Friday, August 16, 2013

For the love of science, the pygmy right whale was NOT originally thought to have gone extinct 2 million years ago!

While I have not yet seen the fake documentary “Megalodon: the monster shark that lives” which has put yet another nail in the coffin of the discovery channel’s reputation for quality programming (what with shows like Moonshiners, Amish Mafia, Auction Kings, Pot Cops, and Weed Country – among others), I have heard that the show has inaccurately reported research from our lab here at Otago in order to support bogus claims that C. megalodon still exists. Now, it’s also important to note as a disclaimer for the uninitiated that the writers never intended their show to be taken at face value as anything but a fake documentary – although it is hardly forgiveable that it was not marketed as such, and that there wasn’t any “WARNING: TOTALLY FAKE” or “100% FANTASY” disclaimer at the beginning of the show.

I won’t be getting into any of the details about C. megalodon survival or other shortcomings of the show, for two reasons: 1) I will discuss the former when it’s appropriate, as I have a paper in preparation on the subject (or rather, the timing of the extinction) and 2) I haven’t actually seen the fake documentary and it would be pretty tacky of me to further rake the muck, and others such as Brian Switek have done a good enough job already (Here and here).

On another note, it is pretty depressing to see what the Discovery Channel has devolved into: the same kind of reality show crap that’s on A&E and The “Learning” Channel. When I was a kid I couldn’t get enough of documentaries with all sorts of beautiful shots of things like reef fish, big cats in their native environment, reptiles in the desert in Africa, and sharks and whales in the open ocean. I ate that stuff up. Nowadays, all it seems like you get on DC is a bunch of rednecks in the swamp, forest, or Alaskan tundra. So many of these shows are deliberate knock-offs of deadliest catch, which I’ll admit can be mildly entertaining. At least Mythbusters and Dirty Jobs, while technically are of the reality show strain, are genuinely aimed at being educational and happen to be really entertaining; however, all of these other Deadliest Catch clones are 5% education, 95% dramatized BS.

Caperea, the baleen whale that, according to the Discovery Channel, was recently rediscovered and formerly thought to be extinct since the Pliocene. 

Okay, rant over, now for some (real) science. In the show, numerous lines of evidence were touted (or completely invented) to indicate that C. megalodon was not in fact extinct, but was still very much alive. One of these arguments was the ‘fact’ that the pygmy right whale (Caperea marginata) had been thought to be extinct for the last two million years and was recently ‘rediscovered’ – which suggests that relatively large bodied marine vertebrates in the open ocean can go undetected, and contribute to someone’s hopes that such a monster as C. megalodon might have survived. However, this is so patently false it’s absurd, and I have a good idea where this misleading tid bit originated from. I mean, the claim is just so... odd that if it weren't a misrepresentation of my lab's researcg, it would be hilariously befuddling. Some of what follows is going to be a brief re-tread of some previous posts on the pygmy right whale I’ve done, so I’ll be brief. Here are a list of things we actually know, written in order so as to tell the story of how the writers got it so damn wrong:

1) The pygmy right whale did not have a published fossil record until 2012. Neobalaenids were not known from the fossil record – at all – until a fragmentary earbone was published from the late Miocene of Australia (read about it here), and a nearly complete skull was published from the late Miocene of Peru (Miocaperea: read more here). This disproves the argument that Caperea was long known only from a Pliocene, pre 2 Ma fossil record. In fact, the fossil record of Caperea has only been known to science for about 11 months.

The skull of Miocaperea pulchra, one of two published neobalaenid fossils. The pygmy right whale fossil record did not exist in the published literature until 2012 (contra the Discovery Channel).

2) Caperea has been known about since the 19th century. It was encountered during southern hemisphere voyages in the 1830’s and 1840’s. Sure, it is a poorly known extant whale – but it is far better known than many ziphiids, some of which are known from thin threads of recorded data. It, however, is by no means anything close to what you could call a cryptid or anything marginally close to a rediscovered ‘living fossil’ like the coelacanth; it was known in the flesh for a century and a half before it ever had a fossil record, quite the opposite of the claim in the show.

