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Post by Supercommunist on Nov 13, 2015 2:34:37 GMT 5
 I remember seeing several studies stating that a thylacoleo's could kill animals far more quickly and efficiently than a similar sized cat. If this animal's bite was really that formidable, why don't we see that many animals with this kind of dentition? Is is just a coincidence, or are there inherent disadvantages in its design? |
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Post by theropod on Nov 13, 2015 3:29:31 GMT 5
That might not be the case at all (could you cite examples of such studies?), based on the latest research its jaws may have served a different purpose alltogether, one distinct from other predatory mammals and congruent with their very distinct anatomy. At SVPCA this year, it was suggested that the teeth weren’t used for killing in some semblance of extant cats, but for holding prey while finishing it off with the crazy thumb claw. svpca.org/abstracts/abstract.php?abstID=00000002045&prog=onA dromaeosaur analogue of sorts, except that it used its jaws for what dromaeosaurs used a combination of their jaws, forelimbs and hindlimbs for, and its enlarged forelimb claw for what dromaeosaurs did with their enlarged hindlimb claw. That the majority of animals, especially mammals, use their jaws as killing weapons and their claws for restraint (if at all) means that evolution favoured the use of jaws for this purpose for some reason, but it doesn’t mean that the exception can not be equally or more effective as a weapon in the rare cases when it does evolve (we all know the examples). The same can of course be said for aberrant jaw morphologies. If one jaw/tooth design is rare, that doesn’t have to mean it’s not effective. But it might not be as efficient (different thing entirely) in most animals, or only viable due to particular physiological and anatomical aspects of the animal in question (e.g. the inherited mechanisms by which its teeth are replaced, which has a marked impact on the kinds of tooth shape a taxon can evolve). Evolution isn”t just about what works best once it’s there, it’s about what is easiest to evolve as a modification of a given set of traits. So given the studies you cite are correct, that doesn’t have to mean this design should be more widespread. By the same logic one could ask why it evolved in this taxon in the first place, if it was used as a killing tool, but less effective in that role. But frankly, I don’t see why its bite should be so particularly damaging (certainly not more so than other macropredaceous carnivores’, and possibly less, not necessarily being adapted for this purpose). The teeth aren’t even very sharp or pointed. Yes, the bite force was supposedly very strong, but that alone doesn’t result in an extraordinarily potent bite. Many animals have evolved extreme bite forces for one reason or another, and many others haven’t and yet have equally or more damaging bites. |
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Post by Supercommunist on Nov 13, 2015 3:43:41 GMT 5
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Post by theropod on Nov 13, 2015 4:04:00 GMT 5
Most of those suggestions is actually consistent with what I posted above (Wroe mentions both forelimb use and resistence to struggling prey, with the key finding of the study being its relatively strong bite force and a skull). The problem is the sensationalist conclusion for the media, which bases on the use of bite force as a proxy for bite damage. Regarding that suggestion, I’ve got severe doubts as to whether using the cheek teeth as "boltcutters" would actually serve it well as a means of killing, or whether they’d serve the same purpose as the analogous teeth in extant carnivorans such as hyaenas do (if this were so incredibly effective, then what keeps modern animals from using their carnassials this way?). And we already know what a metatherian predator adapted for killing something through flesh wounds and blood loss looks like→. EDIT: I think this is the study in question: onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.2007.00389.x/abstractUnfortunately I’ve got no access. |
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Post by Infinity Blade on Nov 13, 2015 4:57:04 GMT 5
That might not be the case at all (could you cite examples of such studies?), based on the latest research its jaws may have served a different purpose alltogether, one distinct from other predatory mammals and congruent with their very distinct anatomy. At SVPCA this year, it was suggested that the teeth weren’t used for killing in some semblance of extant cats, but for holding prey while finishing it off with the crazy thumb claw. svpca.org/abstracts/abstract.php?abstID=00000002045&prog=onA dromaeosaur analogue of sorts, except that it used its jaws for what dromaeosaurs used a combination of their jaws, forelimbs and hindlimbs for, and its enlarged forelimb claw for what dromaeosaurs did with their enlarged hindlimb claw. That the majority of animals, especially mammals, use their jaws as killing weapons and their claws for restraint (if at all) means that evolution favoured the use of jaws for this purpose for some reason, but it doesn’t mean that the exception can not be equally or more effective as a weapon in the rare cases when it does evolve (we all know the examples). The same can of course be said for aberrant jaw morphologies. If one jaw/tooth design