Would a 15-18 m hypothetical pliosaur...

[theropod]

I must correct myself, Rice et al. themselves made in vivo measurements, but they didn’t base their regression on in vivo measurements, at least not for the most part. They did use in vivo data for two of the ten shark taxa in their sample, one of those being the one whose bite force they measured themselves, but that’s all. In fact, they include Carcharodon, namely Wroe et al.’s estimate, in that dataset. The higher value seems to be a result of allometry between those taxa, not because of a method giving higher results.

Obviously incorporating figures achieved using such different methods might create some major problems for the reliability. Also they opted for a weird polynominal function (y=0.0468x²-6.8577x+282.05) rather than a normal power curve. At first glance, this makes sense, because it fits the data, But the resulting relationship is biologically a little absurd, even if it fits this particular (small!) sample well, because it implies inverse correlation between size and bite force up to its minimum at 73.3 cm TL before it rises again. A 73 cm shark would be predicted to bite with just 30 N, but funnily enough a 7.3 cm shark would bite with 234 N. This may be representative of their sample, but it certainly wouldn’t be representative of sharks in general, so it’s an artifact of their sample, not the real relationship.
This choice of model may or may not have major effects on estimates for larger taxa, but I think it’s safe to say that we shouldn’t assume a generalized relationship implying that bite force decreases with size in small sharks, especially not based on such a small sample, and we should try to fit a biologically plausible model to the data, especially if we want to extrapolate from it. If the relationship is already absurd when applied to a generalized shark within the range of sampled sizes, that doesn’t exactly improve my trust in it when applied to something several times longer than any of them.

Still even that wouldn’t eliminate the problem of incorporating data from different methodologies (as well as vastly different feeding styles, this problem gave us Meers’ 2002 20+ ton T. rex bite) into one regression.

So sadly, these estimates for meg aren’t good figures to compare to anything after all. I wish there was a solid set of in vivo measurements for some halfway-comparable extant shark species, but that doesn’t seem to be the case The only ones with in vivo measurements were the Bonnethead shark and of course the Atlantic sharpnose shark, both arguably far too small and ecomorphologically distant to be useful proxies.

Seemingly crocs/pliosaurs remain the only large predators taxa where we can wager a good guess as to in vivo bite force.

[theropod]

Sept 19, 2019 1:23:07 GMT 5 dinosauria101 said:

theropod

I meant jaw size, not bite force. Sorry if that was unclear

I was replying to grey, not you. Anyway, jaw size alone has the same problem. Gharials have huge skulls and jaws. Archegosaurs, Phytosaurs and Pholidosuchians much more so even. That doesn’t mean they were all particularly potent biters.

Generally speaking, a predator adapting to cause large amounts of mechanical damage falls somewhere on a spectrum between specializing in cutting capacity, and in blunt force application (though the total extremes of either aren’t really found in macrophagous predators). This classification is imperfect, but generally adequate. In either case, the jaws don’t necessarily have to be excessively large to be very damaging, as long as they have the means to cause a sufficiently large wound (e.g. by pulling) or affect a sufficiently large part of a vital structure (e.g. crushing a spinal chord or skull).

Meg is more on the slicing side of the spectrum, pliosaurs are more on the blunt side.

[dinosauria101]

Oh, OK.
But didn't pliosaurs have cutting dentiton?

[theropod]

As I said, it is a spectrum, and the absolute extremes don’t really exist, at least not among macropredators. You won’t find a predator that is not producing some degree of force or doesn’t have any adaptation for focusing force on a small area. Just some specialize more in increasing the cutting efficiency, and some more in maximizing the bite force. But you cannot go in both directions at the same time, razor-sharp, blade-like teeth and massive, bone-pulverizing bite forces don’t mix, so there is no "best of both worlds", at best there is an optimum function space where most predators tend to fall, or a morphology particularly suited to a particular situation.

T. rex also technically has a cutting dentition. Pliosaur teeth would vary in their cutting capacity depending on the taxon (higher in trihedral-toothed Pliosaurus, lower in conical-toothed Liopleurodon), but they are far too thick to be very efficient cutting tools. Their shape and size strongly resembles T. rex. As I said I think they would be somewhat comparable in function. More of a puncturing and crushing/shearing than a slicing function. Not surprising given their likely T. rex-like bite force.

