A quick word or two regarding the size of everyone’s favourite extinct shark, Carcharocles
As we have learned to expect from something really large and with really scrappy remains (isolated teeth, with vertebrae or more complete dentitions being known in a small number of poorly- or completely undocumented cases), people do enjoy speculating about its size.
Only in this case, people advising the use of conservative methods are often just drowned out (and trolled and bashed into submission) by the internet movement that understandably enjoys the thought of a species of 60ft shark that killed everything in its path with a single bite, aided by the fact that too many of those people mistake scientific’ enthusiasm (or pretty much any statement they can find anywhere, never mind if it’s just a freaking discovery channel documentary they misconstrue as the new principal scientific reference work out there) for some sort of endorsement of their sensationalism.
That isn’t to say that speculating is wrong–we literally would not get anywhere without it in vertebrate palaeontology. And certainly even liberal methodologies have their place, and for very good reasons that I won’t delve into right now.
But that doesn’t mean they are the only ones deserving of that, and it doesn’t mean that place is necessarily to be the most commonly cited and reproduced estimation, neither does it mean the only way to get an estimate that doesn’t get labeled as "too low" should be by making excessive use of wild assumptions to drive up that size figure (which really is precisely how the 20m+, 100t+ figure that’s so common in this case came into being, no offence).
There is a fundamental difference between nitpicking such a figure to represent this animal’s body size in general, and publishing it as a hypothetical (and, as noted by the authors in question, unreliable) estimate (but see below).
That gets even more comical when it gets to discussing how C. megalodon
compares to other giant predators. I can’t help but be amused by their confidence in such biased comparisons when representing C. megalodon
as an 18-20m critter even though those are the sizes of a handful of individuals in thousands. To jump ahead a bit, there appears to be quite some sensationalism in claims that it is the biggest predator of all time.
Leaving aside the implication of certainty that is expressed in this statement despite the incompleteness of the fossil record (and its fossil record in particular, with most animals people don’t make confident size estimates from teeth), there is a plain and simple lack of data supporting such claims. Certainly it is among the top 2 or 3 contenders, being comparable in size to its contemporary Livyatan melvillei
, to the point where it is warranted to not make any statement about which is larger considering the lack of sufficiently complete fossils, and the lack of a sufficiently large sample of the latter’s population.
I don’t have a problem with the thought that 20m megatooth sharks existed, just like how 1t polar bears exist(ed), but this estimate is useless for all (scientific) intends and purposes because it does not base on solid data, and because it doesn’t relate to a normal individual at all (you know, the kind of megalodon that made all those bite marks, the kind you’d expect and fear to swim into if you were a miocene mysticete, in short, the kind that made up the bulk of the adult population of this species).
Those figures represent hypothetical freak specimens, based on more or less reliable hints, and back when this estimate was published it was conceived as such–deliberately basing on the largest (unreliable, and noted as such by Gottfried and colleagues) and most unusually proportioned report of a great white that was available.Life reconstruction, based on the anatomy of the extant great white shark (adapted from Compagno 1984) and accounting for allometric increase in robusticity as per the data outlined below.
So for a less biased picture, conservative methods are in order, especially when the whole matter already has to be based on a handful of teeth.
Keep in mind the actual meaning of "conservative"; not "the lowest", although the word is often used in that sense, even by myself. Yet in principle I am not an advocate of automatically considering the lowest estimate the most conservative.
In fact, it is not unusual for the lowest estimates to be "liberal" of sorts, when special pleading is used in order to produce a minimum estimate, often under the mistaken impression that it would make it more parsimonious (yet being too small isn’t really any better than being too large).
So here, what I mean is the most parsimonious method, the one that keeps biased (e.g. aimed at producing an extreme estimate in either direction) or otherwise poorly supported assumptions to a minimum, the one avoiding to sum up such biases and instead leaving them to cancel each other out if they can not be avoided. In short, the best and most objective estimate. Unfortunately that use of the term will probably not gain popular acceptance, so lets get back on topic.
