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Post by creature386 on Mar 6, 2014 2:52:24 GMT 5
Your estimates are very similar to what I assumed based on the whale shark (in fact, the difference is mostly smaller than a ton). I think I already said this once about a previous calculation you have done (I lose the overview!). Whatever, I think your estimates are pretty realistic.
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Post by Grey on Mar 6, 2014 2:56:08 GMT 5
Anyway, Lamna is not a good proxy, not related to meg and even smaller than the mako.
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Post by Life on Mar 6, 2014 12:12:02 GMT 5
The robusticity of teeth is not related to the robusticity of the whole animal. Sharks with very robust teeth can be relatively slender-bodied and vice versa. that’s a matter of tooth function and perhaps of size-related necessities, not of overall built. Root thickness is indicative of robustness of chondrocranium itself. Robustness in chondrocranium have correlation with jaw power as well. This is the equation: Robust chondocranium -> Great jaw power -> Thick roots of teeth --- Now, it makes morphological sense for a robust chondocranium to be supported by equally robust body structure. Their might be some evolutionary exceptions but megatoothed sharks do not appear to be among them unless we are assuming bulldog morphology for them which doesn't makes sense. This image is self-explanatory:  Notice enormous ontogenetic differences? These developments aren't superficial. Now, even if you consider GWS, its teeth have thick roots (not as thick as in megatoothed sharks but thick by shark standards nonetheless) Even a juvenile GWS have prominent root structure: www.paleodirect.com/pgset2/sh21-014.htmNow look at this comparison:  Tell me, which shark have most robust morphology (on the whole) in life among these? GWS, right? By the same token, Megalodon may have exceeded robustness of GWS even during early stage of its growth process (juvenile stage). At adulthood, Megalodon may have been like juggernauts (extremely strong and massive). Therefore, this is not a superficial assessment: Robust body structure -> Robust chondocranium -> Great jaw power -> Thick roots of teeth Correlation can be realistically expected in all of these physiological facets, specially in megatoothed sharks. GWS itself verifies this. Otodus and Parotodus have a peculiar tooth morphology for a shark, that’s why their roots also have a peculiar morphology. the Carcharocles lineage derived from these sharks as far as we know, so no wonder they retained some of their features (teeth very thick compared to lamnids), although their morphology became more analogous to Carcharodon. See above. @life you were the one to argue C. megalodon has proportionally longer centra (and that is easily visible in the pictures you posted, although papers so far do not seem note this difference, perhaps indicating this is a result of the position of the vert). If its centra are longer, that makes its vertebrae less robust at lenght parity (and, at least if its vertebral count was higher, its whole vertebral collumn), and lenght parity is what we are talking about since the body mass is estimated from total lenght and total lenght is closely related to the lenght of its vertebral collumn. A more elongate vertebral collumn is not an argument in favour of a more bulky body. Not all vertebra are expected to be elongated in Megalodon, some are and some would not be (depends upon the position). Now, I am not sure why higher count would imply slenderness. Ginsu shark also had 200+ count and it wasn't a slender shark:  Higher count presents the possibility of more liberal tooth length (TL) to body length (BL) dynamics in Megalodon in comparison to such dynamics in GWS, it may also have performance related significance for Megalodon since it became much larger then GWS. However, higher count doesn't necessarily implies small jaw structure in comparison to BL due to following reasons: 1. Megalodon dentition does not gives the vibe of compactness in its jaw structure like in GWS. Megalodon have A3 in its jaw structure in position of I in GWS, A3 in Megalodon is massive unlike I in GWS which is indicative of beginning of bending curvature in jaw structure of GWS. Megalodon most likely had broader and bigger jaw structure at parity, A3 and posterior teeth of Megalodon suggest this. Check this comparsion: Perhaps this can help ?  It is very telling. 2. Higher vertebral count in Megalodon can also be indicative of gigantic caudal fins for this shark. Makes sense for Megalodon to have very big caudal fins to maintain high performance at gigantic sizes. In the nutshell: 1. Strong possibility of relatively larger caudal fins 2. Strong possibility of relatively larger jaw structure Perfect. It is unwise to just upscale GWS to Megalodon proportions and draw inferences about the latter shark from this approach. Evolutionary processes are not so simple, GWS doesn't ticks all physiological adaptations in checklist of Megalodon. If its total lenght was greater relative to its jaw apparatus, that also does not imply greater bulk at the same lenght. Unless you are envisioning it as having undersized jaws for its body size, which is complete speculation and not consistent with its presumed lifestyle as a macrophagous predator. As predatory lineages grow bigger, their weaponery almost always displays hypermorphosis, not the opposite. The dentition lenght in C. carcharias relative to body lenght also does not show negative, but slight positive allometry, so why should C. megalodon follow the exact opposite trend (Why should it then have a large, sharp, raptorial dentition)? See above. I cannot see how there are any Otodus or Carcharocles remains providing evidence that these animals had considerably more robust body shape. The best there is to conclude about it are vertebrae, and those are actually more elongate. Both a greater bulkiness and a greater total lenght than predicted at once are not compatible with reasonable assumptions about anatomy. It is possible C. megalodon had a greater total lenght, if, for example, it had an enlarged caudal lobe like Alopias, or simply a more elongated body (or proportionally longer tail). It is also possible it’s built was stockier, if it was shorter and/or had proportionally bigger jaws. But both are speculation without evidence. Covered above, there are differences in biological adaptations and characteristics of Megalodon and GWS. Gottfried et al. assume a very bulky, but also a relatively short animal. Someone envisioning a 30m Megalodon would envision an animal with a thresher-shark like tail, but not considerably heavier than a 20m shark with normal proportions. Gottfried et al (1996) have assumed no such thing.  