3) Caperea has recently been reinterpreted as a member of the family Cetotheriidae, based on phylogenetic research by my adviser, R. E. Fordyce, and fellow labmate Felix Marx. The Cetotheriidae were formerly known only from the fossil record, and were known – at the time of their writing – to have a fossil record as young as about 2 Ma, based on the youngest fossils of my favorite whale, Herpetocetus. Subsequent work published by myself earlier this year documented Herpetocetus surviving as late as the middle Pleistocene (~1-0.7 Ma). This effectively means that Caperea has been transferred in terms of familial placement – i.e. it’s a cetothere rather than a member of the (formerly) monotypic Neobalaenidae. This obviously doesn’t change the status of Caperea as far as extinctions go; it still has a shitty fossil record, although it’s now identified to be more closely related to a group with a decent fossil record.

Which brings me to point 4) When the Fordyce and Marx phylogeny was published, the LiveScience press release ended up with a pretty misleading title: “Found: Whale thought extinct for 2 million years”. The rest of the article is fine, and accurately describes the research, but I don’t know what happened with the title. When you search on google for details about that research, that article comes up, and I believe that this poorly titled press release happens to be the origin of the “Caperea was thought to be extinct!” myth cited on the fake documentary.

So there you have it. The writers must have seen that press release and latched onto that as gold, to the exclusion of all the good, accurate information on the web regarding the pygmy right whale. Oddly enough, a I wrote a decent synopsis of the research here on my blog (see here), and had the writers of the show bothered to read it, the published article, or even the rest of the mis-titled press release, this misrepresentation of our lab’s research could have been totally avoided.

For more on Caperea:


ted said...

Wasn’t Otodus megalodon (I use Otodus following the update of Cappetta 2012) already understood to have preyed or at least fed on large baleen whales ?

I remember the excellent Nat Geo doc about meg which talked that it employed different technics depending the size of the whale, a crushing, direct attack on smaller whales (cetotherids) like suggested by Brett Kent and an attack on the propulsive structures (tail region) on the larger whales. They also discussed that one on these balaenopterid prey item (explained by Lawrence Barnes) was very large at a possible 21-24 m long, weighing slightly more than O. megalodon. The Nat Geo doc specified that these larger balaenopterids justly occurred during the Pliocene.

There is also this quote by Leonard Compagno (1990) : “various reconstructions of C. megalodon jaws suggest this shark had a predatory apparatus able to inflict mortal wounds even to a fin whale or a blue whale”.

There is also this rib from a large 4 millions years old balaenopterid thought to have been the victim of an unsuccessfull predation attempt by a smaller (4-7 m) shark, heavily suspected to have been a young megatooth shark.

Based on these suggestions, I doubt that megalodon was necessarily limited to the smaller genera only ?

ted said...

Note : I had originally posted the question there ! I post here in case you miss it.

Robert Boessenecker said...

C. megalodon almost certainly subsisted on baleen whales and other marine mammals. However, any discussion of feeding strategies are nothing more than colorful speculation; I often hear the "C. megalodon killed cetaceans by biting off their flukes!" and the only taphonomic evidence from the fossil record that has ever been cited in support of that is Purdy (1996) who observed some bite marks on cetacean caudal vertebrae. No quantitative analysis or anything, just a couple of sentences. So those suggestions of feeding techniques are more or less pure fantasy. It's not unreasonable to speculate that that could have happened - but it's very difficult to demonstrate scientifically. We have about as much evidence for C. megalodon developing a killing strategy by selling them cigarettes. I'm not saying it's impossible - it's just that the scientific work has not yet been done, and there are these megalodon myths that sound 'truthy' and awesome.

