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Post by Life on Mar 9, 2016 16:55:32 GMT 5
The Dining Habits of a Jurassic Sea DragonWhen I was a fossil-crazed tyke, I used to spend hours flipping through a set of LIFE Young Readers Nature Library books my parents had purchased. The multicolored collection was one of my earliest introductions to natural history and science, and all the time I spent with those pages seared a few illustrations onto my memory. One of the most frightening depicted the blue outline of a man projected against the black and white grimace of a monstrous marine reptile with a gape as tall as the human silhouette. This dragon, according to the caption, was Kronosaurus – a 42-foot-long, quad-paddled carnivore that ruled the seas of Cretaceous Australia around 100 million years ago.
I’m a little surprised the book’s simple illustration didn’t give me nightmares. To think that the seas once held a sharp-toothed giant that could snap me up in one quick bite… And even though more recent estimates have downsized Kronosaurus to around 30 feet long, that has barely diminished my imagination’s ability to imagine the destruction the toothy reptile was capable of.
Kronosaurus wasn’t an aberration or evolutionary one-off. It was one of many imposing marine reptiles called pliosaurs. Cousins of the famous, long-necked plesiosaurs, the pliosaurs kept the four-flippered body plan but typically bore huge heads with elongated jaws. They spanned much of the Mesozoic – about 150 million years from their Triassic origin to their Cretaceous extinction – and the largest of them were probably in the neighborhood of 30 to 40 feet long. The biggest were the most massive flesh-eating marine reptiles of all time, but despite the ferocity apparent in their bones, an essential aspect of their predatory lives has remained little-studied – just how did pliosaurs employ their powerful jaws?
To answer this mystery, University of Bristol research associate Davide Foffa worked with a team of paleontologists and visualization experts to create a digital model of a Jurassic pliosaur’s jaw. The animal they chose was a well-preserved specimen of the roughly 155 million year old Pliosaurus kevani found in Dorset, England’s Weymouth Bay. While many other species of Pliosaurus are represented by fragments, this particular seagoing reptile is known from a nearly-complete skull that stretches over six feet long. That’s roughly the size of the Kronosaurus skull that entranced my childhood self.
After using CT scans to create a digital model of the Pliosaurus kevani skull, including reconstructing parts of the lower jaw and cranium that are missing, Foffa and coauthors modeled the extent of muscles used to close those jaws and further investigated how the skull would have coped with forces that would have been caused as the predator twisted or shook its skull to rip apart prey. What they researchers found questions the image of pliosaurs as the rapacious big game hunters they’re often portrayed as.
Just how hard Pliosaurus kevani could chomp differed according to what part of the jaw was doing the biting. While bites at the front part of the jaw were in the relatively meager 2,000 to 4,000 pound range, back jaw bites spiked between 6,000 and 11,000 pounds. That’s pretty impressive, and in the same ballpark as estimates for Kronosaurus, the extinct alligatoroid Deinosuchus, and Tyrannosaurus. As far as prehistoric giants go, Pliosaurus kevani was a prominent member of the bite club.
Despite such a strong bite, though, Pliosaurus kevani had a relatively weak skull. Estimates of skull strength using techniques called beam theory and Finite Element Analysis showed that the predator would likely damage its skull if it tried to twist off chunks of flesh or shake prey to death. And despite my childhood awe at the gape of Kronosaurus, the similarly-sized Pliosaurus kevani could have only swallowed prey 30 inches in diameter or less. Anything larger would have to be broken down into smaller bits. With shaking and twisting being so risky, how could Pliosaurus have done so?
Foffa and colleague propose an alternative way for Pliosaurus to process prey. Instead of violently tearing at or throttling prey, the researchers suggest, big pliosaurs probably nabbed prey and hefted it to the back of the jaw. That’s where all their power was. With the prey positioned just so, they chomped and chomped and chomped until their victim died and started to go to tatters. Whatever couldn’t be swallowed whole was repeatedly gnashed until the dismembered parts were small enough to gulp.
