Top Dog

[theropod]

Feb 6, 2015 21:53:03 GMT 5 Life said:

As for the sperm whale (P. macrocephalus), its sheer size is an impressive anti-predator adaptation but people tend to take Moby Dick related depictions in the movies too seriously. Sperm whales (P. macrocephalus) aren't mindless animals with total disregard of their safety, they are intelligent and social animals like other whales and they care for their young. Adults assume protective roles during times of danger because they are more likely to survive attacks then the younger ones, should a pod run into macro-predators.

To me that sounds like a good thing. Aggression can only bring you so far, "total disregard for safety" is a bad strategy in any case. Sperm whales can be agressive tough.

Their is not a single animal which an adult Megalodon cannot kill with a few bites.

That’s true, but there also isn’t a single animal that would not sustain life-threatening injuries if a 24m Physeter crashed into it. Such a sperm whale would be a very dangerous opponent for pretty much anything that ever lived, including 18-20m Megalodons.

Very large whales might take some minutes to die but they will eventually from major loss of blood. Their is evidence of Megalodon being very aggressive in its attacking strategies, but this shark was smart (intelligent) enough to modify its hunting tactics in accordance with the nature of prey.

Making specific statements about the intelligence of an animal of whom not even a braincase is known seems pointless.
As you remarked so astutely earlier in your post: "its capabilities will never be fully realized from its fossilized records"

If you want to compare intelligence by inference from relatives, it’s cetaceans that will almost certainly come out on top by a large margin, with pliosaurs and sharks following, but that is not particularly relevant in the majority of situations.

[Grey]

I m currently investigating about the giants Peterborough vertebra. Yes there's not only one but two actually. It seems like a number of pliosaurs experts, including those who reidentified it, still believe it is from an extremely large pliosaur. Martill believes it came from a 18-20 m Liopleurodon unknown species individual. And he still suggests that the chances are very slim for that this individual was the largest of its species. Hence, he still considers 25 m as a hypothetical upper limit for this mysterious 'Megapleurodon'.

I m searching for more, it is possible that McHenry was wrong regarding the vertebra he studied.

My point is that if there's indeed one unknown Liopleurodon species reaching on a regular basis 18-20, the upper size of megs and the range of already large male Physeter, on theoretical grounds it could be the largest predator ever.

One can estimate the bite force in a 20 m pliosaur... Martill thinks 40 tons would reasonnable.

[theropod]

That’s interesting, where have you found that information?

It is ridiculously unlikely that this is the largest of its species, there’s not really a debate on that matter. The question is what to take it for, and what species it really is (that requires a proper descrption). In any case, the 25m figure is pulled out if thin air, it’s like saying that Carcharodontosaurus reached 18m long because SGM DIN-1 certainly wasn’t the biggest of its species. That we don’t know the largest individuals of a species doesn’t mean we should make up their sizes. Livyatan would have a similar upper limit following that logic.
Without large population samples there’s no way of knowing these things, all we can think in are comparisons (in that case the comparison would imply a higher average size, given that these size estimates are really correct).

IIRC McHenry didn’t actually contemplate the issue of whether the vertebra was a pliosaur’s or a sauropod’s with any evidence, he merely pointed out both were possibilities and expressed scepticism of its relevance for pliosaur size. The more interesting question regarding him would be whether his size estimates were too low, because they don’t actually imply something all that gigantic even at the upper end.

Regarding bite force, the in vivo skew should be taken into account, but recent bite force estimates for P. kevani could help too, especially in comparison to other dry skull estimates.
Based on McHenry’s proportions for Brachauchenius lucasi (but it could be problematic to assume these) a 20m pliosaur would have a skull over 4m long, which is more than double that of P. kevani. That would imply a bite force over 4 times higher, or 19.3t+ at the 36th tooth position. If you make an estimate based on a crocodilian, it’s quite reasonable that it would be twice that, but the difference between both and between the methods used has to be considered.

An impression I’m definitely getting is that Martill and Forrest are a lot more liberal about pliosaur size than McHenry.