is rare, that doesn’t have to mean it’s not effective. But it might not be as efficient (different thing entirely) in most animals, or only viable due to particular physiological and anatomical aspects of the animal in question (e.g. the inherited mechanisms by which its teeth are replaced, which has a marked impact on the kinds of tooth shape a taxon can evolve). Evolution isn”t just about what works best once it’s there, it’s about what is easiest to evolve as a modification of a given set of traits. So given the studies you cite are correct, that doesn’t have to mean this design should be more widespread. By the same logic one could ask why it evolved in this taxon in the first place, if it was used as a killing tool, but less effective in that role. But frankly, I don’t see why its bite should be so particularly damaging (certainly not more so than other macropredaceous carnivores’, and possibly less, not necessarily being adapted for this purpose). The teeth aren’t even very sharp or pointed. Yes, the bite force was supposedly very strong, but that alone doesn’t result in an extraordinarily potent bite. Many animals have evolved extreme bite forces for one reason or another, and many others haven’t and yet have equally or more damaging bites. Regarding that last part about Thylacoleo's bite potency, do you think it would be like that of a macrophagous crocodilian's in a way? That is, the bite was very strong, but it seems to be used for holding onto prey, not actually killing it, thus possibly making it less potent in a way (the difference being a crocodilian would drown its prey while Thylacoleo apparently dispatched quarry with its hypertrophied thumb claw, which is pretty awesome!). |
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Post by theropod on Nov 13, 2015 12:49:59 GMT 5
In a way those were my thoughts on hearing the new interpretation, yes. The jaws alone may have struggled with inflicting fatal injuries on a large prey item, but in combination with its strength and dexterity it would be able to subdue it, much like what crocs do using their strength aand aquatic advantage.
Of course the bite could still cause terrible damage, but I really doubt it was primarily designed to kill through such means. And the boltcutters seem like they are primarily for feeding, just like carnivoran carnassials.
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Post by Infinity Blade on Dec 16, 2015 5:52:56 GMT 5
Another interesting Duane Nash blog post.It's about Foffa et al. (2014)'s study on the skull of Pliosaurus kevani. Basically, he disagrees with their conclusion that torsional feeding would have taken too great of a toll on its skull, as data presented in the study itself shows that its skull/rostrum strength was nonetheless comparable to those of Nile crocodiles, which still utilize torsional feeding with no problem.
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Post by Grey on Dec 16, 2015 6:09:01 GMT 5
Another interesting Duane Nash blog post.It's about Foffa et al. (2014)'s study on the skull of Pliosaurus kevani. Basically, he disagrees with their conclusion that torsional feeding would have taken too great of a toll on its skull, as data presented in the study itself shows that its skull/rostrum strength was nonetheless comparable to those of Nile crocodiles, which still utilize torsional feeding with no problem. Yes I planned to ask Foffa about this. But I think coherentsheaf disagreed with Nash. |
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Post by theropod on Dec 16, 2015 23:01:19 GMT 5
Even though I don’t necessarily disagree with Nash’s envisioning of pliosaur feeding mechanics, he is disregarding the size component.
Deathrolling at the scales of a large pliosaur is a different thing from a 10 times smaller crocodile doing it, because the magnitude of the forces involved depends on mass (both that of the pliosaur and that of the prey). That may well be why crocodile skull robusticity is so strongly positively allometry.
So even though the skull is comparable in terms of torsional and bending resistance to that of a nile crocodile, that doesn’t necessarily mean it could do the same things as a nile crocodile.
However I also think the quantitative basis for claiming it absolutely couldn’t use any type of rotational feeding is lacking, hence probably why Foffa et al. didn’t claim so and only suggested a safer (and very reasonable imo) alternative.
I could envision rotational feeding being theoretically possible, but at a considerably slower rate of rotation compared to crocodiles to account for the far greater size. Obviously, what applies to its skull also applies to its prey’s tissues, so the resulting forces would remain sufficient.
Also, we do not know the size of the nile crocodile in question. That of a young crocodile will be much less robust than that of a large, old adult, so to which of them is Pliosaurus similar?
Obviously Pliosaurus was an apex predator, and there is fossil evidence for its bite being very potent (the biting-in-half ichthyosaurs part. I wish there was a paper about that…). Pliosaurus itself even has carinated (and undoubtedly very large and pointed) teeth, which probably differed in function from those of crocodiles, so perhaps it simply did not need rotational feeding in order to kill and dismember its prey, and it was more important for its head to maintain a streamlined shape than for it to become excessively robust.