Pliosaurus wasn’t a marauder that only targeted the biggest game, though. To the contrary, Foffa and coauthors point out that gut contents show that cephalopods and sharks made up a large part of the pliosaur diet, while turtles, other plesiosaurs, and the odd dinosaur – perhaps washed out to sea – were rarer menu items. Apex predators they were, but pliosaurs were not monsters hellbent on consuming the biggest and most dangerous creatures they swam alongside. These extraordinary reptiles were generalist predators who had a specific way of catching and pulverizing the abundance of prey that flourished alongside them in the Mesozoic seas.Source: phenomena.nationalgeographic.com/2014/06/30/the-dining-habits-of-a-jurassic-sea-dragon/--- Scientific paper: palaeo.gly.bris.ac.uk/Benton/reprints/2014Foffa-anatomy.pdf (PDF file) --- NOTE: Fellow member Grey brought this to my attention. I believe that this topic deserves its own thread.
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Post by creature386 on Mar 9, 2016 23:26:03 GMT 5
It is definitely hard to make a generalized statement for all pliosaurs (as Foffa et al.'s paper noted, Kronosaurus likely had no such skull weakness problems). Looking at P. kevani's ecosystem, the vast majority of its prey must have been a lot smaller than it and as such constituted the main part of its diet. I believe it was a predator with a wide range of prey, like large modern day crocodiles. I don't rule out that it could have attacked prey with the size of Leedsichthys. Foffa et al.'s paper in fact presents a plausible mechanism for allowing damaging bites:
A less demanding alternative to shake and twist feeding is represented by preferential biting at the large post-symphyseal teeth, as observed in many modern croc- odilians. After capture, prey could be repositioned with a series of inertial bites and then killed by powerful crush- ing bites, in line with the large median teeth. This cycle is repeated until the prey item is killed and the mechanical resistance of prey is weakened (Cleuren & De Vree, 2000).
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Post by Infinity Blade on Mar 10, 2016 2:30:54 GMT 5
I find it illogical to think they weren't.
I discussed this earlier on another thread. Well-resistant to torsion or not, pliosaurs like Pliosaurus still had exceptionally powerful bites that would obviously be very dangerous to even large prey items (even if they couldn't bite and twist, they could still deploy a thylacine-style series of snapping bites to cause further mechanical damage). And I have to question if Pliosaurus' skull really was that weak.
Going by Foffa et al.'s results, the skull/rostrum strength of P. kevani was comparable to that of a Nile crocodile. Although the Nile croc specimen's age isn't really specified (a point theropod brought up), I think a caveat would have been noted if it was a young one. Likewise, although it was operating at a far larger scale than a Nile crocodile would be (thus greater magnitude on the forces involved; another point theropod brought up), it may still have done so at simply a slower pace. And even ignoring all of this, Pliosaurus still had carinae on its teeth, meaning it could kill/dismember large prey with those in conjunction with its high bite force.
"Pliosaurus wasn’t a marauder that only targeted the biggest game, though. To the contrary, Foffa and coauthors point out that gut contents show that cephalopods and sharks made up a large part of the pliosaur diet, while turtles, other plesiosaurs, and the odd dinosaur – perhaps washed out to sea – were rarer menu items. Apex predators they were, but pliosaurs were not monsters hellbent on consuming the biggest and most dangerous creatures they swam alongside. These extraordinary reptiles were generalist predators who had a specific way of catching and pulverizing the abundance of prey that flourished alongside them in the Mesozoic seas."
This part of Switek's article irks me.
All people may have originally assumed was that pliosaurs, with their proportionally giant heads, renowned jaw power, and raptorial teeth, would have been adept big game predators and may have shaken or twisted to dismember such big game. Regardless of how correct this is (especially the latter part), who (among the aforementioned people) is saying that pliosaurs were "monsters hellbent on consuming the biggest and most dangerous creatures they swam alongside"? No one.
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Post by Grey on Mar 10, 2016 3:14:33 GMT 5
Regardless of the skull mechanics, excepted for big pachycormids, a 10m pliosaur was plenty bigger than all the available prey items.