Compagno's right - C. megalodon could have probably killed any fossil cetacean, and most extant cetaceans with one bite. Now - regarding smaller whales - keep in mind that the majority of prey items modern Carcharodon feeds upon are a fraction of its body size - tuna, seals, etc. - Orcas are the predators that take on things much larger than themselves. So, while the jaws of C. megalodon are indeed gigantic and could have chomped most cetaceans in two, it is only reasonable to apply a modern analog - which would suggest C. megalodon would mostly be feeding on prey under 7 meters in length (dolphins, pinnipeds, sea cows, desmostylians, and small baleen whales).

Another point about baleen whale body size - keep in mind that most baleen whales were under 6-8 meters long up until about 5 million years ago or so, and most of the extreme gigantism in cetaceans is Plio-Pleistocene in antiquity (and therefore post-C. megalodon). Caperea is actually on the large size range for Miocene whales.

Thanks for the question! Please don't hesitate to ask more.

ted said...

Thank you for the response !

Well, I often read about O. megalodon (once again I only use Cappetta, used in the incoming paper of Mike Siversson about Cardabiodon :

I've read Lambert and seen that most mysticetes during Miocene and Pliocene were under the 10 m range. However, Alton Dooley findings are hinting of mysticetes in the 13-15 m range conservatively speaking.

In the Nat Geo doc they also mentionned by Lawrence Barnes that around 4 millions years ago, a large balaenopterid, compared to the fin whale, appeared in the Pacific off California. I ignore if this one had any proper description but they used it as a contrast with the smaller cethoterids meg preyed on during Miocene...

Regarding the attacking technic, I know for sure that Brett Kent is preparing a paper discussing (among other things) the difference between the killing technics of Carcharodon and Otodus/Carcharocles.

Another thing, Mike Siversson is so far the only author I've read about who discuss the battles and competitions for supremacy between the lamniforms sharks that appeared 110 millions years ago, and the different groups of marine macropredators they encountered.
The talk is fascinating :

When speaking about Carcharocles megalodon, he points on that the large raptorial physeteroids such as the famous (but somewhat hyped like any new big macropredator found recently) L. melvillei don't seem to have successfully replaced the megatoothed sharks as dominant marine apex predators (at around 36 min), in contrast with the tylosaurines which clearly outcompeted the brutal Cretoxyrhina 80 millions years ago.

I would be very interested to see a proper study about the occurence and respective dominance/competion between the raptorial sperm whales and the Carcharocles lineage.

I had already remarked that megalodon seems to have outlived the large raptorial sperm whales.

Not saying that sharks destroyed the sperm whales but that the predatory mammals seem to have given up since they survived in the form of deep diving squid-eaters specialists.

For know more, we would need to secure the Ica dersert from peru which contains so much material (like an unofficial megalodon skeleton...).

ted said...

Note : I've read some indications of Carcharodon preying on preys items as large or larger than it, bull elephant seals, pilot whales and right whales calves which are quite a match in size for a full grown female Carcharodon :

There is also the rib bone from a large rorqual with a bite marks from what is often suspected to have been a small meg, studied by Kallal and Godfrey. Unfortunately I don't have access to the paper.

Certainly, like most predators, these sharks wouldn't prey all the time on larger preys items, but it seems to me that these indications, while not being absolute evidences, are good hints ?

ted said...

My mistake :

ted said...

Another point (sorry for the multiple posts) that would complicate or facilitate the question, I know that Kent ins his incoming chapter will suggest that megalodon changed its diet and lifestyle the more it grew and that the largest members of the species (18 m +) would have been themselves slow gigantic scavengers intimidating any other scavengers.

ted said...

My point question about the large whales would be : are there some evidences or hints, possibilities, that megalodon may have preyed/ fed on/had the ability to subdue really large baleen whales, below the 5 millions years mark, when large balaenopterids staterd to evolve (Alton Dooley findings, the fin whale-like balaenopterid mentionned by Barnes in the Nat Geo doc, the rib bitten by a smaller shark from a large balaenopterid described by Godfrey and Kalal...) ?

Robert Boessenecker said...

Jeez, where to begin.