[coherentsheaf]

Feb 7, 2015 20:30:07 GMT 5 creature386 said:

While aggressiveness is an advantage, a sperm whale of that size will be dangerous once it starts attacking. I don't exactly how hard it can ram, but coherentsheaf mentioned that the ram of a that large sperm whale would be enough to finish a Megalodon without problems.

not so sure about it any more. It is possible though.

[Grey]

That’s interesting, where have you found that information?

Discussions with Leslie Noé and Dave Martill. I showed some of the conversations to coherentsheaf. Both believe the vertebra are pliosaurids.

The question is what to take it for, and what species it really is (that requires a proper descrption). In any case, the 25m figure is pulled out if thin air, it’s like saying that Carcharodontosaurus reached 18m long because SGM DIN-1 certainly wasn’t the biggest of its species.

How large is supposed to be that Carcharodontosaurus specimen ? If it's 14 m, 18 m as upper estimate is more stretched than 24-25 m for a ~20 m unique pliosaur. Plus, the size of that Carcharodontosaurus specimen itself appears doubtful to me but I'm maybe off.

That we don’t know the largest individuals of a species doesn’t mean we should make up their sizes.

Martill certainly admits this is not a scientific way to go but this is his guess that there were few very large individuals of giants pliosaurs.

I'd quote him from the book Chased by Sea Monsters about that :

That something far, far bigger than cryptoclidus, ophthalmosauus, or metriorhynchus hunts in these waters is obvious from the occasional partial skeleton on the seabed: here and there a complete tail, without a single bone from the rest of the body; elsewhere a head and forelimbs, with no trace of the tail. These are remains of animals as much as 6 metres (20 feet) long that have been quite literally bitten in half. Only a few times in its history has Earth witnessed a predator anything like the size of the culprit. Large male Liopleurodon can reach 21 metres (70 feet) long, and there are thought to be a few exceptional individuals out there that touch 25 metres (82 feet). No one knows for sure, but teeth marks have been found in the bones of prey that can only have been made by a pliosaur that big. This is double the length of the largest land predator of all time, the dinosaur giganotosaurus, which measures a meager 12 metres (40 feet) from head to tail. In the sea, though, animals can grow to be a whole lot bigger and there are one or two marine predators in the same range as Liopleurodon. Sperm whales over 21 metres (70 feet) long have been found, and in the Triassic some ichthyosaurs knock on 25 metres (80 feet). But while sperm whales and ichthyosaurs prey on things like squid, Liopleurodon is equipped to kill much larger animals, making it a meaner monster all round. The head alone is over 3 metres (10 feet) long and home to a fearsome collection of dagger-like teeth, the longest of which are at the tip of the snout.

I strongly think the 'large male Liopleurodon' represent the isolated Peterborough vertebra.

Livyatan would have a similar upper limit following that logic.

While I agree this can be applied to Livyatan as well, I have more difficulties to envision a 24 m Livyatan for now.
Livyatan's holotype range is still 13.5-17.5 m. The range of this pliosaur is 18-20 m (Martill saying 18 m is realistic, 20 m is the upper bar error).
So if this estimate for the pliosaur is accurate, it is larger than the Livyatan holotype.

Because of this, I more easily envision larger 24 m individual than the same in Livyatan.

This guess can also be applied to a lesser extent to megalodon. Of course, its fossil record is vast, but the possibility to found larger teeth from larger individuals is still there. But for now I have the feeling, from the available data, plus the various estimates I did myself on privates teeth, that the maximum size is going to level off at 18-20 m. And I suspect that Pimiento's data will establish 18 m as the maximum size for the species.

On the other hand, it that pliosaur and the estimates are confirmed, we have one individual well within that range.

IIRC McHenry didn’t actually contemplate the issue of whether the vertebra was a pliosaur’s or a sauropod’s with any evidence, he merely pointed out both were possibilities and expressed scepticism of its relevance for pliosaur size. The more interesting question regarding him would be whether his size estimates were too low, because they don’t actually imply something all that gigantic even at the upper end.

For discussing with the two pliosaurs specialists, I suspect (but do not confirm yet), that McHenry has maybe done two errors :

- he used Kronosaurus as model, whereas Noé says using a Cretaceous, differently proportionned brachauchenid to estimate the size of a Jurassic pliosaur is probably inaccurate. Using Liopleurodon is more appropriate in his opinion. I guess Martill would say the same as he refers to this mysterious pliosaur as a Liopleurodon species (both are Callovian).