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Post by theropod on Jul 15, 2016 22:31:31 GMT 5
Yup this seems reasonable though we could have surprised, pliosaurs bite forces, though very high, were previously expected to be significantly higher. But based on a combination of significantly larger pliosaurs and crocodylian in vivo measurements. That way they are bound to end up higher than an FEA or MDA-based estimate. P. kevani ends up having a bite force similar to both a large T. rex and a hypothetical crocodile of similar skull length, and a P. macromerus with a 50% larger skull would be expected to bite even harder (more than 2 times as hard, actually). So while for lack of sheer size they may be unable to rival estimates for ~50t predators, because the largest known pliosaurs are below 20, they do still bite remarkably hard, irrespective of the supposed "weakness" of their skulls. About pliosaur big game hunting, I think the idea of "monsters hellbent on consuming the biggest and most dangerous creatures they swam alongside" is simply fantasy to begin with, because there are not, and have never been, any such animals. That does not mean occasional attacks on exceptionately large prey are automatically excluded (larger than the predator), but for various reasons they must be rare, after all giant marine predators have certain disadvantages at attacking giant prey when compared to terrestrial ones (lacking the edges in mobility and grappling ability) and because they are larger to make up for that, prey larger than them is rare in their environments. In the Kimmeridgian seas in particular, there weren’t actually any animals bigger than Pliosaurus if I’m not forgetting something. I think when Foffa et al. wrote "animals up to half its own length in the Kimmeridgian seas", that’s supposed to be how its understood. After all, name me one large, extant marine predator that regularly kills animals more than half its own length. But you’d be hard-pressed to make an argument saying that there are none that sometimes do it. So I think the question is not "Were pliosaurs big-game hunters?" but rather how often they were, and what constitutes big game. About the possibility itself, I believe I have already posted this elsewhere, but here we go again: scienceblogs.com/tetrapodzoology/2009/07/02/biggest-ever-fish-has-been-revised/Incidentally, some Leedsichthys fin rays (perhaps representing the dorsal fin in one specimen, and a pectoral fin in another) do bear evidence of attack by large predators. What look like curving bite marks appear to have been made by plesiosaurs This would be a good time if anyone has more information on these fossils. Pliosaur bite marks on a Leedsichthys fin would be a good indication of predation imo, since this matches the patterns observable in other predators taking down very large prey, and it is one of the most conceivable ways I can see for a pliosaur to attack an animal bigger than itself.
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Post by Grey on Nov 8, 2016 6:51:38 GMT 5
Yup this seems reasonable though we could have surprised, pliosaurs bite forces, though very high, were previously expected to be significantly higher. But based on a combination of significantly larger pliosaurs and crocodylian in vivo measurements. That way they are bound to end up higher than an FEA or MDA-based estimate. P. kevani ends up having a bite force similar to both a large T. rex and a hypothetical crocodile of similar skull length, and a P. macromerus with a 50% larger skull would be expected to bite even harder (more than 2 times as hard, actually). So while for lack of sheer size they may be unable to rival estimates for ~50t predators, because the largest known pliosaurs are below 20, they do still bite remarkably hard, irrespective of the supposed "weakness" of their skulls. About pliosaur big game hunting, I think the idea of "monsters hellbent on consuming the biggest and most dangerous creatures they swam alongside" is simply fantasy to begin with, because there are not, and have never been, any such animals. That does not mean occasional attacks on exceptionately large prey are automatically excluded (larger than the predator), but for various reasons they must be rare, after all giant marine predators have certain disadvantages at attacking giant prey when compared to terrestrial ones (lacking the edges in mobility and grappling ability) and because they are larger to make up for that, prey larger than them is rare in their environments. In the Kimmeridgian seas in particular, there weren’t actually any animals bigger than Pliosaurus if I’m not forgetting something. I think when Foffa et al. wrote "animals up to half its own length in the Kimmeridgian seas", that’s supposed to be how its understood. After all, name me one large, extant marine predator that regularly kills animals more than half its own length. But you’d be hard-pressed to make an argument saying that there are none that sometimes do it. So I think the question is not "Were pliosaurs big-game hunters?" but rather how often they were, and what constitutes big game. About the possibility itself, I believe I have already posted this elsewhere, but here we go again: scienceblogs.com/tetrapodzoology/2009/07/02/biggest-ever-fish-has-been-revised/Incidentally, some Leedsichthys fin rays (perhaps representing the dorsal fin in one specimen, and a pectoral fin in another) do bear evidence of attack by large predators. What look like curving bite marks appear to have been made by plesiosaurs