Robustness is not strongly correlated with BL in sharks, this image is self-explanatory. Artistic reproductions remain artistic reproductions. Dimitry Bodganov has made hundreds of them, focusing on synapsids. He certainly has not conducted extensive studies on each of them, and surely he has not observed subtle evidence for O.obliquus being particularly robust, that was not noted in any publication. That being said the Otodus in the picture also does not put a Great white to shame in terms of its robusticity. I’m not talking size here, but how stocky it was. Obviously if you compare two vertebrae that are different in size the bigger one will be more massive, that does not mean it is also more robust when scaled at the same lenght. It doesn't?   Using the size trends observed in great whites is good enough for now. But it is not realistic for now that C. megalodon was much bulkier than any extant lamnid (lamnids themselves being very bulky animals), nor that it was much longer than suggested by its jaw size. I would encourage research in other lamniforms to see whether there is a better analogy than Carcharodon. As long as we don’t have one, there is no point in speculating about it. Simply up-scaling GWS to Megalodon proportions and drawing inferences about the latter shark in this manner may be a sound approach from quantitative perspective but not from qualitative perspective. Fossil evidence reveals differences in biological characteristics of both animals, an issue which is not covered in quantitative assessments. This is why I stressed on the importance of both quantitative and qualitative perspectives to draw inferences for Megalodon several pages back to achieve better understanding of physiology of Megalodon. More liberal TL to BL dynamics in Megalodon in comparison to GWS do not imply massive room of error, could be 1 - 4 m in excess (depending upon ontogenetic developments during growth process). And jaw composition of Megalodon isn't a carbon copy of that of GWS either, an assessment based on differences in dentition of both sharks. Furthermore, higher vertebral count in Megalodon can also be indicative of gigantic caudal fins in Megalodon. Makes sense for Megalodon to have very big caudal fins to maintain high performance at gigantic sizes. LifeI don't know. The problem is that the white muscles present in the white shark are not present in the whale shark wich is the only shark to approach the tremendeous size of Megalodon (including the basking if we count the wide range of possible adult size for Megs). Kent bases this on that the whale shark is the only cartilaginous fish to have pushed it size so far, and that it is a filter feeder. So that it is probably the maximum size for a shark with this lifestyle. Thus, he doubts that a shark as large or larger could have kept a lifestyle just as active as the modern laminds which are at best up to around ~6 m long. It is true that Meg may have had unique adaptations that we're not aware about as it is so much bigger than any other predatory shark, but will these unknown adaptions be enough to get around the potential constraints of such a size ? I guess this is impossible to know. But remember that this is applied to potential sizes above 18 m. Whale shark is invalid analogue for Megalodon; whale shark have absolutely different biological characteristics then that of Megalodon with both having different lifestyles as well. Powerful white muscles were a necessity for Megalodon just like they are in other large macro-predatory sharks. Whale sharks do not need powerful white muscles for mobility because they do not have to catch prey items such as marine mammals, whale sharks are planktivores. Gigantism in whale shark isn't indicative of what to expect from Megalodon, the latter shark wasn't a giant due to same reasons. Kent needs to focus on importance and influence of powerful white muscles in Megalodon, anybody should. |
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Post by Grey on Mar 6, 2014 15:25:20 GMT 5
Whale shark is invalid analogue for Megalodon; whale shark have absolutely different biological characteristics then that of Megalodon with both having different lifestyles as well. Powerful white muscles were a necessity for Megalodon just like they are in other large macro-predatory sharks. Whale sharks do not need powerful white muscles for mobility because they do not have to catch prey items such as marine mammals, whale sharks are planktivores. Gigantism in whale shark isn't indicative of what to expect from Megalodon, the latter shark wasn't a giant due to same reasons. Kent needs to focus on importance and influence of powerful white muscles in Megalodon, anybody should. For sure whale shark is different than Meg, and Meg had very probably white muscle. But would the white muscle turn around the physical constraints imposed by the relatively simple cardiovascular system in sharks at such a huge scale so much bigger than any other active predatory selacian in history ? I guess it'd be interesting though to envision the anatomical impact of white muscle at such a large scale. But at the point we are, it is not unreasonnable to suggest the largest Megs may have lived as such and became more and more opportunistics with age. That's the case in many predatory forms. This does not make Meg a giant lethargic blob either like Taipan claimed it was... |
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Post by theropod on Mar 6, 2014 17:19:55 GMT 5
Its teeth are broad, not thick. In fact, they are labiolingually thin, very thin.