I use Carcharocles, because a lot of the taxonomic decisions in Cappetta (2012) are a bit cray-cray. Cappetta has changed his mind numerous times, previously adopting Megaselachus. Carcharocles is really the only stable name that's available; Megaselachus and Procarcharodon are junior synonyms, and Cappetta's choice of using a subgenus for a fossil vertebrate is just... odd, and something that should generally be avoided in vert paleo.

Butch Dooley and Barnes are right that there were larger mysticetes - but they do not appear to have been as common as the smaller varieties. Perhaps it's sampling bias? Maybe, we'd need an entire large analysis to even tell us that. They were certainly less diverse than small bodied mysticetes (~90% of baleen whale assemblages in Miocene).

I don't know Kent and have not heard of his research, but am curious if not skeptical regarding any preservable fossil evidence one could marshal to support any hypothesis for feeding strategy.

I don't have enough time to watch a 40 minute presentation, although I do like Siverson's research. However, the rigorous paleobiologic analysis to demonstrate macroevolutionary interactions between sharks and other marine vertebrates during the Cenozoic simply has not been published. Until it's published, it's just arm waving.

Of course I'm biased, but the macrophagous physeteroids are probably not hyped enough. Livyatan has a 3 m skull with teeth the size of 2 liter bottles... that is something not even paralleled in dinosaurs or marine reptiles (yes, EVEN Kronosaurus, Pliosaurus and Liopleurodon look pathetic next to Livyatan). Certainly more work will always help, but Lambert et al. pretty well demonstrated that C. megalodon and macrophagous sperm whales likely benefited from (and evolved to consume) a surplus of smallish baleen whales during the mid-late Miocene.

ted said...

Indeed, this referral of Cappetta is odd, but I haven't read it yet (the book is 360 euros...) and since it is used recently by Siversson (but he also uses Carcharocles) I guess it is not unreasonnable.

Regarding the macroevolution of lamniforms sharks in competition with others marine groups, sadly most of the time I've seen that a number of potentially valuable and testable datas are never published.

It remains that the various occurence and patterns of dominance can be remarked an that will lamniforms sharks became much smaller and reduced to a few species at the end of the Cretaceous because of the rise of larger tylosaurines forms, the megatoothed sharks do not seem to have known any impact of the rise of the raptorial physeteroids, which, very apparently to me, were much short-lived than C. megalodon (even if this one eventually vanished a bit earlier than usually reported). Once you have time, I really suggest you to check the lecture talk !

Of course, Livyatan is absolutely spectacular and is dwarfing any pliosaur or mosasaur known. Looking at the recent descriptions of P. funkei, P. kevani and the dissertation of Colin McHenry, the largest pliosaurs were in the 10 tonnes body mass range, with only one (P. macromerus) approaching the 20 tonnes range.
He observed that all the apex marine carnivores in history were mostly in the 1-10 tonnes range, including during the Mesozoic, the only notable exception to this pattern being C. megalodon (excluding the teuthivorous S. sikanniensis and P. macrocephalus).
McHenry also pointed on that C. megalodon was gigantophagous and was able to feed on prey potentially as large or larger than itself.
I'm not surprised that L. melvillei, clearly surpassing in size any other marine macrophagous hunter just like C. megalodon, just appeared at the same time, with the rise, diversification and increase in size of baleen whales.

By "hyped", I meant that any new big predator gets its bunch of fame with a number of misconceptions and exagerations about it.

But as an enthusiast of gigantic top predators, I'd definitely enjoy more material from it.

I would be interested in your opinion regarding its sizes estimates, for speaking with various authors (not Lambert et al.) they said that the regression based on a sample of Physeter is likely more reliable since the template, Physeter, is much closer in size range to Livyatan than the 6 m Zygophyseter.

I myself have hard time to envision L. melvillei as a small-headed 16.2-17.5 m raptorial sperm whale (based on Z. varolai isometric scaling), since sperm whales get bigger headed while growing. But I would be interested in your opinion ?

One particular point I've read in lambert et al. (that I couldn't ask him) : they specified L. melvillei to represent "one of the largest bites in vertebrates and certainly the biggest bite for tetrapods".