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Post by Infinity Blade on Dec 17, 2015 4:32:30 GMT 5
Then what about giant extinct crocodilian taxa like Deinosuchus and Purussaurus (which were proposed to have death rolled)? Would they have death rolled at a much slower pace than much smaller extant crocodilians? Is there any reason to suggest that it belonged to a young individual? I mean, even an adult Nile crocodile doesn't have a skull quite as robust as those of the alligatorids in the study that outperformed it (at least proportionately speaking), so I guess it would be reasonable to think that even then the latter would be able to resist proportionately more torsional stress than the former. Just in case anyone wants to know, Foffa et al.'s paper states that the Nile crocodile specimen in question is labeled RVC AN1. Now I wait and see if a certain someone has any info on that specimen... EDIT 5/26/21: RVC AN1 is a Nile crocodile specimen with a total skull length of 501 mm ( link->). If you look at Fig. 10, you can clearly see that this specimen had a robust skull and snout. So clearly this was an adult with a powerful skull. So why they deem Pliosaurus poorly adapted to withstand bending and torsional stress when it's clearly comparable to that of a Nile crocodile (even when corrected for snout length) is beyond me. What I don't understand is how the paper states that Pliosaurus was well-suited for macrophagy when it limits its prey size to animals half its own length. Isn't the definition of macrophagy the act of preying upon and consuming a prey item that isn't small relative to the size of the predator itself? Also, half-bitten ichthyosaurs? |
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Post by Grey on Dec 17, 2015 7:26:37 GMT 5
A predator eating vertebrate animals half its length is certainly macrophagous.
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Post by Infinity Blade on Dec 17, 2015 8:24:18 GMT 5
I thought macrophagous meant that the prey had to be similar in size to (if not larger than) the predator?
Or maybe I've had a partially skewed definition of that word for a few years...
D'oh!
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Post by theropod on Dec 17, 2015 17:10:05 GMT 5
I thought macrophagous meant that the prey had to be similar in size to (if not larger than) the predator? Or maybe I've had a partially skewed definition of that word for a few years... D'oh!I think a working definition for our purposes would be taking prey within its own order of magnitude sizewise, though afaik the official definition of a macropredator is simply everything that isn't a micropredator (i.e. not a suspension-feeder). It's more sensible to refer to an animal as more or less macrophagous than as macrophagous or not macrophagous imo. |
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Post by creature386 on Dec 17, 2015 20:11:15 GMT 5
Just out of curiosity, I googled macropredator and is it actually synonymous with macrophagous carnivore?
From what I found, a macropredator is a large predator while a macrophagous carnivore is a predator that eats large (of course "large" is undefined) prey.
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Post by theropod on Dec 17, 2015 23:06:10 GMT 5
Interestingly it seems to depend on where you look, I’ve read it in the context of taking large prey, some definitions say it refers to a large predator (but I don’t think I’ve actually seen it used like that), others say it can mean both. They might still have, but note that at least Purussaurus’ skull might be "overbuilt" in the way that one would expect for a larger animal, at least relative to mesorostrine crocodilians. No, is there any reason it didn’t? As you know, older, larger crocodiles (which take relatively large tetrapod prey) become increasingly rare, and I’ll wager that the skulls of relatively young individuals are more common in collections. But this is just a possibility that has been left unaccounted for, I’m not implying that it’s necessarily the case. Yes, certainly. And its also noteworthy that alligators or caimans don’t seem to take proportionately larger prey than nile crocodiles (if anything the reverse is true), so prey availability is probably the deciding factor rather than for extant crocodilians. I presume the same may hold true for pliosaurs, especially considering that for something the size of a large Killer Whale the majority of potential prey would be smaller than its own size anyway. I too find that limit strange, and it isn’t really explained where they got it from. As I mentioned above, if the abundance of available prey is taken into account, it is reasonable to assume that most of its prey would have been less than half its body length, but I don’t really see why that should be the upper limit either. There have been mentions of ichthyosaurs that seem to have been bitten in half (by pliosaurs, obviously). e.g. here: blog.everythingdinosaur.co.uk/blog/_archives/2009/10/27/4362958.htmlI don’t remember where, but I’m quite sure that Richard Forrest remarked on it at some point while discussing pliosaurs’ adaptions for devastatingly powerful biting. There is a lack of data, but if the reports are true, their jaws were very effective, with or without inertial feeding. This→ is also quite interesting, although I’m not sure how much of Forrest’s suggestions as to what pliosaurs were capable of bases on real fossils and how much is conjectural. What he reports certainly sounds as if smaller pliosaurs and rhomaleosaurs were capable of selectively targeting prey in a way that made up for their lack of giant size. Combined with the very impressive capabilities of giant pliosaurs’ jaws, I can certainly see them being physically capable of attacking prey their own size or larger, just like modern killer whales, albeit not with the same ease as smaller prey. If there has been a follow-up paper, I’ve missed it, but it would be very interesting to learn more details about the direct evidence of pliosaur predation and the kind of damage they could do. |
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