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Post by creature386 on Apr 2, 2019 15:03:45 GMT 5
1.) I've browsed the Wikipedia articles of recently extinct flightless birds and this is the first one where humans are not mentioned, only rats and cats: en.wikipedia.org/wiki/Ascension_crakeAs for the not-so recent history, I'll have to pass. The only disputable example I'm aware of are South American phorusrhacids though this would have been if anything competition and as the Wikipedia article mentions, it is an unlikely hypothesis for their extinction. 3.) I think with our ability to successfully cooperate in large groups (100 - 150 individuals), we could attack most prey whilst simultaneously being save from most predators. So, pretty close to the top, I'd say. A 100 humans with pointy stick are a force to be reckoned with.
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Post by Infinity Blade on Apr 9, 2019 0:04:21 GMT 5
The Life Before Man thread got me thinking about how I view extinct animals. So one thing I'm kind of unsure about is exactly how well non-tyrannosaurid large specialist theropods would have been at resisting the stresses of large (i.e. at least equal sized) struggling prey with just their mouths, without suffering serious or catastrophic damage to their dentition or their skull.
Yes, I've known for years now that they were less adept at it than the bone crushing tyrannosaurids, but were they necessarily bad at it? I posted some information in the animal feeding apparata thread about large theropod teeth being less compressed than canid canines of comparable size (most modern canids, e.g. wolves, have mediolaterally compressed canines, believe it or not). And canid canines are, of course, still really strong and able to withstand struggling with much larger prey. For carcharodontosaurids in particular, Rayfield (2011) has also listed some features that could have buttressed the skull roof. What's most troublesome, I believe, is the lack of a hard palate to resist torsional stress.
I know they all had strong forelimbs with sharp claws to aid in prey restraint, but not all had forelimbs as relatively long as each other, so the larger the prey, the more difficult to apply the forelimbs, especially if they're proportionately short.
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Post by Infinity Blade on Apr 9, 2019 22:30:18 GMT 5
The Life Before Man thread got me thinking about how I view extinct animals. So one thing I'm kind of unsure about is exactly how well non-tyrannosaurid large specialist theropods would have been at resisting the stresses of large (i.e. at least equal sized) struggling prey with just their mouths, without suffering serious or catastrophic damage to their dentition or their skull. Yes, I've known for years now that they were less adept at it than the bone crushing tyrannosaurids, but were they necessarily bad at it? I posted some information in the animal feeding apparata thread about large theropod teeth being less compressed than canid canines of comparable size (most modern canids, e.g. wolves, have mediolaterally compressed canines, believe it or not). And canid canines are, of course, still really strong and able to withstand struggling with much larger prey. For carcharodontosaurids in particular, Rayfield (2011) has also listed some features that could have buttressed the skull roof. What's most troublesome, I believe, is the lack of a hard palate to resist torsional stress. I know they all had strong forelimbs with sharp claws to aid in prey restraint, but not all had forelimbs as relatively long as each other, so the larger the prey, the more difficult to apply the forelimbs, especially if they're proportionately short. The skull of Allosaurus (for example) has been described as "undoubtedly strong" in the scientific literature ( Antón et al. (2003)). Right now I'm under the impression that it should have been fine against struggling prey.
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Post by theropod on Apr 10, 2019 3:28:15 GMT 5
^That was undoubtedly strong in the dorsoventral plane, not necessarily other planes. But of course their skulls would not fail so easily (that is part of the same rather big misunderstanding that also led to some people believing non-tyrannosauroid theropods had some sort of bone-phobia and would not bite anything with the slightest chance of tooth-on-bone contact, despite abundance trace-fossil evidence to the contrary and teeth that are actually quite robust in absolute terms). Kinetic elements would probably deform and reduce stresses in most situations before they would lead to fracturing. Of course that limits the force that could be excerted or directly opposed by the predator against the prey (e.g. active resistance to lateral or torsional movements: as you say without a secondary palate and a lightweight and narrow skull construction, the skulls would probably yield quite a bit to direct forces applied in those directions, but the animal would probably just use the neck to avoid those forces in the first place), but dorsoventral or anteroposteriorly reinforced skulls could push or pull quite forcefully in those planes (though of course that would primarily result in the teeth cutting through the prey, rather than impaling and holding it), while yielding and only passively holding on against prey movements in others. Komodo dragons can hang onto large prey just fine without their skulls immediately breaking apart.