- he assigned the vertebra as being a cervical but Martill said both vertebra are thoracic.

So far, I've used the Tübingen 5.3 m reportedly subcomplete Liopleurodon specimen from which the thoracic vertebra are 70 mm wide. One of the Peterborough vertebra is reportedly 252 mm>>> 19 m TL.

Certainly I need to check this further but that's certainly way larger than McHenry's estimate based on Kronosaurus.

I also need to know the size of the second vertebra (for some odd reason overlooked by McHenry). Noé said me he saw similar sized vertebra from private collections.

I really doubt that several vertebra would be actually those from a sauropod.


Regarding the bite forces, I had suggested this figure to Martill and he simply agreed on it. But I had indeed calculated that based on P. kevani, the bite fore would be more around the 20 tons.

That's something I've always found odd. Pliosaurs like Liopleurodon are often said to possess one of the most powerful, if not the most powerful, predatory skulls to have ever evolved. And yet a 20 m pliosaur would bite barely stronger than a similar-sized megalodon, in which the great bite force is said to be essentially a consequence of its large size rather than the bite itself ?

A bite force from some Liopleurodon skulls would be interesting to check as well.


Forrest actually has some reservations on this even though he suggested such sizes on his website and apparently said to Max Hawthorne (the novelist I talked about earlier) that in his opinion and the opinion of his colleagues, 20 m pliosaurs in the Late Jurassic are likely.

[theropod]

If it is 13m, which is conservative, then 18m would be just as much or little of a stretch as 25m for a pliosaur with an 18m specimen. It could also be 14m, and 20 for the pliosaur, but you get the picture, the difference between both ranges is not big.

Any size estimate is doubtful to a degree, but as far as I'm concerned this one is atm a lot more reliable than 18-20m pliosaurs.

As for Livyatan, as with the Physeter-based estimate you take into acount, you have to consider a different size estimate could bbe lower. Case in point, McHenry's estimate is almost a perfect analogy, using an animal closer in size but more distantly related, and is includes two figures below 14m. What we end up with are two roughly comparable size ranges, although the pliosaur's is a bit wider, because it's more fragmentary and poorly described.

13.5-17.5 vs 11.6-19

As I wrote, correction for the in vivo difference could change the result significantly. But also, remeember the 18-something kN estimate for meg was for a 103t specimen, which is more than a 20m megalodon would most likely mass (and more than what a pliosaur would mass at any rate).

[theropod]

About that quote: the evidence we're discussing here notwithstanding, but I've got my doubts, cconsidering what kind of source it is from and that the skull lenght it gives for such a pliosaur seems significantly underestimmated.

In fact, replace skull lenght with mandible lenght, and what you get is McHenry's 12.7m P. macromerus, not a 20m+ monster. The difference is certainly present, but again, you get the picture, a 20m pliosaur would rather be expected to have a skull "over 4m" than one "over 3m". So if these bite marks suggest something with a skull 3m or slightly bigger, the most parsimonous explanation is not a 25m beast.

[Grey]

I mainly use the 20 m upper range for envisioning a hypothetical 24-25 m monster. That appears to me less stretched than a 18 m carcharodontosaur. Plus, the difference with theropods is that pliosaurs are mostly believed to have undeterminate growth (but Naish suspects otherwise). Even if this can be applied as well to any theropod. But to a lesser extend IMO.

I conceive that 18-20 m is hard to believe, but still there are paleontologists who believe it because of various factors. And I agree that using Kronosaurus skeletal parts for a Jurassic, differently proportionned pliosaur, can be problematic.

IIRC, your revision of the body mass for megalodon were only slightly lower than those in Gottfried so I still think we can't dismiss this figure.

My point is that pliosaurs are said to have very powerful bites, sharks are said to have not so powerful bite. But at similar size (a 20 m pliosaur would weigh about 90 tons using McHenry volumetric models, which is quite close to the meg's estimate), they would bite with a similar strength ?