So is there a way of making this more objective and exercising some caution in this sense? Yes, I think there is.
Firstly, the most important size metric of a species isn’t the size of the biggest thing you can find some tiny fragment of (btw teeth in general are actually tiny fragments, and scientists don’t bother estimating body size from them in many cases). It’s the species average size that’s most important, most objective, and least error-prone, so that’s what I’m most interested in here.
The background is that Pimiento & Balk 2015 actually estimated it fairly recently, and came up with an average of ~10m for 544 individuals of all ages.
But this still isn’t a very good means of comparison; depending on an animal’s reproductive strategy, the number of immature specimens in such a sample can vary, and accordingly species whose social and ecological adult stage is larger can end up smaller (or vice versa). To account for that, one can take the mean size of a subsample, namely all those that are above the mean size at maturity.
Gottfried et al. 1996 estimated mean sizes at maturity for both females and males based on the Great White shark, and the average of both is 11.9m, which is broadly consistent, if not a bit higher, than what would be indicated by the relative size at maturity of C. carcharias
(cf. Cailliet et al. 1985, Casey & Pratt 1985, McClain et al. 2015). This figure should hence be appropriate to represent the average size when attaining maturity given that there is an approximately equal number of males and females in the population. In Pimiento & Balk’s sample, the average of individuals estimated to be this long or longer is ~14m.
Now, assume we wanted to know the size of a large megalodon. Not crazy-freaky-outlier-large, but still really large. One such specimen is comes from Denmark, and consists of a huge tooth associated with a number of vertebrae, which means that this specimen is, unlike most megatooth sharks, not a tooth lost by some individual at a random moment of its life, but an actual fossil "skeleton" left the traditional fossil way (i.e. dieing) if that word is appropriate.
Unfortunately there’s no telling whether any of the vertebrae are the largest in the collumn, and there is also vague indication of C. megalodon
’s vertebrae being proportioned differently from those of C. carcharodon
. So we’re still stuck with a tooth, but at least we have a more substantial specimen that this tooth once belonged to.
The piece of eviscerating awesome in question is 12.6cm wide and 15.8cm tall, with a 11.9cm tall crown. Based on its massive built, slight tilt and size, it is likely to be one of the first three laterals, which include what is often the widest tooth in the dentition.
There are multiple ways of estimating the size from these measurements. One that is currently very popular is based on individual regressions estimating total length from tooth-crown height in Great White Sharks (Shimada 2001, cited in Pimiento et al. 2010).
Using these regressions for the first three lateral teeth, the mean estimate is 16.8m.
Another method, and one which I personally prefer because it solves a number of the problems associated with using a significantly smaller relative as the sole analogue, is first extrapolating the length of the entire tooth row from the width of the tooth, and then using a regression designed for estimating total length from the length of the tooth row (Lowry et al. 2009, see also Newbrey et al. 2013/in press, and this list of measurements of two cast megalodon dentitions→
. That way differences in proportions within the dentition are reduced to the impact of individual, not interspecific, variation, and the resulting estimate assumes them to follow the same trend in terms of relative jaw size.
Even though the literature seemingly suggests significantly less, I went with an interdental spacing of ~15% in addition to the summed tooth widths, because it corresponds to what one can roughly measure in the most widely spaced pictures of great white shark jaws and it is only fair towards the tested hypothesis to use the most optimistic reasonable regression).
Coincidentally this gives us the same mean size estimate for the three positions, 16.8m. Quite funny actually.
It is an intriguing side note (even though it’s another mere coincidence, it pretty much rules out the whole "these figures are different from the official ones" line of criticism I sometimes get, because these are actually the exact figures that were published) that this size estimate also coincides with the highest one estimated by Gottfried et al. 1996 that was deemed reliable, as well as with the biggest specimen from the nursery described by Pimiento et al. (2010). This was hence the highest proper size estimate in the literature for almost two decades. Even now, only less than 3% of all megalodon specimens in Pimiento & Balk’s dataset record the species reaching or exceeding this size, and at most by about 7%, so I find it quite save to assume that this can be considered representative of a very large
Length estimates are of course only half of the equation. The most determining factor (though unfortunately highly prone to fluctuations) of the animal’s biology is its body mass. And sure enough, estimating body mass from total length in extant sharks has received almost unparalleled attention as far as size estimates go.