Besides, it’s naive to think even a T. rex could completely control and immobilize a Triceratops only by sheer force. Holding on with the jaws to prevent prey escape (i.e. mainly pulling force) and maintain a favourable position or specific motion to increase damage to bone (like some shaking or limited torsion), yes, wrestling prey submission with brute force, is probably unrealistic, as any quadrupedal prey item of similar size would enjoy a big advantage in stability, traction and torque production that would likely mean no matter how strong the jaws and neck were, a theropod would sooner topple over itself than topple over a ceratopsian or sauropod. Irrespective of jaw or neck muscle strength, a theropod body plan just isn’t suitable for that sort of approach. Pulling at a prey item to somewhat manipulate it, in some situations, might be realistic (then again, that’s something most theropods were probably reasonably good at, but would usually simply result in tearing out meat, for the same reasons why great white sharks don’t use their jaws to hold and immobilize prey the way crocodiles do).
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Post by Infinity Blade on Apr 10, 2019 7:08:54 GMT 5
Ah, that might clear up how I view things. What I had in mind was, maybe, a small-ish Allosaurus (~1 tonne?) against perhaps an equal sized (and so probably decently large) Camptosaurus, or perhaps a 2 tonne one against say, an equal sized (thus subadult) sauropod, and how it would go about hunting and killing either of these. I have to admit, I can't even remember if I had wrestling or controlling in mind. But I'm not sure I buy that; I mean, what about grappling mammalian predators? To use their forelimbs to grapple and wrestle necessitates the assumption of a bipedal stance for these predators, while the prey they hold is still going to be standing on all fours. We may even be talking about prey much larger than the predator, though then again, maybe you could argue that they don't kill such prey by actually wrestling or controlling them. I still remember your old post about legs and stability in this thread (see, I remember some things from a few or even several years ago like an elephant, but I forget other things from just a few days ago, lmao), and that while the number of legs to stand on is obviously important, it really depends on a number of other variables*. *For what it's worth, I do know one area where bipedal theropods would seem to have an advantage over their quadrupedal prey in this regard, namely the relative size of the semicircular ear canals (so the sense of balance on a neurosensorial level); bipedal dinosaurs apparently (though perhaps not surprisingly) exhibit relatively larger canals than do quadrupedal dinosaurs, which has been interpreted as an adaptation to the inherently (read: all else being equal, at least) less stable bipedal posture (Georgi et al. 2013).
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Post by theropod on May 5, 2019 19:44:41 GMT 5
Sorry, sort of missed this in the flood of mismatches…
Well those predators tend to go down along with their prey, something a big theropod probably couldn’t do without risking serious injury. It’s hard to see a T. rex hang onto the neck of a Triceratops and pull it down to the ground using its body weight, because it is far taller than its prey, unlike mammalian predators that grapple with their limbs. Also, once on the ground, a quadrupedal predator can immediately return to a four-legged stance and get back up, for a large biped getting back up off the ground would presumably be more difficult.
True, but what I had in mind was something lika a Majungasaurus compared to something like a Giraffe, where the Giraffe may have the advantage of being quadruped, but it has a far higher center of gravity, very gracile and inflexible limbs and a very narrow stance. Whereas a Triceratops has a very low center of gravity, very robust limbs and a broad stance. I don’t think you’d want to get into a wrestling contest with a Triceratops just because getting onto one with a giraffe might be an option. I also don’t think I was specifically thinking of a shoving match, rather how difficult it would be for these animals to maintain stability in normal everyday situations.