[dinosauria101]

Yes, seems more logical now that you put it like that.

[Grey]

What would be the posterior peak bite force in large Carcharocles tough ?

[theropod]

As I noted numerous times, we don’t know the peak or in vivo bite force for Carcharocles, or any macrophagous shark for that matter. We only have computational estimates for some taxa, which record sustained bite forces. Rice et al.’s regression is only for anterior bite forces, and even then it is probably not very useful, as I outlined above.

The only somewhat reliable figures we have for Carcharocles bite force are still those based on Wroe et al.

[Grey]

But because the in vivo based results of Rice are almost twice as high as Wroe's antetior figures, wouldn't be something around twice higher than in Wroe's ?

[theropod]

Sept 19, 2019 4:09:20 GMT 5 Grey said:

But because the in vivo based results of Rice are almost twice as high as Wroe's antetior figures, wouldn't be something around twice higher than in Wroe's ?

Around as much higher would be plausible, which (well, together with the main point of the paper in fact being based around in vivo estimates) is why I initially mistook their figures for being based on in vivo measurements.

But the logic doesn't work, this is not plausible due to Rice et al.'s figures for anterior bite force being that much higher, it is plausible in spite of it, namely because that's a plausible amount for an actual in vivo figure to be higher than an estimate.

In short, its quite possible Rice et al.'s estimates for meg could be approximately correct, but that would then be more by chance than methodological soundness. So I wouldn't use them. Same, obviously, for results based on Erickson et al.'s or Aureliano et al.'s regression equations for bite force (even though, once again, some of the estimates made from them seem to have come out reasonably close, by sheer luck and compensation of other errors, such as an over- or underestimated body mass).

[prehistorican]

Its a bit unusual, on online paleontological communities I've been hearing of pliosaurs not even reaching 15m based on fossil remains. (Which is weird to me because I thought the Aramberri specimen could have been 15m). They seem to have large flippers in proportion to body size in these size charts. What do you guys think?

[creature386]

It is generally agreed here that there is no evidence of pliosaurs reaching a length of 15 m. That being said, these figures in the chart seem awfully small and contradict a lot of the published lengths (some of which you can find on page one). Is this based on self-made reconstructions?

EDIT: Nevermind, I found the source and the justifications:
www.deviantart.com/randomdinos/art/Toothy-Toothy-Whales-Mk-III-630335385
Unpublished, but at least reasonable estimates.

[theropod]

Randomdinos estimates are pretty rigorous, even if they are definitely on the low side.

The size of MoA is a big question mark. Some estimates comparing vertebral diameter and femoral head diameter to Liopleurodon seem to suggest 14+m (which seems unlikely, but I wouldn’t rule it out entirely, as the only people actually working with the material, which is far more complete than just a vertebra, seem to still support these figures), yet McHenry’s estimates based on comparison with Kronosaurus would suggest far smaller sizes. The 9.7 m in the chart is directly taken from McHenry, but the mass is increased to account for the relatively larger diameter of the vertebrae of MoA.

The figure I usually use is the 11.7 m, 15 t mean based on vertebral width, as a middle ground, and because individually shorter vertebrae might belong to a bigger animal if the vertebral count was higher. But that is not to say this is necessarily the most accurate one, in fact one can make a good case for a wide range of possible estimates. Which is why Aramberri as the potentially largest known pliosaur needs to always be taken with a big grain of salt, which of course also makes it all the more important that the rest of the skeleton gets a proper description and a more direct size estimate.

Kronosaurus and Sachicasaurus are obviously far more complete candidates. But this thread is not really concerned with the real biggest pliosaurs as much as with hypothetical properties of pliosaurs at sizes rivaling the other largest known marine predators.

[dinosauria101]

Sept 19, 2019 9:43:14 GMT 5 prehistorican said:

Its a bit unusual, on online paleontological communities I've been hearing of pliosaurs not even reaching 15m based on fossil remains. (Which is weird to me because I thought the Aramberri specimen could have been 15m). They seem to have large flippers in proportion to body size in these size charts. What do you guys think?

Agreed. Those flippers look 2-3 times bigger than normal

[theropod]

No they aren’t, they look quite accurately sized, and certainly not "2-3 times" too big.

[dinosauria101]

Really?
I thought the post a bit above just confirmed what I thought