That morphology, wide but thin, is typical for slashers, and inversely correlated with bite force in sharks.
Not even, especially. Immature shark teeth have proportionally bigger roots and smaller crowns.
Great white sharks have the widest, overally biggest teeth, because they are the ones most specialized for macrophagy. Other sharks more adapted towards gripping (mako, hammerhead, sandtiger...) may have thicker roots and more powerful bites tough.
Tiger sharks are another example of a selachian with very wide teeth, used for sawing. They are not exceptionally bulky, probably less so than makos which have far more slender teeth.
Great white sharks are not more robust than mako sharks at equal lenght, despite great differences in the dentition. The dentition does not seem to have a good correlation with the postcranial morphology in sharks (and other animals too!).
I already noted that. That would invalidate the argument that C. megalodon had "more liberal TL" due to greater spine lenght.
Cretoxyrhina has exceptionally short centra, lenght/height ratio of 0.28-0.31 vs 0.51 in great whites (Newbrey et al. 201x [in press]), in other words it needs more vertebrae in order for the overall proportions to be similar.
Those of C. megalodon are claimed to be comparable to those of great white sharks (Bendix-Almgreen 1983, Kent [unpubl.]). You even claimed they were proportionally longer, which means that if the animal also had more vertebrae, the vertebral collumn as a whole would be more slender.
I am not speaking about tooth lenght. It is very likely C. megalodon had proportionally shorter teeth (at least in the anterior parts of the mouth), because they were proportionately wider. The relative lenght of the teeth is a highly variable factor and should not be relied on imo.
But the combined width of all teeth is related to the jaw size of the animal, and, unless the animal had a proportionally undersized or oversized mouth, this is closely related to its bulk.
We can use known megalodon dentitions as a template to extrapolate the approximate jaw size of the specimen (that is of course where a considerable degree of variability will come into plac), and we can use that jaw size to estimate its overall size based on extant sharks. If it had comparable relationships between jaw size and TL, this method will be sound. If it jaws were proportionally bigger, the estimate will be too high, if its jaws were relatively smaller, it will be too low.
Nothing indicates that C. megalodon had proportionally smaller jaws. As I explained, that would be a highly unusual trend in a macropredatory lineage that grows bigger.
Yes, this has already been suggested. However the caudal fin does not add significantly to the animals bulk, so if more of it was fin, it was less bulky at TL parity, though slightly longer.
If it had a relatively larger jaw and we predict its size based on its tooth jaw size, that would suggest we are overestimating its size.
Gottfried et al produced very conservative TL estimates for the most part (the exception is of course their upper estimates, which were beyond liberal, the highest one was simply based on an exagerated length figure for a great white shark). However their model is als very bulky.
I think I’m in need for an explanation.
How is robusticity not related to how long the body of an animal is? If just its tail (fin) gets longer, that does not add as much to its mass as it does to its lenght, so it’s less robust.
It doesn´t. The only major difference is the pug-nose, which is an artistic speculation.
And it does suggest that C. megalodon had proportionally smaller jaws? You are wrong to say that quantitative assessments automatically disregard the differences between these organisms. In fact, they could help to grasp them more objectively than is currently done.
The qualitative data suggests that C. megalodon was a macrophagous predator, very much like C. carcharias. It would make no sense for such an animal to be bigger relative to its killing apparatus, and nothing suggests it was (neither qualitative nor quantitative characters).
I have already assessed that, there are differences, especially in the proportions of individual teeth. That’s the reason I have stopped to rely on the measurements of single teeth to directly scale up from extant species. If, for example, a great white that has proportionately taller UAs but proportionately lower posteriors is used as a direct analogue that will yield an under or overestimate, depending on what tooth you are comparing.
It does. If so, it total lenght may have been a little higher than predicted, due to the larger caudal fin.
It´s body mass estimate would hardly be affected at all (perhaps a few hundred kilos in a large specimen).
Yes, positive allometry in fin size does make sense, applying to all animals. For example, by the same means we can assume Livyatan had larger fins than Zygophyseter, and we already know that large pliosaurs like the MoA and P. funkei had gigantic fins for their size (otherwise they’d be 15m+).
According to Gottfried et al. no such trend is known in Carcharodon carcharias, but that doesn’t mean it cannot apply to megalodon as a species when compared to carcharias as a species. How large its impact would be is a different story, I think many reconstructions are exagerated.