Don’t get me wrong, I certainly think a T. rex could bite a Triceratops and not let go, in order to prevent it from getting away. In that scenario, it can give way and move with its prey to remain balanced, and it only needs to hold on with as much force as it has, not as much force as the Triceratops may have. I just don’t think it would have the strength and balance to overpower the complete animal with its head and neck alone.
Very interesting regarding the canal sizes! This makes sense, as bipedal dinosaurs would require better balancing ability. But once in a grappling match, I think that would be of limited utility, as it becomes a contest of strength.
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Post by Infinity Blade on May 6, 2019 19:19:49 GMT 5
So, there's got to be a threshold where a biped and a quadruped really are equal in stability. Where would it be, though? I kind of doubt an extreme situation like your Majungasaurus vs. giraffe example is needed for the biped to finally be more stable to any degree. Triceratops would have been incredibly stable even for a quadruped for the reasons you stated (and also its enormous leg muscles), so no surprise if no bipedal animal ever was more or as stable than that thing. What if we took, for example, a modern African elephant? Quadrupedal (and graviportal, might I add), but its legs are nowhere near as robust as those of a Triceratops, doesn't have large and strong leg muscles for its size, and doesn't look like it has as broad of a stance as say, Triceratops ( elephant stance in posterior view). Or if you want something that actually lived with T. rex, what about an equal-sized Edmontosaurus?
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Post by theropod on May 6, 2019 19:49:24 GMT 5
Well those things would probably be less stable than a Triceratops, but how would you propose to quantify this?
By how much force could be applied to them without them toppling? But applied where exactly? And are they allowed to move, so long as they maintain their balance, or are they treated as static objects? How fast is whatever is pulling or pushing them moving? And in what direction? All of those considerations could change the outcome, or the magnitude of that force, potentially differently depending on the animal in question.
The quantitative definition is complicated by so many factors, I’m not sure you can actually make one. It depends too much on the scenario. At best you could wager a guess as to what kind of animal would tend to be less prone to topple over on the whole, given that the difference is either sufficiently large (e.g. Triceratops vs T. rex), or the two animals are sufficiently similar that the differences can be limited to a few factors that are easy to quantify (e.g. if two animals are similar in overall built and size, but one has less cursorial legs and a wider stance, it will probably be more stable). If you want me to define a particular point where a quadruped and a biped "even out" in terms of stability, I’m afraid I can’t give you one.
Unless I’m missing something, it seems pretty clear Edmontosaurus would be more stable than an equal-sized T. rex, since the latter is more cursorial and taller, and the former has the ability to use its forelegs for support when needed. T. rex would basically be an Edmontosaurus, on stilts, without forelimbs.
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Post by Infinity Blade on Jun 24, 2019 19:36:12 GMT 5
Did Ancylotherium really lose traditional sharp chalicothere claws throughout its evolution? The Walking with Beasts companion book claims such, and the documentary model depicts its forefeet as having hoof-like nails. I can't really tell looking at its forelimbs. The second photo, at least, looks like it indeed has hoof-like unguals. Even the first photo, while not looking entirely blunt or hoof-like, shows absurdly shortened manual unguals.