Does that suggests that will it clearly represents the largest macrophagous tetrapod known (excluding the teuthivorous Physeter), does the fact they listed it as "one of the largest vertebrate bites" in contrast means that its bite may not have matched or exceeded the bite of the macrophagous C. megalodon (since the shark is obviously the only non-tetrapod species comparable in macrophagous habit to L. mevillei) ?

I know this is simply a matter of interpretation but since I couldn't ask to Lambert et al. I would be interested in your understanding of it.

Thank you !

ted said...

Bretton Kent in his chapter will discuss the taxonomy and favor Carcharocles too.

Kent has been featured in a number of doc and research about C. megalodon and has described Parotodus benedeni. There was also the article Hell's Teeth about C. megalodon killing behavior, fully readable here :

ted said...

I had got two observations and sentences from respectively Compagno and De Muizon regarding the predatory apparatus potency in both C. megalodon and L. melvillei respectively.

Christian De Muizon about Livyatan :

"Let us be clear, it could not have tackled a 35 meters blue whale. But there was at that time a large number of small baleen whales specimens measuring between 5 and 7 meters and which were all chosen preys for such a sea monster."

Translated from a french journal, Le Figaro.

Leonardo Compagno about C. megalodon :

"Compagno (1990b:57) hypothesized that Carcharodon megalodon "may have been capable of preying on large baleen whales without the cooperative pack-hunting tactics that the smaller killer whale apparently needs to use to subdue difficult prey....Various reconstructions of the jaws of C. megalodon...suggest that this shark had a predatory apparatus capable of inflicting mortal injuries on even a fin whale or blue whale."

The Neogene Sharks, Rays, and Bony Fishes from
Lee Creek Mine, Aurora, North Carolina
Robert W. Purdy, Vincent P. Schneider, Shelton P. Applegate,
Jack H. McLellan, Robert L. Meyer, and Bob H. Slaughter"

Based on this comparison of predatory apparatus, that's why I would think likely (but not demonstrated beyond any doubt) that megalodon eventually "won" the ecological battle for supremacy in the Miocene/Pliocene, the evolution of physeteroids into deep divers specialists and the fact that no impact on the C. megalodon population is known from the rise and fall of various physeteroids, including the spectacular L. melvillei.

ted said...

Also (once again sorry for the multiple posts), what would be your educated guess regarding L. melvillei body mass ?

Of course that's quite tricky, however, looking at the dedicated exhibit in Lima, November 2011, I've read and heard from one of the describers something around 30 tonnes.

Robert Boessenecker said...

Siverson has sort of used it, although in his APP paper published a couple weeks ago, he used Otodus (Megaselachus). Again, in my opinion, and the opinion of numerous other shark workers I've spoken with about it recently (D. Ehret, M. Gottfried, D. Long), Carcharocles (Ehret, Long, myself) and Carcharodon (Gottfried) are far more stable than the more recent uses proposed by Cappetta.

Regarding Olivier's point in the Livyatan paper - my guess is that he left that open because of such beasties like C. megalodon, which would have probably been similar in overall size/total length or slightly smaller.

Regarding body size estimation - the Physeter based estimation is a bit smaller (13+ meters), and much of this is based on the differing skull proportions of Physeter and Livyatan. Obviously, using a closer relative is going to improve matters - which is why the larger estimate based on Zygophyseter is probably more accurate, although seeming absurdly enormous.

Body mass is actually probably a far less useful index in paleontology. Body mass changes from season to season, and depends upon the health of the animal. In many studies of vertebrate paleoecology, body size is more conservatively reflected by total length, so I tend to not bother with mass estimates.

Alternatively, the decline of gigantic sperm whales could also be due to decreasing diversity of small bodied baleen whales during the Mio-Pliocene transition.

ted said...

Fair enough regarding the taxonomic point.

"Regarding Olivier's point in the Livyatan paper - my guess is that he left that open because of such beasties like C. megalodon, which would have probably been similar in overall size/total length or slightly smaller."