A vertebral count greater by 10 or so wouldn’t be sufficient for that marked a difference. The Nat. Geo. model looks nice, but it’s somewhat caricatured imo.
in the end of the day, that’s anyone’s guess though, there hasn’t been the direly needed quantitative assessment yet.
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Post by Grey on Mar 6, 2014 18:07:42 GMT 5
I really don't think that very large thick pectoral fins in a large meg would weigh only few hundreds of kilogramms, no more than the weight of T. rex head. Comparably large whales fins are heavier than this. In the blue whale which has small flippers for its size, their total weight is 1/7 of the total weight of the body. Megs pectorals using the actual reconstructions certainly weighed several tonnes in the large specimens.
In any case I don't see the purpose of this discussion, megalodon proportions based on its few centra are still predicted as building robust thunniform bulky shark typical of a modern lamnid/lamniform. It was probably as bulky, perhaps a bit bulkier, less likely but still possibly a bit slender. All of this excluding the individuals weight variations.
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Post by Life on Mar 6, 2014 19:45:37 GMT 5
ItS teeth are broad, not thick. In fact, they are labiolingually thin. That morphology, wide but thin, is typical for slashers, and inversely correlated with bite force in sharks. Teeth of GWS are not as thin as they may look in the photos. However, teeth of Megalodon are not just broad but thick (double hammer). Not even, especially. Immature shark teeth have proportionally bigger roots and smaller crowns.
In case of Megalodon, opposite is true as apparent from the comparison by Mr. Ehret. Have a good look:
Great white sharks have the widest, overally biggest teeth, because they are the ones most specialized for macrophagy. Other sharks more adapted towards gripping (mako, hammerhead, sandtiger...) may have thicker roots and more powerful bites tough. Tiger sharks are another example of a selachian with very wide teeth, used for sawing. They are not exceptionally bulky, probably less so than makos which have far more slender teeth. And what do you think of Megalodon in this respect? Great white sharks are not more robust than mako sharks at equal lenght, despite great differences in the dentition. The dentition does not seem to have a good correlation with the postcranial morphology in sharks (and other animals too!). Great white sharks exceed robustness of mako sharks at some stage, right? Dentition of Megalodon is heavier then that of GWS even at size parity, it functionally requires relatively more robust chondocranium accordingly. Upon approaching adulthood, dentition of Megalodon becomes much heavier and more robust (see comparison by Mr. Ehret above) and it would functionally require more robust chondocranium at this stage accordingly. Do the math. I already noted that. That would invalidate the argument that C. megalodon had "more liberal TL" due to greater spine lenght.
If GWS is equipped with larger caudal fins, its tooth length to body length dynamics will become more liberal, right?
Now extend this point to Megalodon and my point becomes clear.
Cretoxyrhina has exceptionally short centra, lenght/height ratio of 0.28-0.31 vs 0.51 in great whites (Newbrey et al. 201x), in other words, to have the same degree of slenderness in its vertebral collumn it needs more vertebrae. Those of C. megalodon are claimed to be comparable to those of great white sharks (Bendix-almgreen 1983, Kent). You even claimed they were proportionally longer. This still doesn't supports slenderness assumption. If Megalodon had proportionally larger caudal fins then GWS then this might be one of the reasons for the higher count of the former. In addition, Megalodon proportionally most likely also possessed larger jaw structure and more robust chondocranium (its dental morphology indicates this) and this would imply proportionally more robust built on the whole accordingly. Assessment of Gottfried et al (1996) also lends credibility to mine, details below. Have a good look once again:  This is how Megalodon would have looked in real life. If it had a relatively larger jaw and we predict its size based on its jaw size, that would suggest we are overestimating it. No, the dynamics of its jaw size and body length are a bit different from that of GWS. Gottfried et al produced very conservative estimates. However their model is als very bulky. Gottfried et al (1996) presented both conservative and liberal estimates (15.9 m - 20.3 m). Their anatomical representation seems to be accurate. I think I´m in need for an explanation. How is robusticity not related to how long the body of an animal is? If just its tail gets longer, that does not add as much to its bulk as it does to its lenght. Check artistic depiction of Megalodon above. It doesn´t. The only major difference is the pug-nose, which is an artistic speculation. Adult O. obliquus have more bulkier and stockier appearance in comparison to that of an adult GWS. The qualitative data suggests that C. megalodon was a macrophagous predator, very much like C. carcharias. It would make no sense for such an animal to be bigger relative to its killing apparatus. I have already asessed that, there are differences, especially in the proportions of individual teeth. ThatS the reason I have stopped to rely on the measurements of single teeth to directly scale up from extant species. It does. If so, it total lenght may have been a little higher than predicted, due to the larger caudal fin. It´s body mass estimate would hardly be affected at all (perhaps a few hundred kilos in a large specimen), compared to the values you get from extant lamniform lenght-weight regressions and the body lenght estimated based on the lenght