Definitely, there's something odd here.

[Grey]

As for Livyatan, as with the Physeter-based estimate you take into acount, you have to consider a different size estimate could bbe lower. Case in point, McHenry's estimate is almost a perfect analogy, using an animal closer in size but more distantly related, and is includes two figures below 14m. What we end up with are two roughly comparable size ranges, although the pliosaur's is a bit wider, because it's more fragmentary and poorly described.

13.5-17.5 vs 11.6-19

Excluding respectively the distantly related Kronosaurus and Physeter, the Peterborough pliosaur is still larger than Livyatan. Plus, my 19 m figure is only one of those possible, that's just an estimate I've made based on one Liopleurodon specimen. The original size estimate range (using the 13 m estimate for the Harvard Kronosaurus, which is likely after all according to Roger Benson) was 17-20 m.

So the plio is still somewhat larger to me (as of now).

In one email, Buchy said too that the vertebra, if pliosaurid, would have come from a 20 m pliosaur.

About that quote: the evidence we're discussing here notwithstanding, but I've got my doubts, cconsidering what kind of source it is from and that the skull lenght it gives for such a pliosaur seems significantly underestimmated.

In fact, replace skull lenght with mandible lenght, and what you get is McHenry's 12.7m P. macromerus, not a 20m+ monster. The difference is certainly present, but again, you get the picture, a 20m pliosaur would rather be expected to have a skull "over 4m" than one "over 3m". So if these bite marks suggest something with a skull 3m or slightly bigger, the most parsimonous explanation is not a 25m beast.

You forget that Jurassic pliosaurs are assumed to have a different ratio between body size and skull than Cretaceous pliosaurs. Hence, it still possible that McHenry's estimate for the Cumnor mandible is off (assuming the reconstruction is correct). Noé still estimates the Cumnor monster to have been +17 m.
Anyway I wasn't referring to the jaws size figure in that quote but to the size of the "male Liopleurodon". Originally, WWD gave a skull length of 4 m for the 24 m Liopleurodon. Th ratio used here or by Noé or others Jurassic pliosaurs specialists is 1.6, not the ratio used by McHenry.

On a side note, I'm not sure I'd call McHenry that conservative, at least he wasn't always.

He considered pliosaurs with "in engineering terms, the skull is the most powerful raptorial feeding apparatus developed by any vertebrate".

When Predator X was annunced, at the first he considered it "this thing is likely to have been both the biggest biting carnivore of all time, and the biggest carnivore of all time."

And here's the original abstract of the reidentification of the Peterborough vertebra :

Just when you thought it was safe to go back to the water - the biggest pliosaur yet
COLIN McHENRY, DAVID MARTILL, LESLIE NOE AND ARTHUR CRUICKSHANK

Department of Zoology, University of Queensland, St Lucia, Brisbane, Queensland, Australia2
Department of Geology, Portsmouth University, Burnaby Building, Burnaby Street, Portsmouth

Divisions of Geology & Biology, School of Environmental and Applied Sciences, University of
Derby, Kedleston Road, Derby

Earth Sciences Sector, Leicestershire Museums Service, College Street, Leicester and Department of
Geology, University of Leicester, University Road, Leicester
Kronosaurus from the Albian of Queensland, estimated length c. 13 m, has always been regarded as
the largest pliosaur. Historical records of Oxford Clay (Callovian) faunas have indicated that another
large pliosaur lived earlier (Middle Jurassic - Early Cretaceous). Comparisons of Kronosaurus with
this historical material show that the cervical vertebrae of the Jurassic form were about 40% larger
than Kronosaurus. Estimates of the overall length of the new form range from 17-20 m. This equates closely with modern whales and is larger than
extant toothed whales Orca and Physeter.


Of course he may have revised some points during his dissertation but I'm not sure if he's still of the same opinion as of now. I had asked him about pliosaurs size, and while he has not responded yet, he said me the question is "very interesting but thorny". So, not sure if his thesis mirrors his definitive belief about that.

[Grey]

Regardless, what is the opinion of anyone regarding the thread question ?