That's indeed what I thought too.
However, I'm not sure that C. megalodon grew smalightly smaller. Based on the available evidences (upper size estimate range among various authors and works), the largest C. megalodon grew larger than the largest estimate of L. melvillei based on the upper estimate of Z. varolai. Still they overall are in the same ballpark, but it doesn't seem that Livyatan has outclassed C. megalodon in its largest accepted estimates.

A new method, published by Siverson soon, is based on the total upper teeth width (jaw perimeter) using as template not only the white shark but also others lamniforms such as the mako and the porbeagle and applying this on the complete set of teeth owned by Gordon Hubbell.
The method will be used in a paper about Cardabiodon, I don't know if he will discuss C. megalodon, but from his talks and my discussions with him, I know he obtains a maximum size of almost 20 m.

Fair enough regarding the size estimate. The main problem I've heard for Zygophyseter is the basis on a much smaller taxon, increasing the potential error by linear scaling. I don't think L. melvillei was as short as 13.5 m but I don't see it as an exact 16-17.5 m version of Zygo. Given that physeteroids gets bigger headed while growing up.
Don't get me wrong ! I'm not biased toward Carcharocles (the bigger the better I must admit as an amateur enthusiast). But the fact that L. melvillei shows a skull width of 1.9 m (which is monstrous for sure, bulkier than a similar long Physeter skull), whereas conservative estimates of C. megalodon jaws width alone are around 1.8-2.1 m, disturbs me when I read claims that the giant physeteroid was perhaps larger.

When you were saying that " C. megalodon could have probably killed any fossil cetacean, and most extant cetaceans with one bite", were you also including L. melvillei ?

Regarding the extinction of the giants raptorial sperm whales, certainly I admit there would be multiple factors.
But why the decreasing diversity of small mysticetes would have affected something like L. melvillei and S. oxymycterus whereas C. megalodon as a contemporary top predator potentially vulnerable to the same phenomenon would have survived...?

I think interestin to remark that there was no replacement of the sharks by the contemporary physeteroids, in contrats with what happened during the Late Cretaceous (tylosaurines and mosasaurines grew larger, Cretoxyrhina goes exctinct and lamniforms sharks become no larger than 3-4 m) or during the Early Cretaceous (the rise of the large, stocky Cardabiodontids coincides with the slow decline of the pliosaurs in the same niche...).

ted said...

Or perhaps have you some suggestion that Livyatan was even larger than what is published ?

I've found this link, the only tooth sold in private collection :

ted said...

I have missed the body mass point.

I fully agreed that body mass has too muc variation depending on a number of factors. But I still see that these are used as mean values in a number of works. McHenry uses body mass range in his dissertation about the macroevolution patterns of oceanic apex predators.

I guess that since in two similarly long species, one can be naturally bulkier and usually heavier at parity (let's compare a porbeagle shark with a mako), body mass can be an interesting point.

In the case of L. melvillei, I would be curious if its body mass was lower, similar or superior than a Physeter. I know its skull is wider at a same length, but I doubt it is has high (the spermaceti chamber is obviously much larger in Physeter), thus I was wondering if that "around 30 tonnes" quote from Lima was justifiable.

Robert Boessenecker said...

Gottfried et al. (1996) estimated C. megalodon to be ~16 meters in body length, and Shimada (2003) has an estimate that is about 14 meters. That's smaller than the estimate by Lambert et al. for Livyatan based on scaling with Zygophyseter (~17 meters), hence my statement.

The issue isn't really with applying body mass to fossil vertebrates, it's interpreting what body mass means in living vertebrates. The interface between body size and ecology is where we make inferences about fossils, using fossil body size estimates to inform us about paleoecology. Modern marine mammals - and most vertebrates - have seasonally varying body masses, although their skeletal lengths do not vary. Therefore, to have any sort of useful discussion about body size and paleoecology, skeletal length is what we really want to talk about. See Pyenson and Sponberg (2011) for more on this:

Lastly, I'm going to make a request that you post in a single comment, it will make following your writing much easier.

ted said...

Thank you for the link and sorry for the multiple posts again.