of its dentition. Megalodon in comparison to GWS have: > Jaw structure > Vertebral column (caudal fin included) > Heavier dentition > More robust chondocranium Do the math now. Gottfried et al (1996) did some: "Our skeletal reconstruction of C. megalodon (Fig. 7) conforms to very robust shark that is more massively proportioned, particularly in the head region, than the living white shark. In comparison to living white sharks, the head of the megatooth is reconstructed as being blunter and wider (signifying correspondingly stouter jaws and greater musculature mass to power them), and with somewhat pig-eyed appearance (based on allometric decrease in the size of the orbit as living white sharks grow larger). The fins are interpreted as being quite similar, although proportionally slightly larger then those of living white sharks [fin growth in C. carcharias is approximately isometric (L. J. V. Compagno, unpublished data)]. We have interpreted the megatooth fins as being slightly larger and thicker in proportion because the megatooth is so massive that it is reasonable to assume relatively larger fins for propulsion and control of its movements." This is Fig. 7: |
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Post by Grey on Mar 6, 2014 19:56:31 GMT 5
There's not only Gottfried et al. who envision a robust Otodus/Carcharocles reconstruction, Jeremiah did too. Even though he's not strictly an author, I've not seen criticism about his work, the 7.5 m Otodus.  One can try to scale up this reconstruction to the published size of Megalodon. The only potential important criticism I'd have with Gottfried reconstruction is the pug-nose. |
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Post by theropod on Mar 6, 2014 20:56:34 GMT 5
Grey: The whole fin weighs more. But a bit of a difference in the lenght of the fins will not add a huge amount of mass. Megalodon’s dentition is still apparently most similar to great whites among extant sharks. The teeth are broad, triangular blades. They are thicker than analogous great white teeth, most likely this is related to the square-cube law. There is no reason to presume it means the whole animal was considerably stockier, certainly not beyond what is indicated by intraspecific strends in C. carcharias, and even less if its vertebral collumn was more slender. Nope. Check the spreadsheet I’ve attached earlier, actually makos appear to be (insignificantly) bulkier based on the published TL-body mass regressions. Size parity depends on the size estimate. Of course at Gottfried et al.’s relatively short size figures, based on tooth height, it is. If you use jaw perimeter-based estimates (which give estimates at least 1m longer than aforementioned study), probably not, because the dentition is thicker, but also shorter at dentition-lenght parity. The math is that this doesn’t appear to play a significant role in the morphology of extant sharks. Selachians with various tooth morphologies can each be rather robust or slender bodied. C. megalodon having somewhat more robust jaws, simply due to size-related trends, is not out of the question, but the whole animal being considerably bulkier is too much speculation, especially if you assume it was also additionally elongated due to longer fins. Yes, but then it certainly isn’t also bulkier at the same lenght, it’s fork lenght and body lenght are left unaffected. At the same total lenght, it will be less massive. It’s not that I do not see your point. I also agree that it likely had proportionally bigger fins, given it had a lifestyle similar to extant lamnids. I’m just not agreed with your conclusion that this was evidence for both a proportionally greater lenght than predicted, and at the same time a more stocky creature. The former appears reasonable (in that case, I suggest we should revert to fork lenght for comparisons, and, importantly, quantify the extent of this difference), the latter does not. An animal the size of C. megalodon is already faced with biological constraints related to locomotion in water. Reynolds numbers for large, fast swimming animals are always very high. Great whites and Makos, especially the latter, appear to have highly optimised morphologies for efficient swimming. The fastest extant aquatic animals (xiphiids, Isthiophorids, sphyraenids). The majority of animals similar in size to C. megalodon, very fast taxa among them, are also rather more slender than bulkier (the genus Balaeonoptera, Physeter, but also basking and whale sharks). Is it realistic that Megalodon would have an even stockier body shape (let’s ignore the fins and focus just on the body) than the already very robust extant lamnidae? For all we know, no. That does not mean it didn’t have a deep, tunniform body shape, but saying it must have outbulked all closely related taxa, and thus all animals of similar size, perhaps with the exception of right whales, is exagerating it by far. That’s also not what Gottfried et al. suggested. They used the trends observed in great white sharks to extrapolate its proportions. Their weight estimates were somewhat liberal, but their TL estimates (excluding the wrong upper figure yielded by direct sizing) were conservative in exchange. What they did was envisioning a relatively short but bulky shark, with relatively larger, more robust jaws. The only exception is their speculative maximum size for which they unfortunately used the same lenght/weight relationship (but that shark would have had proportionately smaller teeth and, hence, jaws). The assessment by Gottfried et al. does not assume more liberal tooth height to body dynamics. It uses the exact same tooth-height to body dynamics that the great white shark has, which is the key problem because those indeed make the estimate conservative. Of course C. megalodon has a larger jaw structure, it is