[theropod]

Excluding respectively the distantly related Kronosaurus and Physeter, the Peterborough pliosaur is still larger than Livyatan.Yes, a little. Still, you get what I mean, if we assumed 25-39% larger size for any  taxon known from single or very few specimens (that really depends on whether this is really a new species), then we would also have to assume 22-24m Livyatan and 16-19m Carcharodontosaurus. I just want to show what it leads to, baseless speculation. How useful can that be?
Also you have to consider the size estimates for this pliosaur are even more tentative, being known only from two vertebrae only one of which a measurement is known from, without even being 100% certain its a pliosaur. So there are even more assumptions involved here.

Plus, my 19 m figure is only one of those possible, that's just an
estimate I've made based on one Liopleurodon specimen. The original size
estimate range (using the 13 m estimate for the Harvard Kronosaurus,
which is likely after all according to Roger Benson) was 17-20 m.

I took that figure because it was the only one there was an actual estimate for (the one you provided). For all we know, the others could be an arbitrary range, or mere guesses.
Could you remind me of why that 13m Kronosaurus is still likely? I seem to recall you posted the information earlier.

You forget that Jurassic pliosaurs are assumed to have a different ratio
between body size and skull than Cretaceous pliosaurs. Hence, it still
possible that McHenry's estimate for the Cumnor mandible is off
(assuming the reconstruction is correct). Noé still estimates the Cumnor
monster to have been +17 m.

I didn’t forget that, just wanted to point out the discrepancy. I think I’ve already posted that tetzoo post where Naish suggested the same.
EDIT: here it is: scienceblogs.com/tetrapodzoology/2007/12/15/cumnor-monster-mandible/

On a side note, I'm not sure I'd call McHenry that conservative, at least he wasn't always.

I didn’t actually call McHenry conservative, I called the others liberal. Although for our intends and purposes, that’s not much of a difference.
It depends on how you define conservative tough. Conservative is not necessarily the lowest estimate, it is the most parsimonous estimate. It is also possible to be liberal and come up with a very low estimate, it’s just rare.

In that sense, I’m currently undecided about his lenght figures, I’d really like to see the description of that Tübingen Liopleurodon (Was it really 5.3m long? Buchy’s thesis states 5m IIRC, and I seem to recall figures indicating it was rounded up) and perhaps some more evidence that pliosaurid pliosaurs had smaller skulls than brachaucheniids before I do, but I think his pliosaur weight estimates are conservative as in "the most reliable for now", frankly because estimates of 30t or similarly low figures for 18m pliosaurs as have been proposed earlier don’t seem in accordance with their morphology (remember coherentsheaf’s GDI on Rhomaleosaurus, which also indicated that these estimates were far too low).

Thanks for the abstract. It definitely predates McHenry’s thesis, but it’s possible his emphasis was just on the better remains, after all it’s main focus was Kronosaurus.

About Bite Force:
Of course, depending on the skull lenght of the pliosaur, this is not conclusive at all at the moment. But for C. megalodon, the mean estimate from regression equations which I posted elsewhere suggests 89.9t for a 20m meg, while isometric scaling from McHenry suggests 75.4t for a Pliosaur of that lenght. So the Megalodon is somewhat heavier, although not astronomically, and its bite force would be 16.4t at the back of the toothrow when scaling from Wroe et al. 2008. Scaled down to the same weight as the pliosaur, the shark’s bite force would be 14.6t. So at the same size, the pliosaur would bite about a third harder, possibly more based on what Forrest wrote. But we really need to get a compatible size estimate for the weymouth bay pliosaur in order to get reliable figures.

Reference:
Wroe, Stephen; Huber, Daniel R., Lowry, Dayv; McHenry, Colin R.; Moreno, Karen, Clausen P.; Ferrara Toni L.; Cunningham E., Dean, Mason N.; Summers, Adam P.:    Three‐dimensional computer analysis of white shark jaw mechanics: how hard can a great white bite?.    Journal of Zoology,    Vol. 276    (2008);    4;    pp. 336-342

[Grey]

I use for the Peterborourgh pliosaur the range of 18-20 m (or 17-20 m for that matter), the range considered likely by Martill and based on the original estimate.

