chilean tooth, broken in half by geological pressures, not pathologic, which is reportedly around 15 cm in slant height but in width, even excluding the space of the broken part, was exceeding 15 cm as well.
So if true, absolutely colossal predatory animals.
Notice. I'd like to know the measurements and especially width of this particular specimen :
Bretton Kent however, though earlier agreed that the larger megs reached or exceeded a bit 20 m TL, has revised his approach and thinks that there is no conclusive evidence that megalodon reached 18 m, though he's pretty certain the largest megalodons very likely reached this size. (Kent 2013, personnal communication).
But he thinks that given of the physiological constrainsts in sharks, the very large megalodons would have been thus primarily scavengers, because far too massive to get fast and elusive preys items, but able to scare off any other predator in the sea from their, reminding a similar proposition regarding the life history in T. rex.
However, others experts respectfully disagree with him as there is nothing as obligatory, gigantics marine scavengers known at any time, and in addition we cannot know the specific adaptions a uniquely sized predatory shark could have achieved.
Chuck Ciampaglio told me that if the bull shark was a fossil species, we couldn't predict its freshwater lifestyle.
He and Mike Siversson did the same analogy with giraffes and gigantics sauropods, which possessed gigantic necks that by our knowledge in biology we could speculate to be impossible to exist. But they exist.
In summary, megalodon was certainly very very large and a size mark of 18 m is already pretty certain. Higher sizes are quite possible or likely depending the methodology you favor.
Personnally, I don't see any reason to not favor the tooth height, though, all the methods are presumably valuable at one given time.
Ciampaglio suggested me that crown or tooth lenght were perhaps usefull at one life stage but once the shark became larger, tooth width was more adapted.
A few words about the weight.
So far, the only rigorous prediction made for the megatooth shark body mass is from Gottfried et al.
It seems that no other authors rejects it, as there is nothing better made at now and it is highly worked stuff, and though they perceived some issues :
-the method is based on the white sharks, but the white sharks often get fat when growing at large sizes. Was megalodon fat ?
- the white shark is maybe not the best model. Using a mako we get slightly lower predictions than Gottfried's predictions. Using a porbeagle, we get something quite heavier than a white shark as model (92 tons for a 18 m meg).
-often, larger animals are lighter than what would have been predicted from a smaller individual (seen among whales).
-two similar-sized sharks of the same species can have a body eight vastly varying, up to 50 %, and depending numerous factors (quantity of food in stomach, size of the liver, fat, gender...)
Anyway, I think the statement of Gottfried fits well in this fantastic creature : "a shark weighing as much as 7 or 8 Tyrannosaurus rex dinosaurs".
Something we can notice as well, is that though megalodon size has been heavily discussed, another major problem is that authors don't have all the time access to all the available, and possible, the most interesting and revelant specimens for experiment their methods and predictions (cf : Gottfried and Shimada using the same specimen in their 7 years separated works). Many teeth specimens are under private collections, and all the measurements are not all the time reported, and if so, not always correct or reliable. This is the very irritating part around.
Megalodon is almost more a property of privates all around the world than actual researchers, though some famous privates work with scientists, and actually become themselves experts (Hubbell).
I hope all of this summarizes well the whole problematic, though I might have forgotten some details and points.
Awaiting your comments and queries.