roughly 3 times bigger in linear terms! It also has a larger jaw structure at upper anterior height parity. But it certainly has no larger jaw structure at jaw size parity, that’s an obvious impossibility. It is IMPOSSIBLE for it to have both relatively bigger jaws (~greater bulk) AND be proportionally longer relative to its jaws. That is plainly a physical impossibility, an animal cannot both have proportionally larger and proportionally smaller jaws at the same time. That is the speculative life restoration from a documentary, not a fact. Nobody knows for sure how C. megalodon was built, everybody is just hypothesizing based on more or less sound principles. In this case, a version of a white shark with larger fins and a proportionately deeper body. But there’s no certainty as to what it really looked like, until someone describes a complete skeleton. Even if they are, it is not possible that it’s jaws were both bigger and smaller relative to its body at once. Either the animal is longer than predicted by its jaw size, which would then most likely imply it was more elongated or merely had larger tail and/or fins (which is a good explanation for the higher vertebral count, it just doesn’t have major impact on its size, considering how weight between animals whose only difference is the size of the fin won’t be too different), or it was shorter, with proportionally bigger jaws. We cannot judge its accuracy for now, no complete megalodon skeleton is described to date. The estimate of 20.3m (20.2m actually, no idea why 20.3 is so persistent even though it’s miscited) should not be taken seriously, at least not for the specimen they used. It based on a great white of exceptional proportions (the malta female when assumed to be 7.1m long), largely due to an unreliable total lenght figure that was probably overestimated by a huge margin (other estimates for the specimen have been as low as 5.2m!). Literally, that’s like finding an isolated tiger canine, and then picking a tiger thought to have particularly small canines, due to a particularly gigantic yet unreliable body size estimate, to scale it up. The resulting animal has comically tiny teeth for its body size, because the body size for the scaling proxy was most likely wrong, and even if not, unusually large in proportional terms. So? Larger fins do not make the animal bulkier, but less bulky. Just like a relatively longer tail does not make a lizard bulkier. I cannot see how it does. Could you post a source for that? The situation with Otodus obliquus is the same as, or even worse than, with C. megalodon. It’s actual proportions are not known, what is presumed about its built is speculation, and, afaik, no evidence for it being bulkier beyond what would be predicted by the size trends in extant lamniforms has been brought forth. Neither is there any published account that actually postulates this taxon to have been particularly stocky, based on whatever evidence.
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Post by Grey on Mar 7, 2014 2:25:56 GMT 5
Fair enough. Now a larger size for all the flippers could have a not so unsignificant impact on the total weight. Larger pectorals would induce a larger size for all the fins and the tail.
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Post by theropod on Mar 7, 2014 3:10:30 GMT 5
So far I was only talking about the tail, the propulsory system, because that’s an explanation for the slightly higher vertebral count that meg apparently had. The pectorals and dorsal fin are used for stability and are a different matter entirely. Still, whether that will really impact the body mass considerably is questionable, I could not find figures on shark body segment masses, but the fins are alltogether relatively flat and not very muscular (obviously optimizing the ratio between the drag they can produce and the weight and metabolic cost). You stated blue whale flippers were 1/7 the weight of the whole body. Where’s that figure from? That would suggest they’d mass more than 14t (=more than 7t each) in average- sized individuals (and perhaps twice that much in the largest!). Here’s a fin whale flipper with a human for scale:  Assuming a similar ratio (since the two have similar proportions) and that it’s from an average individual, that flipper should weigh 3.5t. That seems to be a big overestimate. A few tons is certainly possible for the flippers of large blue whales, but a seventh of the whole body weight looks exagerated. Also, although shark pectoral fins are larger, are they as robustly built, with such thick support structures? I doubt it, although more fleshy than actinopterygian fins, shark fin skeletons are fairly gracile, composed of thin, raylike radialia. So just making them somewhat longer, will that really contribute considerably to the weight of the animal? Don’t forget that basically means making the radialia and/or the distalmost (thin) part of the vertebral collumn longer, not more. |
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Post by Life on Mar 7, 2014 3:24:04 GMT 5