Regarding C. megalodon estimates, having longly looked at it, Gotfried estimate of 15.9 m was a conservative maximum based on a large tooth and a sample of white sharks as templates, but was not intended to represent the maximum size in the species, which he suggested by direct sizing with the largest alleged white sharks. He figured a max of around 20.3 m. Darren Naish mentionned it in the article.

Shimada predicted 14-15.1 m but Pimiento using his method predicted 16.8 m for one individual in the Gatun nursery (2010), hence I was doubting that Shimada (and Gottfried) represented a maximum estimate in each case.

But I have a limited trust in these methods, in that tooth height appears highly unreliable, and that these are based on only C. carcharias as model, which is not so related.

However, the method based on upper jaw perimeter, soon published about Cardabiodon ricki, bases not only on the great white datas but also on others lamniforms potentially more related to C. megalodon. Since it can be used through the complete set of teeth of Gordon Hubbell and that there is a strong correlation between jaw perimeter and total body length, I think this is more reliable (or least worst) than methods based on tooth height. Once again, I ignore if the paper will discuss C. megalodon size, nor the details yet but having looked at Siverson talks I know he estimates the owner of the complete set in Hubbell's collection to have been around 11-12 m, and using isolated larger teeth, he came up with lengths around 19 m TL. I know the paper discussing this method is going to be released in the month to Acta Palaeontologica Polonica.

Despite the uncertainties, I guess they were both reasonnably in the same ballpark, I tend to make an analogy with Pseudorca and Carcharodon today, in terms of biology and ecology.

Are you aware about any new paper regarding L. melvillei's related works ?

ted said...

I've seen that you're finishing a paper listing C. megalodon extinction earlier than usually listed (4-3 millions years I think).

Does this will change the usual reasons given to the demise of the shark (Ice Age = ocean level drop = destruction of C. megalodon nurseries = cannibalism/Ice Age = new patterns in whales migration toward polar regions = unavailability of appropriate preys for C. megalodon = starvation, cannibalism, competition from smaller, less vulnerable predators) ?

Some suggested that the occurence of new larger balaenopterids in the Pliocene would have prevented C. megalodon to attack new larger preys, but if Compagno is right in that C. megalodon would have had the ability to subdue even the largest modern whales, I guess these speculations are unlikely ?

Or perhaps, while size of these preys wouldn't prevent such a large predator to prey on them, their more advanced biology allowing to reach great speeds, would have posed a problem to the giant shark ?

ted said...

Hello Robert,

Regarding whales size in Pliocene, I was discussing with Stephen Godfrey about the ~3 millions years old rib bone from a large balaenopterid showing failed predation, quite possibly from a juvenile megalodon, given the presence in the area of teeth from juveniles of this species and the common association of megalodon teeth with mysticetes bones though the possibility of a large individual of another lamnid species was suggested, as well as, at a lesser extend, the possibility of some macrophagous odontocete...
As megalodon seems to have lasted longer in the Atlantic than in the Pacific like you suggested, that seems reasonnable to me.

After reading Kallal et al. I asked the approx. dimension of the balaenopterid to Godfrey, and he responded me the size of a living fin whale.

I guess that gigantism started to seriously occur and becoming common at this time among mysticete ?

Also, I don't have the details yet, but discussing with french interested who had the occasion to read the update of Cappetta (2012), it seems that the status of Otodus for megalodon (and its ancestral forms so) is solid.

Sadly I have to admit I don't have the mean and time at now to buy the book (370 euros !).

Darius Nau said...

This is sort of an old discussion, but these are the papers in question:

Using the toothrow-regression from Lowry et al. 2009:
(it’s the first result, posting the pdf-link direction somehow won’t work)

The problematic variable is tooth-spacing within the toothrow, which is somewhat variable. However it is constrained by the function of those teeth in cutting.

going by this jaw:
which appears to have similar spacing to typical modern C. megalodon jaw casts, an appropriate percentage to add to the summed tooth widths seems to be ~15%, though I know other jaws that have no spacing at all.