The following is a graph showing 6 [!] different regression equations between total length and body mass for the extant white shark, C. carcharias
. In order to avoid biases I’ve applied all of them and marked the mean, maximum and minimum estimates:
As apparent from the exponents, most of these studies found positively allometric growth in terms of body mass, i.e. larger sharks get bulkier. From this we can actually estimate the change in body shape, since the component of the weight difference not explained by isometry is necessarily due to a thicker body, i.e. a bigger crosssection. A 5m Great White shark is predicted to mass 1196kg, scaled up to 14m by isometry alone that’s 26255kg, but a 14m shark is actually predicted to mass 29
255 (strange coincidence, but not evidence for the existence of the flying spaghetti monster). That’s a difference of 11.4%, so we know a 14m shark has a body crosssection 11.4% larger, since length is out of the picture having already been accounted for in both methods. All we need to do now is take the square root of that, giving us 5.6%, and we’ve got the percentage that it is deeper and wider respectively (assuming it didn’t get disproportionately bigger in one of these dimensions compared to the other, of course).
That is also what my reconstruction bases on, unimaginative as you may call it (since it’s the boring bulked-up great white you almost always see when it’s comes to restoring meg’s body shape), at least it bases on scientific principles. I’m certainly open to other possibilities with regard to its morphology, in the end we all have to accept it is almost completely speculative, it’s just that I have not yet seen any convincing arguments to suggest they are more likely than this (i.e. disproportionately elongated or compact sharks).
So as you can see, the average adult megalodon is predicted to be ~29t in mass, no more than 32t and no less than 26t, and the large specimen from Denmark is expected to be ~52t (within a range from 46 to 57t). The average of the entire population would be ~10t, similar to a very large bull orca (which is impressive enough considering that that average figure corresponds to what is usually a large sub-adult).
And yes, there are a few megalodons that realistically reached or exceeded the 18m-mark (at which length they’d be expected to weigh in at ~64t), and some exceptional fossils do seem to indicate lengths of ~20m (and probably ~89t). But their overall relevance is in no proportion to their size. Consider this; of the 544 teeth in Pimiento & Balk’s sample, none produced an estimate higher than 17.9m, so individuals significantly above that size are obviously too rare for much of a demographic impact. Unless, that is, there ends up being convincing proof that this is a result of some erraneous method, such as a consistent and pronounced sampling bias towards small specimens (very unlikely) or unreliable size estimates (more likely since I am by no means claiming the method always gives us realistic estimates, but currently it seems like if anything the systemic bias here is towards enlarging size estimates).
Most fossil organisms are represented by small samples, and it is likely that they are centered around the average and that "maximum size" remains unknown in virtually all of them. That’s because the likelihood of finding exceptionally large (or small) individuals is typically lower than finding normal-sized ones, and the small number of individuals known for most of them is not in favour of finding such exceptions.
So please guys, when you talk about body sizes, be a bit more precise, differentiate, and don’t mix average, large, small and maximum-sized specimens up all the time, because it does lead to totally unwarranted conclusions.
is not an 18m shark, nor for that matter is there any species of 18m sharks. Only a species (possibly two if one includes Rhincodon
) that occasionally gets that big. There is no species of 1t bear either, and sperm whales aren’t 24m long and don’t weigh 130t, occasional outsized specimens notwithstanding.
This species of shark was big, huge even. Any animal averaging 14m long and close to 30t is positively enormous. It’s nothing except sad that for some people, that just isn’t enough and they have to judge everything by the most extreme examples they can dig up anywhere.
PS: I do realize this looks like a rant, and honestly, it is. I’m sure we all have issues that annoy us, some more than others. That doesn’t mean I am not appropriately impressed by C. megalodon
or anything like that, just that I think some people are overdoing it in that regard.