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Post by dinosauria101 on Jun 24, 2019 22:17:23 GMT 5
They look a bit like a transition between hooves and claws to me
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Post by Infinity Blade on Aug 19, 2019 1:01:00 GMT 5
I tried finding reliable comparisons between the properties of bone and ivory. But I have what seems to be conflicting information. Can someone help me? Vollrath et al. (2018) claim that bone is twice as tough as ivory, while ivory is twice as strong (they appear to mean flexural strength, which equals tensile strength if the material is homogenous). However, they don't seem to have a source for this, meaning this is either the original source for the claim and I'm supposed to take their word for it or they got this information somewhere else. Note that this isn't a primary research article, meaning this was not a "materials and methods" type paper. On the other hand, Rajaram (1986) has some data. According to him, the ultimate tensile strength of ivory is 110 MPa when dry, and 36 MPa when wet, while bovine femur bone has an ultimate tensile strength of 99.2 MPa when wet (frustratingly there is no data for dry femur bone). However, even wet bovine femur bone has a significantly higher elastic modulus compared to that of dry ivory. Chen et al. (2008) report bovine femur bone as having a tensile strength of 144 MPa (at least in the longitudinal direction). According to this->, the ultimate tensile strength of bone is some 130 MPa, with yield strength being 104-121 MPa. Edit: what do you know, a paper finding the tensile strength of cortical bone to be just as, if not higher, than that of dentin (the primary component of proboscidean ivory). Young's modulus is similar too, with dentin being slightly superior. www.researchgate.net/figure/The-tensile-strength-and-elastic-moduli-of-PEEK-CFR-PEEK-PMMA-and-mineralized-human_tbl1_282769397This table seems to be consistent with the one above. Dentin has markedly higher compressive strength, though. www.scielo.br/scielo.php?script=sci_arttext&pid=S1806-83242009000200012It also seems to more or less agree with something I posted about bone having a compressive strength of 170 MPa.
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Post by Infinity Blade on Aug 30, 2019 22:23:54 GMT 5
You know how some people argue that extinction is a natural occurrence and that "therefore" it's okay to let species go extinct? That's flawed for the obvious reason that we humans are the ones causing extinction, but even discounting this (i.e. even if we weren't the causes of extinction), wouldn't the argument just be committing the naturalistic fallacy? Or would it then have a point?
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Post by creature386 on Aug 30, 2019 22:32:11 GMT 5
It's a naturalistic fallacy, plain and simple.
My death is natural, too, but I wouldn't want it to happen tomorrow.
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Post by theropod on Sept 21, 2019 3:27:47 GMT 5
Why would someone use a polynomial function for a body mass~length (or similar) regression? I just noticed a paper using a polynomial function to model something (in this case body mass of alligators) one would ordinarily use a power curve for the second time in a row.
In this case Delany & Abercrombie 1986, for body mass of American alligators. > x<-c(200,400,600) > -154.3+6.173*(x)-0.085*(x^2)+0.0005063*(x^3) [1] 1730.7 21118.1 82310.3
Firstly the equation gives a totally ludicrous result, no 200 cm crocodilian weighs 1.7 t, and no 600 cm crocodilian weighs 82 t either. But it must be in cm (funny how most authors seem to find it superfluous to clearly state what f***ing units they used for their calculations), because putting in the length in meters, unless a 2 m alligator weighs negative 142 kg. What the heck is up with that?
Secondly why would someone use this form for the model in the first place? Especially in 1986, presumably without proper software to facilitate fitting it (whereas linear, log transformed regression would be much easier to do by hand with a calculator, as well as presumably a biologically more sensible relationship).
Delany, M.F. and Abercrombie, C.L. 1986. American Alligator Food Habits in Northcentral Florida. The Journal of Wildlife Management 50 (2): 348–353.
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Post by creature386 on Sept 21, 2019 14:40:18 GMT 5
Unfortunately, I can't access the paper and my college library is closed until Monday, so here a few guesses: If an equation cannot be justified on a deductive basis (e.g. from mathematical principles like the square cube law), the only justification left would be an empirical one. Now, my guess would be that it maybe gives good results for alligators in a certain age range, but their sample clearly included alligators with the sizes 1.3 to 3.9 m. I don't know. Did they use their equation for anything? If so, what results did they get?
EDIT: Theropod sent it to me. It seems like the equation is so strange to account for diet changes with size, but with the lack of any meaningful units (I even tried foot and pounds and it gave negative results), we have no idea what it means.
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