Megalodon’s dentition is still apparently most similar to great whites among extant sharks. Do you honestly think that I am to be reminded about this? For an intelligent and passionate individual such as you, it shouldn't be difficult to follow an argument, decode it properly and not make discussion more complicated. --- Assessment --- Recheck this comparison: Perhaps this can help ? Photo of (actual) GWS dentition featured in comparison from OP is in this source: paleobiology.si.edu/pdfs/sharktoothKey.pdf (PDF file) What differences you see? I notice following: 1. Dentition (on the whole) covers more surface area. 2. A3 of Megalodon is massive in comparison to I of GWS. 3. A3 along with P1, P2, P3 and P4 indicate broader and larger jaw dimensions for Megalodon at parity and also proportionally. Now that a case of broader and larger jaw dimensions have been established, we move towards robustness factor. Which shark have more robust dentition? Megalodon NOTE: More robust dentition functionally requires more robust chondocranium accordingly. In the nutshell: A) Broader jaw structure B) More robust chondocranium Now (A) and (B) also imply greater musculature mass and... --- Assessment --- The teeth are broad, triangular blades. They are thicker than analogous great white teeth, most likely this is related to the square-cube law. There is no reason to presume it means the whole animal was even stockier. What is the relevance of square-cube law in this matter? Megalodon dentition remains more robust then that of GWS in all stages of growth of both. Here is another comparison from Grey: Both types of comparisons from OP validate my assessment. More robust dentition is not a superficial development in Megalodon, their is a whole biology behind it; biology which I have attempted to clarify to you in this response. Nope. Check the spreadsheet I’ve attached earlier, actually makos appear to be (insignificantly) bulkier based on the published TL-body mass regressions. ? Size parity depends on the size estimate. Of course at Gottfried et al.’s relatively short size figures, based on tooth height, it is. If you use jaw perimeter-based estimates (which give estimates at least 1m longer than aforementioned study), probably not, because the dentition is thicker, but also shorter at dentition-lenght parity. See my assessment above The math is that this doesn’t appear to play a significant role in the morphology of extant sharks. What does morphology of extant sharks have to do with Megalodon? In simplest terms: Megalodon represents a more robust and modified evolutionary design of GWS. Selachians with various tooth morphologies can each be rather robust or slender bodied. C. megalodon having somewhat more robust jaws, simply due to size-related trends, is not out of the question, but the whole animal being considerably bulkier is too much speculation, especially if you assume it was also additionally elongated due to longer fins. I understand that Megalodon baffles us with its morphological characteristics but I have done my utmost to clarify its morphology in this response; Megalodon is more robust irrespective of size-related trends (see my assessment above). Yes, but then it certainly isn’t also bulkier at the same lenght, it’s fork lenght and body lenght are left unaffected. At the same total lenght, it will be less massive. I think that you are confused about what I am trying to convey (English is not my native language so my statements may sound confusing). 1. The baseline of my argument is dental parity (see comparison done by OP above) 2. Focus had been on tooth length to body length dynamics 3. Megalodon seems to have more liberal tooth length to body length dynamics than in GWS. Situation is like this: GWS: Tooth length of 3 inch + 171 vertebrae (including caudal fin) Megalodon: Tooth length of 3 inch + 200(+) vertebrae (including caudal fin) Therefore, Megalodon seems to have more liberal tooth length to body length dynamics in comparison to that of GWS (this leaves some [positive] room of error for size estimates of Megalodon obtained through methods devised to estimate the size of GWS). Your argument is that this implies that Megalodon have relatively more slender build but you are wrong, don't focus on body length parity. It’s not that I do not see your point. I also agree that it likely had proportionally bigger fins, given it had a lifestyle similar to extant lamnids. I’m just not agreed with your conclusion that this was evidence for both a proportionally greater lenght than predicted, and at the same time a more stocky creature. The former appears reasonable (in that case, I suggest we should revert to fork lenght for comparisons, and, importantly, quantify the extent of this difference), the latter does not. An animal the size of C. megalodon is already faced with biological constraints related to locomotion in water. Reynolds numbers for large, fast swimming animals are always very high. Great whites and Makos, especially the latter, appear to have highly optimised morphologies for efficient swimming. The fastest extant aquatic animals (xiphiids, Isthiophorids, sphyraenids). The majority of animals similar in size to C. megalodon, very fast taxa among them, are also rather more slender than bulkier (the genus Balaeonoptera, Physeter, but also basking and whale sharks). Is it realistic that Megalodon would have an even stockier body shape (let’s ignore the fins and focus just on the body) than the already very robust extant lamnidae? For all we know, no. that does not mean it didn’t have a deep, tunniform body shape, but saying it must have outbulked all closely related taxa, and thus all animals of similar size, perhaps with the exception of right whales, is exagerating it by far. That’s also not what Gottfried et al. suggested. They used the trends observed in great white sharks to extrapolate its proportions. Their weight estimates were somewhat liberal, but their TL estimates (excluding the wrong figure yielded by direct sizing) were conservative in exchange. What they did was envisioning a relatively short but bulky shark, with relatively larger, more robust jaws. The only exception is their speculative maximum size for which they unfortunately used the same lenght/weight relationship. I am not suggesting that Megalodon wasn't streamlined, my point is that it was/is more robust than GWS in all stages of growth of both. In sharks, it is not just the shape of the body structure that determines their speed (several factors are involved). Asessment by Gottfried et al. does not assume more liberal tooth height to body dynamics. It