Using the upper range, I have no real difficulties to envision a 24 m pliosaur, way easier than from a 17.5 m Livyatan. Comparatively, using a 20 % larger hypothetical specimen, this is 24 m pliosaur against 21 m Livyatan. And 16.8 m for the carcha specimen you talk me about (if it really is 14 m).

I'm not too much in these hypothetical upper sizes, I just posted Martill guess. If you want to have an argument about this, this is with him, not with me.

I certainly assume, here and now, it is pliosaurid. Of the original team, only McHenry revised it in his thesis, and I don't know his current opinion on this. Noé, Martill and the late Cruickshank all considered it pliosaurid. So I certainly await for more information from McHenry, but as of now I'm definitely reconsidering the case, and whillingly exclude McHenry estimate based on the revised size of the potentially anatomically different Kronosaurus.

A 13 m Kronosaurus is likely according to Benson because people are often dissmissive of the MCZ specimen, calling it "Plasterosaurus" for example but Romer & Lewis provided measurements of some of the individual vertebrae, and also explained how their length measurement for the postcrania derived from articulated lengths in the field jackets. So he thinks it is harder to question than is often said.

Anyway, that's possibly irrelevant to the discussion here.


Yes, Naish who closely worked with Martill (they co-wrote an article about "Megapleurodon"). Noé argues too we have to use a 1.6 ratio for Jurassic pliosaurs.
So, here I don't use the Cretaceous ratio proposed by McHenry for Jurassic pliosaurs.

In the first description of the Aramberri pliosaur, Buchy reports the Tübingen skeleton at exactly 5.3 m. So I assume the 5 m figure for her thesis is lower rounded. Also, it is reportedly subcomplete.

Note that using that precise measurement of the skeleton scaled to the femoral head size in respective specimens, you get exacly 17 m for the Aramberri pliosaur.

Anyway, the Tübingen Liopleurodon is reported uncatalogued, so no formal description available. Buchy's data is based on pers. observations.

Yes, I agree that 30 tons estimates for a 18 m pliosaur are definitely more fitting for a mosasaur shaped animal.


I have to say, on this topic I'm not too much interested in the body mass estimates. Both in megalodon and pliosaurs, there's a vast possibility. Siversson estimates a 18-20 m Megalodon would weigh 50-60 tonnes. Gottfried's data is higher. Same with pliosaurs, Forrest's 8 m, 8 tonnes Rhomaleosaurus suggest McHenry's weight range could be in the lower limit. So I would simply state roughly that at similar size, they would be similar in weight (even if probably untrue in absolute terms).

But even with your adjusted calculation, I find the pliosaur bite force lower than expected. A saltwater croc theoretically 3 times lighter than a 3.3 tonnes white shark bites almost twice harder.

What did Forrest write ? If you refer to his article where he suggests 50 tonnes bite force for P. kevani, he rejects it as now.

If you refer to the previous articles where he explained that pliosaurs were more powerfully jawed than crocs, yes that's intriguing.

Pliosaurs are often said to have the most powerful biting apparatus known but strangely the bite forces estimates resulted in litterature, though high, are not as monstrous as expected.

[Infinity Blade]

I'm still kind of in shock that a (~6,000kg) Kronosaurus supposedly has a weaker bite than a Tyrannosaurus about its size (~30kN vs. ~35-57kN) honestly (though these were apparently conservative estimates). Same with P. kevani (~32-48kN vs. ~35-57kN).

[Grey]

Here's what Forrest said :

"If you compare the skull of a large pliosaur to a crocodile, it is very clear it is much better built for biting... by comparison with a crocodile, you have something like three or four times the cross-sectional space for muscles. So you have much bigger, more powerful muscles and huge, robust jaws."

[creature386]

Feb 8, 2015 20:08:41 GMT 5 Infinity Blade said:

I'm still kind of in shock that a (~6,000kg) Kronosaurus supposedly has a weaker bite than a Tyrannosaurus about its size (~30kN vs. ~35-57kN) honestly (though these were apparently conservative estimates). Same with P. kevani (~32-48kN vs. ~35-57kN).

Same here. I prefer Forrest's numbers (5 to 15 t for a P. kevani; even though the higher end sounds a bit too high).