This would be a good time if anyone has more information on these fossils. Pliosaur bite marks on a Leedsichthys fin would be a good indication of predation imo, since this matches the patterns observable in other predators taking down very large prey, and it is one of the most conceivable ways I can see for a pliosaur to attack an animal bigger than itself. Yes I agree. I pointed out on the stark contrast with early estimates of 15 tonnes plus bite pressures, based on the early monstrous sizes estimates for P. funkei. They're among the supreme chompers in the history of life on Earth there's no question about this but claims that the regular pliosaur bitten harder than any T. rex are wrong from this standpoint (especially if we acknowledge that Sue would have bitten even harder than the estimates extrapolated from Stan). I concur though that these estimates for pliosaurs could conservative since the muscle volumes are hard to understand because some muscles groups exceeds the bone boundary (muscle pterygoideus in crocodiles - and we simply don't know this about pliosaurs). Other factors are the muscle lines of action which influence the efficiency of the biting. Regardless, Foffa et al. figures of prey size are directly based on McHenry's recording of Kronosaurus confirmed food sources and the known stomach contents of a Liopleurodon specimen indicating mainly cephalopods remains. I agree this is somewhat premature to conclude a 10 m pliosaur couldn't attack a 10 m pachycormid simply because we have no evidence for this. On the other hand, McHenry privately said that he'd expect something like Simolestes to be able to handle an adult Leedsichthys based on modern crocs analogies. However, IIRC, the Leedsichthys bite marks were healed, indicating a failed predation attempt from the potential pliosaurid-agressor. The point is that the large pliosaurs were plenty big enough to dominate any potential prey items of their time, even if they didn't target 16 m pachycormids on a regular basis, they didn't need to be 25 m long or to have a bite force 3 times exceeding T. rex for that.
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Post by theropod on Nov 8, 2016 22:09:45 GMT 5
The pterygoid muscles don’t exceed the bone boundary, they lack it alltogether. The question is whether crocodiles are unique in terms of their hypertrophy of that particular muscle group. In any case, it’s a major variable, of course applying to many animals.
What’s the regular pliosaur to you? P. kevani is obviously vastly bigger than most pliosaurs, so I think nobody would ever argue that the average pliosaur was a match for the largest T. rex in terms of bite force. Comparing Sue to all pliosaurs is like comparing the Monster Of Aramberri to all tyrannosaurs. Pliosaurs are a rather speciose taxon by now, and not all of them are gigantic, just like not all tyrannosaurs are. And for obvious and understandable reasons the research has focused on the big ones, not Peloneustes.
It’s really no different for T. rex though, let alone tyrannosauroidea as a whole. McHenry used Sue, which ended up similar to Kronosaurus and rather lower than estimated for P. kevani by Foffa et al.. Bates & Falkingham used Stan, which may not be huge overall but back then had its skull restored at 1.4m, which still makes it one of the biggest T. rex skulls in existence. Obviously the MBD method is not exactly comparable to the dry skull method, and I think its apparent that it produces higher results, especially since nobody is citing anything but the 57kN-estimate to correct for any perceived underestimation that could be left. The resultant figure is pretty much at the lower bound of the range that would be realistic for sue when following McHenry’s estimate, which fits well with its slightly bigger skull implying a slightly stronger bite (so if we want something comparable to in-vivo estimates, I’d expect sue to fall in the 60-70kN-range), but most T. rex specimens have smaller skulls than used for Stan and should have lower bite forces.
If we count some relatively obscure specimens (MoA, NHM symphysis), I think there are pliosaurs out there that have a shot at biting harder than any known T. rex, if we consider that more "normal" giant pliosaurs are roughly a match for a large T. rex. The "regular pliosaur", being considerably smaller than Kronosaurus or Pliosaurus kevani, stands no chance, and never really stood one to begin with.
Interesting piece of information regarding the bite marks being healed. You wouldn’t happen to remember where you found that information? The line I quoted above is all I recall ever finding on the issue, and it’s been bugging me for years that I don’t have more information.
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Post by Grey on Nov 8, 2016 23:41:10 GMT 5
I quote directly Foffa on this, that's where the uncertainty is.
That's semantic and that's not from me, pliosaurs have been often described with a bite force dwarfing the bite force of T. rex priors to these studies, even by pliosaurs experts. But you obviously need a very large pliosaur to get a bite force rivalling or un excess of Tyrannosaurus. I'm not in segregating Sue while comparing T. rex to others organisms, it is just as representative as any other specimen. I ignored though that Stan skull length was estimated too large back then. Interestingly, the lower estimates proposed by McHenry for the Monster of Aramberri would rather indicate a skull size suggesting a bite force similar to the 70 kn you and I predict for Sue.