uses the exact same tooth-height to body dynamics that the great white shark has, which is the key problem because those indeed make the estimate conservative. My focus is not on tooth length to body length based assumptions of Gottfried et al (1996), my focus is on their anatomical representation of Megalodon (even with assumption of matching tooth length to body length dynamics in both sharks, Gottfried et al (1996) conclude proportionally a more robust build for Megalodon). This assessment remains valid even if observations made by me are taken in to consideration. Of course C. megalodon has a larger jaw structure, it is roughly 3 times bigger in linear terms! It also has a larger jaw structure at Upper anterior height parity. But it certainly has no larger jaw structure at jaw size parity. You are making strange assumption, who is assuming jaw size parity here? Focus on dental parity like I have, not on jaw size parity and body length parity. At dental parity, Megalodon seems to have possessed larger jaw structure coupled with more robust chondocranium then GWS. It is IMPOSSIBLE for it to have both relatively bigger jaws (~greater bulk) AND be proportionally longer. That is plainly a physical impossibility, an animal cannot both have proportionally larger and proportionally smaller jaws at the same time. Covered above That is the speculative life restoration from a documentary, not a fact. Nobody knows how C. megalodon would have looked in real life. That speculative life restoration have some merit. This is how Megalodon is expected to look in life:  Even if they are, it is not possible that it’s jaws were both bigger and smaller relative to its body at once. Either the animal is longer than predicted by its jaw size, which would then most likely imply it was more elongated or merely had larger tail and/or fins (which is a good explanation for the higher vertebral count, it just doesn’t have major impact on its size since weight is correlated more strongly with fork lenght than with TL), or it was shorter, with proportionally bigger jaws. We cannot judge its accuracy for now, no complete megalodon skeleton is described to date. The estimate of 20.3m should not be taken seriously, at least not for the specimen they used. Covered above It based on a great white of exceptional proportions (the malta female when assumed to be 7.1m long), and used an unreliable total lenght figure that was probably overestimated by a huge margin (other estimates for the specimen have been as low as 5.2m!). Literally, that’s like finding an isolated tiger canine, and then picking a tiger that has particularly small canines, due to a particularly gigantic yet unreliable body size estimate, to scale it up. Have you read this article? www.jostimages.de/haiartikel/mollet_et_al_1996cha10.pdf (PDF file) So? Larger fins do not make the animal bulkier, but less bulky. Just like a relatively longer tail does not make a lizard bulkier. Covered above I cannot see how it does. Could you post a source for that? The situation with Otodus obliquus is the same as, or even worse than, with C. megalodon. It’s actual proportions are not known, what is presumed about its built is speculation, and, afaik, no evidence for it being bulkier beyond what would be predicted by the size trends in extant lamniforms has been brought forth. You need a source to figure this out? |
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Post by Grey on Mar 7, 2014 3:27:30 GMT 5
The frozen fins of a 2120 kg great white were 79 kg. Do the math on a 60 tonnes Megalodon in which we can assume longer, thicker fins if it has indeed a more massive torso.
Sharks fins have no bones but are fairly massive to support the animal.
And I'm a little bit tired of these subjects which deserve no discussion as such. Your goal is just to debate about anything in that thread or never be agreed about it and just to shrunk megalodon as much as possible ? I will have to leave the forum for several months soon, when I'm back may I expect that you'll have successfully established Megalodon at 10 m adult average length with a carcharhinid-like body ? Not so private joke...
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Post by Life on Mar 7, 2014 3:50:13 GMT 5
The frozen fins of a 2120 kg great white were 79 kg. Do the math on a 60 tonnes Megalodon in which we can assume longer, thicker fins if it has indeed a more massive torso. Sharks fins have no bones but are fairly massive to support the animal. And I'm a little bit tired of these subjects which deserve no discussion as such. Your goal is just to debate about anything in that thread or never be agreed about it and just to shrunk megalodon as much as possible ? I will have to leave the forum for several months soon, when I'm back may I expect that you'll have successfully established Megalodon at 10 m adult average length with a carcharhinid-like body ? Not so private joke... And the name of this new representation would be: Isurus Megalus Lamna Pygmus  -- On a serious note, I absolutely welcome contributions of theropod (He is very passionate debater, we need people like him).  |
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Post by Grey on Mar 7, 2014 3:51:48 GMT 5
As for the sizes estimates, all I have to say is that the equations by Shimada and Gottfried for Megalodon are both considered by their respective authors as "conservative". Period. Based on the available evidences and most up to date works, 18 m is confident. And Carcharocles was likely not a slender built shark, a robust bulky structure appears probably, though something a bit less heavy built is also possible, like would suggest Siverson, an almost 20 m shark with a very heavy set of jaws.
But such a field does not deserve all these so-called debates.
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