And I am absolutely open to change my mind should future (or presently undocumented *wink*wink*) discoveries or revolutionary new methods change this.–––References:
Bendix-Almgreen, Svend E. (1983): Carcharodon megalodon from the Upper Miocene of Denmark, with comments on elasmobranch tooth enameloid: coronoïn. Bulletin of the geological Society of Denmark, 32 pp. 1-32.
Cailliet, Gregor M.; Natanson, Lisa J.; Welden, Bruce A.; Ebert, David A. (1985) Preliminary studies on the Age and Growth of the White Shark, Carcharodon carcharias, Using Vertebral Bands. Memoirs of the Southern California Academy of Sciences, 9 (Biology of the White Shark, a Symposium.) pp. 49-60.
Casey, John G.; Pratt, Harold L. (1985) Distribution of the White Shark, Carcharodon carcharias, in the Western North Atlantic. Memoirs of the Southern California Academy of Sciences, 9 (Biology of the White Shark, a Symposium.), pp. 2-14.
Compagno, Leonard J.V. (1984): Sharks of the World. An Annotated and Illustrated Catalogue of Shark Species Known to Date. Part 1 – Hexanchiformes to Lamniformes. FAO Fisheries Synopsis, 125 (4) pp. 1-249.
Kallal, Robert J.; Godfrey, Stephen J.; Ortner, D. J. (2010): Bone Reactions on a Pliocene Cetacean Rib Indicate Short-Term Survival of Predation Event. International Journal of Osteoarchaeology, 22 (3), pp. 253-260.
Kohler, Nancy E.; Casey, John G.; Turner, Patricia A. (1995): Length-Length and Length-Weight Relationships for 13 Shark Species from the Western North Atlantic. Fishery Bulletin, 93 pp. 412-418.
Lowry, Dayv; Castro, Andrey L. F. de; Mara, Kyle; Whitenack, Lisa B.; Delius, Bryan; Burgess, George H.; Motta, Philip: (2009): Determining shark size from forensic analysis of bite damage. Marine Biology, 156 pp. 2483-2492.
McClain, Craig R.; Balk, Meghan A.; Benfield, Mark C.; Branch, Trevor A.; Chen, Catherine; Cosgrove, James; Dove, Alistair D.M.; Gaskins, Lindsay C.; Helm, Rebecca R.; Hochberg, Frederick G.; Lee, Frank B.; Marshall, Andrea; McMurray, Steven E.; Schanche, Caroline; Stone, Shane N.; Thaler, Andrew D. (2015): Sizing ocean giants: patterns of intraspecific size variation in marine megafauna. PeerJ, 3 (715) pp. 1-69.
Mollet, Henry F.; Cailliet, Gregor M. (1996): Using Allometry to Predict Body Mass from Linear Measurements of the White Shark. In: Klimley, Peter A.; Ainley, David G.: Great White Sharks: the biology of Carcharodon carcharias. San Diego, pp. 81-89.
Newbrey, Michael G.; Siverson, Mikael; Cook, Todd D.; Fotheringham, Allison M.; Sanchez, Rebecca L. (2013, in press): Vertebral morphology, dentition, age, growth, and ecology of the large lamniform shark Cardabiodon ricki. Acta Palaeontologica Polonica, in press, dx.doi.org/10.4202/app.2012.0047
Pimiento, Catalina; Balk, Meghan A. (2015): Body-size trends of the extinct giant shark Carcharocles megalodon: a deep-time perspective on marine apex predators. Paleobiology, 41 (3), pp. 479-490.
Pimiento, Catalina; Ehret, Dana J.; MacFadden, Bruce J.; Hubbell, Gordon (2010): Ancient Nursery Area for the Extinct Giant Shark Megalodon from the Miocene of Panama. PLoS ONE, 5 (5), pp. 1-9.
Tricas, Timothy C.; McCosker, John E. (1984): Predatory Behaviour of the White Shark (Carcharodon carcharias) with notes on its biology. Proceedings of the California Academy of Sciences, 43 (14), pp. 221-234.