I indeed extrapolated a similar bite force to Sue. You need something like the Cumnor Monster or MoA to exceed this, which are somewhat problematic specimens themselves (Cumnor could be overeconstructed according to Forrest). Regarding the NHM symphysis, although I acknowledge it as being the largest potential macropliosaur known, I remember blaze comparing it to the larger Liopleurodon specimen and resulting in an estimated size of just around 10 m. Which would possibly put it below Sue.
The whole point is not that no pliosaur matched or exceeded Tyrannosaurus in bite force but it appears claims of bite strenght exceeding several times that of T. rex are simply wrong at this stage. This is part of the whole myth surrounding pliosaurs alleged super-powers.
I think this healed bite mark comes from Martill 1986 but I need to investigate this further.
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Post by theropod on Nov 9, 2016 4:06:36 GMT 5
Only giant pliosaurs have ever been described (really only guesstimated apart from the two studies we are discussing) in terms of bite force in the first place, and as we all know. More specifically, it was P. funkei in particular that was significantly hyped in terms of size (and everything else) back then. Obviously that’s where the problem lies. What I mean is that no "regular pliosaur" has ever even gotten enough attention to have its bite force guesstimated, much like no regular-sized T. rex has ever gotten that attention either. The difference is that T. rex size ranges from 10-12.3m, while Pliosaur size ranges from 3 to 12, perhaps more. Basically as inaccurate as they were due to lack of scientific methodology, earlier, more liberal bite force estimates for Pliosaurs were never relevant in that regard in the first place
I know about the issues with the Cumnor mandible, having talked to Forrest about that leads me to ignore it for now.
Regarding the NHM symphysis, that is within the range McHenry estimated for it. Right now there is no perfect figure and a wide range is plausible. I was talking about upper estimates. If there are pliosaurs with 3m skulls that would put their bite forces at approximately twice that of T. rex. The Cumnor monster would have fit the bill if it were reliable, I’m not sure if the same head-body proportions can be applied to the giant symphysis if it is more similar to Simolestes, but really the only way to tell more about that would be if someone got round to properly describing it and its most likely affinities. Until then, there’s some possibility, but it’s not very strong. In that case, we’re back to P. kevani and funkei, which are in a very similar ballpark to the largest T. rex specimens, and the MoA, which may be a little higher up the scale.
Now, while we all know that bite force is not a good predictor of prey size when comparing it among such vastly different animals, since pliosaur teeth are rather similar to T. rex teeth we could perhaps draw some parallels about the damage caused by a bite from that. Also, does anyone know some documented example of those ichthyosaurs supposedly bitten in half?
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Post by Grey on Nov 9, 2016 4:31:45 GMT 5
That's only semantics, even other than the Svalbard case, before those studies pliosaurs biting power has been pretty much hyped, including Richard Forrest. Or the Monster of Aramberri ability to bite granite... Obviously, I refer the regular "large" pliosaurs. When Forrest refers to pliosaurs able to bite through a car, you know he does not refer to Simolestes or the average-sized Liopleurodon.
What did Forrest tell you about the Cumnor jaw? I agree, though I still happen to consider it valid for, especially in the light of McHenry's remarks.
Yup, the NHM symphysis definitely deserves more attention. And I'd appreciate to see a picture of it at least.
MoA, P. funkei and P. kevani can indeed be considered the largest/more powerful biters among pliosaurs but I keep in mind Benson et al. considerations that Kronosaurus, at least in terms of skull size (thus bite force) if not of full size, is the pinnacle of pliosaurs macroevolution. Benson estimating the Harvard specimen to have been longer of only about 1 meter, which would make it about 12 m long....which would increase the potential size of MoA that being said.
A study regarding bite marks on plesiosaurians from large macropredaceous pliosaurs is definitely needed. Forrest made various allusions to ichthyosaurs bitten in half but I know no reference to this.
I could certainly ask him more details.
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Post by Infinity Blade on May 17, 2017 4:05:55 GMT 5
Does anyone here wonder if pliosaurs could ram? No one has ever done a finite element analysis on their skulls or anything to see if their skulls could withstand the forces incurred from ramming, but I've read from two scientific authors who have suggested that pliosaurs could ram prey ( Lingham-Soliar, 1998; Zammit & Kear, 2011). What do you guys think?
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